Patent ID: 8437645
Filing Date: 2013-05-07
Classification: H04B

Abstract:
1. An optical communication system comprising: at least a transmitter apt to emit a differential phase shift keying (DPSK) optical signal having a bit-rate equal to R, the transmitter comprising a laser source, an optical modulator for phase modulating an output of the laser source so as to generate the DPSK optical signal phase-modulated among two phase levels differing by 180° and a differential precoder electrically connected to the optical modulator for driving the optical modulator; at least a receiving system for receiving the differential phase shift keying optical signal; wherein the receiving system comprises a coherent optical receiving device to coherently receive the propagated DPSK optical signal and to emit at least one electrical signal related to the received DPSK optical signal, and wherein the receiving system further comprises: a local oscillator apt to emit an optical field having a phase; an optical hybrid apt to mix the optical field and the received DPSK optical signal, the optical hybrid has at least a pair of output ports for respectively outputting either two in phase components or quadrature components of the received DPSK optical signal with respect to the phase of the optical field of the local oscillator; at least one photodetector connected to at least one output port of the above pair of output ports for detecting at least one of the either two in-phase components or two quadrature components and for generating a first electrical signal (I) directly proportional to the at least one of the either in-phase or quadrature components; and an optical phase locked loop (OPLL) configured for locking the phase of the optical field of the local oscillator to a phase of the received DPSK optical signal and wherein the at least one electrical signal consists of the first electrical signal (I), the OPLL comprises a multiplier connected to an output of each of the at least one and a further photodetector for multiplying the above first and second electrical signal in order to obtain a control signal for controlling a frequency of the optical field of the local oscillator; at least one electrical filter for filtering the at least one electrical signal and having −3 dB double-side bandwidth greater than or equal to 0.44 R and lower than or equal to 0.68 R, and at least one squarer for squaring the at least one filtered electrical signal; and, an optical link optically connecting the transmitter and the receiving system for transmitting the DPSK optical signal from the transmitter to the receiving system.