Diode laser-based chemical and biological sensor

Abstract

A-compact, diode laser-based sensor has applications in biological and chemical analysis. Unlike existing optical waveguide-based sensors, no external coupling to external optical fibers or waveguides is required to perform optical chemical, immunological or nucleic acid-based assay or to detect the presence of toxic or otherwise important chemicals. The sensor includes a surface-sensitive diode laser having a substrate layer, an n-contact layer positioned on a bottom surface of the substrate, an n-clad layer overlying the top surface of the substrate, a first guide layer overlying the n-clad layer, a quantum well layer overlying the first guide layer, a second guide layer overlying the first quantum well layer, a p-clad layer overlying the second guided layer and a p-doped cap layer overlying the p-clad layer. A pair of electrodes separated by a surface-sensitive region is positioned on the cap layer. The surface active region includes an oxide layer grown on the thick cap layer and an absorbing or non-absorbing film deposited on the oxide layer. For internal reflection, inorganic material coatings are applied to end facets or Bragg reflectors are etched in the cap layer. Detectors are positioned proximate the diode laser for detecting changes in film thickness or refractive index, absorption or other optical properties resulting from film deposition, surface reactions such as immunological or ion-exchange reactions, or other detectable processes.