Simultaneous Frequency Locking and Frequency Noise Reduction for Coherent Multichannel Applications

Careful control of the frequency spacing between the transmitters in coherent multichannel communications is important to avoid crosstalk. Earlier locking systems1,2 have been based on optical frequency references. We propose a new method that simultaneously establishes a fixed relative frequency separation between channels (determined electrically) and reduces the frequency noise associated with the phase noise of the individual lasers within the locking bandwidth in the submegahertz range. Our method thus allows direct frequency modulation of the locked lasers for Gbit/s use.