Abstract:
Disclosed is a retro-reflective type optical signal processing device and method, particularly to a device includes a set of optical mirror planes with retro-reflective type layout and configuration, and a set of micro-shutters controlled by microelectromechanical actuators, whereas the optical signals in propagation can be blocked or partially blocked in terms of the position of said a set of micro-shutters corresponding to the optical signal transmission path, thereby the method of said approach to determine the range of attenuated optical signal is a variable optical attenuation function demonstrated by present invention. Such a retro-reflective type optical signal processing device and method further comprises a set of three reflective mirrors and micro-shutters with reflective mirrors. Thereby this device has the capability to switch  2  sets of retro-reflected optical light transmission paths, the method of said approach is a demonstration of 2×2 optical switching function.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention is related to a retro-reflective type optical signal processing device and method, particularly to an optical signal processing device and method for attenuating optical signal, and for switching a set of retro-reflected optical signals by changing the position of a micro-shutter in the light transmission route of retro-reflective light path configuration.  
         BACKGROUND OF INVENTION  
         [0002]    With the rapid development of optical communication, particularly the optical communication network, a 100% optical system eliminating optical/electrical conversion has become the mainstream of the development. An optical communication network requires direct processing of the optical signal per se, such as controlling the intensity of the optical signal by means of an optical attenuator so as to perform dynamic manipulation of signals at each channel to an appropriate degree, to maintain optimum performance and safety of the optical transmission active and passive components, to simplify the system. The switching between different optical paths relies on optical switches. A high-performance, low-cost optical signal processing device has, thus, become an essential component in such system.  
           [0003]    Most conventional optical signal processing devices use switching devices of the mechanical types, where such mechanical switches usually involve high production cost resulted from the precision alignment and calibration of optical paths, inability of being produced in batches, and the disadvantages of being easily worn. The use of micro-mechanical-electrical system (MEMS) to produce optical signal processing devices can not only dramatically reduce components sizes, but also allow batch production by adopting processes similar to those adopted in semi-conductors, while providing high production precision and reducing production cost at the same time.  
         DESCRIPTION OF PRIOR ART  
         [0004]    MEMS optical signal processing devices have been adopted in the production of variable optical attenuators and optical switches, described as follows:  
           [0005]    1) A variable optical attenuator developed by Robinson in U.S. Pat. No. 6,137,941 (&#39;941 patent) is illustrated in FIG. 1A. The variable optical attenuator comprises: a focusing lens; a 2-fiber capillary having an input optical waveguide and an output optical waveguide; an MEMS reflective mirror and an MEMS pivot for supporting and pivoting the reflective mirror. The reflective mirror is static- or piezo-electrically driven to revolve about the pivot. The reflective mirror at a flat position  111  reflects off an incident beam from the input waveguide to be refracted by the focusing lens so as to become a refracted beam, that is then reflected off by the reflective mirror to be refracted by the focusing lens so as to enter the output waveguide. In an optimum state, the optical signal completely enters the output end. The angle of the reflective mirror changes when the reflective mirror is pivoted to a reflective position  112 . Hence, pivoting of the reflective mirror changes the angle of the reflective mirror and the optical path of the reflected beam, such that only part of the reflected beam enters the output waveguide for reducing the intensity of the reflected beam entering the output waveguide, thereby attaining the variable function of the light attenuator. Further, as shown in FIG. 1A, the &#39;941 patent further discloses a digital mirror device to replace the pivoted reflective mirror. However, because the reflective mirror of the optical attenuator in the &#39;941 patent has a highly sensitive angle of reflection, such as 20 db@0.1°, 40 db (0.35°, or even better, an automatic high-precision control apparatus  113  is needed to vary the reflective mirror. As compared to this invention, the materials as used, the structure as adopted, the production and operation processes are all different. In this invention, there is no need for a complicated, high-precision automatic control apparatus or any corresponding high-precision component thereby eliminating the costly production processes and simplifying the production process that allows easy assembly and improves the pass rate.  
           [0006]    2) A variable optical attenuator with profiled blade developed by O&#39;Keefe and etc in U.S. Pat. No. 6,246,826 (&#39;826 patent) is illustrated in FIG. 1B. The variable optical attenuator includes an input fiber  121  and an output fiber  122 ; two ball lenses  123 ,  124 ; an optical attenuator  125  having an actuator  126  and a profiled blade  127  mounted between the input fiber  121  and output fiber  122 . A comb drive or other actuating means drives parallel advancement of the blades of different profiles mounted to the actuator for blocking part of the optical signal being transmitted thereby attaining the variable function of the light attenuator. The &#39;826 patent, however, requires high-precision alignment and calibration of the optical path formed by the input fiber  121 , two ball lens  123 ,  124 , and output fiber  122 . In addition to the difficulty involved in the alignment and calibration, the overall errors of the system are so significant to result in costly batch production. As compared to the second embodiment of this invention, the materials as used, the structure as adopted, and the production and operation processes are all different. This invention further allows retro-reflective optical signal processing and only requires alignment and calibration among an input fiber, an output fiber and a retro-reflector thereby eliminating the complicated, high-precision alignment and calibration process. As compared to the &#39;826 patent, this invention eliminates the costly production processes and simplifies the production process that allows easy assembly and improves the pass rate.  
           [0007]    3) An optical attenuator developed by Aksyuk and etc in U.S. Pat. No. 6,173,105 (&#39;105 patent) is illustrated in FIG. 1C. The variable optical attenuator  130  comprises: an input fiber  131  and an output fiber  132 ; an optical attenuator having a profiled shutter  133  and an actuator. The actuator further comprises an upper polysilicon capacitive plate  134  and a lower polysilicon capacitive plate  135 . The profiled shutter is connected to the upper capacitive plate  134  by means of a cantilever beam  136 . The optical attenuator is provided between the input fiber  131  and output fiber  132 . The static-electrically driven actuator provided between the two parallel capacitive plates drives vertical movement of the shutter  131  between the input fiber  131  and output fiber  132 . Through the lever linked to the upper capacitive plate  134 , the shutter  133  moves vertically between the input fiber  131  and output fiber  132 , thereby blocking part of the optical signal being transmitted to attain the variable function of the light attenuator. As compared to the second embodiment of this invention, the materials as used, the structure as adopted, and the production and operation processes are all different. Further, the back reflection caused by the shutter in the &#39;105 patent requires an additional isolator to be provided to the front end of the input fiber thereby increasing the insertion loss and production cost of the entire device.  
