Abstract:
Multi-wavelength fiber-optic processors based on a fault-tolerant scheme using a macro-pixel to control an optical beam are described. The macro-pixel system uses multiple device pixels per beam to provide a robust digital technique for amplitude control and routing, enabling a module with high optical beam alignment tolerance and resistance to catastropic failure. In one embodiment, the macropixel is implemented via small tilt micromirrors fabricated via optical microelectromechanical systems (MEMS) technology. The system includes fault tolerant fiber-optic processors that can implement add-drop wavelength routing, optical power level conditioning per wavelength, 2×2 optical crossconnects, and 1×N and M×N type broadcast-gain controlled switches. The system can simultaneously and independently implement optical power conditioning and wavelength routing for any wavelength channel. An optical signal processor is constructed using a fiber lens collimator, optical fibers butt-coupled to the fiber lens, and an optical MEMS-based macro-pixel device with three independently controllable tilt mirror states. Multiple processors can be interconnected to realize a crossconnect subsystem of multiple attenuators and switches that can be applied to N-wavelength multiplexed fiber-optic networks or to form broadcast 1×N and M×N optical switches with independent gain controls.

Description:
This application claims the benefit of U.S. provisional patent application, Ser. No. 60/292,249, filed May 18, 2001. 
    
    
     FIELD OF INVENTION 
     This invention relates to fiber-optic (FO) processors using micromirror controls and, more particularly, to macro-pixel optical MEMS device-based FO processor structures used for implementing add-drop wavelength routing, 2×2 crossconnect switching, and wavelength optical gain controls for light signal processing in various optical networks such as wavelength division multiplexed (WDM) optical communications, distributed sensor networks, and photonic signal processing systems requiring optical routing and gain control. 
     BACKGROUND OF INVENTION 
     It is well known that an excellent choice for light control is via the use of mirrors. Mirrors provide high reflectivity over broad bandwidths, as desired in WDM systems. Today, an excellent method for making actively controlled mirrors is via microelectromechanical system (MEMS) technology that promises to offer low cost compact optical modules via the use of low cost batch fabrication techniques similar to semiconductor electronic chip production methods. MEMS technology has been previously proposed to realize fiber optic beam control modules. 
     Various FO switches have been proposed using optical MEMS technology. The include 2×2 structures, wavelength add-drop (A-D) filters, and N×N crossconnects. For example, 2×2 type switches have been described in M. F. Dautartas, A. M. Benzoni, Y. C. Chen, G. E. Blonder, B. H. Johnson, C. R. Paola, E. Rice, and Y.-H. Wong, “A silicon-based moving-mirror optical switch,”  Journal of Lightwave Technology , Vol. 10, No. 8, pp. 1078-1085, August 1992; and N. A. Riza and D. L. Polla, “Microdynamical fiber-optic switch,” U.S. Pat. No. 5,208,880, May 4, 1993, FO switches are proposed using the electronically controlled actuation of a single micromirror fabricated using micromaching techniques used in MEMS chip fabrication. More recently, others have used this “single micromirror per optical beam” control approach to realize 1×N and 2×2 switches. These works using MEMS or other mechanical means are described in W. J. Tomlinson and R. E. Wagner, “Optical switch,” U.S. Pat. No., 4,208,094, Jun. 17, 1980; H. J. Ramsey and M. L. Dakss, “Piezoelectric optical switch,” U.S. Pat. No., 4,303,302, Dec. 1, 1981; T. Tanaka, Y. Tsujimoto, H. Serizawa, and K. Hattori, “Optical switching device,” U.S. Pat. No. 4,304,460, Dec. 8, 1981; J. -P. Laude, “Switching device between optical fibers,” U.S. Pat. No. 4,484,793, Nov. 27, 1984; F. H. Levinson, “Optical coupling device utilizing a mirror and cantilevered arm,” U.S. Pat. No. 4,626,066, Dec. 2, 1986; G. E. Blonder, “Radiation switching arrangement with moving deflecting element,” U.S. Pat. No. 4,932,745, Jun. 12, 1990; A. M. Benzoni, “Magnetic activation mechanism for an optical switch,” U.S. Pat. No. 5,042,889, Aug. 27, 1991; G. A. Magel and T. G. McDonald, “Optical switch using spatial light modulators,” U.S. Pat. No. 5,155,778, Oct. 13, 1992; G. A. Magel, “Fiber optic switch with spatial light modulator device,” U.S. Pat. No. 5,199,088, Mar. 30, 1993; J. J. Pan, “1×N Electromechanical optical switch,” U.S. Pat. No. 5,359,683, Oct. 25, 1994; M. Ghezzo, C. P. Yakymyshyn, and A. R. Duggal, “Integrated microelectromechanical polymeric photonic switching arrays,” U.S. Pat. No. 5,367,584, Nov. 22, 1994; J. E. Ford, “Fiber optic switching device and method using free space scanning,” U.S. Pat. No. 5,621,829, Apr. 15, 1997; L. Yang, G. R. Trott, K. Shubert, K. Salomaa, and K. W. Carey, “Mechanical fiber optic switch,” U.S. Pat. No. 5,699,463, Dec. 16, 1997; T. G. McDonald, “Using an asymmetric element to create a 1×N optical switch,” U.S. Pat. No. 5,774,604, Jun. 30, 1998; J.-J. Pan, J.-Y. Xu, and C. J.-L. Yang, “Efficient electromechanical optical switches,” U.S. Pat. No. 5,838,847, Nov. 17, 1998; V. A. Aksyuk, D. J. Bishop, J. E. Ford, and J. A. Walker, “Freespace optical bypass-exchange switch,” U.S. Pat. No. 5,943,454, Aug. 24, 1999; V. A. Aksyuk, D. J. Bishop, and C. Randy, “Micro-machined optical switch with tapered ends,” U.S. Pat. No. 6,108,466, Aug. 22, 2000. 
