U.S. patent application number 11/739422 was filed with the patent office on 2008-05-22 for compact optical multiplexer and demultiplexer.
Invention is credited to Dongsheng Han, Fahua Lan, Zhenli Wen, Kevin Dapeng Zhang.
Application Number | 20080118243 11/739422 |
Document ID | / |
Family ID | 39321714 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080118243 |
Kind Code |
A1 |
Wen; Zhenli ; et
al. |
May 22, 2008 |
COMPACT OPTICAL MULTIPLEXER AND DEMULTIPLEXER
Abstract
Spatially-efficient optical multiplexers and optical
demultiplexers include elements interrelating along orthogonal
axes. A transmission block of extreme thinness has highly
reflective coatings on opposed parallel surfaces. Lasers of
multiplexer are on one side of transmission block with transmission
axes perpendicular to transmission block surface. An associated
multiplexed signal transmitting port on opposite side of
transmission block has receiving axis parallel to transmission
block surface on that side. Detectors of demultiplexer are on one
side of transmission block with reception axes perpendicular to
transmission block surface. An associated multiplexed signal
receiving port on opposite side of transmission block has receiving
axis parallel to transmission block surface on that side. A unitary
structure performs both optical multiplexer functions and optical
demultiplexer function with a single thin transmission block.
Related optical signal processing methods are included.
Inventors: |
Wen; Zhenli; (Shanghai,
CN) ; Zhang; Kevin Dapeng; (Fiemont, CA) ;
Han; Dongsheng; (Zhuhai City, CN) ; Lan; Fahua;
(Pudong Shanghai, CN) |
Correspondence
Address: |
NORTH WEBER & BAUGH LLP
2479 E. BAYSHORE ROAD, SUITE 707
PALO ALTO
CA
94303
US
|
Family ID: |
39321714 |
Appl. No.: |
11/739422 |
Filed: |
April 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60866729 |
Nov 21, 2006 |
|
|
|
Current U.S.
Class: |
398/43 |
Current CPC
Class: |
G02B 6/2938 20130101;
G02B 6/4214 20130101; G02B 6/4215 20130101; G02B 6/29367 20130101;
G02B 6/4246 20130101; G02B 6/2746 20130101 |
Class at
Publication: |
398/43 |
International
Class: |
H04J 14/00 20060101
H04J014/00 |
Claims
1. An optical multiplexing and demultiplexing apparatus comprising:
(a) an optical signal transmission block having on opposite first
and second sides thereof corresponding parallel planar first and
second surfaces substantially covered by respective highly
reflective first and second coatings; (b) a first signal source
comprising: (i) a first laser capable of producing transmitted
signals at a first transmission wavelength, the first laser being
positioned on the first side of the transmission block with the
transmission axis of the first laser oriented at and substantially
normal to the first surface of the transmission block; and (ii) a
first lens associated with the first laser, the first lens
reorienting transmitted signals an acute tilt angle from the first
laser through shifting a distance between an optical axis of the
first lens and the transmission axis of the first laser along a
redirected transmission pathway to a corresponding first admission
window in the first coating; (c) a second signal source comprising:
(i) a second laser capable of producing transmitted signals at a
second transmission wavelength, the second laser being positioned
on the first side of the transmission block separated along the
first surface of the transmission block from the first laser with
the transmission axis of the second laser oriented at and
substantially normal there the first surface of the transmission
block; and (ii) a second lens associated with the second laser, the
second lens reorienting transmitted signals an acute tilt angle
from the second laser through shifting a distance between optical
axis of the second lens and the optical axis of the second laser
along a redirected transmission pathway parallel to the redirected
transmission pathway of the transmitted signals from the second
laser to a corresponding second admission window in the first
coating; (d) a multiplexed signal transmitting port on the second
side of the transmission block, the transmitting port being
positioned to receive transmitted signals from the first and second
lenses emerging in mutual optical alignment as a multiplexed
transmission signal from a multiplexed signal egress window in the
second coating following reflections of the transmitted signals
from the first and second lenses within the transmission block
between the first and second coatings; and (e) a demultiplexer
cooperative with the transmission block for separating a
multiplexed reception signal into constituent received signals at
respective first and the second reception wavelengths.
2. An apparatus as recited in claim 1, wherein: (a) the receiving
axis of the transmitting port is parallel to the second surface of
the transmission block; and (b) the apparatus further comprises a
prism positioned between the multiplexed signal egress window and
the transmission port, the prism being capable of bending the path
of the multiplexed transmission signal into optical alignment with
the receiving axis of the transmitting port.
3. An apparatus as recited in claim 1, further comprising: (a) a
first transmission filter at the first admission window, the first
transmission filter being operative at the first transmission
wavelength to exclude from the transmission block signals other
than transmitted signals at the first transmission wavelength; and
(b) a second transmission filter at the second admission window,
the second transmission filter being operative at the second
transmission wavelength to exclude from the transmission block
signals other than transmitted signals at the second transmission
wavelength.
4. An apparatus as recited in claim 1, wherein the demultiplexer
comprises: (a) a multiplexed signal receiving port on the first
side of the transmission block positioned to deliver the
multiplexed reception signal into the transmission block through a
multiplexed signal admission window in the first coating; and (b) a
plurality of optical detectors positioned on the second side of the
transmission block with the optical receiving axis of each of the
detectors being oriented at and substantially normal to the second
surface of the transmission block, each of the detectors being
tuned to a respective of the first and second reception wavelengths
of the received signals, and each of the detectors having
associated therewith: (i) an egress window in the second coating;
and (ii) a lens capable of reorienting received signals emerging
from the transmission block at the egress window through a shift
distance between the optical receiving axis of a third lens and the
receiving axis of the associated detector.
5. An apparatus as recited in claim 4, wherein: (a) the
transmitting axis of the receiving port is parallel to the first
surface of the transmission block; and (b) the demultiplexer
further comprises a prism positioned between the multiplexed signal
admission window and the receiving port, the prism being capable of
bending the path of the multiplexed reception signal out of
alignment with the transmitting axis of the receiving port toward
the a multiplexed signal admission window.
6. An apparatus as recited in claim 4, wherein the detectors are
selected from the group of detectors comprising PIN detectors and
APD detectors.
7. An apparatus as recited in claim 1, wherein the first and second
coatings comprise tantalum oxide (Ta.sub.2O.sub.5).
8. An apparatus as recited in claim 1, wherein the first and second
coatings comprise silicon oxide (SiO.sub.5).
9. An apparatus as recited in claim 1, wherein the first and second
lasers are selected from the group of lasers consisting of FP
lasers, DFB lasers, and VCSEL lasers.
10. An optical multiplexing and demultiplexing apparatus
comprising: (a) an optical signal transmission block having on
opposite first and second sides thereof parallel planar first and
second surfaces; (b) highly reflective first and second coatings
substantially covering the first and second surfaces, respectively;
(c) a plurality of lasers positioned on the first side of the
transmission block with the transmission axis of each of the lasers
being oriented at and substantially normal to the first surface of
the transmission block, each of the lasers producing transmitted
signals at a respective individual transmission wavelength, and
each of the lasers having associated therewith: (i) an admission
window in the first coating; and (ii) a lens capable of reorienting
transmitted signals an acute tilt angle from the associated laser
through shifting a distance between the optical axis of lens and
the transmission axis of the associated laser along a redirected
transmission pathway to the associated admission window; (d) a
multiplexed signal transmitting port on the second side of the
transmission block positioned to receive transmitted signals from
the plurality of lasers, the transmitted signals emerging in mutual
optical alignment as a multiplexed transmission signal from the
transmission block at a multiplexed signal egress window in the
second coating following reflections of the transmitted signals
toward the transmitting port within the transmission block between
the first and second coatings; and (e) a demultiplexer cooperating
with the transmission block for separating a multiplexed reception
signal into constituent detected signals at respective reception
wavelengths.
11. An apparatus as recited in claim 10, wherein: (a) the receiving
axis of the transmitting port is parallel to the second surface of
the transmission block; and (b) the apparatus further comprises a
prism positioned between the multiplexed signal egress window and
the transmission port, the prism being capable of bending the path
of the multiplexed transmission signal into alignment with the
receiving axis of the transmitting port.
12. An apparatus as recited in claim 10, wherein the demultiplexer
comprises: (a) a multiplexed signal receiving port on the first
side of the transmission block positioned to deliver a multiplexed
reception signal containing a plurality of received signals at
respective optical wavelengths into the transmission block through
a multiplexed signal admission window in the first coating; and (b)
a plurality of optical detectors positioned on the second side of
the transmission block with the receiving axis of each of the
detectors being oriented at and substantially normal to the second
surface of the transmission block, each of the detectors being
tuned to a respective of the reception wavelengths of the received
signals, and each of the detectors having associated therewith: (i)
an egress window in the second coating; and (ii) a lens capable of
reorienting received signals emerging from the transmission block
at the corresponding egress window through shifting a distance
between the optical axis of the lens and the receiving axis of the
associated detector.
13. An apparatus as recited in claim 12, wherein: (a) the
transmitting axis of the receiving port is parallel to the first
surface of the transmission block; and (b) the apparatus further
comprises a prism positioned between the multiplexed signal
admission window and the receiving port, the prism being capable of
bending the path of the multiplexed reception signal out of
alignment with the transmitting axis of the receiving port toward
the multiplexed signal admission window.
14. An apparatus as recited in claim 13, wherein the prism
comprises fused silica.
15. An apparatus as recited in claim 13, wherein the angle of the
prism is about 46.9 degrees.
16. An apparatus as recited in claim 13, wherein the prism engages
the first surface of the transmission block.
17. An apparatus as recited in claim 16, wherein the prism is
bonded to the first surface of the transmission block using an
epoxy adhesive having an optical index approximately to the optical
index of fused silica.
18. An apparatus as recited in claim 12, wherein further associated
with each of the detectors is a reception filter operating at the
reception wavelength of the associated detector, the reception
filter blocking from the associated detector signals other than
received signals at the reception wavelength of the associated
detector.
19. An apparatus as recited in claim 10, wherein further associated
with each of the lasers is a transmission filter operating at the
transmission wavelength of the associated laser, the transmission
filter blocking from the transmission block signals other than
transmitted signals at the transmission wavelength of the
associated laser.
20. An optical multiplexing and demultiplexing apparatus
comprising: (a) an optical signal transmission block having on
opposite first and second sides thereof corresponding parallel
planar first and second surfaces substantially covered by highly
reflective first and second coatings, respectively; (b) a
multiplexed signal receiving port on the first side of the
transmission block positioned to deliver multiplexed reception
signals containing received signals at respective first and second
reception wavelengths into the transmission block through a
multiplexed signal admission window in the first coating; (c) a
first signal receiver comprising: (i) an optical first detector
positioned on the second side of the transmission block with the
receiving axis of the first detector being oriented at and
substantially normal to the second surface of the transmission
window; and (ii) a first reception filter at a first egress window
in the second coating, the first reception filter being operative
at the first reception wavelength to exclude from the first
detector signals other than received signals at the first reception
wavelength emerging from the transmission block through the first
egress window following reflections of the multiplexed reception
signals within the transmission block between the first and second
coatings; (d) a second signal receiver comprising: (i) an optical
second detector positioned on the second side of the transmission
block with the receiving axis of the second detector being oriented
at and substantially normal to the second surface of the
transmission block; and (ii) a second reception filter at a second
egress window in the second coating, the second reception filter
being operative at the second reception wavelength to exclude from
the second detector signals other than received signals at the
second reception wavelength emerging from the second surface of the
transmission block through the second egress window following
reflections of the multiplexed reception signals within the
transmission block between the first and second coatings; and (e) a
multiplexer cooperative with the transmission block for combining
transmitted signals at respective first and second transmission
wavelengths into a multiplexed transmission signal.
