U.S. patent application number 14/925719 was filed with the patent office on 2017-05-04 for tunable optical module for optical communication.
The applicant listed for this patent is DiCon Fiberoptics, Inc.. Invention is credited to Ho-Shang Lee, Yu-Sheng Yang.
Application Number | 20170127158 14/925719 |
Document ID | / |
Family ID | 58638421 |
Filed Date | 2017-05-04 |
United States Patent
Application |
20170127158 |
Kind Code |
A1 |
Lee; Ho-Shang ; et
al. |
May 4, 2017 |
Tunable Optical Module for Optical Communication
Abstract
Light of at least two wavelengths is collimated in a forward
path towards a reflector and light of at least one of the
wavelengths is focused and detected in a return path, using in both
paths a lens unit including a first convex surface and a second
surface. A diffraction element diffracts the collimated light of
the at least two wavelengths into different wavelength components.
The reflector is moved so that one or more of the different
wavelength components will be focused by the lens unit in the
return path and detected. The second surface reflects the light of
the at least two wavelengths from an input port towards the first
convex surface and the first convex surface collimates the
reflected light of the at least two wavelengths in the forward
path, or the first convex surface focuses the one or more
wavelength components towards the second surface that reflects the
one or more wavelength components to an output port in the return
path. The first convex surface can be replaced by a GRIN lens
performing the focusing and collimating functions.
Inventors: |
Lee; Ho-Shang; (El Sobrante,
CA) ; Yang; Yu-Sheng; (Kaohsiung City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DiCon Fiberoptics, Inc. |
Richmond |
CA |
US |
|
|
Family ID: |
58638421 |
Appl. No.: |
14/925719 |
Filed: |
October 28, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 1/38 20130101; H04Q
2011/0015 20130101; H04Q 2011/003 20130101; H04Q 2011/0018
20130101; H04Q 2011/0016 20130101; H04Q 2011/0026 20130101; H04Q
11/0005 20130101 |
International
Class: |
H04Q 11/00 20060101
H04Q011/00 |
Claims
1. A tunable optical device, comprising: an input port and an
output port; a lens unit collimating light of at least two
wavelengths from the input port in a forward path and focusing
light of at least one of said at least two wavelengths to the
output port in a return path, said lens unit including a first
convex surface and a second surface; a reflector; at least one
diffraction element that is located in the forward path and/or the
return path between the lens unit and the reflector and that
diffracts said collimated light of said at least two wavelengths
into different wavelength components; and an actuator that moves
the reflector so that one or more of said different wavelength
components will travel in said return path to the lens unit and be
focused to said one output port by the lens unit; wherein the
second surface reflects the light of the at least two wavelengths
from the input port towards the first convex surface and the first
convex surface collimates the reflected light of the at least two
wavelengths in the forward path, or said first convex surface
focuses the one or more wavelength components towards said second
surface that reflects the one or more wavelength components to the
output port in the return path.
2. The device of claim 1, wherein when the second surface reflects
the light of the at least two wavelengths from the input port
towards the first convex surface and the first convex surface
collimates the reflected light of the at least two wavelengths in
the forward path, said first convex surface focuses the one or more
wavelength components to the output port in the return path without
involving said second surface.
3. The device of claim 1, wherein said first convex surface
collimates the light of the at least two wavelengths from the input
port in the forward path without involving the second surface and
focuses the one or more wavelength components towards said second
surface that reflects the one or more wavelength components to the
output port in the return path.
4. The device of claim 1, wherein the actuator that moves the
reflector so that an intensity of said one or more wavelength
components is controlled to be of a desired value.
5. The device of claim 4, wherein the actuator rotates the
reflector about two different axes, wherein rotation of the
reflector about one of the axes causes selection from the at least
two wavelengths the one or more wavelength components that travel
in the return path, and rotation about the other one of the axes
causes attenuation of said one or more of said different wavelength
components.
6. The device of claim 1, wherein the at least one diffraction
element diffracts said collimated light of the at least two
wavelengths from the lens unit into different wavelength components
towards the reflector, and said reflector reflects the different
wavelength components towards the at least one diffraction element
so that the different wavelength components are diffracted.
7. The device of claim 1, further comprising an optical source
providing light of one or more desired wavelengths to the input
port, so that the device functions as a transceiver.
