Advances in semiconductor laser mode and beam engineering

The performance of a semiconductor laser for many applications is often largely determined by how well the laser beam profile and optical spectrum are matched to the application's requirements. The beam profile and spectrum, in turn, are primarily determined by the lasing optical mode(s) and any subsequent mode/beam conversion as the mode out-couples from the laser cavity. We discuss optical mode and beam engineering theory and some of the many methods for engineering diode laser modes and beams. We expand a time-varying confinement factor analysis of diode laser dynamics with photon-photon resonance (PPR) effects to multi-cavity systems, such as vertical cavity surface emitting laser (VCSEL) arrays. We compare this analysis to the previous coupling coefficient analysis of diode laser dynamics as applied to VCSEL arrays. We propose a two-dimension complex refractive index waveguide model for 2x1 photonic crystal VCSEL array that enables the analysis of array geometry on the complex coupling coefficient and the effects of symmetric and asymmetric index suppression tuning on the array optical modes and beams. We calculate the small-single modulation response using our multi-cavity time-varying confinement factor analysis to determine that lower mode suppression enables stronger PPR effects, as does increased array asymmetry. We use guided mode expansion to model photonic crystal structures to evaluate the effects of photonic crystal geometry and epitaxial layer thicknesses on the modal resonances, losses, and asymmetry in vertical emissions. Experimental analysis of optical power measurements of VCSELs arrays shows imaginary coupling coefficient decreasing as photonic crystal lattice period is increased, and a combination of optical power and beam profile measurements show array supermode transitions associated with a dip in imaginary coupling coefficient as current injection to the two cavities is increased. We propose a Fourier method of analyzing laser array beam profiles that enables a more resilient analysis of coherence and beam-steering in VCSEL arrays. The theory and models presented in this work link the VCSEL array geometry and current injection to the optical modes and the PPR modulation enhancement, guiding future work on the optimization of array design and current biasing. The experimental analysis supports our models, and the associated computational methods will enable automated coherence tuning of VCSEL arrays