Optical waveguide spectrum analyzer and method

In a method of analyzing spectral data utilizing an instrument having a single strand optical waveguide which carries light from a sample located remotely of the instrument, a light responsive detector, a diffraction grating which receives light from the waveguide and produces a plurality of angularly displaced light intensities corresponding to the spectral content of the light, a drive motor which rotates the grating to direct light intensities of different wavelengths toward the detector, and a sensor which produces a potentiometer output signal corresponding to the position of the grating, said sensor comprising a rotary conductive plastic potentiometer means for producing an output signal which varies substantially linearly throughout 360 degrees, with said sensor, said motor, and said grating being mounted on a single shaft and being free to rotate through 360 degrees, the steps of:

• introducing monochromatic light into the single strand waveguide, positioning the grating to cause light at the zero order peak and the first order peak in the spectrum of the monochromatic light to impinge upon the detector, determining the grating content (K) for the instrument according to the relationship ##EQU3## where .alpha..sub.0 is the value of the sensor signal at the zero order peak, .alpha..sub.1 is the value of the sensor signal at the first order peak, and .lambda..sub.m is the first order wavelength of the monochromatic light, and setting up a table of calibration data for the instrument according to the relationship
• .alpha.=sin.sup.-1 (K.lambda.),
• where .lambda. is the wavelength of light impinging upon the detector and .alpha. is the value of the sensor signal corresponding to each impinging wavelength;
• said grating positioning step being accomplished solely by electrical energizing of said motor by signals derived from said potentiometer operative throughout the 360 degrees of rotation of said shaft.