Optical communication system and optical transmitting device

• US 5,786,918 A
• Filed: 12/19/1995
• Issued: 07/28/1998
• Est. Priority Date: 09/08/1993
• Status: Expired due to Fees

• Current Assignee: KDDI Corporation
• Original Assignee: Kokusai Densin Denwa Kabushiki Kaisha
• Inventors: Tanaka, Hideaki, Suzuki, Masatoshi, Yamamoto, Shu, Edagawa, Noboru, Taga, Hidenori, Akiba, Shigeyuki
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US08/575,174
• Time in Patent Office: 952 Days
• Field of Search: 359/122, 359/135, 359/138, 359/156, 359/161, 359/173, 359/179, 359/181, 359/186, 359/188, 375/285, 375/292, 375/296, 375/297, 375/242, 375/289
• US Class Current: 398/98
• CPC Class Codes: H04B 10/25077 using soliton propagation
• CPC Class Codes: H04J 14/08 Time-division multiplex systems

Abstract

An optical communication system of a construction wherein the average wavelength dispersion value of the transmission optical fiber used, the optical output intensity of each optical amplifier repeater inserted in the transmission optical fiber and the widths of return-to-zero optical pulses transmitted over the transmission line are determined so as to compensate for the pulse compression effect by the nonlinear optical effect produced on the optical pulses by the pulse spreading effect by the wavelength dispersion effect. An optical multiplexer in the optical transmitting device time-division multiplexes the return-to-zero optical pulses, and the optical multiplexed signal is provided as an alternating-amplitude optical signal with the amplitudes of the return-to-zero optical pulses alternated.

Claims

1. An optical communication system, comprising:

an optical fiber transmission line having a required number of optical amplifier repeaters connected to a transmission optical fiber at required intervals,

an optical transmitting device for transmitting over said optical fiber transmission line optical multiplexed signals obtained by optical time-division multiplexing return-to-zero optical pulses having digital information, and

an optical receiving device having an optical demultiplexer for receiving and demultiplexing said optical multiplexed signals received from said optical fiber transmission line into original optical signals,

an average wavelength dispersion value of said transmission optical fiber, an optical output intensity of each of said optical amplifier repeaters and widths of said return-to-zero optical pulses being determined so as to compensate for a pulse compression effect by a nonlinear optical effect produced on said optical pulses and a pulse spreading effect by a wavelength dispersion effect produced on said optical pulses,

said optical transmitting device further comprising an optical multiplexer for time-division multiplexing said return-to-zero optical pulses into said optical multiplexed signals to have alternate amplitudes of said return-to-zero optical pulses;

said optical demultiplexer in said optical receiving device comprising an optical splitter for branching said optical multiplexed signals into a plurality of optical signals and an optical time-division demultiplexer for dividing each repetition rate of each branched optical signal to an original transmission rate by a rectangular synchronizing optical gate of a width about the same as the full time slot at a transmission rate after multiplexing.

2. An optical communication system according to claim 1,

in which said optical transmitting device comprises pulsed light source means for generating said return-to-zero optical pulses, an optical splitter for branching the output from said pulsed light source means into a plurality of outputs, a plurality of optical modulators for modulating the respective outputs from said optical splitter by modulation signals, and said optical multiplexer time-division multiplexing the outputs from said plurality of optical modulators on a bit-interleave basis;

and

said optical multiplexer comprising an optical coupler for combining the output from one of said optical modulators and a delayed at least one modulated output from at least one of said optical modulators, and means for alternating the amplitudes of said return-to-zero optical output pulses from said optical coupler.

3. An optical communication system according to claim 1,

in which, said optical transmitting device comprises, a single-wavelength laser for continuously emitting light of a fixed amplitude;

an optical splitter for branching the output from said single-wavelength laser into a plurality of outputs;

a plurality of optical modulators, each modulating one of said plurality of outputs by a modulating signal;

a plurality of optical soliton pulse train generating parts which receive the outputs from said optical modulators and generate return-to-zero optical pulses; and

said optical multiplexer for time-division multiplexing the outputs from said optical soliton pulse train generating parts on a bit-interleave basis; and

said optical multiplexer comprising an optical coupler whereby the modulated output from one of said plurality of optical modulators, which has passed through one of said plurality of optical soliton pulse train generating parts, is combined with a delayed at least one modulated output from at least one other of said plurality of optical modulators which has passed through the other of said plurality of optical soliton pulse generating parts; and

means for alternating the amplitudes of output return-to-zero optical pulses from said optical coupler.

