Development of a high-speed, high-spectral-resolution grating spectrometer for a low-cost VCSEL swept-source laser diode for hydrogen gas sensing

This paper presents the design and characterization of a high-speed, high-spectral-resolution grating spectrometer for a low-cost vertically emitting VCSEL swept-source laser diode for the detection of hydrogen in the 850 nm range. The laser beam is spectrally dispersed using an optical grating, and the resulting intensity profile is recorded in a time-resolved manner using an avalanche photodiode detector (APD) mounted on a linear stage. Periodic variations in wavelength can be detected by recording the intensity signal in a time-resolved manner. In pulsed mode, the system enables the analysis of spectral emission as a function of current and temperature modulations. This allows the investigation of the dynamic tuning behavior of the VCSEL and the optimization of a sawtooth-shaped control signal for fast tuning of the emission spectrum. The developed grating spectrometer achieved a temporal resolution of 20 ns with a spectral resolution of 0.059 nm. The spectrometer developed enables the characterization of a self-built high-speed VSCEL swept source. With a tuning speed of 10 nm/ms and a spectral shift of 4 nm, precise and cost-efficient detection of hydrogen concentrations is possible. Furthermore, the beam quality and polarization were measured as a function of the tuning parameters using a wavefront sensor and polarimeter.