Showing papers on "Signal beam published in 1988"

3-dimensional vision system utilizing coherent optical detection

Abstract: A three-dimensional optical scanning vision system capable of producing high-resolution images in real-time includes an optical source for producing a source light beam. The source light beam is directed to a beam splitter which splits it into a local oscillator beam and a signal beam. The local oscillator beam is directed toward a photodetector, while the signal light beam is directed toward a target. Light reflected from the target is received by the beam splitter and directed toward a retroreflector which returns the beam to the beam splitter interface. Quarter wave plates and the retroreflector insure that the return light beam and the local oscillator beam are collimated and have the same polarization state. Mixing of the local oscillator beam and the return light beam occurs at the beam splitter interface, thus providing coherent optical detection by the photodetector. The photodetector thus provides an output signal providing a high degree of information about the target. The system also includes scanner optics to scan the signal light beam across the target. A processor is also included for outputting a three-dimensional image of the target, and for controlling the scanner optics.

Two‐wave mixing with time‐modulated signal in Bi12SiO20 theory and application to homodyne wave‐front detection

Abstract: We theoretically analyze a two‐wave mixing interaction in photorefractive Bi12SiO20 crystals in which the amplitude of the signal beam is time modulated at high frequency. Calculations of the photoinduced space‐charge field are derived for a sinusoidal modulation of the input signal. Due to the time‐integrating properties of the nonlinear crystal, the transmitted signal exhibits a differential gain when the modulating frequency is much greater than the inverse of the material response time. Application to coherent homodyne detection of wave fronts carrying spatial and temporal information is also presented.

Optical signal amplification at 1.3 μm by two-wave mixing in InP:Fe

Abstract: Two-wave mixing experiments demonstrate amplification of optical signals using the photorefractive effect in InP:Fe. Signal beam amplification was obtained at both 1.06 mu m and 1.32 mu m with gains of 13 dB/cm and 11 dB/cm, using alternating electric fields of up to +or-10/sup 4/ V/cm. Differential amplification at data rates exceeding the material response time is demonstrated.

Optical correlator system

Abstract: An optical correlator system, comprising a laser to generate a signal beam, an image means located in the path of the signal beam to spatially modulate the signal beam, and first and second matched filters. A multiple beam generating holographic lens is located in the path of the modulated signal beam to partially transmit the signal beam and to deflect a first matrix of replicas of the signal beam onto the first matched filter. A mirror is located in the path of the partially transmitted signal beam to reflect that transmitted beam back to the holographic lens, which deflects a second matrix of replicas of the signal beam onto the second matched filter. With an alternate embodiment, a series of holographic lenses and beam splitters are alternatively arranged along the path of the signal beam. Each holographic lens generates two matrices of beams, with each matrix of beams being focused on an associated matched filter. Each beam splitter partially reflects the signal beam back to the preceding holographic lens, and partially transmits the signal beam to the following holographic lens.

High-resolution laser spectroscopy based on polarisation-modulated optical phase conjugation in a demountable cathode discharge

Abstract: Doppler-free laser spectroscopy based on polarisation-modulated optical phase conjugation in a demountable hollow-cathode discharge is a sensitive analytical method, as a visible coherent laser beam is generated as the signal. Because the conjugate signal beam is a time-reversed replica of the probe beam, the optical signal can be detected conveniently and efficiently. Spectral resolution is excellent as both Doppler and Lorentzian broadenings are negligible. Taking advantage of the polarisation properties of the phase-conjugate wavefront, we demonstrate a novel polarisation-modulated detection scheme in this spectroscopic method using a relatively low-power continuous-wave laser and the hyperfine structure of the sodium 3s 2S1/2 to 3p 2P3/2 transition. Some advantages of the polarisation-modulated degenerate four-wave mixing are discussed.

Coherent optical detection through two-wave mixing in photorefractive materials.

Abstract: Photorefractively induced index-of-refraction phase gratings are shown to combine coherently the optical fields of a strong pump and a suitably amplitude- or phase-modulated signal beam in such a way that an apparent amplification of the modulating waveform appears as intensity modulation of the transmitted signal and pump beam intensities. The source of the signal gain is shown to be the square-law (intensity) detection of the coherently combined pump and modulated signal beams, just as in coherent optical communication systems in which a strong local-oscillator field is coherently added with a weak optical signal field by a beam splitter.

Evaluation of power penalty due to beat noise induced by connector reflection

Abstract: Power penalties caused by beat noise in a received optical signal beam were evaluated experimentally and theoretically. It was found that power penalties could be suppressed when the beam relative intensity noise was reduced to less than −135 dB/Hz below 2.4 Gbit/s. This goal can be satisfied using a commercially available physical contact optical connector, which has less than −20 dB reflection.

