Sensitivity of the linewidth enhancement factor to structure and threshold level in strained semiconductor lasers

Abstract

Summary form only given. The carrier-induced coupling of the gain change to the refractive index change in the active region of a semiconductor laser is described by the linewidth enhancement factor (or /spl alpha/-parameter). Important characteristics dependent on /spl alpha/ include the laser linewidth, modulation-induced wavelength chirp, gain guiding and sensitivity to feedback. In addition non-linearities described by /spl alpha/ place limitations on the performance of high-power semiconductor lasers. Thus low-/spl alpha/ operation is often desirable in practical devices. The benefits of strain in leading to reduced /spl alpha/-parameter in semiconductor quantum well lasers is well-known. However, the design space involved also includes as the properties of the resonator. In particular, the threshold modal gain (G/sub th/), is determined by resonator properties (length L, internal losses /spl alpha//sub i/ and facet reflectivities R/sub 1/ & R/sub 2/) through the threshold condition: G/sub th/=g/sub th//spl Gamma/=/spl alpha//sub i/+(In(R/sub 1/R/sub 2/)/sup -1//2L). It is essentially independent of the active medium providing the material gain (g). Of course the modal gain and material gain are related through the optical confinement factor (/spl Gamma/), which is generally proportional to the quantum well width. In the work we use a sophisticated model to examine the dependence of the /spl alpha/-parameter on device structure and composition. In particular, the sensitivity of the /spl alpha/-parameter to the operating regime (i.e., threshold level) for different structures is investigated.