Opto-tactile probe based on spherical coupling for inner dimension measurement

An opto-tactile 1D probe, based on spherical coupling of light energy, is designed for precision measurement of inner dimension microstructures with high aspect ratio. The probe consists of an incident fiber, a spherical coupler and an effluent fiber. Light energy imported through the incident fiber is transmitted in the reversal direction via the coupler and guided out through the effluent fiber to a photodetector. When the coupler probes the sidewall of a microstructure, the incident fiber is deflected at a particular angle, and the effluent fiber moves accordingly. So the lateral displacement of the coupler is transformed into the deflection of output beam. Thus, the shadowing effect of microstructures with high aspect ratios can be eliminated. The new probe is low cost and easy to exchange and fabricate, and it has a probing force of less than 1 µN. Measurements of micro-holes and fuel injection nozzles indicate that for microstructures with an aspect ratio of up to 15:1, a resolution of up to 0.04 µm can be achieved, and high precision diameter and cylindricity measurement of micro-holes can be carried out.