     Other related works on switching includes E. Ollier, C. Chabrol, T. Enot, P. Brunet-Manquat, J. Margail, and P. Mottier, “1×8 Micro-mechanical switches based on moving waveguides for optical fiber network switching,” 2000 IEEE/LEOS International Conference on Optical MEMS, pp. 39-40, Kauai, Hi., August 2000; R. T. Chen, H. Nguyen, and M. C. Wu, “A high-speed low-voltage stress-induced micromachined 2×2 optical switch,” IEEE Photonics Technology Letters, Vol. 11, No. 11, pp. 1396-1398, November 1999; S. Nagaoka, “Compact latching-type single-mode-fiber switches fabricated by a fiber-micromachining technique and their practical applications,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 5, No. 1, pp. 36-45, January/February 1999; A. A. Yasseen, J. N. Mitchell, J. F. Klemic, D. A. Smith, and M. Mehregany, “A rotary electrostatic micromirror 1×8 optical switch,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 5, No. 1, pp. 26-32, January/February 1999; H. Toshiyoshi, D. Miyauchi, and H. Fujita, “Electromagnetic torsion mirrors for self-aligned fiber-optic crossconnectors by silicon micromachining,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 5, No. 1, pp. 10-17, January/February 1999; M. Makihara, M. Sato, F. Shimokawa, and Y. Nishida, “Micromechanical optical switches based on thermocapillary integrated in waveguide substrate,” Journal of Lightwave Technology, Vol. 17, No. 1, pp. 14-18, January 1999; S.-S. Lee, L. S. Huang, C.-J. Kim, and M. C. Wu, “Free-space fiber-optic switches based on MEMS vertical torsion mirrors,” Journal of Lightwave Technology, Vol. 17, No. 1, pp. 7-13, January 1999; C. Marxer and N. F. de Rooij, “Micro-opto-mechanical 2×2 switch for single-mode fibers based on plasma-etched silicon mirror and electrostatic actuation,” Journal of Lightwave Technology, Vol. 17, No. 1, pp. 2-6, January 1999; J. E. Ford and D. J. DiGiovanni, “1×N Fiber bundle scanning switch,” IEEE Photonics Technology Letters, Vol. 10, No. 7, pp. 967-969, July 1998; V. Aksyuk, B. Barder, C. R. Giles, R. Ruel, L. Stulz, and D. Bishop, “Low insertion loss packaged and fibre connectorised MEMS reflective optical switch,” Electronics Letters, Vol. 34, No. 14, pp. 1413-1414, July 1998; C. Marxer, C. Thio, M.-A. Gretillat, N. F. de Rooij, R. Battig, O. Anthamatten, B. Valk, and P. Vogel, “Vertical mirrors fabricated by deep reactive ion etching for fiber-optic switching applications,” Journal of Microelectromechanical Systems, Vol. 6, No. 3, pp. 277-285, September 1997; R. A. Miller, Y. C. Tai, G. Xu, J. Bartha, and F. Lin, “An electromagnetic MEMS 2×2 fiber optic bypass switch,” Transducers&#39;97, pp. 89-92, Chicago, Ill., June 1997; S. S. Lee, E. Motamedi, and M. C. Wu, “Surface-micromachined free-space fiber optic switches with integrated microactuators for optical fiber communication systems,” Transducers&#39;97, pp. 85-87, Chicago, Ill., June 1997; H. Toshiyoshi and H. Fujita, “Electrostatic micro torsion mirrors for an optical switch matrix,” Journal of Microelectromechanical Systems, Vol. 5, No. 4, pp. 231-237, December 1996; S. S. Lee, L. Y. Lin, and M. C. Wu, “Surface-micromachined free-space fibre-optic switches,” Electronics Letters, Vol. 31, No. 17, pp. 1481-1482, August 1995; L. A. Field, D. L. Burriesci, P. R. Robrish, and R. C. Ruby, “Micromachined 1×2 optical fiber switch,” Transducers&#39;95, pp. 344-347, Stockholm, Sweden, June 1995; R. M. Boysel, T. G. McDonald, G. A. Magel, G. C. Smith, and J. L. Leonard, “Integration of deformable mirror devices with optical fibers and waveguides,” Proceedings of SPIE, Vol. 1793, pp. 34-39, 1992; K. Hogari and T. Matsumoto, “Electrostatically driven micromechanical 2×2 optical switch,” Applied Optics, Vol. 30, No. 10, pp. 1253-1257, April 1991; K. Hogari and T. Matsumoto, “Electrostatically driven fiber-optic micromechanical on/off switch and its application to subscriber transmission systems,” Journal of Lightwave Technology, Vol. 8, No. 5, pp. 722-727, May 1990. 
