U.S. patent application number 15/790961 was filed with the patent office on 2018-02-15 for diverged-beam communications system.
The applicant listed for this patent is 8 RIVERS CAPITAL, LLC, PALMER LABS, LLC. Invention is credited to William J. Brown, Aleksander Edward Osadzinski, Miles R. Palmer.
Application Number | 20180048390 15/790961 |
Document ID | / |
Family ID | 52432961 |
Filed Date | 2018-02-15 |
United States Patent
Application |
20180048390 |
Kind Code |
A1 |
Palmer; Miles R. ; et
al. |
February 15, 2018 |
DIVERGED-BEAM COMMUNICATIONS SYSTEM
Abstract
An apparatus is provided that includes a modulator and an
optical transmitter coupled to the modulator and configured to emit
an optical beam that the modulator is configured to modulate with
data. The optical transmitter may thereby be configured to emit the
optical beam carrying the data and without artificial confinement
for receipt by an optical receiver configured to detect and recover
the data from the optical beam. The optical transmitter may be
configured to emit the optical beam with a divergence angle greater
than 0.1 degrees, and with a photonic efficiency of less than
0.05%. The photonic efficiency may relate a number of photons of
the optical beam detectable by the optical receiver, to a number of
photons of the optical beam emitted by the optical transmitter.
Inventors: |
Palmer; Miles R.; (Chapel
Hill, NC) ; Osadzinski; Aleksander Edward; (Cary,
NC) ; Brown; William J.; (Durham, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PALMER LABS, LLC
8 RIVERS CAPITAL, LLC |
DURHAM
DURHAM |
NC
NC |
US
US |
|
|
Family ID: |
52432961 |
Appl. No.: |
15/790961 |
Filed: |
October 23, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14593149 |
Jan 9, 2015 |
9847834 |
|
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15790961 |
|
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61925889 |
Jan 10, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 10/116 20130101;
H04B 10/1123 20130101; H04B 10/503 20130101; H04B 7/0617
20130101 |
International
Class: |
H04B 10/112 20060101
H04B010/112; H04B 7/06 20060101 H04B007/06; H04B 10/50 20060101
H04B010/50; H04B 10/116 20060101 H04B010/116 |
Claims
1. An apparatus comprising: a demodulator; and an optical receiver
coupled to the demodulator and configured to detect an optical beam
that carries data the demodulator is configured to recover, the
optical receiver being configured to detect the optical beam
emitted without artificial confinement from an optical transmitter
configured to emit the optical beam modulated with the data,
wherein the optical receiver is configured to detect the optical
beam emitted with a divergence angle greater than 0.1 degrees, and
with a photonic efficiency of less than 0.05%, the photonic
efficiency relating a number of photons of the optical beam
detectable by the optical receiver, to a number of photons of the
optical beam emitted by the optical transmitter.
2. The apparatus of claim 1, wherein the optical receiver is
configured to detect the optical beam at least in some instances in
which the optical receiver does not have a line-of-sight to the
optical transmitter.
3. The apparatus of claim 1 comprising an array of optical
receivers including the optical receiver, or the optical receiver
includes an array of detectors configured to detect the optical
beam, and wherein optical receivers of the array of optical
receivers or detectors of the array of detectors are configured to
selectively activate and deactivate based on their orientation with
respect to the optical transmitter.
4. The apparatus of claim 1, wherein the optical beam includes an
incident beam, and a reflected beam produced by reflection of the
incident beam, the optical receiver in at least one instance being
configured to preferentially detect the reflected beam, and avoid
direct detection of the incident beam.
5. The apparatus of claim 1, wherein the optical receiver includes
an array of detectors configured to detect the optical beam, the
array having a size larger than a spot size of the optical beam at
the optical transmitter.
6. The apparatus of claim 5, wherein the optical beam is spatially
multiplexed to serve multiple optical receivers, the array of
detectors being arranged in a pattern of detectors that corresponds
to a pattern of emitters of the optical transmitter that are
independently modulated.
7. The apparatus of claim 1 further comprising a
wavelength-specific or wavelength-tunable filter to enable the
optical receiver to detect the optical beam that is spectral
multiplexed to serve multiple optical receivers.
8. The apparatus of claim 1, wherein the optical receiver is
configured to detect the optical beam with an adjustable focus to
facilitate a match of the optical receiver to characteristics of
the optical beam, the adjustable focus in at least one instance
including focus of the optical receiver at some intermediate point
between the optical transmitter and optical receiver.
9. The apparatus of claim 1 further configured to receive a
heartbeat signal for orientation of the optical receiver and
optical transmitter, the heartbeat signal being modulated to carry
or indicate a location of the optical transmitter, or a signal to
cause the optical receiver to return its location or an indication
of its location to the optical transmitter.
10. The apparatus of claim 1, wherein the optical receiver includes
a camera configured to capture a portion of the optical beam, and
electronics with which the camera is configured to communicate to
drive coarse or fine steering based on the captured portion of the
optical beam to at least partially orient the optical receiver and
optical transmitter.
11. The apparatus of claim 1, wherein the optical receiver includes
a plurality of photodiodes positioned around a periphery of and
that are shadowed by a limiting aperture of the optical receiver,
the photodiodes being configured to detect relative powers of the
optical beam, the optical receiver further including electronics
with which the photodiodes are configured to communicate to drive
coarse or fine steering based on the relative powers of the optical
beam to at least partially orient the optical receiver and optical
transmitter.
12. The apparatus of claim 1 further comprising a pointing system
operable based on guidance provided by the optical receiver based
on reception of a broad optical beam by a separate optical receiver
or detector.
13. The apparatus of claim 1 further comprising one or more lenses
of high-index material to increase an optical gain of the optical
receiver.
14. The apparatus of claim 1, wherein the optical receiver being
configured to detect the optical beam includes being configured to
detect the optical beam that is time division multiplexed.
15. The apparatus of claim 14, wherein the optical receiver being
configured to detect the optical beam that is time division
multiplexed includes being configured to detect optical beams that
are time division multiplexed and emitted from a plurality of
optical transmitters.
16. The apparatus of claim 1 further configured to change a data
rate or modulation of the optical beam based on a signal to noise
ratio (SNR) or data integrity of the optical beam.
17. The apparatus of claim 1, wherein the apparatus is embodied as
a mobile device equipped with the demodulator and optical
receiver.
18. The apparatus of claim 1 further configured to use forward
error correction to control errors in the data recovered by the
demodulator.
19. The apparatus of claim 1 further configured to select the
optical transmitter based on communication with one or more optical
transmitters, and wherein the optical receiver includes electronics
to drive coarse or fine steering to at least partially orient the
optical receiver and the optical transmitter so selected.
20. The apparatus of claim 1, wherein the optical receiver includes
an avalanche photodiode (APD) configured to detect the optical
beam.
21. The apparatus of claim 1 further comprising pointing and
tracking.
22. The apparatus of claim 21, wherein the pointing and tracking
includes a pan-and-tilt control.
23. The apparatus of claim 1, wherein the optical receiver is
configured to select the optical transmitter from a plurality of
optical transmitters based on a characteristic of optical beams
from the plurality of optical transmitters.
24. The apparatus of claim 1 further configured to decrypt the data
recovered from the optical beam.
25. A method comprising: detecting, by an optical receiver, an
optical beam emitted without artificial confinement from an optical
transmitter configured to emit the optical beam modulated with
data; and recovering the data from the optical beam so detected;
wherein the optical beam detected by the optical receiver has been
emitted from the optical transmitter with a divergence angle
greater than 0.1 degrees, and with a photonic efficiency of less
than 0.05%, the photonic efficiency relating a number of photons of
the optical beam detectable by the optical receiver, to a number of
photons of the optical beam emitted by the optical transmitter.
26. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam by the optical receiver that
does not have a line-of-sight to the optical transmitter.
27. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam by the optical receiver of an
array of optical receivers including the optical receiver, or by
the optical receiver including an array of detectors, and wherein
the method further comprises selectively activating or deactivating
the optical receivers of the array of optical receivers or
detectors of the array of detectors on their orientation with
respect to the optical transmitter.
28. The method of claim 25, wherein the optical beam includes an
incident beam, and a reflected beam produced by reflection of the
incident beam, and detecting the optical beam includes
preferentially detecting the reflected beam, and avoiding direct
detection of the incident beam.
29. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam by the optical receiver
including an array of detectors having a size larger than a spot
size of the optical beam at the optical transmitter.
30. The method of claim 29, wherein the optical beam is spatially
multiplexed to serve multiple optical receivers, the array of
detectors being arranged in a pattern of detectors that corresponds
to a pattern of emitters of the optical transmitter that are
independently modulated.
31. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam that is spectral multiplexed to
serve multiple optical receivers, and the method further comprises
wavelength-specific or wavelength-tunable filtering the optical
beam to enable the optical receiver to detect the optical beam.
32. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam with an adjustable focus to
facilitate a match of the optical receiver to characteristics of
the optical beam, the adjustable focus including focus of the
optical receiver at some intermediate point between the optical
transmitter and optical receiver.
33. The method of claim 25 further comprising receiving a heartbeat
signal for orientation of the optical receiver and optical
transmitter, the heartbeat signal being modulated to carry or
indicate a location of the optical transmitter, or a signal to
cause the optical receiver to return its location or an indication
of its location to the optical transmitter.
34. The method of claim 25 further comprising capturing a portion
of the optical beamby a camera; and driving coarse or fine steering
based on the captured portion of the optical beam to at least
partially orient the optical receiver and optical transmitter.
35. The method of claim 25, wherein the optical receiver includes a
plurality of photodiodes positioned around a periphery of and that
are shadowed by a limiting aperture of the optical receiver, and
wherein the method further comprises: detecting relative powers of
the optical beam by the photodiodes; and driving coarse or fine
steering based on the relative powers of the optical beam to at
least partially orient the optical receiver and optical
transmitter.
36. The method of claim 25 further comprising operating a pointing
system based on guidance provided by the optical receiver based on
reception of a broad optical beam by a separate optical receiver or
detector.
37. The method of claim 25 further comprising one or more lenses of
high-index material increasing an optical gain of the optical
receiver.
38. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam that is time division
multiplexed.
39. The method of claim 38, wherein detecting the optical beam that
is time division multiplexed includes detecting optical beams that
are time division multiplexed and emitted from a plurality of
optical transmitters.
40. The method of claim 25 further comprising changing a data rate
or modulation of the optical beam based on a signal to noise ratio
(SNR) or data integrity of the optical beam.
41. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam at a mobile device equipped
with the optical receiver.
42. The method of claim 25 further comprising using forward error
correction to control errors in the data recovered.
43. The method of claim 25 further comprising selecting the optical
transmitter based on communication with one or more optical
transmitters; and driving coarse or fine steering to at least
partially orient the optical receiver and the optical transmitter
so selected.
44. The method of claim 25, wherein detecting the optical beam
includes detecting the optical beam with an avalanche photodiode
(APD).
45. The method of claim 25 further comprising pointing and
tracking.
46. The method of claim 45, wherein the pointing and tracking
includes a pan-and-tilt control.
47. The method of claim 25 further comprising selecting the optical
transmitter from a plurality of optical transmitters based on a
characteristic of optical beams from the plurality of optical
transmitters.
48. The method of claim 25 further comprising decrypting the data
recovered from the optical beam.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] The present application is a division of U.S. patent
application Ser. No. 14/593,149, entitled: Diverged-Beam
Communications System, filed on Jan. 9, 2015, which claims priority
to U.S. Provisional Patent Application No. 61/925,889, entitled:
Beam Communications System, filed on Jan. 10, 2014, the contents of
both of which are incorporated herein by reference in their
respective entireties.
TECHNOLOGICAL FIELD
[0002] The present disclosure relates generally to optical
communications and in particular, diverged-beam optical
communications.