           [0008]    Items 1) to 3) as described above are prior art relevant to the second embodiment of this invention. Items 4) and 5) as described below are prior art relevant to the third embodiment of this invention.  
           [0009]    4) A micro-electro-mechanical optical switch and method of manufacture thereof developed by Zhang in U.S. Pat. No. 6,229,640 (&#39;640 patent) is illustrated in FIG. 1D. The optical switch comprises: a first optical signal input fiber  201   a,  a second optical signal input fiber  201   c,  a first optical signal output fiber  201   b,  a second optical signal output fiber  201   d,  and an optical switch actuator  225 . The optical switch actuator  225  comprises: a static comb drive  226  and a shutter  227  driven by the comb drive  226  to move forwards and backwards in a horizontal direction. As shown in FIG. 1D, when the comb drive  226  drives the shutter  227  to move backwards, optical signals from the first optical signal input fiber  201   a  and second optical signal input fiber  201   c  may each bypass by the shutter  227  to enter the optical actuator  225  and to leave the second optical signal output fiber  201   d  and first optical signal output fiber  20   b,  respectively. As shown in FIG. 1E, when the shutter  227  moves forwards, the shutter  227  blocks and reflects off the two incident beams and changes their optical paths, such that optical signals from the first optical signal input fiber  201   a  and second optical signal input fiber  201   c  are reflected off by the shutter  227  of the optical switch actuator  225  to leave the first optical signal output fiber  201   b  and second optical signal output fiber  201   d,  respectively, thereby attaining the variable function of the light attenuator by blocking or allowing the light beams to pass through. In the &#39;640 patent, high-precision alignment and calibration and assembly is required among the relative positions of five components, including the first optical signal input fiber  201   a,  second optical signal input fiber  201   c,  first optical signal output fiber  201   b,  second optical signal output fiber  201   d,  and shutter  227 . As compared to the third embodiment of this invention, the materials as used, the structure as adopted, and the production and operation processes are all different. Further, the third embodiment in this invention only requires a single assembling process between the optical signal transmission end and retro-reflective type optical signal processing device, thereby eliminating the inter-coupling between individual components and significantly reducing production lead time and cost while improving the pass rate at the same time.  
           [0010]    5) An optical switch developed by Aksyuk and etc in U.S. Pat. No. 6,205,267 (&#39;267 patent) is illustrated in FIGS. 1C and 1F. The &#39;267 patent uses the basic structure of the optical attenuator  30  described in Item 3) while controlling the shutter  133  to completely block or not to block an optical path. A circulator  231  is further implemented. A control apparatus  235  may close the optical switch such that the shutter  133  is completely absent from the optical path, such that an optical signal from the input fiber  131  may enter a first port  232  of the circulator  231  to leave the output fiber  132  from a second port  233 .  
           [0011]    On the other hand, the control apparatus  231  may open the optical switch such that the shutter  133  completely blocks the optical path, such that an optical signal from the input fiber  13  is reflected off by the shutter  133  to enter circulator  231  to be guided to a new optical path through a third port  234 , serving as a 1×2 optical switch. As compared to the third embodiment of this invention, the materials as used, the structure as adopted, and the production and operation processes are all different. Further, the &#39;267 patent further involves the following defects:  
           [0012]    1. The production cost increases due to the additional circulator.  
           [0013]    2. The insertion loss is significant for the entire device (including the circulator).  
         SUMMARY OF INVENTION  
         [0014]    Hence, it is an object of this invention to provide a retro-reflective type optical signal processing device that can be produced easily in batch type production environment with lower cost, while reliability and operation stability is achieved via present invention.  
           [0015]    According to this invention, a set of retro-reflective optical elements of the present invented device enables that the incident optical signal will be retro-reflected after twice reflection of light among incident light path, the reflective surface of two mirrors of said a set of retro-reflective optical elements, and the output light path. Thereby the reflected output optical signal light path is in parallel with the light path of incident optical signal, and their light propagation direction is opposite, in the other words, the light transmission direction of input and output signal is opposite direction. The said a set of retro-reflective optical elements can be made by means of silicon micro-fabrication technology, or be assembled by integration of several optical components, such as prisms, lenses, or reflective mirrors.  
           [0016]    Further, the micromachined shutter is allocated at the transmission route of the said device. The optical beams in propagation can be blocked or partially blocked in terms of the position of said shutter corresponding to the transmission path, thereby the method of said approach to determine the range of attenuated optical signal is a variable optical attenuation function demonstrated by present invention. The said shutter is controlled and actuated via micro-actuators.  
           [0017]    A further main embodiment is that such a retro-reflective type optical signal processing device and method further comprises a set of three reflective mirrors and micro-shutters with reflective mirrors. Likewise, this device has the capability of 2×2 optical switch function by composing two sets of two parallel ports consist of first port as the input channel and the second port as the output channel of each sets. The two different optical signals from two input ports of each sets transmit toward a retro-reflective unit including three reflective mirror planes, where the shutter is at the position enabling the said optical signals passing by, in which the shutter is an ON state, thereafter the two sets of retro-reflected optical signals transmit backward independently to the output ports of each corresponding sets. Furthermore, when the shutter is allocated at the position of an OFF state, thus the two different optical signals from two input ports of each sets transmit toward the said reflective mirror surface of said shutter, the incoming signals will reflected independently toward the corresponding output ports of opposite sets. Thereby this device has the capability to switch  2  sets of retro-reflected optical light transmission paths by holding the shutter at an ON state or an OFF state so as to 2×2 optical switching function is demonstrated by the said retro-reflective type optical signal processing device.  
           [0018]    Embodiments of the present invention can provide a retro-reflective type optical signal processing device and method, having the function of a variable optical attenuator, that the high attenuation resolution is realized by a simple structure and is easily driven and controlled.  
           [0019]    Another embodiment of this invention is to provide 2×2 optical switching function by allowing the forward transmission and reflection of a set of two parallel incident optical signals in the retro-reflective type light configuration.  
           [0020]    A further embodiment of this invention is to provide a retro-reflective type optical signal processing device and method that does not need isolator to eliminate the back-reflected light in the transmission route of input channel.  
           [0021]    A further embodiment of this invention is to provide a retro-reflective type optical signal processing device and method that only requires a single assembling process to align, place, assemble, and fix the fibers, the said a set of retro-reflective optical elements, and micromachined shutter to form the invented device, thereby the production cost is reduced.  
