Showing papers on "Signal beam published in 2002"

Non-contact radar system for reconstruction of scenes obscured under snow and similar material

Abstract: A system and method for imaging objects obscured by a covering layer of snow. The system preferably utilizes a continuous-wave radar generating short-wavelength radio-frequency (RF) signal beam scanned over angular displacements following a scanning pattern toward a target area. Reflections of the RF signal from objects buried beneath the snow are registered by an array of RF detectors whose signal magnitudes are summed and correlated with scan direction to generate a signal providing spatial object information, which by way of example, is visually displayed. The radio-frequency beam may be scanned over the scene electronically, or by either mechanically or electromechanically modulating antenna direction or the orientation of a beam deflector. The system is capable of generating multiple image frames per second, high-resolution imaging, registration of objects to a depth exceeding two meters, and can be implemented at low cost without complex signal processing hardware.

Optical fiber communication system using optical phase conjugation as well as apparatus applicable to the system and method of producing the same

Abstract: An optical fiber communication system according to the present invention has, for example, first and second phase conjugators. The first phase conjugator converts a signal beam from a first optical fiber into a first phase conjugate beam. The first phase conjugate beam is supplied to the second phase conjugator by a second optical fiber. The second phase conjugator converts the first phase conjugate beam into a second phase conjugate beam. The second phase conjugate beam is transmitted by a third optical fiber. The second optical fiber is composed of a first portion located between the first phase conjugator and a system midpoint and a second portion located between the system midpoint and the second phase conjugator. The total dispersion of the first optical fiber substantially coincides with the total dispersion of the first portion, and the total dispersion of the second portion substantially coincides with the total dispersion of the third optical fiber. By the construction, waveform distortion by chromatic dispersion or nonlinearity is compensated for.

Method and apparatus for phase correlation holographic drive

Abstract: A holographic storage apparatus for recording data in a holographic medium includes at least one light source for generating a reference beam and a signal beam. The reference beam is preferably a phase beam of unchanging phase content. The apparatus also includes a holographic medium placed in a path of the reference beam and a path of the signal beam. The holographic medium has a first face and both the reference beam and the signal beam enter the holographic medium through the first face. The holographic medium also includes a data reflective surface. The reference beam and the signal beam interfere in the holographic medium to create a hologram only after at least one of the reference beam and the signal beam have reflected off of the data reflective surface.

Pattern characteristics of harmonic and intermodulation products in broadband active transmit arrays

Abstract: A three-term power series model for the nonlinearity in the power amplifiers of an active array is used to explore the radiation characteristics of the harmonics and intermodulation products. This model leads to simple equations for predicting the beam-pointing direction and the aperture amplitude taper of the spurious signals. Cases of a single transmit signal, dual transmit signals within a single beam and dual beam operations are analyzed. This model shows that the second and third harmonics are co-boresighted with the fundamental signal but have squared and cubed aperture amplitude distributions. The third-order intermodulation products in general have beam-pointing directions offset from the fundamental signal beam(s). Graphical methods of locating the intermodulation beams in (u, v) space are outlined and illustrated by example.

Beam intensity striations and applications.

Abstract: The single-element spectrogram for a continuous broadband signal, plotted as a function of range, has been shown to exhibit striated bands of intensity maxima and minima. The slope of the striations is an invariant of the modal interference and is described by a waveguide invariant parameter “beta.” The striation pattern is analyzed and modeled in this paper for the beam outputs of a horizontal line array obtained by conventional beamforming. Array beamforming makes it possible to measure the waveguide invariant parameter for weak signals due to the enhancement of signal levels by the array gain over that of a single element. It is shown that the signal beam spectrogram as a function of range exhibits the same striation pattern as that (predicted) for a single element. Specifically, for a broadside signal, the beam striation is identical to that of a single-element plus a constant signal gain. For a nonbroadside target, the signal beam intensity will be modified by a frequency-bearing dependent signal gain due to the signal spread over multiple beams, nevertheless the beam spectrogram retains the same striation pattern (slope) as for a single element. The sidelobe beams (outside the canonical cones containing the signal arrivals) exhibit an entirely different striation pattern as a function of frequency and range. For array processing, it is shown that a fast range-rate, close range target and a distant, slow range-rate interference source will have a different striation pattern (slope) in the corresponding beam spectrograms as a function of time, assuming no prior knowledge of the source ranges. The difference in the striations between the beam spectrograms can be used in array processing to suppress the interference contribution. A 5–7 dB interference suppression is demonstrated using simulated data.