BACKGROUND
[0003] The concept of free space optical (FSO) communications using
lasers dates back to the invention of the laser. However,
difficulties with generating and modulating high-power lasers have
restricted the use of FSO to line-of-sight systems using
tightly-collimated beams. Very low-power and low-modulation-rate
with diverged pulses of light has been used in a few niche
applications such as remote controls for televisions and other
appliances. Even during the telecom boom of the late 1990's and
early 2000's when billions of dollars of investment was made in
components and systems, FSO systems did not reach beyond collimated
beams in line-of-sight configurations. There are several existing
companies selling FSO line-of-sight systems, but these systems
require precise alignment and skilled installation. These systems
costs start around US $10,000 per link, and only a few thousand
systems are shipped per year.
[0004] Therefore, it would be desirable to have a system and method
that takes into account and resolves at least some of the issues
discussed above, as well as possibly other issues.
BRIEF SUMMARY
[0005] The present disclosure relates generally to a system and
method of FSO communications and in particular, diverged-beam FSO
communications. Two converging trends have led to the system and
method example implementations of the present disclosure. The first
is the exponential rise in the use of and demand for bandwidth,
particularly by households and mobile devices. Real-time delivery
of video to houses and mobile devices requires massive amount of
bandwidth and this will increase with 4K video, video conferencing,
over-the-top (OTT) services and other uses. To date this need has
been met by cable, digital subscriber line (DSL), fiber to the home
(FTTH) and cellular radio technologies for mobile. But available
bandwidth is starting to run short in all cases except FTTH, which
remains too expensive for deployment to every house and building.
The second trend is the decrease in the cost of laser and detector
components due both to technology development and to the increased
use of photonic components in all types of applications. Advances
in components and a drastic increase in market need for bandwidth
provide the stage for the system and method of example
implementations of the present disclosure.
[0006] The starting point for the FSO system of example
implementations is the premise that photon creation and detection
is on a Moore's law type curve. Laser output powers and detector
array sizes and sensitivity are increasing while costs are
decreasing. All previous laser-based FSO systems are based on
collimated beams with narrow divergence and tight angular tracking
of both transmitters and receivers. In contrast, for the system of
example implementations, cheap photons can be broadcast over a
range of angles and large detectors can accept from a range of
angles leading to increased angular tolerance between transmitters
and receivers. Multiple beam paths between transmitter and receiver
reduce the impact of weather such as rain, fog and snow. Since each
bit of information requires some number of photons, cheap photons
lead to cheaper bits, which in term lead to more affordable higher
bit rate systems. Enough cheap photons lead to non-line-of-sight
(NLOS) systems where only a minute fraction of the photons emitted
by the transmitter arrive at the receiver, while still being
sufficient to achieve very-high bit rates. Optical frequencies mean
that there are terabits of bandwidth available for use by the
system. The system can solve the last mile and mobile bandwidth
market needs by the innovation of diverged laser beam FSO
communications.
[0007] The present disclosure thus includes, without limitation,
the following example implementations:
EXAMPLE IMPLEMENTATION 1
[0008] An apparatus comprising a modulator; and an optical
transmitter coupled to the modulator and configured to emit an
optical beam that the modulator is configured to modulate with
data, the optical transmitter thereby being configured to emit the
optical beam carrying the data and without artificial confinement
(e.g., in free space) for receipt by an optical receiver configured
to detect and recover the data from the optical beam, wherein the
optical transmitter is configured to emit the optical beam with a
divergence angle greater than 0.1 degrees, and with a photonic
efficiency of less than 0.05%, the photonic efficiency relating a
number of photons of the optical beam detectable by the optical
receiver, to a number of photons of the optical beam emitted by the
optical transmitter.
EXAMPLE IMPLEMENTATION 2
[0009] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
transmitter being configured to emit the optical beam includes
being configured to emit an incident beam directed at a reflector
to produce a reflected beam by reflection of the incident beam, the
optical transmitter being configured to emit the incident beam for
receipt of the reflected beam by the optical receiver.
EXAMPLE IMPLEMENTATION 3
[0010] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
transmitter includes an array of emitters configured to emit the
optical beam, the array having a size larger than a spot size of
the optical beam at the optical transmitter.
EXAMPLE IMPLEMENTATION 4
[0011] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
transmitter further includes an optic through which the array of
emitters is configured to emit the optical beam, the emitters of
the array being configured to emit respective collimated beams but
with different angles due to a spatial extent of the array, the
array thereby being configured to produce the optical beam composed
of the respective collimated beams and whose divergence angle is
set by the size of the array and focal length of the optic.
EXAMPLE IMPLEMENTATION 5
[0012] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
transmitter further includes an optic through which the array of
emitters is configured to emit the optical beam, the array being
situated away from a focus of the optic, the emitters of the array
being configured to emit respective diverging beams, the array
thereby being configured to produce the optical beam composed of
the respective diverging beams and whose divergence angle is set by
the size of the array and a degree of de-focus due to the situation
of the array away from the focus of the optic.
EXAMPLE IMPLEMENTATION 6
[0013] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
transmitter is configured to perform multiplexing to serve multiple
optical receivers.
EXAMPLE IMPLEMENTATION 7
[0014] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
transmitter is configured to emit the optical beam with an
adjustable focus or astigmatism, the adjustable focus enabling
adjustment of a diameter of the optical beam at a given distance
from the optical transmitter, and the astigmatism causing the
optical beam to have different vertical and horizontal
divergences.
EXAMPLE IMPLEMENTATION 8
[0015] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the apparatus is
further configured to transmit a heartbeat signal for orientation
of the optical transmitter and optical receiver, the heartbeat
signal being modulated to carry or indicate a location of the
optical transmitter, or a signal to cause the optical receiver to
return its location or an indication of its location to the optical
transmitter.
EXAMPLE IMPLEMENTATION 9
[0016] An apparatus comprising a demodulator; and an optical
receiver coupled to the demodulator and configured to detect an
optical beam that carries data the demodulator is configured to
recover, the optical receiver being configured to detect the
optical beam emitted and without artificial confinement from an
optical transmitter configured to emit the optical beam modulated
with the data, wherein the optical receiver is configured to detect
the optical beam emitted with a divergence angle greater than 0.1
degrees, and with a photonic efficiency of less than 0.05%, the
photonic efficiency relating a number of photons of the optical
beam detectable by the optical receiver, to a number of photons of
the optical beam emitted by the optical transmitter.
EXAMPLE IMPLEMENTATION 10
[0017] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
receiver is configured to detect the optical beam at least in some
instances in which the optical receiver does not have a
line-of-sight to the optical transmitter.
EXAMPLE IMPLEMENTATION 11
[0018] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the apparatus
comprises an array of optical receivers including the optical
receiver, or the optical receiver includes an array of detectors
configured to detect the optical beam, and wherein optical
receivers of the array of optical receivers or detectors of the
array of detectors are configured to selectively activate and
deactivate (e.g., switch on and off) based on their orientation
with respect to (e.g., alignment with) the optical transmitter.
EXAMPLE IMPLEMENTATION 12
[0019] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical beam
includes an incident beam, and a reflected beam produced by
reflection of the incident beam, the optical receiver in at least
one instance being configured to preferentially detect the
reflected beam, and avoid direct detection of the incident
beam.
EXAMPLE IMPLEMENTATION 13
[0020] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
receiver includes an array of detectors configured to detect the
optical beam, the array having a size larger than a spot size of
the optical beam at the optical transmitter.
EXAMPLE IMPLEMENTATION 14
[0021] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical beam
is spatially multiplexed to serve multiple optical receivers, the
array of detectors being arranged in a pattern of detectors that
corresponds to a pattern of emitters of the optical transmitter
that are independently modulated.
EXAMPLE IMPLEMENTATION 15
[0022] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, the apparatus further
comprising a wavelength-specific or wavelength-tunable filter to
enable the optical receiver to detect the optical beam that is
spectral multiplexed to serve multiple optical receivers.
EXAMPLE IMPLEMENTATION 16
[0023] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
receiver is configured to detect the optical beam with an
adjustable focus to facilitate a match of the optical receiver to
characteristics of the optical beam, the adjustable focus in at
least one instance including focus of the optical receiver at some
intermediate point between the optical transmitter and optical
receiver.
EXAMPLE IMPLEMENTATION 17
[0024] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the apparatus is
further configured to receive a heartbeat signal for orientation
(e.g., alignment) of the optical receiver and optical transmitter,
the heartbeat signal being modulated to carry or indicate a
location of the optical transmitter, or a signal to cause the
optical receiver to return its location or an indication of its
location to the optical transmitter.
EXAMPLE IMPLEMENTATION 18
[0025] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
receiver includes a camera configured to capture a portion of the
optical beam, and electronics with which the camera is configured
to communicate to drive coarse or fine steering based on the
captured portion of the optical beam to at least partially orient
(e.g., align) the optical receiver and optical transmitter.
EXAMPLE IMPLEMENTATION 19
[0026] The apparatus of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical
receiver includes a plurality of photodiodes positioned around a
periphery of and that are shadowed by a limiting aperture of the
optical receiver, the photodiodes being configured to detect
relative powers of the optical beam, the optical receiver further
including electronics with which the photodiodes are configured to
communicate to drive coarse or fine steering based on the relative
powers of the optical beam to at least partially orient the optical
receiver and optical transmitter.
EXAMPLE IMPLEMENTATION 20
[0027] A method comprising modulating an optical beam with data;
and emitting by an optical transmitter, the optical beam carrying
the data and without artificial confinement for receipt by an
optical receiver configured to detect and recover the data from the
optical beam, wherein the optical beam is emitted with a divergence
angle greater than 0.1 degrees, and with a photonic efficiency of
less than 0.05%, the photonic efficiency relating a number of
photons of the optical beam detectable by the optical receiver, to
a number of photons of the optical beam emitted by the optical
transmitter.
EXAMPLE IMPLEMENTATION 21
[0028] The method of any preceding or subsequent example
implementation, or combinations thereof, wherein emitting the
optical beam includes emitting an incident beam directed at a
reflector to produce a reflected beam by reflection of the incident
beam, the incident beam being emitted for receipt of the reflected
beam by the optical receiver.
EXAMPLE IMPLEMENTATION 22
[0029] The method of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical beam
is emitted by an array of emitters of the optical transmitter, the
array having a size larger than a spot size of the optical beam at
the optical transmitter.
EXAMPLE IMPLEMENTATION 23
[0030] The method of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical beam
is emitted by the array of emitters through an optic, the emitters
of the array emitting respective collimated beams but with
different angles due to a spatial extent of the array, the array
thereby producing the optical beam composed of the respective
collimated beams and whose divergence angle is set by the size of
the array and focal length of the optic.
EXAMPLE IMPLEMENTATION 24
[0031] The method of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical beam
is emitted by the array of emitters through an optic, the array
being situated away from a focus of the optic, the emitters of the
array emitting respective diverging beams, the array thereby
producing the optical beam composed of the respective diverging
beams and whose divergence angle is set by the size of the array
and a degree of de-focus due to the situation of the array away
from the focus of the optic.
EXAMPLE IMPLEMENTATION 25
[0032] The method of any preceding or subsequent example
implementation, or combinations thereof, the method further
comprising performing multiplexing to serve multiple optical
receivers.
EXAMPLE IMPLEMENTATION 26
[0033] The method of any preceding or subsequent example
implementation, or combinations thereof, wherein the optical beam
is emitted with an adjustable focus or astigmatism, the adjustable
focus enabling adjustment of a diameter of the optical beam at a
given distance from the optical transmitter, and the astigmatism
causing the optical beam to have different vertical and horizontal
divergences.
