Showing papers on "Signal beam published in 1994"

Laser-induced thermal acoustics: simple accurate gas measurements

Abstract: Laser-induced thermal acoustics (LITA), an optical four-wave mixing technique, has been used for sensitive measurement of the sound speed, thermal diffusivity, acoustic damping rate, and complex susceptibility of a gas. In LITA, laser-induced acoustic waves scatter laser light into a coherent, modulated signal beam. A simple expression accurately describes the signal. Atmospheric sound speeds accurate to 0.5% and transport properties accurate to 30% have been measured in a single shot without calibration. LITA spectra have been taken of weak spectral lines of NO2 in concentrations of less than 50 parts in 10^9. Signal reflectivities up to 10^4 are estimated.

Time gated imaging through scattering material using polarization and stimulated raman amplification

Abstract: An apparatus for imaging into or through scattering materials (17) includes a source (20) for producing a broadband laser reference beam (R) and a Stokes illumination beam (Si) correlated to the reference beam The Stokes illumination beam is transmitted into the scattering material to obtain a Stokes signal beam (Ss) having a first image carrying component and a first nonimage component The reference beam and the Stokes signal beam are then separately delayed (Rd, Sd) and polarized (Rp, Sp), after which they are combined to produce a combined beam (C) having a Stokes component and a reference component A Stimulated Raman amplifier (30) responsive to the combined beam produces an amplified signal beam (A) in which the image carrying component has been amplified by a higher gain factor than the nonimage component

Contour mapping of the spatiotemporal state of polarization of light.

Abstract: A novel interferometric polarimeter capable of mapping a spatiotemporal change in the state of polarization (SOP) of light is described. The polarimeter has a reference beam of light with two orthogonal linearly polarized components that interfere with the counterpart components of an elliptically polarized signal beam. The resultant interference pattern is recorded by a computer by the use of a wideband metal-oxide semiconductor video camera. The interference pattern reduces to the ellipticity and azimuth of the ellipse at an instant of time, by which the spatiotemporal change in the SOP is mapped. No optical elements are used for the control of polarization in the polarimeter, and this allows for the mapping of a rapid change in the SOP. Successful experiments are demonstrated by generating an elliptically polarized beam whose SOP varies in space and time.

Deamplification response of a traveling-wave phase-sensitive optical parametric amplifier.

Abstract: We have investigated the phase-sensitive deamplification response of a traveling-wave degenerate optical parametric amplifier that consists of a type II phase-matched KTP crystal pumped by the second harmonic of a Q-switched mode-locked Nd:YAG laser. Experimental results are in good agreement with the theory of an optical parametric amplifier in which the Gaussian-beam nature of the various fields along with the diffraction of the amplified signal beam is taken into account. Because of the phenomenon of gain-induced diffraction, maximum deamplification is limited to only ≃3 dB.

Optical fiber amplifier

Abstract: PURPOSE: To prevent the occurrence of an optical surge when becoming a non- signal state without bringing on a loss of a signal beam and without increasing an increase index by monitoring two optical outputs with a photodetector and controlling excitation light with a light intensity ratio of light of both wavelengths. CONSTITUTION: An optical band-pass filter 10 transmits selectively through light of a wavelength λ1, and the optical band-pass filter 11 transmits selectively through the light of the wavelength λ2. At this time, the wavelength λ2 whose wavelength is selected to one in the vicinity of the wavelength λ1. The optical band-pass filter 11 is provided with a narrow wavelength band characteristic, and cuts off the light of the wavelength of λ1. The light intensity ratio of respective wavelengths λ1, λ2 light received by the photodetectors 12, 13 is changed according to the change of the input level of the input signal of the wavelength λ1, and the ratio is changed large under the non-signal state. Thus, when the light intensity ratio of respective wavelengths λ1, λ2 detected by the photodetectors 12, 13 becomes a prescribed reference value or below, the occurrence of the optical surge is suppressed by performing no amplification.

Tunable IR laser source with optical parametric oscillators in series

Abstract: A tunable IR laser source is described. A Q-switched Nd:YAG laser at 1.064 µm is used to pump two optical parametric oscillators (OPO's) in series. The first OPO uses a LiNbO(3) crystal and works in the vicinity of degeneracy. Its signal beam (adjusted to 1.82 µm) is used to pump the second OPO, which uses a AgGaSe(2) crystal and covers the range 2.6-6 µm. The conversion efficiency between the energy produced by this OPO in the signal and idler beams (λ(s) = 2.6 µm and λ(i) = 6 µm, respectively) and the input energy at 1.064 µm is 1.75%.

