MODAL PROPERTIES OF DEPRESSED CLADDING SEMICONDUCTOR WAVE-GUIDES AND LASERS

The TE modal properties of three symmetric core (uniform, parabolic, a nd linear) depressed cladding slab waveguide structures are investigat ed for situations appropriate for use as lasers and routing waveguide, The results show that if the confinement factor, or mode size, is the criterion for comparison, there is little difference between the stan dard and depressed cladding cases for guides which are near the cutoff of the higher order modes, The primary difference is in the fraction of the mode which overlaps the cladding regions, which is always small er for the depressed cladding cases, We show that there are numerous c ombinations of conditions leading to spot sizes comparable to the vacu um wavelength of light, Experimental data are presented for three para bolic core depressed cladding AlxGa1-xAs heterostructures doped to for m lasers, In particular, the measured Gaussian equivalent spot size de duced from farfield measurements agree well with model situations for the largest core sizes, The largest Gaussian equivalent near-field spo t size was similar to 1.2 mu m, and resulted in a divergence angle of similar to 30 degrees (full width half power) and a threshold current density only 50% larger than a standard small optical cavity laser str ucture optimized for maximum confinement factor, The scaling laws of a mplifiers and lasers with confinement factor are discussed, Experiment al routing tests were performed using rib delineated raised cosine S b ends, The symmetric depressed cladding laser structure was found to ha ve a much lower bend loss than the standard structure, leading to tigh ter routing geometries with an etch depth which did not penetrate the quantum well,