8. The device of claim 7, further comprising a dichroic filter
coating on said second surface to reflect light from the input port
and transmit light from the optical source.
9. The device of claim 8, further comprising a second reflector
that reflects light from the optical source to the dichroic filter
coating.
10. The device of claim 7, further comprising a dichroic filter
between the convex surface and the at least one diffraction element
to transmit light from the input port and reflect light from the
optical source.
11. The device of claim 10, wherein the dichroic filter is a
coating on the at least one diffraction element.
12. The device of claim 1, further comprising a photodetector
package that includes an aperture and a photodetector aligned to
the aperture for receiving light directed to the output port.
13. The device of claim 12, wherein the input port is movable to
align a desired wavelength component of the diffracted different
wavelength components with the aperture, and wherein the aperture
does not transmit the diffracted different wavelength components
that are not the desired wavelength component to the
photodetector.
14. The device of claim 1, said lens unit including a lens element
with said first convex surface having an optical axis and said
second surface is at a slanted angle to and on one side of the
optical axis.
15. The device of claim 1, said lens unit including a convex lens
and a transparent block with a surface at a slanted angle to an
axis of the convex lens.
16. The device of claim 1, further comprising an optical fiber
ferrule at the input port and a photodetector package at the output
port, and a container that contains the optical fiber ferrule, the
lens unit, the at least one diffraction element, the reflector, the
actuator and the photodetector package.
17. The device of claim 16, further comprising an optical source
providing light of one or more desired wavelengths to the input
port so that the device functions as a transceiver, said container
also containing the optical source.
18. The device of claim 1, wherein said second surface is a
reflecting surface.
19. An optical tuning method, comprising: collimating light of the
at least two wavelengths from an input port in a forward path
towards a reflector and focusing light of at least one of said at
least two wavelengths to an output port in a return path, using a
lens unit including a first convex surface and a second surface;
using at least one diffraction element located in the forward path
and/or the return path between the lens unit and the reflector to
diffract said collimated light of the at least two wavelengths into
different wavelength components; and moving the reflector so that
one or more of said different wavelength components will travel in
said return path to the lens unit and be focused to said one output
port by the lens unit; wherein the second surface reflects the
light of the at least two wavelengths from the input port towards
the first convex surface and the first convex surface collimates
the reflected light of the at least two wavelengths in the forward
path, or said first convex surface focuses the one or more
wavelength components towards said second surface that reflects the
one or more wavelength components to the output port in the return
path.
20. The method of claim 19, wherein when the second surface
reflects the light of the at least two wavelengths from the input
port towards the first convex surface and the first convex surface
collimates the reflected light of the at least two wavelengths in
the forward path, said first convex surface focuses the one or more
wavelength components to the output port in the return path without
involving said second surface.
21. The method of claim 19, wherein said first convex surface
collimates the light of the at least two wavelengths from the input
port in the forward path without involving the second surface and
focuses the one or more wavelength components towards said second
surface that reflects the one or more wavelength components to the
output port in the return path.
22. The method of claim 19, wherein the input port is moved to
align a desired wavelength component of the diffracted different
wavelength components with an aperture and a photodetector, and
wherein the aperture does not transmit the diffracted different
wavelength components that are not the desired wavelength component
to the photodetector, and wherein said input port is fixed in
position after said alignment.
23. The method of claim 19, further comprising passing the light
directed to the output port through an aperture to a photodetector
aligned to the aperture for detection.
24. The method of claim 23, further comprising adjusting a
dimension of the aperture to determine a bandwidth of the
wavelength component(s) that passes the aperture to the
photodetector.
25. A tunable optical device, comprising: an input port and an
output port; a lens unit collimating light of at least two
wavelengths from the input port in a forward path and focusing
light of at least one of said at least two wavelengths to the
output port in a return path, said lens unit including a first
convex surface and a second surface; a reflector; at least one
diffraction element that is located in the forward path and/or the
return path between the lens unit and the reflector and that
diffracts said collimated light of the at least two wavelengths
into different wavelength components; and an actuator that moves
the reflector so that one or more of said different wavelength
components will travel in said return path to the lens unit and be
focused to said one output port by the lens unit; wherein said
first convex surface collimates the light of the at least two
wavelengths from the input port in the forward path without
involving the second surface and focuses the one or more wavelength
components towards said second surface that reflects the one or
more wavelength components to the output port in the return
path.