21. An apparatus as recited in claim 20, wherein: (a) the
transmitting axis of the receiving port is parallel to the first
surface of the transmission block; and (b) the apparatus further
comprises a prism positioned between the multiplexed signal
admission window and the receiving port, the prism being capable of
bending the path of the multiplexed reception signal out of
alignment with the transmitting axis of the receiving port toward
the multiplexed signal admission window.
22. An apparatus as recited in claim 20, further comprising: (a) a
first lens positioned to reorient received signals from the first
reception filter through shifting a distance between the first lens
and the receiving axis of the first detector; and (b) a second lens
positioned to reorient received signals from the second reception
filter through shifting a distance between the second lens and the
receiving axis of the second detector.
23. An apparatus as recited in claim 22, wherein the first and
second lenses are selected from the group of lenses comprising
A-lenses, D-lenses, Grin-lenses, and Ball-lenses.
24. An apparatus as recited in claim 22, wherein the first and
second lenses reorient received signals from the first and second
reception filters, respectively, through a tilt angle of
approximately 13.5 degrees.
25. An apparatus as recited in claim 20, wherein the multiplexer
comprises: (a) first and second lasers positioned on the first side
of the transmission block with the optical transmission axis of
each of the lasers being oriented at and substantially normal to
the first surface of the transmission block, the first and second
lasers producing transmitted signals at the first and second
transmission wavelengths, respectively, and each of the lasers
having associated therewith: (i) an admission window in the first
coating; and (ii) a lens capable of reorienting transmitted signals
from the associated laser into the transmission block by
redirecting the transmitted signals through an acute tilt angle
away from the transmission axis of the associated laser along a
redirected transmission pathway to the associated admission window;
(b) a multiplexed signal transmitting port on the second side of
the transmission block positioned to receive transmitted signals
from the plurality of lasers, the transmitted signals emerging in
mutual optical alignment as a multiplexed transmission signal from
the second surface of the transmission block through a multiplexed
signal egress window in the second coating following reflections of
the transmitted signals toward the transmitting port within the
transmission block between the first and second coatings.
26. An apparatus as recited in claim 25, wherein: (a) the receiving
axis of the transmitting port is parallel to the second surface of
the transmission block; and (b) the apparatus further comprises a
prism positioned between the multiplexed signal egress window and
the transmission port, the prism being capable of bending the path
of the multiplexed transmission signal into optical alignment with
the receiving axis of the transmitting port.
27. An apparatus as recited in claim 26, wherein the prism
comprises fused silica.
28. An apparatus as recited in claim 26, wherein the angle of the
prism is about 46.9 degrees.
29. An apparatus as recited in claim 26, wherein the prism engages
the second surface of the transmission block.
30. An apparatus as recited in claim 29, wherein the prism is
bonded to the second surface of the transmission block using an
epoxy adhesive having an optical index approximately to the optical
index of fused silica.
31. An apparatus as recited in claim 25, wherein the lens is
selected from the group of lenses comprising A-lenses, D-lenses,
Grin-lenses, and Ball-lenses.
32. An apparatus as recited in claim 25, wherein the lens redirects
the transmitted signals through a tilt angle of approximately 13.5
degrees.
33. An apparatus as recited in claim 20, wherein the transmission
block comprises fused silica.
34. An apparatus as recited in claim 20, wherein the width of the
transmission block measured between the first and second surfaces
thereof if approximately 10.0 millimeters.
35. A method for processing a plurality of optical signals at a
corresponding plurality of respective individual wavelengths, the
method comprising the steps of: (a) covering opposed parallel first
and second planar surfaces on respective first and second sides of
an optical signal transmission block with highly reflective first
and second coatings; (b) positioning a plurality of lasers on the
first side of the transmission block with the transmission axis of
each of the lasers oriented at and substantially normal to the
first surface of the transmission block, each of the lasers being
capable of producing transmitted signals at a distinct transmission
wavelength; (c) reorienting the transmitted signals into the
transmission block through the first surface thereof along parallel
paths at an acute tilt angle to the transmission axis of each
respective laser; (d) reflecting within the transmission block
between the first and second coatings the transmitted signals
reoriented into the transmission block through the first surface
thereof, and (e) receiving in a signal transmission port on the
second side of the transmission block the transmitted signals
emerging in mutual optical alignment as a multiplexed transmission
signal from the second surface of the transmission block following
reflections of the transmitted signals within the transmission
block between the first and second coatings.
36. A method as recited in claim 35, further comprising the steps
of: (a) orienting the receiving axis of the transmission port
parallel to the second surface of the transmission block; and (b)
bending the path of the multiplexed transmission signal into
optical alignment with the receiving axis of the transmitting
port.
37. A method as recited in claim 35, further comprising the steps
of: (a) forming through the first coating a plurality of admission
windows corresponding in one-to-one relation to the plurality of
lasers; (b) filtering signals passing through each of the admission
windows to the transmission wavelength of the transmitted signals
produced by the laser corresponding thereto; and (c) forming a
multiplex signal egress window in the second coating.
38. A method as recited in claim 35, further comprising the steps
of: (a) delivering into the transmissions block through the first
surface thereof a multiplexed reception signal containing a
plurality of received signals at respective reception wavelengths;
(b) positioning a plurality of optical detectors on the second side
of the transmission block with the receiving axis of each of the
detectors being oriented at and substantially normal to the second
surface of the transmission block, each of the detectors being
capable of detecting received signals at a respective reception
wavelength; (c) reflecting within the transmission block between
the first and second coatings received signals delivered into the
transmission block through the first surface thereof, and (d)
reorienting into alignment with the receiving axis of each of the
detectors received signals at the respective reception wavelength
corresponding thereto, the received signals emerging from the
second surface of the transmission block following reflecting
within the transmission block between the first and second
coatings.
39. A method as recited in claim 38, further comprising the steps
of: (a) forming through the second coating a plurality of egress
windows corresponding in one-to-one relation to the plurality of
detectors; and (b) forming a multiplex signal access window in the
first coating.
40. A method as recited in claim 38, further comprising the step of
tuning each of the detectors to the reception wavelength
corresponding thereto.
41. A method as recited in claim 40 wherein the step of tuning
comprises the step of filtering to a respective individual
reception wavelength received signals emerging from the
transmission block at each egress window.
42. A method as recited in claim 38, wherein the step of delivering
comprises the steps of: (a) positioning a multiplexed signal
receiving port on the first side of the transmission block with the
transmission axis of the receiving port oriented parallel to the
first surface of the transmission block; (b) transmitting the
multiplexed reception signal from the receiving port; and (c)
bending the path of the multiplexed transmission signal from the
transmission axis of the receiving port into a non-perpendicular
angle of incidence with the first surface of the transmission
block.
Description
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 60/866,729, entitled "Multiplexer and
Demultiplexer Structure for High-Speed Optical Transceivers," filed
Nov. 21, 2006, which application is incorporated herein by
reference in its entirety.
BACKGROUND
[0002] A. Technical Field
[0003] The present invention relates generally to the processing of
optical signals, and more particularly, to the multiplexing and the
demultiplexing of optical signals.
[0004] B. Background of the Invention
[0005] An optical multiplexer merges into mutual optical alignment
as a single multiplexed signal a plurality of optical signals that
are each at a different optical wavelength. For example, optical
signals produced at different optical wavelengths by a
corresponding number of distinct lasers may be combined by an
optical multiplexer into a multiplexed transmitted signal that can
then be retransmitted from a single multiplexed signal transmitting
port. In an optical system, therefore, an optical multiplexer is
the interconnecting link between a plurality of optical fibers
bearing a corresponding plurality of transmitted signals and a
single optical fiber on which that plurality of signals is able to
be communicated in the form of a multiplexed transmission
signal.
[0006] An optical demultiplexer reverses this process, separating a
multiplexed signal that includes a plurality of signals at distinct
wavelengths into that corresponding plurality of constituent
signals. Thus, a multiplexed received signal from a single signal
receiving port can be converted by an optical demultiplexer into
the separate received signals at respective individual wavelengths
that are included in the original multiplexed received signal. In
an optical system, therefore, an optical demultiplexer is the
interconnecting link between a single optical fiber on which a
multiplexed received signal is being communicated and a plurality
of optical fibers that each bears an individual of the received
signals that had been included in that original multiplexed
received signal.
SUMMARY OF THE INVENTION
[0007] The present invention includes teachings directed toward the
design and construction of a spatially-efficient optical
multiplexer. The present invention also pertains to the design and
construction of a spatially-efficient optical demultiplexer.
[0008] In another aspect, the present invention provides a unitary
structure that is capable of performing both, the function
associated with an optical multiplexer, and the function associated
with an optical demultiplexer. Such a structure, an optical
multiplexer and demultiplexer, is advantageous in reducing the
overall size and cost of components in optical systems.
[0009] The present invention also encompasses methods for
processing plural optical signals at a corresponding plurality of
distinct optical wavelengths. In particular, the teachings of the
present invention relate to the consolidation of such plural
optical signals into multiplexed signals, and to the separation of
multiplexed signals into the constituent plural optical signals
thereof.
[0010] Certain features and advantages of the present invention
have been generally described in this summary section; however,
additional features, advantages, and embodiments are presented
herein or will be apparent to one of ordinary skill in the art in
view of the drawings, specification, and claims hereof.
Accordingly, it should be understood that the scope of the
invention shall not be limited by the particular embodiments
disclosed in this summary section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Reference will be made to embodiments of the invention,
examples of which may be illustrated in the accompanying figures.
These figures are intended to be illustrative, not limiting.
Although the invention is generally described in the context of
these embodiments, it should be understood that doing so is not to
be construed as evidencing any intention whatsoever to limit the
scope of the invention to those particular embodiments.
[0012] FIG. 1 is a diagram illustrating the interactions among
typical elements of a known optical multiplexer.
[0013] FIG. 2 is a diagram depicting an embodiment of an optical
multiplexer that incorporates teachings of the present
invention.
[0014] FIG. 3 is an enlarged diagrammatic depiction of a lens, a
transmission filter, and an admission window associated with each
of the lasers that is used to provide a transmitted signal as an
input to the multiplexer of FIG. 2.
[0015] FIG. 4 is an enlarged diagrammatic depiction of the prism
that is used to affect the path of the multiplexed transmitted
signal produced by the multiplexer of FIG. 2
[0016] FIGS. 5A and 5B are related diagrams that illustrate,
respectively, the transmission of a multiplexed transmitted signal
in one direction through a multiplexed transmitted signal isolator
at the input side of the multiplexed signal transmitting port of
the multiplexer of FIG. 2, and the absorption of a multiplexed
transmitted signal attempting to pass in the opposite direction
through the multiplexed transmitted signal isolator.
[0017] FIGS. 6A and 6B are related diagrams that illustrate an
aspect of spatial efficiency promoted by the teachings of the
present invention, making comparative reference, respectively, to
the optical transmission block from the known optical multiplexer
of FIG. 1, and to the optical transmission block from the inventive
optical multiplexer of FIG. 2.
