PADERBORN, Germany – On 30 June 2006, the Univ. Paderborn in Germany and CeLight Israel announce the worldwide first realtime synchronous optical quadrature phase shift keying data transmission with standard lasers. This breakthrough was achieved in the consortium "Key Components for Synchronous Optical Quadrature Phase Shift Keying Transmission" funded by the European Commission. The innovative "synQPSK" modulation scheme can quadruple optical fiber capacity when combined with additional polarization division multiplex, and allows for a purely electronic equalization of fiber chromatic and polarization mode dispersions.
Using an integrated-optical 90° hybrid and a local laser, a coherent optical receiver was constructed, where the received optical QPSK signal is down-converted to the electrical domain in phase and in quadrature. After analog-to-digital conversion a digital signal processor recovers the carrier in realtime and demodulates data. It closely tracks even large amounts of phase noise introduced by the utilized standard distributed-feedback lasers with a sum linewidth of 4 MHz. At a line rate of 400 Mbaud, corresponding to 800 Mb/s, the achieved bit error ratio is within the threshold of a state-of-the-art forward error correction scheme (FEC). These findings have just been reported at the Coherent Optical Technologies and Applications meeting of the Optical Society of America.
Most recently, the researchers in Paderborn have doubled the data rate, thereby significantly improving the bit error ratio. Further benefits are expected from the planned incorporation of QPSK modulators from Photline, France, balanced photoreceivers from the Univ. Duisburg-Essen, Germany, miniaturized 90° hybrid front ends and advanced microelectronic circuits. But even today’s results allow to predict unproblematic operation with an in-band or even with no FEC at 10 Gbaud (4 x 10 Gb/s per wavelength with polarization multiplex).
The partners believe that their synQPSK technology will allow for an evolutionary, graceful growth of optical transmission capacity in an economically sensitive environment.