Showing papers on "Signal beam published in 1998"

Confocal optical scanning system employing a fiber laser

Abstract: A confocal optical scanning system (10) using a flexible optical emissive fiber or fiber laser (11) and having a lasing cavity (12) defined within the fiber. The system in-couples a signal beam (36) produced when a probe beam (32) generated by the fiber laser is reflected from a scanned object (34) back into the lasing cavity. The perturbation created in the cavity by the in-coupling of the signal beam (36) is detected by a transducer (46). Specifically, the perturbation may be the signal beam itself, an oscillation mode of the cavity induced by the in-coupled signal beam or a combination of the signal beam and the probe beam. In a preferred embodiment of the invention the system also has a polarizing assembly (100) for altering a signal polarization of the signal beam and rotate it to either a resonant polarization supported by the cavity or a non-resonant polarization not supported by the cavity.

Improved method and apparatus for measuring material properties using transient-grating spectroscopy

Abstract: The invention provides an apparatus for measuring a property of a sample (using, e.g., ISTS) that includes: 1) an excitation laser that generates an excitation laser beam; 2) an optical system aligned along an optical axis that separates the excitation laser beam into at least three sub-beams; 3) an imaging system aligned along the optical axis that collects the sub-beams and focuses them onto the sample to form an optical interference pattern that generates a time-dependent response in the sample; 4) a probe laser that generates a probe laser beam that diffracts off the time-dependent response to form a signal beam; 5) a detector that detects the signal beam and in response generates a radiation-induced electronic response; and 6) a processor that processes the radiation-induced electronic response to determine the property of the sample.

Method and device for measuring the concentration of ions implanted in semiconductor materials

Abstract: A method and apparatus that determines a concentration of ions implanted in a material is described. The method includes the steps of: (1) passing an excitation pulse through a diffracting mask (e.g., a phase or amplitude mask) to generate at least two excitation laser sub-pulses; (2) irradiating a region of the material with a 'grating' pattern, formed by overlapping two excitation laser sub-pulses in time and space to initiate a time-dependent response (e.g., a change in refractive index) in the region; (3) diffracting a probe laser pulse having a duration that is at least as long as the time-dependent response off the region to generate a time-dependent signal beam; (4) detecting the time-dependent signal beam to generate a signal waveform; and (5) processing the signal waveform to determine the concentration of ions implanted in the material.

Optical storage medium, optical storage method, optical storage apparatus, optical reading method, optical reading apparatus, optical retrieving method and optical retrieving apparatus

Abstract: An optical storage medium of the present invention enables storage of data with high precision at high speed, and rewriting of data at high speed without an erasing process. Optical storage, reading and retrieving methods and optical storage, reading, and retrieving apparatuses using the medium are also provided. The optical storage medium has at least a polarization-sensitive member having the photo-induced birefringence property, such as a member made of polyester polymer having cyanoazobenzene as a side chain. The above apparatuses have spatial light modulator capable of modulating polarization. The modulator provides information of bit of two-dimensional data to each corresponding pixel by application or non-application of a voltage, and modulates the polarization of the beam incident on each pixel. Thereby, a signal beam transmitted through the spatial light modulator having a spatial polarization modulation corresponding to the two-dimensional data is obtained. The signal beam illuminates the optical storage medium, and at the same time, a reference beam illuminates the same region in the medium where the signal beam illuminates. Thus a hologram of the polarization modulation of the signal beam corresponding to the two-dimensional data is stored in the optical storage medium.

Method and system to align holographic images

Abstract: A method and a system to re-align onto a detector array a holographic image of a Fourier region hologram stored in a medium, with the medium spinning around a first axis, and the hologram being generated by a reference beam and a signal beam. In generating the hologram, the reference beam is incident on the medium with respect to a second axis at a second-axis-incident angle, and a third axis at a third-axis-incident angle, such that the holographic image of the hologram when reproduced by the reference beam is aligned onto the detector array. Also, the three axes are substantially orthogonal to each other. As the medium spins, the medium's orientation can change through tilting with respect to the second and the third axes so that the holographic image when reproduced by the reference beam is not aligned onto the detector array. In one embodiment, the holographic image is re-aligned onto the detector array by tilting the reference beam such that when re-aligned, the incident angle of the reference beam on the medium with respect to the second axis is intentionally tilted to be different from the second-axis-incident angle, and with respect to the third axis to be different from the third-axis-incident angle.