           [0022]    The structure of the retro-reflective type optical signal processing device and the details of the method of this invention can be fully understood by referring to the detailed descriptions in accompaniment of the following drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0023]    [0023]FIG. 1A is a schematic view of a variable optical attenuator disclosed in U.S. Pat. No. 6,137,941.  
         [0024]    [0024]FIG. 1B is a schematic view of a variable optical attenuator with profiled blade disclosed in U.S. Pat. No. 6,246,826.  
         [0025]    [0025]FIG. 1C is a schematic view of a variable optical attenuator with profiled blade disclosed in U.S. Pat. No. 6,246,826, that may also serve as an optical switch disclosed in U.S. Pat. No. 6,205,267  
         [0026]    [0026]FIGS. 1D and 1E are schematic views of a micro-electro-mechanical optical switch and method of manufacture disclosed in U.S. Pat. No. 6,229,640.  
         [0027]    [0027]FIG. 1F is a schematic view of an optical switch disclosed in U.S. Pat. No. 6,205,267.  
         [0028]    [0028]FIG. 2A is a schematic view of a first type of a first embodiment of the retro-reflective type optical signal processing device according to this invention.  
         [0029]    [0029]FIG. 2B is a schematic view of a second type of a first embodiment of the retro-reflective type optical signal processing device according to this invention.  
         [0030]    [0030]FIG. 3A is a perspective, schematic view of a second embodiment of the retro-reflective type optical signal processing device according to this invention.  
         [0031]    [0031]FIG. 3B is a schematic view showing the second embodiment of the retro-reflective type optical signal processing device according to this invention under the assembling and operative state.  
         [0032]    FIGS.  3 C˜ 3 G are schematic views taking alone lines C-C′ in FIG. 3A, showing the actual manufacturing process of the second embodiment of the retro-reflective type optical signal processing device according to this invention.  
         [0033]    [0033]FIG. 3H is a perspective, schematic view of a second embodiment of the retro-reflective type optical signal processing device array according to this invention.  
         [0034]    [0034]FIG. 4A is a perspective, schematic view of a third embodiment of the retro-reflective type optical signal processing device according to this invention.  
         [0035]    [0035]FIG. 4B is a schematic view showing the third embodiment of the retro-reflective type optical signal processing device according to this invention under the assembling and operative state.  
         [0036]    [0036]FIG. 4C is a schematic view taking alone lines D-D′ in FIG. 4A, showing the third embodiment of the retro-reflective type optical signal processing device according to this invention.  
         [0037]    [0037]FIG. 4D is a perspective, schematic view of a third embodiment of the retro-reflective type optical signal processing device array according to this invention.  
         [0038]    [0038]FIG. 5A is a perspective, schematic view of a fourth embodiment of the retro-reflective type optical signal processing device according to this invention.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0039]    The following descriptions of this invention should be referred to the accompanying drawings. Persons skilled in the art should realize that the following descriptions are provided for exemplary purposes rather than limiting the scope of this invention.  
         [0040]    The followings are descriptions with respect to an exemplary embodiment for manufacturing the retro-reflective type optical signal processing devices according to this invention. In this embodiment, polysilicon deposited by Low Pressure Chemical Vapor Deposition (LPCVD) serves as a structural material; the lens surface is made by sputtered gold; silicon dioxide serves as a sacrificial layer. An actuator suspension structure having a shutter is fabricated by etching the sacrificial layer and the silicon structural layer. The features of a variable optical attenuator and an optical switch are achieved by applying appropriate voltages to control the actuator driving the shutter for blocking part or all of the optical signal transmission. The fabrication of the components, in fact, does not completely coincide with the method as described. Persons skilled in the art can certainly make modifications and changes to such a method without departing from the spirits and scope of this invention. For example, the sequence of the method for manufacturing the retro-reflective type optical signal processing devices as described below may be changed to fabricate similar structures having identical effects.  
         [0041]    Prior art illustrated in FIGS.  1 A˜ 1 D have been described and not repeated herein.  
       First Embodiment  
       [0042]    [0042]FIGS. 2A and 2B illustrate a first type and a second type of the first embodiment of a retro-reflective type optical signal processing device according to this invention, respectively. The first type of the retro-reflective type optical signal processing device  30  comprises: paired parallel fibers having an input fiber  302  and an output fiber  303 , for inputting an incident optical signal  304  and outputting a reflective optical signal  305 , respectively; a retro-reflective micro-mechanical-electrical reflector  32  having a first reflective mirror  321  and a second reflective mirror  322  normal to the first reflective mirror  321 ; a microactuator  33  for actuating a shutter  331  to move along the PQ directions and to block part of the incident optical signal  304  so as to attenuate optical signal. A first type of the retro-reflective type optical signal processing device  30  reflects the incident optical signal  304  off the first reflective mirror  321  and reflective mirror  322  to form a reflective optical signal  305  leaving the output fiber  303 . The detailed method for assembling and aligning the device may be referred to the second embodiment of this invention.  
         [0043]    The second type of the retro-reflective type optical signal processing device  34  comprises: an input fiber  351  and an output fiber  352  having a centerline therebetween, for inputting an incident optical signal  353  and outputting a reflective optical signal  354 , respectively, the input fiber  351  and output fiber  352  each forming an included Θ with the centerline  355 ; a retro-reflective micro-mechanical-electrical reflective unit  36 , having a reflective mirror  361 ; a microactuator  37  for actuating a shutter  371  to move along the PQ directions and to block part of the reflective optical signal  354  so as to attenuate optical signal. In assembling the second type of the retro-reflective type optical signal processing device  34 , one only needs to place the centerline  355  at a position normal to the reflective mirror  361 , and align the reflective optical signal  354  with the output fiber  352 , the reflective mirror  361  will reflect the incident optical signal  353  off the reflective mirror  361  to form a reflective optical signal  354  leaving from the output fiber  352 .  
         [0044]    In the first type, the incident optical signal  304  is parallel to the reflective optical signal  305 . In the second type, the incident optical signal  353  is not necessarily parallel to the reflective optical signal  354 . In the first to third embodiments of the retro-reflective type optical signal processing device of this invention, the microactuator of the shutter can be an MLMS actuator including the electrostatic actuator, the thermal actuator, the electrothermal actuator, the electromagnetic actuator, and the piezoelectric actuator, which are all related to conventional art easily mastered by persons skilled MEMS techniques. Hence, other than the MEMS electrostatic actuator described in the second embodiment, this invention does not provide further explanations with respect to the other types of MEMS actuators.  
