U.S. patent application number 10/081498 was filed with the patent office on 2003-08-28 for planar lightwave wavelength device using moveable mirrors.
Invention is credited to Aksyuk, Vladimir Anatolyevich, Doerr, Christopher Richard, Fuchs, Dan T..
Application Number | 20030161574 10/081498 |
Document ID | / |
Family ID | 27752956 |
Filed Date | 2003-08-28 |
United States Patent
Application |
20030161574 |
Kind Code |
A1 |
Aksyuk, Vladimir Anatolyevich ;
et al. |
August 28, 2003 |
Planar lightwave wavelength device using moveable mirrors
Abstract
A method and apparatus are disclosed for adjusting the phase of
an optical signal by varying the path length of the optical signal
using one or more moveable mirrors. The phase adjustment techniques
of the present invention may be employed in various optical
devices, including 1.times.n optical switches. The position of the
mirrors may be controlled, for example, using micromachined control
elements that physically move the mirror along the lightpath. An
exemplary 2-by-2 optical switch includes two waveguides configured
to include a coupler region. A mirror is positioned at the output
of each waveguide. The position of at least one of the mirrors may
be adjusted along the optical path and the mirrors reflect the
light exiting from the end of the waveguides back into the same
waveguide after an adjustable phase delay due to the round trip
through an adjustable air gap between the waveguides and
corresponding mirrors. A received optical signal is split in the
coupler region into two generally equal components and the phase of
at least one component of the optical signal is adjusted by
controlling the relative position of the mirrors. The optical
components are then recombined and the optical signal appears at
the appropriate output port of the optical switch. The present
invention may also be applied in wavelength selective optical
switches that support multiple optical channels. A number of
techniques are also disclosed for fabricating optical devices in
accordance with the present invention.
Inventors: |
Aksyuk, Vladimir Anatolyevich;
(Piscataway., NJ) ; Doerr, Christopher Richard;
(Middletown, NJ) ; Fuchs, Dan T.; (Summit,
NJ) |
Correspondence
Address: |
Ryan, Mason & Lewis, LLP
Suite 205
1300 Post Road
Fairfield
CT
06430
US
|
Family ID: |
27752956 |
Appl. No.: |
10/081498 |
Filed: |
February 22, 2002 |
Current U.S.
Class: |
385/16 |
Current CPC
Class: |
G02B 6/3546 20130101;
G02B 6/2861 20130101; G02B 6/3596 20130101; G02B 6/122 20130101;
G02B 6/3516 20130101; G02B 6/12019 20130101; G02B 2006/12145
20130101 |
Class at
Publication: |
385/16 |
International
Class: |
G02B 006/26; G02B
006/35 |
Claims
We claim:
1. An optical device, comprising: at least one waveguide for
carrying an optical signal; and at least one mirror having an
adjustable position to vary a path length of said optical
signal.
2. The optical device according to claim 1, wherein said mirror is
controlled by a micromachine control element that positions said
mirror in a desired position along an optical path.
3. The optical device according to claim 1, wherein said mirror is
positioned at an end of said at least one waveguide.
4. The optical device according to claim 1, wherein said mirror is
fabricated in the waveguide material deposited on a substrate.
5. The optical device according to claim 1, wherein said optical
signal is a wavelength-division multiplexed (WDM) signal comprising
N wavelength channels and wherein said optical device further
comprises a demultiplexer for producing a plurality of
demultiplexed output signals from said input WDM signal and at
least one mirror associated with each of said N wavelength
channels.
6. The optical device according to claim 5, wherein a plurality of
said waveguides carry each of said N wavelength channels.
7. A method for adjusting a phase of an optical signal, said method
comprising the steps of: receiving said optical signal; and
adjusting a position of a mirror along a path of said optical
signal.
8. The method according to claim 7, wherein said adjusting step is
performed by a micromachine control element that positions said
mirror in a desired position along an optical path.
9. The method according to claim 7, wherein said mirror is
positioned at an end of at least one waveguide.
10. The method according to claim 7, wherein said mirror is
fabricated from a waveguide deposited on a substrate.
11. The method according to claim 7, wherein said optical signal is
a wavelength-division multiplexed (WDM) signal comprising N
wavelength channels and wherein said method further comprises the
step of demultiplexing said optical signal to produce a plurality
of demultiplexed output signals from said input WDM signal.
