Abstract: A system includes a light source and a grating cube. The grating cube includes a transmission volume holographic grating positioned between two prisms. The transmission volume holographic grating diffracts part of a light source emission toward a reflective surface, producing diffracted light. At least some of the diffracted light is reflected off of the reflective surface, producing feedback light. The feedback light is fed back to the light source, thereby causing the light source emission to have the same wavelength as the feedback light.

Abstract: A fingerprint reader is described. The fingerprint reader includes an illumination source that produces light and a camera. An optical window is also part of the reader. The window is positioned so that light from the illumination source passes through the optical window and then is reflected to the camera for imaging a person's fingerprint. A filter may be positioned on or proximate to the optical window. The filter prevents ambient light from reaching the camera. In some situations, the filter will be a dielectric mirror, a dielectric filter, a holographic mirror, a holographic filter, a dichroic mirror or a dichroic filter.

Abstract: An eyepiece assembly for use in a rifle scope may include an eyepiece that is made of a material that is transparent to light. A holographic reticle may be positioned within the eyepiece. The eyepiece assembly may also include a chrome reticle. The chrome reticle may be positioned so that the chrome reticle is aligned with the holographic reticle. A cover portion may be attached to the eyepiece.