4. An optical communication system according to claim 2 or 3, in which said means for alternating the amplitudes of said output return-to-zero optical pulses comprises a plurality of polarization controllers disposed before said optical coupler for said modulated output and said delayed modulated output, respectively;

and a polarizer provided after said optical coupler.

5. An optical communication system according to claim 2 or 3, in which said means for alternating the amplitudes of said output return-to-zero optical pulses comprises a plurality of attenuators disposed before said optical coupler for said modulated output and said delayed modulated output, respectively.

6. An optical transmitting device, for transmitting return-to-zero optical pulses having digital information after time-division multiplexing comprising:

pulsed light source means for generating said return-to-zero optical pulses;

an optical splitter for branching an output from said pulsed light source into a plurality of outputs;

a plurality of optical modulators for each modulating one of the outputs from said optical splitter by a modulating signal; and

an optical multiplexer for time-division multiplexing the outputs from said plurality of optical modulators on a bit-interleave basis;

said optical multiplexer having an optical coupler for combining the modulated output from one of said plurality of optical modulators and a delayed at least one modulated output from at least another one of said plurality of optical modulators.

8. An optical transmitting device according to claim 6 or 7, further comprising:

a plurality of polarization controllers disposed before said optical coupler for controlling polarities of said modulated output and said delayed modulated output, respectively, and

a polarizer disposed after said optical coupler to successively alternate amplitudes of said output return-to-zero optical pulses.

9. An optical transmitting device according to claim 6 or 7, further comprising:

a plurality of attenuators disposed before said optical coupler for said modulated output and said delayed modulated output, respectively, to successively alternate amplitudes of said return-to-zero optical pulses.

10. An optical transmitting device according to claim 6 or 7, further comprising:

a plurality of optical amplifiers disposed before said optical coupler for said modulated output and said delayed modulated output, respectively, to successively alternate amplitudes of said return-to-zero optical outputs.

11. An optical transmitting device according to claim 6 or 7, wherein means is disposed for changing at least one of the branching ratio of said optical splitter and a combining ratio of said optical coupler to successively alternate amplitudes of said return-to-zero optical pulses.

13. An optical transmitting device according to claim 6 or 7, wherein said optical coupler comprises a polarized beam splitter, and a plurality of polarization controllers are disposed before said polarized beam splitter for said modulated output and said delayed modulated output, respectively, to generate alternating-amplitude optical signals of perpendicularly intersecting states of polarization.

7. An optical transmitting device, for transmitting return-to-zero optical pulses having digital information after time-division multiplexing, comprising:

pulsed light source means for generating said return-to-zero optical pulses, said pulsed light source means comprising a single wavelength laser for continuously emitting light of a fixed amplitude;

an optical splitter for branching the output from said single-wavelength laser into a plurality of outputs;

a plurality of optical modulators for each modulating one of said plurality of outputs by a modulating signal;

a plurality of optical soliton pulse train generating parts which receives the outputs from said optical modulators and generate return-to-zero optical pulses; and

an optical multiplexer for time-division multiplexing the outputs from said optical soliton pulse train generating parts on a bit-interleave basis;

said optical multiplexer having an optical coupler whereby the modulated output from one of said plurality of optical modulators, which has passed through one of said plurality of optical soliton pulse train generating parts, is combined with a delayed at least one modulated output from at least one of said plurality of optical modulators.

12. An optical transmitting device according to 6 or 7, wherein said means for successively alternating the amplitudes of said return-to-zero optical pulses comprises an optical modulator which modulates the output from said optical coupler by a sinusoidal or rectangular wave of a speed one half the transmission rate after multiplexing.