OPTICAL FIBER BUNDLE DISPLACEMENT SENSOR USING AN AC-MODULATED LIGHT SOURCE WITH SUBNANOMETER RESOLUTION AND LOW THERMAL DRIFT

摘要

An optical fiber-bundle displacement sensor with subnanometer order resolution and low thermal drift is proposed. The setup is based on a carrier amplifier system and involves techniques to eliminate fluctuation in the light power of the source. The achieved noise level of the sensor was 0.03 nm/root Hz. The stability was estimated by comparing the outputs of two different sensors from the same target for 4 ks (67 min). The relative displacements between the fiber bundle ends of the two sensors and the target surface varied in the area of 400 nm depending on the ambient temperature variation at 2 degrees C. However, the difference in output between the two sensor systems is within 2 nm for more than 1 hour of measurement. It is expected that it would be reduced to within the area of 0.1 nm if the ambient temperature were controlled to within +/-0.1 degrees C. It is concluded that the stability of the sensors is sufficiently good to be used with nanotechnological instruments. [References: 15]