Track-changing utilizing phase response of resonators

Abstract: A device and method of track changing an optical signal beam in response to the frequency selective phase characteristics of a resonator. The resonator is side-coupled to a single optical beam and only affects that beam's phase, without disturbing its amplitude to any significant degree. For all resonator and input beam configurations, the phase-shift at a resonant frequency is always π, thus the relative switching characteristics are similar regardless of the exact configuration. Track changing is accomplished through interferometry. The signal, after having interacted with the resonator, is made to interfere with a reference beam. The reference beam is created by dividing an input signal into two paths, one which interacts with the resonator, the other which serves as the reference. In an alternative embodiment, the device acts as a mode converter. The resonator converts an even system-mode to an odd system-mode (or vise versa). At the output of the device is an interference filter, or mode filter, which redirects the signal according to the phase response of the resonator.

Excitation and bistability of self-trapped signal beams in optical parametric oscillators.

Abstract: In a doubly resonant degenerate optical parametric oscillator below threshold the signal beam can be trapped in the form of stable bright temporal or spatial solitons. We characterize these soliton families and discuss how to excite them.

Optical storage medium, optical storage method, optical reading method, optical reading apparatus, optical retrieving method and optical retrieving apparatus

Abstract: An optical storage medium of the present invention enables storage of data with high precision at high speed, and rewriting of data at high speed without an erasing process. Optical storage, reading and retrieving methods and optical storage, reading, and retrieving apparatuses using the medium are also provided. The optical storage medium has at least a polarization-sensitive member having the photo-induced birefringence property, such as a member made of polyester polymer having cyanoazobenzene as a side chain. The above apparatuses have spatial light modulator capable of modulating polarization. The modulator provides information of bit of two-dimensional data to each corresponding pixel by application or non-application of a voltage, and modulates the polarization of the beam incident on each pixel. Thereby, a signal beam transmitted through the spatial light modulator having a spatial polarization modulation corresponding to the two-dimensional data is obtained. The signal beam illuminates the optical storage medium, and at the same time, a reference beam illuminates the same region in the medium where the signal beam illuminates. Thus a hologram of the polarization modulation of the signal beam corresponding to the two-dimensional data is stored in the optical storage medium.

Method and device for measuring thin films and semiconductor substrates using reflection mode geometry

Abstract: The invention provides both a method and apparatus that measures a property of a structure that includes at least one layer. The apparatus features a laser (e.g., a microchip laser, described below) that generates an optical pulse, and a diffractive mask that receives the optical pulse and diffracts it to generate at least two excitation pulses. An optical system, (e.g., an achromat lens pair) receives the optical pulses and spatially and temporally overlaps them on or in the structure to form an excitation pattern that launches an acoustic wave. The acoustic wave modulates a property of the structure, e.g., it generates a time-dependent “surface ripple” or modulates an optical property such as the sample's refractive index or absorption coefficient. Surface ripple is defined as a time-dependent change in the morphology of the surface; its peak-to-null amplitude is typically a few angstroms or less. The apparatus also includes a light source that produces a probe beam that reflects off the modulated property to generate a signal beam. An optical detection system receives the reflected signal beam and in response generates a light-induced electrical signal. An analyzer analyzes the signal to measure the property of the structure.

Picosecond all-optical polarization switching in InGaAsP MQW's at 1.52 μm

Abstract: An all-optical switch operating at a wavelength of 1.52 /spl mu/m is demonstrated. The switch makes use of electron spin polarization in a multiple-quantum-well semiconductor structure. The polarization change of a signal beam was observed to recover with a time constant of 20 ps determined by the spin relaxation time.

Quantum-nondemolition measurements using cold trapped atoms: Comparison between theory and experiment

Abstract: In this paper we present a detailed theoretical analysis of a recent quantum-nondemolition experiment in optics using cold atoms in a magneto-optical trap as a nonlinear medium. A signal beam and a meter beam from two independent lasers are coupled within a Λ-type three-level scheme in the D1 line of 87Rb atoms. The experimental results for the relevant quantum correlations of the fields, that represent up to now the best achievements for a single back-action evading measurement, are found in a remarkably good agreement with the theoretical predictions from a fully quantum model for three-level atoms in a doubly resonant cavity.