26. The device of claim 25, further comprising an optical source
providing light of one or more desired wavelengths to the input
port, so that the device functions as a transceiver.
27. The device of claim 26, further comprising a dichroic filter
between the convex surface and the at least one diffraction element
to transmit light from the input port and reflect light from the
optical source.
28. The device of claim 27, wherein the dichroic filter is a
coating on the at least one diffraction element.
29. A tunable optical device, comprising: an input port and an
output port; a lens unit collimating light of at least two
wavelengths from the input port in a forward path and focusing
light of at least one of said at least two wavelengths to the
output port in a return path, said lens unit including a
focus/collimation element and a surface; a reflector; at least one
diffraction element that is located in the forward path and/or the
return path between the lens unit and the reflector and that
diffracts said collimated light of said at least two wavelengths
into different wavelength components; and an actuator that moves
the reflector so that one or more of said different wavelength
components will travel in said return path to the lens unit and be
focused to said one output port by the lens unit; wherein the
surface reflects the light of the at least two wavelengths from the
input port towards the focus/collimation element and the
focus/collimation element collimates the reflected light of the at
least two wavelengths in the forward path, or said
focus/collimation element focuses the one or more wavelength
components towards said surface that reflects the one or more
wavelength components to the output port in the return path.
30. The device of claim 29, wherein said focus/collimation element
comprises a convex lens or a GRIN lens and a transparent block with
a surface at a slanted angle to an axis of the convex or GRIN lens.
Description
BACKGROUND
[0001] This invention relates generally to the optical components
used in optical communication networks, and specifically to a
hybrid optical module that combines an electrically-tunable optical
filter, optical source(s) and a novel lens unit.
[0002] Optical communication networks are built by combining
sub-systems, modules, or components which perform specific
functions, including the function of selecting or removing a
particular wavelength or group of wavelengths. Briefly, multiple
optical signals can be transmitted simultaneously by encoding them
in separate carrier wavelengths similar to the way radio stations
use different carrier frequencies to which the end user tunes.
Encoding multiple signals using different carrier wavelengths is
referred to as Dense Wavelength Division Multiplexing (DWDM). A
general description of optical networking functions and
applications can be found in "Introduction to DWDM Technology", by
S. Kartalopoulos, Wiley-Interscience, 2000. In this application,
"multiple" means "more than one."
[0003] DWDM Technology has been widely deployed in long haul
communications networks. Recently, this technology started
migrating to short-haul optical communications networks, for
applications such as Digital TV delivery, Fiber-to-the-Home (FTTH),
Internet access, Local Area Networks, back-haul connections for
cellular base stations, Wi-Fi hotspots, and other forms of
broadband access. In prior networks, it has been typical for only
one specified wavelength to reach the receiver of an end user, who
also sends a single wavelength back to the network. This
transmitter-receiver (transceiver) module at the end user is called
a bi-directional wavelength add-drop module. However, with
increasing demands for bandwidth and network flexibility, multiple
wavelengths may be broadcast or delivered to an end user, and then
one wavelength (or potentially a small range of wavelengths) is
selected by the end user. There is, therefore, a strong demand to
provide an integrated module that combines a photodetector with a
tunable optical filter, to select particular wavelength(s) from a
multiple-wavelength DWDM optical signal, which also includes a
transmitter or a group of transmitters to send a different
wavelength or a band of different wavelengths back to the network.
Furthermore, to meet the requirements and needs of short-distance
optical systems, these tunable transceivers have to be compact,
reliable, inexpensive, and producible on a large scale. There is
also a demand for sub-assemblies of the above system that may not
include all of the components of the system to serve as building
blocks of the system.
SUMMARY OF THE INVENTION
[0004] One embodiment of the invention is directed to a tunable
optical device, comprising a reflector, an input port and an output
port and a lens unit collimating light of at least two wavelengths
from the input port in a forward path and focusing light of at
least one of the at least two wavelengths to the output port in a
return path. The lens unit includes a first convex surface and a
second surface. The device also has at least one diffraction
element that is located in the forward path and/or the return path
between the lens unit and the reflector and that diffracts the
collimated light of the at least two wavelengths into different
wavelength components; and an actuator that moves the reflector so
that one or more of the different wavelength components will travel
in the return path to the lens unit and be focused to the one
output port by the lens unit. The second surface reflects the light
of the at least two wavelengths from the input port towards the
first convex surface and the first convex surface collimates the
reflected light of the at least two wavelengths in the forward
path, or the first convex surface focuses the one or more
wavelength components towards the second surface that reflects the
one or more wavelength components to the output port in the return
path.
