Optimization of optical transmission capacity

Patent metadata

Field	Value
Publication number	US-9584260-B2
Application number	US-201414198867-A
Country	US
Kind code	B2
Filing date	Mar 6, 2014
Priority date	Mar 6, 2014
Publication date	Feb 28, 2017
Grant date	Feb 28, 2017

Abstract

A method for transmitting a coherent optical data signal includes receiving a data signal from an interface, and encoding the data signal with a forward error correcting (FEC) encoder according to a mix of modulation formats. The FEC encoder generates an FEC encoded signal which is used to generate modulation symbols according to the modulation formats. The FEC encoded signal of modulation symbols is spectrally shaped to generate a shaped signal, and pre-distorted before transmission. The shaped signal is pre-distorted by adding a predetermined amount of chromatic dispersion to generate a smoothed signal, and the smoothed signal is transmitted according to the modulation formats.

First claim

What is claimed is:

1. A method comprising:
receiving a data signal from an interface;
encoding and modulating the data signal with a Forward Error Correcting (FEC) encoder and according to a first modulation format and a second modulation format to generate an FEC encoded signal;
generating, from the FEC encoded signal, a first plurality of symbols according to the first modulation format and a second plurality of symbols according the second modulation format;
interleaving the first plurality of symbols with the second plurality of symbols across time and optical polarization, such that, during a first time period, at least one of the first plurality of symbols is transmitted with a first polarization and at least one of the second plurality of symbols is transmitted with a second polarization, and, during a second time period, at least one of the first plurality of symbols is transmitted with the second polarization and at least one of the second plurality of symbols is transmitted with the first polarization;
spectrally shaping the first and second plurality of symbols to generate, respectively, a first shaped signal and a second shaped signal;
pre-distorting the first and second shaped signals by adding a predetermined amount of chromatic dispersion to generate, respectively, a first smoothed signal and a second smoothed signal; and
optically transmitting the first and second smoothed signals.

2. The method of claim 1 , wherein the first and second modulation formats comprise Quadrature Amplitude Modulation (QAM) or Phase Shift Keying (PSK).

3. The method of claim 1 , wherein the first and second time periods are consecutive and repeat for a duration of transmission.

4. The method of claim 1 , wherein the first plurality of symbols and second plurality of symbols are interleaved with an unequal ratio.

5. An apparatus comprising:
an interface configured to receive a data signal;
at least one Forward Error Correcting (FEC) encoder configured to FEC encode and modulate the data signal according to a first modulation format and a second modulation format and generate first and second FEC encoded signals;
at least one symbol generator configured to generate from the first and second FEC encoded signals a first plurality of symbols according to the first modulation format and the second plurality of symbols encoded according the second modulation format;
an interleaver configured to interleave the first plurality of symbols with the second plurality of symbols across time and optical polarization, such that, during a first time period, at least one of the first plurality of symbols is transmitted with a first polarization and at least one of the second plurality of symbols is transmitted with a second polarization, and, during a second time period, at least one of the first plurality of symbols is transmitted with the second polarization and at least one of the second plurality of symbols is transmitted with the first polarization;
a pulse shaping filter configured to spectrally shape the interleaved first and second plurality of symbols and generate, respectively, a first shaped signal and a second shaped signal;
a pre-distortion filter configured to add a predetermined amount of chromatic dispersion to the first and second shaped signals and generate, respectively, a first smoothed signal and a second smoothed signal; and
an optical transmitter configured to transmit the first and second smoothed signals.

6. The apparatus of claim 5 , wherein the at least one FEC encoder comprises a quadrature amplitude modulation (QAM) encoder configured to encode the data signal with forward error correction compatible with QAM, and a phase shift keying (PSK) encoder configured to encode the data signal with forward error correction compatible with PSK, the QAM encoder generating a QAM FEC encoded signal and the PSK encoder generating a PSK FEC encoded signal.

7. The apparatus of claim 6 , wherein the at least one symbol generator comprises a QAM symbol generator and a PSK symbol generator, the QAM symbol generator configured to generate a plurality of QAM symbols from the QAM FEC encoded signal, and the PSK symbol generator configured to generate a plurality of PSK symbols from the PSK encoded signal.

8. The apparatus of claim 5 , wherein the pulse shaping filter is configured to generate a first polarized signal with at least one of the first or second pluralities of symbols, and generate a second polarized signal with at least another one of the plurality of symbols, and wherein the optical transmitter is configured to transmit the first polarized signal with the first polarization, and transmit the second polarized signal with the second polarization.

9. The apparatus of claim 5 , wherein the interleaver is configured to interleave the first plurality of symbols and the second plurality of symbols with an unequal ratio.

10. An apparatus comprising:
an interface configured to receive a first data signal and a second data signal;
a first Forward Error Correcting (FEC) encoder configured to FEC encode and modulate the first data signal according to a first modulation format and generate a first FEC encoded signal;
a second FEC encoder configured to FEC encode and modulate the second data signal according to a second modulation format and generate a second FEC encoded signal;
a first symbol generator configured to generate a first plurality of symbols from the first FEC encoded signal according to the first modulation format;
a second symbol generator configured to generate a second plurality of symbols from the second FEC encoded signal according to the second modulation format;
a symbol interleaver configured to interleave the first plurality of symbols with the second plurality of symbols across time and optical polarization, such that, during a first time period, at least one of the first plurality of symbols is transmitted with a first polarization and at least one of the second plurality of symbols is transmitted with a second polarization, and, during a second time period, at least one of the first plurality of symbols is transmitted with the second polarization and at least one of the second plurality of symbols is transmitted with the first polarization;
an optical transmitter configured to transmit the interleaved first plurality of symbols and second plurality of symbols.

11. The apparatus of claim 10 , wherein the first encoder is configured to encode only according to the first modulation format, the second encoder is configured to encode only according to the second modulation format, the first symbol generator is configured to generate symbols only according to the first modulation format, and the second symbol generator is configured to generate symbols only according to the second modulation format.

12. A method comprising:
receiving a first data signal and a second data signal;
encoding and modulating the first data signal with a first Forward Error Correcting (FEC) encoder according to a first modulation format to generate a first FEC encoded signal;
encoding and modulating the second data signal with a second FEC encoder according to a second modulation format to generate a second FEC encoded signal;
generating a first plurality of symbols from the first FEC encoded signal according to the first modulation format;
generating a second plurality of symbols from the second FEC encoded signal according to the second modulation format;
interleaving the first plurality of symbols with the second plurality of symbols across time and optical polarization, such that, during a first time period, at least one of the first plurality of symbols is transmitted wit

Assignees

• Cisco Tech Inc

Inventors

• Fludger Chris
• Kupfer Theodor
• Forghieri Fabrizio
• Poggiolini Pierluigi
• Bosco Gabriella
• Carena Andrea
• Curri Vittorio

Classifications

• H04B10/5161

  Combination of different modulation schemes · CPC title

• H04B10/2569

  due to polarisation mode dispersion [PMD] · CPC title

• H04B10/61

  Coherent receivers · CPC title

• H04J14/06

  Polarisation multiplex systems · CPC title

• H04B10/25137 Primary

  using pulse shaping at the transmitter, e.g. pre-chirping or dispersion supported transmission [DST] · CPC title