Edge-emitting LED refractometer

We report an edge-emitting light-emitting diode (LED) based refractive index sensor that operates by monitoring changes in the light-current slope efficiency in response to variations in the surrounding medium. The sensing mechanism relies on the sensitivity of the cavity facet reflectivity and optical mode properties to the external refractive index. A theoretical model is developed to describe the dependence of the slope efficiency on the surrounding refractive index, and the results are validated experimentally. The limit of detection is evaluated based on the measured noise characteristics and is found to be on the order of 10 −4 RIU for the fabricated device.