Sensitivity and scattering in a monolithic heterodyned laser biochemical sensor

We discuss the sensitivity of a novel biochemical sensor based on the heterodyne detection of the optical frequency shift between two monolithically integrated frequency-tunable lasers. A hundred-fold improvement may be obtained by replacing the traditional ridge waveguide structure with a quasisymmetrically clad channel waveguide, which we demonstrate in a simple coupled-cavity sensor. In most cases, the optical scattering from biomolecules bound to such a waveguide will be negligible.