     Add-drop switches have also been proposed using MEMS. For instance, one such switching module is described in W. J. Tomlinson, “Wavelength-selective optical add/drop using tilting micromirrors,” U.S. Pat. No. 5,960,133, Sep. 28, 1999; J. E. Ford, J. A. Walker, V. Aksyuk, and D. J. Bishop, “Wavelength selectable add/drop with tilting micromirrors,” IEEE LEOS Annual Mtg., IEEE, N.J., postdeadline paperPD2.3, November 1997, where apart from the limitations of using a single micromirror per beam, this 4-port switch is not reversible and does not form a 2×2 switch that can be used to form larger N×N switch matrices. Other examples of add-drop switches using MEMS includes V. A. Aksyuk, B. P. Barber, D. J. Bishop, P. I. Gammel, C. R. Giles, “Micro-opto-mechanical devices and method thereof,” U.S. Pat. No. 5,995,688, Nov. 30, 1999; C. R. Giles, B. Barber, V. Aksyuk, R. Ruel, L. Stulz, D. Bishop “Reconfigurable 16-channel WDM drop module sing silicon MEMS optical switches,”  IEEE Photonics Technology Letters , Vol. 11, No. 1, pp. 63-65, January 1999; V. A. Aksyuk, D. J. Bishop, J. E. Ford, R. E. Slusher, “Article comprising a wavelength selective add-drop multiplexer,” U.S. Pat. No. 5,974,207, Oct. 26, 1999; C. Pu, L. Y. Lin, E. L. Goldstien, R. W. Tkach, “Micro-machined optical add/drop multiplexer with client configurability,” 2000  IEEE/LEOS International Conference on Optical MEMS , pp. 35-36, Aug. 21-24, 2000. Similarly, in S. Glöckner, R. Goring, and T. Possner, “Micro-opto-mechanical beam deflectors,”  Optical Engineering , Vol. 36, No. 5, pp. 1339-1345, May 1997; P. M. Hagelin, U. Krishnamoorthy, J. P. Heritage, O. Solgaard, “Scalable optical cross-connect switch using micromachined mirrors,”  IEEE Photonics Technology Letters , Vol. 12, No. 7, pp. 882-884, July 2000; and L. Y. Lin, E. L. Goldstein, and R. W. Tkach, “Free-space micromachined optical switches with submillisecond switching time for large-scale optical crossconnects,”  IEEE Photonics Technology Letters , Vol. 10, No. 4, pp. 525-527, April 1998, a single micromirror per beam that can be rather large in size is used, leading to slow millisecond range switching speeds. 