EXAMPLE IMPLEMENTATION 27
[0034] The method of any preceding or subsequent example
implementation, or combinations thereof, the method further
comprising transmitting a heartbeat signal for orientation of the
optical transmitter and optical receiver, the heartbeat signal
being modulated to carry or indicate a location of the optical
transmitter, or a signal to cause the optical receiver to return
its location or an indication of its location to the optical
transmitter.
[0035] These and other features, aspects and advantages of the
present disclosure will be apparent from a reading of the following
detailed description together with the accompanying drawings, which
are briefly described below. The present disclosure includes any
combination of two, three, four, or more features or elements set
forth in this disclosure, regardless of whether such features or
elements are expressly combined or otherwise recited in a specific
implementation description herein. This disclosure is intended to
be read holistically such that any separable features or elements
of the disclosure, in any of its aspects and implementations,
should be viewed as intended, namely to be combinable, unless the
context of the disclosure clearly dictates otherwise.
[0036] It will therefore be appreciated that the above Summary is
provided merely for purposes of summarizing some example
implementations so as to provide a basic understanding of some
aspects of the disclosure. As such, it will be appreciated that the
above described example implementations are merely examples of some
implementations and should not be construed to narrow the scope or
spirit of the disclosure in any way. It will be appreciated that
the scope of the disclosure encompasses many potential
implementations, some of which will be further described below, in
addition to those here summarized. Further, other aspects and
advantages of implementations disclosed herein will become apparent
from the following detailed description taken in conjunction with
the accompanying drawings which illustrate, by way of example, the
principles of the described implementations.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0037] Having thus described the disclosure in the foregoing
general terms, reference will now be made to the accompanying
drawings, which are not necessarily drawn to scale, and
wherein:
[0038] FIG. 1 illustrates a diverged-beam communications system
according to various example implementations of the present
disclosure;
[0039] FIG. 2A illustrates an optical transceiver array including a
plurality of optical transceivers (sometimes referred to as
transceiver modules), according to various example
implementations;
[0040] FIG. 2B illustrates a transceiver module in further detail,
in accordance with some example implementations;
[0041] FIGS. 2C and 2D illustrate a transceiver module and
highlight a pointing system thereof, in accordance with some
example implementations;
[0042] FIG. 3 illustrates an optical transceiver array retrofitted
to existing network infrastructure such as a cell tower, in
accordance with some example implementations;
[0043] FIGS. 4A and 4B illustrate a mobile device that may be
equipped with an optical transceiver, in accordance with some
example implementations;
[0044] FIGS. 5A and 5B illustrate example techniques for achieving
beam divergence using an extended source of an array of emitters,
in accordance with some example implementations;
[0045] FIGS. 6A and 6B illustrate optical receivers in accordance
with example implementations;
[0046] FIG. 7A illustrates an optical transmitter including one or
more dynamic optics configured to enable an adjustable focus of the
optical beam, in accordance with some example implementations;
[0047] FIGS. 7B, 7C and 7D illustrate use of dynamic optic(s) to
enable astigmatism in the optical transmitter whereby the vertical
divergence may be different than the horizontal divergence, in
accordance with some example implementations;
[0048] FIG. 7E illustrates use of dynamic optic(s) to enable
pointing adjustment at the optical transmitter, in accordance with
some example implementations;
[0049] FIG. 8 illustrates beam dithering according to some example
implementations;
[0050] FIGS. 9A, 9B and 9C illustrates an optical receiver
including dynamic optic(s) configured to enable an adjustable focus
of the optical beam (FIG. 9A), and for a line-of-sight (LOS) case
(FIG. 9B), and a non-LOS (NLOS) (FIG. 9C), in accordance with some
example implementations;
[0051] FIGS. 9D and 9E illustrates use of dynamic optic(s) to
enable pointing adjustment at the optical receiver, in accordance
with some example implementations;
[0052] FIG. 10 illustrates a few techniques for at least an initial
alignment between optical transmitter and receiver for
communication, in accordance with some example implementations;
[0053] FIGS. 11A and 11B illustrate two examples for alignment
between the optical transmitter and receiver that may be at least
partially accomplished within the optical receiver, in accordance
with some example implementations;
[0054] FIGS. 12A and 12B illustrate respectively spectral
multiplexing and spatial multiplexing that may be implemented by
the diverged-beam communications system, in accordance with some
example implementations;
[0055] FIGS. 13-17, 18A and 18B illustrate various scenarios in
which the diverged-beam communications system may be deployed, in
accordance with some example implementations; and
[0056] FIG. 19 illustrates various operations in a method according
to example implementations.
DETAILED DESCRIPTION
[0057] The present disclosure will now be described more fully
hereinafter with reference to example implementations thereof.
These example implementations are described so that this disclosure
will be thorough and complete, and will fully convey the scope of
the disclosure to those skilled in the art. Indeed, the disclosure
may be embodied in many different forms and should not be construed
as limited to the implementations set forth herein; rather, these
implementations are provided so that this disclosure will satisfy
applicable legal requirements. As used in the specification and the
appended claims, for example, the singular forms "a," "an," "the"
and the like include plural referents unless the context clearly
dictates otherwise. Also, for example, reference may be made herein
to quantitative measures, values, relationships or the like. Unless
otherwise stated, any one or more if not all of these may be
absolute or approximate to account for acceptable variations that
may occur, such as those due to engineering tolerances or the
like.
[0058] As described hereinafter, example implementations of the
present disclosure relate to optical communications, and more
particularly diverged-beam optical communications. Example
implementations of the present disclosure are primarily described
in the context of free space optical (FSO) communications. It
should be understood, however, that example implementations may be
equally applicable in contexts other than that traditionally
associated with FSO communications, that is, communications through
air, outer space, vacuum or the like. For example, example
implementations may be equally applicable to communications through
water or any other liquid, solution or suspension, and any other
matter or medium through which an optical beam may propagate
without an optical fiber cable, waveguide or transmission line.
These and other similar means of artificial confinement may present
a contrast in index of refraction that leads to mode confinement
therein to carry or otherwise guide an optical beam. Thus, example
implementations may be more generally considered applicable to
optical communications including the propagation of optical beams
between a transmitter and a receiver without artificial confinement
such as by optical fiber cable, waveguide, transmission line or the
like.
[0059] As explained in greater detail below, a diverged-beam
communications system of example implementations generally includes
an optical transmitter configured to emit a diverging optical beam
carrying data, and a receiver configured to detect the optical beam
and recover the data from it. The system may be deployed in a
number of different scenarios in which the optical transmitter and
receiver may equipped by a number of different types of fixed or
mobile communications devices and structures configured to transmit
and/or receive data, or otherwise support the transmission and/or
reception of data. Examples of suitable communications devices and
structures include masts, telescopic masts, towers, poles, trees,
buildings, balloons, kites, land vehicles (e.g., automobiles,
trains), watercraft (e.g., boats, ships), spacecraft (e.g.,
artificial satellites), celestial bodies (e.g., planets, moons),
aircraft (e.g., airplanes, helicopters, unmanned aerial vehicles,
dirigibles), computers (e.g., desktop, laptop), tablet computers,
smartphones, and any of a number of other types of devices equipped
for or otherwise capable of wireless communication.
[0060] The diverged optical beam from the optical transmitter and
appropriate acceptance angle at the optical receiver mean that the
position of the optical transmitter and/or receiver may move while
maintaining communications throughput. The speed of motion may be
limited by the spot size of the optical beam at the optical
receiver, the acceptance angle of the optical receiver and a
feedback rate of the optical transmitter and/or receiver tracking.
This may be desirable for a number of scenarios, but may also open
up additional FSO communications applications that are now either
inaccessible or extremely expensive. These include, for example,
FSO communications between a ground-based, fixed structure such as
a mast or tower and an aircraft. Also enabled is communications
between two aircraft. It may also be possible to communicate
between spacecraft and a ground-based, fixed structure, in which in
some examples the spacecraft may operate in a broadcast mode. Very
high-power emitters (e.g., 10 to 1,000's of Watts or more) may be
used in some applications.
[0061] Another benefit of the diverged optical beam may be its ease
of initial alignment and alignment adjustment for what are
nominally point-to-point scenarios. One example scenario involves
optical communications between two ground-based, fixed structures
such as between a tower and building, where the optical transmitter
and receiver are initially setup. Simple tracking, either
electronically controlled or manual, may facilitate easier setup,
minimizing technician time or allowing the end user to set up the
equipment. This may also enable ad hoc type networks where the
diverged-beam communications system may only be used for a short
time and needs to be quickly set up and taken down. Some example
potential scenarios include sporting events, fairs or other
gatherings where the system combined with Wi-Fi could be used to
provide bandwidth to 100's to 100,000's of users with high
throughput, less equipment and rapid setup and take down times.
Disaster response scenarios may also be supported with rapid
deployment of the system in areas where network equipment has been
damaged or destroyed. Furthermore, there are numerous military
scenarios both for troops and support personnel in areas with
active fighting and also in bases and camps where bandwidth needs
may change based on number of personnel and amount of equipment.
The system may be easily taken down and redeployed as the locations
where bandwidth is needed changes over time.
[0062] The diverged beam and in some examples a larger acceptance
angle at the optical receiver may have a number of benefits over
collimated beams when there are scatterers in the beam. For a
collimated beam, any scatterer may predominately scatter light out
of the beam, and may therefore be just a source of attenuation.
Potential scatterers include weather-related scatterers such as
rain, snow, ice, hail and fog, as well as non-weather scatterers
such as leaves, branches, smoke, wires and others.
[0063] In the diverged-beam communications system of example
implementations, scattering does not necessarily mean that a photon
is lost. In particular, for multiple scatterings there may be
photons that may be initially scattered on a path that will take
the photons out of the beam path to the optical receiver that may
then subsequently be scattered back into the beam path to the
optical receiver. This may happen more often in situations where
there is significant scattering at angles close to zero forward
angle, which is the case for scatters within an order of magnitude
of the wavelength of the light, such as fog. In one particular
example, droplet size for fog can peak around 2 microns, which may
be close to wavelengths of interest for the system in some
examples, which may range from 0.4 microns up to 1.6 microns. Just
like one can see light from the headlights of a car in foggy
conditions well before the car can be seen, the system of example
implementations may still receive light in conditions where imaging
or collimated beams will be invisible.
[0064] Signal degradation for scatterers such as fog may eventually
reach the point that the data rate cannot be maintained, at which
point the diverged-beam communications system may increase the
output power or slow down the data rate or modify its modulation
scheme, its error correction scheme, its encoding scheme, its
network stack protocols, or any combination of these, to maintain
sufficient signal-to-noise ratio (SNR) and/or data integrity. In
instances in which the degradation is due to too low photon number
or photonic efficiency, then increasing the output power may be
sufficient to maintain the data rate. In instances in which the
degradation is due to increased multipath dispersion, then the data
rate may be lowered. The system may continue to monitor performance
and then increase the data rate, lower the output power and/or
adjust any of the other of the aforementioned modifications, as
conditions improve. The system in some examples may include
multiple sets of drive and detection electronics for different data
rates. In general, the data rate dynamic range for a given driver
may be around one order of magnitude or a factor of 10. Thus one
set of electronics may support 1 Gb/s down to 100 Mb/s, but
additional electronics may be used for data rates below 100 Mb/s
down to 1 Mb/s or even slower. More generally, some example
implementations of the present disclosure may support
communications at bitrates in the range of megabits per second up
to terabits per second or more, and which bitrates may at times be
dynamically adjustable using a number of different techniques.
[0065] FIG. 1 illustrates a diverged-beam communications system 100
according to various example implementations of the present
disclosure. As shown, the system includes one or more of each of a
number of components, including an optical transmitter 102 (one
shown, and at times referred to as an optical source) and an
optical receiver 104 (two shown as optical receivers 104a, 104b,
and at times referred to as an optical detector) configured for
fixed or mobile communication. In some examples, one or more
optical transmitters and receivers may be co-located in the form of
one or more optical transceivers. And in some examples, one or more
optical transceivers may function as optical relay nodes configured
to receive (via its receiver) an optical beam carrying data, and
retransmit (via its transmitter) another optical beam carrying the
same or similar data. The system of example implementations may
therefore include various combinations of one or more optical
transmitters, receivers and/or transceivers (some of which may
function as relay nodes).