Optical parametric amplifying variable spatial filter

Abstract: An optical parametric amplifier system is used to illuminate an object of interest with a signal beam, and parametrically mix the signal beam from the object with a pump beam to produce a down converted idler beam which maintains an image of the object of interest but which has a frequency which equals the difference between the frequencies of the pump beam and the signal beam. A signal laser is used to illuminate the object of interest, while a pump laser produces the pump beam. A beam combiner mirror produces a combined output by receiving and combining the pump beam and the signal beam. Finally, a nonlinear crystal receives and down converts the combined output of the beam combiner mirror to produce the idler beam by parametrically mixing the signal beam with the pump beam. When a KDP nonlinear crystal is used, the crystal optic axis may be rotated with respect to the direction of propagation of the idler beam to spectally score and amplify the image of the object of interest.

Wavefront conjugation and amplification for optical communication through distorting media.

Abstract: Combining double-phase conjugation with various coherent amplifiers leads to an amplified beam (forward or conjugated) derived from a local laser but bearing the transversal phase pattern of a received signal beam from a remote laser. We suggest several uses in optical communication through a distorting atmosphere.

Efficient dynamic phasefront modulation system for free-space optical communications

Abstract: An optical communications system is disclosed for correcting in real-time the wavefront distortions of a beam from a coherent optical transmitting source The system includes a collimating lens and beam splitter for receiving a distorted wavefront signal beam and splitting the beam into a pump beam and a weaker intensity signal beam The system includes a detector and computer for measuring the beam distortion and specifying a compensatory wavefront The weaker intensity signal beam is modified in a 2-D spatial light modulator according to a compensatory wavefront A photo-refractive material is used to couple energy from the pump beam to the compensated wavefront signal beam thereby producing a corrected and intensity-enhanced communications beam

Unidirectional ring resonator in photorefractive bismuth silicon oxide with two pump beams

Abstract: Experiments using a new photorefractive gain mechanism involving two pump beams are described. A ring resonator is used to provide a frequency‐shifted signal beam. The gain with two pumps of equal intensity is found to exceed that with a single pump by about a factor of 4.

Device for optical heterodyne or homodyne detection of an optical signal beam and receiver provided with such a device

Abstract: A device for optical heterodyne detection is described, using only two adjustable elements influencing the state of polarisation and having a limited control range (51, 52) in order to realize an endless polarisation control. In a first embodiment a temporary loss of signal intensity of at most 3 dB is accepted. This signal loss is avoided if a circuit of non-adjustable optical components (81, 82, 83) is incorporated in the heterodyne detection device.

Optical head device

Abstract: PURPOSE:To eliminate a complex optical system and to enable easy differential detection by providing a polarizing means whose polarizing direction is perpendicular to the front surfaces of two photoelectric converting means arrayed in the moving direction of image re-formation of recording pits CONSTITUTION:Light emitted by a light source 1 is transmitted through a beam splitter (BS) 2, and polarized and image-formed to form an irradiation beam spots 20 on a recording track on a recording medium 73 Reflected light which is varied in angle of polarization by a recording pit travels backward and is reflected by the BS 2 and passed through mutually orthogonal polarizing plates 4 and 5 to form signal beam spots 22 on the photoelectric converting elements 6 and 7 The elements 6 and 7 are so arranged that the spot 22 moves from the element 6 to the element 7 according to the movement of the recording pit The output signal of the element 6 is passed through a delay element 8, the output of the element 7 is inputted directly to a subtracting circuit 9, and the differential output from which the influence of light quantity variation is removed appears at an output terminal 10

Compensating pulse-to-pulse fluctuations and increasing spectral reproducibility of phase-matched CARS measurements.

Abstract: The compensation of pulse-to-pulse fluctuations and the improvement of spectral reproducibility of scanned coherent anti-Stokes Raman scattering (CARS) spectra of dispersing media are discussed. A simple reference CARS setup is presented that needs a minimum number of optical components as a result of using the same optical path for both signals. Variations in spectral profile were found to be caused by mechanical play in the translation stage, which is used to adjust the matching angle. Using retroreflection, the matching angle adjustment is made insensitive to these mechanical imperfections. The multiple interference of probe and signal beam that may occur in thin cuvette walls and its effect on the detected CARS signals are shown, and possible solutions are discussed.

Improvements in apparatus for the positional detection of objects

Abstract: Apparatus for the positional detection of objects in which a holographic image of the sample object is recorded on a photographic plate, which includes a laser source (40), a double convex lens (42) a collimating mirror (44), a holographic recording plate (46) and an object support (48). The lens (42) directs both the reference and signals onto the collimating mirror (44) and the object support (48) respectively. The signal beam by interference with the reference beam produces a three dimensional holographic image of the object on the recording plate (46).