[0005] Another embodiment of the invention is directed to an
optical tuning method, comprising collimating light of at least two
wavelengths from an input port in a forward path towards a
reflector and focusing light of at least one of the at least two
wavelengths to an output port in a return path, using a lens unit
including a first convex surface and a second surface. At least one
diffraction element located in the forward path and/or the return
path between the lens unit and the reflector is used to diffract
the collimated light of the at least two wavelengths into different
wavelength components. The reflector is moved so that one or more
of the different wavelength components will travel in the return
path to the lens unit and be focused to the one output port by the
lens unit. The second surface reflects the light of the at least
two wavelengths from the input port towards the first convex
surface and the first convex surface collimates the reflected light
of the at least two wavelengths in the forward path, or the first
convex surface focuses the one or more wavelength components
towards the second surface that reflects the one or more wavelength
components to the output port in the return path.
[0006] Still another embodiment of the invention is directed to a
tunable optical device, comprising a reflector, an input port, an
output port and a lens unit collimating light of at least two
wavelengths from the input port in a forward path and focusing
light of at least one of the at least two wavelengths to the output
port in a return path, the lens unit including a focus/collimation
element and a surface. The device includes at least one diffraction
element that is located in the forward path and/or the return path
between the lens unit and the reflector and that diffracts the
collimated light of the at least two wavelengths into different
wavelength components; and an actuator that moves the reflector so
that one or more of the different wavelength components will travel
in the return path to the lens unit and be focused to the one
output port by the lens unit. The surface reflects the light of the
at least two wavelengths from the input port towards the
focus/collimation element and the focus/collimation element
collimates the reflected light of the at least two wavelengths in
the forward path, or the focus/collimation element focuses the one
or more wavelength components towards the surface that reflects the
one or more wavelength components to the output port in the return
path.
[0007] All patents, patent applications, articles, books,
specifications, other publications, documents and things referenced
herein are hereby incorporated herein by this reference in their
entirety for all purposes. To the extent of any inconsistency or
conflict in the definition or use of a term between any of the
incorporated publications, documents or things and the text of the
present document, the definition or use of the term in the present
document shall prevail.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGS. 1A and 1B illustrate prior art instruments of a
wavelength tunable filter and a bi-directional transmitter-receiver
(called transceiver for short) respectively.
[0009] FIG. 2A shows one embodiment of the present invention. One
of the multiple wavelengths from an incident signal is selected by
a tunable filter and sent to an integrated photodetector in a
compact assembly in a container. FIG. 2B shows another embodiment
of the present invention, which exchanges the location of the
photodetector with that of the input optical fiber. FIG. 2C shows
another embodiment of the present invention where the multiple
wavelengths from an incident signal are diffracted once instead of
twice.
[0010] FIGS. 3A through 3C show a slanted dome lens, which is used
to reflect, collimate/focus, and combine the optical power. FIGS.
3D through 3F illustrate another lens assembly functioning in the
same way.
[0011] FIGS. 4A and 4B illustrate how an optical signal consisting
of multiple wavelengths is reflected, and also combined at an
optical interface. FIG. 4A shows an optical ray that is either
totally reflected or refracted at an optical interface, if the
incident angle is more or less than the critical angle,
respectively. FIG. 4B illustrates a ray that is reflected at the
optical interface by a reflective coating, if the incident angle is
less than the critical angle. FIG. 4C illustrates a dichroic thin
film coating that is used to transmit or reflect light in two
wavelength bands.
[0012] FIG. 4D shows spectral locations of two respective bands of
FIG. 4C that are transmitted or reflected by the dichroic
coating.
[0013] FIG. 5 shows an embodiment of the present invention that
adds a signal wavelength to the embodiment shown in FIG. 2A.
[0014] FIG. 6A shows yet another embodiment of the present
invention, in which the location of the diode laser package in FIG.
5 is oriented to be more compact.
[0015] FIG. 6B illustrates another embodiment in which a dichroic
filter is interposed between the dome lens and the diffraction
grating. FIG. 6C illustrates a variation of this embodiment in
which the dichroic filter is directly coated on one side of the
grating substrate, opposite to the grating.