     Other mechanically implemented optical crossconnects are described in P. M. Hagelin, U. Krishnamoorthy, J. P. Heritage, O. Solgaard, “Scalable optical cross-connect switch using micromachined mirrors,”  IEEE Photonics Technology Letters , Vol. 12, No. 7, pp. 882-884, July 2000; H. Laor, “Compact optical matrix switch with fixed location fibers,” U.S. Pat. No. 6,097,860, Aug. 1, 2000; O. Solgaard, J. P. Heritage, and A. R. Bhattaral, “Multi-wavelength cross-connect optical switch,” U.S. Pat. No. 6,097,859, Aug. 1, 2000; M. T. Fatchi and J. E. Ford, “Free-space optical signal switch arrangement,” U.S. Pat. No. 6,002,818, Dec. 14, 1999; R. L. Jungerman and D. M. Braun, “Optical cross-connect switch using a pin grid actuator,” U.S. Pat. No. 5,841,917, Nov. 24, 1998; F. H. Levinson, “Optical matrix switch,” U.S. Pat. No. 4,580,873, Apr. 8, 1986; G. J. G. Broussaud, “Optical switch for a very large number of channels,” U.S. Pat. No. 4,365,863, Dec. 28, 1982; T.-K. Koo, “Optoelectronic data entry means having plurality of control means to direct part of radiation in channel from radiation source to output channel,” U.S. Pat. No. 3,548,050, Mar. 7, 1972; D. T. Neilson, V. A. Aksyuk, S. Arney, N. R. Basavanhally, K. S. Bhalla, D. J. Bishop, B. A. Boie, C. A. Bolle, J. V. Gates, A. M. Gottlieb, J. P. Hickey, N. A. Jackman, P. R. Kolodner, S. K. Korotky, B. Mikkelson, F. Pardo, G. Raybon, R. Ruel, R. E. Scotti, T. W. Van Blarcum, L. Zhang, and C. R. Giles, “Fully provisioned 112×112 micro-mechanical optical crossconnect with 35.8 Tb/s demonstrated capacity,” OFC Technical Digest, Postdeadline, pp.PD12-1-PD12-3, Baltimore, Md., March 2000; H. Laor, J. D&#39;Entremont, E. Fontenot, M. Hudson, A. Richards, and D. Krozier, “Performance of a 576×576 optical cross connect,” National Fiber Optic Engineers Conference, pp. 276-281, Chicago, Ill. September 1999; L. Y. Lin, E. L. Goldstein, J. M. Simmons, and R. W. Tkach, “High-density micromachined polygon optical crossconnects exploiting network connection-symmetry,” IEEE Photonics Technology Letters, Vol. 10, No. 10, pp. 1425-1427, October 1998. 
     Single pixel per beam MEMS-based variable FO attenuators have also been proposed such as described in J. E. Ford and J. A. Walker, “Dynamic spectral power equalization using micro-opto-mechanics,”  IEEE Photonics Technology Letters , Vol. 10, No. 10, pp. 1440-1442, October, 1998, V. Askyuk, B. Barber, C. R. Giles, R. Ruel, L. Stulz, and D. Bishop, “Low insertion loss packaged and fibre connectorized MEMS reflective optical switch,”  IEE Electronics Lett ., Vol. 34, No. 14, pp. 1413-1414, Jul. 9, 1998, and B. Barber, C. R. Giles, V. Askyuk, R. Ruel, L. Stulz, and D. Bishop, “A fiber connectorized MEMS variable optical attenuator,”  IEEE Photon. Technol. Lett. , Vol. 10, No. 9, pp. 1262-1264, September 1998. Apart from the tolerance limited single pixel control approach, attenuation control in these modules is implemented in an analog fashion by carefully moving a micromirror per beam (or wavelength) through a continuous range of positions. For instance, in both the cited V. Askyuk, et.al. designs, a micromirror is linearly translated to partially block a beam and hence cause attenuation. In the J. Ford, et.al. design case, a micromirror is translated through many small sub-micron size steps to form a varying reflection surface, and this ultra-small motion makes the module very sensitive to vibrations. Thus, extensive module calibration and costly and complex control electronics are required to maintain the high performance of these analog-type FO MEMS-based modules. Other related works on mechanical or MEMS based VOAs are described in works such as V. A. Aksyuk, D. J. Bishop, P. L. Gammel, C. R. Giles, “Article comprising a light actuated micromechanical photonic switch,” U.S. Pat. No. 6,075,239, Jun. 13, 2000; E. E. Bergmann, D. J. Bishop, “Moving mirror switch,” U.S. Pat. No. 6,031,946, Feb. 29, 2000; P. Colbourne, J. Obhl, N. Teltelbaum, “Variable optical attenuator,” U.S. Pat. No. 5,915,063, Jun. 22, 1999; J. E. Ford, K. W. Goossen, “Level setting optical attenuator,” U.S. Pat. No. 5,900,983, May 4, 1999; C. M. Garrett, C Fan, D. Cugalj, D. Gransden, “Voltage controlled attenuator,” U.S. Pat. No. 5,745,634, Apr. 28, 1998; J. E. Ford, D. A. B. Miller, M. C. Nuss, J. A. Walker, “Attenuation device for wavelength multiplexed optical fiber communications,” U.S. Pat. No. 5,745,271, Apr. 28, 1998; R. Wood, V. Dhuler, E. Hill, “A MEMS variable optical attenuator,” 2000 IEEE/LEOS International Conf. on Optical MEMS, pp. 121-122, Kauai, Hi. 21-24 August 2000; K. W. Goossen, J. A. Walker, D. T. Neilson, J. E. Ford, W. H. Knox, “Micromechanical gain slope compensator for spectrally linear optical power equalization,” IEEE Photonic Technology Letters, Vol. 12, No. 7, pp.831-833, July 2000; F. Chollet, M. de Labachelerie, H. Fujita, “Compact evanescent optical switch and attenuator with electromechanical actuation,” IEEE Journal of Selected Topics in Quantum Electronics, Vol.5, No. 1, January/February, 1999; F. Chollet, M. de Labachelerie, H. Fujita, “Electromechanically actuated evanescent optical switch and polarization independent attenuator”, Proc. IEEE MEMS Conf., pp.476-481, 1998. 