12. An optical switch, comprising: means for receiving said optical
signal; means for splitting said optical signal into at least two
optical components; a moveable mirror for adjusting a phase of at
least one of said optical components by adjusting a position of
said mirror along a path of said optical component; and means for
recombining said at least two optical components.
13. The optical switch of claim 12, wherein said means for
receiving comprises at least one waveguide for carrying said
optical signal.
14. The optical switch of claim 12, wherein said means for
splitting and recombining said optical signals is a coupler region
between two adjacent waveguides, a star coupler, an arrayed
waveguide router or a multimode interference waveguide.
15. The optical switch of claim 12, wherein said mirror is
controlled by a micromachine control element that positions said
mirror in a desired position along an optical path.
16. The optical device of claim 12, wherein said mirror is
positioned at an end of said at least one waveguide.
17. The optical device of claim 12, wherein said mirror is
fabricated from waveguide material deposited on a substrate.
18. The optical device of claim 12, wherein said optical signal is
a wavelength-division multiplexed (WDM) signal comprising N
wavelength channels and wherein said optical switch further
comprises a demultiplexer for producing a plurality of
demultiplexed output signals from said input WDM signal and at
least one mirror associated with each of said N wavelength
channels.
19. A method for switching an optical signal, said method
comprising the steps of: receiving said optical signal; splitting
said optical signal into at least two optical components; adjusting
a phase of at least one of said optical components by adjusting a
position of a mirror along a path of said optical component; and
recombining said at least two optical components.
20. The method according to claim 19, wherein said adjusting step
is performed by a micromachine control element that positions said
mirror in a desired position along an optical path.
21. The method according to claim 19, wherein said optical signal
is a wavelength-division multiplexed (WDM) signal comprising N
wavelength channels and wherein said method further comprises the
step of demultiplexing said optical signal to produce a plurality
of demultiplexed output signals from said input WDM signal.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to mechanisms for manipulating
light in optical circuits and in waveguide chips and, more
particularly, to optical devices for routing multi-wavelength
optical signals.
BACKGROUND OF THE INVENTION
[0002] Many innovations for optical communication systems have
involved the manner in which light waves are switched and
manipulated. In many optical transmission applications, it is
necessary to perform one or more of the following actions on light:
switching, attenuation, routing to different locations or
manipulating the phase of light. Such actions are critical for
realization of the optical networks that are the foundation of
global communications systems.
[0003] Optical communication systems increasingly employ wavelength
division multiplexing (WDM) techniques to transmit multiple
information signals on the same fiber, and differentiate each user
sub-channel by modulating a unique wavelength of light. WDM
techniques are being used to meet the increasing demands for
improved speed and bandwidth in optical transmission applications.
In optical communication networks, such as those employing WDM
techniques, individual optical signals are often selectively routed
to different destinations. Thus, a high capacity matrix or
cross-connect switch is often employed to selectively route signals
through interconnected nodes in a communication network.
[0004] At the heart of these cross-connect switches is the single
switching unit. Single switching units should exhibit low
manufacturing and operation costs, small losses of the optical
signal when passing through the switch (low insertion loss), and
high blocking of unwanted signals (high extinction ratio). Many
switches used in optical communication networks are manual, and are
relatively cheap to manufacture, but expensive to operate. In
addition, available switches tend to prevent high switching speed
and flexibility. Electronic switches first convert the optical
signal into an electronic signal, perform the switching and then
convert back into optical signals. These conversions are very
expensive and the switches are complex to manage but allow
considerable flexibility. As networks grow and become dense,
however, electronic switches become increasingly expensive and
harder to fabricate.
[0005] Therefore, optical switches that operate directly on the
light wave are favorable. Optical switches are often realized in
optical waveguides that can be manufactured with low cost and
enable easy multiplexing and de-multiplexing of the WDM signal
using waveguide grating routers (WGR). For a detailed discussion of
waveguide grating routers, such as optical star couplers, see U.S.
Pat. No. 4,904,042 to Dragone. Switching in waveguides is often
accomplished by applying phase or amplitude changes using an
electrooptic effect or a thermooptic effect. The electrooptic
effect usually requires special and expensive waveguide materials,
such as InP or LiNbO.sub.3, that exhibit nonlinear effects and are
used for fast switching and specialized applications. Thermooptic
switching (a heat induced change in the index of refraction) in
waveguides is robust and is extensively used in combination with
WGR in optical waveguide circuits. However, thermooptic switches
suffer from high power consumption and limit the complexity of
circuits that can be built due to thermal crosstalk and maximum
power limitations.
