Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-02-25
2003-02-25
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S291000, C359S292000, C359S299000, C359S238000
Reexamination Certificate
active
06525863
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a basic multi-technology application of cascaded optical beam-formers or beam spoilers and, more particularly, to the use of such beam-formers in fiber-optic (FO) attenuators and switch modules using a micro-electromechanical systems MEMS-EO beam-former approach to three dimensional (3-D) beam control. In one embodiment, the invention uses the physical cascading of two 3-D beam-formers, namely, an electronically controlled optical MEMS two axis micro-mirror with optional z-axis translational control coupled with an electronically controlled EO liquid crystal device 3-D beam-former to form a robust single beam attenuation and routing module. These dual 3-D beam-former based high speed, robust, fault-tolerant FO structures can be used for routing and attenuating multiple light signals in optical networks such as wavelength division multiplexed (WDM) optical communications, distributed sensor networks, and photonic signal processing systems and can also be deployed in free-space optical applications such as laser communications, metrology instrumentation, and optical read/write data systems.
BACKGROUND OF INVENTION
The programmable 3-D optical beam-former scanner module is a basic building block for many optical applications as it can be used to accomplish routing in fiber communications networks, photonic signal processing, distributed optical sensing, and optical controls. This 3-D scanner module can also be used to form variable optical attenuators used in building blocks for several key optical systems such as attenuators required as equalizers in wavelength division multiplexed (WDM) fiber-optic (FO) communication systems using non-uniform gain optical amplifiers. Other important applications include polarization dependent loss compensation in fiber optic networks, optical component testing, wavelength tunable receivers, and optical detector protection.
The desired features for such a 3-D beam-forming module include wide angle scans with fine angular controls, focus/defocus capability, polarization independence, low optical loss (e.g.,<1 dB), low inter-beam crosstalk (<−30 dB), multiple simultaneous beams generation, robustness to catastrophic failure, low electrical power consumption, and simple to align low cost designs for large scale commercial production and deployment. Depending on the application, 3-D beam-former module switching speeds can range from nanoseconds to several milliseconds.
For centuries, an excellent choice for light scan control has been 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 micro-electromechanical 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. Optical MEMS technology using micro-mirrors has been previously proposed to realize fiber optic beam control modules to form attenuators and switches. In these cases, a micro-mirror acts to deflect or obstruct a single light beam in one or two dimensions, thus routing or attenuating it to a given fiber-optic channel. Both analog and digital states of the micro-mirror have been used for routing and attenuation. In analog mirror control, a micro-mirror sweeps through a continuous range of angles or translational positions. In digital micro-mirror operation, the micro-mirror has two distinct states such as +10 and −10 degree tilt states. Examples of such applications of the micro-mirror are described in 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; 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; J. E. Ford, J. A. Walker, V. Aksyuk, and D. J. Bishop, “Wavelength selectable add/drop with tilting micro-mirrors,” IEEE LEOS Annual Mtg., IEEE, NJ., postdeadline paperPD2.3, November, 1997, N. A. Riza and S. Sumriddetchkajom, “Versatile multi-wavelength fiber-optic switch and attenuator structures using mirror manipulations,” Optics Communications, Vol. 169, pp. 233-244, Oct. 1, 1999, P. Colboume et. al., “Variable optical attenuator,” U.S. Pat. No. 5,915,063, Jun. 22, 1999, F. H. Levinson, “Optical coupling device utilizing a mirror and cantilevered arm,” U.S. Pat. No. 4,626,066, Dec. 2, 1986, T. G. McDonald, “Using an asymmetric element to create a 1×N optical switch,” U.S. Pat. No. 5,774,604, Jun. 30, 1998, and H. Laor, J. D' Entremont, E. Fontenot, M. Hudson, A. Richards, and D. Krozier, “Performance of a 576×576 Optical Crossconnect,” pp. 276-281, National Fiber Optic Engineers Conf. Proceedings, Sept. 26-30, 1999.
All previous micro-mirror MEMS-based optical control structures have not exploited the 3-D beam control aspect to form the FO switches and attenuators. This is because a typical mirror provides 1-D and 2-D scans, without any focus/defocus controls. It is well known that freespace propagation of beams leads to beam spreading, eventually causing loss between the fiber input-output ports. Furthermore, when input to output path distances get large (e.g., >50 cm), slight vibrations or mechanical misalignments due to component finite tolerances or environmental conditions can cause partial loss of signal or even catastrophic failure. In particular, for the large (N×N where N>100) port count switch matrices, the input to output freespace distance are forced to be large (e.g., >50 cm), causing a high chance for switch failure. Today, there is no mechanism for providing tolerance to the mentioned failures in an optical switch matrix as the mirrors can intrinsically provide only 2-D tilt controls.
Another problem with the previously proposed analog drive MEMS-based modules is that they require the micro-mirror to deliver both coarse beam angular deflections and fine high resolution beam alignment, leading to requiring precise analog voltage control, adding to the cost of the component. Furthermore, it is well known that mechanically actuated optical mirrors perform well across a range of large angular motions (e.g., ±45 degrees), but suffer greatly for fine tweaking (e.g., <±0.5 degrees) due to inertia limits . In addition, the mechanics and electronics required for fine mirror control become large, power consuming, heavy, and expensive. On the other hand, electro-optic (EO) materials such as liquid crystals (LC's) can be used to form high resolution low power 3-D optical beam-formers using milliwatt level electrical power with small, lightweight and low cost designs. Such a 3-D EO beam-former was described in N. A. Riza and Shifu Yuan, “Demonstration of a liquid crystal adaptive alignment tweaker for high speed infrared band fiber-fed free-space systems,”
Optical Engineering
, Vol. 37, No. 6, June, 1998. Also in G. D. Love, “Liquid Crystal Phase Modulator for unpolarized light,” Applied Optics, pp. 2222-2223, Vol. 32, No. 13, May 1, 1993 and N. A. Riza and Shifu Yuan, “Robust Packaging of Photonic RF Modules using Ultra-Thin Adaptive Optical Interconnect Devices,” SPIE Conf. on
Optical Technology for Microwave Applications VIII
, Vol. 3160, pp. 170-177, San Diego, August 1997, the NLC device is described in a reflective arrangement with a fixed mirror. Furthermore, G. D. Love proposes a setup for unpolarized light for astronomical image sharpening where typically the optical receiving apertures are very large (several meters diameter) telescopes implying that the adaptive optics is also large with very high (e.g., a million pixel) space bandwidth product processing.
The focus of this application is optical fiber-based polarized light control for small aperture (a millimeter or so diameter
Beusse James H.
Beusse Brownlee Bowdoin & Wolter P.A.
Epps Georgia
Nuonics, Inc.
Thompson Tim
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