Patent ID: 9525491
Filing Date: 2016-12-20
CPC Classification: H04B

Claim Text:
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.