         [0045]    For explanations relevant to the prior art or to this invention, all terminologies of the input/output units in this specification, such as input fiber, output fiber, optical signal input unit, optical signal output unit are given in reference to the device of this invention or prior art. For example, an input fiber refers to a fiber for inputting an optical signal to the device of prior art or this invention; and an optical signal input unit refers to a unit for outputting an optical signal from the device of prior art or this invention.  
         [0046]    In the first to third embodiments of the retro-reflective type optical signal processing device of this invention, any optical signal path formed by any incident optical signal and its reflective optical signal may further include a collimating lens, collecting lens, a ball lens, a cylindrical lens, a refractor such as Fresnel lens, other non-spherical lenses and optical components so as to enhance the transmission efficiency and coupling efficiency of the optical signal in the retro-reflective type optical signal processing device, and to reduce signal dissipation in transmission by refracting the optical signal in the optical path. Further, the shutter in the first to third embodiments of this invention may block part of the incident optical signal or the reflective optical signal so as to attenuate the optical signal.  
       Second Embodiment  
       [0047]    [0047]FIG. 3A is a perspective, schematic view of a second embodiment of the retro-reflective type optical signal processing device according to this invention. FIG. 3G is a schematic view taking alone lines C-C′ in FIG. 3A. In FIG. 3A, the retro-reflective type optical signal processing device  40  of this invention is fabricated over a platform  42  of a silicon substrate by means of micro-fabrication process, as shown in FIGS.  3 C˜ 3 G that will be described in details later on.  
         [0048]    The retro-reflective type optical signal processing device  40  of this invention comprises: paired parallel fibers having an input fiber  402  and an output fiber  403  for inputting an incident optical signal  405  and outputting an reflective optical signal  404 , respectively; a retro-reflective micro-mechanical-electrical reflective unit  43 , having a first reflective mirror  44  and a second reflective mirror  45  each forming an included angel of 45° with the platform  42  of the silicon substrate  41 , the first reflective mirror  44  and second reflective mirror  45  forming an included angle of 90° therebetween that takes the form of a 90° V-groove and intersecting at a baseline  407  of the V-groove; a comb-drive microactuator  400  provided on the platform  42 , the comb-drive microactuator  400  being an MEMS static-electrically driven actuator, having a first comb unit  410 , a second comb unit  420 , a third comb unit  430 , a suspended comb unit  440 , and a shutter  460  defining a shutter centerline  461 . The first, second and third comb units  410 ,  420 ,  430  are constructed of plural stators  411 ,  421 ,  431 , respectively, the plural stators  411 ,  421 ,  431  are spaced apart by a gap d and connected to a first base  412 , a second base  422 , and a third base  432  at their rear ends, respectively. The suspended comb unit  440  are constructed of plural rotors  441  spaced apart by a gap d and, respectively, connected to a cantilever  442  over a fourth base  447 , a fifth base  448 , a sixth base  449  and a seventh base  454  through a first elastic suspension unit  443 , a second elastic suspension unit  444 , a third elastic suspension unit  445 , and a fourth elastic suspension unit  446  that are connected to the cantilever  442 , such that the suspended comb unit  440  is suspended among the first elastic suspension unit  443 , second elastic suspension unit  444 , third elastic suspension unit  445  and fourth elastic suspension unit  446 . The shutter  460  faces the first reflective mirror  44  and second reflective mirror  45  and is connected to and supported by a center of the suspended comb unit  440  to move along the PQ directions with the suspended comb unit  440  of the comb-drive microactuator  400 .  
         [0049]    [0049]FIG. 3B is a schematic view showing the second embodiment of the retro-reflective type optical signal processing device according to this invention under the assembling and operative state. As shown in FIG. 3B, one feature of the second embodiment of this invention lies in that, only a single process is needed to assemble the retro-reflective type optical signal processing device  40 . The assembling process aligns a centerline  406  of the paired parallel fibers (or 2-fiber capillary) with the baseline  407  formed of intersecting the first reflective mirror  44  and second reflective mirror  45 , such that the incident optical signal  404  is able to project towards the first reflective mirror  44  at an incident angle of 45°, and then reflected off by the second reflective mirror  45  at a reflective angle of 45°. Because the second reflective mirror  45  and first reflective mirror  44  are normal to one another by an included angle of 90°, a reflective optical signal  405  is formed by reflecting the incident optical signal  404  that is projected towards the second reflective mirror  45  at an incident angle of 45°, off the second reflective mirror  45  at a reflective angle of 45°. In an optimum state, the reflective optical signal  405  is completely coupled into the output fiber  403  to complete a retro-reflective optical signal processing process. Further, the input port of the input fiber  402  and the output port of the output fiber  403  may be connected to a light source and a signal sensor (not shown), respectively, to assist in assembling and positioning.  
         [0050]    The optimum positioning by adopting above-mentioned assembling step is not exclusive. Such as shown in FIG. 3A, as long as the incident optical signal  404  of paired parallel fibers, reflective optical signal  405 , and centerline  406  of the paired parallel fibers are co-planar, and the reflective optical signal  404  is projected towards the first reflective mirror  44  at an angle less then 45°, the incident optical signal  404  will be surely parallel to the reflective optical signal  405  and projected towards an opposite direction while the vertical distance between the two parallel signals varies along with the incident position. Hence, by continuously adjusting the incident optical signal  404  projecting towards the first reflective mirror  44  at an appropriate incident angle that subjects the vertical distance between the incident optical signal  404  and reflective optical signal  405  in parallel equals to the gap between the centers of the paired parallel fibers, the reflective optical signal  405  may completely enter the output fiber  403 .  
         [0051]    As shown in FIG. 3A, the retro-reflective type optical signal processing device  40  of this invention may further comprises: a silicon nitride or a silicon oxide insulating layer  46  between the silicon substrate  41  and electrodes to prevent shorting circuits between electrodes, a first electrode  47 , a second electrode  48  and a third electrode  49  electroplated above the insulating layer. The first electrode  47  represents voltage applied to the first comb unit  410 , the second electrode  48  represents voltages applied to the second comb unit  420  and third comb unit  430 , and the third electrode  49  represents voltage applied to the suspended comb unit  440 .  