Optical fiber terminations, optical couplers and optical coupling methods

Abstract: An optical coupler for coupling a signal light beam from a signal port ( 100 ) and a pump light beam from a pump port ( 110 ) into a common port ( 120 ) for coupling the pump and signal beams into a double-clad (DC) optical fiber ( 122 ) comprising a core ( 123 ), an inner clad ( 124 ) and an outer clad ( 125 ). The DC optical fiber has a section of coreless fiber ( 128 ) joined to it to form an extension piece. A free-space optical arrangement ( 130 ) combines the pump and signal light beams onto the common port so that the signal light beam is focused onto the core aperture at the buried interface ( 121 ) between the DC optical fiber and the coreless extension piece. The high power density signal beam focus is thus moved away from a more sensitive air:glass interface into a buried interface which has a higher damage threshold. In this way, higher signal beam powers can be handled. The invention allows higher power DC pumped amplifiers and lasers to be fabricated.

InGaAs multiple quantum well modulating retro-reflector for free-space optical communications

Abstract: Modulating retro-reflectors provide means for free space optical communication without the need for a laser, telescope or pointer tracker on one end of the link. These systems work by coupling a retro-reflector with an electro- optic shutter. The modulating retro-reflector is then interrogated by a cw laser beam from a conventional optical communications system and returns a modulated signal beam to the interrogator. Over the last few years the Naval Research Laboratory has developed modulating retro-reflector based on corner cubes and large area Transmissive InGaAs multiple quantum well modulators. These devices can allow optical links at speeds up to about 10 Mbps. We will discuss the critical performance characteristics of such systems including modulating rate, power consumption, optical contrast ratio and operating wavelength. In addition a new modulating retro-reflector architecture based upon cat s eye retroreflectors will be discussed. This architecture has the possibility for data rates of hundreds of megabits per second at power consumptions below 100 mW.

Demonstration of improved beam quality in an image-rotating optical parametric oscillator

Abstract: We performed laboratory and numerical modeling studies of an optical parametric oscillator with 90° intracavity image rotation. We found that the signal beam was more symmetric than that from comparable cavities without image rotation, and it had low values of the beam quality factor, M2. Oscillator performance agreed well with our numerical model.

Optical information recording and reproducing apparatus having volume holographic memory

Abstract: A description is provided of an optical information recording and reproducing apparatus. The apparatus comprises: a holographic memory made of a photorefractive crystalline material; a support portion for detachably supporting the memory; a reference beam supplying portion for supplying a coherent reference beam of a first wavelength incident on the memory; a signal beam generating portion for supplying a coherent signal beam of the first wavelength, which is modulated in accordance with image data, incident on the memory, intersecting therein the signal beam with the reference beam, and generating a three-dimensional interference pattern of the beams; a detecting portion for detecting a diffracted light from a refractive index grating of the interference pattern in the memory, due to irradiation of the reference beam; and a medium position adjusting portion for moving a position of the support portion in accordance with a signal corresponding to positioning images from the detection portion. The memory includes a nonvolatile refractive index grating corresponding to a three-dimensional interference pattern of a coherent reference beam and a coherent signal beam, the coherent signal beam being modulated in accordance with positioning images.

Rotation correlation multiplex holography

Abstract: Holography in which an array of overlapping holograms is recorded or reconstructed in a recording medium, holograms being produced by interference of a reference beam and a signal beam, in which the reference beam is a phase beam which consists essentially of a multitude of rays of varying angle of incidence and non-uniform phase, in which the process comprises changing the orientation of the phase beam for recording or reconstructing different holograms, wherein phase beam orientation is changed relative to the medium while maintaining the medium stationary in order to enable recording or reconstruction of individual holograms at a given location of the medium.

