Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-09-24
2001-08-28
Schwartz, Jordan M. (Department: 2873)
Optical waveguides
With optical coupler
Switch
C385S007000
Reexamination Certificate
active
06282336
ABSTRACT:
FIELD OF INVENTION
In this invention, a 2×2 fiber-optic (FO) switch using electronically controlled light beam deflectors such as acousto-optic deflectors is described. The switch structure can be modified to serve as variable FO attenuators and frequency shifters. The basic no moving parts FO switch/attenuator structure can be used for routing and controlling multiple light signals in optical networks such as wavelength division multiplexed (WDM) optical communications, distributed sensor networks, and photonic signal processing systems requiring optical routing and gain control. The high speed, high isolation 2×2 optical switch and attenuator, with the additional capability of handling high optical powers, can be used in optical switching instrumentation for: (a) telecommunication optical fiber line protection manufacturers, (b) fiber-optic line remote sensing and testing manufacturers using optical time domain reflectometers, (d) optoelectronic component manufacturing and test factories, and (e) distributed environmental optical sensor manufacturers for chemical, temperature, and pressure detection.
BACKGROUND OF INVENTION
The fiber-optic (FO) switch is a basic building block for many optical applications such as routing in fiber communications networks, photonic signal processing, distributed optical sensing, and optical controls. The desired features for a FO switch include low optical loss (e.g., <1 dB), low interchannel crosstalk (<−30 dB), polarization independence, robustness to catastrophic failure, and simple to align low cost designs for large scale commercial production and deployment. Depending on the application, FO switching speeds can range from nanoseconds to several milliseconds. Fast sub-microseconds (e.g., 100 ns) switching speeds are required in internet type packet switched FO networks.
Similarly, variable fiber-optic attenuators are the basic building blocks for several key optical systems. Presently, these attenuators are required as equalizers in wavelength division multiplexed (WDM) optical communication systems using non-uniform gain optical amplifiers. Other important applications include polarization dependent loss compensation in fiber optic networks, optical component testing, and optical receiver protection. Hence, a variable fiber-optic attenuator with fast sub-microseconds duration speed with exceptionally high attenuation dynamic range (e.g., 50 dB) control is a present challenge to the optical community.
Over the years, attempts have been made to realize acoustooptic (AO) FO switches as AO technology has speeds in the submicrosecond regime. These include works such as W. E. Stephens, P. C. Huang, T. C. Banwell, L .A. Reith, and S. S. Cheng, “Demonstration of a photonic space switch utilizing acousto-optic elements,”
Opt. Eng
. 29 (3):183-190, 1990, D. O. Harris and A. Vanderlugt, “Acousto-optic photonic switch,”
Opt. Lett
. 14 (21):1177-1179, 1989, D. O. Harris, “Multichannel acousto-optic crossbar switch,”
Appl. Optics
30, 4245-4256, Oct. 10, 1991, D. O. Harris and A. Vanderlugt, “Multichannel acousto-optic crossbar switch with arbitrary signal fan-out,”
Appl. Optics
32, pp. 1684-1686, April 1992, E. Tervonen, A. T. Friberg, J. Westerholm, J. Turunen, and M. R. Taghizadeh, “Programmable optical interconnections by multilevel synthetic acousto-optic holograms,”
Opt. Lett
. 16:1274-1276, 1991, M. L. Wilson, D. L. Fleming, and F. R. Dropps, “A fiber optic matrix switchboard using acoustooptic bragg cells,”
SPIE
988, 56-62, 1988, and K. Wagner, R. T. Weverka, A. Mickelson, K. Wu, C. Garvin, and R. Roth, Chapter 14, Low-loss acousto-optic photonic switch,” pp.479-492, in Acousto-optic Signal Processing, Editors N. J. Berg and J. M. Pellegrino, 2
nd
Edition, Marcel Dekker, 1996. All these switches have been unable to realize the goal for high >50 dB isolation optical switching. Moreover, some approaches require lossy passive N:1 beam combiners, others require multichannel AO devices with limited crosstalk levels, and some even require multimode output fibers that limit signal modulation bandwidths and are incompatible with single mode telecommunication fibers. In addition to making larger N×N switches, these prior art design switches do not scale well as, for instance, there is a limit (e.g., 64) to the number of channels presently possible in a multichannel AO device. This type of design also requires N drive frequencies that are different, making the drive hardware complex, costly, and hard to control as the switch scale grows. If a Fourier optics type design is used, there are limitations to the number of spots the system can resolve in the output fiber plane, and the lens focal length and size can become big in order to reduce interchannel spatial crosstalk.