[0018] FIG. 7 is a diagram depicting an embodiment of an optical
demultiplexer incorporating teachings of the present invention.
[0019] FIG. 8 is an enlarged diagrammatic depiction of an egress
window, a reception filter, and a lens associated with each of the
optical detectors that is used to acquire individual reception
signals produced by the demultiplexer of FIG. 7.
[0020] FIG. 9 is an enlarged diagrammatic depiction of a prism that
is used to affect the path of the multiplexed reception signal
provided as an input to the demultiplexer of FIG. 7.
[0021] FIG. 10 is a diagram depicting an embodiment of an optical
multiplexer-demultiplexer incorporating teachings of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] In the following description, for purpose of explanation,
specific details are set forth in order to provide an understanding
of the invention. It will be apparent, however, to one skilled in
the art that the invention may be practiced without these details.
One skilled in the art will recognize that embodiments of the
present invention, some of which are described below, may be
incorporated into a number of different optical components,
devices, and systems. Structures and devices shown in block diagram
are illustrative of exemplary embodiments of the invention and are
meant to avoid obscuring the invention. Furthermore, connections
between components within the figures are not intended to be
limited to direct connections. Rather, connections between these
components may be modified, reconfigured, or otherwise changed,
including by the addition of intermediary components.
[0023] Reference in the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure,
characteristic, or function described in connection with the
embodiment is included in at least one embodiment of the invention.
The appearances of the phrase "in one embodiment" in various places
in the specification are not necessarily all referring to the same
embodiment.
[0024] FIG. 1 depicts an example of a known optical multiplexer 10.
Multiplexer 10 includes a first laser 11, a second laser 12, a
third laser 13, and a fourth laser 14 that each produce transmitted
signals at respective distinct wavelengths. Thus, first laser 11
produces a first transmitted signal L.sub.1 at a first transmission
wavelength .lamda..sub.1, while second laser 12 produces a second
transmitted signal L.sub.2 at a second transmission wavelength 2.
Third laser 13 produces a third transmitted signal L.sub.3 at a
third transmission wavelength .lamda..sub.3, and fourth laser 14
produces a fourth transmitted signal L.sub.4 at a fourth
transmission wavelength .lamda..sub.4. It is the function of
multiplexer 10 to merge transmitted signals L.sub.1, L.sub.2,
L.sub.3, and L.sub.4 into a single multiplexed transmitted signal
L.sub.M that can be presented to the input side of a multiplexed
signal transmitting port 18 for retransmission.
[0025] Toward that end, positioned among lasers 11, 12, 13, and 14
and multiplexed signal transmitting port 18 is an optical signal
transmission block 20. Transmission block 20 has on a first side 22
thereof a planar first surface 24 and on an opposed second side 26
thereof a planar second surface 28 that is parallel to first
surface 24. As measured between first surface 24 and second surface
28, transmission block 20 has a width W.sub.20.
[0026] First laser 11 and third laser 13 are disposed on first side
22 of transmission block 20 with the optical transmission axis of
each directed toward first surface 24 at an angle of incidence
.alpha.. Second laser 14 and fourth laser 14 are disposed on second
side 26 of transmission block 20 with the optical transmission axis
of each directed at second surface 28 at an equal angle of
incidence .alpha.. Multiplexed signal transmitting port 18 is
located on first side 22 of transmission block 20 with the input
side of multiplexed signal transmitting port 18 facing first
surface 24 of transmission block 20.
[0027] The location on first surface 24 at which each respective
transmission axis is oriented is the location at which a
transmitted signal traveling along that transmission axis will
enter transmission block 20. As used hereinafter, the expression
"admission window" employed by reference to a transmitted signal is
intended to refer to the location on a surface of a transmission
block, such as transmission block 10, at which that transmitted
signal is intended or able to enter into the transmission block.
Thus as illustrated in FIG. 2, the transmission axis of first laser
11 is oriented at a first admission window 31 on first surface 24
of transmission block 10, while the transmission axis of second
laser 12 is oriented at a second admission window 32 on second
surface 28 of transmission block 10. Meanwhile, the transmission
axis of third laser 13 is oriented at a third admission window 33
on first surface 24 of transmission block 10, and the transmission
axis of fourth laser 14 is oriented at a fourth admission window 34
on second surface 28 of transmission block 10.
[0028] The output side of each of lasers 11, 12, 13, and 14 is
provided with a corresponding transmitted signal isolator that
prevents any portion of a transmitted signal reflected externally
or internally by other components of multiplexer 10 from reaching
the output side of the laser, as this could cause damage to the
laser otherwise interfere with optimum laser operation. Thus, a
shown in FIG. 1, a first transmitted signal isolator 61 is
positioned at the output side of first laser 11, a second
transmitted signal isolator 62 is positioned at the output side of
second laser 12, a third transmitted signal isolator 63 is
positioned at the output side of third laser 13, and a fourth
transmitted signal isolator 64 is positioned at the output side of
fourth laser 14.
[0029] A transmission filter is associated with each of lasers
11-14 and is positioned at and about the admission window on first
surface 24 or second surface 28 of transmission block 20 at which
the transmission axis of individual of lasers 11-14 is oriented.
Each filter passes signals at the transmission wavelength with each
respective laser functions. Thus, each transmission filter also
bars passage of transmitted signals, or of reflected components of
transmitted signals, at any other wavelength. From the interior of
transmission block 20, these transmission filters function as
mirrors, reflecting back toward the interior of transmission block
20 any transmitted signals at those other wavelengths that
approaches first surface 24 or second surface 28 of transmission
block 20 from the interior thereof.
[0030] As accordingly illustrated in FIG. 1, a first transmission
filter 71 is positioned on first surface 24 of transmission block
20 at and about first admission window 31 at which are directed the
transmission axis of first laser 11 and any first transmitted
signal L.sub.1 at first transmission wavelength .lamda..sub.1
produced thereby. First transmission filter 71 passes signals at
first transmission wavelength .lamda..sub.1 and bars passage of
signals at any other optical wavelength.
[0031] Thus, first transmission filter 71 permits first transmitted
signal L.sub.1 to enter transmission block 20 at first admission
window 31 at an angle of refraction A.sub.1 from the perpendicular
to first surface 24 of transmission block 20 at first admission
window 31. Correspondingly, first transmission filter 71 bars
passage into transmission block 20 at first admission window 31 of
signals and components of signals at any wavelength other than at
first transmission wavelength .lamda..sub.1. Finally, first
transmission filter 71 also reflects back toward the interior of
transmission block 20 signals and components of signals at any
optical wavelength other than first transmission wavelength
.lamda..sub.1.
[0032] Each of the balance of the transmission filters shown in
FIG. 1 will be described individually below.
[0033] As illustrated in FIG. 1, a second transmission filter 72 is
positioned on second surface 28 of transmission block 20 at and
about second admission window 32 at which are directed the
transmission axis of second laser 12 and any second transmitted
signal L.sub.2 at second transmission wavelength .lamda..sub.2
produced thereby. Second transmission filter 72 passes signals at
second transmission wavelength .lamda..sub.2 and bars passage of
signals at any other transmission wavelength.
[0034] Thus, second transmission filter 72 permits second
transmitted signal L.sub.2 to enter transmission block 20 at second
admission window 32. Correspondingly, second transmission filter 72
bars passage into transmission block 20 at second admission window
32 of signals and components of signals at any wavelength other
than at second transmission wavelength .lamda..sub.2. Finally,
second transmission filter 72 also reflects back toward the
interior of transmission block 20 signals and components of signals
at any optical wavelength other than second transmission wavelength
.lamda..sub.2. Therefore, as shown, second transmission filter 72
reflects back toward the interior of transmission block 20 first
transmitted signal L.sub.1, which is at a wavelength different from
second transmission wavelength .lamda..sub.2.
[0035] First transmitted signal L.sub.1 thus commences a series of
reflections interior of transmission block 20 that collectively
progress first transmitted signal L.sub.1 toward multiplexed signal
transmitting port 18 in a direction parallel to first surface 24
and second surface 28 of transmission block 20. In that series of
reflections, first transmitted signal L.sub.1 is accompanied after
second admission window 32 by second transmitted signal L.sub.2 as
shown.
[0036] A third transmission filter 73 is positioned on first
surface 24 of transmission block 20 at and about third admission
window 33 at which are directed the transmission axis of third
laser 13 and any third transmitted signal L.sub.3 at third
transmission wavelength .lamda..sub.3 produced thereby. Third
transmission filter 73 passes signals at third transmission
wavelength .lamda..sub.3 and bars passage of signals at any other
optical wavelength.
[0037] Thus, third transmission filter 73 permits third transmitted
signal L.sub.3 to enter transmission block 20 at third admission
window 33. Correspondingly, third transmission filter 73 bars
passage into transmission block 20 at third admission window 33 of
signals and components of signals at any wavelength other than at
third transmission wavelength .lamda..sub.3. Finally, third
transmission filter 73 also reflects back toward the interior of
transmission block 20 signals and components of signals at any
optical wavelength other than third transmission wavelength
.lamda..sub.3. Therefore, as shown, third transmission filter 73
reflects back toward the interior of transmission block 20
transmitted signals L.sub.1-L.sub.2, which are at wavelengths
different from third transmission wavelength .lamda..sub.3.
[0038] Second transmitted signal L.sub.2 thus commences and joins
first transmitted signal L.sub.1 in a shared series of reflections
interior of transmission block 20 that collectively progress second
transmitted signal L.sub.2 and first transmitted signal L.sub.1
toward multiplexed signal transmitting port 18 in a direction
parallel to first surface 24 and second surface 28 of transmission
block 20. In that series of reflections, second transmitted signal
L.sub.2 and first transmitted signal L.sub.1 are accompanied after
third admission window 33 by third transmitted signal L.sub.3 as
shown.
[0039] Finally, a fourth transmission filter 74 is positioned on
second surface 28 of transmission block 20 at and about fourth
admission window 34 at which are directed the transmission axis of
fourth laser 14 and any fourth transmitted signal L.sub.4 at fourth
transmission wavelength .lamda..sub.4 produced thereby. Fourth
transmission filter 74 passes signals at fourth transmission
wavelength .lamda..sub.4 and bars passage of signals at any other
optical wavelength.
[0040] Thus, fourth transmission filter 74 permits fourth
transmitted signal L.sub.4 to enter transmission block 20 at fourth
admission window 34. Correspondingly, fourth transmission filter 74
bars passage into transmission block 20 at fourth admission window
34 of signals and components of signals at any wavelength other
than at fourth transmission wavelength .lamda..sub.4. Finally,
fourth transmission filter 74 also reflects back toward the
interior of transmission block 20 signals and components of signals
at any optical wavelength other than fourth transmission wavelength
.lamda..sub.4. Therefore, as shown, fourth transmission filter 72
reflects back toward the interior of transmission block 20
transmitted signals L.sub.1-L.sub.3, which are at wavelengths
different from fourth transmission wavelength .lamda..sub.4.
[0041] Third transmitted signal L.sub.3 thus commences and joins
transmitted signals L.sub.1-L.sub.2 in a shared additional
reflection interior of transmission block 20 that progress
transmitted signals L.sub.1-L.sub.3 toward multiplexed signal
transmitting port 18 in a direction parallel to first surface 24
and second surface 28 of transmission block 20. After fourth
admission window 34, transmitted signals L.sub.1-L.sub.3 are
accompanied by fourth transmitted signal L.sub.4 as shown.