         [0052]    An actuating control apparatus (not shown) and additional voltage control are implemented to generate a potential difference between the second electrode  48  and third electrode  49  thereby causing the electrostatic attractive force between the second comb unit  420  and third comb unit  430 , and to generate zero potential different between the first electrode  47  and third electrode  49  thereby causing simultaneous-advancement displacement of the suspended comb unit  440  of the comb-drive microactuator  400  and the shutter  450  in the P direction. On the other hand, an external voltage may be applied to generate a potential difference between the first electrode  47  and third electrode  49  thereby causing the electrostatic attractive force between the first comb unit  410  and suspended comb unit  440 , and to generate a zero potential difference between the second electrode  48  and third electrode  49  thereby causing simultaneous movement of the suspended comb unit  440  of the comb-drive microactuator  400  and the shutter in the Q direction.  
         [0053]    Furthermore, the fourth base  447 , fifth base  448 , sixth base  449  and seventh base  450  of the suspended comb unit  440  are connected to the electrode  48 ; that is, equal potential is maintains between the suspended comb unit  440  and the large-area electrode  48  located therebeneath so as to ensure no sticking phenomenon between the suspended comb unit  440  of the comb-drive microactuator  400  and the bases due to electrostatic attraction during the forward and backward movement.  
         [0054]    By independently controlling the potential differences between the second electrode  47  and third electrode  48  and between the firs electrode  46  and third electrode  48 , as well as the magnitudes of electrostatic forces of the plural stators  411 ,  421 ,  431  and rotors  441 , the advancement of the shutter in the P direction may be varied.  
         [0055]    As shown in FIG. 3B, in the second embodiment of the retro-reflective type optical signal processing device  40 , a shutter  460  may be provided next to the incident optical signal  404  or the reflective optical signal  405 . The shutter  460  may include any opaque substances. The shutter may also be configured to various microstructures, such as spheres, triangles, rectangles or polygons. The shutter  460  may be made from one or more materials, or a material having a light pervious characteristic that may be transformed into light impervious in response to heat treatment or pressure. The shutter  40  is connected to the comb-drive microactuator  400  that is controlled by an externally applied voltage through the actuating control apparatus as described above, thereby actuating the shutter, such that the shutter is able to move along the PQ directions based on different control signals to all distances within a blocking range, or to remain still at any position of all distances, for blocking part of the incident optical signal  404  or part of the reflective optical signal  405 . Because blocking range due to shutter movement may range from 0% (no blocking) to 100% (all blocking), another feature of the second embodiment of the retro-reflective type optical signal processing device  40  of this invention lies in that, the reflective optical signal  405  may be selected and varied by selecting and varying the incident optical signal  404 , so as to serve a variable optical attenuator to be implemented in an optical communication network(s).  
         [0056]    FIGS.  3 C˜ 3 G are schematic views taking alone lines C-C′ in FIG. 3A, showing the actual manufacturing process of the second embodiment of the retro-reflective type optical signal processing device according to this invention.  
         [0057]    First, a retro-reflective reflective lens surface is etched on a silicon substrate by anisotropic wet etch. Because the etching rate of a (110) plane of silicon under particular etching conditions is less than that of a (100) plane of silicon, two (110) planes of silicon that form a  450  with the silicon substrate surface are exposed after a given etching time (see FIG. 3C). A high reflectivity metal film is then sputtered over the two (110) planes of silicon by sputtering, electroplating, or chemical deposition to form a first reflective mirror  491  and a second reflective mirror  492  (see FIG. 3D). The first reflective mirror and second reflective mirror may be fabricated by the above-described bulk silicon microfabrication, electroplating, sputtering, or other processes, replaced by various optical components capable of reflection, such as those composed of prisms, lenses, or reflective mirrors. The optical components used by the first reflective mirror  491  and second reflective mirror  492  may vary from one to more.  
         [0058]    A silicon nitride insulating layer  494  is then deposited to prevent from short circuits between electrodes. An electrode layer  495  is next electroplated thereabove by electroplating or sputtering. A sacrificial layer  496  is the fabricated by chemical deposition process (see FIG. 3E). A comb-drive microactuator structure and a shutter  497  are then fabricated by chemical deposition process and anisotropic etch (see FIG. 3F). The sacrificial layer  496  is finally removed by anisotropic etch so as to cause the suspension structure comb-drive microactuator to suspend above the lower capacitive plate (see FIG. 3G).  
         [0059]    As shown in FIG. 3H, plural retro-reflective type optical signal processing devices  40  according to the second embodiments may also be embodied to construct a retro-reflective type optical signal processing device array  450 , including: a retro-reflective micro-mechanical-electrical reflective unit  464  having a first reflective mirror  462  and a second reflective mirror  463 , a first retro-reflective type optical signal processing device  451 , a second retro-reflective type optical signal processing device  452 , and a third retro-reflective type optical signal processing device  453  that are the same as the retro-reflective type optical signal processing device  40  as shown in FIGS. 3A and 3B. Details of the comb-drive microactuator, electrodes, and actuating control apparatus are the same and, thus, not repeated herein. A diagram is used in FIG. 3H to represent a comb-drive microactuator, wherein the first retro-reflective type optical signal processing device  451  is actuated by a comb-drive microactuator  466  for completely blocking a first reflective optical signal  471  of the first retro-reflective type optical signal processing device  451 ; the second retro-reflective type optical signal processing device  552  is actuated by a second comb-drive microactuator  476  for partially blocking a second reflective optical signal  472  of the second retro-reflective type optical signal processing device  452 ; the third retro-reflective type optical signal processing device  453  is actuated by a third comb-drive microactuator  486  not blocking a third reflective optical signal  473  of the third retro-reflective type optical signal processing device  453 . One feature of this retro-reflective type optical signal processing device array  450  lies in that, each of the retro-reflective type optical signal processing devices  451 ,  452 ,  453  may independently vary an optical signal. Another feature of this embodiment lies in that, the retro-reflective micro-mechanical-electrical reflective unit  464  having a first reflective mirror  462  and a second reflective mirror  463  may serve to vary retro-reflective optical signal of optical signals from different channels at each of the retro-reflective type optical signal processing devices  451 ,  452 ,  453 . Furthermore, the first retro-reflective type optical signal processing device  451 , second retro-reflective type optical signal processing device  452  and third retro-reflective type optical signal processing device  453  in the retro-reflective type optical signal processing device array  450  as shown in FIG. 3H may also be provided next to the first incident optical signal  474 , second incident optical signal  475  and third incident optical signal  476 , such that each of the retro-reflective type optical signal processing devices may serve to vary optical signals of an incident optical signal along an incident optical path. Furthermore, plural retro-reflective type optical signal processing device arrays  450  in this embodiment may be, at desires, embodied to construct a single or plural lenses structure array, serving as a network retro-reflective type optical signal processing device having the feature of a variable optical attenuator, for ready implementation in an optical communication network(s).  
