| Semiconductor lasers are used in a wide variety of commercial, medical, and industrial applications, ranging from compact disk players to welding. Years of research and innovations in the field have established these devices as an enabling technology where compact, economical, and efficient laser light sources are required. One problem with semiconductor lasers is that the quality of the light beam emitted degrades when multiple lateral modes lase simultaneously. This is particularly true for semiconductor lasers that operate at high output power levels. A light beam of low quality diverges more rapidly and the focused spot size is larger than it otherwise could be if it were diffraction limited, making the device less useful. Semiconductor lasers with a very narrow lateral dimension (width ∼2 μm) will emit light in a single lateral mode that is diffraction limited, but even these narrow devices lase in multiple modes when driven to their highest output power levels. Moreover, the small size of the device inherently limits the total output power.; The central thesis of this work is that structures can be integrated into the laser that introduce optical loss to only high-order lateral modes and thus prevent them from lasing and degrading the beam quality. Several concepts for modifying the lateral waveguide to create filtering of the lateral modes are examined, including the use of waveguide bend loss, waveguide frustration, and the addition of scattering loss. Each of the concepts tested improves the stability of the beam and prevents the oscillation of high order modes. Stable single lateral mode output power is demonstrated in lasers over the entire range of drive currents tested when frustrating waveguide filters or frustrating scattering waveguide filters are incorporated into the devices. This improves the single lateral mode power output from 500 mW to 800 mW. |