[0042] Transmitted signals L.sub.1-L.sub.4 thereafter emerge in
mutual optical alignment from first surface 24 of transmission
block 20 as multiplexed transmission signal L.sub.M and enter the
input side of multiplexed signal transmitting port 18 for
retransmission in consolidated form.
[0043] In achieving this result, among all of transmitted signals
L.sub.1-L.sub.4, first transmitted signal L.sub.1 engages in the
longest path of travel interior of transmission block 20. Entering
transmission block 20 through first transmission filter 71 at first
admission window 31, first transmitted signal L.sub.1 travels
across transmission block 20 to second admission window 32 on
second surface 28. There first transmitted signal L.sub.1 is
reflected back toward the interior of transmission block 20 by
second transmission filter 72. Returning across transmission block
20 to third admission window 33 on first surface 24, first
transmitted signal L.sub.1 is reflected toward the interior of
transmission block 20 a second time, on this occasion by third
transmission filter 73. First transmitted signal L.sub.1 then
passes across transmission block 20 again to fourth admission
window 34 on second surface 28. There first transmitted signal
L.sub.1 is reflected toward the interior of transmission block 20
by fourth transmission filter 74. Finally, first transmitted signal
L.sub.1 travels across transmission block 20 for the last time,
emerging from first surface 24 of transmission block 20 as part of
multiplexed transmission signal L.sub.M.
[0044] Second transmitted signal L.sub.2 engages in a less lengthy
path of travel interior of transmission block 20, but one that is
nonetheless longer than that traveled by third transmitted signal
L.sub.3 or fourth transmitted signal L.sub.4. Entering transmission
block 20 through second transmission filter 72 at second admission
window 32, second transmitted signal L.sub.2 travels across
transmission block 20 to third admission window 33 on first surface
24. There second transmitted signal L.sub.2 is reflected toward the
interior of transmission block 20 by third transmission filter 73.
Second transmitted signal L.sub.2 then passes across transmission
block 20 again to fourth admission window 34 on second surface 28.
There second transmitted signal L.sub.2 is reflected toward the
interior of transmission block 20 by fourth transmission filter 74.
Finally, second transmitted signal L.sub.2 travels across
transmission block 20 for the last time, emerging from first
surface 24 of transmission block 20 as part of multiplexed
transmitted signal L.sub.M.
[0045] The path of travel undertaken interior of transmission block
20 by third transmitted signal L.sub.3 even shorter, and less
complicated. Entering transmission block 20 through third
transmission filter 73 at third admission window 33, third
transmitted signal L.sub.3 travels across transmission block 20 to
fourth admission window 34 on second surface 28. There third
transmitted signal L.sub.3 is reflected toward the interior of
transmission block 20 by fourth transmission filter 74. Third
transmitted signal L.sub.3 then travels across transmission block
20, emerging from first surface 24 of transmission block 20 as part
of multiplexed transmission signal L.sub.M.
[0046] Fourth transmitted signal L.sub.4 enters transmission block
20 through fourth transmission filter 74 at fourth admission window
34 and then simply travels across transmission block 20 without
experiencing any internal reflections whatsoever to emerge from
first surface 24 of transmission block 20 as the final component of
multiplexed transmission signal L.sub.M.
[0047] A demultiplexer configured according to the principles
illustrated in known multiplexer 10 of FIG. 1 would use a
multiplexed signal receiving port in place of multiplexed signal
transmitting port 18 and a plurality of optical detectors
positioned on both sides of transmission block 20 in place
individually of lasers 11-14. The demultiplexer would process
signals traveling in directions essentially opposite from those
indicated for multiplexed transmission signal L.sub.M and
transmitted signals L.sub.1-L.sub.4 in multiplexer 10 in FIG.
1.
[0048] The multiplexed transmitted signal receiving port of the
multiplexer would direct into transmission block 20 through first
surface 24 thereof a multiplexed reception signal made up of
constituent received signals at respective distinct optical
wavelengths. The multiplexed reception signal would then be
reflected internally of transmission block 20 between the opposed
surfaces thereof and deconstructed in the process into those
constituent received signals. These would then be delivered
individually through transmission filters 71-74 to a corresponding
of the optical detectors for retransmission independently.
[0049] Several disadvantages presented in multiplexer 10, as well
as in a correspondingly configured known demultiplexer of the type
described immediately above, have been recognized by the
coinventors of the present invention and resolved through the
teachings thereof. A sampling of some of those disadvantages will
be presented immediately below, following which the present
invention will be disclosed by making reference to exemplary
embodiments thereof.
[0050] The overall size of multiplexer 10, or of a correspondingly
configured known demultiplexer, is relatively large. The size of
such optical devices is largely a function of the thickness
W.sub.20 of transmission block 20. For example, lasers, such as
lasers 11-14, used in a TO-56 package, or of optical detectors of a
correspondingly configured known demultiplexer, have diameters of
about 5.6 mm. The distance between the transmission axes of lasers
of this size, or between receiving axes of corresponding optical
detectors, should be greater than about 6.2 mm. For a typical angle
of incidence .alpha.=about 13.5 degrees in air of optical
transmission signals or of optical reception signals relative to
transmission filters 71-74, it should be the case that angle of
refraction A.sub.1=about 9.3 degrees. Under such conditions,
however, it will be necessary that transmission block 20 have a
width W.sub.20=20 mm. Such a dimension in transmission block 20 is
incompatible with compact sizing requirements associated with
contemporary transceivers, such as the Xenpak receiver or the X2
transceiver.
[0051] To facilitate easy coupling with a transceiver or the
efficient replacement of components thereof, the constituent
elements of a demultiplexer or of a multiplexer, should relate
functionally to each other and to the overall architecture of the
transceiver along functional axes that harmonize with axes standard
in industry. That is not the case with multiplexer 10, or with a
correspondingly configured demultiplexer, where the transmission
axes of lasers 11-14 are at a relatively arbitrary angle of
incidence .alpha. to the surfaces of transmission block 20, or
where the receiving axis of multiplexed signal transmitting port 18
is at another incidentally determined angle to the surfaces of
transmission block 20 and to the transmission axes of lasers 11-14.
Such are less than ideal spatial relationships among functional
components in subsytems intended for use in increasingly modularly
related optical systems, such as optical systems employing optical
transceivers.
[0052] Due to the absence from multiplexer 10, or from a
correspondingly configured demultiplexer, of ideal spatial
relationships among functional components, optical multiplexer
functions must be preformed by structures distinct from the
structures that perform optical demultiplexer functions. Should
both functions be required in a single transceiver, for example,
distinct hardware must be dedicated to each function. Furthermore,
distinct spaces must be accorded in that single optical device to
multiplexer hardware and to demultiplexer hardware. Transceiver
size and cost are both impacted adversely.
[0053] Isolators, such as transmitted signal isolators 61-64, can
be the most costly components in a multiplexer, such as multiplexer
10. Accordingly, the resort to the use of a proliferation of such
isolators to protect the plurality of lasers 11-14 employed in
multiplexer 10 is less than desirable.
[0054] Although the present invention provides a unitary structure
that is capable of performing both, the function associated with an
optical multiplexer, and the function associated with an optical
demultiplexer, the present invention also includes teachings
directed toward the design and construction individually of a
spatially-efficient optical multiplexer and of a
spatially-efficient optical demultiplexer. Accordingly, these
individual aspects of the present invention will first be explored
completely, before discussing the combination of both in an
inventive unitary optical multiplexer and demultiplexer.
[0055] FIG. 2 depicts one embodiment of an optical multiplexer 100
incorporating teachings of the present invention. Multiplexer 100
is so configured as to be capable of combining four input
transmitted signals at respective distinct optical wavelengths into
a single output that takes the form of a multiplexed transmission
signal. A smaller or a larger number of such input transmission
signals may be combined into a single multiplexed transmission
signal output in other embodiments of the present invention.
Centrally, multiplexer 100 includes an optical transmission block
102 that has on a first side 104 thereof a planar first surface 106
and on an opposed second side 108 thereof a planar second surface
110 that is parallel to first surface 106. As measured between
first surface 106 and second surface 110, transmission block 102
has a width W.sub.102. In the embodiment of the invention shown in
FIG. 2, transmission block 102 is made of a silicon-based optically
transparent material. Nonetheless, other optically transmitting
materials may be particularly suited for use in other embodiments
of the present invention.
[0056] Transmission block 102 is rendered internally and externally
reflective of optical signals by a highly reflective first coating
112 on first surface 106 and a highly reflective second coating 114
on second surface 110. In the embodiment of the invention depicted
in FIG. 2, coatings 112, 114 may be layers of tantalum oxide
(Ta.sub.2O.sub.5) or silicon oxide (Si.sub.2O.sub.4). In other
embodiments alternative, reflective coatings may prove
advantageous. Coatings 112, 114, may deposited or applied to first
surface 106 and to second surface 110, respectively, in any manner
and at any stage of fabrication that is consistent with the
conditions of use intended for multiplexer 100. It is not
necessary, however, that each of coatings 112, 114, be identical in
material composition or in thickness. Neither is it essential
according to teachings of the present invention that coatings 112,
114, be deposited or applied contemporaneously or in identical
manners.
[0057] Formed through first coating 112 at selected locations along
first surface 106 are a plurality of admission windows at which
first surface 106 of transmission block 102 is neither internally
nor externally reflective of optical signals. The plurality of
admission windows depicted in FIG. 2 includes a first admission
window 122, a second admission window 124, a third admission window
126, and a fourth admission window 128. The number of admission
windows in a reflective coating, such as first coating 112, will
vary with and generally correspond at least to the number of
optical transmission signals at distinct optical wavelengths that
are to be combined by a multiplexer, such as multiplexer 100.
Therefore, a smaller or a greater number of such admission windows
may be required in other inventive multiplexer embodiments.
[0058] Admission windows in first coating 112 are created by any
process harmonious with the methods by which a multiplexer, such as
multiplexer 100, is to be manufactured. Thus, for example, the
admission windows in first coating 112 may be formed by masking the
location of each intended admission window when first coating 112
is originally deposited on or applied to transmission block 102.
Alternatively, first coating 112 may be deposited or applied to the
entirety of first surface 106, while portions of first coating 112
are removed subsequently at each location intended for an admission
window.
[0059] Also included in multiplexer 100 is a plurality of lasers
that are positioned on the same side of transmission block 102, in
the case illustrated in FIG. 2 on first side 104. Each of the
lasers is capable of producing transmitted signals at a respective
individual transmission wavelength, wherefore a smaller or a larger
number of lasers may be employed in other embodiments of the
invention, depending on the number of transmitted signals to be
combined into a single multiplexed transmission signal. The
transmission axis of each of the lasers is desirable oriented at
and substantially normal to first surface 106 of transmission block
102.
[0060] The plurality of lasers shown in the embodiment of FIG. 2
includes a first laser 132, a second laser 134, a third laser 136,
and a fourth laser 138. First laser 132 produces transmitted
signals J.sub.132 at a first transmission wavelength
.lamda..sub.132 and has a transmission axis T.sub.132 that is
oriented at and substantially normal to first surface 106 of
transmission block 102. Second laser 134 produces transmitted
signals J.sub.134 at a second transmission wavelength
.lamda..sub.134 and has a transmission axis T.sub.134 that is also
oriented at and substantially normal to first surface 106. Third
laser 136 produces transmitted signals J.sub.136 at a third
transmission wavelength .lamda..sub.136 and has a transmission axis
T.sub.136 that is oriented at and substantially normal to first
surface 106. Finally, fourth laser 138 produces transmitted signals
J.sub.138 at a fourth transmission wavelength .lamda..sub.138 and
has a transmission axis T.sub.138 that is in addition oriented at
and substantially normal to first surface 106 of transmission block
102. Appropriate lasers for use in multiplexer 100 include FP
lasers, DBF lasers, and VCSEL lasers.
