Trace gas sensing and monitoring
Optical spectrum of single mode BTJ-VCSEL
With their excellent single mode performance together with a reasonable current tunability, long-wavelength VCSELs are ideal light sources for optical sensing applications. For this purpose, the wavelength selective absorption of gas molecules is exploited. Since fundamental absorption resonances for most of the relevant gas molecules are in the 3-10 µm wavelength range, BTJ-VCSELs usually detect higher order resonances in the near infrared up to 2 µm. The identification and interpretation of the absorption lines requires a certain wavelength-agility of the laser sources in order to scan the emission wavelength over the wavelength range of interest. Typically, a tunability size of 1 nm is required for this application. Fortunately, the long-wavelength BTJ-VCSELs can be tuned by at least 1 nm with up to several million scans per second. This can be easily accomplished by a simple current tuning. It is an advantage of the short cavity length of VCSELs that the wavelength tuning is strictly continuous, keeping the spectral purity constant over the entire tuning range.
The wavelength range covered by the InP-based VERTILAS VCSEL technology is 1300-2050 nm, and standard wavelengths as well as customer-specific wavelengths and tuning ranges are available. Accordingly, numerous gases can be detected with these sources. For instance, water vapor in the 1800 nm regime, methane and ethane around 1680 nm, and carbon dioxide in the 2000 nm regime are among the detectable variety. With their low-cost potential, the long-wavelength VCSELs are expected to drastically reduce the cost of optical gas sensing instruments and to make new applications feasible. This particularly holds true for mobile systems, where the low power consumption of VCSELs represents a decisive additional advantage over competing DFB-laser based systems.
The wavelength range covered by the InP-based VERTILAS VCSEL technology is 1300-2050 nm, and standard wavelengths as well as customer-specific wavelengths and tuning ranges are available. Accordingly, numerous gases can be detected with these sources. For instance, water vapor in the 1800 nm regime, methane and ethane around 1680 nm, and carbon dioxide in the 2000 nm regime are among the detectable variety. With their low-cost potential, the long-wavelength VCSELs are expected to drastically reduce the cost of optical gas sensing instruments and to make new applications feasible. This particularly holds true for mobile systems, where the low power consumption of VCSELs represents a decisive additional advantage over competing DFB-laser based systems.
Power and wavelength variation over current