Holographic digital data storage system compatible with a cd/dvd player

Abstract: PURPOSE: A system for saving holographic digital compatible with a CD player and a DVD player is provided to reduce the equipment cost by adding holographic optical elements. CONSTITUTION: A system for saving holographic digital data compatible with a CD player and a DVD player includes a light source(102) generating a reference beam; a holographic optical element(104) recording an interference pattern of the reference beam and a plurality of beams having the specific size, thereby generating a plurality of reproducing beams corresponding to the specific sized beams if the reference beam is irradiated; a beam splitter(106) splitting the reproducing beams into reflecting beams and projecting beams, and using one of reflecting beams and projecting beams as a holographic reference beam; a spatial light modulator(122) modulating one of reflecting beams and projecting beams to correspond to a holographic input signal, thereby generating a holographic signal beam; a media(110) storing an interference pattern of the holographic reference beam and the holographic signal beam, reflecting the holographic reference beam for generating a CD/DVD reflecting beam proceeding the opposite direction of the holographic reference beam; a signal sensing element displaying the holographic reproducing beam and sensing the CD/DVD reflecting beam in case that holographic reference beam is irradiated.

Semiconductor device for rapid optical switching by modulated absorption

Abstract: This invention relates to a semiconductor device for switching or modulating optical signals, cross-connects and switches built of such devices as well as a method of switching or modulating optical signals. The semiconductor device has a photodetector having a low electrical capacitance Cd, a detector absorbing layer for absorbing an optical signal beam, a modulator having a low capacitance Cm and a modulator absorbing layer exhibiting an electric field-dependent absorption coefficient. The modulator absorbing layer is used for absorbing an optical power beam, which is to be modulated or switched. The device has a low resistivity region between the photodetector and the modulator such that the electric field-dependent absorption coefficient is altered uniformly and rapidly throughout the modulator absorbing layer during absorption of the optical signal beam in the detector absorbing layer. The device is equipped with a high resistivity element in series with the low resistivity region for minimizing a net charge flow to and from the device. This type of device can be used in modulating or switching optical signals including communications signals in WDM and DWDM networks.

Process for holographic multiplexing

Abstract: A method of recording holograms includes: generating a first signal-beam from a signal-beam source and a first reference beam from a reference-beam source; recording a first hologram in a holographic medium from an interference between the first signal beam and the first reference beam; shifting the reference-beam source after the act of recording the first hologram; generating a second signal beam from the signal-beam source and a second reference beam from the reference-beam source after the act of shifting the reference-beam source following the recording of the first hologram; and recording a second hologram in the holographic medium from an interference between the second signal beam and the second reference beam.

System and method for performing selected optical measurements utilizing a position changeable aperture

Abstract: A system and method for performing selected optical measurements on a sample is provided utilizing an optical coherence domain reflectometer which includes a diffraction grating. A broad band light source produces light having a short coherence length. A beamsplitter splits the light into a signal beam and a reference beam. A reference mirror is disposed to receive the reference beam. A lens brings the signal beam to focus on the sample. A diffraction grating receives reflections from the sample and from the reference mirror, the reflections being incident on the diffraction grating with respect to said diffraction grating normal such that a positive diffraction order from one of the reflections and a negative diffraction order from the other one of the reflections and a negative diffraction order from the other one of the reflections propagate along a common path. A lens collects the diffracted order from the diffraction grating directed along the common path and brings the diffracted orders to focus on a detector, the detector producing an output of said positive and negative diffracted orders received. A computer processes the output from the detector. In other versions of the invention, reflections from the sample are not directed onto the diffraction grating but instead are combined with a diffracted order from reflections from the reference mirror.