[0006] Recently, micro electro mechanical systems (MEMS) switches
have been introduced for network applications. MEMS switches are
usually movable mirrors that change the propagation direction of
light, or block light. For a discussion of a wavelength-selective
add-drop multiplexer that uses movable mirrors to add and/or drop
spectral components from a wavelength-division-multiplexed optical
signal, see, for example, U.S. Pat. No. 5,974,207 to Aksyuk et al,
assigned to the assignee of the present invention and incorporated
by reference herein. To change the propagation direction of the
light, or block the light, a shutter must be moved a distance long
enough to move the shutter in and out of a light beam or tilt the
shutter with an angle larger than the angular width of the optical
beam. These displacements are usually challenging to make with MEMS
actuators that excel at microscopic motion. If switching can be
achieved by motion that is the size of the optical wavelength
(about 1-2 .mu.m for common communications systems), MEMS switches
could be implemented in waveguides and other systems.
SUMMARY OF THE INVENTION
[0007] Generally, a method and apparatus are disclosed for
adjusting the phase of an optical signal by varying the path length
of the optical signal using one or more moveable mirrors. The phase
adjustment techniques of the present invention may be employed in
various optical devices, including 1.times.n optical switches that
introduce a phase change and recombine the optical signal to switch
a received optical signal to a desired output port. This phase
changing method can also be employed for pulse-shaping
applications, where phase changes of the different spectral
components of a wave are phase delayed in different amounts, as
well as for dispersion compensation devices, polarization
manipulation devices, and other apparatuses where a phase change is
required.
[0008] In an exemplary 2-by-2 optical switch, two waveguides
configured to include a coupler region carry light signals in both
directions. A mirror is positioned at the output of each waveguide.
The position of at least one of the mirrors may be adjusted along
the optical path and the mirrors reflect the light exiting from the
end of the waveguides back into the same waveguide after an
adjustable phase delay due to the round trip optical path through
an adjustable air gap between the waveguides and corresponding
mirrors. A received optical signal is split in the coupler region
into two generally equal components. Thereafter, the phase of at
least one component of the optical signal is adjusted in accordance
with the present invention, by controlling the relative position of
the mirrors to introduce a phase change. The optical signal
components are then recombined in the coupler region to accomplish
constructive or destructive interference, based on the introduced
phase change. In this manner, the optical signal appears at the
desired output port.
[0009] The position of the mirrors may be controlled, for example,
using micromachined control elements that physically move the
mirror along the light path. The present invention may also be
applied in wavelength selective optical switches that support
multiple optical channels. A number of techniques are disclosed for
fabricating optical devices in accordance with the present
invention.
[0010] The present invention thus combines phase-senstivite
waveguide structures with micromachined actuators that move small
amounts to realize a switch. The present invention can be used for
any light switching application, in addition to the exemplary
communications applications, as would be apparent to a person of
ordinary skill in the art. For example, the present invention can
be applied to make an add-drop multiplexer (ADM). An ADM is often
needed in an optical network when it is desirable to remove (drop)
light of a given wavelength from a fiber or add light of a given
wavelength to the fiber.
[0011] A more complete understanding of the present invention, as
well as further features and advantages of the present invention,
will be obtained by reference to the following detailed description
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates an exemplary conventional (prior art)
2-by-2 Mach-Zhender interferometer optical switch;
[0013] FIG. 2 illustrates an exemplary 2-by-2 optical switch in
accordance with the present invention;
[0014] FIG. 3 illustrates an optical switch that includes the
optical switch of FIG. 2 and at least one optical circulator to
separate incoming and outgoing light;
[0015] FIG. 4 illustrates a block diagram of 2-by-2 wavelength
selective optical switch in accordance with the present invention
that supports n optical channels;
[0016] FIG. 5 illustrates an exemplary implementation of the
wavelength selective switch of FIG. 4;
[0017] FIG. 6 is a schematic diagram of a micro electromechanical
systems (MEMS) mirror that may be fabricated using silicon
technologies in accordance with one embodiment of the present
invention;
[0018] FIG. 7A is a side view of an embodiment of a monolithic
optical switch in accordance with the present invention;
[0019] FIG. 7B is a top view of the embodiment of a monolithic
optical switch fabricated in accordance with the present invention
showing some of the design parameters; and
[0020] FIGS. 8A through 8H, collectively, illustrate side and top
views of an exemplary process for fabricating the optical switch of
FIGS. 7A and 7B.
