A monolithic chemical sensor using tandem heterodyned sampled grating DBR lasers

Summary form only given. The sensor consists of a pair of frequency-tunable diode lasers, an optical field combiner, and an integrated high-speed photodetector. The combined fields produce a heterodyne signal at the detector, equal to the difference in optical frequencies. A portion of the ridge waveguide of one of the lasers is exposed to the fluid to be measured, such that the optical evanescent field at the edge of the waveguide penetrates into the fluid. The round-trip phase through the laser cavity then becomes sensitive to the index of refraction of the fluid, such that any change in the fluid index will cause a shift in the laser´s optical frequency, and resulting heterodyne signal. The sensor is ideally suited to immunoassays, in which the sensing surface is coated with antibodies specific to an antigen to be detected. We have used sampled-grating distributed Bragg reflector (SGDBR) lasers because their wide tunability affords a large dynamic range, as well as a possible spectral signature to distinguish between similar biochemical species