Spatial optical transmission apparatus and method

Abstract: A spatial optical transmission apparatus includes: a light signal transmitting device for generating a signal beam which is modulated in accordance with a signal to be transmitted and is intensity-modulated with a lower frequency compared with a signal transmission speed; and a light signal demodulating device for receiving the signal beam from the light signal transmitting device by a detector, adjusting the direction of a locally oscillated beam based on the received signal beam so as to have a predetermined relationship with the direction of the signal beam so that intensity-modulated components in an output signal from the detector falls within a predetermined range of intensity, thereby aligning the wavefront of the signal beam with the wavefront of the locally oscillated beam, and extracting signal components which correspond to the transmitted signal from signal components modulated in accordance with the transmitted signal in the signal beam.

Narrow linewidth BBO optical parametric oscillator utilizing extraordinary resonance

Abstract: Optical parametric oscillators using non-linear crystals cut for the type I interaction have an extraordinary pump beam which generates ordinary signal and idler beams. The use of an optical element to rotate the signal beam before sending this signal beam to a grating element allows for the grating element to have its dispersion plane oriented coplanar with the extraordinary crystal plane of the non-linear crystal. In this manner, for non-linear crystals which have relatively narrow acceptance angles, such as BBO crystals, the reduction in angular aperture of the parametric gain in the extraordinary plane will produce a reduction in the linewidth of the produced output. The grating translates the angular variations into variations in wavelength. If no rotator was used in the optical parametric oscillator, then in order to get the maximum efficiency out of the grating, the dispersion plane of the grating should be orthogonal to the extraordinary plane of the crystal, and therefore the narrow angular acceptance of the crystal would not result in a narrow output linewidth.

Electronic perimeter warning system

Abstract: Apparatus and method are disclosed to provide an electronic perimeter warning system to prevent the ingress or egress of persons or machines from a selected area such as in an area along the perimeter of a roof under construction. Battery powered signal transmitters and receivers establish a signal beam between two locations. When the continuity of the signal beam is broken, an alarm is sounded to warn the person who is crossing the signal beam of imminent danger.

Bistability and symmetry breaking in distributed coupling of counterpropagating beams into nonlinear waveguides

Abstract: By using a modal approach, the distributed coupling of two inhomogeneous, transient waves with opposite angles of incidence into nonlinear waveguides is studied. We show that cross modulation and the coherent interaction via a dynamic grating, nonlinearily induced by the excited counterpropagating leaky waves, provide a longitudinal feedback. This feedback is the necessary prerequisite for bistability to occur. We show that bistability may even appear when one incident beam is weak. Consequently, modulation of the strong signal beam by a weak control pulse can be achieved. Furthermore, we demonstrate that the symmetry of the input signal can be broken beyond a certain intensity and that set-reset flip-flop operation with finite beams is feasible. We demonstrate that the mechanism responsible for this flip-flop operation differs considerably from that acting in the plane-wave case. The optical nonlinearities may be caused by either virtual or real carrier excitation, which models the behavior of semiconductors as well as nonlinear polymers or organic dyes well below or close to a resonance, respectively. For real carrier excitation the interplay of carrier relaxation, diffusion, and the propagation of the excited fields is taken into account.

Point-diffraction interferometer utilizing separate reference and signal beam paths

Abstract: A split-path point-diffraction interferometer (SPPDI) comprising separate signal and reference beam paths is disclosed. A beamsplitter is used to divide a linearly polarized converging incident signal beam into separate signal and reference beam paths prior to focus. The reference beam path comprises a diffracting aperture located at the focal point of the signal beam. The diffracting aperture in the reference beam path produces an expanding, diffraction-limited reference wavefront. The signal and reference beam paths comprise linear polarizers whose yaw, pitch, and roll orientation may be freely adjusted. Yaw and pitch adjustment of one or more linear polarizers provides for adjustment of fringe spacing and orientation. Roll adjustment of one or more linear polarizers provides for adjustment of fringe contrast and intensity. Beam turning mirrors are used to direct the signal and reference beams to a beam combiner. Polarizing analysers are placed in the combined output beams produced by the beam combiner. A double-pass embodiment of an SPPDI comprising a beam splitter and compact laser source is disclosed.