[0066] As explained above, the optical transmitters 102, receivers
104 and/or transceivers (including both transmitters and receivers)
may be equipped by a number of different types of fixed or mobile
communications devices and structures configured to transmit and/or
receive data, or otherwise support the transmission and/or
reception of data. Examples of suitable communications devices and
structures include masts, telescopic masts, towers, poles, trees,
buildings, balloons, kites, land vehicles, watercraft, spacecraft,
celestial bodies, aircraft, computers, tablet computers,
smartphones, and any of a number of other types of devices equipped
for or otherwise capable of wireless communication.
[0067] The optical transmitter 102 may include one or more
emitters, and coupled with appropriate supporting electronics and
any appropriate optics, may be configured to emit an optical beam
carrying data. The optical receiver 104 may include one or more
detectors, and coupled with appropriate supporting electronics and
any appropriate optics, may be configured to detect the optical
beam and recover the data from it. The optical transmitter and its
supporting electronics may be part of an assembly that in some
examples also includes a modulator 106, pointing system 108 and/or
control system 110. The optical transmitter may be configured to
emit an optical beam that the modulator may be configured to
modulate with data from a data source 112. The optical receiver may
be configured to detect the optical beam that an included
demodulator in its associated electronics may be configured to
demodulate to recover the data from it. And although shown
separately, in some examples, the modulator in some examples may be
included in the optical transmitters' associated electronics.
[0068] In accordance with example implementations, the optical
transmitter 102 may be configured to emit the optical beam such
that the beam diverges as it propagates from the optical
transmitter. The optical beam may be slightly diverged to produce a
narrow divergence beam 114, or more heavily diverged to produce a
wide divergence beam 116. A more diverged beam is useful for moving
optical receivers 104 such as those equipped by a vehicle or
handheld by a user.
[0069] Because of the availability of effectively unlimited numbers
of discrete channels, and the inherent lack of interference between
multiple optical signals, the diverged-beam communications system
100 in more simple example implementations may use on/off keying
(OOK) as its primary modulation scheme. This modulation scheme may
become insufficient based on any of a number of factors such as
increased distance between the optical transmitter 102 and receiver
104, atmospheric conditions, increasing bandwidth requirements,
optical transmitter power limitations and the like. The system may
manage this insufficiency in a number of different manners such as
by using multiple optical transmitters operating at different
frequencies, and/or by using additional coding schemes. Suitable
examples of additional coding schemes include optical dual binary
modulation (ODB), single polarization state phase modulation
(DPSK), differential quadrature phase shift keying (DQPSK), and
dual polarization quadrature state phase modulation (DP-QPSK).
[0070] Errors in data transmission between the optical transmitter
102 and receiver 104 may be controlled in a number of different
manners, such as by the use of conventional error-correcting codes
and/or forward error correction.
[0071] In some examples, the diverged-beam communications system
100 may use any of a number of different techniques to achieve
adequate SNR in daylight conditions. Examples of suitable
techniques that may facilitate the SNR include the use of high
transmission powers, laser line narrowing, narrow bandpass receiver
filtering, pseudo-random code modulation, signal averaging,
adaptive shading and the like.
[0072] In some examples, a single optical transmitter 102 may serve
multiple receivers residing within the cone of its optical beam,
such as by employing any of number of different multiplexing
techniques. Examples of suitable techniques include those based on
space, time, frequency (spectrum), polarization, angular momentum,
code or some combination of one or more thereof. In more particular
examples, conventional channel access methods, such as code
division multiple access (CDMA), time division multiple access
(TDMA), frequency spacing and the like, may be used. In other
examples, spatial division multiple access (SDMA)--three degrees of
freedom, angular division multiple access (ADMA)--three degrees of
freedom, polarization division multiple access (PDMA)--one degree
of freedom, and the like, may be used. The system of example
implementations may therefore offer up to ten or more degrees of
dimensional separation versus the three degrees available with
radio frequencies.
[0073] In some examples, the optical transmitter 102 may be
configured to encrypt the data before its transmission. Examples of
suitable encryption schemes that may be used by the transmitter for
this purpose include conventional techniques for high-speed RF
networks, such as the KASUMI block cipher or SNOW 3G stream cipher
with the UEA1 or UEA2 confidentiality and UIA1 or UIA2 integrity
algorithms. The optical receiver 104 may be identified by fixed or
removable trust hardware. Alternatively, for example, existing IEEE
802.11 security protocols may be used, especially for purely data,
versus voice and data, communications.
[0074] In some examples, the optical-beam divergence may be
dynamically alterable by an electronically-controlled focusing
mechanism at the optical transmitter 102. Among other advantages,
this may allow reduced divergence in instances in which the optical
beam is locked onto a fixed optical receiver 104, or a mobile
receiver that is not expected to move much if at all for at least
some portion of the duration of communication between the
transmitter and receiver.
[0075] In some examples, the power of the optical beam may be
electronically alterable by the optical transmitter 102. Among
other advantages, this may allow the diverged-beam communications
system 100 to conserve energy and/or provide increased safety. In
some examples in which the optical beam is locked onto a fixed
optical receiver 104, or a mobile receiver that is not expected to
move much if at all for at least some portion of the duration of
communication between the transmitter and receiver, the beam
divergence and/or power may be reduced.
[0076] The pointing system 108 may be configured to point the
optical transmitter 102 in the general direction of one or more
optical receivers 104, such as in accordance with any of a number
of different techniques. The pointing system may operate under
direction of the control system 110 configured to direct the
pointing system to point the optical transmitter in a chosen
direction to ensure broad coverage of an area likely to contain one
or more receivers. For example, the optical transmitter may
transmit a code to one or more possible receivers indicating an
availability of service. In an environment such as a city, a set of
one or more broad optical beams functioning as a heartbeat signal
may be broadcast throughout the city to create an optical underlay
that may provide positioning by helping detect the location of one
or more receivers and provide appropriate orientation (e.g.,
alignment) instructions or guidance. In another example, a radio
frequency (RF) system may broadcast a heartbeat signal to create an
RF underlay and provide control for the diverged-beam
communications system 100. As described herein, orientation between
the optical transmitter and optical receiver may be primarily
described in the context of their alignment. It should be
understood, however, that the optical transmitter and optical
receiver may be oriented or otherwise positioned in manners other
than in what may be considered a traditional alignment, such as in
at least some non-line-of-sight (NLOS) cases.
[0077] An optical receiver 104 may request service in a number of
different manners, such as via a broad optical beams and/or the RF
system, providing or indicating its location to the control system
110 (e.g., via GPS or other geolocation method, or using timestamps
embedded into the optical communications channels). This and other
locations described herein may be represented in any of a number of
different manners, such as by a geolocation or a location relative
to another component of the diverged-beam communications system 100
(e.g., the location of the optical receiver relative to the optical
transmitter 102). The control system may calculate or select an
optical transmitter perhaps from a plurality of such optical
transmitters, calculate or select the direction in which to point
the selected optical transmitter, and steer the selected
transmitter to point it in the selected direction using the
pointing system 108. In addition, the broad optical beams and/or
the RF system may provide guidance as to the location of the
optical transmitter, and convey commands to the receiver for
appropriate movement to obtain detection, initial
acquisition/handshake, and/or to optimize reception.
[0078] In some examples, narrow-angle, high-resolution pointing
costs may be relatively high, but beam divergence may result in
increased laser (optical) costs because of the increased power
requirement. As such, there may be a tradeoff between laser costs
and pointing costs and an optimum range of operation with a
sufficiently high transmission efficiency and moderate laser and
pointing costs.
[0079] As to pointing costs, current simple tracking systems
arranged to provide two-axis motion, such as those used in home
security cameras, offer 0.2 degrees of pointing resolution for
approximately $20. Current military systems achieve roughly 0.001
degrees of pointing precision for about $5M. In terms of beam
divergence, a moderately-powerful laser beam can be diverged to
produce a 100 meter spot size at a distance of a few hundred meters
to a few kilometers. Beam divergence may be produced using any of a
number of different techniques, including beam divergence through
optical, mechanical, electro-optical and optical-mechanical
techniques, and the like. These techniques can include beam
divergence as well as beam steering, either through an aperture or
directly.
[0080] As an example of one suitable pointing system 108, tracking
accuracy of 0.1 degrees can be achieved at a reasonable cost, and
an optical transmitter 102 (e.g., laser) producing a sufficiently
powerful beam that can travel up to 100 km. In some examples, the
performance of the pointing system may be improved through other
components such as by adding appropriate optics to either or both
the optical transmitter or receiver 104. Examples of suitable
optics for this purpose include microelectromechanical systems
(MEMS) mirrors, dynamic optics such as steerable liquid lenses,
deformable mirrors, and the like. These devices may have a fairly
small angular tuning range, for example existing steerable liquid
lenses tune +/-0.6 degrees, but may have fine control and
relatively low cost. An array of optical transmitters may serve up
to 10,000 receivers 104 using such a pointing resolution, and may
achieve data rates much superior to current cellular data
systems.
[0081] In some examples, either or both of the optical transmitter
102 or optical receiver 104 may include respectively an array of
optical transmitters or optical receivers (or respectively an array
of emitters or detectors--as described in greater detail below). An
array of optical transmitters (or emitters) may be arranged in
multiple directions, with the array in some examples forming a
two-dimensional (2D) or three-dimensional (3D) shape (e.g., cube,
sphere, hemisphere). Similarly, an array of optical receivers (or
detectors) may be arranged in multiple directions. In these and
other similar examples, a pointing system 108 may be omitted with
optical transmitters (emitters) or optical receivers (detectors) of
a respective array being configured to selectively activate and
deactivate based on their orientation (e.g., alignment) with
respect to a desired optical receiver or optical transmitter. In
some examples, this selective activation and deactivation may be
accomplished by the optical transmitters (emitters) or optical
receivers (detectors) of a respective array being configured to
selectively switch on and off. And in some examples, their
orientation may be inferred based on the relative powers of the
received optical beams, or according to some other algorithm.
[0082] In some deployments of the technology, atmospheric
conditions such as fog can be problematic, especially if going
completely horizontally through the fog. In one example, a backup
long-wavelength infrared (e.g., 8-15 .mu.m) system may be used. In
another example, shorter wavelengths may be used at higher power
with time gating of the receiver to range gate the photons to only
those that travel on a direct or nearly-direct line to the optical
receiver 104, which may reduce if not eliminate scattered light and
improve SNR. In another example, RF systems may be used as a backup
at lower data rates.
[0083] In certain scenarios (e.g., tracking a vehicle, mobile
device), a wide, highly-diverged beam may be necessary because a
narrow beam may not be able to accurately track the optical
receiver 104. In these examples, use of reflected beams, with
reflections occurring off one or more surfaces such as the sides of
buildings, ground surfaces or other surfaces, with those
reflections occurring based on use of sufficiently wide and
powerful beams. As described herein, references to reflection may
refer equally to specular reflection and diffuse reflection or
scattering such as that due to Lambertian reflectance.
[0084] Direct reception can be accomplished using a direct optical
receiver 104a configured to intercept an incident beam.
Alternatively, a reflected optical receiver 104b may be used to
detect a reflected beam produced from a reflector 118 (including
instances of a scattered beam produced from a scatterer). In one
example, a single receiver may be configured to serve as either or
both a direct receiver and reflected receiver. The receivers can
detect the beam and recover the data. Because the beam is diverged,
orientation (e.g., alignment) may not be as critical and reception
may be obtained in the wide field of the beam, or anywhere the beam
is reflected. In some examples, the optical transmitter 102 may
direct the optical beam at a reflector or point of reflection on a
reflector predetermined to provide an acceptable likelihood of
direct or reflected reception by one or more optical receivers. In
these and other similar examples, one or more of the optical
receivers may (if desired) provide feedback back to the optical
transmitter to guide it into a more desired orientation with the
respective optical receiver(s).
