A Measurement Platform for Characterization of Quantum Cascade Lasers

Abstract: A measurement platform has been built to characterize quantum cascade lasers regrown at KTH by measuring their spectral and electrical properties at room temperature. Since the current source used in this work had a compliance voltage which was too low to get above threshold, an adapter was made to put an external voltage source in series with it, raising the voltage over the laser. The adapter was first simulated using OrCAD PSPICE and then soldered together and put inside a plastic box with connections for the voltage source, current source and laser mount. A software was made using LabView to automate the electrical characterization. It ramps the current over a specified range, records current, voltage and output power of the laser and saves the data in a file. The platform was tested using a QCL sample borrowed from III-V Lab, France. The L-I-V curve and the spectrum of the sample was measured at different optical output power levels and temperatures. From the L-I-V curves the slope efficiency, , and the threshold current, Ith were extracted and in turn used to calculate the characteristic temperatures T0 = 40K and T1 = 10K. This led to the conclusion that either the sample had degraded or the thermal dissipation was not efficient enough, since typical values for these temperatures lie around 200K. From the spectral measurement results, a qualitative analysis was made that indicated a slight increase of mode wavelength with rising temperature as well as mode jumps to longer wavelength modes. It could also be seen that the laser showed single-mode behaviour that became more unstable as temperature or current or both were increased. Unstable multi-mode behaviour was seen at an optical output power of 60mW at 20oC. After tests and analysis, suggestions on possible future improvements of the platform were made.