Abstract: A multi-element diffraction grating is disclosed. The multi-element diffraction grating may be configured to diffract incident radiation with high dispersion using at least two holographic optical elements. The multi-element diffraction grating may include a first volume phase grating that is one of the holographic optical elements. The multi-element diffraction grating may also include at least one additional volume phase grating that is the second holographic optical element. The first volume phase grating and each of the additional volume phase gratings may be positioned relative to each other such that the radiation propagates through and is diffracted by the first volume phase grating and each of the additional volume phase gratings.

Abstract: A multi-element diffraction grating is disclosed. The multi-element diffraction grating may be configured to diffract incident radiation with high dispersion using at least two holographic optical elements. The multi-element diffraction grating may include a first volume phase grating that is one of the holographic optical elements. The multi-element diffraction grating may also include at least one additional volume phase grating that is the second holographic optical element. The first volume phase grating and each of the additional volume phase gratings may be positioned relative to each other such that the radiation propagates through and is diffracted by the first volume phase grating and each of the additional volume phase gratings.

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: A multi-element diffraction grating is disclosed. The multi-element diffraction grating may be configured to diffract incident radiation with high dispersion using at least two holographic optical elements. The multi-element diffraction grating may include a first volume phase grating that is one of the holographic optical elements. The multi-element diffraction grating may also include at least one additional volume phase grating that is the second holographic optical element. The first volume phase grating and each of the additional volume phase gratings may be positioned relative to each other such that the radiation propagates through and is diffracted by the first volume phase grating and each of the additional volume phase gratings.