DETAILED DESCRIPTION
[0021] FIG. 1 illustrates an exemplary conventional 2-by-2
Mach-Zhender interferometer optical switch 100 having two input
ports 110-1, 110-2 and two output ports 120-1, 120-2, two 3 dB
couplers 151 and 152, and at least one thermooptic phase shifter
140. Generally, the optical switch 100 accepts an incoming signal
at an input port 110-1 or 110-2 and selectively passes the optical
signal to one of the output ports 120-1 or 120-2. (For a discussion
of Mach Zhender interferometers, see, for example, Katsunari
Okamoto, "Fundamentals of Optical Waveguides," p. 159, Academic
Press (2000)).
[0022] Generally, the optical switch 100 accepts an incoming signal
of multiple wavelength channels at an input port 110-1 or 110-2,
which is then split into two equal parts in waveguides 130-1 and
130-2 at the 3 dB coupler 151. The phase of the signal in waveguide
130-1 can be changed, affecting the way in which the signals
interfere when recombined at the second coupler 152 to selectively
pass the optical signal to one of the output ports 120-1 or 120-2
or divide the intensity between them. Typically, the phase change
is achieved by the thermooptic effect with heater 140 by varying
the temperature of the waveguide 130-1 in which the optical signal
travels. It has been found, however, that the necessary temperature
change requires significant power consumption and significant
cross-talk between nearby switches on the same chip limiting the
amount of switches that can be put on one chip and the complexity
of a switch system that can built.
[0023] According to one feature of the present invention, a phase
change is achieved in an optical signal by varying the optical path
length of the signal using one or more moveable mirrors. FIG. 2
illustrates an exemplary 2-by-2 optical switch 200 in accordance
with the present invention. As shown in FIG. 2, the optical switch
200 has two waveguides 210 and 220, each carrying light in both
directions. The two waveguides 210 and 220 are configured to
include a coupler region 225, in a known manner. As discussed
hereinafter, the optical switch 200 is configured in a reflective
mode (this also helps in reducing by a factor of 2, the necessary
chip area needed for the switch). Thus, an input to a single
waveguide, such as the input 210-i (or 220-i) to the waveguide 210
(or 220), is both an input port and an output port of the optical
switch 200.
[0024] As shown in FIG. 2, mirrors 230, 240 are positioned at the
output of each waveguide 210, and 220. The position of at least one
of the mirrors 230, 240 may be adjusted along the optical path. The
mirrors 230, 240 reflect the light exiting from the end of the
waveguides back into the waveguides 210, 220 after an adjustable
phase delay due to the round trip through the adjustable air gap
250 between the waveguides 210, 220 and mirrors 230, 240,
respectively. It is noted that the gap 250 can also be filled with
index matching material to get more efficient coupling in and out
of the waveguides. However, diffraction losses can be minimized by
reducing the gap 250 to a necessary minimum.
[0025] Generally, an optical signal applied to the input of a
single waveguide, such as the input 210-i to the waveguide 210, is
split in the coupler region 225 into two generally equal
components. Thereafter, in accordance with the present invention,
the phase of at least one component of the optical signal is
adjusted, as desired, by controlling the relative position of the
mirrors 230, 240 to introduce a relative phase change in the
reflected light. The optical components are then recombined in the
coupler region 225 to accomplish constructive or destructive
interference, based on the introduced phase change. In this manner,
the optical signal appears at the appropriate output port of the
optical switch 200.
[0026] As previously indicated, each waveguide 210 and 220 in the
optical switch 200 of FIG. 2 potentially carries light in both
directions. FIG. 3 illustrates an optical switch 300 that includes
the optical switch 200 of FIG. 2 and at least one optical
circulator 310 that separates incoming and outgoing light, in a
known manner. The exemplary optical switch 300 includes one optical
circulator 310 connected to the bottom waveguide 220 of the optical
switch 200. In this manner, the optical circulator 310 allows
bi-directional communication on the waveguide 220.
