Single longitudinal mode external cavity semiconductor lasers and their application in the optical generation of radio-frequency signals by heterodyne phase locking

Single-longitudinal mode semiconductor lasers are important light sources for wavelength division multiplexing (WDM), radio frequency/microwave photonics, and many other applications. In this dissertation, we have studied the principle, characteristics, and applications of different types of single longitudinal mode semiconductor lasers, with special emphasis on hybrid structure semiconductor lasers including external cavity semiconductor lasers (ECSLs) with bulk gratings and fiber grating semiconductor lasers.; High spectral purity cavity design and laser linewidth reduction were studied for bulk grating ECSLs. An ECSL based on an improved cavity design with a commercial laser diode of 5% anti-reflection coating was implemented at wavelength 830 nm. Stable single longitudinal external cavity mode operation was demonstrated with a side mode suppression ratio (SMSR) of 38 dB, and a linewidth of less than 50 kHz. ECSLs with wavelength around 1590 nm and 980 nm were implemented with single angled facet (SAF) laser diodes to provide low reflectivity (<10-4). SMSR better than 50 dB was demonstrated together with a narrow linewidth (∼37 kHz) and a large tuning range (>70 nm).; Fiber Bragg gratings with narrow spectral bandwidth were theoretically studied, and experimentally manufactured. Novel hybrid semiconductor lasers consisting of conically lensed fiber gratings and SAF diodes have been demonstrated with stable single longitudinal mode operations over more than 85 mA current range. High SMSR of 50 dB with narrow spectral linewidth (<150 kHz) has been achieved. For the first time, the detuned-loading effect of such lasers was found experimentally and explained theoretically. The application of such lasers in WDM systems was also studied. High speed modulation at 2.5 Gbit/s has been successfully demonstrated. The dynamic chirp was measured to be 21 MHz/mA, more than an order of magnitude less than for normal single mode semiconductor lasers.; Finally, we have studied theoretically and experimentally the optical generation of highly coherent radio frequency signals by heterodyne phase locking two narrow linewidth ECSLs. A two loop configuration was invented with the first loop used to improve the frequency acquisition and the second loop to achieve phase noise reduction. An additional phase advance circuit was designed to increase the loop bandwidth. Upon these designs, a high spectral purity RF signal at 711 MHz was generated with a center carrier linewidth of less than 1 millihertz. The noise level was measured to be not more than -110 dBc/Hz over the entire spectral range. The total phase variance was determined to be 1.19 x 10-4 rad2, which is the lowest number ever reported with any optical method.