Optical modulator and method of encoding communications traffic in a multilevel modulation format

Patent metadata

Field	Value
Publication number	US-9525491-B2
Application number	US-201114352681-A
Country	US
Kind code	B2
Filing date	Oct 19, 2011
Priority date	Oct 19, 2011
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

An optical modulator is described, comprising—an optical splitter to receive an optical carrier signal and split it into sub-signals; modulation assemblies, each comprising a binary optical modulator to apply a binary phase shift keyed (BPSK) modulation to a respective optical sub-signal to form a BPSK modulated optical sub-signal. Modulation assemblies comprise a phase-shifter, each to apply a phase shift to the respective BPSK modulated optical sub-signal in dependence on a pre-selected modulation format; an encoding apparatus to receive communications traffic to map into symbols, and to generate and transmit a respective drive signal to the optical modulator of a modulation assembly, each drive signal to cause the optical modulator to apply said BPSK modulation, to encode the symbols onto the respective optical carrier sub-signal; and a combiner to receive each BPSK modulated optical sub-signal to form an output optical signal having said multilevel modulation format.

First claim

The invention claimed is:

1. An optical modulator comprising:
an optical splitter arranged to receive an optical carrier signal and arranged to split power of the optical carrier signal into a plurality of optical carrier sub-signals;
a plurality of modulation assemblies each arranged to receive a respective one of said optical carrier sub-signals, wherein each modulation assembly comprises a binary optical modulator arranged to receive the respective optical carrier sub-signal and arranged to apply a binary phase shift keyed (BPSK) modulation to said optical carrier sub-signal to form a respective BPSK modulated optical sub-signal for use in mapping a pair of symbols symmetric about an origin on a symbol constellation, and wherein at least some of the plurality of the modulation assemblies comprise a phase-shifter, each said phase-shifter being arranged to receive the respective BPSK modulated optical sub-signal and being arranged to apply a respective phase shift to the respective BPSK modulated optical sub-signal in dependence on a pre-selected multilevel modulation format to generate a phase shifted BPSK modulated optical sub-signal, wherein two of the modulation assemblies are utilized when the pre-selected multilevel modulation format is quadrature PSK (QPSK) and four of the modulation assemblies are utilized when the pre-selected multilevel modulation format is 8-PSK;
an encoding apparatus arranged to receive communications traffic bits to be transmitted and arranged to map each communications traffic bit into a respective symbol of the symbol constellation based on the multilevel modulation format, the encoding apparatus being arranged to generate and transmit a respective drive signal to the binary optical modulator of a respective one of the modulation assemblies, each drive signal being arranged to cause a respective binary optical modulator to apply said BPSK modulation to thereby encode the respective pair of symbols of the symbol constellation onto the respective optical carrier sub-signal, and wherein the respective phase shift, where applied, causes the respective pair of symbols to be phase-positioned about the origin so as to have different phase locations from other symbols for mapping on the symbol constellation;
an output; and
a combiner arranged to receive outputs from the respective modulation assemblies and arranged to combine the outputs from the respective modulation assemblies to generate an output optical signal at the output.

2. The optical modulator as claimed in claim 1 , wherein the optical modulator further comprises a modulation format controller arranged to select the pre-selected multilevel modulation format from a set of multilevel modulation formats and to select a number of modulation assemblies from the plurality of modulation assemblies for operational use based on the pre-selected multilevel modulation format.

3. The optical modulator as claimed in claim 1 , wherein the plurality of modulation assemblies has at least one modulation assembly not containing a phase-shifter.

4. The optical modulator as claimed in claim 1 , wherein each phase-shifter comprises a variable phase-shifter and the optical modulator further comprises a phase shift controller arranged to generate and transmit a respective phase shift control signal to each variable phase-shifter, each phase shift control signal being arranged to cause a respective variable phase-shifter to be arranged to apply a respective phase shift in dependence on the pre-selected multilevel modulation format.

5. The optical modulator as claimed in claim 1 , wherein one or more of the modulation assemblies further comprise a gain element arranged to apply one of a positive gain and a negative gain to the respective BPSK modulated optical sub-signal to respectively amplitude position symbols for mapping on the symbol constellation.

6. The optical modulator as claimed in claim 1 , wherein each modulation assembly further comprises a variable gain element arranged to apply one of a positive gain, a negative gain and zero gain to the respective BPSK modulated optical sub-signal to respectively amplitude position symbols for mapping on the symbol constellation, and wherein the optical modulator further comprises a gain controller arranged to generate and transmit a respective gain control signal to each variable gain element, each gain control signal being arranged to cause a respective variable gain element to be arranged to apply a respective gain in dependence on the pre-selected multilevel modulation format.

7. The optical modulator as claimed in claim 1 , wherein the pre-selected multilevel modulation format has an even number of symbols and the encoding apparatus is arranged to receive the communications traffic bits and the encoding apparatus is arranged to map each communications traffic bit into a corresponding index number pair, b, m, where b is indicative of a binary drive signal to be provided to the binary optical modulator of the respective modulation assembly, m.

8. A method of encoding communications traffic bits onto an optical carrier signal in a multilevel modulation format, the method comprising:
receiving an optical carrier signal and splitting power of the optical carrier signal into a plurality of optical carrier sub-signals;
receiving communications traffic bits to be transmitted and mapping each communications traffic bit on to a symbol constellation based on a pre-selected multilevel modulation format;
encoding a respective pair of symbols symmetric out an origin of the symbol constellation onto a respective optical carrier sub-signal by applying a binary phase shift keyed (BPSK) modulation to the respective optical carrier sub-signal to form a respective BPSK modulated optical sub-signal;
applying a respective phase shift to at least some of the BPSK modulated optical sub-signals in dependence on the multilevel modulation format to generate a respective phase shifted BPSK modulated optical sub-signal, wherein the respective phase shift, where applied, causes the respective pair of symbols to be phase-positioned about the origin so as to have different phase locations from other symbols for mapping on the symbol constellation; and
combining each phase shifted BPSK modulated optical sub-signal and non-phase shifted BPSK modulated optical sub-signal, at a common output to thereby form an output optical signal, wherein two of the optical carrier sub-signals are utilized when the pre-selected multilevel modulation format is quadrature PSK (QPSK) and four of the optical carrier sub-signals are utilized when the pre-selected multilevel modulation format is 8-PSK.

9. The method as claimed in claim 8 , wherein the method comprises selecting the pre-selected multilevel modulation format from a set of multilevel modulation formats and to select a number of BPSK modulation stages for operational use based on the pre-selected multilevel modulation format.

10. The method as claimed in claim 8 , wherein for the BPSK modulated optical sub-signals, at least one BPSK modulated optical sub-signal is not subjected to applying the phase shift.

11. The method as claimed in claim 8 , wherein one of a positive gain and a negative gain is applied to at least one of the BPSK modulated optical sub-signals to respectively amplitude position symbols for mapping on the symbol constellation.

12. The method as claimed in claim 8 , wherein a respective gain is applied to each BPSK modulated optical sub-signal in dependence on the pre-selected multilevel modulation format, the gain being one of a positive gain, a negative gain and zero gain to respectively amplitude position symbols for mapping on the symbol conste

Assignees

• Cavaliere Fabio
• ERICSSON TELEFON AB L M (publ)

Inventors

• Cavaliere Fabio

Classifications

• H04B10/5053

  using a parallel, i.e. shunt, combination of modulators · CPC title

• H04B10/5561 Primary

  Digital phase modulation · CPC title