US 7,116,917 B2 · Optical transmitter and optical transmission system

Abstract

The present invention suppresses to a minimum the degradation of the transmission quality caused by chromatic dispersion characteristic of an optical transmission medium, and the interplay between the chromatic dispersion and non-linear optical effects in dense WDM transport systems. A baseband input data signal is pre-coded in advance by a pre-coding unit, phase modulation is carried out using a pre-coded signal by the optical phase modulating unit, and the phase modulated optical signal is converted to an RZ intensity modulated signal by the optical filter unit that performs phase-shift-keying to amplitude-shift-keying conversion. For example, an optical phase modulating unit generates an encoded DPSK phase modulated signal using a differential phase shirt keying (DPSK) format, and a phase modulated signal is converted to an RZ intensity modulated signal by the optical filter unit disposed downstream of the optical phase modulating unit.

Claims24

Dependent claims

An optical transmitter comprising:

a light source which is a single mode longitudinal light source;
a pre-coding device that receives an NRZ signal and generates a pre-coded NRZ signal or a differential pre-coded NRZ signal whose logic inverts each time a mark bit is input;
an optical phase modulating device that uses a Mach-Zehnder optical intensity modulator driven by either the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device, and carries out optical phase modulation of the optical phase of a single longitudinal mode optical signal from the light source using the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the-coding device and outputs an RZ optical phase modulated signal in which a plurality of duobinary optical signal components are included in an optical RZ signal spectrum with carrier suppressions;
and
an optical filter device that converts the RZ optical-phase modulated signal generated by the optical phase modulating device to an RZ optical intensity modulated signal and outputs an RZ optical intensity modulated signal from an output terminal.

2 more elements

An optical transmitter further comprising:

a dual mode beat pulse light source that generates two longitudinal mode signals which synchronizes with a data signal and which have the mode spacing between the two longitudinal mode signals that is an integral multiple of the data line rate, and which mode signals are mode-locked with each other;
a pre-coding device that receives an NRZ signal, and carries out code conversion such that an RZ optical phase modulated signal output from the optical transmitter has a logic identical to the input NRZ signal;
and outputs a pre-coded NRZ signal or a differential pre-coded NRZ signal;
and
an optical phase modulating device in which is driven by either the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device, and carries out optical phase modulation of an optical pulse train generated by the dual mode beat pulse light source has undergone optical phase modulation by using a the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device, and outputs from an output terminal an RZ optical phase modulated signal in which a plurality of duobinary optical signal components are included in an optical RZ signal spectrum with carrier suppression.

2 more elements

An optical transmitter, further comprising a light source which is a dual mode beat pulse light source that generates two longitudinal mode signals which synchronize with a data signal and which have a mode spacing between the two longitudinal mode signals that is an integral multiple of the data line rate, and which are mode-locked with each other;

a pre-coding device that receives an NRZ signal and carries out code conversion such that an RZ optical phase modulated signal output from the optical transmitter has a logic identical to the input NRZ signal;
an optical phase modulating device which uses a Mach-Zehnder optical intensity modulator driven by either a pre-coded NRZ signal or a differential pre-coded NRZ signal generated by the pre-coding device, and carries out optical phase modulation of an optical pulse train generated by the dual mode beat pulse light source using the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device, and outputs an RZ optical phase modulated signal in which a plurality of optical duobinary signal components are included in an optical RZ signal spectrum with carrier suppression;
and
an optical filter device that converts an the RZ optical phase modulated signal generated by the optical phase modulating device to an RZ optical intensity modulated signal having either the identical logic or the inverted logic of the input NRZ signal, and outputs the RZ optical intensity modulated signal from an output terminal.

1 more element

An optical transmission system using a single channel or wavelength division multiplexing channels, comprising:

an optical transmitter that comprises:
a light source that is either a single longitudinal mode light source or a dual mode beat pulse light source;
a pre-coding device that receives an NRZ signal and generates a pre-coded NRZ signal or a differential pre-coded NRZ signal whose logic inverts each time a mark bit is input;
an optical phase modulating device that uses a Mach-Zehnder optical intensity modulator driven by either the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device and performs optical phase modulation on a signal from the light source using the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device and outputs an RZ optical phase modulated signal in which a plurality of optical duobinary signal components are included in an optical RZ signal spectrum and have a suppressed carrier component;
and an optical filter device that converts an the RZ optical phase modulated signal generated by the optical phase modulating device into an RZ optical intensity modulated signal and outputs the RZ optical intensity modulated signal from an output terminal;
an optical transmission medium that transmits the RZ optical intensity modulated signal output by the optical transmitter;
and
an optical receiver that receives the RZ optical intensity modulated signal output by the optical transmitter via the optical transmission medium, demodulates and directly detects the transmitted RZ optical intensity modulated signal to convert the RZ optical intensity modulated signal into a baseband electrical signal.

5 more elements

An optical transmission system using a single channel or wavelength division multiplexing channels, comprising:

an optical transmitter that is provided with:
a light source that is a single longitudinal-mode light source or a dual mode beat pulse light source;
a pre-coding device that receives an NRZ signal and carries out code conversion of the input NRZ signal such that the an RZ optical phase modulated signal output from the optical transmitter has a logic identical to the input NRZ signal and outputs a pre-coded NRZ signal or a differential pre-coded NRZ signal;
and an optical phase modulating device that is driven by either the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device and performs optical phase modulation on a signal from the light source using the pre-coded NRZ signal or the differential pre-coded NRZ signal generated by the pre-coding device;, and outputs an RZ optical phase modulated signal in which a plurality of optical duobinary signal components are included in an optical RZ signal spectrum and have a suppressed carrier component;
an optical transmission medium that transmits a the RZ optical phase modulated data signal with sinusoidal RZ optical intensity modulation that has been output by the optical transmitter;
an optical receiver that receives the RZ optical phase modulated signal output by the optical transmitter via the optical transmission medium, and after passing through an optical filter device that converts the RZ optical phase modulated signal to an RZ optical intensity modulated signal, demodulates and directly detects the RZ optical intensity modulated signal to convert to a baseband electrical signal.

3 more elements

Dependencies are inferred from the claim text.

Optical transmitter and optical transmission system

Life of this patent

Optical transmitter and optical transmission system

Life of this patent

Abstract

Claims24