A novel optical-fiber displacement sensor is proposed and demonstrated. It consists of a laser diode light source, an optical-fiber probe, and two photodetectors. The bundling of the probe is sectioned into three parts: a centrally positioned fiber in the bundle for illumination, the first-neighbor fibers for receiving (part I), and the remaining fibers for receiving (part II). The ratio of the difference to the sum of the output signals from the part I and the part II receiving fibers can eliminate the variation in the sensitivity of the sensor to reflectivity of the target. The performance of the sensor is geometrically analyzed. The working distance is determined by the distance from the centered illuminating fiber to the boundary between the part I and the part II receiving fibers. The experimental measurements made with three different reflectivity targets confirm that the sensor performance is independent of the three reflectivities, as predicted by the analysis.

The performance of a multifiber optical lever was geometrically analyzed by extending the Cook and Hamm model [Appl. Opt. 34, 5854-5860 (1995)] for a basic seven-fiber optical lever. The generalized relationships between sensitivity and the displacement detection limit to the fiber core radius, illumination irradiance, and coupling angle were obtained by analyses of three various types of light source, i.e., a parallel beam light source, an infinite plane light source, and a point light source. The analysis of the point light source was confirmed by a measurement that used the light source of a light-emitting diode. The sensitivity of the fiber-optic lever is inversely proportional to the fiber core radius, whereas the receiving light power is proportional to the number of illuminating and receiving fibers. Thus, the bundling of the finer fiber with the larger number of illuminating and receiving fibers is more effective for improving sensitivity and the displacement detection limit.

In a nanometer order nanoindentation test, roundness or truncation of the indenter tip cannot be avoided. In this paper, we have analyzed the indentation problem of a rounded triangular indentation into a layered elastic half-space by a finite element analysis and then established a method to estimate the intrinsic elastic modulus of the film from the nanoindentation data. The method was applied to analyze the nanoindentation data of a less-than-10 nm penetration depth on a 10 nm thick diamondlike carbon film deposited on a 50 nm thick magnetic layer.

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 0.03nm/√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 °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 °C. It is concluded that the stability of the sensors is sufficiently good to be used with nanotechnological instruments.

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