Coherent homodyne optical communication receivers with photorefractive optical beam combiners

Abstract: The principles of operation and the results of performance measurements are reported of a new type of coherent optical receiver that used a dynamic volume index of refraction grating formed inside a photorefractive material to coherently combine signal and local oscillator light prior to photodetection. Because the refractive index grating is formed by the interference pattern generated where mutually coherent optical beams overlap, the receiver can automatically adjust to changes in angle of arrival or optical wavefront profiles which occur on time scales longer than the grating formation time. The grating appears stationary to high-speed phase modulation imposed on the signal beam and coherently diffracts local oscillator light into the signal beam direction. Performance measurements are reported for a prototype system that used two independent Nd:YAG lasers at 1.064 /spl mu/m, an iron-doped indium phosphide photorefractive crystal, and a four-slot phase modulation signal format. A receiver BER of 10/sup -6/ was obtained at received signal powers that corresponded to an average of 70 detected signal photons per bit at a source data rate of 50 Mb/s, 130 detected signal photons/bit at 220 Mb/s, and about 400 detected signal photons/bit at a 325 Mb/s source data rate. Quantum-limited operation corresponds to an average of six detected signal photons per transmitted information bit for this signal format. >

Optical image processing by an atomic vapour

Abstract: ATOMIC vapours can exhibit large optical nonlinearities1. When laser light is tuned in resonance with an atomic transition, the absorption cross-section of the atom can become very large, typically seven orders of magnitude larger than the cross-sectional area of its electron cloud2. Because of these strong nonlinearities, different laser beams can interact with one another in an atomic vapour, even at intensities as low as a few milliwatts per cm2. This raises the question1 of whether atomic vapours can be used as nonlinear optical elements for parallel optical image processing. A well-known example of an all-optical image processor is the optical correlator: laser beams with imprinted images interact in a nonlinear medium to produce a signal beam, the intensity distribution of which is related to the correlation integral of (and hence the degree of similarity between) the input images. Here we demonstrate the use of a caesium-atom vapour as the active medium in such an optical correlator. We show that this system compares favourably with others currently in use, particularly with regard to its power requirements.

Two-way line monitor

Abstract: A two-way line monitor has a signal beam splitter, first and second optical sensors and a mirror. The beam splitter is positioned on the light axis and angled so as to receive first and second input lights at 20 to 40 degrees of the angle of incidence. The first and second optical sensors arranged so as to receive first and second sample lights, reflected from the beam splitter and the mirror, at around 20 degrees of the angle of incidence.

Methods and systems for analyzing data

Abstract: A method and system for searching for a given sequence in a data base having a multitude of reference sequences stored or identified therein. In accordance with this method, a light beam is modulated with patterns representing the reference sequences, and with a pattern representing the given sequence, and a correlation signal is generated representing the correlation of the reference and given sequences. Optical diffraction patterns may be used to represent the given and reference sequences. In one embodiment, a multitude of first diffraction patterns, each one representing the given sequence, are formed in an optical medium, and a light beam is modulated with each of those multitude of diffraction patterns to form a multi-channel signal beam. Each channel of that beam is then modulated with a respective one second diffraction pattern representing one of the reference sequences to form a multi-channel correlation beam. The intensity of each channel of the correlation beam is then measured to determine whether the given sequence correlates with any of the reference sequences.

Control of a launched polarization state of a frequency modulated beam coincident with an optical fiber principal axis

Abstract: In an optical communication system for transmitting an optical fiber which may include an optical amplifier comprising an optical isolator, a polarization control system comprises at a send end a launch polarization controller for giving a launched state to the signal beam launched to the optical fiber. Received at a receive end as a received beam of a received state of polarization, the signal beam is split by polarization into first and second beams, each including a reception component of the modulating frequency and of a variable optical intensity. A detection signal is produced from the first and the second beams to have the modulating frequency and a variable electric intensity. Controlled by a launch controller supplied with the detection signal, the launch polarization controller keeps the launched state to minimize at the receive end the electric intensity. Preferably, the received beam is split into four beams, which are given four differents direction of polarization and, from which the detection signal is produced.

Free space optical transmission system

Abstract: A spatial optical transmission apparatus includes: a light signal transmitting device for generating a signal beam which is modulated in accordance with a signal to be transmitted and is intensity-modulated with a lower frequency compared with a signal transmission speed; and a light signal demodulating device for receiving the signal beam from the light signal transmitting device by a detector, adjusting the direction of a locally oscillated beam based on the received signal beam so as to have a predetermined relationship with the direction of the signal beam so that intensity-modulated components in an output signal from the detector falls within a predetermined range of intensity, thereby aligning the wavefront of the signal beam with the wavefront of the locally oscillated beam, and extracting signal components which correspond to the transmitted signal from signal components modulated in accordance with the transmitted signal in the signal beam.