     It is very important to note that all the above works cited in mechanically motivated and optical MEMS-related components or subsystems use the principle of “a single mirror element controls a single fiber-optic beam.” This is unlike the proposed embodiments in this application where a “Macro-pixel” or multiple mirrors controls a single optical beam. 
     Many advanced optical networking applications require subsystems that can simultaneously and independently control various parameters of an optical beam, such as amplitude level, time delay, and routing path. The need and method to accomplish parts of these tasks has been pointed out in such works as N. A. Riza, “High Speed Fiber-Optic Switch,” U.S. Pat. No. 6,282,336, issued Aug. 28, 2001, and in N. A. Riza and S. Sumriddetchkajorn, “Micromechanics-based Wavelength Sensitive Fiber-Optic Beam Control Structures and Applications,” Applied Optics, Vol. 39, No. 6, pp. 919-932, Feb. 20, 2000, and N. Antoniades, et.al., “Engineering the performance of DWDM metro networks,” NFOEC 2000 Conf. Proc., pp. 204-211, Denver, Aug. 27-31, 2000. 
     It is the purpose of this application to introduce FO processors that have the capability to independently and simultaneously accomplish these key tasks of controlling optical beam amplitude level and routing path on a per wavelength basis. It is also the purpose of this application to introduce a processor that accomplishes simultaneous broadcasting of optical signals to different ports of the switch. These processors are unique in their use of a digitally controlled FO module using optical MEMS-based macro-pixel devices to form compact and fault-tolerant multiwavelength structures to simultaneously accomplish the gain and routing beam processing tasks. Specifically, these processors and their beam control submodules incorporate the unique “macro-pixel” approach to beam controls that has been introduced by N. A. Riza in earlier works such as described in N. A. Riza, “Fault-tolerant fiber-optical beam control modules,” U.S. Pat. No. 6,222,954, issued Apr. 24, 2001; N. A. Riza and S. Sumriddetchkajorn, “Digitally controlled fault-tolerant multiwavelength programmable fiber-optic attenuator using a two dimensional digital micromirror device,”  Optics Letters , Vol. 24, No. 5, pp. 282-284, Mar. 1, 1999; N. A. Riza and S. Sumriddetchkajorn, “Small tilt micromirror device-based multiwavelength three-dimensional 2×2 fiber-optic switch structures,”  Optical Engineering , Vol. 39, No. 2, pp. 379-386, February 2000; and N. A. Riza and S. Sumriddetchkajorn, “Fault-tolerant dense multiwavelength add-drop filter with a two-dimensional digital micromirror device,”  Applied Optics , Vol. 37, No. 27, pp. 6355-6361, Sep. 20, 1998. This application is the first disclosure of macro-pixels based on digital operation small tilt micromirrors coupled with a fiber collimator lens used simultaneously to accomplish the tasks of light routing and amplitude controls with broadcast capability. Specifically, it is shown how several processors for WDM signal controls can be devised using a macro-pixel based optical beam control module. The simultaneous yet independent routing and gain control attributes for any wavelength of proposed fault-tolerant processors make them a powerful conditioning tool for optical beams in WDM fiber-optic networks and is the subject of this invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1   a  illustrates a retroreflective architecture N-wavelength Add-Drop processor using specially designed beam control modules based on optical MEMS; 
         FIG. 1   b  is an enlarged view of element A if  FIG. 1   a ; 
         FIG. 1   c  shows element A of  FIG. 1  in a drop mode; 
         FIG. 1   d  shows a typical structure of a macropixel MEMS device consisting of K micromirrors, each mirror with its predetermined size and placement; 
         FIG. 2   a  shows a beam control module “B” using four fiber ports (one in and three out), one fiber collimator lens, and one 3-state optical MEMS macro-pixel micromirror device set in the main in-main out mode where light input from IN 1  travels partly to OUT 1  and partly to the power monitoring port OUT 3 ; 
         FIG. 2   b  shows device B set in the add in-drop out mode where light input from IN 1  travels partly to OUT 2  and partly to the power monitoring port OUT 3 ; 
         FIG. 3   a  shows beam control module using four fiber ports (two in and two out), one fiber collimator lens, and one 3-state optical MEMS macro-pixel micromirror device set in the drop mode where light input from IN 2  travels partly to OUT 1  and partly to the power monitoring port OUT 2 . 
