Matthias Reggentin: Analysis and mitigation of single mode emission limiting factors in high-power RW-DFB laser..., Kartoniert / Broschiert

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This thesis analyzes the spectral and tuning behavior of high-power GaAs-based DFB laser diodes, with special focus on mode hops. Two types of 780 nm DFB lasers were studied: (1) devices with a uniform Bragg grating, HR rear facet, and AR front facet, and (2) devices with both facets AR-coated and a built-in phase shift. Because the facet position relative to the Bragg grating varies after cleaving, certain rear-facet phase conditions cause mode hops during current tuning, especially in configuration (1). Numerical simulations identified these critical phase conditions and revealed the mechanisms behind mode hops-mainly carrier accumulation and temperature gradients. Experiments confirmed the simulation results, including tests with devices featuring an adjustable rear-facet phase via a micro-heater.

The study also found that mechanical strain from mounting strongly influences the lasers' spectral properties; low-temperature bonding successfully prevents this issue.

Phase-shift DFB lasers (configuration (2)) at 780 nm and 1064 nm were demonstrated, offering wide mode-hop-free tuning and record-high output powers of around 100 mW from a single facet. Additionally, tilted ridge waveguides were used to greatly reduce facet reflectivity, easing AR-coating requirements and improving device consistency.