[0085] Turning now more particularly to the optical transmitter
102, in some examples, the optical transmitter may include one or
more emitters in the form of one or more at least partially
coherent (coherent or partially coherent) lasers configured to emit
optical beams of visible, ultraviolet or infrared light. That is,
the optical transmitter may be configured to operate and emit
optical beams in the visible range (e.g., 400-700 nm), ultraviolet
range (e.g., 200-400 nm in wavelength) or infrared range (e.g., 700
nm-1 mm) of the electromagnetic spectrum. In particular examples of
infrared light, the optical transmitter may be configured to
operate and emit optical beams in the short-wavelength infrared
range (e.g., 1.4-3 .mu.m wavelength), or any one or more of the O,
E, S, C, L or U infrared bands. Examples of suitable lasers include
solid-state lasers, laser diodes, solar lasers and the like. In a
more particular example, as explained in greater detail below, the
laser may be a vertical cavity surface emitting laser (VCSEL).
[0086] In some examples, the optical transmitter 102 may be
composed of one or more fixed-frequency or tunable lasers. In
either case, by either deploying multiple fixed-frequency lasers
with different frequencies, or tuning multiple tunable lasers to
different frequencies, the diverged-beam communications system 100
may employ multiple discrete frequencies. In some examples, the
system may operate over a range of frequencies as broad as 500 THz,
with a per-channel bandwidth of from 0.1 MHz to 1000 MHz, which may
provide between 500,000 and 5,000,000,000 discrete channels of
operation.
[0087] FIG. 2A illustrates an optical transceiver array 200 that in
some examples may correspond to a plurality of optical transceivers
202 (sometimes referred to as transceiver modules) each of which
includes an optical transmitter 102 and receiver 104, and an
example of which is shown in greater detail in FIG. 2B. As shown,
the transceiver array may have a suitable number of cells along its
width 204 as well as it height 206. In one example, the transceiver
array may include m.times.n transceiver modules with m=70 and n=30.
In one example, the diameter of the optics (e.g., apertures) on
each of the transmitter and receiver in the transceiver module may
be 3-4 inches, resulting in rectangular transceiver of
approximately 4-5 inches high and 7-8 inches wide. In other
examples, larger or smaller optics may be used. Larger optics may
be generally associated with longer connection ranges. The optics
may be of many types, including low-cost molded plastic lenses,
Fresnel lenses, mirrors and the like. Further, other shapes besides
the square or rectangular shape shown may be used for the
transceiver array. In one example a triangular structure may be
used, while in another example an octagonal structure may be used.
In other examples, as shown in FIG. 2C, existing network
infrastructure, such as cell towers, may be used regardless of
their geometry. FIG. 2B illustrates a transceiver module 202 in
further detail, in accordance with some example implementations. As
shown, for example, the transceiver may include an optical
transmitter 102 with one or more emitters such as one or more laser
diodes (an array of emitters 208 being shown for example). One or
more optics 210, 212 (e.g., one or more lenses, mirrors) may be
used to spread a collimated beam from the emitters, and refocus the
beam and produce a relatively broad and partially collimated (e.g.,
diverged) optical beam. In another example, the optic(s) may be
configured to converge a collimated beam from the emitters to a
point between the optical transmitter and optical receiver 104, at
which point the beam may be spread for receipt by the optical
receiver.
[0088] As also shown, the transceiver module 202 may contain an
optical receiver 104 with one or more detectors such as one or more
PIN photodiodes, avalanche photodiodes (APDs), photomultiplier
tubes (PMTs) or the like (an array of detectors 214 being shown for
example). The receiver may be used to detect an incoming optical
signal, and one or more optics 216 (e.g., one or more lenses,
mirrors) may be used to focus incoming light onto the receiver. A
pointing system 108 such as a pan-and-tilt control may be used to
move both the optical transmitter and receiver and aim them at the
appropriate areas. The pointing system 108 may be generally
configured to point the transceiver module 202. In some examples,
however, the optical transmitter 102 or receiver 104 may be pointed
independent of the other. As shown in FIGS. 2C and 2D, in some
examples, the pointing system may further include a receiver
pointing system 218 configured to specifically point the optical
receiver. As also shown, in some examples, the receiver pointing
system may be located within the transceiver module. A receiver
pointing system may allow alignment of the optical receiver to an
incoming beam to optimize the signal. The beam may carry data, or
as explained below, may carry a heartbeat.
[0089] FIG. 3 illustrates one or more optical transceiver arrays
202 retrofitted to existing network infrastructure 300 such as a
cell tower. In a scenario such as that shown in FIG. 3, each
transceiver array may provide 120.degree. of coverage, and three
arrays may provide 360.degree. of coverage. Or in some examples, a
single transceiver array may be configured to provide 360.degree.
of coverage, such as by an array arranged in multiple directions
forming a 3D shape. These arrays may include a wide range of
numbers of optical transmitters 102 and receivers 104, from under
ten to hundreds, to thousands and up to a million or more. In some
examples, each user may be rapidly switched between the optical
transmitters and receivers, which may facilitate safe operation of
the system.
[0090] FIGS. 4A and 4B illustrate a mobile device 400 such as a
smartphone that may be equipped with an optical transceiver 402
including an optical transmitter 102 and receiver 104, in
accordance with some example implementations. As shown, the mobile
device may include one or more upper and lower transceiver optics
(apertures) in order to be able to receive an appropriate reflected
beam. In the example shown, a primary receive lens 404 and primary
transmit lens 406 may be located at the bottom of mobile
transceiver, and a secondary receive lens 408 and secondary
transmit lens 410 may be located at the top of the mobile device.
In one example, an optical duplexer 412 may be used in conjunction
with a lower light pipe 414 and an upper light pipe 416 to guide
the light appropriately from either the primary or secondary lenses
to the optical transceiver.
[0091] In some examples, the mobile device 400 may be an existing,
retrofitted mobile device, or manufactured as an integrated mobile
device. The mobile device of some examples may combine GPS location
and device orientation with knowledge of an optical transmitter 102
or an optical relay node to enable the mobile device to initiate or
respond to initiation of transmit-receive handshake protocols to
optimize an optical link between the optical transmitter/optical
relay node. The mobile device in some examples may include a
digital interface, receiver optics with steerable sunlight shading,
laser transmitter/modulator, beam director and
receiver/demodulator.
[0092] As indicated above, beam divergence in the diverged-beam
communications system 100 may be produced using any of a number of
different techniques. In one example, a point source emitter such
as a laser diode or an optical fiber may be used in the optical
transmitter 102, and a diverged beam may be generated by the use of
appropriate optics such as concave lenses, convex mirrors or convex
lenses where the light source is not at the focus. FIGS. 5A and 5B
illustrate example techniques for achieving beam divergence using
an extended source of an array of emitters 208 such as VCSELs,
where the extended source is larger than the spot size of the
optical beam at the optical transmitter. As shown in FIG. 5A, the
transmitter with the extended source may be placed at the focus of
one or more optics 502 (e.g., optics 210, 212). The emitters of the
array may emit respective collimated beams 504 but with different
angles due to the spatial extent of the array. This may produce an
overall diverging beam whose divergence angle may be set by the
size of the array and focal length of the optics.
[0093] As shown in FIG. 5B, the array of emitters 208 may be
situated closer to or farther from the optics 502, and thereby away
from its focus 506, to increase the degree of divergence. In this
situation, the emitters may emit respective diverged beams 508,
again with different angles. The divergence angle in this situation
may be set by the size of the array and degree of de-focus due to
the situation of the array away from the focus of optics.
[0094] In another example, the transmitter 102 may use a source
emitter with an inherent divergence that is close to the desired
system divergence. For example, the divergence angle of VCSEL
lasers may be less than the divergence of edge-emitting laser
diodes and may approach the divergence needed by the system. In
this case, no additional optics may be needed. It should be noted
that some combination of the aforementioned approaches may also be
used to achieve the desired system beam divergence. It should also
be noted that it may be advantageous for the divergence in the
vertical and horizontal directions to be different.
[0095] A transmitter 102 with an extended source of an array of
emitters may also lead to different power limits for desired
operation, which in some examples may at least in part relate to
eye safety. Most laser power limit calculations are predicated on a
collimated beam where the light can be focused to a very small
point, on the order of 20 microns. In the far field, this may be
the correct limit for the extended source, since it will appear to
be nearly a point source. In the far field, the diverged-beam
communications system 100 may already be below a desired power
limit since the beam is diverging. In the near field, closer to the
transmitter, however, the power level may be greater than the
desired power limit for collimated beams. The extended nature of
the source emitters may increase this limit since an extended
source may not be focused to a single spot, but rather may be
focused to an area. This limit may depend on the beam divergence
and distance between the transmitter and to where the emitters are
focused, but may increase the desired power limit. In turn, this
may simplify system design and reduce cost if some or all of the
power limit monitoring is not needed.
[0096] Although the transmitter 102 may employ any of a number of
different types of emitters, VCSEL arrays are a particularly
suitable example of a type of emitter that may also naturally lead
to extended sources. A VCSEL array has an array of individual
diodes that may be wired in parallel, which may lead to a higher
than desirable input capacitance for high frequency high data rate
applications. One current 2W VCSEL array has approximately 1000
diodes in parallel each with a nominal 0.4 pF capacitance, which
produces an input capacitance of 400 pF. In some examples, the
wiring may be reconfigured to power the VCSEL array as 10 different
sub-arrays connected in a parallel configuration, each of the
arrays having 100 diodes and thus a capacitance of 40 pF. The
connected sub-arrays may be driven using 10 separate amplifier
modulators each driving 40 pF.
[0097] In another example, the wiring may be reconfigured to
connect the 10 sub-arrays in a series configuration, which may
reduce the capacitance to 4 pF (40 pF/10) and allow driving all
1000 diodes with a single amplifier modulator, eliminating problems
of synchronizing and phasing the multiple amplifiers. The driving
voltage for the series configuration may also be increased tenfold,
which may increase the efficiency of driving the array since it can
be easier to drive a higher voltage load at lower current than a
lower voltage load at higher current. Power losses may also be
decreased.
[0098] In accordance with example implementations, then, an array
of emitters such as VCSELs may be arranged in various parallel
and/or series configurations to optimize the electrical design from
both the maximum data throughput rate and power efficiency points
of view. The electrical drive waveform may also be tailored to
minimize the impact of turn-on and/or turn-off overshoot or
oscillations due to relaxation resonances, off-state bounce and
other effects. The waveform may depend on how many individual
VCSELs are in series or parallel or some combination thereof.
[0099] In addition to the above, VCSELs may provide a number of
other benefits to example implementations of the present
disclosure. VCSELs may be easier to directly modulate since each
laser element inherently has a short cavity. Direct modulation may
lead to simpler and less expensive system design. The higher
reliability of each laser along with the parallel nature of the
array may lead to very high system reliability and long MTBF
(mean-time-between failures). Even if a few lasers within the array
fail, the overall decrease in power may be minimal. The extended
nature of the VCSEL array and high efficiency may minimize issues
of heat generation and transport out of the array.
[0100] Both of these may be important for high bandwidth, low cost
FSO systems. VCSEL arrays may also include a larger number of
elements per array, higher overall output power and higher
modulation bandwidth. VCSELs are typically quite efficient, above
40% in some cases. In some examples, the same array may include
VCSELs with multiple wavelengths, and an array may include
independently-controlled or modulated subsections. The available
wavelengths may also expand. Currently most VCSEL arrays are
between 800 nm and 900 nm, but wavelengths may become available
over the visible range of 400 nm up to 800 nm as well as some of
the more typical telecom wavelengths including around 1310 nm and
around 1550 nm. Part of the VCSEL array may operate as the
heartbeat (explained in greater detail below) where it may be
modulated at a much slower rate than a data portion of the array
and generate a desired power level.
