Wavelength division multiplex bothway optical communication system
First Claim
1. A wavelength division multiplex bothway optical communication system comprising:
- an optical communication cable;
a first terminal station; and
a second terminal station coupled with said first terminal station through said optical communication cable,each first and second terminal station includinga) a transmitter having a laser for converting a transmission electrical signal to an optical signal,b) an optical receiver for receiving said optical signal which is subject to conversion to said electrical signal, andc) a two-beam interference type first filter having a zero phase input port and a pi phase input port coupled with an output of said laser and an input of said optical receiver, respectively, said first filter having periodical characteristics of passband and attenuation band for wavelengths in a communication wavelength band,d) a zero phase output port and a pi phase output port with one port being coupled with said optical communication line and the other port being free standing, and said optical communication cable being coupled with the zero phase output port of one terminal station and the pi phase output port of the other terminal station,e) wavelength control means for controlling an oscillation wavelength of said laser so that said oscillation wavelength coincides with a center of a passband of said first filter, said wavelength control means including1) monitor means for monitoring a wavelength of an output of the laser,2) a comparator for comparing a strength of an output of said monitor means with a predetermined threshold level to provide an output, and3) control means for adjusting said oscillation wavelength of the laser based upon the output of said comparator so that said oscillation wavelength coincides with the passband of said first filter,wherein a wavelength band of the laser in the first terminal station being essentially a same as the wavelength of the laser in the second terminal station in said communication wavelength band.
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Accused Products
Abstract
Bothway optical communication is carried out through a wavelength division multiplex system between two terminal stations (11a, 12a), each having a two-beam interference type filter (15) coupled with an optical cable (10) for multiplexing and/or de-multiplexing transmitted light and received light. The filter (15) has passbands and attenuation bands having periodic characteristics for the wavelength in the communication wavelength band. The wavelength of the transmitted light is essentially the same as the wavelength of the received light in each terminal station, with a small offset of the two wavelengths less than 5 nm. The oscillation wavelength of the laser (21) for transmission is adjusted so that it coincides with the passband of the filter, which doubles as a reference wavelength of the oscillation wavelength of the laser. Preferably, the two-beam interference type filter (15) is a Mach Zehnder type asymmetrical interferometer having a pair of directional couplers (F1, F2) connected to each other through a pair of optical fibers (f1, f2) so that the period of the passbands and/or the attenuation bands of the filter (15) is adjustable.
38 Citations
10 Claims
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1. A wavelength division multiplex bothway optical communication system comprising:
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an optical communication cable; a first terminal station; and a second terminal station coupled with said first terminal station through said optical communication cable, each first and second terminal station including a) a transmitter having a laser for converting a transmission electrical signal to an optical signal, b) an optical receiver for receiving said optical signal which is subject to conversion to said electrical signal, and c) a two-beam interference type first filter having a zero phase input port and a pi phase input port coupled with an output of said laser and an input of said optical receiver, respectively, said first filter having periodical characteristics of passband and attenuation band for wavelengths in a communication wavelength band, d) a zero phase output port and a pi phase output port with one port being coupled with said optical communication line and the other port being free standing, and said optical communication cable being coupled with the zero phase output port of one terminal station and the pi phase output port of the other terminal station, e) wavelength control means for controlling an oscillation wavelength of said laser so that said oscillation wavelength coincides with a center of a passband of said first filter, said wavelength control means including 1) monitor means for monitoring a wavelength of an output of the laser, 2) a comparator for comparing a strength of an output of said monitor means with a predetermined threshold level to provide an output, and 3) control means for adjusting said oscillation wavelength of the laser based upon the output of said comparator so that said oscillation wavelength coincides with the passband of said first filter, wherein a wavelength band of the laser in the first terminal station being essentially a same as the wavelength of the laser in the second terminal station in said communication wavelength band. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification
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- Resources
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Current AssigneeNippon Telegraph and Telephone Corporation
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Original AssigneeNippon Telegraph and Telephone Corporation
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InventorsTsuchiya, Toshiyuki, Kobayashi, Ikutaro, Tokura, Nobuyuki
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Primary Examiner(s)Moore, David K.
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Assistant Examiner(s)NEGASH, KINFE MICHAEL
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Application NumberUS08/181,089Time in Patent Office600 DaysField of Search359/110, 359/132, 359/113-114, 359/124, 359/127, 359/143, 359/152, 359/153, 359/161, 359/162, 359/177, 359/179, 359/187, 385/24US Class Current398/42CPC Class CodesH04J 14/02 Wavelength-division multipl...