[0016] FIGS. 7A and 7B shows a photodetector package with a small
aperture to accept only a single wavelength (or, potentially, a
single wavelength range) directed to the photodetector chip. FIG.
7A is a cross-section view of the photodetector package and FIG. 7B
shows the entrance window of the photodetector package, with the
aperture in the center.
[0017] Identical components are labeled by the same numerals in
this application. The optical paths and the angles of diffraction
in the figures are not drawn to scale.
DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
[0018] The present invention utilizes a lens unit, which can be a
novel lens or novel lens assembly, having the functions of
processing optical signals for filtering, attenuation, detection,
and transmission, together in a single module. The lens is used to
integrate an optical tunable filter, attenuator, photodetector,
diode laser(s), and an optical port, in a compact unit.
[0019] FIG. 1A, excerpted from U.S. Pat. No. 7,899,330, illustrates
how a diffraction grating and a Micro-Electro-Mechanical-System
(MEMS) based mirror are used to select a wavelength from a group of
wavelengths, that have been angularly dispersed via a diffraction
grating. The optical power of an input fiber 121 carrying multiple
wavelengths is collimated by a lens assembly 101 and then enters a
diffraction grating 103, which disperses different wavelengths in
slightly different angles, as illustrated by rays 104, 105, and
106, respectively. One wavelength is selectively reflected by the
rotatable mirror 109 (its rotation is indicated by 114) back to an
output fiber 122, after passing through the diffraction grating 103
a second time. The rotation angle of the mirror is controlled by
the control voltage 112. (Note that element 108 is a quarter wave
plate that rotates the polarization of the optical beam by 90
degrees.)
[0020] FIG. 1B illustrates a bi-directional transmitter-receiver
module of the prior art, which allows the photodetector to receive
only a single wavelength .lamda..sub.R and sends a different
wavelength .lamda..sub.T back to the optical fiber.
[0021] FIG. 2A illustrates one embodiment (or device) 220 of the
present invention in which a signal with multiple wavelengths from
an optical port is filtered, attenuated and then sent to a
photodetector. An input optical signal travels from an input port,
through a lens unit and a diffraction element towards a reflector
in a forward path, and is reflected by the reflector back towards
the diffraction element and then to the lens unit in a return path
to an output port, where the return signal is detected, as
described below. An input optical fiber 201 at an input port
carries an optical signal consisting of at least two wavelengths,
such as multiple wavelengths .lamda..sub.1, .lamda..sub.2,
.lamda..sub.3, and .lamda..sub.4, for example. Obviously a larger
or fewer number of wavelengths than four may be used and are within
the scope of the invention. For example, input fiber 201 may carry
only two wavelengths of light. The fiber end 201A is embedded in a
ceramic or glass ferrule 202. For convenience of assembly, the
fiber can be terminated at the end surface 202A of ferrule 202.
Then an additional optical fiber for bringing in the signal is
optically connected with Fiber stub 201A at the end surface 202A.
The signal exits the fiber at the other end surface 202B of the
ferrule 202, and spread outs with an angle that is determined by
the Numerical Aperture NA of the fiber, as represented by the three
rays, 203A, 203B and 203C. Then the multi-wavelength signal is
reflected at a slanted surface 212 of the lens 210, by either total
internal reflection, or by use of a reflective coating, if the
incident angle to the slanted surface 212 is more or less than the
critical angle, respectively. The lens 210 has an optical axis that
is denoted by dashed line 216. The slanted surface 212 is created
by methods such as tilting the lens end and then polishing toward
the optical axis 216. Surface 212 is on one side of and at a
slanted angle relative to axis 216 and is located in a position
opposite to the convex surface 215 of lens 210.
[0022] The reflection of the multi-wavelength signal at slanted
surface 212 is described in more detail in FIG. 4. FIG. 4A depicts
a ray, either 412 or 415, that is incident on an optical interface
410 from a high index material n.sub.2 such as glass 402, to a low
index material n.sub.1 such as air 401. Line 404 is the normal to
the interface surface 410. Ray 415 experiences total internal
reflection at the optical interface 410 because its incident angle
.theta..sub.L is larger than the critical angle .theta..sub.C. In
contrast, incident ray 412 is refracted at the interface 410 and
exits as ray 413, in accordance with Snell's law. When the incident
angle is smaller than the critical angle as illustrated in FIG. 4B,
a reflective coating 435, such as a dielectric thin-film stack or
simply a reflective metal, is coated onto the slanted surface 433
(or surface 212 in FIG. 2A).
