Direct optical n-state phase shift keying

Abstract

A unique optical encoder is employed that utilizes an optical phase modulator, in which an arbitrary phase shift can be realized. The phase modulator is driven by an electrical signal, where the voltage amplitude is proportional to a desired arbitrary phase shift. However, any amplitude noise or poor rise and fall times of the driving voltage translates directly into phase errors. These problems are eliminated by employing a digital phase switch. One encoder, in accordance with the invention, employs an optical phase modulator that can switch the optical phase in a binary manner, wherein the two phase states of the modulator can be chosen to differ by any desired arbitrary angle depending on the splitting ratio of the optical signal to be modulated.

Description

technical field

[0001] The invention relates to an optical transmission system, in particular to phase shift keying of optical signals. Background technique

[0002] Recently, there has been growing interest in alternative optical modulation formats for use in high bit rate optical communication systems. To this end, optical differential phase shift keying (ODPSK) is a promising candidate to increase system capacity, range, and spectral efficiency. However, until now, only Optical Differential Binary Phase Shift Keying (ODBPSK) and Optical Differential Quadrature Phase Shift Keying (ODQPSK) have successfully demonstrated higher bit rates, where Shift keying (ODBPSK) in the titled "2.5Tb / s (64×42.7Gb / s) transmission over 40×100km NZDSF using RZ-DPSK format and full Raman Gb / s) Transmission Over 40×100km NZDSF Using RZ-DPSKFormat and All-Raman-Amplified Spans)", by A.H.Gnauk et al., OFC 2002 is described in the article, while Optical Differential Quadrature Phase Shift Keyi...

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