High-accuracy micro-encoder based on the higher-order diffracted light interference

A new type of high-accuracy optical encoder based on higher-order diffracted light interference is proposed. For a relative movement between the scale grating and the encoder head, the encoder provides sinusoidal signals whose period (0.53 μm) is one-sixth of that (3.2 μm) of the scale grating, from which the displacement or revolution angle can be accurately determined. The proposed micro-encoder structure includes a laser diode, two-segment photodiodes, polyimide waveguides, and a micro-grating that makes ±3 order beams diffracted by the scale grating interfere coaxially, all on the same silicon substrate (3×2 mm²)