Research On Two Wavelengths Fiber Interferometry For Step Height On-line Measurement

ABSTRACT:An optical fiber stabilized and simultaneous two wavelengths interferometric system, which is suitable for on-line measurement of a step height with large range and high precision, is proposed. By employing a fiber Bragg grating as an in-fiber reflective mirror, two different wavelengths are working simultaneously and independently in the same interferometer and two interferometric signals of each wavelength are detected simultaneously and respectively. By operating four phases of the interferometric signals detected by the measurement system, the change of optical path difference of the interferometer, which is the height of the step, is available. By employing a feedback loop which compensates the influences induced by the environmental disturbances, the system is robust enough for on-line measurement. The two wavelengths interferometry makes measuring span range from sub-nanometer to half a synthetic-wavelength that could be larger than lmm. The fiber Michelson high coherence interferometry makes the measurement resolution less than lnm and the standard deviation of measuring a gauge block with the height of1mm is0.6nm.