Highly efficient hologram enhancement in Bi12TiO20 fibre-type crystal

Abstract: Experimental results for two-wave mixing experiments in a single Bi12TiO20 fibre-type crystal at a wavelength of 6328 nm under transverse ac electric field are reported An exponential gain factor Γ=47 cm-1, which is much higher than the absorption coefficient (06 cm-1), is obtained It is observed that the signal beam enhancement is in fact signal beam depletion for spatial frequencies higher than FB, which is determined by fibre geometry An unusually strong dependence of response time on the recording beams intensities ratio reflects the nonlinearities of the multi-two-wave mixing process

Method and apparatus for measuring surface movement of an object using a polarizing interfeometer

Abstract: A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam A photon multiplier senses the phase shift and develops an electrical signal A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading

Aircraft landing systems

Abstract: An MLS system comprising ground based equipment which includes a microwave signal transmitter arranged to feed microwave signals to radiator elements of an array antenna via phase shifter modules one of which is provided for each of the said elements, whereby the production of a scanned microwave signal beam is facilitated, signal monitor/detector means effective to provide a detected sample signal derived from the scanned beam, filter means responsive to the detected sample signals for providing a filtered signal derived in dependence upon effective sidelobe signals in the said beam, and comparator means responsive to the filtered signal for providing a transmitter shutdown signal when the filtered signal exceeds a predetermined threshold level for more than a predetermined time during a predetermined number of successive scans.

Phase and birefringence aberration correction

Abstract: A Brillouin enhanced four wave mixing phase conjugate mirror corrects phase aberrations of a coherent electromagnetic beam and birefringence induced upon that beam. The stimulated Brillouin scattering (SBS) phase conjugation technique is augmented to include Brillouin enhanced four wave mixing (BEFWM). A seed beam is generated by a main oscillator which arrives at the phase conjugate cell before the signal beams in order to initiate the Brillouin effect. The signal beam which is being amplified through the amplifier chain is split into two perpendicularly polarized beams. One of the two beams is chosen to be the same polarization as some component of the seed beam, the other orthogonal to the first. The polarization of the orthogonal beam is then rotated 90° such that it is parallel to the other signal beam. The three beams are then focused into cell containing a medium capable of Brillouin excitation. The two signal beams are focused such that they cross the seed beam path before their respective beam waists in order to achieve BEFWM or the two signal beams are focused to a point or points contained within the focused cone angle of the seed beam to achieve seeded SBS, and thus negate the effects of all birefringent and material aberrations in the system.

Bidirectional pumping light amplifier

Abstract: PURPOSE:To allow bidirectional pumping with only one pumping beam source by dividing a pumping beam from the single pumping beam source into two beams so as to input the beams into the incident side and outgoing side. CONSTITUTION:A pumping beam source 13 is permitted to emit by the drive of a driving power source circuit 14, the pumping beam from the pumping beam source 13 are separated by an optical multiplexer/demultiplexer 15 and are projected on the both edges of active element doped fiber 1 through an optical multiplexer/demultiplexer 16 and an optical multiplexer/demultiplexer 17. The signal beam directed to the incident side signal beam transmitting fiber 2 is amplified by the stimulated emission of the active element excited by the pumping beam projected in both directions while passing through the active element doped fiber 1, and the amplified beams are directed to outgoing side signal beam transmitting fiber 3. Thus, bidirectional excitation is allowed by operating only one pumping beam source 13, only single driving power source circuit 14 is necessitated for the pumping power source and the light amplifier is made compact at low cost.

Optical quantum non-demolition measurements

Abstract: We discuss some theoretical and experimental aspects of quantum non-demolition (QND) measurements in the optical domain. The efficiency of a QND measurement can be characterized using three criteria, which describe respectively the quality of the quantum measurement, the non-destruction of the signal, and the conditional variance of the output signal beam, given the output meter beam (quantum-state-preparation criterion). Quantitative limits can be defined with respect to these criteria, delimiting "classical" and "quantum" domains of operation. We describe the implementation of two experiments which fulfill these criteria, using either three-level atoms inside a doubly-resonant optical cavity, or semiconductors emitters and receivers.

