Abstract: An encoder having a code scale and an emitter detector module is disclosed. The code scale includes alternating reflective and opaque stripes. The emitter-detector module includes a light source that generates light and directs a portion of the generated light to the imaging element and a photodetector that generates a signal representing an intensity of light having a linear polarization in a predetermined direction received by the photodetector, the light source and the photodetector are encapsulated in a transparent medium, wherein there is a gap between the transparent medium and the code scale. The predetermined direction is chosen to reduce the intensity of light received by the photodetector that is reflected from an interface between the transparent medium and the gap. A polarization filter can also be included in the light source to further improve the rejection of the light reflected from the interface of the transparent medium and the gap.