Abstract

Extended-cavity diode lasers with diffraction gratings have been well developed for atomic spectroscopy applications. Commercially available devices can be tuned over several nanometers without any mode hops allowing high resolution spectroscopy. Tuning over large intervals usually involves motors for moving the grating. This well controlled movement is necessarily slow. Smaller scans, over several tens of GHz, can be achieved via piezoelectric mounts and can therefore be cycled at rates as high as several hundreds of Hz. However such fast scans suffer from hysteresis and lack of reproducibility. Spectroscopic applications usually do not ask for fast scans. Still extended cavity diode lasers can prove useful in other fields. For instance the growing field of optical processing of radio-frequency signals deals with bandwidths of several tens of GHz which must be processed with MHz resolutions. In these applications the generation of microsecond to millisecond long pulses, chirped over more than 10 GHz is demanded. Together with such high chirp rates, high linearity and reproducibility of the chirp is necessary. For such specifications an electro-optic crystal as the tuning element in the extended cavity is an attractive solution. In the existing devices, the electro-optic crystal can tune nothing but the cavity length [1,2]. Hence the tuning range is limited to one free spectral range of the extended cavity, before a mode hop occurs, and cannot therefore exceeds a few GHz. In addition increase of this range means shortening of the extended cavity length which rapidly increases the linewidth.

© 2000 IEEE