Substrate radiation losses in GaAs heterostructure lasers

Double-heterostructure (DH) diode lasers with a thin Ga1-xAlxAs layer between the active GaAs region and the GaAs substrate or superstrate are analyzed. In these devices power flows through the thin Ga1-xAlxAs layer and is radiated into the substrate or superstrate. Three methods for computing the laser thresholds are developed and compared. The first is an analytic perturbation technique, which yields accurate results in many cases of practical interest. The second and third are rapidly convergent numerical iteration techniques. The former utilizes overlap integrals to compute absorption losses and thresholds; the latter includes all losses and gains directly in the formulation. We show that conventional DH diode lasers can be designed with thick active GaAs layers and still achieve lowest order TE-mode operation. These devices will produce better collimated, higher power output beams than do similar devices with thinner active regions. Transverse-mode control is achieved because all higher order modes have increased penetration through the thin Ga1-xAlxAs , and therefore exhibit inereased radiation losses into the substrate or superstrate. A design example is included in which it is shown that with proper choice of the Ga1-xAlxAs-layer thickness the TE0-mode threshold increases by 5 percent compared with a 110-percent increase in the TE1threshold. These results are virtually independent of the substrate power-absorption coefficient. Threshold current densities are computed for a set of diodes studied experimentally by Casey and Panish and the results are shown to be in excellent agreement.     

Single-lobe `Y? coupled laser diode arrays

`Y? Coupled laser arrays have been fabricated with flared waveguides at the output facet to expand the near-field spot and increase the near-field fill factor to greater than 80%. The far-field radiation pattern is predominantly single-lobe, and power outputs of 150mW CW have been obtained with threshold currents as low as 130mA.     

Reformulation of the coupled-mode theory of multiwaveguide systems

We show that by proper reformulation the coupled-mode theory of Hardy and Streifer can be reconciled with that of Haus et al based on a variational principle. The new formulation has the merit of leading to simpler coupled-mode equations while giving marginally more accurate results.     

Single-lobe phased-array diode lasers

We show mathematically that the lowest-order supermode of a real-refractive-index phase-locked semiconductor diode laser array, which radiates into a single narrow far-field lobe, is favoured by its lower threshold when the gain in the interspaces between the waveguides exceeds that of the waveguides themselves.     

Advances in diode laser pumps

Diode laser pumps for solid-state lasers are reviewed with special emphasis on current and future capabilities. Included are discussions of pumps for CW (continuous-wave) and quasi-CW operation, and end- and side-pumping configurations     

Coupling strength and influence in cleaved-coupled-cavity lasers

The coupling between the segments of a C3 laser is calculated, and threshold plots for small gap perturbations are shown to differ substantially. Cases of strong, intermediate and weak coupling are compared.