Photoelastic waveguides and their effect on stripe-geometry GaAs/Ga1−xAlxAs lasers

Abstract

A II-VI semiconductor diode laser has a strained layer disposed on top of the structure. This strained layer, having a thickness of between about 0.05 microns and 2 microns, is either a single film or a stack of films, preferably of metal. The strain field produced by this layer in the semiconductor layer structure produces a change in the refractive index of the structure, due to the photo-elastic effect. By virtue of this effect a strain-induced waveguide is provided in the diode laser, with a strained layer in an edge, stripe or window structure. Furthermore, a tensely-strained layer covering the entire structure is used to produce a strain field similar to that which occurs when the structure is bent. This strain field will produce strain-enhanced gain in the underlying structure, which allows for operation of the laser at a lower threshold Current. 17 Claims, 3 Drawing Sheets 7 7 7 7777. Z222222222

Stress-induced effects by the anodic oxide in ridge waveguide laser diodes

“…The influence of stresses introduced during processing in oxide-insulated laser diodes and related stress-induced changes of the refractive index, which depend on the thickness and on the shape of the oxide layer, was reported at the beginning of the development of laser diodes [2]- [4]. Their further study was cast aside because the built-in effective refractive index step in conventional devices exceeded the influence of this effect.…”

“…Although the computational approach resulting from [10], that we use here, can also be used for the anisotropic case, in the following, an isotropic average value for Young's modulus and Poisson's ratio will be used, as in [2].…”

“…This effect is called the photoelastic effect; it is similar to the electrooptic effect, which is the effect of an applied electric field on the dielectric constant of a crystal. In the following, the same constants as in [2] are used to compute the changes of the refractive index for the TE wave from the strain distribution. That is, the change of the dielectric constant is given by where the photoelastic coefficients are and .…”

Mapping of mechanical strain induced by thin and narrow dielectric stripes on InP surfaces

“…As a first approximation, we use an analytic edge force model [1][2][3][4]8] in a plane strain approximation to describe the stress in the InP owing to the SiN x stripe. Using this 2D approximation, we write the stress tensor as 2…”

“…Several groups have worked in the past on demonstration of feasibility of photo-elastic waveguides in semiconductor materials, where the guiding structure is defined through application of mechanical stress via a patterned dielectric film at the surface [1][2][3][4][5].…”