[0023] The incident rays represented by 203A, 203B, and 203C in
FIG. 2A and the reflected rays 204 and their subsequent rays (206,
208, etc.) remain in an optical plane, here defined as the x-y
plane indicated in 260. The signal reflected at the surface 212 in
FIG. 2A continues to travel inside the dome lens 210, to hit a
convex surface (or dome) 215, that has focus length f and
collimates the signal into a parallel beam 206 before entering the
diffraction grating 230 for wavelength-dependent angular
dispersion. The diameter of parallel beam 206 can range from 0.3 to
2.5 millimeters depending on the requirements of wavelength
resolution. The smaller the wavelength difference is between
adjacent channels (typically ranging from a few nanometers down to
0.2 nanometer for optical communication networks), the larger the
focus length (and therefore the beam diameter) that is required.
The multiple wavelengths .lamda..sub.1, .lamda..sub.2,
.lamda..sub.3, and .lamda..sub.4 are dispersed at slightly
different angles, and one beam 208 which may contain one or more of
these wavelengths (or component[s] having wavelengths within one or
more wavelength ranges) is selectively reflected by the rotatable
MEMS mirror 212 to a beam 209 that enters the grating 230 a second
time for further wavelength separation (see U.S. Pat. No.
7,899,330). The returned beam 209 containing one or more wavelength
components (or component[s] having wavelengths within one or more
wavelength ranges) exits the grating as the beam 231 and is focused
by the dome 215 of lens 210, exiting the lens via an end surface
217, to a spot 235 within an aperture 245 of an entrance window
242. The end surface 217 is situated on the side of lens 210 that
is opposite to the slanted surface 212, with respect to the optical
axis 216. As used herein in this application, the term "wavelength
components" will include components having wavelengths within one
or more wavelength ranges.
[0024] The MEMS mirror, mounted on a substrate 223, has two
rotational axes, 225 and 226. The axis 225 is used to selectively
reflect one or more wavelengths or wavelength ranges to a
photodetector 241, while having the beam remain in the optical
plane x-y. In some cases, there is also a need to attenuate the
signal strength for the photodetector. Thus the other rotational
axis 226 is used to tune the optical beam slightly out of the x-y
plane, in order to reduce or attenuate the optical power of the
beam that reaches the photodetector 241.
[0025] A more detailed structural view of the photodetector package
240 shown in FIG. 2A, is shown in FIGS. 7A and 7B. In FIG. 7A, the
selected wavelength (or wavelength ranges centered at)
.lamda..sub.i is focused within an aperture 703 in an entrance
window 706, which is coated with a reflective or absorptive
(opaque) material 708, with the exception of the aperture area 703.
Adjacent wavelengths (or wavelength ranges centered at)
.lamda..sub.i-1 and .lamda..sub.1+1 in the beam 231 focused to
package 240, that enter the lens dome 215 (these adjacent
wavelengths are not shown in FIG. 2A) with angles slightly
different from .lamda..sub.i, are thus focused outside the aperture
703, and are therefore blocked from reaching the photodetector 704.
The diameter of a circular aperture 703, for example, typically
ranges from a few micrometers to a few tens of micrometers. The
bandwidth of a selected wavelength component(s) or wavelength
ranges that can pass the aperture decreases with the size of the
aperture. Thus, aside from the tunable filtering capability
(performed by grating 230 and the MEMS mirror 212) depicted and
described in reference to FIG. 2A above, the aperture size 703
provides another design parameter for determining the bandwidth of
the light entering the photodetector 241. The smaller the aperture
size, the narrower will be the bandwidth of the selected wavelength
component(s) or wavelength range(s). The ferrule 202 shown in FIG.
2A is free to move around (indicated by arrows 219) before being
fixed in place, in order to optically align .lamda..sub.i to the
aperture 703. The photodetector chip 704 is bonded to the base of a
housing 710 and electrically wired to two electrodes 721 and 722,
in order to output a current once an optical beam is impinged on
it. FIG. 7B shows an "overhead" or plan view of the entrance window
706 and aperture 703. An opaque coating is coated on a thin disk
706, with the exception of the aperture area 703. Other methods,
such as opening a pin hole in the center of a metal disk to create
an aperture, are also within the scope of the present
invention.
