ABSTRACT
In order to calculate the near-field, far-field, and spectral characteristics of the PCDFB lasers, we employ the time-domain Fourier-transform (TDFT) approach developed specifically for that purpose. 8 By analyzing the propagation equations for the optical field, it is quite clear that the primary figure of merit governing the performance of PCDFB lasers is the product of the threshold gain and the linewidth enhancement factor (LEF). The threshold gain (scaled by the confinement factor 1) comprises contributions from the internal loss of the lasing material, reflectivity losses from the uncoated facets, and any diffraction loss that is particularly important for tilted gainguided laser stripes used in a-DFB and rectangular-lattice PCDFB lasers. Whereas a mid-IR PCDFB structure should perform relatively well even when this figure of merit is rather large,for edge emitters it is always advantageous to minimize both the internal loss and the LEF as much as possible. However, we will see below that this conclusion does not hold for surface-emitting PCDFB devices. Experimental results to date indicate that both the internal loss and LEF for current mid-IR antimonide "W" active regions may be relatively attractive at lower temperatures in the 77 K range, although they may become substantially larger at higher T.