Color resolving optical system and color resolving method

Abstract: PURPOSE:To provide a color resolving optical system simple in constitution, capable of miniaturization and high in productivity by constituting a color resolving functional element with a volume hologram. CONSTITUTION:A reflection type volume hologram 1 is constituted so that three holograms 10-12 are laminated. Only a red signal beam 4, a green signal beam 6 and a blue signal beam 8 are light path-deflected respectively by the holograms 10-12 at certain angles. The volume hologram 1 functions as the color resolving functional element, resolves color and deflects an optical path. An object beam 3 transmitting through an image pickup lens 2 and made incident on the volume hologram 1 is reflected by the volume hologram 1. Then, the object beam 3 is resolved into the red signal beam 4, the green signal beam 6 and the blue signal beam 8, and they are made incident on the corresponding image pickup element 5 for red signal, the image pickup element 7 for green signal and the image pickup element 9 for signal, respectively. Further, by giving an image forming function to the volume hologram 1 also, the simple color resolving optical system unnecessitating the image pickup lens is realized.

Information recording device

Abstract: PURPOSE:To record a high quality two dimensional information hologram on a moving recording medium. CONSTITUTION:Two dimensional information pattern formed by a spatial light modulator 8 is irradiated by parallel beams and diffracted light beams are imaged on the surface of a recording medium surface 11 through a relay lens system 18 and 7. Thus, the image formed on the forming position has the same light wave surface of the diffracted image at the spatial light modulator 8 and the size of the image is recduced to the size decided by the magnification of the system, 18 and 7. That is, the phases of the image formed on the medium 11 are constant over the surface of the medium 11, therefore, the interference image generated by the interference between the above image and a reference beam 10 only include the carrier waves of spatial frequencies only determined by the incident angles of the reference beam 10 and signal beam 9 and no higher order spatial frequency components are inclined. Therefore, if the moving speed of the medium 11 and the spatial frequency of the carrier waves are made compatible, no degradation of higher order spatial frequency components caused by the movement of the medium occurs. Thus, an information recording device is provided with less number of errors in information recording and with a high reliability.

Electronic-signal-noise suppression system

Abstract: PURPOSE: To provide a noise suppressing system used in a laser measuring system in which a beam sampler divides a laser beam into a signal beam and a sample beam CONSTITUTION: A signal beam 128 passes through an optical system before it is received with a detector 122, but a sample beam 126 is directly received with the detector 122 A beam sampler 116 is selected so that the sample beam 126 received has steady state intensity slightly higher than the signal beam received A detecting circuit has two linear wide-band photo detector generating signal current and sample current having opposite polarity each other The sample photo current is divided into two component current, and one current has a dc current value practically same as the signal photo current This component is combined with the signal photo current, and eliminates undesirable noise component of the original laser beam A dividing circuit is controlled with a feedback loop and retains the direct current part of the output current zero as shown in the second enbodiment

Optical fiber amplifier and optical fiber amplifier control circuit

Abstract: PURPOSE:To switch to an excellent system between a forward exciting system and a backward exciting system according to the level of an inputted signal beam when an excitation light beam is made incident on a doped fiber and the signal beam is amplified. CONSTITUTION:The excitation light beam is made incident on a first multiplexer/demultiplexer 321 connected in front of the doped fiber 33 from a first exciting laser diode module 311 by the forward exciting system, and the excitation light beam is made incident on a second multiplexer/demultiplexer 322 connected backward from a second exciting laser diode module 312 by the backward exciting system. The intensity of an input beam is detected by a control circuit 36 through an optical blancher 34, and the forward exciting system and the backward exciting system are switched continuously according to the detected result.

Photorefractive limiting quadratic processor

Abstract: Limiting quadratic processing and compansion in photorefractive two beam coupling is disclosed. Two-beam coupling in photorefractive barium titanate employs the imaged intensity of the signal to amplify the reference beam while maintaining the phase of the reference beam. The phase distorted signal beam is converted to that of the controlled phase of the reference beam. The high pump limit of amplification in this two-beam coupling device produces an amplitude compressed output to reduce multiplicative noise. Lost contrast of the image is thereafter restored. Beam clean-up of a non-intelligence bearing beam can be carried out by a similar process; a low pass filter consisting of a pinhole plate can be used in place of the second photorefractive crystal in the Fourier plane and only the planar wavefront portion will pass through the pinhole and may be collimated by a lens to provide a cleaned planar output beam.