Real time image inversion using four-wave mixing

Abstract: An intensity inverter includes an optically nonlinear medium and a reference beam having a uniform transverse intensity distribution and having the same wavelength as the signal beam. The reference beam is directed into the nonlinear medium. A readout beam having the same wavelength as the signal beam and counterpropagating with respect to the reference beam is also directed into the nonlinear medium. When the signal beam is directed into the nonlinear medium, the signal beam and the reference beam interact to form a hologram within the nonlinear medium, thereby diffracting a portion of the readout beam, the undiffracted portion of the readout beam having imposed on it an inversion of the signal.

Theory of intracavity-pumped photorefractive phase-conjugate mirror

Abstract: We present a new type of phase-conjugate mirror that is based on an externally driven Fabry-Perot interferometer with intracavity-pumped photorefractive material, which is probed by the signal beam. It is shown theoretically that such a configuration leads to multivalued solutions and possibly to bistability. This configuration also permits optical control of the resonator output and electrical control of the phase-conjugate reflectivity.

Method and apparatus for determining the sign of the direction of a particle stream

Abstract: In a method in which a heterodyne-laser-Doppler method is used for the demination of the sign of the direction of a particle stream, the beam from a laser source is directed by means of an optical arrangement used as an emitter optical system to a measuring volume in an interferometer device. A frequency difference between the emitted laser beam and the laser beam returning into the optical arrangement is measured through heterodyne reception by means of the same optical arrangement used as a receiving optical system; this returning laser beam is frequency-shifted because of scattering by particles moving with the same speed in the particle stream and because of the Doppler effect. In the method according to the invention, an additional Doppler shift with a definite sign then is alternately impressed on the laser beam in exactly defined areas of beam paths, the additional Doppler shift being preferably considerably smaller than the Doppler shift generated by the particle movement. The exact direction of the particle stream then is determined from the received scattered back laser beam by comparison of this scattered back laser beam with a laser source reference beam. The additional Doppler shift can be impressed on a reference beam or emitted beam split from the laser beam, on the laser beam scattered back by the measuring volume or on the emitted beam and signal beam flowing in opposite directions in the optical arrangement.

Transillumination imaging system using the antenna properties of heterodyne detection

Abstract: In a transillumination imaging system in which a body (H) is illuminated by transparency by a beam of light (FS, F1), a beam splitter (S1) derives from this beam (FS) a beam fraction (F'1) whose frequency is shifted by a frequency changer (CF). The beam (F3) obtained is combined with the signal beam (F2) produced by illumination of the medium (H). A detector (D) receives these beams and supplies a photocurrent having a frequency intermediate between the frequency of the signal beam (F2) and that of the frequency-shifted beam (F3). A privileged direction of the diffused light is thus isolated in the signal beam. Application: medical imaging.

Fiber raman amplification optical communication system

Abstract: PURPOSE: To improve receiving sensitivity by separating the wave lengths of a signal beam and an excited beam by a branching filter on the receiving side and directly detecting the intensity change of the signal beams due to modulation and the intensity change of the excited beam corresponding to the intensity change of the signal beam respectively different photodetectors. CONSTITUTION: Beams projected from a signal light source 11 and an excited light source 12 are mixed with each other by an optical mixer 13 such as a half mirror, a wave length separating film and a polarized light separating film and made incident upon an optical fiber 15 through a lens 14. A signal from and an excited beam made incident upon an optical fiber 15 are projected from a projection end by mutually applying/receiving optical energy. The projected beam is made incident upon the branching filter 17 and separated at its wave length into a signal beam and an excited beam, respective beams are made incident upon photodetectors 19, 20 arranged in a single photodetecting machine 18 and direct detection signals inversed to each other can be obtained. The signals are amplified by a differential amplifier 21 and sent to a demodulating circuit. Since the intensity change of the excited beam on the receiving side due to the amplification of the signal beam has almost the same amplitude of the intensity change of the signal beam, the receiving intensity can be improved. COPYRIGHT: (C)1989,JPO&Japio

Structure of lasing modes generated as a result of a four-wave interaction with feedback

Abstract: The diffraction approximation is used to determine the structure of the radiation generated as a result of a four-wave interaction with feedback and the conditions for phase conjugation are identified. Phase conjugation can be expected in the case of a signal beam with a smooth distribution of the amplitude if the transverse size of this beam decreases as a result of passing through a feedback loop. In the case of a multimode signal beam it is additionally necessary to ensure that the resonator length or the length of the nonlinear medium exceeds the spreading length of the transverse inhomogeneity of the field.