[0061] Each of the lasers shown in FIG. 2 is associated with a
corresponding one of the admission windows formed in first coating
112 on first surface 106 of transmission block 102. Thus, first
admission window 122 is associated with first laser 132, second
admission window 124 is associated with second laser 134, third
admission window 126 is associated with third laser 136, and
finally, fourth admission window 128 is associated with fourth
laser 138.
[0062] Located between each laser of multiplexer 100 and the
admission window associated therewith are a pair of additional
associated structures.
[0063] The first of these additional associated structures is an
optical filter that is positioned on first surface 106 of
transmission block 102 filling the associated admission window.
Each such optical filter operates at the transmission wavelength of
the associated laser, thereby blocking from entry into or egress
from transmission block 102 through the admission window in which
it is located any signal other than transmitted signals at the
transmission wavelength of the associated laser. From the interior
of transmission block 102, these transmission filters function as
mirrors, reflecting back toward the interior of transmission block
102 any transmitted signals at those other wavelengths that
approaches first surface 106 or second surface 110 of transmission
block 102 from the interior thereof.
[0064] Thus, a first transmission filter 142 operating at first
transmission wavelength .lamda..sub.132 is positioned in first
admission window 122. First transmission filter 142 permits first
transmitted signals J.sub.132 to enter transmission block 102 at
first admission window 122, but bars passage into transmission
block 102 at first admission window 122 of transmitted signals and
components of transmitted signals at any wavelength other than at
first transmission wavelength .lamda..sub.132. In addition, first
transmission filter 142 reflects back toward the interior of
transmission block 102 transmitted signals and components of
transmitted signals at any wavelength other than at first
transmission wavelength .lamda..sub.132.
[0065] A second transmission filter 144 operates at second
transmission wavelength .lamda..sub.134 and is positioned in second
admission window 124. Second transmission filter 144 permits second
transmitted signals J.sub.134 to enter transmission block 102 at
second admission window 124, but bars passage into transmission
block 102 at second admission window 124 of transmitted signals and
components of transmitted signals at any wavelength other than at
second transmission wavelength .lamda..sub.134. In addition, second
transmission filter 144 reflects back toward the interior of
transmission block 102 transmitted signals and components of
transmitted signals at any wavelength other than at first
transmission wavelength .lamda..sub.134.
[0066] A third transmission filter 146 that operates at second
transmission wavelength .lamda..sub.136 is positioned in third
admission window 126. Third transmission filter 146 permits third
transmitted signals J.sub.136 to enter transmission block 102 at
third admission window 126, but bars passage into transmission
block 102 at third admission window 126 of transmitted signals and
components of transmitted signals at any wavelength other than at
third transmission wavelength .lamda..sub.136. In addition, third
transmission filter 142 reflects back toward the interior of
transmission block 102 transmitted signals and components of
transmitted signals at any wavelength other than at third
transmission wavelength .lamda..sub.32.
[0067] Finally, a fourth transmission filter 148 operating at
fourth transmission wavelength .lamda..sub.138 is positioned in
fourth admission window 128. Fourth transmission filter 148 permits
fourth transmitted signals J.sub.138 to enter transmission block
102 at fourth admission window 128, but bars passage into
transmission block 102 at fourth admission window 128 of
transmitted signals and components of transmitted signals at any
wavelength other than at fourth transmission wavelength
.lamda..sub.138. In addition, fourth transmission filter 148
reflects back toward the interior of transmission block 102
transmitted signals and components of transmitted signals at any
wavelength other than at fourth transmission wavelength
.lamda..sub.138.
[0068] The second additional associated structure located between
each laser of multiplexer 100 and the admission window associated
therewith is a lens that is positioned in close proximity to the
output side of each laser in alignment with the transmission axis
thereof. Each lens is capable of reorienting transmitted signals
from the associated laser through an acute angle away from the
transmission axis of that laser and along a redirected transmission
pathway to the associated transmission filter positioned in the
associated admission window.
[0069] Thus, as seen in FIG. 2, a first lens 152 is associated with
first laser 132 and positioned at the output side of first laser
132 between first laser 132 and first transmission filter 142 in
first admission window 122. A second lens 154 associated with
second laser 134 is positioned between the output side of second
laser 134 and second transmission filter 144 in second admission
window 124. Similarly, associated with third laser 136 is a third
lens 156 that is positioned between the output side of third laser
136 and third transmission filter 146 in third admission window
126. Finally, associated with fourth laser 158 is a fourth lens 148
that is positioned between the output side of fourth laser 158 and
fourth transmission filter 148 in fourth admission window 128.
[0070] Multiplexer 100 also includes a multiplexed signal
transmitting port 160 that is disposed on second side 108 of
transmission block 102. Multiplexed signal transmitting port 160 is
positioned to receive transmitted signals from the plurality of
lasers in multiplexer 100, once those transmitted signals are
placed in mutual optical alignment as a single multiplexed
transmission signal J.sub.M by being reflected within transmission
block 102 toward multiplexed signal transmitting port 160 between
the first coating 112 and second coating 114. As seen in FIG. 2,
multiplexed transmission signal J.sub.M emerges from transmission
block 102 at a multiplexed transmitted signal egress window 162 in
second coating 114.
[0071] Multiplexer 100 further includes a prism 164 positioned
between multiplexed signal egress window 162 and multiplexed signal
transmission port 160. Prism 164 is capable of bending the path of
multiplexed transmission signal J.sub.M into optical alignment with
the optical receiving axis R.sub.160 of transmitting port 160.
Advantageously then, receiving axis R.sub.160 of multiplexed signal
transmitting port 160 can be made to be parallel to second surface
110 of transmission block 102. This harmonizes the functional axis
of multiplexed signal transmitting port 160 with axes otherwise
standard in industry, facilitating easy coupling and replacement of
a multiplexer, such as multiplexer 100, as a modular component
among others in a complex optical system.
[0072] Transmitted signals from the plurality of lasers in
multiplexer 100 are optically aligned by repeated internal
reflections within transmission block 102 between first side 104
and second side 108 thereof. The series of reflections undergone by
each of the transmitted signals progresses the transmitted signals
within transmission block 102 toward multiplexed signal
transmitting port 160 in a direction parallel to first side 104 and
second side 108.
[0073] In achieving this result, among all of the transmitted
signals, fourth transmitted signal J.sub.138 engages in the longest
path of travel interior of transmission block 102. Entering
transmission block 102 through fourth transmission filter 148 at
fourth admission window 128, fourth transmitted signal J.sub.138
travels across transmission block 102 slightly in the direction of
multiplexed signal transmission port 160 to second coating 114 on
second surface 110. There fourth transmitted signal J.sub.138 is
reflected back across transmission block 102, again trending in the
direction of multiplexed signal transmitting port 160, to first
coating 112 on first surface 106. Reflections continue, sending
fourth transmitted signal J.sub.138 across transmission block 102
to second coating 114 and back across transmission block 102 to
first surface 106, always in the direction of multiplexed signal
transmitting port 160. On this second return to first surface 106,
however, fourth transmitted signals J.sub.138 encounters third
transmission filter 146 in third admission window 126. There,
fourth transmitted signal J.sub.138 is reflected onward between
first surface 106 and second surface 110 in the direction of
multiplexed signal transmitting port 160, but fourth transmitted
signals J.sub.138 is joined in those additional internal
reflections by third transmitted signal J.sub.136, which enters
transmission block 102 through third transmission filter 146 in
third admission window 126.
[0074] Third transmitted signal J.sub.136 and fourth transmitted
signals J.sub.138 are optically aligned from third admission window
126 onward during subsequent internal reflections. Those
reflections continue between first coating 112 on first surface 106
and second coating 114 on second surface 110, until third
transmitted signal J.sub.136 and fourth transmitted signals
J.sub.138 encounter second transmission filter 144 in second
admission window 124. There, third transmitted signal J.sub.136 and
fourth transmitted signal J.sub.138 are reflected onward between
first surface 106 and second surface 110 in the direction of
multiplexed signal transmitting port 160, but third transmitted
signal J.sub.136 and fourth transmitted signal J.sub.138 are joined
in those additional internal reflections by second transmitted
signal J.sub.134, which enters transmission block 102 through
second transmission filter 144 in second admission window 124.
[0075] Second transmitted signal J.sub.134, third transmitted
signal J.sub.136, and fourth transmitted signal J.sub.138 are
optically aligned from second admission window 124 onward during
subsequent internal reflections. Those reflections continue between
first coating 112 on first surface 106 and second coating 114 on
second surface 110, until second transmitted signal J.sub.134,
third transmitted signal J.sub.136, and fourth transmitted signals
J.sub.138 encounter first transmission filter 142 in first
admission window 122. There, second transmitted signal J.sub.134,
third transmitted signal J.sub.136, and fourth transmitted signal
J.sub.138 are reflected onward between first surface 106 and second
surface 110 in the direction of multiplexed signal transmitting
port 160, but second transmitted signal J.sub.134, third
transmitted signal J.sub.136, and fourth transmitted signal
J.sub.138 are joined in those additional internal reflections by
first transmitted signal J.sub.132, which enters transmission block
102 through first transmission filter 142 in first admission window
122.
[0076] Thereafter, first transmitted signal J.sub.132, second
transmitted signal J.sub.134, third transmitted signal J.sub.136,
and fourth transmitted signal J.sub.138 are optically aligned as
multiplexed transmission signal J.sub.M, which makes a single
transit across transmission block 102 to multiplexed signal egress
window 162, through prism 164, and then toward multiplexed signal
transmitting port 160 for retransmission.
[0077] The input side of multiplexed signal transmitting port 160
is provided with an optical isolator that prevents any portion of a
multiplexed transmitted signal that enters multiplexed signal
transmitting port 160 from being reflected from multiplexed signal
transmitting port 160 back into multiplexer 100. Such an event
could cause damage to the lasers employed therein, or otherwise
interfere with optimum operation. Thus, as shown in FIG. 2, a
multiplexed transmitted signal isolator 166 is positioned at the
output side of multiplexed signal transmitting port 160 between
transmitting port 160 and prism 164.
[0078] Selected portions of multiplexer 100 will be addressed in
further detail relative to the enlarged depictions presented in
FIGS. 3-5.
[0079] FIG. 3 is a diagrammatic depiction of a typical laser and
the set of lens, transmission filter, and admission aperture
associated therewith in multiplexer 100. There, first laser 132 is
shown and first admission window 122 that is associated therewith.
Between first laser 132 and first admission window 122, the
associated first transmission filter 142 and first lens 152 also
appear. First laser 132 produces transmitted signals J.sub.132 at
first transmission wavelength .lamda..sub.132. Transmitted signals
J.sub.132 emerge from the output side of first laser 132 directed
toward first surface 106 of transmission block 102 and in alignment
with transmission axis T.sub.132 of first laser 132.