         FIG. 3   b  shows device C set in the main in-main out mode where light input from IN 1  travels to OUT 1 . 
         FIG. 4  shows devices B and C with four 1:N WDM devices to form a fully programmable N-wavelength A-D processor with completely independent routing and gain controls of all wavelengths through both main-in main-out mode and A-D mode; 
         FIG. 5  shows how devices B and C of  FIGS. 2-3  can be used with four 1:N WDM devices to form a fully programmable N-wavelength 2×2 crossconnect subsystem with completely independent routing and gain controls of all wavelengths through both straight state mode and crossed state mode; 
         FIG. 6   a  shows device B used to form a M×N multi-broadcast crossconnect optical switch with independent gain controls per output port; and 
         FIG. 6   b  shows device B in K binary tree stages interconnected to realize a 1×N multi-broadcast optical switch with independent gain controls per output port. 
     
    
    
     SUMMARY DESCRIPTION OF THE INVENTION 
     Multi-wavelength fiber-optic processors based on a unique fault-tolerant scheme using a macro-pixel to control an optical beam are disclosed. The disclosed macro-pixel invention uses multiple device pixels per beam to provide a robust digital technique for amplitude control and routing thereby creating a module with high optical beam alignment tolerance and resistance to catastrophic failure. A preferred embodiment of the invention is implemented via small tilt micromirrors fabricated with optical microelectromechanical systems (MEMS) technology. This embodiment provides fault tolerant fiber-optic processors that can implement add-drop wavelength routing, optical power level conditioning per wavelength, and 2×2 optical crossconnects. Specifically, the disclosed processor can simultaneously and independently implement optical power conditioning and wavelength routing for any wavelength channel, realizing a powerful processor. The basic control modules in the processors use a fiber lens collimator, at most four linearly displaced fibers butt-coupled to the fiber lens, and one optical MEMS-based macro-pixel device with at most three independently controllable tilt mirror states. The processors can be interconnected to realize a crossconnect subsystem of multiple attenuators and switches that can be applied to N-wavelength multiplexed fiber-optic networks. The processors can be interconnected to form broadcast 1×N and M×N optical switches with independent gain controls. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1   a , there is shown one embodiment of a retroreflective architecture N-wavelength Add-Drop processor  10  using beam control modules based on optical MEMS. This processor can accomplish gain conditioning for both add and drop signals or a main signal. Light containing N wavelengths labeled as λ 1 , λ 2 , . . . , λN enter the processor from the Main IN fiber port  12 . These wavelengths pass through a first circulator device  14  and enter a fiber coupled 1:N wavelength division multiplexer (WDM) device  16  that physically separates the wavelengths into independent output fiber ports  18  labeled a to N where N can be any number. These N wavelengths then enter N fiber connected beam control modules  20   a - 20   n . Each module  20  uses two fiber ports  22 ,  24 , one fiber collimator lens  26 , and one 3-state optical MEMS macro-pixel micromirror device  28 . The top module  20   a  (see  FIG. 1   c ) is set in retroreflective main in/main out mode for wavelength λ 1  with any excess λ 1  power blocked at the noise block  30 . Hence, as shown, λ 1  retroreflects in the module  20   a  and travels back to the first WDM device  16  and exits from a Main Out port  32  of the circulator  14 . Because gain control may be required for the incoming λ 1 , some of the micromirrors in module  20   a  may be set in a non-retroreflective mode to direct part of the optical energy to the noise block  30 . In this way, module  20   a  can independently control the amplitude and routing direction of the input wavelength λ 1 . In comparison, the bottom module  20   n  (see  FIG. 1   b ) may be set in a non-retroreflective add in/drop out mode where wavelength λN is dropped out of the network and wavelength λ′N is added into the network main flow signals. Here, the required micromirrors in module  20   n  are set to direct the λN drop signal labeled D to the non-retroreflective port  24  of module  20   n  and simultaneously direct the λ′N add signal labeled A to the other non-retroreflective port  22  of module  20   n . In this example, two reject path rays A and D are generated towards the noise block  30  so that optical gain control for both the add and drop wavelength λ′N is executed. Note that because the same optical path is followed by both the add and drop wavelength in the module  20   n , the add and drop wavelengths in this processor acquire the same value of gain control limiting the total flexibility of the processor. One embodiment of this invention addresses this issue. As shown in  FIG. 1   a , the ports  24  are of modules  20  are connected to ports  34   a - 34   n  of a second WDM device  36  identical to device  16 . Device  36  is connected to a second fiber-connected circulator  38  that provides an add port  40  and a drop port  42 . The light signal λ′N is input to the processor  10  via the add port  40  of the second circulator  38 . The signal λN is dropped from the processor  10  via the drop port  42  of this second circulator  38 . 