Fringe scanning method

Abstract: PURPOSE:To perform uniform fringe scanning without disturbing a wave front over the entire range of beam, by performing fringe scanning while the phase scanning between reference beam and signal beam is changed by the voltage applied to a member having electrooptical effect. CONSTITUTION:When the voltage from an oscillator 15 is applied to the electrooptical crystal 18 provided on the common beam path 2 of reference beam and signal beam as crystal apply voltage 17 through an amplifier 16, the phase difference between the reference beam and the signal beam receives relative modulation in proportion to said voltage to perform fringe scanning. When the applied voltage data at this time is taken in a computer and the image processing of the interference fringe pattern subjected to modulation is performed, the interpolation between fringes can be performed and the profile of an object to be measured can be measured with measuring resolving power higher than lambda/4.

Method and apparatus for detecting profile error of article surface

Abstract: An optical non-contact detection of profile errors of a surface or surfaces of an article, such as an industrial product is carried out by a coherent signal bea of light introduced along an imaginary plane and projected onto the surface of the article at a large angle of incidence. The signal beam of light is reflected from the surface toward the same imaginary plane and traveled past optical system toward a photosensitive material on which a separate reference beam of light is projected. A hologram of the surface is formed on the photosensitive material, which is used for an analysis of the profile errors of the surface.

Frequency response measurement and SNR improvement of three infrared detectors.

Abstract: A comparison of three different infrared detectors in the 10.6-μm region is presented. A method for measuring the frequency response from dc up to 100 MHz in a continuous way is developed. We show that the flatness of the frequency response does not only depend on the electronic circuit following the detector, matching the impedance between the detector and the preamplifier, but also on the parallelism of the local oscillator and the signal beam. The signal-to-noise ratio of the detector signal is improved and reaches the theoretical limit by chopping only the signal beam and detecting the spectral analyzed intermediate frequency signal with the lock-in technique. Detecting the signal in this new way suppresses externally detected noise, which is omnipresent in weak signal detection.

Optical system with an optically addressable plane of optically bistable material elements

Abstract: This device is an all-optical digital architecture for carrying out compuions. Residue number system addition and multiplication tables are produced on an optically-addressable plane composed of optically bistable material. The plane of optically bistable material devices represents a residue number system addition or multiplication tables and is addressed by two intersecting signal beams from the top and a bias beam from the bottom. A combination of two signal beams exceeds the material transmission threshold in the intersection region letting bias light emerge as a position encoded signal beam.

Apparatus for detecting profile error of article surface

Abstract: An optical non-contact detection of profile errors of a surface (10) or surfaces of an article, such as an industrial product is carried out by a coherent signal beam (S) of light introduced along an imaginary plane and pro­jected onto the surface of the article at a large angle of incidence. The signal beam of light is reflected from the surface toward the same imaginary plane and traveled past optical system (14b, 12b, 46) toward a photosensitive material (48) on which a separate reference beam (R) of light is projected. A hologram of the surface is formed on the photosensitive material, which is used for an analysis of the profile errors of the surface.

Wave-Mixing In Liquid Crystal And Mercury Cadmium Telluride

Abstract: We report signal beam amplification in degenerate two-wave mixing experiment at λ = 10.6 μm wavelength in nematic liquid crystals operating near the phase transition temperature. Theoretical results and experimental data are presented. We also present two and four-wave mixing experiments in Hg0.78Cdo.22Te at low temperature.

Phase conjugation of pulsed CO2 laser radiation by four-wave mixing in CCl4

Abstract: An experimental investigation was made of phase conjugation under conditions of degenerate four-wave interaction of CO2 laser radiation in carbon tetrachloride as a function of various parameters of the signal radiation and of the experimental geometry. It was found that the conjugation accuracy for a single-mode signal beam with a divergence of 2 mrad was 87%, but when a phase plate introducing a divergence of 70 mrad was used, the accuracy was 77%. The reflection efficiency and the phase conjugation quality depended strongly on the ratio of the energy density of the signal wave to the energy density of the pump wave. An investigation was made of the dependence of the reflection coefficient on the angular mismatch between the counterpropagating pump waves and on the matching of the optical paths of the interacting waves.

Optical correlator system

Abstract: An optical correlator system comprising a laser to generate a signal beam, a film to spatially modulate that beam, and a beam splitter to split the signal beam into two component beams. The first component beam is directed onto a first side of a multiple holographic lens, which generates from the component beam a first matrix of individually converging beams and a second matrix of individually diverging beams. The second component beam is directed onto a second side of the holographic lens, which generates from this component beam a third matrix of individually converging beams and a fourth matrix of individually diverging beams. The beams of the first and third matrices are focused by the holographic lens onto first and second matched filters, respectively, and correcting optical elements are used to focus the beams of the second and fourth matrices onto third and fourth matched filters, respectively.