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Applications

Trace gas sensing and monitoring

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. 

 

Optical communications and datacom

Similar to their short-wavelength counterparts at 850 nm that have been most widely used in high-speed data communications, long-wavelength VCSELs with wavelengths ranging from 1300 nm to 1550 nm will have numerous applications in optical communications. Because of significantly smaller fiber attenuation as well as smaller fiber dispersion at these longer wavelengths, significantly larger distances and bandwidths can be achieved. In particular, long-wavelength single mode VCSELs with modulation rates of up to 10 Gbit/s enable broadband optical links with transmission distances that are up to over ten kilometers in length. The single mode BTJ-VCSEL exhibit an excellent spectral performance with a side mode suppression ratio (SMSR) well exceeding 40 dB. In many applications where power levels around 1 mW are sufficient, the long-wavelength VCSELs may act as a substitute for expensive DFB lasers. Emerging higher-capacity networks (i.e. 10 Gigabit Ethernet) will benefit from the availability of long-wavelength VCSELs.