       FIG. 1   d  illustrates one example of a macropixel MEMS device, such as device  28 , consisting of K micromirrors where K represents a number of individual micromirrors  44 , each mirror having a predetermined size and placement. All micromirrors  44  are designed to maintain three tilt states, i.e., tilt angles of flat or 0 degrees, −θ 2 /2, and +θ 1 /2. The dashed lines A,D in the fiber collimators  26  represent the central or chief rays for the converging/diverging light beams. The fiber lens output/input beams at the lens-freespace boundary are collimated or parallel beams with various angle of direction with respect to the central axis of the fiber-lens. These angles can be 0 degrees, −θ 2 , +θ 1 , and θ 1 +θ 3 , and depend on whether module  20  operates in the add/drop mode of  FIG. 1   b  or the main in/main out mode of  FIG. 1   c . For the main in/main out mode, the micromirrors  44  are set to two tilt angles of 0 degrees (signal main in to main out) and +θ 1 /2 (main in to noise block) with respect to the central fiber lens axis which also is retroreflective with the top fiber port. For the add/drop mode, the micromirrors  44  are set to two tilt angles of +θ 1 /2 degrees (signals A to noise block and signals D to noise block) and −θ 2 /2 (signals A to D and D to A) with respect to the central fiber lens axis. As mentioned in the earlier cited N. A. Riza works, amplitude control for the beams is set by selecting which mirrors in the macropixel are set to which desired tilt states of each micromirror. In module  26 , the micromirror is required to have 3 independent tilt states. The angles on these tilt states depends on the type of fiber lens used plus the size and placement of the fiber cores that are butt coupled or located near one facet of the fiber lens. Hence, any number of tilt angle designs for the macropixel mirror based device/chip can be chosen for making a module  26  with low loss and minimum crosstalk. This macropixel design used in module  26  to make a multi-wavelength processor is a feature of this invention. Note that any other reference axis for design of module  26  can also be chosen, implying that the tilt angles have the same relative tilts but perhaps different absolute plus or minus values in degrees. The tilt angles of the micromirrors are controlled by drive unit  46  in accordance with specifications from the micromirror or manufacturer. 
       FIGS. 2   a  and  2   b  illustrate another form of beam control module  48  having four fiber ports  50 ,  52 ,  54  and  56  (one in and three out), one fiber collimator lens  58 , and one 3-state optical MEMS macro-pixel micromirror device  60 . Module  48  is essentially the same in design as module  26  in  FIG. 1 , except that two fibers have been added to receive light signals that were previously directed into noise block  30 . The angle notations θ 1 , θ 2 , θ 3  are the same as for module  26  in FIG.  1 . Module  48  basically works as a 1×2 FO switch that has independent optical gain control capability for the input signal. This again is possible through the “Macropixel” fiber-optic beam control approach described above. Module  48  in  FIG. 2   a  is set in the main in/main out mode where light input from IN 1  port  50  travels partly to OUT 1  port  52  (i.e., using micromirror setting of −θ 2 /2 degrees) and partly to a power monitoring port OUT 3  port  56  (i.e., using micromirror setting of (θ 1 +θ 3 )/2 degrees). In  FIG. 1   b , module  48  is set in the add in/drop out mode where light input from IN 1  port  50  travels partly to OUT 2  port  54  (i.e., using micromirror setting of −θ 1 /2 degrees) and partly to the power monitoring port  56  (i.e., using micromirror setting of (θ 1 +θ 3 )/2 degrees). Thus the light coming in from IN 1  port  50  can be sent either to ports  52  and  54 , with the desired level of independent power controls. Again, the typical structure of the macropixel MEMS device used to make module  48  comprises K micromirrors, each mirror with its predetermined size and placement. All micromirrors are designed to maintain three tilt states, i.e., tilt angles of flat or +θ 2 /2, θ 1 /2 and (θ 1 +θ 3 )/2. This notation is again based on the  FIG. 1   b  fiber lens central axis reference and the relative tilt state values that are important when designing these modules. 