Measurement and theoretical modeling of quantum beats in picosecond time-resolved degenerate four-wave mixing and polarization spectroscopy of OH in atmospheric pressure flames

Abstract: Using tunable ultraviolet picosecond laser pulses pump-probe degenerate four-wave mixing (DFWM) and polarization spectroscopy experiments were conducted in atmospheric pressure flames to investigate the temporal signal behavior in selected rotational transitions of the OH $A{}^{2}\ensuremath{\Sigma}--X{}^{2}\ensuremath{\Pi} (0,0)$ electronic band. The relaxation behavior of simultaneously excited main and satellite transitions in the Q and P branches was studied in premixed stoichiometric methane-air and hydrogen-oxygen flames. Experimental signal traces are compared with expressions from a detailed theoretical treatment of the signal generation process using perturbation calculations. The theoretical approach consists in calculating the energy density in the signal field mode taking into account the frequency spread of the pump and probe beam radiation, collisional relaxation effects, and the polarization configuration of the incident beams. Relaxation times for population and orientation deduced from the fitting algorithm are in good agreement with DFWM line-shape studies [S. Williams et al., J. Chem. Phys. 104, 3947 (1996)]. It is shown that quantitative agreement with experimental data obtained for different polarization configurations of pump, probe, and signal photons can be achieved when appropriate time correlated interactions of pump and probe photons are taken into account. In addition, it is shown that due to the frequency spread of the employed laser pulses the different frequency components in the signal beam contribute with different amplitude to the oscillating and nonoscillating parts in the temporal development of the signal intensity depending on the relative strength of the simultaneously excited transitions.

Coherent Laser Spectroscopy and Doppler Lidar Sensing in the Atmosphere

Abstract: The principles of coherent laser spectroscopy are briefly reviewed in which a signal beam is heterodyned with an optical local oscillator beam. The frequency and single mode selectivity this provides is shown to be very advantageous. This is illustrated by recent work on the properties of different classes of light field, including the fractal character of Gaussian-Lorentzian light, and by several aspects of laser physics. In equivalent practical applications to remote sensing in the atmosphere, coherent Doppler lidar provides a powerful technique. This is illustrated by measurements of wind fields and aircraft wake vortices. Airborne equipments have been used for measurements of true airspeed, wind shear warning and atmospheric backscatter levels. Future space-borne lidars could potentially measure the global wind field—of great benefit for numerical weather forecasting and climate studies.

Optical interconnection for holographic memories and method for using the same

Abstract: An optical interface of a holographic memory system electrically selects one of several optical pathways to store or retrieve an image from a holographic memory by activating liquid crystal polarization rotators and novel liquid crystal gratings. In a preferred embodiment a spatial light modulator, a pixelized readout device (i.e., focal-plane array), a series of polarizing optical components, liquid-crystal polarization rotators, liquid-crystal beam-steering devices, and interconnecting and imaging optics are provided. The parallel interconnection accepts a laser-beam input, divides the beam among multiple paths, imparts a data-bearing spatial signature on a signal beam by means of a spatial light modulator, steers a reference beam by means of liquid-crystal beam-steering devices, and directs the appropriate beams into the recording medium. The interconnection functions are realized within a solid-optical assembly requiring no air-glass interfaces, and the beam-steering functions for the reference beam are accomplished by non-mechanical means using liquid-crystal devices.

Holographic storage system incorporated therein a parabolic mirror

Abstract: A holographic storage system implements both a rotational and an angular multiplexings in combination. The system comprises a light source, a pair of wedge prisms, a beam splitter, a first, a second, a third and a parabolic mirrors, a SLM(spatial light modulator) and a storage medium. In the system, a light beam emitted from the light source is split into a reference and a signal beams by the beam splitter. The signal beam reflected by the first mirror to the SLM which modulates data in the firm of pages. The modulated signal beam falls into the storage medium, while the reference beam is reflected by the second mirror to the wedge prisms which deflect the reference beam to an arbitrary position on the third mirror. The deflected reference beam is reflected onto the parabolic mirror by the third mirror. The deflected reference beam is converged onto the storage medium by the parabolic mirror. In the storage medium, the modulated signal beam interferes with the converged reference beam to thereby generate an interference pattern therebetween, wherein the interference pattern contains information of the modulated signal beam. The holographic storage system has a size reduced by incorporating therein the third mirror and the parabolic mirror provided with an opening.