[0101] Turning now to the optical receiver 104, a number of
communication systems have used fairly small PIN photodiodes or
APDs, which may be suitable in some example implementations. The
small size enables high bandwidth and also matches the core size of
fiber optics, which ranges from .about.5 microns up to 200 microns
or more. In accordance with example implementations, the beam may
be centimeters to many meters across at the detector, which may
benefit from the collection of photons from an aperture that is a
centimeter up to many centimeters across. This may be accomplished
with optics, such as lenses, mirrors and the like, but there may be
a trade-off between the acceptance angle and the aperture size.
This may be mitigated by using an optical receiver with a larger
detector. The detector may be as large as the collection aperture,
and the optical receiver may not have any optics. In another
example, the optical receiver may include a very large area
detector and only have optical filtering in front of the detector,
or may have microlenses in front of individual detectors that make
up a detector array.
[0102] FIG. 6A illustrates an optical receiver 104 in accordance
with one example implementation of the present disclosure. As
shown, similar to the optical transmitter 102, the optical receiver
may include an extended source of an array of detectors 214 and one
or more optics 602 (the array of detectors having a size larger
than the spot size of the optical beam at the optical transmitter).
An array of detectors may have advantages similar to an array of
emitters at the optical transmitter. For example, by building a
detector based on many small detectors, the overall system
bandwidth may remain quite high. Likewise if a few detectors fail,
the impact on the overall system performance may be reduced.
[0103] FIG. 6B illustrates a similar optical receiver but further
including one or more optics such as one or more hemisphere lenses
604 of a high-index material, such as ruby, sapphire, or some
plastics or glasses, place in close proximity to the array of
detectors 214 to increase the optical gain. This increase may go as
the square of the index of refraction of the material. Shown as a
single lens right in front of the array of detectors, in some
examples, the lens may instead be an array of microlenses over
respective detectors of the array of detectors, which may reduce
the impact of fill factor on the array. These microlenses may be
formed and arranged to cover as much area as possible over and
between detectors in the array of detectors.
[0104] In the case of an array of detectors 214 with additional
optics, the acceptance angle of the optical receiver 104 may be as
high if not much higher than previous FSO systems since the optical
gain does not need to be as large to maintain the same or similar
optical aperture. As size of the detector increases from 200
microns up to 500 microns, and then to 1 mm and more, the
acceptance angle may increase from a fraction of a degree up to
several degrees, while maintaining an aperture size of 0.1 to 100
or more centimeters.
[0105] Briefly returning to FIG. 1, in some examples, the diverged
nature of the optical beam and the changing conditions in
non-line-of-sight (NLOS) cases may be improved by having adjustable
focus, astigmatism and/or pointing adjustment in the optical
transmitter 102 and/or receiver 104, which may be implemented in
any of a number of different manners. In some example
implementations, the optical transmitter 102 and/or receiver 104
may include one or more dynamic optics that may be configured to
enable one or more of the aforementioned adjustable focus,
astigmatism or pointing adjustment. These dynamic optic(s) may
include one or more surfaces that may change over time, and that in
some examples may be electrically controlled. Examples of suitable
dynamic optics included liquid lenses, deformable mirrors and the
like. More particular examples include liquid lenses manufactured
by Varioptic or Optotune. Liquid lenses in particular are generally
designed for imaging applications such as cell phone cameras, but
may be adapted for the diverged-beam communications system 100.
They are relatively small and low cost and may be operated by a
voltage or current across a membrane in the device. There are also
liquid lenses with astigmatism available, such as the Visayan from
Varioptic.
[0106] FIG. 7A illustrates an optical transmitter 102 including one
or more dynamic optics 702 configured to enable an adjustable focus
of the optical beam. For the optical transmitter, an adjustable
focus may enable adjustment of the beam diameter at a given
distance from the optical transmitter, from diverging 702 to
quasi-collimated 704 to converging 706. For example, in a short
range setup of 100 m up to 1 km, it may be desirable to increase
the beam divergence so that the power level is below the desired
power limit over as much of the beam path as possible. Conversely,
in instances in which the beam is to travel more than 1 km, up to
10 km or more, it may be desirable to decrease the beam divergence
so that the power level at the receiver stays above the threshold
required for a given data rate. Likewise, in some weather
conditions such as fog, it may be desirable to decrease the beam
divergence since there may be additional beam divergence generated
by the scattering of the fog.
[0107] FIGS. 7B, 7C and 7D illustrate use of dynamic optic(s) 702
to enable astigmatism in the optical transmitter 102 whereby the
vertical divergence 708 may be different than the horizontal
divergence 710 (focusing in the vertical axis is different than in
the horizontal axis). This may be desirable in cases such as a
tower-to-ground scenario where horizontal beam spread may be more
than the vertical beam spread. The optical receiver 104 may be
within a few meters of the ground vertically, but anywhere within
tens or hundreds of meters horizontally particularly at distances
of 1 km or more from the tower.
[0108] FIG. 7E illustrates use of dynamic optic(s) 702 to enable
pointing adjustment at the optical transmitter 102. As explained
above in the context of the pointing system 108, the dynamic
optic(s) may enable tuning the optical beam from straight 712 to
+/-0.6 degrees 714, 716, although it should be understood that
larger or smaller angles are possible. In some examples, this may
allow and adjustment resolution of .about.8 bits or 256 counts (1.2
degrees/256=80 micro-radians of resolution).
[0109] As shown in FIG. 8, in some examples, the diverged-beam
communications system 100 and method of example implementations may
support multiple beams from a single transmission point, such as
from an array of multiple optical transmitters 102, or a
transmitter with an array of emitters 208, which may support rapid
beam dithering 802. This beam dithering may then in turn be used to
mitigate scintillation and fading effects which degrade the quality
of service of narrow beams. A broad beam may be rapidly dithered
with a dither angle that is much less than the beam angle, which
may result in a beam that consistently hits a desired optical
receiver 104 while averaging out scintillation and fading effects.
This dithering or rapid beam path shifting may also offer increased
safety, with beams being shifted that the beam paths never dwell in
one area for an undesirable amount of time.
[0110] FIG. 9A illustrates an optical receiver 104 including
dynamic optic(s) 902 configured to enable an adjustable focus of
the optical beam. This adjustable focus may facilitate a match of
the optical receiver to characteristics of the optical beam. So for
a LOS case, as shown in FIG. 9B, the optical receiver may desire an
infinite or nearly infinite focus since the incoming beam may be
effectively collimated at the receiver. For LOS in weather, it may
be desirable to focus at some intermediate point between the
optical transmitter 102 and receiver since the scattering due to
rain, snow, fog or other may generate an effective source point
between the optical transmitter and receiver. As shown in FIG. 9C,
this may be similarly the case for NLOS in which it may be likewise
desirable to focus on some intermediate point between the optical
transmitter and receiver.
[0111] FIGS. 9D and 9E illustrates use of dynamic optic(s) 902 to
enable pointing adjustment at the optical receiver 104. As shown,
the dynamic optic(s) may allow adjustment of a quasi-collimated
beam so that it hits a single detector or a subset of an array of
detectors 214 of the optical receiver. This may be accomplished at
the same time as adjustment of the focus at the optical
receiver.
[0112] At least an initial alignment between optical transmitter
102 and receiver 104 for communication may be accomplished in any
of a number of different manners. FIG. 10 illustrates a few example
techniques introduced above. As shown, the diverged-beam
communications system 100 may be configured to provide high-power,
high-speed optical communications 1002. In some examples, in some
examples, an RF system may underlay the diverged-beam
communications system, and provide low-power RF communication 1004
between the optical transmitter and receiver to establish their
location and assist in their alignment. This RF communication may
include an RF heartbeat signal composed of a set of one or more RF
signals that may assist in alignment of the optical transmitter and
receiver. And in some examples described in greater detail below,
the optical transmitter may be configured to emit an optical
heartbeat 1006 (an optical heartbeat signal) composed of a set of
one or more broad optical beams, which may assist in alignment of
the optical transmitter and receiver. In some examples, the
heartbeat signal may be modulated to carry or indicate the location
(geographic location) of the optical transmitter, and/or a signal
may cause the optical receiver to return its location or an
indication of its location to the optical transmitter, so that the
optical transmitter and receiver may be aligned (or their
orientation with respect to each other or the optical beam may be
otherwise adjusted). The optical transmitter and receiver may know
their locations, or in some examples may acquire their locations
such as via GPS or other geolocation method. Or in some examples,
the optical transmitter or receiver may determine the location of
the other such as using timestamps embedded into the heartbeat
signal.
[0113] In accordance with example implementations, an optical
heartbeat emitted by the optical transmitter 102 may be an optical
beam that is at or below a desired power limit in all cases, and
which may be modulated at a slower rate than the system's
high-power, high-speed optical communications 1002. For the
alignment case, the optical transmitter may emit the heartbeat
(optical or RF). The optical receiver 104 may detect the heartbeat,
such as through a camera with a large field of view (e.g., 10's of
degrees up to 180 degrees or more) configured to capture at least a
portion of the heartbeat. The optical receiver may identify the
optical transmitter heartbeat, and move, if needed, to align with
the optical transmitter. Or in some examples including an array of
optical receivers, one or more of the optical receivers of the
array most-closely aligned with the optical transmitter may be
selectively activated (e.g., switched on) with the other optical
receivers selectively deactivated (e.g., switched off), without
movement of any of the optical receivers. Other techniques for
selective activation or deactivation of optical receivers may be
employed, including techniques based on the relative power of the
received optical beam, or through the heartbeat. In any event, the
optical receiver may then through an associated transmitter
(optical or RF) transmit a heartbeat back to the optical
transmitter. The optical transmitter through an associated receiver
may receive the receiver heartbeat, and begin transmitting
high-speed optical communications. In some examples, the receiver
heartbeat may also guide the optical transmitter into increased
alignment with the optical receiver, such as before transmission of
high-speed optical communications.
[0114] In some examples, the optical transmitter 102 may monitor
the heartbeat from the optical receiver 104. In instances in which
the optical receiver heartbeat falls below a threshold level or
other criteria, the optical transmitter may disable high-power,
high-speed optical communications 1002. The optical transmitter may
then wait until it picks up or otherwise detects the receiver
heartbeat again (above the threshold level or other criteria), and
then reestablish high-power, high-speed optical communications. The
shutdown time may be sufficient to keep the optical exposure level
below the desired power limit, but may allow reestablishment of the
high-speed optical communications as quickly as possible (e.g., on
the order of milliseconds or faster). For example, a tree branch
waving back and forth in the beam path may interrupt the beam for a
fraction of a second each time it passed through the beam, but a
sufficiently-fast restart may minimize any impact on communications
throughput.
[0115] In some examples, alignment between the optical transmitter
102 and receiver 104 may be at least partially accomplished within
the optical receiver, and according to a number of different
techniques. FIGS. 11A and 11B illustrate two examples. As shown in
FIG. 11A, the optical receiver may include a filter or a
partial-pickoff mirror 1102 configured to reflect a portion of the
detected optical beam through appropriate optic(s) 1104 and to a
camera 1106. The camera may be configured to capture the reflected
portion of the optical beam, and communicate with electronics of
the optical receiver to drive coarse steering (e.g., motor, receive
pointing system 218) and/or fine steering (e.g., MEMS mirror,
dynamic optic or other method) based on the captured reflected
portion of the optical beam. In some examples, the array of
emitters 208 of the optical transmitter may include one or more
emitters, or the optical transmitter may include one or more
additional emitters, configured to emit an optical beam at a rate
less than the frame rate of the camera to allow tracking, lock-in
and heartbeat.