Specifically, because AO devices work on the principle of diffraction to implement 1 to N beam deflection, even a high 99% diffraction leads to a 1% leakage light in the non-switched port, implying a near 100:1 or 20 dB switch isolation. In this case, a single AO device serves to form a minimum 1×2 FO switch where N=2. Thus, so far it has not been possible to form a very high optical isolation (e.g., >50 dB) switch using diffraction-based devices like AO devices even for the simple 1×2 switch configuration. The 2×2 switch is the highly sought after FO switch as many 2×2 switches can be combined to form large N×N switch matrices. It is also highly desirable to form high dynamic range (e.g., 50 dB) and high resolution (0.1 dB) FO attenuators working at high sub-microsecond domain speeds.
SUMMARY OF THE INVENTION
The present invention is directed to a resolution of the above described prior art deficiencies by providing both high speed FO 2×2 switches and FO attenuators with high isolation and dynamic ranges using beam deflection devices such as acousto-optics. Earlier, as shown in N. A. Riza, “Acousto-optic device-based high-speed high-isolation photonic switching fabric for signal processing,”
Optics Letters
, Vol. 22, No. 13, July 1997 and N. A. Riza and J. Chen, “Ultrahigh—47-dB optical drop rejection multiwavelength add-drop filter using spatial filtering and dual bulk acousto-optic tunable filters,”
Optics Letters
, Vol. 23, No. 12, June 1998, it is possible to realize a high isolation 1×2 switching configuration by using two AO devices in a cascade with the AO devices operating in an orthogonal drive setting. In other words, only one AO device is driven at any instant. These were 1×2 switch structures and not the highly desired 2×2 structures. In the present invention, this 1×2 structure is modified in a unique way using an image inversion concept to realize the 2×2 switch. For example, a Dove prism is used as the image inversion device to realize the invention. Previously, the Dove prism has been deployed in AO signal processing systems such as in N. A. Riza, “In-line interferometric time integrating acoustooptic correlator,”
Applied Optics
, Vol. 33, No. 14, pp. 3060-3069, May 10, 1994.
This inventive 2×2 FO switch structure is based on an image inversion scheme coupled with orthogonal drive beam deflection devices such as AO devices. The unique spatial filtering techniques inherent in the switch design make it a high isolation structure that can also form FO attenuators and frequency shifters. The structure is reversible with analog optical gain control and fine beam alignment controls. High power optical beams can also be used in the bulk crystal-based deflector units deployed to make the switch/attenuator modules.
REFERENCES:
patent: 5450224 (1995-09-01), Johansson
patent: 6134358 (2000-10-01), Wu et al.
W.E. Stephens, P.C. Huang, T.C. Banwell, L.A. Reith, S.S. Cheng, Demonstration of a photonic space switch utilizing acousto-optic elements, Optical Engineering, Mar. 1990, Vo. 29, No. 3, pp. 183-190.*
Dan O. Harris, A. Vanderlugt, Acousto-optic photonic switch, Optics Letters, Nov. 1, 1989, vol. 14, No. 21, pp. 1177-1179.*
Dan O. Harris, Multichannel
Beusse James H.
Light Bytes, Inc.
Schwartz Jordan M.
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