Homodyne coherent detection of ASK and PSK signals performed by a subcarrier optical phase-locked loop

Optical transmission systems based on homodyne coherent detection of two amplitude-shift keying (2-ASK) and pilot carrier two phase-shift keying (2-PSK) signals have been implemented. ASK data has been transmitted at 2.5 Gb/s, while 2.5- and 10-Gb/s PSK systems have been tested. The proposed architecture is based on a new optical phase-locked loop founded on subcarrier modulation and leads to new compact integrated receivers and new transmission formats, thus opening new opportunities for future optical systems.