Dynamics, Noise Properties, and Spectral Characteristics of Semiconductor Lasers with External Coupling.
This thesis is a study of the dynamics, noise properties, and linewidth of semiconductor lasers with external coupling. In Chapter 2, a general formalism is developed for obtaining the optical-field equations of semiconductor lasers with external coupling. This formalism is applied to three different types of lasers: (1) a diode laser coupled to an external mirror, (2) an injection-locked diode laser, and (3) an axially coupled two-section diode laser. The resulting equations are the basis for the studies and discussions given in Chapters 3, 4, and 5. The third chapter considers single-mode semiconducor lasers coupled to an external mirror. Light trapped for many round trips inside the external cavity is taken into account. Analytical expressions for the frequency and intensity fluctuation spectra, the laser linewidth and the modulation response are obtained. The fundamental mechanism that prevents the mode locking in semiconductor lasers with an external feedback is identified. The observed data on the intensity noise and modulation response are elucidated. An injection-locked semiconductor laser is studied in Chapter 4. The origin and importance of the facet's amplitude reflectivities are described. The instability and locking bandwidth are investigated in depth. It is shown that, depending on the detuning of the lasing frequency, the relative-intensity noise can be reduced or increased. It is also demonstrated on a general basis that the locked laser's linewidth is the same as that of the injected field. The dynamics and laser linewidth of an axially coupled two-section semiconductor laser are scrutinized in the last chapter. A formula is obtained for the laser linewidth. This formula explains the experimental observations that the linewidth is nearly inversely proportional to the power with a nonzero intercept. Finally, the contribution to the reduction in dynamic frequency chirping of two-section lasers is clarified.
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- Engineering: Electronics and Electrical; Physics: Optics