Patent ID: 7720392
Filing Date: 2010-05-18
Classification: G02F,H04B,H04L

Abstract:
1. A method for setting a driving voltage of a differential quadrature phase shift modulator which has a first Mach-Zehnder modulator capable of outputting first differential phase-shift modulated signal light by application of a first driving voltage signal forming a differential voltage signal based on first data and a second Mach-Zehnder modulator capable of outputting second differential phase-shift modulated signal light by application of a second driving voltage signal forming a differential voltage signal based on second data, and which outputs differential quadrature phase-shift modulated light by means of merging said first signal light and said second signal light, wherein driving voltage signals to be applied to said first and second Mach-Zehnder modulators in said differential quadrature phase-shift modulator are set, said method comprising: acquiring signal quality of said differential quadrature phase-shift modulated light output from said differential quadrature phase-shift modulator, said signal quality being deteriorated due to an extinction ratio of the differential quadrature phase shift modulator; and adjusting to lessen, in accordance with the signal quality acquired, an amplitude of one of said first and second driving voltage signals than an appropriate condition thereof, in which said first and second driving voltage signals are under control so as to maximize a power of said differential quadrature phase-shift modulated light.