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Wavelength locked loops for optical communication networks

Optical communication systems based on dense wavelength division multiplexing (DWDM) would benefit from the ability to adjust the operating wavelength of a laser transmitter. Previous attempts, including thermal adjustment, etalon based wavelength locking, and various types of optical frequency and phase locked loops such as the Pound-Drever-Hall technique suffer from weaknesses including sensitivity to noise at their zero crossings and non-signed error signals which require calibrated differential receivers. In this paper, we describe a new servocontrol circuit technique for wavelength locked feedback loops which overcome many of these concerns. Experimental results are presented illustrating this technique, in which a Fabry-Perot laser is locked to a commercially available DWDM filter within an accuracy of about 3 nm without the need fort thermoelectric cooling.