       Third Embodiment  
       [0060]    [0060]FIG. 4A is a perspective, schematic view of a third embodiment of the retro-reflective type optical signal processing device according to this invention. FIG. 4B is a schematic view showing the third embodiment of the retro-reflective type optical signal processing device according to this invention under the assembling and operative state. FIG. 4C is a schematic view taking alone line D-D′ in FIG. 4A, showing the third embodiment.  
         [0061]    As shown in FIG. 4A, the retro-reflective type optical signal processing device  50  of this invention is fabricated over a platform  52  of a silicon substrate  51 . As shown in FIG. 4B, the retro-reflective type optical signal processing device  50  of this invention comprises: a first pair of parallel fibers and a second pair of parallel fibers, the first pair of parallel fibers including a first optical signal input unit  502  and a first optical signal output unit  503 , the second pair of parallel fibers including a second input fiber  508  and a second output fiber  509 , the first input fiber unit  502  and second input fiber  508  serving to input a first incident optical signal  504  and a second incident optical signal  510 ; a micro-mechanical-electrical retro-reflective unit  53 , having a first reflective mirror  54 , a second reflective mirror  55  and a third reflective mirror  56 , the second reflective mirror  55  being provided a location parallel to the platform  52  of the silicon substrate  51  (see FIG. 4A), the first reflective mirror  54  and third reflective mirror  56  facing one another and normal to the second reflective mirror  55  to form a U-groove having two right angles, the first reflective mirror  54  and second reflective mirror  55  intersecting at a first baseline  516  of the U-groove and the second reflective mirror  55  and third reflective mirror  56  intersecting at a second baseline  517  of the U-groove; a comb-drive microactuator  500  provided on the platform  52  (see FIG. 4A). In this embodiment, the comb-drive microactuator  500  serving as an actuator is the same as the comb-drive microactuator  400  as shown in FIG. 3A. Details of the comb-drive microactuator are not repeated therein. Brief descriptions with respect to the functions of a suspended comb unit  500  (identical to the suspended comb unit  440  in FIG. 3A) and a shutter  560  connected to and supported by a center of the suspended comb unit  500 , are provided. The feature that differs the shutter  560  from the shutter  460  in FIG. 3A lies in that, an upper surface of the shutter  560  is plated with a high reflectivity metal film to form a fourth reflective mirror  57 . Because the shutter  560  may be actuated by the comb-drive microactuator  500  to move between or to remain still at a first position and a second position, it serves as movable reflective mirror. The fourth reflective mirror  57  may serve to reflect optical signal under an OFF state (such as the first position); details of the device serving as an optical switch will be described later on.  
         [0062]    When the first pair of parallel fibers and second pair of parallel fibers form the retro-reflective type optical signal processing device  50  of this invention, the operation of the optical switching function of the retro-reflective type optical signal processing device  50  is obtainable by the followings operation. When the shutter  560  is actuated by the comb-drive microactuator  500  to the first position (OFF state), the first incident optical signal  504  from the first optical signal input unit  502  and the second incident optical signal  510  from the second optical signal input unit  508  are each reflected off by the fourth reflective mirror  57  of the shutter  560  to form a first reflective optical signal  511  and a second reflective optical signal  505  leaving through the second optical signal output unit  509  and first optical signal output unit  503 , respectively. When the shutter  560  is actuated by the comb-drive microactuator  500  to the second position (ON state), a first incident optical signal  504  from the first optical signal input unit  502  is reflected off by the second reflective mirror  55  and third reflective mirror  56  to form a third reflective optical signal  512  leaving through the first optical signal output unit  503 ; a second incident optical signal  510  from the second optical signal input unit  508 is reflected off by the second reflective mirror  55  and first reflective mirror  54  to form a fourth reflective optical signal  513  leaving through the second optical signal output unit  509 . Hence, another feature of the retro-reflective type optical signal processing device  50  of this invention lies in that, when the shutter  560  remains still at the OFF state, optical signal from Fiber A may be switched to Fiber D and optical signal from Fiber C may be switched to Fiber B. When the shutter  50  remains still at the ON state, optical fiber from Fiber A may be switched to Fiber B and optical           optical signal from Fiber C may be switched to Fiber A, as narrated at the left hand side of FIG. 4B.  
         [0063]    OFF: A→D, C→B  
         [0064]    ON: A→B, C→D  
         [0065]    Hence, another feature of the retro-reflective type optical signal processing device  50  of this invention lies in that, by adopting the electrostatic driven process as described in the second embodiment and the switching operation described above, the comb-drive microactuator  500  is able to actuate the shutter  560  to the ON state or OFF state so as to allow the optical signals to pass or reflected to change the direction of the optical signals, thereby attaining the switching function of an optical switch, for ready implementation in an optical communication network(s).  
         [0066]    [0066]FIG. 4C is a schematic view taking alone lines D-D′ in FIG. 4A. The processing method the third embodiment of this invention is substantially identical to that disclosed in FIGS.  3 C˜ 3 G. The feature the differs that third embodiment from the second embodiment lies in that, on a silicon substrate, a vertical groove having functions equivalent to two normal retro-reflective mirrors is etched on a (100) plane of silicon by anisotropic wet etch. Because the etching rate of a (110) plane of silicon subjected to an etchant (such as KOH) is less than that of a (100) plane of silicon, two (110) planes of silicon that form a 90° with the silicon substrate surface are exposed after a given etching time. A groove having vertical sidewalls may also be etched from the silicon substrate by anisotropic dry etching. A high reflectivity metal film is then sputtered over the groove by sputtering, electroplating, or chemical deposition to form a first reflective mirror  54 , a second reflective mirror  55  and a third reflective mirror  56 . The remaining steps are not repeated herein. The cross-section of the silicon substrate along lines D-D′ is shown in FIG. 4C.  
