Long-wavelength VCSELs for applications in absorption spectroscopy: tuning rates and modulation performances

摘要

We used direct absorption spectroscopy for characterization of long-wavelength VCSELs (VERTILAS, Germany). Gasmixture CO:CO_2=1:1 (total pressure 0.1 – 0.5 bar) provided in the tuning ranges of lasers a multitude of absorption linesspaced by intervals from 1 to 60 GHz that allowed the absolute calibration of laser scans. We measured tuning rates ofthe VCSELs in 0-50 0C temperature interval in dependence on injection current and modulation frequency varied from 0up to 6.5 mA and 500 kHz respectively. The continuous tuning range of the 1577.5-nm VCSEL with single-modeoutput of up to 1.5 mW was found to be of 9.61 nm (38.62 cm-1). The temperature tuning rates for all VCSELs understudy were in the range between -0.4 and -0.5 cm-1/ 0C. The current tuning rates, varied from laser to laser between -1.9and -2.2 cm-1/mA at low injection currents and modulation frequencies, were found to be twice as big for all lasers athigh injection currents and decreased by factor 2 and 5 at modulation frequencies of 300 and 500 kHz respectively. Aphase shift between the amplitude and frequency modulations was measured by fine tuning VCSEL with a DC injectioncurrent to display the end of a laser scan in respect to a local maximum in laser power. The phase shift changed from 0to – 0.3 rad with modulation frequency raised from 500 Hz to 500 kHz. The results of phase shift measurements havebeen compared with those obtained recently for DFB lasers with different methods.