Vertical-Cavity Surface-Emitting Lasers with Improved Wide-Temperature Dependence

Licentiate thesis, 2025

The vertical-cavity surface-emitting laser (VCSEL) is the preferred light source for high-speed and power-efficient short-reach optical interconnects (OIs) in high-performance computing systems, datacenters, and other short-range optical networks. Such OIs typically operate over a temperature range of 0 to 80°C. However, some emerging applications of VCSEL-based OIs, such as in automotive optical networking and optical networks in some military systems, require operation over a much wider temperature range, e.g. from -40 to 125°C. With the VCSEL being the most temperature sensitive component of the OI, and uncooled/unheated operation required for cost and power efficiency, there is a demand for VCSELs with reduced temperature dependence, operating over a wider temperature range.

The temperature dependence of VCSEL performance stems from variations in optical gain and mismatches between gain spectrum and resonance wavelength shifts. Methods to mitigate these effects include using VCSELs with appropriate gain-cavity detuning and gain engineering to broaden optical gain spectrum.

This thesis investigates 850 nm VCSELs optimized for operation over a large temperature range. Key studies include the correlation of threshold current with performance parameters (Paper A) and the design of chirped QW VCSELs to stabilize performance across temperatures (Paper B). Insights into designing robust VCSELs for extreme environments are presented.