Fiber optic displacement sensor

Abstract

A novel low cost interferometric displacement sensor has been developed which tracks distance from the tip of a fiber optic probe. A unique interrogation technique is used which produces a 32-bit phase word, giving the system a dynamic range greater than 109. Therefore, a displacement resolution of less than 0.01 nm can be achieved with a full range of 6 mm. The measurement range can be extended beyond 10 m by simply adjusting the digital fringe counter and sacrificing resolution yet maintaining the greater than 109 dynamic range. Demodulation rates of 40 kHz have been achieved which facilitates dynamic measurements. Results from an application to hard disk (HD) profilometry are presented.