Technology overview

Synchronous quadrature phase shift keying (QPSK) transmission combined with return-to-zero (RZ) coding and polarization division multiplex is an extremely attractive modulation format for metropolitan area and long haul fiber communication. Compared to standard intensity modulation the line rate is 4 times lower, the needed number of photons per bit less than half as high, the tolerance to chromatic dispersion about 8 times better, the tolerance to polarization mode dispersion about 3 times better, and the tolerance against fiber nonlinearities, in particular cross phase modulation, is excellent. Moreover, all linear optical distortions (polarization transformations, polarization mode dispersion, chromatic dispersion) can be equalized without losses in the electrical domain. Distinct advantages exist also over all other modulation formats, including duobinary, DPSK and DQPSK. So far, synchronous QPSK has not been realized because the necessary components were not vailable, for example lasers with linewidths in the lower kHz region. For the implementation of synchronous RZ-QPSK transmission with polarization division multiplex this project aims at the realization of all necessary components which can not be found on the market: LiNbO₃ QPSK modulators in the transmitter, LiNbO₃ optical 90° hybrids, InP balanced photoreceivers - reliably co-packaged with the 90° hybrids - and SiGe/CMOS integrated electronic circuits for signal conditioning in the receiver. Standard distributed-feedback (DFB) lasers are tolerable for signal and local oscillator lasers due to a novel carrier recovery concept that requires no phase-locked loop. It is implemented in the receiver by analog-to-digital conversion and subsequent CMOS signal processing. The symbol rate is 10 Gsymbols/s which amounts to 40 Gbit/s, plus FEC overhead. All components and contributions shall be validated in a synchronous QPSK polarization division multiplex transmission testbed.

 

 

Imprint | Univ. Paderborn | CeLight | Photline | IPAG | Univ. Duisburg-Essen