We describe a widely tunable coupled-cavity semiconductor laser with a nearly continuous tuning capability of approx100 nm. A below threshold model for coupled-cavity devices using a transfer matrix approach that takes into account the tilt of the facets forming the gap between the coupled sections was developed and is presented. Nonlinear fits of the below-threshold spectra to the model were used to extract device parameters. These fits and parameters were then used to understand the operation of the devices and the direction to take to improve the performance of the devices. It is observed that for facet angles >=7 deg, a two-section coupled-cavity device works like an injection-locked laser, while for angles <=4 deg, the sections work as a truly-coupled system.
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