Signal beam

About: Signal beam is a research topic. Over the lifetime, 1881 publications have been published within this topic receiving 20717 citations.

Linear phase encoding for holographic data storage with a single phase-only spatial light modulator.

Abstract: A linear phase encoding is presented for realizing a compact and simple holographic data storage system with a single spatial light modulator (SLM). This encoding method makes it possible to modulate a complex amplitude distribution with a single phase-only SLM in a holographic storage system. In addition, an undesired light due to the imperfection of an SLM can be removed by spatial frequency filtering with a Nyquist aperture. The linear phase encoding is introduced to coaxial holographic data storage. The generation of a signal beam using linear phase encoding is experimentally verified in an interferometer. In a coaxial holographic data storage system, single data recording, shift selectivity, and shift multiplexed recording are experimentally demonstrated.

Amplification of optical signals in Bi(12)TiO(20) crystal by photorefractive surface waves.

Abstract: We have demonstrated experimentally beam amplification by coupling between the signal beam and the photorefractive surfaces wave in Bi12TiO20 crystal. A gain of 16,000 has been measured, with an output signal-to-noise ratio of >20 for weak input signals.

Optical spatial solitons supported by photoisomerization nonlinearity in a polymer.

Abstract: We present a theory for a new type of optical spatial soliton that is based on the angle hole burning mechanism of photoisomerization in some polymers. We predict that the photoisomerization nonlinearity can support steady-state dark and bright spatial solitons in the polymer. We also discuss the dependence of the FWHM of the spatial soliton on wavelengths of the background beams and on the ratio of the intensity of the background beam to that of the signal beam.

Phase-insensitive hologram readout technique

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.

Apparatus and method for increasing the bandwidth of a laser beam

Abstract: A method and apparatus is disclosed that provides a laser output beam having a broad bandwidth and an intensity smooth over time. The bandwidth of the laser output can be varied easily by varying the intensity of a broadband source. The present invention includes an optical modulation apparatus comprising a narrowband laser that outputs a horizontally polarized beam (a "signal beam") and a broadband laser that outputs a vertically polarized beam (a "pump beam") whose intensity varies rapidly. The two beam are coupled into a birefringent laser material so that the respective polarizations coincide with the principal axes of the material. As the two beams travel through the material, the polarization preserving properties of the birefringent material maintain the respective polarizations of the two beam; however there is coupling between the two beams as a result of cross phase modulations, which induces a bandwidth change of the signal beam. The amount of bandwidth change is dependent upon the average intensity of the pump beam. The beams are coupled out from the birefringent material and the modulated signal beam is separated by a polarization selector. The modulated signal beam now has a wider bandwidth, and its shape remains smooth in time. This signal beam can be applied to incoherence inducing systems. The different bandwidths required by these different incoherence inducing systems can be obtained by varying the intensity of the pump beam. The United States Government has rights in this invention pursuant to Contract No. W7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.