Robust Diode Lasers for Monitoring and Measurement Technologies

Diode-laser spectroscopy has been popular for trace gas metrology of light molecules due to its high specificity. However, the spectrometers are bulky and expensive, and the laser diodes are prone to optical feedback and mode instability. These systems have been largely relegated to the laboratory where they can be operated by highly trained personnel. For industrial and field spectrometers, it is essential that the diode laser be small, robust, and exhibit single-mode tuning without intervention by trained operators. The primary impediment to a simple, single-mode tunable diode laser has been the lack of electro-optic control over the cavity length, which ensures that the number of halfwaves in the laser cavity remains constant as the laser tunes. In Phase I, Vescent Photonics, Inc., will demonstrate a large-stroke electro-optic phase tuner that will enable a small, monolithic, entirely solid-state design for a tunable diode laser. The phase tuner will be used to demonstrate single-mode tuning of a laser diode and spectroscopy of selected light molecules. In Phase II, the phase tuner, a wavelength-selective element, and an off-the-shelf laser diode will be integrated into a monolithic, external-cavity tunable diode laser in a package measuring approximately 2 cm x 1 cm x 3 mm. The technology can accommodate several laser diodes, leading to a multi-laser module that can be tuned to hit transitions in many trace gas species and combustion products that are important for the protection of the environment. Stable, monolithic, tunable diode lasers make miniature spectrometers possible. They will be able to tune over their range in 10¿100 ¿s time scales, greatly increasing sensitivity by allowing rapid averaging of spectra. The laser module can be integrated with folded cavities, high-finesse cavities, or evanescent coupling in planar waveguide structures to make robust molecule sensors for monitoring and measurement technologies. Truly robust tunable diode lasers will have many potential commercial applications. Besides emissions monitoring, trace gas detection is useful for medical diagnostics of exhaled breath, food storage, and process control in semiconductor manufacturing. Within telecommunications, there is a need for robust tunable diode lasers as channel sources and for sparing in wavelength division multiplexing (WDM) networks.