[0080] First lens 152 is optically aligned with transmission axis
T.sub.132 of first laser 132 at a focal length F.sub.152 away from
the output side of first laser 132. Focal length F.sub.152 is
determined by the nature of first laser 132 and other performance
criteria intended for multiplexer 100. For example, if a laser
transmits an optical signal with a small beam spot on the order of
1 microns, is all too easy to produce undesirable amounts of beam
divergence during optical manipulation of the optical signals
produced. In order to achieve a suitable beam diameter of J.sub.132
after first lens 152, for example 500 um, focal length F.sub.152 is
maintained quite small, in a range of from about 0.8 to about 1.0
millimeters.
[0081] It is the function of first lens 152 to reorient transmitted
signals J.sub.132 from first laser 132 through an acute tilt angle
.mu..sub.152 away from transmission axis T.sub.132 along a
redirected transmission pathway P.sub.132 to first admission window
122. The distance between laser's axis T.sub.132 and first lens'
optical axis 151 determines the tilted angle .mu..sub.152 of
P.sub.132. There transmitted signals J.sub.132 pass through first
transmission filter 142 and enter transmission block 102 at an
angle of refraction B.sub.132 from the perpendicular P.sub.122 to
first surface 106 of transmission block 102 at first admission
window 122.
[0082] Tilt angle .mu..sub.152 of beam P.sub.132 is set equal to
the angle of incidence in air for first transmission filter 142.
Reorienting the transmission pathway for transmitted signals
J.sub.132 in this manner permits the desirable result of being able
to position first laser 132 with transmission axis T.sub.132
oriented at and substantially normal to first surface 106 of
transmission block 102. This harmonizes the functional axis of
first laser 132 with axes otherwise standard in industry,
facilitating easy coupling and replacement of a multiplexer, such
as multiplexer 100, as a modular component among others in a
complex optical system. In one embodiment of multiplexer 100,
satisfactory performance has been achieved with tilt angle
.mu..sub.152=13.5 degrees. Suitable lenses for use as first lens
152 include A-type lenses, D-type lenses, Grin lenses, and Ball
lenses.
[0083] FIG. 4 depicts prism 164 on second side 108 of transmission
block 102 in multiplexer 100. Prism 164 is made from fused silica
and is bonded to second surface 110 of transmission block 102 by an
epoxy adhesive possessed of an optical index close to that of fused
silica. Prism 164 has a longest face 168 that is perpendicular to
second surface 110 and an inclined face 170 that forms a dihedral
incline angle .sub.170 with longest face 168.
[0084] Multiplexed transmission signal J.sub.M emerges from
transmission block 102 through multiplexed signal egress window 162
and enters prism 164 through the side thereof that is secured to
transmission block 102. Incline angle .sub.170 is calculated to
permit prism 164 to bend the path of multiplexed transmission
signal J.sub.M into alignment with receiving axis R.sub.160 of
multiplexed signal transmitting port 160. Optimally, the path of
multiplexed transmission signal J.sub.M would then be parallel to
second surface 110 of transmission block 102, and multiplexed
signal transmitting port 160 could be positioned on second side 108
of transmission block 102 with receiving axis R.sub.160 parallel to
second surface 110. In one embodiment of the inventive technology,
it has been found to facilitate this objective by setting incline
angle .sub.170=49.6.+-.0.1 degrees.
[0085] The longitudinal positioning of prism 164 along second
surface 110 of transmission block 102 at multiplexed signal egress
window 162 can be used to determine the separation distance D from
second surface 110 of the path that transmission signal J.sub.M
travels after passing through prism 164. This in turn is equivalent
to determining how far away from second surface 110 it is necessary
to position receiving axis R.sub.160, and in turn how to dispose
multiplexed signal transmitting port 160 relative to the other
elements of multiplexer 100. Altering the location of prism 164 in
the manner suggested by two-sided arrow S in FIG. 4 will
correspondingly vary separation distance D of multiplexed
transmission signal J.sub.M from second surface 110. Shifting prism
164 in the direction indicated by the left side of arrow S will
reduce separation distance D, while shifting prism 164 in the
direction indicated by the right side of arrow S will increase
separation distance D.
[0086] FIGS. 5A and 5B are related diagrams that illustrate in
exploded perspective the elements and operation of multiplexed
transmission signal isolator 166 that is located on the input side
of multiplexed signal transmitting port 160 in multiplexer 100 of
FIG. 2.
[0087] Multiplexed transmission signal isolator 166 is a
dual-stage, free space isolator that includes a first polarized
disc 172, a second polarized disc 174, and a third polarized disc
176. First polarized disc 172 and second polarized disc 174 are
disposed in an aligned, parallel relationship sandwiching a first
garnet crystal 178 therebetween. On the opposite side of second
polarized disc 174 from first garnet crystal 178 is a second garnet
crystal 180. Second garnet crystal 180 is in turn sandwiched
between second polarized disc 174 and third polarized disc 176,
which are also in an aligned, parallel relationship. Receiving axis
R.sub.160 of multiplexed signal transmitting port 160 is included
in FIGS. 5A and 5B by way of perspective.
[0088] During the use of multiplexed transmission signal isolator
166, third polarized disc 176 of multiplexed transmission signal
isolator 166 is positioned in close proximity to multiplexed signal
transmitting port 160, while third polarized disc 176 is located
remotely therefrom. From this it can be appreciated that
multiplexed transmission signal J.sub.M shown in FIG. 5A is
successfully entering the input side of multiplexed signal
transmitting port 160. On the other hand, multiplexed transmission
signal J.sub.M shown in FIG. 5B is attempting, due to reflection or
otherwise within multiplexed signal transmitting port 160, to
escape therefrom along receiving axis R.sub.160. In this attempt,
multiplexed transmission signal J.sub.M is as intended, entirely
unsuccessful.
[0089] The transparent direction of each of polarized discs 172,
124, and 176 is indicated by a diametrically disposed broken line
thereupon. When the polarization direction of an optical signal
passing through a portion of multiplexed transmission signal
isolator 166 is aligned with the transparent direction of that
portion, the optical signal passes without obstruction. On the
other hand, if the polarization direction of an optical signal
passing through a portion of multiplexed transmission signal
isolator 166 is perpendicular to the transparent direction of that
portion of multiplexed signal transmitting port 160, the optical
signal is completely absorbed and blocked from passage. In FIG. 5A,
multiplexed transmission signal J.sub.M passes without significant
absorption through polarized discs 172, 174, and 176 of multiplexed
transmission signal isolator 166. In the other direction of
propagation, however, as shown in FIG. 5B, multiplexed transmission
signal J.sub.M is completely absorbed by second polarized disc 174
and first polarized disc 172.
[0090] Generally, transmitted signals in optical systems are
polarized, and the wavelength intervals maintained between plural
lasers in a single optical device are quite small. For example, in
an LX4 optical transceiver system, the transmission wavelengths of
four lasers, such as lasers 132, 134, 136, and 138 in multiplexer
100 would be, respectively, 1275 nanometers, 1300 nanometers, 1325
nanometers, and 1350 nanometers. At these wavelength intervals, a
single dual-stage free space isolator, such as multiplexed
transmission signal isolator 166, is sufficient to prevent the
return from multiplexed signal transmitting port 160 of any portion
of a multiplexed transmission signal received thereby.
[0091] FIGS. 6A and 6B are related diagrams that illustrate an
aspect of spatial efficiency promoted by the teachings of the
present invention. FIG. 6A depicts optical transmission block 20
from known optical multiplexer 10 shown in FIG. 1, as well as the
pathways of transmitted signals L.sub.1-L.sub.4 and multiplexed
transmission signal L.sub.M into, within, and out of transmission
block 20. By way of comparison, FIG. 6B depicts optical
transmission block 102 from inventive optical multiplexer 100 shown
in FIG. 2 and includes the pathways of transmitted signals
J.sub.132-J.sub.138 and multiplexed transmission signal J.sub.M
into, within, and out of transmission block 102.
[0092] As seen in FIG. 6A, in known multiplexer 10, internal
reflections of transmitted signals in transmission block 20 occur
exclusively at transmission filters 71-74. Therefore, in
multiplexer 10, first transmitted signal L.sub.1 experiences only
three reflections within transmission block 20 and, following only
four transits of transmission block 20, emerges therefrom in
optical alignment with the other transmitted signals
L.sub.2-L.sub.4 as multiplexed transmission signal L.sub.M.
[0093] The spatial relationships among typical components in a
known multiplexer, such as multiplexer 10 of FIG. 1, ultimately
determine the minimum width able to be used in the transmission
block thereof. For example, the distance between adjacent lasers,
such as lasers 11-14, is about 6.2 millimeters. Typically, a common
angle of incidence .alpha.=13.5 degrees is maintained for the
transmitted signal from each of those lasers with each of the
associated transmission filters 71-74. Each of those transmitted
signals then enters transmission block 20 at an angle of refraction
A.sub.1=9.3 degrees. Under these particular constraints,
transmission block 20 will necessarily have a width W.sub.20=20
millimeters. Such a size in transmission block 20 can, however,
become an impedance to reducing size in new optical devices, such
as optical transceivers.
[0094] As seen in FIG. 6B by contrast, in inventive multiplexer
100, internal reflections of transmitted signals in transmission
block 102 occur not only at transmission filters 142, 144, 146, and
148, but at first coating 112 and at second coating 114. Therefore,
in multiplexer 100, first transmitted signal J.sub.132 experiences
twelve reflections within transmission block 102, so that following
thirteen transits of transmission block 102, first transmitted
signal J.sub.132 emerges from transmission block 102 in optical
alignment with the other transmitted signals J.sub.134-J.sub.138 as
multiplexed transmission signal J.sub.M.
[0095] The cumulative distance of travel of transmitted signals
within transmission block 102 is thus increased by several times
relative to the cumulative distance of travel of transmitted
signals within transmission block 20 in known multiplexer 10.
Correspondingly, width W.sub.102 of transmission block 102 need be
only a fraction of width W.sub.20 that is required in transmission
block 20 of known multiplexer 10. Employing teachings of the
present invention, it is possible to construct a multiplexer of
reduced size having a transmission block, such as transmission
block 102, having a width W.sub.102=10 millimeters only. This in
turn nets further advantages not directly related to the optical
device into which transmission block 102 might become incorporated.
For example, a smaller die can be used to manufacture transmission
blocks, such as transmission block 102, than are required to
manufacture transmission blocks for known multiplexers.
[0096] According to another aspect of the present invention, an
optical signal multiplexer, such as multiplexer 100, can be made to
include demultiplexing means cooperative with the transmission
block thereof for separating a multiplexed reception signal into
constituent received signals at respective distinct reception
wavelengths. One embodiment of structures performing the function
of a demultiplexing means according to teachings of the present
invention is presented in FIG. 7 as a demultiplexer 200.
[0097] Demultiplexer 200 is so configured as to be capable of
separating a single multiplexed reception signal containing four
received signals at respective distinct optical reception
wavelengths into those constituent received signals for separate
subsequent processing. In other embodiments of the present
invention, a smaller or a larger number of such received signals
may be included in a single multiplexed reception signal that is to
be thusly deconstructed.
[0098] Centrally, demultiplexer 200 includes an optical
transmission block 202 that may be similar in material composition,
physical configuration, and method of manufacture to transmission
block 102 of multiplexer 100 in FIG. 2. Thus transmission block 202
has on a first side 204 thereof a planar first surface 206 and on
an opposed second side 208 thereof a planar second surface 210 that
is parallel to first surface 206. As measured between first surface
206 and second surface 210, transmission block 202 has a width
W.sub.202.