Tunable phase-matched optical parametric oscillators based on a cylindrical crystal

Abstract: The use of cylindrical nonlinear crystals is a good way to extend the angular-tuning capability of optical parametric oscillators We consider the example of a 1064-nm-pumped KTiOPO4 optical parametric oscillator phase matched in the x–z plane A 315° angular tuning is demonstrated, limited by the spectral range of the mirrors The measured slope efficiency and threshold energy are compared with the values published for a similar optical parametric oscillator that uses a parallelepipedic crystal We study the beam quality of the emitted signal The experiments with a plano–plano cavity point out the spatial-filtering effect due to the short focal length of the cylindrical crystal placed in the cavity A simple model based on the coupling of the pump and the signal Gaussian beams in the cavity is developed We then investigate the respective effects of the different experimental parameters on the output beam quality: radius of curvature of the mirrors, cavity length, crystal radius, pump-beam waist size, and spectral-tuning range of the signal beam These calculations lead to the definition of the optimum configuration associated with a low M2 independent of the emitted wavelength An experimental demonstration of that solution is given with excellent results: M2<15 is obtained, constant over 9° angular tuning

Direct optical modulation type wavelength converter

Abstract: A direct optical modulation (DOM) type wavelength converter is provided. The provided wavelength converter is a gain-clamped semiconductor optical amplifier (GC-SOA), which does not require a continuous wave (CW) signal, or a semiconductor laser in itself, and reduces a coupling loss between the GC-SOA or the semiconductor laser and an optical fiber while improving an emission threshold of a laser. Therefore, the provided wavelength converter converts a wavelength of an input signal beam having a low intensity by controlling the intensity of the input signal.

Cascading optical switch three dimensional switch fabric system and method

Abstract: The present invention cascaded optical switching system includes architectures that provide three dimensional optical signal beam steering utilizing two dimension optical signal beam steering devices. A plurality of cascaded optical switches form a cascaded multi-dimensional optical switch fabric and direct an optical signal beam from one of the plurality of optical switches to another of the plurality of optical switches in a different dimension. In one embodiment, an incidence corrective device is included in a cascaded optical switch fabric and directs an optical signal beam in a shallow angle so that it strikes the next optical switch at a corrected incidence angle. A corrected incidence angle permits an optical signal beam to be forwarded at a relatively shallow angle to an optical switch located in a relatively close proximity on the optical switch fabric. The present invention also provides for refocusing of spreading optical signal beams and mitigation of signal loss.

Wollaston prism phase-stepping point diffraction interferometer and method

Abstract: A Wollaston prism phase-stepping point diffraction interferometer for testing a test optic. The Wollaston prism shears light into reference and signal beams, and provides phase stepping at increased accuracy by translating the Wollaston prism in a lateral direction with respect to the optical path. The reference beam produced by the Wollaston prism is directed through a pinhole of a diaphragm to produce a perfect spherical reference wave. The spherical reference wave is recombined with the signal beam to produce an interference fringe pattern of greater accuracy.

Novel technique for group velocity dispersion measurements in optical fibers

Abstract: A novel technique of measuring group velocity dispersion (GVD) in optical fibers is introduced. The technique utilizes stimulated Raman scattering to couple small modulations from a pump beam to a signal beam. By measuring the coupling efficiency, a numerical value for the group delay difference between both beams is derived. Furthermore, we calculate the GVD from the measured data and show the good agreement with a conventional measurement technique.

Coherent and incoherent spatial solitons in bulk nematic liquid crystals

Abstract: Nematic liquid crystals are suitable materials for nonlinear wave propagation. A reorientational nonlinearity can be observed at very low optical intensities and the saturating response of the medium allows for the formation of 3D solitary waves. In this paper we review our recent theoretical and experimental results on spatial soliton formation in a nematic liquid crystal cell. Optical induced waveguiding at mW powers with either a coherent or an incoherent pump is demonstrated. Spatial readdressing of a signal beam in the soliton-waveguide is also shown.

Ultrasonic vibration detection using frequency matching

Abstract: In order to probe an object in motion subject to surface displacement, for example, caused by ultrasonic wave propagation, a laser beam is split into a first portion and a second portion. The first is scatted off the object to generate a signal beam. The frequency shift produced in the signal beam due to motion of the object is measured, and this is used to adjust the frequency of one or both portions of the laser beam so that both beams have substantially the same frequency. The surface displacements are measured by comparing the second portion of the laser beam and the signal beam after frequency adjustment.

