Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2001-03-01
2003-07-22
Feild, Lynn D. (Department: 2839)
Optical waveguides
With optical coupler
Plural
Reexamination Certificate
active
06597830
ABSTRACT:
TECHNICAL FIELD
The invention relates to a waveguide-type optical matrix switch which performs the switching and control operation of optical paths using optical waveguides provided on a substrate. The invention also relates to an optical ADM (optical add-drop multiplexer) having the function of performing optical-signal through, drop, and add.
BACKGROUND ART
In recent years, the advance of practical use of an optical communication system has led to a demand for an optical communication system having higher capacity and higher performance. In particular, in order to more stably and more efficiently operate many optical transmission lines, it has become necessary to properly recombine optical transmission paths upon occurrence of troubles of transmission paths and according to traffic. Further, also within an optical transmission apparatus, the recombination of optical paths within the apparatus upon occurrence of troubles of the optical device or the like has become necessary.
In order to cope with these demands, for example, there is a report on the use of an optical switch using a diffusion-type optical waveguide comprising an electrooptic crystal, typified by lithium niobate (LN), which has been mainly doped with titanium or the like through the surface of a substrate by thermal diffusion.
This optical switch is reported in “Daikibo Doharokata Hikari Matorikkusu Suicchi (Large Waveguide Optical Matrix Switch)” [Hideaki Okayama and Masato Kawahara, Singakugiho], TECHNICAL REPORT OF TEICE SSE 94-214, OCS 94-95 (1995-02), PP 67-72, or “Studies on a 128-Line Photonic Space-Division Switching Network Using LiNbO
3
Switch Matrices and Optical Amplifiers”, (C. Burke, M. Fujiwara, M. Yamaguchi, H. Nishimoto, and H. Honmon, OSA Proceeding on photonic switching, 1991, Vol. 8, pp 2-6).
An optical matrix switch formed by integrating this type of optical switches is reported in “Polarization Independent-DC Drift Free Ti:LiNbO
3
4×4 Matrix Optical Switch” [Y. Nakabayashi, J. Ushioda, M. Kitamura, 2nd Optoelectronics Communications Conference (OECC'97) Technical Digest, July 1997, Seoul, KOREA, 9C5-3, pp 202-203].
There is also a report on an optical matrix switch which utilizes, for example, a change in refractive index of optical waveguides by thermooptic effect using a heater mounted on a part of quartz- or polymer-based optical waveguides. This optical switch is reported in “DC-drift Free Polarization independent Ti:LiNbO
3
8×8 Optical Matrix Switch” [Y. Nakabayashi, M. Kitamura, T. Sawano, 22nd European Conference on Optical Communication-ECOC'96, Oslo, ThD. 2.4.4, 157-4.160].
Here a single device having an optical path-switching function is called an “optical switch,” and a device or optical circuit, which can realize the switching of paths of a larger number of inputs and a larger number of outputs through a combination of a plurality of optical switches, is called an “optical matrix switch.” The way of combining optical switches within the optical matrix switch is called a “network.”
In the optical matrix switch used in the switching of the conventional transmission path, reducing the level of crosstalk to approximately not more than −40 dB is required from the viewpoint of ensuring the transmission quality.
Also in the case where an optical matrix switch is used in the switching of path within the apparatus, minimizing the level of the crosstalk is desired. For most of the conventional optical switches reported up to now, however, meeting this requirement for low crosstalk level is difficult due to the performance of the optical switch per se.
Further, for example, in a multi-wavelength communication system using EDFA (erbium doped fiber amplifier), it is known that the optical power varies from a channel for one wavelength to a channel for another wavelength, for example, due to the dependency of the optical amplification factor of EDFA upon the wavelength and that this limits the transmission distance. Therefore, in a relay apparatus, for example, in a multi-wavelength communication system using EDFA, the function of eliminating the uneven optical power between the channels for respective wavelengths is necessary.
The optical matrix switch for the recombining light transmission paths is generally incorporated into a relay apparatus in a multi-wavelength communication system. For this reason, the optical matrix switch per se preferably has the function of, controlling the power of each optical channel from the viewpoint of reducing the size of the relay apparatus.
Accordingly, it is an object of the invention to solve the above problems of the prior art and to provide an optical matrix switch which can reduce crosstalk between channels and can, if necessary, control the power of optical channels.
FIG. 7
is a diagram showing the construction of a conventional optical ADM.
This optical ADM is provided along an optical transmission path having a plurality of channels (for example, 32 channels). An optical amplifier (AMP)
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is connected on the upstream side of the optical ADM, and a demultiplexer
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for demultiplexing a multiplexed optical signal to different wavelengths is connected to the optical amplifier
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. 1×2 optical switches
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having an identical construction are connected respectively to output lines of the demultiplexer
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. For the optical switch
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, one of the output terminals is a drop terminal, while one of input terminals in a 2×1 optical switch
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is connected to the other output terminal of the optical switch
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. The other input terminal in the 2×1 optical switch
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is used as an add terminal. An attenuator (ATT)
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is connected to the output terminal of the 2×1 optical switch
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, and each input terminal of a multiplexer
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is connected to each output terminal of the attenuator
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in a 1:1 relationship. Further, an optical amplifier (AMP)
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, which amplifies the multiplexed optical signal and output to the downstream side, is connected to the output terminal of the multiplexer
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. Here optical devices, such as optical switches
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,
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, are connected to each other through an optical fiber. A photodetector (PD)
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is coupled to the optical fiber for connecting the attenuator
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to the multiplexer
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. An automatic level controller (ALC)
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for controlling the attenuator
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is connected to the photodetector
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.
The optical ADM shown in
FIG. 7
is provided at a point C which is along an optical transmission line provided between points A and B distant from each other. A multiplexed optical signal from the point A is amplified in the optical amplifier to
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, and is then demultiplexed in the demultiplexer
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. According to the switching by the 1×2 optical switch
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, the demultiplexed signals are dropped at the point C (that is, is withdrawn to the outside of the system) or sent to the 2×1 optical switch
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for transmission to the point B without drop. When the demultiplexed signals have been sent to the 2×1 optical switch
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, they are then sent to the attenuator
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through the 2×1 optical switch
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, where the control of the attenuation for output level matching is performed. The control of the attenuation in the attenuator
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is performed by controlling the gain or light transmission level of the attenuator
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through the automatic level controller
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based on a photoelectric conversion signal by the photodetector
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. The optical signals from each of the attenuators
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are multiplexed in the multiplexer
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, and the multiplexed light is amplified in the optical amplifier
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and sent toward the point B. When the 2×1 optical switch
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is switched to the add side, optical information from the point C is input into the 2×1 optical switch
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and is added to the multiplexed, optical signal from the point A. This type of ADM is described in detail, for example, in Masaki Fukui et al., “1580 mn band all-optic
Nakabayashi Yukinobu
Yokoyama Jun
Feild Lynn D.
Le Thanh-Tam
McGinn & Gibb PLLC
NEC Corporation
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