[0099] Transmission block 202 is rendered internally and externally
reflective of optical signals by highly reflective coatings on the
faces thereof that may be similar in material composition, physical
configuration, and method of manufacture to first coating 112 and
second coating 114 of multiplexer 100 in FIG. 2. Accordingly,
transmission block 202 of demultiplexer 200 carries a highly
reflective first coating 212 on first surface 206 and a highly
reflective second coating 214 on second surface 210.
[0100] Formed through second coating 214 at selected locations
along second surface 210 are a plurality of egress windows at which
second surface 210 of transmission block 202 is neither internally
nor externally reflective of optical signals. The plurality of
egress windows depicted in FIG. 7 includes a first egress window
222, a second egress window 224, a third egress window 226, and a
fourth egress window 228. The egress windows of demultiplexer 200
may be similar in material composition, physical configuration, and
method of manufacture to the admission windows of multiplexer 100
in FIG. 2. The number of egress windows in a reflective coating,
such as second coating 214, will vary with and generally correspond
at least to the number of received signals at distinct optical
wavelengths that are to be separated from a multiplexed reception
signal by a demultiplexer, such as demultiplexer 200. Therefore, a
smaller or a greater number of such egress windows may be required
in other inventive demultiplexer embodiments.
[0101] Also included in demultiplexer 200 is a plurality of optical
detectors that are positioned on the same side of transmission
block 202, in the case illustrated in FIG. 7 on second side 208.
Each of the detectors is tuned to recognize and to retransmitting
received signals at a respective individual reception wavelength,
wherefore a smaller or a larger number of detectors may be employed
in other embodiments of the invention, depending on the number of
received signals to be separated out of a single multiplexed
reception signal. The reception axis of each of the detectors is
desirable oriented at and substantially normal to second surface
210 of transmission block 202.
[0102] The plurality of detectors shown in the embodiment of FIG. 7
includes a first detector 232, a second detector 234, a third
detector 236, and a fourth detector 238. First detector 232
recognizes received signals K.sub.232 at a first reception
wavelength .lamda..sub.232 and has a reception axis R.sub.232 that
is oriented at and substantially normal to second surface 210 of
transmission block 202. Second detector 234 recognizes received
signals K.sub.234 at a second reception wavelength .lamda..sub.234
and has a reception axis R.sub.234 that is also oriented at and
substantially normal to second surface 210. Third detector 236
recognizes received signals K.sub.126 at a third reception
wavelength .lamda..sub.236 and has a reception axis R.sub.236 that
is oriented at and substantially normal to second surface 210.
Finally, fourth detector 238 recognizes received signals K.sub.238
at a fourth reception wavelength .lamda..sub.238 and has a
reception axis R.sub.238 that is in addition oriented at and
substantially normal to second surface 210 of transmission block
202. Appropriate detectors for use in demultiplexer 200 include PIN
detectors and ADP detectors.
[0103] Each of the detectors shown in FIG. 7 is associated with a
corresponding one of the egress windows formed in second coating
214 on second surface 210 of transmission block 202. Thus, first
egress window 222 is associated with first detector 232, second
egress window 224 is associated with second detector 234, third
egress window 226 is associated with third detector 236, and
finally, fourth egress window 228 is associated with fourth
detector 238.
[0104] Located between each detector of demultiplexer 200 and the
egress window associated therewith are a pair of additional
associated structures.
[0105] The first of these additional associated structures is an
optical filter that is positioned on second surface 210 of
transmission block 202 filling the associated egress window. Each
such optical filter operates at the reception wavelength of the
associated detector, thereby blocking from entry into or egress
from transmission block 202 through the egress window in which it
is located any signal other than received signals at the reception
wavelength of the associated detector. From the interior of
transmission block 202, these reception filters function as
mirrors, reflecting back toward the interior of transmission block
202 any received signals at those other wavelengths that approaches
first surface 206 or second surface 210 of transmission block 202
from the interior thereof.
[0106] Thus, a first reception filter 242 tuned to first reception
wavelength .lamda..sub.232 is positioned in first egress window
222. First reception filter 242 permits first received signals
K.sub.232 to emerge from transmission block 202 at first egress
window 222, but bars passage out of transmission block 202 at first
egress window 222 of received signals and components of received
signals at any wavelength other than at first reception wavelength
.lamda..sub.232. In addition, first reception filter 242 reflects
back toward the interior of transmission block 202 received signals
and components of received signals at any wavelength other than at
first reception wavelength .lamda..sub.232.
[0107] A second reception filter 244 tuned to second reception
wavelength .lamda..sub.234 is positioned in second egress window
224. Second reception filter 244 permits second received signals
K.sub.234 to emerge from transmission block 202 at second egress
window 224, but bars passage out of transmission block 202 at
second egress window 224 of received signals and components of
received signals at any wavelength other than at second reception
wavelength .lamda..sub.234. In addition, second reception filter
244 reflects back toward the interior of transmission block 202
received signals and components of received signals at any
wavelength other than at second reception wavelength
.lamda..sub.234.
[0108] A third reception filter 246 tuned to third reception
wavelength .lamda..sub.236 is positioned in third egress window
226. Third reception filter 246 permits third received signals
K.sub.236 to emerge from transmission block 202 at third egress
window 226, but bars passage out of transmission block 202 at third
egress window 226 of received signals and components of received
signals at any wavelength other than at third reception wavelength
.lamda..sub.236. In addition, third reception filter 246 reflects
back toward the interior of transmission block 202 received signals
and components of received signals at any wavelength other than at
third reception wavelength .lamda..sub.236.
[0109] Finally, a fourth reception filter 248 tuned to fourth
reception wavelength .lamda..sub.238 is positioned in fourth egress
window 228. Fourth reception filter 248 permits fourth received
signals K.sub.238 to emerge from transmission block 202 at fourth
egress window 228, but bars passage out of transmission block 202
at fourth egress window 228 of received signals and components of
received signals at any wavelength other than at fourth reception
wavelength .lamda..sub.238. In addition, fourth reception filter
248 reflects back toward the interior of transmission block 202
received signals and components of received signals at any
wavelength other than at fourth reception wavelength
.lamda..sub.238.
[0110] The second additional associated structure located between
each detector of multiplexer 200 and the egress window associated
therewith is a lens that is positioned in close proximity to the
input side of each detector in alignment with the reception axis
thereof. Each lens is capable of reorienting received signals from
the reception filter positioned in the associated egress window
through an acute angle into alignment with the reception axis of
the associated detector and along a redirected reception pathway to
detector.
[0111] Thus, as seen in FIG. 7, a first lens 252 is associated with
first detector 232 and positioned at the input side of first
detector 232 between first detector 232 and first reception filter
242 in first egress window 222. A second lens 254 associated with
second detector 234 is positioned between the input side of second
detector 234 and second reception filter 244 in second egress
window 224. Similarly, associated with third detector 236 is a
third lens 256 that is positioned between the input side of third
detector 236 and third reception filter 246 in third egress window
226. Finally, associated with fourth detector 238 is a fourth lens
248 that is positioned between the input side of fourth detector
238 and fourth reception filter 248 in fourth egress window
228.
[0112] Demultiplexer 200 also includes a multiplexed signal
receiving port 260 that is disposed on first side 204 of
transmission block 202. Multiplexed signal receiving port 260 is
positioned to direct a multiplexed reception signal R.sub.M into
transmission block 202 at a multiplexed reception signal admission
window 262 in second coating 214. Thereupon, multiplexed reception
signal K.sub.M is separated into the constituent received signals
thereof by being reflected within transmission block 202 between
the first coating 112 and second coating 114 toward the detectors
of demultiplexer 200.
[0113] Demultiplexer 200 further includes a prism 264 positioned
between multiplexed reception signal admission window 262 and
multiplexed signal receiving port 260. Prism 264 is capable of
bending the path of multiplexed reception signal K.sub.M out of
optical alignment with the optical transmitting axis T.sub.260 of
multiplexed signal receiving port 260 and into transmission block
202 at multiplexed reception signal admission window 262.
Advantageously then, transmitting axis T.sub.260 of multiplexed
signal receiving port 260 can be made to be parallel to first
surface 206 of transmission block 202. This harmonizes the
functional axis of multiplexed signal receiving port 260 with axes
otherwise standard in industry, facilitating easy coupling and
replacement of a demultiplexer, such as demultiplexer 200, as a
modular component among others in a complex optical system.
[0114] A multiplexed reception signal K.sub.M transmitted from
multiplexed signal receiving port 260 includes by way of example,
first received signal K.sub.232 at first reception wavelength
.lamda..sub.232, second received signal K.sub.234 at second
reception wavelength .lamda..sub.234, third received signal
K.sub.126 at third reception wavelength .lamda..sub.236, and fourth
received signal K.sub.238 at fourth reception wavelength
.lamda..sub.238. The received signals contained in multiplexed
reception signal K.sub.M remained optically aligned during repeated
internal reflections of multiplexed reception signal K.sub.M within
transmission block 202 between first side 204 and second side 208
thereof.
[0115] The series of reflections progresses the received signals
within transmission block 102 away from multiplexed signal
receiving port 260 in a direction parallel to first side 204 and
second side 208. As these internal reflections bring the
constituents of multiplexed reception signal K.sub.M in turn to
each of the reception filters on first side 204 of transmission
block 202, the constituent received signal at the optical
wavelength passed by that particular reception filter emerges from
transmission block 202 and is directed to the associated detector
for retransmission. The remaining constituent received signals from
multiplexed reception signal K.sub.M continue internal reflections
in transmission block 202 away from multiplexed signal receiving
port 260. When the next reception filter is reached, another
constituent received signal is separated from the group. The
process continues until each received signals have been separated
from all others.
[0116] In achieving this result, first received signal K.sub.232
engages in the shortest path of travel interior of transmission
block 202. First received signal K.sub.232 enters transmission
block 202 at multiplexed reception signal admission window 262 with
the other constituent received signals in multiplexed reception
signal K.sub.M and makes but a single transit of transmission block
202 to first reception filter 242 in first egress window 222.
There, first received signal K.sub.232 emerges from transmission
block 202, as first reception wavelength .lamda..sub.232 thereof is
the optical wavelength that is able to pass through first reception
filter 242.
[0117] Second received signal K.sub.234, third received signal
K.sub.126, and fourth received signal K.sub.238 are, however,
reflected back toward first surface 206 of transmission block 202
by first reception filter 242. Following a first reflection at
first surface 206, a second reflection at second surface 210, and
finally yet a third reflection at first surface 206 again, this
group of remaining constituent received signals reach second
reception filter 244 in second egress window 224. There second
received signal K.sub.234 emerges from transmission block 202, as
second reception wavelength .lamda..sub.234 thereof is the optical
wavelength that is able to pass through second reception filter
244.
[0118] Third received signal K.sub.126, and fourth received signal
K.sub.238 are, however, reflected back toward first surface 206 of
transmission block 202 by second reception filter 244. Following a
first reflection at first surface 206, a second reflection at
second surface 210, and finally yet a third reflection at first
surface 206 again, this group of remaining constituent received
signals reach third reception filter 246 in third egress window
226. There, third received signal K.sub.236 emerges from
transmission block 202, as third reception wavelength
.lamda..sub.236 thereof is the optical wavelength that is able to
pass through third reception filter 246.