[0026] FIGS. 3A through 3C illustrate the geometry of the lens 210
with a dome surface 215 at one end of the rod for focusing or
collimating the beam, and a slanted reflective surface 212 at the
other end of the lens 210. The rod is shown as a rectangle here but
other shapes are also applicable. Dashed line 216 is the optical
axis of the dome lens 210. FIG. 3C is a perspective view of the
dome lens 210, and FIGS. 3A and 3B are its front and side views,
respectively.
[0027] FIGS. 3D through 3F illustrate another embodiment of lens
assembly 300 that provides the same functionality as dome lens 210
in FIGS. 3A through 3C. A traditional convex lens 301 that serves
to focus the beam is assembled via a tubing 303 with an optical
block 302, which has a slanted surface 312 for reflecting an
incoming beam 311 (and potentially transmitting an outgoing beam
316 to the input port). Dashed line 305 is the optical axis of the
lens assembly 300. Slanted surface 312 is slanted with respect to
and on one side of axis 305 and is located in a position opposite
to lens 301. Other lens assemblies having at least one convex
surface for focus, as well as a slant surface opposite to the lens,
are also within the scope of the present invention. Aside from
using traditional convex lens 301 in FIG. 3D, other lenses such as
Graded Index (GRIN) lens having focus/collimation capability
without a convex surface may be used instead and are also within
the scope of the present invention. In such event, slanted surface
312 will be slanted with respect to and on one side of the axis
(not shown) of the GRIN lens and is located in a position opposite
to the GRIN lens located in the position of convex lens 301 in FIG.
3D.
[0028] To make the tunable receiver more convenient for
installation inside a Multi-Source Agreement (MSA) pluggable cage
assembly such as Compact Form-factor Pluggable (CFP), and Small
Form Factor Pluggable (SFP) cages it may be necessary to orient the
ferrule 202 of the optical fiber 201 such that it lines up with the
dome lens 210, with the ferrule 202 protruding out of the front
panel of MSA pluggable cage assemblies. All of the components of
the device 220 may be contained within a compact container shown in
dotted line in FIG. 2A. FIG. 2B is an alternative embodiment (or
device) 220' to embodiment 220 and shows that the locations of
ferrule 202 and photodetector 240 are swapped or reversed, in
comparison with FIG. 2A. Here in FIG. 2B, the light from the input
fiber 201 enters the flat surface 217 of the lens, and then reaches
the dome 215, without involving slanted surface 212 in the forward
path. Instead, the returned beam 204 in the return path from the
grating is reflected at the slanted surface 212, and then enters
the photodetector 240. In contrast, in the embodiment or device 220
of FIG. 2A, for beam 231 that is focused by dome 215 directly to
photodetector package 240 in the return path, slanted surface 212
is not involved. With the exception of the positions of the ferrule
202 and photodetector 240 and the differences noted above, one
skilled in the art will recognize that the operation of the
embodiment shown in FIG. 2B is otherwise the same as the operation
of the embodiment shown in FIG. 2A. In both embodiments 220 and
220', the diffraction element 230 is located in both the forward
and return paths to diffract the signal twice. While this is
desirable since diffracting the wavelengths twice results in better
angular and spatial separation between the wavelength components,
this is not required. In still another variation as shown in device
220'' of FIG. 2C, the diffraction element 230 is located in only
the forward path (and not in the return path) and to diffract the
signal only once and not twice. In the return path, beam 209 is
reflected and not diffracted by reflector 207 to convex surface 215
for focusing to the photodetector 240. Obviously, instead of being
located only in the forward path, the diffraction element 230 may
swap places with reflector 207 so that it is located in only the
return path (and not in the forward path). Instead of employing
only one diffraction element 230, more than one diffraction element
may be used in the forward path and/or the return path to diffract
the optical signal more than twice, as shown in U.S. Pat. No.
7,899,330. All such and other variations are within the scope of
the invention.
