A detailed model is developed for analyzing fiber grating external cavity lasers for both static and small-signal modulation conditions. The chip and package parasitics and leakage current induced distortion are included. The composite system is solved analytically in the small-signal regime using a Volterra functional series expansion method. As an application of the model, a thorough analysis of the appearance of nulls close to the harmonics of the cavity resonance frequency in the noise and modulation spectra is given. We show that the appearance of these nulls can be explained using the interplay of amplitude and phase coupling between laser diode and external resonant cavity. A signal flow graph approach is introduced which identifies methods of minimizing the nulls.
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