Optical waveguides – Accessories – Attenuator
Reexamination Certificate
1999-12-14
2001-08-28
Lee, John D. (Department: 2874)
Optical waveguides
Accessories
Attenuator
C385S005000, C385S010000, C385S037000
Reexamination Certificate
active
06282361
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a multi-channel variable optical attenuator suitable for the wavelength division multiplexing (WDM) system.
2. Description of Related Prior Art
In the WDM system, optical communications can be made in a large capacity and at a high speed by transmitting wavelength multiplexed light comprising a plurality of signal lights each having a different wavelength in a 1.55um band through an optical fiber accompanied by an optical amplifier. Even if each of signal lights output from a transmitting station is of the same optical level, their optical levels at the receiving station may be varied due to the gain slope of the optical amplifier or the transmission characteristics of the optical fiber. The variation among the optical levels of the signal lights causes an erroneous transmission. Accordingly, it is desirable that the optical levels of respective signal lights should be equalized.
Otsuka et al. has presented an optical de-mulitplexer and an variable optical attenuator which is individually provided for each of de-multiplexed signal lights in the Electronics Society Conference of IEICE (the Institute of Electronics, Information and Communication Engineers) 1997, B-10-101. In this optical attenuator, the attenuation amount of respective signal lights is controlled based on both of the incoming and the outgoing wavelength multiplexed light.
Nakata et al. has presented a variable optical attenuator comprising two polarizing plates, a Faraday rotator, a permanent magnet and an electromagnet in the same Conference of IEICE 1997 C-3-48. In this attenuator, the attenuation amount depends on the Faraday rotation angle controlled by the magnetic field. To use this attenuator in the WDM system and to equalize the optical levels of the signal lights, the same number of the attenuator as that of the signal lights are necessary.
Kawai et al. has presented in the same Conference 1997 B-10-61 that a variable optical attenuator provided with a Mach-Zender interferometer and a heating device to heat up one of paired waveguides of the Mach-Zender interferometer. In this attenuator, the attenuation is performed by varying the phase of the light transmitting in the heated waveguide. To use this type of attenuator in the WDM system, a plurality of attenuators are necessary, too.
In the conventional examples mentioned above, the same number of monitoring devices as that of the signal lights are needed to equalize the optical levels of respective signal lights because the individual attenuator is controlled by the corresponding monitoring device. Consequently, the volume of the equipment, which contains the multi-channel attenuator, will be large and the additive control circuitry will be complicated. Moreover, it will take a long time to equalize the optical levels of respective signal lights when such levels are varied signal to signal or fluctuate.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a multi-channel variable optical attenuator having a compact size and a simple structure, solving the above problems.
The multi-channel variable optical attenuator of the present invention is for wavelength multiplexed light which contains a plurality of signal lights and each of signal lights has a specific wavelength different from that of other signal lights. The multi-channel attenuator comprises a master control circuitry, a plurality of optical waveguides, a plurality of attenuation adjusting portions, and a control circuitry. The master control circuitry detects the optical levels of the wavelength multiplexed light and outputs a master control signal derived from the detected levels. The signal lights each having a different wavelength propagate through the corresponding waveguides. The attenuation adjusting portion, which is provided in the waveguide, attenuates the signal lights. The control circuitry, based on the master control signal output from the master control circuitry, controls the attenuation amount of the respective signal lights by a rate specific to the respective adjusting portions.
The optical attenuating portion may include a Mach-Zender interferometer that has a pair of optical waveguides and at least one of the paired optical waveguides is provided with a phase adjusting portion for varying a phase of light propagating therethrough.
It is favorable that the Mach-Zender interferometers provided in the respective waveguides have different configurations, and the control signal output from the control circuitry is single and commonly applied to the Mach-Zender interferometers so as to attenuate respective signal lights by the specific rate.
It is also possible that the Mach-Zender interferometers provided have the same configuration, and the control signal output from the control circuitry is different to respective phase adjusting portions so as to attenuate respective signal lights by the specific rate.
The phase adjusting portion may include a temperature varying device and the phase of light propagating through one of the paired waveguide where the temperature varying device is formed, is varied by temperature.
Further, the multi-channel variable optical attenuator of the present invention may contain an arrayed waveguide grating (AWG) de-multiplexer in a front side section. The wavelength multiplexed light is de-multiplexed in the AWG and the signal lights each having a different wavelength are conducted to the attenuator and attenuated by the amount specific to respective signal lights so as to equalize the optical level of respective signal lights.
The multi-channel variable optical attenuator of the present invention may contain the AWG multiplexer in the rear section. The signal lights are inputted to the AWG multiplexer, multiplexed in the AWG and the wavelength multiplexed light is output.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5812710 (1998-09-01), Sugaya
patent: 5881199 (1999-03-01), Li
patent: 5923450 (1999-07-01), Dugan et al.
patent: 5982960 (1999-11-01), Akiba et al.
patent: 6208441 (2001-03-01), Jones et al.
“Power Control in ADM Node Using High-Speed, Compact-Size Optical Spectrum Monitor”, by Otsuka et al., Electronics Society Conference of IEICE, 1997, B-10-101 (with English translation).
“Magneto Optical Variable Optical Attenuator”, by Nakada et al., Electronics Society Conference of IEICE, 1997, C-3-48 (with English translation).
“Variable Optical Attenuator Based on PLC Technology for Gain Control in WDM Linear-Repeater”, by Kawai et al., Electronics Society Conference of IEICE, 1997, B-10-61(with English translation).
Nakazato Koji
Nishimura Masayuki
Doan Jennifer
Lee John D.
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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