         [0067]    As shown in FIG. 4D, plural retro-reflective type optical signal processing device  50  according to the third embodiment of this invention may also be embodied to construct a retro-reflective type optical signal processing device array  550 , including: a first retro-reflective type optical signal processing device  551 , a second retro-reflective type optical signal processing device  552  and a third retro-reflective type optical signal processing device  553 , that are the same as the retro-reflective type optical signal processing device  50  shown in FIGS. 3 and 4B. Details of the comb-drive microactuator, electrodes, and actuating control apparatus are the same and, thus, not repeated herein. A comb diagram is used in FIG. 4D to represent a comb-drive microactuator, wherein the first retro-reflective type optical signal processing device  551  and third retro-reflective type optical signal processing device  553  are actuated by a first comb-drive microactuator  571  and a third comb-drive microactuator  573  to an OFF state, respectively. The second retro-reflective type optical signal processing device  552  is actuated by a second comb-drive microactuator  572  to an ON state. One feature of the embodiment of the retro-reflective type optical signal processing device array  550  lies in that, each of the retro-reflective type optical signal processing devices  551 ,  552 ,  553  may each perform as an optical switch. Another feature of this embodiment lies in that, the retro-reflective micro-mechanical-electrical reflective unit  564  having a first reflective mirror  561 , a second reflective mirror  562  and a third reflective mirror  563  may serve to perform the optical switching function of an optical switch. Furthermore, plural retro-reflective type optical signal processing device arrays  550  in this embodiment may be, at desires, constructed into a single or plural lenses structure array, serving as a 1×2 or 2×2 switch array, for ready implementation in an optical communication network(s).  
       Fourth Embodiment  
       [0068]    [0068]FIG. 5A is a perspective, schematic view of a fourth embodiment of the retro-reflective type optical signal processing device according to this invention under the assembling and operative state. The retro-reflective type optical signal processing device  60  according to the fourth embodiment comprises: paired parallel fibers, having an input fiber  602  and an output fiber  603 , for inputting an incident optical signal  604  and outputting a reflective optical signal  605 , respectively; a retro-reflective micro-mechanical-electrical reflective unit  62 , having a first reflective mirror  621  and a second reflective mirror  622  normal to the silicon substrate  61 , each forming an included angle of 45° with a vertical plane on a silicon substrate  61 , the two reflective mirrors forming an included angle of 90° therebetween to take a form of a 90° V-groove and intersecting at a baseline  607  of the V-groove; a microactuator  63  provided on the substrate  61 , for actuating a shutter  631  to move along the PQ directions based on different control signals to all distances within a blocking range, or to remain still at any position of all distances, for blocking part of the incident optical signal  604  or part of the reflective optical signal  605 . Because the blocking range due to shutter movement may range from 0% (no blocking) to 100% (all blocking), one feature of the fourth embodiment of the retro-reflective type optical signal processing device  60  of this invention lies in that, the reflective optical signal  605  may be varied by varying the incident optical signal  604 , so as to serve as a variable optical attenuator for ready implementation in an optical communication network(s).  
         [0069]    As shown in FIG. 5, one feature of the fourth embodiment of this invention lies in that, only a single assembling process is needed to assemble the retro-reflective type optical signal processing device  60 . The assembling process comprises the steps of: placing a centerline  606  of the paired parallel fibers (or 2-fiber capillary) to be normal to a normal plane  610 ; and aligning the centerline  606  with the baseline  607  formed of intersecting the first reflective mirror  621  and second reflective mirror  622 , such that the incident optical signal  604  is able to project towards the first reflective mirror  621  at an incident angle of 45°, and then reflected off by the second reflective mirror  622  at a reflective angle of 45°. Because the second reflective mirror  622  and first reflective mirror  621  are normal to one another by an included angle of 90°, a reflective optical signal  605  is formed by reflecting the incident optical signal  604  that is projected towards the second reflective mirror  622  at an incident angle of 45°, off the second reflective mirror  622  at a reflective angle of 45°. In an optimum state, the reflective optical signal  605  is output from the output fiber  603  100% to complete a retro-reflective optical signal processing process. Further, the input port of the input fiber  602  and the output port of the output fiber  603  may be connected to a light source and a signal sensor, respectively, to assist in assembling and positioning.  
         [0070]    The optimum positioning by adopting above-mentioned assembling step is not exclusive. Such as shown in FIG. 5, so long as the incident optical signal  604  of paired parallel fibers, reflective optical signal  605 , and centerline  606  of the paired parallel fibers are co-planar, and the reflective optical signal  604  is projected towards the first reflective mirror  44  at an angle less then 45°, the incident optical signal  604  will be surely parallel to the reflective optical signal  605  and projected towards an opposite direction while the vertical distance between the two parallel signals varies along with the incident position. Hence, by continuously adjusting the incident optical signal  604  projecting towards the first reflective mirror  621  at an appropriate incident angle that subjects the vertical distance between the incident optical signal  604  and reflective optical signal  605  in parallel equals to the gap between the centers of the paired parallel fibers, the reflective optical signal  605  may completely enter the output fiber  603 .  
         [0071]    As shown in FIG. 5, the retro-reflective reflective mirror and shutter in the fourth embodiment of this invention may be fabricated by MEMS techniques, such as anisotropic etch or three-dimensional self-alignment structure, or by other techniques for fabricating the optical reflective components and their assembly. Furthermore, plural retro-reflective type optical signal processing devices  60  according to the fourth embodiments may be, at desires, embodied to construct a single or plural lenses structure array, serving as a single channel or multiple channels network retro-reflective type optical signal processing device having the feature of a variable optical attenuator, for ready implementation in an optical communication network(s).  
         [0072]    In the first to fourth embodiments, the retro-reflective micro-mechanical-electrical reflective units, shutters and microactuators in the retro-reflective type optical signal processing devices may be fabricated by adopting wafer-level or packaging technology for fabricating pertinent components in the system in an integral manner to respective wafer, or by adopting bonding or die bonding technology for securing all components made independently to respective wafer. Conventional wafer-wafer bonding technology is then adopted to bond and preload the two wafers. The wafers are than cut to obtain the optical signal processing devices. The manufacturing process is then concluded by the optical fiber positioning step, sealing step, and housing step.  
         [0073]    The above embodiments are intended for describing this invention without limiting the scope that this invention may be applied. Modifications made in accordance with the disclosures of this invention without departing from the spirits of this invention are within the scope of this invention.  