       FIGS. 3   a  and  3   b  illustrate another form of beam control module  62  using four fiber ports  64 ,  66 ,  68 ,  70  (two in and two out), one fiber collimator lens  72 , and one 3-state optical MEMS macro-pixel micromirror device  74 . Module  62  is similar in design to module  48 . The key difference is that in module  62 , the fiber ports are labeled and used differently, and the macropixel micromirror device  74  has different tilt states. Specifically, module  62  has two input fiber ports labeled IN 1  and IN 2  and two output ports labelled OUT 1  and OUT 2 . In  FIG. 3   a , module  62  is set in the drop mode where light input from IN 2  port  64  travels partly to OUT 1  port  68  (i.e., using micromirror setting of ƒ 1 /2 degrees) and partly to a power monitoring OUT 2  port  70  (i.e., using micromirror setting of −θ 2 /2 degrees). In  FIG. 3   b , module  62  is set in the main in/main out mode where light input from IN 1  port  64  all travels to OUT 1  port  68  (i.e., using micromirror setting of (θ 1 +θ 3 /2) degrees). Thus the light coming in from IN 1  port  64  is sent to OUT 1  port  68 , while light coming in from IN 2  port  66  is sent partly to OUT 1  port  68  and partly to the power monitoring port  70  to get the desired level of independent power controls. Again, the typical structure of the macropixel MEMS device used to make module  62  consists of K micromirrors, each mirror with its predetermined size and placement. All micromirrors are designed to maintain three tilt states, i.e., tilt angles of flat or −θ 2 /2, θ 1 /2, and (2θ 1 +θ 3 )/2, considering the central fiber lens reference axis aligned with the IN 2  port  66 . 
       FIG. 4  illustrates an add/drop processor  76  using the devices  48  and  62  with four 1:N WDM devices  16  or  36  to form a fully programmable N-wavelength A/D processor with completely independent routing and gain controls of all wavelengths through both main-in/main-out mode and add/drop mode. Hence, unlike the processor  10  in  FIG. 1 , the processor  76  can independently control the optical power levels of add and drop signals. The operation of the processor  76  is otherwise similar to the processor  10  in FIG.  1 . Device  48  and device  62  form a set that contains the beam amplitude control features. The specific macropixel settings used for devices  48  and  62  are described with regard to FIG.  2  and FIG.  3 . Conventional optical amplifiers  78  buffer the input and output signals of the processor  76 . 
     It would be highly desirable to realize a fully symmetric 2×2 switching processor architecture that could be used to make larger N×M multiwavelength crossconnects. The processors  10 ,  76  in FIG.  1  and  FIG. 4  are add/drop processors and may not be useful to implement a 2×2 router. For example, the add signals from the Add port  80  of the processor  76  cannot flow to the drop port  82  of the processor. Hence, the processor  76  cannot be used as a basic 2×2 building block for a N×M large crossconnect. 
       FIG. 5  shows a modified processor  84  that solves the 2×2 switching processor issue. Specifically,  FIG. 5  shows devices  48  and  62  used with four 1:N WDM devices (two devices  16  and two devices  36 ) to form a fully programmable N-wavelength 2×2 crossconnect subsystem with completely independent routing and gain controls of all wavelengths through both straight state mode and crossed state mode. In this case, device  48  is a 3-state module while device  62  is a 2-state module. The key design change compared to the processor  76  is that the number of devices  48  and  62  are doubled, i.e., a new set of devices  48  and  62  are added between the second pair of WDM devices  16  and  36  which couple the IN 2  and main OUT 2  ports. The processor  84  has two input ports labeled Main IN 1  (port  86 ) and Main IN 2  (port  88 ), and two output ports labeled Main OUT 1  (port  90 ) and Main OUT 2  (port  92 ). The states of this processor are Main IN 1  to Main Out  1 , Main IN 2  to Main Out  2 , Main IN 1  to Main Out  2 , and Main IN 2  to Main Out  1 . These configurations can be applied to any input wavelength of the N-wavelength set entering the processor  84  via its two input ports  86 ,  88 . The specific macropixel settings used for devices  48  and  62  are described in  FIG. 2 ,  FIG. 3 , and FIG.  5 . Devices  48  contain the beam amplitude control features while devices  62  act as 2×1 switch arrays. 
     In some network applications such as a M×N broadband optical crossconnect system, it is desirable to be able to simultaneously broadcast desired levels of an input optical signal to several output ports of a switch. This capability should exist for any of the N input signals introduced via the independent N input fiber ports. In prior art systems, this capability is severely constrained because optical switches for routing operate in a strictly digital routing format, i.e., for a simple most common 1×2 optical micromirror-based switch, all light either gets routed to one output port or the other output port, but not simultaneously to both output ports with a desired level of optical power distribution. The device  48  of the present invention provides broadcast and gain control capability at all output ports.  FIG. 6   a  shows one arrangement of devices  48  used to form a M×N multi-broadcast crossconnect optical switch with independent gain controls per output port.  FIG. 6   b  shows how devices  48  in K binary tree stages (stage  1  through stage K) interconnected to realize a 1×N multi-broadcast optical switch  94  with independent gain controls per output port. This 1×N switch is used to create the M×N crossconnect in  FIG. 6   a . In these examples, device  48  is a 3-state module and is used to implement an optically broadband (or wavelength independent) M×N crossconnect switch with independent optical gain controls across all output ports and simultaneous multi-broadcast capability of the N input signals to the M output ports.