We describe a method of tailoring the laser spectrum of Fabry-Pérot (FP) laser diodes using a spatially varying refractive index. The cavity geometry is determined by a perturbative transmission matrix calculation of the threshold gain of the longitudinal modes and solution of the corresponding inverse problem. Single-mode FP lasers with predetermined wavelength, and twocolor FP lasers with predetermined mode spacing in the terahertz region are designed and experimentally demonstrated.
The wavelength spectra of ridge waveguide Fabry Perot lasers can be modified by perturbing the effective refractive index of the guided mode along very small sections of the laser cavity. One way of locally perturbing the effective index of the lasing mode is by etching features into the ridge waveguide such that each feature has a small overlap with the transverse field profile of the unperturbed mode, consequently most of the light in the laser cavity is unaffected by these perturbations. A proportion of the propagating light is however reflected at the boundaries between the perturbed and the unperturbed sections. Suitable positioning of these interfaces allows the mirror loss spectrum of a Fabry Perot laser to be manipulated. In order to achieve single longitudinal mode emission, the mirror loss of a specified mode must be reduced below that of the other cavity modes. Here we review the latest results obtained from devices containing such features. These results clearly demonstrate that these devices exceed the specifications required for a number of FTTH and Datacomms applications, such as GEPON, LX4 and CWDM. As well as this we will also present initial results on the linewidth of these devices.
An approximate solution for electron trajectories in a cylindrical field is presented and discussed in connection with the 127° spectrometer originally proposed by Hughes and Rojansky. The approximate solution is compared to a numerical one, and is used to calculate the line shape in a few special cases.
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