[0027] FIG. 4 illustrates a 2-by-2 wavelength selective switch 400
that supports n optical channels. As shown in FIG. 4, the optical
switch 400 includes two bi-directional waveguides 410, 420, a
multiplexing phase switch 450 and a mirror array 480 having p
mirrors. Input light from waveguides 410 or 420 is separated into
the different intermediate parts 460-o-l to 460-o-p (usually in
waveguides) by the multiplexing phase switch 450, this light
impinges on the mirror array 480 and is reflected back into the
multiplexing phase switch 450 that channels the signal to the
waveguides 410 or 420. The phase of one or more of the n optical
channels is adjusted by varying the position of one or more mirrors
in the mirror array 480. In this manner, each of the different
component wavelengths can be selectively switched to either
waveguide 410, 420. One embodiment of the multiplexing phase switch
450 is discussed below in conjunction with FIG. 5.
[0028] FIG. 5 illustrates an exemplary implementation of the
multiplexing phase switch 450 of FIG. 4. As previously indicated,
the present invention achieves switching using the destructive
interference of two optical components of the same optical signal.
However, in order to get good extinction ratio the intensity
splitting has to be very accurate usually barred by manufacturing
tolerances. Thus, it is known to employ three or more copies
(orders) of the same optical signal to cancel the optical signal,
removing the limitations due to manufacturing difficulties. As
shown in FIG. 5, the multiplexing phase switch 450 includes a first
star coupler 510, an array of waveguides 540 and a second star
coupler 550.
[0029] The first star coupler 510 splits the incoming signals into
different similar parts. The waveguide array 540 includes n
waveguides with different lengths to enable the multiplexing at the
second star coupler. A second star coupler 550 focuses each of the
n channels and creates m copies (orders) of each channel. Thus, at
the output of the second star coupler 550, there are m copies of
each of the n channels. Thus, the waveguide array 570 includes
m.times.n independent waveguides and the mirror array 580 has
m.times.n mirrors. In one implementation, there are 3 copies of
each of the n channels (m=3) to provide +1.sup.st order, 0 order
and -1.sup.st order copies of each channel. In one exemplary
implementation, the 0 order copy of the optical signal includes 40%
of the optical intensity while the +1.sup.st order and -1.sup.st
order copies of each channel have 30% of the optical intensity
(this ratio varies between channels). The phase of each of the m
copies of the n channels is adjusted independently in accordance
with the present invention by varying the position of the
corresponding mirror in the mirror array 580. This is fully
described in U.S. Pat. No. 6,049,640 to Doerr, entitled
"Wavelength-Division-Multiplexing Cross-Connect Using Angular
Dispersive Elements and Phase Shifters," incorporated by reference
herein.
[0030] FIG. 6 is a schematic diagram of a micro electromechanical
systems (MEMS) mirror assembly 600 that may be fabricated using
silicon technologies in accordance with one embodiment of the
present invention. As shown in FIG. 6, the mirror assembly 600
includes a reflective portion 610 that is held in position using
four silicon springs 615-a, b, c, d, and is kept at ground
potential. A voltage V is applied to an electrode 620 underneath
the mirror to move the mirror closer to the electrode. Fabrication
is done, for example, using a three layer polysilicon surface
micromachining process similar to the one discussed in D. Keoster
et al., "Multiuser MEMS Processes (MUMPS) Introduction and Design
Rules," Rev. 4, MCNC MEMS Technology Applications Center, Research
Triangle Park, N.C. 27709 (Jul. 15, 1996), incorporated by
reference herein.
[0031] An electrically-controlled movable mirror capable of
accomplishing similar function may have different design and may be
fabricated by a variety of different micromachining techniques. For
example, a suitably reflective suspended movable
electrostatically-controlled membrane can be used instead of a
reflective plate suspended on microfabricated springs, as described
in U.S. Pat. No. 5,949,571, entitled "Mars Optical Modulators,
incorporated by reference herein.
[0032] As described in the previous paragraph, the moving mirror
manufacturing is by a process separate from the waveguide
manufacturing process. This enables the flexibility to optimize
both processes for the waveguide manufacturing and mirror array
manufacturing and use existing well-proven manufacturing processes
at the expense of having to integrate the two chips later. This is
done by active alignment of the two pieces and attachment by an
adhesive, solder or other similar technique. However, as discussed
below in conjunction with FIGS. 7A and 7B, an embodiment of the
invention is presented where the MEMS mirrors are manufactured on
the waveguide chip enabling a monolithic switch.
