| Tunable semiconductor lasers are the key devices in optical communications. They can be used as wavelengths backup and inventory management with a lower system cost. And in the reconfigurable optical networks, tunable semiconductor lasers can provide automatic wavelength configuration, which improve the efficiency and the flexibility of the network a lot. What is more, tunable semiconductor lasers are also widely used in high resolution spectroscopy, atomic clock, as well as sensing. Among kinds of tunable semiconductor lasers, tunable external-cavity diode laser is outstanding because of its wide tuning range and narrow linewidth. In this thesis, models of different external cavities are built and analyses are performed to study the characteristics of the external feedback. The main contents are as follows:(1) This thesis introduces the basic principles of semiconductor lasers. With the analysis of the grating cavity, the mode selecting and wavelength tuning principles of external-cavity diode lasers are described.(2) Based on the relevant theories, the external cavity models of Littrow and Littman-Metcalf configurations are built with the ray-trace software Zemax. Optimizations to maximize the coupling efficiency are also performed.(3) Based on the models established, the feedback characteristics are analyzed. With the macro in Zemax, the grating tuning feedback characteristics of the different external cavities are studied.(4) With the help of the Littrow and Littman-Metcalf models, a way to tune the diode laser with a rotating lens is proposed and simulations are performed. Moreover, the new method is validated by experiments. |
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