Tunable single-frequency semiconductor lasers are needed for applications in coherent optical systems: communications; optical sensors; spectroscopy. Desirable characteristics of lasers for heterodyne detection are a narrow linewidth combined with the ability to tune over a large wavelength range. In contrast to lasers for conventional communications. they should be directly frequency modulated (FM) over a large bandwidth without intensity modulation (IM). There is presently a need for a simple technique to monitor the tuning and coherence properties of such sources. We present an all-fiber interferometric apparatus that can be used to measure the tuning rate, range, and linearity of tuning as well as the laser linewidth in quasi-real time. The system was used to characterize cleaved coupled cavity (C3) lasers which-exhibit the above properties with varied bias currents, temperature, modulation frequency, and optical feedback levels. This technique could be used to characterize any of the variety of the two-section lasers recently proposed for tunability.1

© 1988 Optical Society of America

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