Abstract
Vertical-cavity surface-emitting lasers (VCSELs) are widely used in short-range optical data transmission and optical sensing. Tailored heating and infrared illumination with large two-dimensional parallel-driven VCSEL arrays are gaining more and more attention. In the latter fields as well as in high-speed datacom the laser performance is limited by internal heating at high operating currents or elevated ambient temperatures, resulting in a saturation of the achievable output power and a reduction of the device lifetime. The average internal temperature Ti in the laser cavity is a key parameter to assess new VCSEL designs for applications involving high thermal stress. A versatile experimental method to determine Ti should be easy to employ in standard test environments. The increase of the internal temperature above the ambient level Ta is commonly quantified by the thermal resistance RTh = ΔTi / ΔPdiss, which relates the temperature change ΔTi to a change of dissipated power ΔPdiss. It is well known that the emission wavelength λ can be used as an indicator for Ti, because the optical cavity length depends on Ti and directly affects λ. In the conventional experimental approach, the coefficient C = dλ/dTi is either assumed to be constant [1], which introduces an error due to its material composition dependence, or C is (correctly) determined from < 100 ns range pulsed operation of the laser [2], which, however, requires high-frequency equipment and must be done with much care. We have devised a new method to evaluate RTh based on easily measurable light–current–voltage (LIV) curves for different Ta and associated optical spectra at a reduced number of operation points [3]. No empirical parameter is needed and nonlinearities due to temperature-dependent thermal conductivities are automatically included. Both single-mode and multi-mode devices can be analyzed by monitoring the wavelength shifts of fixed transverse modes. Here we apply this method to determine the maximum lasing temperature of various VCSELs and show that it is a figure of merit for temperature stability.
© 2017 IEEE
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