[0116] As shown in FIG. 11B, in another example, the optical
receiver may include a plurality of photodiodes 1108 (four
illustrated as photodiodes 1108a, 1108b, 1108c, 1108d) positioned
around a periphery of and that may be shadowed by a limiting
aperture 1110. In this example, the photodiodes may be configured
to detect a relative power of the detected optical beam at the
photodiodes (relative to the overall power of the detected optical
beam at the detector 214), and communicate with electronics of the
optical receiver 104 to drive coarse steering (e.g., motor, receive
pointing system 218) and/or fine steering (e.g., MEMS mirror,
dynamic optic). In some examples, only three photodiodes may be
used, such as photodiodes 1108a, 1108b and 1108c located
approximately 120 degrees apart around a circle. In a more
particular example, the feedback control could be summarized as
follows for the relative powers detected at the respective
photodiodes: [0117] If [photodiode 1108b>photodiode 1108c], then
pan in a first direction (e.g., right); [0118] If photodiode
1108b<photodiode 1108c, then pan in an opposite, second
direction (e.g., left); [0119] If [photodiode 1108a>(photodiode
1108b+photodiode 1108c)/2], then tilt a third direction (e.g.,
down); and [0120] If [photodiode 1108a<(photodiode
1108b+photodiode 1108c)/2], then tilt an opposite, fourth direction
(e.g., up).
[0121] Although described in the context of steering or panning the
optical receiver 104, as explained above, in some examples
including an array of optical receivers, alignment may be
accomplished without movement of an optical receiver. In these
examples, one or more of the optical receivers of the array
most-closely aligned with the optical transmitter may be
selectively activated (e.g., switched) on with the other optical
receivers selectively deactivated (e.g., switched off), without
movement of any of the optical receivers.
[0122] As explained above, in some examples, a single optical
transmitter 102 may serve multiple receivers, such as those
residing within the cone of its optical beam (for the LOS case). As
explained above, this may be accomplished in a number of different
manners, such as according to one or more multiplexing techniques.
FIG. 12A illustrates one example multiplexing technique, namely,
spectral multiplexing. As shown, the array of emitters 208 of the
optical transmitter may be divided into groups of one or more
emitters with different, respective wavelengths (shown as .lamda.1,
.lamda.2, .lamda.3, .lamda.4, and with a separate emitter for the
aforementioned heartbeat). The emitters of the groups may be
arranged in the array by region, as shown; or in other examples,
the emitters may be interspersed with one another. The optical
receivers 104 may include one or more wavelength-specific or
wavelength-tunable filters 1202 in front of all or parts of one or
more of their detectors 214. In some examples, tunable filters may
be dynamically tunable as the wavelength of the emitters shift due
to various conditions such as changing environmental conditions,
particularly temperature.
[0123] In addition to or in lieu of spectral multiplexing, the
diverged-beam communications system 100 in some examples may employ
spatial multiplexing (SMX), such as in a manner shown in FIG. 12B.
As shown, the array of emitters 208 of the optical transmitter may
be arranged in a pattern of emitters (e.g., pattern of groups of
one or more emitters) that may be independently modulated (shown as
region 1, region 2, region 3, region 4, and with a separate emitter
for the aforementioned heartbeat). The array of detectors 214 at
the optical receiver 104 may be similarly arranged in a
corresponding pattern of detectors. In some examples, the system
may use spatial multiplexing in clear conditions. The system may
then turn off or reduce the spatial multiplexing in the event of
significant scattering (e.g., from weather) or a NLOS case,
potentially reducing overall bandwidth but maintaining
communication capacity.
[0124] Further features of the diverged-beam communications system
100 in various examples include the optical transmitter 102 trying
multiple paths and/or signalling the user to turn or move their
optical receiver 104 to optimize their alignment and increase the
received signal speed and quality of service. This signaling to the
user may be accomplished in a number of different manners such as
by text, symbols, speech, tones or other optical, acoustical,
tactile or other signals. In more particular examples, the optical
transmitter may signal the user to move to a window, or move to
their front, rear, left or right. In another particular example,
the optical transmitter may signal the user to turn in a circle,
and signal the user as to when to stop turning. Or in yet another
example, the optical transmitter may signal the user to move, turn
or tilt the optical receiver.
[0125] In some examples, retro-reflection may be used to facilitate
safe power levels. In accordance with these examples, the optical
transmitter 102 or array of optical transmitters may emit short
pulses, and include one or more detectors or other sensors
configured to monitor any return (reflected) signals. A
large-intensity reflection at a very short time delay may indicate
an object in the transmit beam at close range, which may cause the
optical transmitter or array to stop emitting that beam in favor of
a different emitter or different transmitter of the array. The
speed of response of the system may facilitate safe operation, as
the beam may be cut off before reaching certain known and regulated
energy thresholds that can only occur with sufficient accumulation
of light energy over a sufficiently long period of time.
[0126] In some examples, 3D modeling of the environment of the
diverged-beam communications system 100 may be used to optimize its
throughput. This may be accomplished using existing terrain and
urban architecture databases and imagery, data collected by system,
or any combination thereof. In a more particular example,
retro-reflection intensities and time delays can be used to effect
a LIDAR-type capability. From the 3D model of the environment,
optimum beam paths may be predicted, both for fixed and mobile
optical transmitters 102 and receivers 104. In the case of mobile
optical receivers, the path of the receiver may be modeled into the
3D model to create an optimum beam path for reception by the mobile
user. The 3D model may be adaptive, responding to changes such as a
good reflector 118 (e.g., a parked truck that moves to a different
location). Beam reflection and transmission intensity information
obtained by the system may be used to improve the initial 3D model,
or to create a new 3D model. In one example, a fixed-delay router
(optical relay node) may be used in which the same components and
frequencies may be used in both the large-scale external carrier
systems (e.g., cell phone macrocell sites) and local router
systems. This may provide economies of scale and commonality that
improves system efficiencies.
[0127] In some examples, steerable relay beams may be generated by
the diverged-beam communication system 100. Cooperating
users/routers may relay signals from macrocell to mobile or other
users.
[0128] In some examples, autonomous fixed or mobile optical
transmitters, receivers or transceivers (sometimes referred to as
cell nodes) may be deployed, such as in the form of very low-weight
and low-power optical relay nodes. In these examples, the
lightweight optical relay nodes may be deployed in the air (e.g.,
in balloons, unmanned aerial vehicles, dirigibles) or on buildings,
towers, poles, trees or other locations above ground level. In one
example, these autonomous optical transmitters, receivers or
transceivers may be solar powered.
[0129] In some examples, exterior, interior, or both light guides
may be used to propagate signals from the diverged beam
communication system.
[0130] In some examples, rapid beam frequency scanning may be used
for security, interference suppression and/or SNR improvement to
combat solar background and multipath distortion. In one example,
an all-semiconductor akinetic laser may be electrically tuned and
avoid the use of any mechanical or electro-mechanical
components.
[0131] In some examples, an ad-hoc network may be created, with
active users contributing to and forming the network.
[0132] In some examples, the diverged-beam communication system 100
may be integrated into existing mobile data transmission devices
such as mobile phones, tablets, or personal computers by use of a
piggyback device, similar to some mobile phone batteries, where the
optical components may be integrated with the existing mobile
device.
[0133] In some examples, mechanical baffles may be used in the
optical receiver architecture to allow for selection of a single
beam from the optical transmitter, thus reducing multipath problems
and the effect of incident sunlight on the receiving system. In
another example, optical collimators at the optical receiver 104
may reject signals outside of a narrow acceptance range,
ameliorating multipath effects.
[0134] Multipath factors and interference in the diverged-beam
communication system 100 may be addressed in a number of ways. In
one example, the likely strongest signal path (whether direct or
reflected) between the optical transmitter 102 and receiver 104 may
be short enough that other paths with signal strength above a
rejection threshold are insufficiently longer or shorter than the
stronger signal path to cause inter-symbol interference. This
situation may apply to relatively short paths at relatively low
data rates. In one example, coding may be used to mitigate the
effects of multipath interference. In another example, optical
signals may be frequency division encoded to account for the
smearing of the pulses in the multipath environment and to reduce
inter-symbol interference. The receiver may reconstruct the
signals. As such, orthogonal frequency division multiplexing (OFDM)
may be used to combat the multipath issue. In another example,
synchronized receiver time gating may be used to restrict photons
to only those that travel the shortest or most efficient path.
[0135] To further illustrate the diverged-beam communications
system 100 of example implementations, reference will now be made
to FIGS. 13-17, 18A and 18B, which illustrate various scenarios in
which example implementations may be deployed. As explained above,
certain optical receivers 104a may detect incident beams from an
optical transmitter 102, while other optical receivers 104b (or
even the same receivers) may detect reflected beams (including
scattered beams) from a reflector 118 (including a scatterer). FIG.
13 illustrates a scenario in which a building 1302 may block an
emitted optical beam (shown as blocked incident beam 1304) from
reception by an optical receiver 104b. As shown, though, a point of
reflection 1306 on an appropriate reflector such as the ground or
another building may produce a reflected beam 1308 that may be
received by the optical receiver 104b. The optical receiver here
may be fixed or mobile, although for a mobile receiver, additional
alignment to the incident or reflected beam may be desired or
required, and sensitivity issues may require additional
consideration.
[0136] FIG. 14 illustrates an example deployment of the
diverged-beam communications system 100 in a fixed-receiver
environment. As shown, an array of optical transmitters, such as of
an optical transceiver array 200, may be placed on a host building
1402, tower or other location. The optical transmitters may produce
beams including an incident beam 1404 with a direct line-of-sight
(LOS) to one or more optical receivers 104a (shown in a building
1406), and another, second incident beam 1408 that may be reflected
or scattered to produce a reflected/scattered beam 1410 detectable
by one or more optical receivers 104b (shown in another building
1412). In another example, not shown in the figure, the
reflected/scattered beam may be produced by the direct
line-of-sight beam. The optical receiver 104a may receive light
directly from the direct line-of-sight beam, and it may also
receive direct line-of-sight light from the second beam. The second
beam may be used to generate the reflected/scattered beam, which
may be Lambertian in nature and scatter light over a full 180
degrees. This second beam may then be received by optical receiver
104b. In another example not shown in the figure, a fixed
reflective or scattering surface, or both types of surfaces, may be
attached at an initial point of incidence of the second beam to
generate a reflected/scattered beam that may more efficiently
direct the light to the optical receiver 104b.
[0137] As indicated above, the optical receivers 104a, 104b in the
scenario of FIG. 14 may be fixed. In other examples, and as more
particularly described below in an example scenario, either or both
of the optical receivers may instead be moveable or mobile within a
certain area. In one example, a user may physically carry or place
their receiver to differing locations within a certain area. In
another example, the either or both receivers may be equipped with
devices that allow them to move autonomously in one or more (e.g.,
six) degrees of freedom to improve reception.
[0138] FIG. 15A illustrates reception of an incident beam 1502
through a window 1504 of a building (e.g., building 1410, 1412),
vehicle or other structure, which beam may reflect off a ceiling,
floor or wall to create a reflected beam 1506. FIG. 15B illustrates
a similar scenario in which the incident beam is received by a
router (optical relay node) 1508 for relay as another incident
beam, which similarly may reflect off a ceiling, floor or wall to
create a reflected beam. In either instance, the incident beam may
be directly received. The reflected beams may also be directly
received, or they may result in remnant radiation 1510 in the form
of propagated radiation such as what may pass through a doorsill
gap 1512. Because the system can adapt to the various power levels
ranging from those which occur in directly received incident or
reflected beams to those occurring in propagated radiation, the
transmission path is not critical and the system can pick up
incident, reflected, or remnant radiation as required.