[0029] In addition to detecting one or more wavelength out of
multiple wavelengths, the end clients or customers in an optical
network often need to add a signal back to the network, for a
variety of purposes, including network supervision. FIG. 5
illustrates another embodiment of the present invention, which adds
a signal with a wavelength .lamda..sub.T that is different from the
received wavelengths to the optical assembly shown in FIG. 2A. A
laser diode package 510 includes the basic elements of a laser
diode 511 (its emitting wavelength being either fixed or tunable),
a focusing lens 513, a housing 517 and the laser diode's electrodes
518, 519, and 520. A beam 512, with wavelength .lamda..sub.T, is
emitted by laser diode 511, and is focused by a lens 513, either
spherical or aspherical, and then hits the slanted surface 212,
which is coated with a dichroic filter 531, comprising a stack of
dielectric thin film layers. The dichroic filter transmits
wavelength .lamda..sub.T from the laser diode, but reflects the
incident wavelengths (.lamda..sub.1, .lamda..sub.2, .lamda..sub.3,
.lamda..sub.4, etc.) from the input optical fiber 201. The laser
signal AT is then focused to the fiber end 202B, and then is
transmitted out on fiber 201. Furthermore, multiple wavelengths
.lamda..sub.T1, .lamda..sub.T2 and .lamda..sub.T3, for example,
emitted from multiple diode lasers, respectively, can be
multiplexed by an optical multiplex (not shown in the FIG. 5) as a
transmission band .lamda..sub.T to come out as a beam 515 and then
enters the dichroic filter 531. Each individual laser can be turned
on or off to dynamically choose particular wavelength(s) for being
added back to the network.
[0030] FIGS. 4C and 4D illustrate how a dichroic filter functions
(including the dichroic filter 531 of FIG. 5). A dichroic filter
465 is coated onto the interface 463 of a glass and air. Line 460
is the normal to the interface 463. A ray 431 carrying a multiple
of wavelengths that is incident onto the interface 463 with an
angle .theta..sub.i less than the critical angle .theta..sub.c, is
reflected by the dichroic filter 465. In contrast, a beam carrying
a wavelength .lamda..sub.T passes the dichroic filter 465. The
spectral locations of the laser diode wavelength .lamda..sub.T and
the multiple received wavelengths .lamda..sub.1, .lamda..sub.2,
.lamda..sub.3 and .lamda..sub.4 (or a wavelength band of received
wavelengths) are shown in FIG. 4D. Wavelength .lamda..sub.T is
outside of the band of received wavelengths, typically by a few
tens of nanometers or more.
[0031] In order to make the assembly of tunable optical add-drop
module even more compact, the laser diode package 617 can be
re-oriented to be side-by-side with the photodetector package 240,
as shown in FIG. 6A. A reflective mirror 631 is added to re-direct
the rays 612 that are emitted from the laser diode 611 and focused
by lens 613, to the optical interface 212.
[0032] Instead of coating the dichroic filter on the slanted
surface 212, as shown in FIGS. 5 and 6A, the dichroic filter 667
may be interposed between the dome surface 215 and the diffraction
grating 230, as shown in the embodiment of the present invention
depicted in FIG. 6B. The collimated beam 206, which carries a
multiple of wavelengths closely packed in a band, transmits through
the dichroic coating 667 in the return path. The beam 662 emitted
from the laser diode 661, with wavelength .lamda..sub.T, is
collimated by a lens 663 to become a collimated beam 664, which is
reflected by the dichroic filter 667 and then focused by surface
215 to the fiber end 202B of the optical fiber 201 at the input
port.
[0033] Instead of using a separate substrate 668, coated with a
dichroic filter 667 (as shown in FIG. 6B), in another embodiment
the dichroic filter 667 can be coated directly to the flat side of
the grating substrate 230, as shown in FIG. 6C, in order to save
space. The dotted line denoted by 265 in each of FIGS. 2A-2C, 5,
6A-6C represents a container containing all of the components of
each of the devices shown in such figures.
[0034] While the invention has been described above by reference to
various embodiments, it will be understood that changes and
modifications may be made without departing from the scope of the
invention, which is to be defined only by the appended claims and
their equivalents. For example, lens 210 with a dome surface 215 as
shown in FIGS. 5, 6A, 6B and 6C may be replaced by the combination
of lens 301, tubing 303 and surface 312 shown in FIG. 3D. Moreover,
instead of using the traditional convex lens 301 of FIG. 3D in the
embodiments of FIGS. 5, 6A, 6B and 6C, other lenses such as Graded
Index (GRIN) lens having focus/collimation capability without a
convex surface may be used and are also within the scope of the
present invention.
* * * * *