         [0074]    Nomenclature Sequence Listing  
         [0075]    Prior Art:  
         [0076]    [0076] 111 —flat position  
         [0077]    [0077] 112 —reflective position  
         [0078]    [0078] 113 —automatic high-precision control apparatus  
         [0079]    [0079] 121 ,  131 ,  602 —input fiber  
         [0080]    [0080] 122 ,  132 ,  603 —output fiber  
         [0081]    [0081] 123 ,  124 —ball lens  
         [0082]    [0082] 125 ,  130 —variable optical attenuator  
         [0083]    [0083] 126 ,  63 —actuator  
         [0084]    [0084] 133 —profiled blade  
         [0085]    [0085] 134 —upper capacitive plate  
         [0086]    [0086] 135 —lower capacitive plate  
         [0087]    [0087] 136 —cantilever beam  
         [0088]    [0088] 201   a —first optical signal input fiber  
         [0089]    [0089] 201   b —first optical signal output fiber  
         [0090]    [0090] 201   c —second optical signal input fiber  
         [0091]    [0091] 201   d —second optical signal output fiber  
         [0092]    [0092] 225 —optical switch actuator  
         [0093]    [0093] 226 —comb drive  
         [0094]    [0094] 127 ,  227 ,  560 ,  631 —shutter  
         [0095]    [0095] 231 —circulator  
         [0096]    [0096] 232 —first port  
         [0097]    [0097] 233 —second port  
         [0098]    [0098] 234 —third port  
         [0099]    [0099] 235 —control apparatus  
         [0100]    This Invention:  
         [0101]    [0101] 30 ,  34 ,  40 ,  50 ,  60 —retro-reflective type optical signal processing device  
         [0102]    [0102] 33 ,  37 —microactuator  
         [0103]    [0103] 331 ,  371 ,  460 —shutter  
         [0104]    [0104] 41 ,  51 ,  61 —silicaon substrtat  
         [0105]    [0105] 42 ,  52 —plateform  
         [0106]    [0106] 32 ,  36 ,  43 ,  53 ,  464 ,  564 ,  62 —retro-reflective micro-mechanical-electrical reflective unit  
         [0107]    [0107] 44 ,  54 ,  321 ,  462 ,  491 ,  561 ,  621 —first reflective mirror  
         [0108]    [0108] 45 ,  55 ,  322 ,  463 ,  492 ,  562 ,  622 —second reflective mirror  
         [0109]    [0109] 46 ,  494 —insulative layer  
         [0110]    [0110] 47 —first electrode  
         [0111]    [0111] 48 —second electrode  
         [0112]    [0112] 49 —third electrode  
         [0113]    [0113] 56 ,  563 —third reflective mirror  
         [0114]    [0114] 57 —foruth reflective mirror  
         [0115]    [0115] 400 ,  500 —comb-drive microactuator  
         [0116]    [0116] 302 ,  351 ,  402 —input fiber  
         [0117]    [0117] 303 ,  352 ,  403 —output fiber  
         [0118]    [0118] 304 ,  353 ,  404 —incident optical signal  
         [0119]    [0119] 305 ,  354 ,  405 —reflective optical signal  
         [0120]    [0120] 355 ,  406 —centerline of parallel fibers  
         [0121]    [0121] 361 —reflective mirror  
         [0122]    [0122] 410 —first comb unit  
         [0123]    [0123] 420 —second comb unit  
         [0124]    [0124] 430 —third comb unit  
         [0125]    [0125] 440 —suspended comb unit  
         [0126]    [0126] 411 ,  421 ,  431 —stators  
         [0127]    [0127] 412 —first base  
         [0128]    [0128] 422 —second base  
         [0129]    [0129] 432 —third base  
         [0130]    [0130] 441 —rotors  
         [0131]    [0131] 442 —cantiliver  
         [0132]    [0132] 443 —first suspension unit  
         [0133]    [0133] 444 —second suspension unit  
         [0134]    [0134] 445 —third suspension unit  
         [0135]    [0135] 446 —fourth suspension unit  
         [0136]    [0136] 447 —foruth base  
         [0137]    [0137] 448 —fifth base  
         [0138]    [0138] 449 —sixth base  
         [0139]    [0139] 450 ,  550 —retro-reflective type optical signal processing device array  
         [0140]    [0140] 451 ,  551 —first retro-reflective type optical signal processing device  
         [0141]    [0141] 452 ,  552 —second retro-reflective type optical signal processing device  
         [0142]    [0142] 453 ,  553 —third retro-reflective type optical signal processing device  
         [0143]    [0143] 454 —seventh base  
         [0144]    [0144] 461 —shutter centerline  
         [0145]    [0145] 466 ,  571 —first comb-drive microactuator  
         [0146]    [0146] 467 ,  572 —second comb-drive microactuator  
         [0147]    [0147] 468 ,  573 —third comb-drive microactuator  
         [0148]    [0148] 471 —first reflective optical signal  
         [0149]    [0149] 472 —second reflective optical signal  
         [0150]    [0150] 473 —third reflective optical signal  
         [0151]    [0151] 474 —first incident optical signal  
         [0152]    [0152] 475 —second incident optical signal  
         [0153]    [0153] 476 —third incident optical signal  
         [0154]    [0154] 495 —electrode  
         [0155]    [0155] 496 —sacraficial layer  
         [0156]    [0156] 497 —comb-drive microactuator structure adnshutter  
         [0157]    [0157] 502 —first optical signal input unit  
         [0158]    [0158] 503 —first optical signal output unit  
         [0159]    [0159] 504 —first incident optical signal  
         [0160]    [0160] 505 —second reflective optical signal optical signal  
         [0161]    [0161] 506 —centerline of first parallel optical fibers  
         [0162]    [0162] 507  centerline of —second parallel optical fibers  
         [0163]    [0163] 508 —second optical signal input unit  
         [0164]    [0164] 509 —second optical signal output unit  
         [0165]    [0165] 510 —second incident optical signal  
         [0166]    [0166] 511 —first reflective optical signal optical signal  
         [0167]    [0167] 512 —third reflective optical signal optical signal  
         [0168]    [0168] 513 —fourth reflective optical signal optical signal  
         [0169]    [0169] 516 —first baseline  
         [0170]    [0170] 517 —second baseline  
         [0171]    [0171] 604 —incident optical signal  
         [0172]    [0172] 605 —reflective optical signal optical signal  
         [0173]    [0173] 606 —centerline of parallel optical fibers  
         [0174]    [0174] 407 ,  607 —baseline  
         [0175]    [0175] 610 —normal plane of a retro-reflective micro-mechanical-electrical reflective unit