Showing papers on "Signal beam published in 1985"

Remote measurement of physical variables with fiber optic systems - methods, materials and devices

Abstract: Methods, materials and devices for the remote measurement of physical variables with fiber optic systems use a single excitation light source for generating through the use of at least one luminescence converter, both a signal beam and a reference beam, and allow the transmission of both beams through a single fiber to a single photodetector, thus producing photo-electric signals the relative intensities of which are only minimally affected by changes of the intensity of the interrogating light beam, optical losses, or detector drift. In contrast to the prior art, the luminescent materials of this invention can be used either as transducers for physical parameters or as means for processing information from other optical transducers, without requiring a change in the luminescence properties of said materials under the influence of the measured parameter. Furthermore, the techniques and devices of this invention allow the use of luminescent materials for converting a measurand with a low coefficient of change under the action of the parameter being measured into a measurand with a large coefficient of change.

Optically actuated optical switch apparatus and methods

Abstract: A switch capable of switching an optical beam without employing conventional mechanical, electrical, or optical devices The switch includes a switching medium which may be a solid, liquid, gas, or supercritical gas A signal or switched beam is directed into and through the switching medium In order to change the path of the signal beam as it travels through the switching medium, the refractive index of the switching medium is changed This change in refractive index is caused by a control beam selectively directed into the switching medium The control beam produces a transient refractive index gradient within the switching medium This gradient may be a thermal gradient and may constitute a thermal lens The switch of the current invention is capable of picosecond response times and may serve as a fiber optics communications switch as well as an element in an optical computer

Dynamic Optical Cross-Correlator Using A Liquid Crystal Light Valve And A Bismuth Silicon Oxide Crystal In The Fourier Plane

Abstract: A complete real-time cross-correlator using both a photoconductive bismuth silicon oxide [Bi12Si020 (BSO)] liquid crystal light valve for data input and a photorefractive BSO crystal as a dynamic holographic filter is presented. Some specific properties of this dynamic optical processor are reported. The following optimum operating conditions of the light valve were used in the experiment: driving voltages, 30 Vrms; frequency, 300 Hz; and writing energy of the light valve in the blue-green spectral range, 150 /uJ cm -2. For a 15µm thick pentylcyanobiphenyl (PCB) liquid crystal layer, the measured spatial resolution at 50% MTF is 12 1p mm-1, thus ensuring a potential processing capability of 300X:300 pixels. The optimized time constant of the operating optical processor, including both the light valve and the photorefractive BSO crystal, is around 50 ms for 0.2 mW cm-2 incident intensity on the light valve at the green line of an argon laser. Experimental cross-correlation results for various types of digital or analog data written on the light valve are shown in this paper. Compensation of the residual distortions of the incident signal beam emerging from the light valve has been achieved by generation of a phase conjugate wavefront diffracted by a high efficiency holographic lens recorded on dichrornated gelatin.

Recursive optical filter system

Abstract: An optical notching or filtering system in which a beam of optical radiation is passed through the optical filtering means a multiplicity of times. The optical filtering means has an optical Fourier transform means (12), a spatial filter (14), optical inverse Fourier transform means (16), and a reflector array (18). After an input optical signal beam undergoes a filtering pass by being directed through the transform means, the filter, and the inverse transform means, the reflector array re-introduces the beam for a multiplicity of subsequent filtering passes. Four embodiments of the system of the invention having various configurations of the reflector arrays for use with one- and two-dimensional spatial filters are disclosed. The various embodiments are set forth as being used in a heterodyning optical notching filter systsm.

Method and device for Doppler laser velocimetry with homodyne detection

Abstract: The laser velocimeter with homodyne detection is constructed from a laser 1 whose linearly polarised radiation is applied in 10 to an optical system 2 of the Mach-Zender interferometer type. The measurement beam strikes the object, whose velocity is to be measured, either directly or through a telescope 8. The signal beam S and the local oscillator beam OL are produced with a slight angular offset between them before striking a double detector 5. The angular offset is chosen so that the wavefronts of the two beams are offset by a half wavelength over the whole surface of the double detector 5. A comparison of the phases of the signals received by the two detectors gives the sign of the velocity.

Sensitivity, Noise and Optical Crosstalk in Heterodyne Acousto-Optical Signal Processors

Abstract: It has been suggested that the optical scattering effect in a heterodyne acousto-optical system can be ignored because its beat frequency with the reference beam is outside of the IF passband of the heterodyne detection. Our analysis concludes that this is not true. A finite point spread function convolving with the reference beam of a heterodyne spectrum analyzer causes mixing of photons with different frequency shifts and thus generates IF noise. A signal beam with finite scattering level also contributes to optical cross-talk by mixing with scattered reference beam. This problem is made clear below by analytical derivation and experimental data.© (1985) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Color light signal using light emitting diodes

Abstract: A colour light signal especially adapted to railroad use has a cluster of diodes in place of a conventional incandescent source and each diode is located behind a collimating lens (the diodes may be located behind individual lenses or the entire cluster of diodes may be behind a single lens, if desired) and is positioned so the on-axis energy emitted from each diode is so directed that the combined wavefront is seen by the lens to originate at its focus, so that the dispersed energy is collimated into a signal beam of high-intensity and high directionality.