Patent ID: 8471191

Claim:
An optical navigation system for sensing relative movement between the system and a surface, the system comprising: an illuminator having a coherent light source having a single wavelength to illuminate a portion of the surface; a detector to receive light reflected from the portion of the surface, the detector including a speckle-based sensor configured to sense movement based on changes in a complex interference pattern created by the light reflected from the portion of the surface; an enclosure enclosing the illuminator and the detector, the enclosure having a filter-window covering the detector and through which light reflected from the portion of the surface is transmitted to the detector, the window being substantially transparent to at least one wavelength of light emitted by the light source; and wherein the filter-window comprises multiple layers including at least two filtering layers including a first filter-window to block light having wavelengths shorter than the wavelength of the light source, and a second filter-window to block light having wavelengths longer than the wavelength of the light source.