[0033] FIG. 7A is a side view of an embodiment of a monolithic
optical switch 700 in accordance with the present invention. As
shown in FIG. 7A, the optical switch 700 is fabricated in the
waveguide layer 710 on a substrate 720. The waveguide layer 710 is
comprised on an upper and lower cladding 712, 714 and a higher
index core glass 718 within which the light is guided. An exemplary
process for fabricating the optical switch 700 is discussed further
below in conjunction with FIG. 8.
[0034] The optical switch 700 includes a mirror 750 that may be
embodied as a reflective material, such as gold, deposited on the
cladding and core material. The position of the mirror 750 is
varied by applying a voltage to the terminal, V, as shown in FIG.
7A. The mirror 750 is shown in FIG. 7A in a default position, with
no voltage applied. As the applied voltage increases towards a
maximum value, the mirror 750 moves to the right in the figure,
towards the grounded electrode 760. As shown in FIG. 7A, the mirror
750 is positioned at the output of waveguide core 718 and may be
adjusted along the optical path. The mirror 750 reflects the light
exiting from the end of the waveguide 718 back into the waveguide
718 after an adjustable phase delay due to the round trip through
the adjustable air gap 740 between the waveguide 718 and mirror
750. It is noted that the optical path of the light may expand in
the air gap 740 therefore a minimal gap 740 is desired. Index
matching fluid or beam shaping at the end of the waveguide can be
used to relax this constraint.
[0035] FIGS. 8A through 8H illustrate an exemplary process for
fabricating the optical switch 700 of FIGS. 7A and B. As shown in
FIGS. 8A (side view) and 8B (top view), the process is initiated
with waveguides 810 having a lower and upper cladding and a higher
index core glass, deposited on a substrate 820. Thereafter, as
shown in FIGS. 8C (side view) and 8D (top view), metal is deposited
on the waveguides 810 for the electrical connections (ground (0V)
and V) discussed above in conjunction with FIGS. 7A and 7B.
[0036] As shown in FIGS. 8E (side view) and 8F (top view), two
holes are then etched in the glass 810 to form the front and rear
surfaces of the mirror 750. In addition, the substrate 820 is
released, for example, by wet etching through the holes that were
etched to remove portions of the substrate, to avoid a short on the
bottom and allow movement of the mirror 750. Finally, as shown in
FIGS. 8G (side view) and 8H (top view), angular depositions are
applied to the etched mirror to provide a reflective and electrode
surfaces using shadow mask evaporation.
[0037] FIG. 7B illustrates a top view of an exemplary embodiment of
an optical switch 700 fabricated in accordance with the present
invention. It is generally desired to be able to move the mirror a
distance of 1 2
[0038] (for a round trip phase shift of 2.pi.). Thus, for typical
wavelengths of 1.5 .mu.m, it is generally desired to be able to
move the mirror a distance of larger than 0.75 .mu.m. Mirror
movement of 1.9 .mu.m is obtained in an exemplary implementation
where the membrane length, L, is 2.times.10.sup.-4 m, the membrane
thickness, t, is 2.times.10.sup.-6 m, the trench width (electrode
spacing), d, is 2.times.10.sup.-6 m and the maximum applied
voltage, V, is 100V. In this embodiment, the maximum distance, Y,
that a mirror can be moved is obtained from the approximate formula
as follows: 2 Y 1 64 E L 4 V 2 t 3 d 2 1.2 m ,
[0039] where .epsilon..congruent.8.85.times.10.sup.-12 F/m is the
dielectric constant of air and E.congruent.73GPa is Young's modulus
(a property of the silica glass).
[0040] It is to be understood that the embodiments and variations
shown and described herein are merely illustrative of the
principles of this invention and that various modifications may be
implemented by those skilled in the art without departing from the
scope and spirit of the invention. For example, in one variation,
the mirror can be positioned at a variable angle so that the light
returned to the waveguide can be attenuated by a desired amount by
deflecting a certain portion of the light so that it is not
captured by the waveguide. Also the actuation mechanism of the
mirror may be changed to thermal actuation, magnetic actuation or
other by modification of the mirror actuators 700 or 600
accordingly. Another variation can change the nature of the
waveguide to be manufactured from different materials like
polymers. Another variation may include partially reflecting
mirrors enabling Fabry-Perot like interferometers.
* * * * *