2.3 High-power, single spatial mode, narrow ridge waveguide lasers
In addition to the many design considerations for high-power and single-mode operation described in detail in Sections 2.1 and 2.2, the purpose of this section is to give more insight into specific details of quantitative dependencies between crucial parameters of ridge waveguide diode lasers.
This laser type is particularly suitable for this type of demonstration, because its structure in both the transverse vertical and lateral directions is clear and relatively simple to build and has proven to deliver highly reliable, high-power, and single spatial mode laser products suitable for a broad range of applications. Far-field patterns and single-mode operation can be controlled easily. However, stringent dimensional tolerances are required to achieve good performance in these weakly index-guided laser devices. This includes, in particular, ridge width w and height, as well as the residual thickness t of the p-type cladding layer outside the ridge, which can be linked to the ridge height. Moreover, it is known that, as the ridge narrows, the sidewall integrity becomes an important factor in the laser performance (Legge et al., 2000). Nonradiative recombination and optical losses at etched sidewalls, in particular with narrow ridge widths, degrade the laser performance. In addition, the small lasing volume in narrow ridge lasers may increase the optical losses due to process-related scattering leading ...