Pretreatment method for hologram recording medium

Abstract: Disclosed is a pretreatment method for a hologram recording medium used in the hologram recording method in which information signals loaded on signal beam are recorded by injecting coherent signal beam and reference beam to the hologram recording medium which is exposed to first light having first wavelength of ultraviolet band or short-wavelength visible light band in advance in order to generate light-induced absorption, wherein the coherent signal beam and reference beam each having longer wavelength than the first wavelength. The pretreatment method comprises subjecting the hologram recording medium to oxidation treatment prior to the irradiation of the first light has been completed.

Study of laser-induced damage in PPLN

Abstract: Periodically-poled lithium niobate (PPLN) is a well- established nonlinear material for down converting the output from a solid state laser, the pump wavelength, to generate an emission close to 4 micrometers . A simple OPO configuration was used with a resonated signal beam passing through a heated PPLN crystal, to avoid photo-refraction. A Q-switched Nd:YAG pump laser was used for generating short- duration, high-intensity one micron pulses. Direct modulation of the diode sources enable the emission to be controlled. The pump beam had good beam quality, with an M 2 of about 1.8 in each axis, and modulated average power in excess of 6 W. Damage to PPLN crystals used in the solid state laser has been observed. Irreversible damage of the nonlinear medium has been recorded: initially to the output face of PPLN crystals, but latterly to the bulk structure. These observations were made over a range of pumping conditions and OPO configurations. Estimates of the damage threshold have been surprisingly low, of the order of 1.5 J/cm 2 .

Highly tunable dispersion compensator

Abstract: A method and device for providing tunable dispersion compensation by splitting an incoming optical beam and then recombining interferometrically two sub-beams which have been passed through fixed dispersive (dispersion producing) elements. The polarization of the incoming optical signal is controlled and the signal beam is split into sub-beams at a ratio dependent on the polarization. The sub-beams are directed to each of two interferometer arms. The return beams are interfered e.g. by placing a quarter waveplate at 45° to the two orthogonal polarization axes. This produces a near-lossless beam with a tunable amount of dispersion dependent on the ratio of beam split.

Method and apparatus for probing objects in motion

Abstract: In order to probe an object in motion subject to surface displacement, for example, caused by ultrasonic wave propagation, a laser beam is split into a first portion and a second portion. The first is scatted off the object to generate a signal beam. The frequency shift produced in the signal beam due to motion of the object is measured, and this is used to adjust the frequency of one or both portions of the laser beam so that both beams have substantially the same frequency. The surface displacements are measured by comparing the second portion of the laser beam and the signal beam after frequency adjustment.

All-optical wavelength converter and converting method therefor

Abstract: A wavelength converter for converting wavelength of a signal beam combined to a pump beam. The wavelength converter comprises a mode converting region for converting mode of the pump beam; a direction combining region for combining the signal beam to the pump beam; and wavelength converting region for converting the wavelength of the signal beam combined to the pump beam. The mode converting region and the wavelength converting region are formed as integrated by nonlinear polymeric material to construct a polymeric waveguide extended along propagation direction. The wavelength converting region includes the nonlinear polymer poled to a predetermined direction. According to the present invention, a DFG device, a cascade wavelength converting device, and second harmonic generation device of higher energy converting efficiency can be developed.

Weak-wave advancement in nearly collinear four-wave mixing

Abstract: We identify a new four-wave mixing process in which two nearly collinear pump beams produce phase-dependent gain into a weak bisector signal beam in a self-defocusing Kerr medium. Phase matching is achieved by weak-wave advancement caused by cross-phase modulation between the pump and signal beams. We relate this process to the inverse of spatial modulational instability and suggest a time-domain analog.

Optical switch cascading system and method with variable incidence angle correction

Abstract: The present invention is an efficient system and method for cascading optical switches. A plurality of cascaded optical switches form a cascaded optical switch fabric and direct an optical signal beam from one of the plurality of optical switches to another of the plurality of optical switches. In one embodiment of the present invention, a variable incidence corrective device is included in a cascaded optical switch fabric. The incidence corrective device directs an optical signal beam in a shallow angle so that it strikes the next optical switch at a corrected incidence angle. A corrected incidence angle permits an optical signal beam to be forwarded at a relatively shallow angle to an optical switch located in a relatively close proximity on the optical switch fabric. The present invention also provides for refocusing of spreading optical signal beams and mitigation of signal loss.