Optical sensor

This invention relates to an optical sensor for testing a biochemical sample. The sensor includes a resonant mirror device 1 and a prism 2 disposed adjacent the device 1 for coupling an input beam of light to the device 1. The input beam of light having a comb spectrum with a uniform spacing between adjacent lines or bands of the spectrum is produced by a comb spectrum source 10. The comb spectrum may be produced by a diode laser with multiple longitudinal modes. The input beam of light is polarized by a polarizer 4 to provide equal TE and TM components. The resonant mirror device is arranged in the paths of said input beam of light such that resonance is excited for at least one of said components, An analyser 11 is arranged to receive said components of the beam of light reflected from the device 1 for producing an output beam having a spectrum including a series of bright and/or dark lines or bands corresponding to the lines or bands of the comb spectrum of the input beam. When a sensing layer of the resonant mirror device is sensitized by the chemical sample, an angular shift in the resonance angle takes place and this causes the lines or bands of the output spectrum to be swept across a reference point where detector means 12 is located to count the number of lines or bands swept across the reference point. The angular shift in the resonance angle is equal to the product of the distance between adjacent lines of the comb spectrum and the number of lines swept across the reference point.