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Simulation and Implementation of an Optical Encoder

Luis Acevedo, Marc Desmulliez
The incoherent wave front emitted from a LED can be modelled by analysing the Optical Scattered Distribution Function (BSDF) produced by the surface reflection of a Lambertian wave. [read more]

The incoherent wave front emitted from a LED can be modelled by analysing the Optical Scattered Distribution Function (BSDF) produced by the surface reflection of a Lambertian wave.

In our application, the 300 microns diameter LED is used within a monolithically integrated optical encoder. The incident light source from the LED is impinging onto the index grating manufactured at the surface of the substrate of the LED and further transmitted to a scale grating with a diffraction order of +1 and -1. Surfaces to determine the brightness (power /unit-area/steradian) and intensity (power/steradian), and scattering allow us to compare these optical outputs with those obtained with a Harvey function analysis of the component. Moreover, this theoretical model is compared to the output parameters measured by a real LED (2013 LED) device as shown in Figures (1, 2) and simulated source in Figures (3, 4) below.

By analysing the behaviour of the rays of the light source in this simulating environment, the optical encoder can be analysed and the geometric configuration of the system such as the gratings period and pitch, the distance between LED and photodetectors, can be optimised to reduce optical crosstalk and increase output throughput.