[0119] Fourth received signal K.sub.238 is, however, reflected back
toward first surface 206 of transmission block 202 by third
reception filter 246. Following a first reflection at first surface
206, a second reflection at second surface 210, and finally yet a
third reflection at first surface 206 again, this remaining
constituent received signal reaches fourth reception filter 248 in
fourth egress window 228. There, fourth received signal K.sub.238
emerges from transmission block 202, as fourth reception wavelength
.lamda..sub.238 thereof is the optical wavelength that is able to
pass through fourth reception filter 248.
[0120] Selected portions of demultiplexer 200 will be addressed in
further detail relative to the enlarged depictions presented in
FIGS. 8 and 9.
[0121] FIG. 8 is a diagrammatic depiction of a typical detector and
the set of lens, reception filter, and egress aperture associated
therewith in demultiplexer 200. There, first detector 232 is shown
and first egress window 222 that is associated therewith. Between
first detector 232 and first egress window 222, the associated
first reception filter 242 and first lens 252 also appear. First
detector 232 recognizes received signals K.sub.232 at first
reception wavelength .lamda..sub.232. Received signal K.sub.232
must, however, be directed to the input side of first detector 232
in alignment with reception axis R.sub.232 of first reception
filter 242.
[0122] First lens 252 is optically aligned with reception axis
R.sub.232 of first detector 232 at a focal length F.sub.252 away
from the input side of first detector 232. Focal length F.sub.252
is determined by the nature of first detector 232 and other
performance criteria intended for demultiplexer 200. It is the
function of first lens 252 to reorient received signal K.sub.232
from first reception filter 242 through an acute tilt angle
.mu..sub.252 into alignment with reception axis R.sub.232 of first
detector 232. The distance between first detector's axis R.sub.232
and first lens' optical axis 251 determines the tilted angle
.mu..sub.252 of beam K.sub.232. Then received signal K.sub.232 can
enter first detector 232 to be recognized and retransmitted
thereby.
[0123] Tilt angle .mu..sub.252 of the beam K.sub.232 is set equal
to the angle of incidence in air for first reception filter 242.
Reorienting the pathway for first received signals K.sub.232 in
this manner permits the desirable result of being able to position
first detector 232 with reception axis R.sub.232 oriented at and
substantially normal to second surface 210 of transmission block
202. This harmonizes the functional axis of first detector 232 with
axes otherwise standard in industry, facilitating easy coupling and
replacement of a demultiplexer, such as demultiplexer 200, as a
modular component among others in a complex optical system.
[0124] FIG. 9 depicts prism 264 attached to first surface 206 of
transmission block 202 in demultiplexer 200. Prism 264 may be
similar in material composition, physical configuration, method of
manufacture, and manner of attachment to prism 164 of multiplexer
100 in FIG. 2. Prism 264 has a longest face 268 that is
perpendicular to first surface 206 of transmission block 202 and an
inclined face 270 that forms a dihedral incline angle
.delta..sub.270 with longest face 268.
[0125] Multiplexed reception signal K.sub.M emerges from
multiplexed signal receiving port 260 along transmitting axis
T.sub.260 and enters prism 164 through longest face 268 thereof.
Incline angle .delta..sub.170 is calculated to permit prism 264 to
bend the path of multiplexed reception signal K.sub.M out of
alignment with transmitting axis T.sub.260 and into transmission
block 202 through the face of prism 164 that is attached thereto.
Optimally, incline angle .sub.270 is so established that
transmitting axis T.sub.260 of multiplexed signal receiving port
260 and the initial path of multiplexed reception signal K.sub.M
can be parallel to first surface 206 of transmission block 202.
This harmonizes the functional axis of multiplexed signal receiving
port 260 with axes otherwise standard in industry, facilitating
easy coupling and replacement of a demultiplexer, such as
demultiplexer 200, as a modular component among others in a complex
optical system. In one embodiment of the inventive technology, it
has been found to facilitate this objective if incline angle
.delta..sub.270=49.6.+-.0.1 degrees.
[0126] The longitudinal positioning of prism 264 along first
surface 206 of transmission block 202 at multiplexed reception
signal admission window 262 can be used to determine the separation
distance E from first surface 206 of the path along which
multiplexed reception signal K.sub.M initially travels to reach
prism 264. This in turn is equivalent to determining how far away
from first surface 206 it is necessary to position transmitting
axis T.sub.260, and in turn how to dispose multiplexed signal
receiving port 260 relative to the other elements of demultiplexer
200. Altering the location of prism 264 in the manner suggested by
two-sided arrow S in FIG. 9 will correspondingly vary separation
distance E of multiplexed reception signal K.sub.M from first
surface 206. Shifting prism 264 in the direction indicated by the
left side of arrow S will reduce separation distance E, while
shifting prism 264 in the direction indicated by the right side of
arrow S will increase separation distance E.
[0127] For similar reasoning as that presented relative to the
comparison conducted using FIGS. 6A and 6B, the teachings of the
present invention enable transmission block 202 of demultiplexer
200 to have a width W.sub.202 that is substantially reduced in
width. The increased number of internal reflections of signals
attainable in a transmission block, such as transmission block 202,
advantageously enables width W.sub.202 thereof to be as small as 10
millimeters. Therefrom corresponding economies of size reduction
can be attained in all related optical devices and manufacturing
methodologies.
[0128] According to yet another aspect of the present invention, an
optical signal demultiplexer, such as demultiplexer 200, can be
made to include multiplexing means cooperative with the
transmission block thereof for combining transmitted signals at
respective transmission wavelengths into a single multiplexed
transmission signal. One embodiment of structures performing the
function of a multiplexing means according to teachings of the
present invention has been presented in FIG. 2 as a multiplexer
100.
[0129] A single optical device both the functions of multiplexer
100 of FIG. 2 and the functions of demultiplexer 200 of FIG. 7 is
shown by way of completeness in FIG. 10 as a
multiplexer-demultiplexer 300. In FIG. 10, any reference character
that is identical to a reference character used in FIG. 2 or 7 is
intended to identify an element that is structurally and
functionally identical among the figures in which that same
reference character appears.
[0130] Centrally, multiplexer-demultiplexer 300 includes an optical
transmission block 302 that may be similar in material composition,
physical configuration, and method of manufacture to either or both
of transmission block 102 of multiplexer 100 in FIG. 2 or
transmission block 202 of demultiplexer 200 in FIG. 7. Thus
transmission block 302 has on a first side 304 thereof a planar
first surface 306 and on an opposed second side 308 thereof a
planar second surface 310 that is parallel to first surface 306. As
measured between first surface 306 and second surface 10,
transmission block 302 has a width W.sub.302.
[0131] Transmission block 302 carries a highly reflective first
coating 312 on first surface 306 and a highly reflective second
coating 314 on second surface 310. Formed through first coating 312
at selected locations along first surface 306 are a plurality of
admission windows at which first surface 306 of transmission block
302 is neither internally nor externally reflective of optical
signals. Formed through second coating 314 at selected locations
along second surface 310 are a plurality of egress windows at which
second surface 310 of transmission block 302 is neither internally
nor externally reflective of optical signals. For simplicity, these
admission windows and egress windows are not labeled in FIG.
10.
[0132] Multiplexer-demultiplexer 300 is so configured as to be
capable, through teachings of the present invention presented
relative to multiplexer 100 and demultiplexer 200, of combining
four transmitted signals at respective distinct optical
transmission wavelengths in to a single multiplexed transmission
signal, and of separating a single multiplexed reception signal
containing four received signals at respective distinct optical
reception wavelengths into those constituent received signals. One
or more of the distinct optical transmission wavelengths may be
identical to a corresponding one of the distinct optical reception
wavelengths. In other embodiments of the present invention, a
smaller or a larger number of transmitted signals or received
signals may be effectively manipulated by a
multiplexer-demultiplexer, such as multiplexer-demultiplexer 300,
and the number of transmitted and received may or may not be
identical in any given inventive embodiment thereof without
departing from the teachings of the present invention.
[0133] For similar reasoning as that presented relative to the
comparison conducted using FIGS. 6A and 6B, the teachings of the
present invention enable transmission block 302 of
multiplexer-demultiplexer 300 to have a width W.sub.302 that is
substantially reduced in width. The increased number of internal
reflections of signals attainable in a transmission block, such as
transmission block 302, advantageously enables width W.sub.302
thereof to be as small as 10 millimeters.
[0134] The present invention also contemplates a method for
processing a plurality of optical signals at a corresponding
plurality of respective individual wavelengths. That method
includes the step of covering opposed parallel first and second
planar surfaces on respective first and second sides of an optical
signal transmission block with highly reflective first and second
coatings. A plurality of lasers capable of producing transmitted
signals at distinct transmission wavelengths are positioned on the
first side of the transmission block with the transmission axis of
each of the lasers oriented at and substantially normal to the
first surface of the transmission block. Transmitted signals from
the lasers are reorienting into the transmission block through the
first surface thereof along parallel paths at an acute tilt angle
to the transmission axis of each respective laser. The transmitted
signals are then reflected within the transmission block between
the first and second coatings in a direction that is parallel to
the first and second surfaces and away from the lasers. Following
these reflections, the transmitted signals emerge in mutual optical
alignment from the second surface of the transmission block as a
multiplexed transmission signal, which is received in a signal
transmission port on the second side of the transmission block.
[0135] The method may also includes the steps of orienting the
receiving axis of the transmission port parallel to the second
surface of the transmission block, and bending the path of the
multiplexed transmission signal into optical alignment with the
receiving axis of the transmitting port. Additionally, a plurality
of admission windows are formed through the first coating
corresponding in one-to-one relation to the plurality of lasers,
and signals passing through each of the admission windows are
filtered to the transmission wavelength of the transmitted signals
produced by the laser corresponding thereto. A multiplex signal
egress window is formed in the second coating.
[0136] According to another aspect of the present invention, a
method as described above also includes the steps of delivering
into the transmissions block through the first surface thereof a
multiplexed reception signal containing a plurality of received
signals at respective reception wavelengths, and positioning a
plurality of optical detectors capable of detecting received
signals at a respective reception wavelength on the second side of
the transmission block with the receiving axis of each of the
detectors oriented at and substantially normal to the second
surface of the transmission block. The received signals delivered
into the transmission block are reflecting within the transmission
block between the first and second coatings in a direction that is
parallel to the first and second surfaces and toward the detectors.
Following these reflections, the received signals emerge from the
second surface of the transmission block and are reoriented into
alignment with the receiving axis of each of the detectors.
[0137] The step of delivering comprises the steps of positioning a
multiplexed signal receiving port on the first side of the
transmission block with the transmission axis of the receiving port
oriented parallel to the first surface of the transmission block,
transmitting the multiplexed reception signal from the receiving
port, and bending the path of the multiplexed transmission signal
from the transmission axis of the receiving port into a
non-perpendicular angle of incidence with the first surface of the
transmission block.
[0138] The method also involves the steps of forming a plurality of
egress windows through the second coating corresponding in
one-to-one relation to the plurality of detectors, and forming a
multiplex signal access window in the first coating. Each of the
detectors is tuned to the reception wavelength corresponding
thereto, and the step of doing so includes the step of filtering to
a respective individual reception wavelength received signals
emerging from the transmission block at each egress window.
[0139] The foregoing description of the invention has been
described for purposes of clarity and understanding. It is not
intended to limit the invention to the precise form disclosed.
Various modifications may be possible within the scope and
equivalence of the appended claims.
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