[0139] FIG. 15C illustrates more particularly the router (optical
relay node) 1508 according to some example implementations. As
shown, the router may include an outside arrangement and an inside
arrangement. The outside arrangement may include one or more
outside optical receivers with one or more an outside detectors
1514 configured to receive an optical beam, and the inside
arrangement may include one or more inside optical transmitters
with one or more inside emitters 1516 configured to retransmit the
optical beam. Although not separately shown, in some examples, the
inside arrangement may also include one or more inside optical
receivers with one or more inside detectors configured to receive
an optical beam, and the outside arrangement may include one or
more outside optical transmitters with one or more outside emitters
configured to retransmit the optical beam. In one particular
example, the outside and inside detectors may cover an area of 100
cm2, and provide 1000 photons/bit; and the inside and outside
emitters may cover .+-.45 degrees. The inside emitter may be
capable of 20 degrees pointing, while the outside emitter may be
capable of 0.5 degrees pointing.
[0140] FIG. 16 illustrates an example deployment of the
diverged-beam communications system 100 in a mobile-receiver
environment. As shown, again, an array of optical transmitters,
such as of an optical transceiver array 200, may be placed on a
host building 1402, tower or other location. The optical
transmitters may produce beams including an incident beam 1602 that
produces building-reflected beams 1604, as well as ground-reflected
beams 1606. These beams including the incident and reflected beams
may then be received by one or more optical receivers 104a, 104b.
In some examples, the receivers may intentionally "look away" from
the incident beam to obtain a more stable, although
lower-power-level beam than the direct beam. For example, radiation
reflected from a building or the ground may be more constant than
the direct radiation from the transceiver array. This determination
may be made in a number of different manners, such as by SNR. As
such, the optical receivers may preferentially detect or otherwise
lock onto a reflected beam, and avoid direct detection of the
incident beam.
[0141] FIG. 17 illustrates an example deployment of the
diverged-beam communications system 100 in urban and rural (e.g.,
wooded) environments. Yet again, this example includes an array of
optical transmitters, such as of an optical transceiver array 200,
placed on a host building 1402, tower or other location. As
illustrated in this scenario, incident beams 1702 from the optical
transmitters may be scattered from normal, relatively-homogeneous
atmospheric particulates, and thereby produce reflected/scattered
beams 1704. Additionally, the incident beams may be scattered from
inhomogeneous atmospheric particulates, such as water vapor 1706
arising from a roof vent, or fog, clouds, smoke or the like, and
thereby produce additional reflected/scattered beams. These
reflected/scattered beams may be received by fixed or mobile
optical receivers. In some examples, shorter wavelengths such as
blue to ultraviolet wavelengths may be beneficial due to their
larger degree of scattering.
[0142] FIGS. 18A and 18B illustrate other example deployments of
the diverged-beam communications system 100 in urban and rural
(e.g., wooded) environments. In these examples, the system includes
one or more artificial satellites 1802, such as in a proliferated
network of satellites, equipped with optical transmitters or
transceivers including optical transmitters (not separately shown).
In this scenario, the satellites may be configured to transmit
nearly or effectively vertical optical beams in urban environments
and/or rural environments. These beams may be received by fixed or
mobile optical receivers. These beams may be received by fixed or
mobile optical receivers. In some examples, longer wavelengths such
as red to infrared wavelengths may be beneficial due to their
better penetration of clouds 1804, as shown in FIG. 18B.
[0143] FIG. 19 illustrates various operations in a method 1900
according to example implementations of the present disclosure. As
shown at blocks 1902 and 1904, the method may include respectively
modulating an optical beam with data; and emitting by an optical
transmitter, the optical beam carrying the data and without
artificial confinement for receipt by an optical receiver
configured to detect and recover the data from the optical beam.
The optical beam may be emitted with a divergence angle greater
than 0.1 degrees, and with a photonic efficiency of less than
0.05%. Or in another example, the optical beam may be emitted with
a divergence angle greater than 0.1 degrees, and with a photonic
efficiency of less than 0.01%. And the photonic efficiency may
relate a number of photons of the optical beam detectable by the
optical receiver, to a number of photons of the optical beam
emitted by the optical transmitter.
[0144] Example implementations of the present disclosure therefore
provide a diverged-beam communications system 100 and method for
optical communications, and more particularly diverged-beam
communications. In contrast to conventional FSO communications, the
system and method of example implementations use much broader beams
and much higher power levels. A significant portion of the power of
the optical beam may be "wasted" relative to more conventional FSO
communications, but the broader beams make pointing and tracking
either completely unnecessary or easy and affordable. These high
power broad beams also enable flexibility for mobile users, higher
quality of service, and the feasibility of non-line-of-sight (NLOS)
and obstructed line-of-sight applications in which reflection and
scattering propagation may enable high data rate throughputs and
high quality of service.
[0145] The diverged-beam communications system 100 and method may
employ a high-power solid state laser or other emitter for high
data rate wireless communications above 1 Gb/s, and in some
examples up to 1 Tb/s or more. In some examples, the system may
also optimize beam divergence for each communications link. The
beam divergence angles may be fixed or slowly or rapidly varied.
The system does not require line of sight between the optical
transmitter 102 and optical receiver 104. The emitter emission
powers used in the diverged-beam communications system may be such
that very high data transmission rates are achievable even with
multiple reflections.
[0146] The diverged-beam communications system 100 may be
contrasted with traditional FSO transmission in a number of
different manners, such as based on the photonic or transmission
efficiency and divergence of its optical beam. Here, photonic
efficiency may relate a number of photons detectable by the optical
detector, to a number of photons of the beam emitted by the optical
transmitter. In this regard, the number of photons detectable by
the optical detector may be defined or otherwise constrained by its
acceptance angle. In some examples, photonic efficiency may be
represented as a ratio (E) of the number of photons (A.sub.R)
detected by the optical receiver 104 divided by the number of
photons (A.sub.T) emitted by the optical transmitter 102
(E=A.sub.R/A.sub.T). The factor E may be affected by many
variables, including beam divergence or beam width.
[0147] While the traditional approach may achieve high efficiency
of transmission (E=10%-90%), it requires a very narrow beam with a
divergence on the order of 0.0005-0.005 degrees, which in turn
requires that it be pointed with extreme precision at a higher
cost. The diverged-beam communications system of example
implementations, on the other hand, uses a far broader beam. In
some examples, its beam may only achieve a photonic efficiency of
0.01%-0.00001%, but through a broader beam with beam divergence on
the order of 0.2-6 degrees, which may relax pointing requirements
such that the pointing system is highly affordable. In other
examples, the beam divergence angles may be in the range of 0.02-20
degrees, 0.1-10 degrees, or the like. In a more general case, in
some examples, the diverged-beam communications system may operate
with a beam divergence greater than 0.1 degrees, and with a
photonic efficiency of less than 0.01%. Or in other examples, the
diverged-beam communications system may operate with a beam
divergence greater than 0.1 degrees, and with a photonic efficiency
of less than 0.05%.
[0148] In existing FSO line-of-sight systems, the optical
transmitters are typically only 0.01-10 mW, or perhaps 30-50 mW.
These FSO systems have been limited by the cost of lasers and
safety concerns, which has meant that power levels over about 100
mW or over 1 W have been economically infeasible and/or unsafe.
These systems have therefore sought to minimize laser power. By
contrast, the diverged-beam communications system 100 of various
example implementations of the present disclosure seeks to utilize
an increased if not the maximum available laser power.
[0149] In the diverged-beam communications system 100, power of the
optical transmitter 102 may not be a limitation of the system, and
may only present economic challenges related to energy consumption
and cost. Existing wireless RF systems use a macrocell tower
architecture that expends 5 kW to 50 kW of peak power to service
approximately 1000 customers. This is approximately 5-50 peak watts
per customer. The utilization fraction or duty cycle of this power
consumption is quite low, approximately 0.1-1%, limited by spectrum
utilization. The energy costs of current wireless RF systems are
only in the range of US $0.1-1 per customer per month. Current
high-speed wireless RF systems charge approximately US $30-100 per
customer per month. Thus tower energy costs are covered by only
about 0.1-1% of the price of the service.
[0150] Economically, the diverged-beam communications system 100 of
example implementations may be challenged by energy costs in that
energy costs exceeding a reasonable fraction of total service
costs, say 10%, may cause economic issues. Thus, in some examples,
the system may operate at about 100 W-1000 W peak power per
customer based on energy consumption at typical spectrum
utilization rates. The higher-end power output may be particularly
beneficial in areas with more frequent dense fog, and the lower-end
may be useful in areas of more clear air. As demonstrated above,
these power levels may be ten times to over one million times that
of existing FSO systems. This may be the case, for example, where
the system uses the higher-end power output only when necessary to
drive signals through dense fog, which may occur only in a few
percent of geographical areas, and then only a few percent of the
hours per month.
[0151] The diverged-beam communications system 100 and method of
example implementations may also operate without an unobstructed
direct LOS, enabling communications with optical receivers 104 with
a highly obstructed or even completely blocked LOS to the optical
transmitter 102. In some examples, the receiver may even
intentionally "look away" from the optical transmitter in order to
improve quality of service since the reflected beam may have much
less variation than a direct, incident beam.
[0152] The diverged-beam communications system 100 and method of
example implementations may support multiple beams from a single
transmission point, such as from an array of multiple optical
transmitters 102, or a transmitter with an array of emitters 208,
which may improve reliability and quality of service. The system
may also support rapidly shifting or dithering optical beams from
one transmitter or emitter to another such that the beam paths
never dwell in one spot long enough to present an undesired
situation. This constantly shifting beams and paths may also enable
constantly finding new more optimal paths to maintain a constantly
high quality of service. Moreover, this dithering of broad optical
beams may be accomplished with a dither angle much less than the
beam angle, and may increase the likelihood that the beams hits its
intended optical receiver and average out scintillation and fading
effects.
[0153] Example implementations of the present disclosure may be
implemented with any combination of hardware and software. If
implemented as a computer-implemented apparatus, the examples may
be implemented using means for performing some or all of the steps
and functions described above.
[0154] Example implementations of the present disclosure can be
included in an article of manufacture (e.g., one or more computer
program products) having, for instance, a computer-readable storage
medium which, as a non-transitory device capable of storing
information, may be distinguishable from computer-readable
transmission media such as electronic transitory signals capable of
carrying information from one location to another.
Computer-readable medium as described herein may generally refer to
a computer-readable storage medium or computer-readable
transmission medium. The computer-readable storage medium has
embodied therein, for instance, computer readable program code
means, including computer-executable instructions, for providing
and facilitating the mechanisms of example implementations. In this
regard, the computer-readable storage medium may have
computer-readable program code portions stored therein that, in
response to execution by a processor (hardware processor), cause an
apparatus to perform various functions described herein. The
article of manufacture can be included as part of a computer system
including the aforementioned processor, or provided separately. Or
in some examples, the article of manufacture may be included in
electronics of one or more components of the diverged-beam
communications system 100, such as the optical transmitter 102,
optical receiver 104, modulator 106, pointing system 108, control
system 110 and/or data source 112.
[0155] Many modifications and other implementations of the
disclosure set forth herein will come to mind to one skilled in the
art to which these disclosure pertain having the benefit of the
teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is to be understood that the
disclosure are not to be limited to the specific implementations
disclosed and that modifications and other implementations are
intended to be included within the scope of the appended claims.
Moreover, although the foregoing descriptions and the associated
drawings describe example implementations in the context of certain
example combinations of elements and/or functions, it should be
appreciated that different combinations of elements and/or
functions may be provided by alternative implementations without
departing from the scope of the appended claims. In this regard,
for example, different combinations of elements and/or functions
than those explicitly described above are also contemplated as may
be set forth in some of the appended claims. Although specific
terms are employed herein, they are used in a generic and
descriptive sense only and not for purposes of limitation.
* * * * *