Abstract: A multilayer optical disk system, which includes an optical disk unit having a number of connected optical disks. A number of light sources, such as diode lasers, are used to provide a number of light beams of different wavelengths. A wavelength multiplexer combines the light beams into a single beam which is then axially dispersed so that light of different wavelengths are simultaneously focuses onto the different optical disks. A wavelength demultiplexer splits light reflected from the optical disks according to wavelength to produce separate beams which are then separately detected.

Abstract: A method of designing a holographic optical element (diffractive grating) that transforms a set of waves into another set of waves in order to minimize aberrations in the phase of the output wavefront, includes the steps: (a) define continuous input parameters that characterize the propagation vector components of the incoming wavefront and the desired output wavefront; (b) formulate integral equations for the optimal grating vector components; and (c) solve the integral equations for the optimal grating vector components to minimize the difference between the actual and desired output wavefronts.

Abstract: A method of producing a desired hologram for a holographic optical element for use in imaging a multi-dimensional array of points, in which two coherent recording beams are utilized to produce an interference pattern which is recorded to form the desired hologram, characterized in that one or both of the recording beams have an aspherical wavefront derived from one or more intermediate holograms each reconstructed by the use of a read out beam having a geometry and/or wavelength different from the beams for recording the respective intermediate hologram.