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Showing papers on "Signal beam published in 1978"


Patent
31 Jan 1978
TL;DR: In this paper, a light beam deflection system and frequency shift arrangement disposed up-stream of a focussing lens is presented, where the modulated beam is deflected and is then directed along with the unmodulated beam through the lens so that the beams combine with each other to form a read-out interference pattern on the hologram.
Abstract: A hologram-containing storage medium is rapidly scanned or swept by a sinusoidal spatial fringe pattern, the spatial frequency of which varies with time. This may be achieved by the use of a suitable light beam deflection system and frequency shift arrangement disposed up-stream of a focussing lens. The deflection system and frequency shift arrangement may incorporate a pair of light beams, such as those obtained from a laser, a source of coherent monochromatic light. A single deflector-frequency shifter, such as an acousto-optic element and an electro-mechanical deflector may be disposed in the path of one of the beams, with a prescribed carrier modulation frequency applied to shift the frequency of that one beam relative to that of the other beams. The modulated beam is deflected and is then directed along with the unmodulated beam through the focussing lens so that the beams combine with each other to form a read-out interference pattern on the hologram. Alternatively, a respective frequency shifter, such as an acousto-optic modulator may be disposed in the path of each of the pair of beams and a separate modulation frequency signal applied to each modulator. The frequency difference between the two signal sources represents the temporal frequency carrier component of the interference pattern. The beams are also deflected relative to one another and the light which is then diffracted by the hologram impinges upon a single photo-detector, whereby a signal representative of the original data, together with the imparted modulation components, is derived. The temporal and spatial modulation components introduced in the signal beam by the frequency-shift, deflection system are then removed, to obtain only the original data. In accordance with the invention, a constant scan frequency may be used or the frequency shift of a light beam may be caused to vary with time (e.g. ω(t)=kt) so as to effectively create a travelling optical chirp. In each case, the interference pattern created on the hologram for reading out the data will contain a translating sinusoidal fringe system with a time varying spatial frequency, and the output of the photo-detector represents the integral of the product of hologram transmissivity and the illumination intensity pattern, which may then be demodulated to obtain the original data.

22 citations


Book ChapterDOI
01 Jan 1978
TL;DR: In this paper, the authors proposed a control transparency for holographic memory in lithium niobate (Niobate) crystals and investigated the erasing of data by means of a He-Cd laser and the rewriting of information.
Abstract: Physical processes ocurring when holograms are recorded in lithium niobate crystals are considered. The data are recorded with the use of a He-Ne laser. The erasing of data by means of a He-Cd laser and the rewriting of information are studied. The proposed holographic memory differs from the known arrangements in that it is provided with a control transparency. The results of investigating an orthoferrite transparency are presented.

6 citations


Patent
06 Nov 1978
TL;DR: In this paper, an improved phase measuring method and apparatus for measuring the relativehase and amplitude of an applied optical signal beam at a number of points in a plane is presented, where the combination of the signal beam and a reference beam are simultaneously directed onto a pair of photodector arrays, the reference beam on one array being π/2 radians out of phase with the reference beacon on the other array.
Abstract: An improved phase measuring method and apparatus for measuring the relativehase and amplitude of an applied optical signal beam at a number of points in a plane. The combination of the signal beam and a reference beam are simultaneously directed onto a pair of photodector arrays, the reference beam on one array being π/2 radians out of phase with the reference beam on the other array. Respective interference patterns are formed on the photodector arrays, points on the arrays are sampled, and the desired amplitude and phase of the signal beam at the sampling points is determined by a series of computational steps.

1 citations