Process and apparatus for generating at least three light bundles of different wavelength, especially for displaying color images

Abstract: In a process and an apparatus for generating at least three light bundles of different wavelength for displaying color images, one of these light bundles having a longest wavelength and another of the light bundles having a shortest wavelength, which light bundles are obtained by an OPO and further nonlinear optical component elements from a signal beam and/or idler beam of the OPO and/or a primary light bundle, from which a beam exciting the OPO is also derived, it is provided that at least a partial light bundle is separated from the primary light bundle for exciting the OPO, in that the light bundle with the longest wavelength and the light bundle with the shortest wavelength are obtained from the signal beam and/or idler beam of the OPO by way of frequency multiplication and/or frequency mixing with another partial light bundle of the primary light bundle by excluding components of light bundles other than the generated light bundles with the shortest and longest wavelengths for image display.

High-efficiency volume hologram recording with a pulsed signal beam

Abstract: We present an efficient photorefractive volume hologram recording technique with a pulsed signal beam and continuous reference-beam illumination. The grating envelope can be simply controlled by manipulation of the duty cycle of the signal beam. Thus, for any grating coupling strength and different initial reference-signal intensity ratios, the diffraction efficiency can be maximized with this technique and can be greatly increased in comparison with that of the conventional recording technique.

Receiver-beam characterization for the SMA

Abstract: This paper describes the measurement and subsequent data analysis of the signal beam of the receiver system of the Submillimeter Array (SMA). To measure the receiver beam patterns, a 2-axis planar scanning stage is mounted on top of the receiver assembly. Scanning in a plane orthogonal to the optical path, the near-field measuring system maps out both the amplitude and phase at frequencies of 242 and 265 GHz. By analyzing the measured patterns we can inspect the alignment of an individual receiver, and the optical assembly common to all frequency bands. The data also allows us to determine how the receiver couples to the beam waveguide that feeds the SMA antennas. The measured beam patterns of two different receivers, covering frequency bands of 176 - 256 and 250 - 350 GHz, are presented, as well as the analysis of these data. We believe that this is the first time such a rigorous full vectorial radio alignment technique has been applied to millimeter or submillimeter receiving systems for radio astronomy.

Method and device for generating phase conjugate light and covering wavelength, and system with the device, and manufacture of the device.

Abstract: PROBLEM TO BE SOLVED: To achieve a phase conjugate light generator which is efficient, fast, broadband, and also polarized-wave-independent, by splitting a signal beam of light into planes of polarization orthogonal to each other, and generating each phase conjugate beam of light for synthesizing polarized waves. SOLUTION: A signal beam of light ES is split into polarized waves of a first polarization component ES1 and a second polarization component ES2 by a first polarization beam splitter(PBS) 32. The first polarization component ES1 is supplied to a first DFB laser diode 1 (#1) and the first phase conjugate beam of light EC1 is outputted. Moreover, a second DFB laser diode 1 (#2) is used for the second polarization component ES2 and the second phase conjugate beam of light EC2 is outputted. These polarization components ES1 and ES2 are orthogonal to each other. And, the first and second polarization beams of light EC1 and EC2 are polarization-synthesized for obtaining one phase conjugate beam of light EC.

Polarisation-independent linear homodyne detection of optical phase modulation with adaptive photodetectors

Abstract: A simple configuration for the linear homodyne detection of fast phase modulation in the presence of relatively slow polarisation/phase drift in the signal beam is proposed and experimentally demonstrated. It uses adaptive photodetectors which are based on principles of dynamic photorefractive holographic recording (two-wave mixing or photo-EMF effect).

Spatially variant and coherent illumination method for undersea object detection and recognition

Abstract: Increased optical range of target detection and recognition is always a problem in the marine environment. The inherent optical properties of light absorption and scattering in water, compounded by suspended particulate matter scattering, limit both radiative and information transfer for image formation. Methods for the formation of images in scattering media generally rely upon temporal or spatial methodologies. Some interesting designs have been developed in an attempt to circumvent or overcome the scattering problem. Time gating is a temporal example of image formation whereby a light source is pulse projected toward a target and the detector is time gated to accept image forming illumination from a specific range. To be successful at eliminating much of the backscatter problem, this method requires range information and loses the simplicity of a continuous light source. Holography is one example of an image formation method requiring specific spatial relationships, i.e. mutual coherence between a reference beam and a signal beam. The coherence allows the formation of an interference pattern that carries the signal information on a "spatial carrier". In order for the method to be of use, the medium in which the beams are carried must preserve the coherence or phase spatially across the beams and in relation to the reference beam. In water, the distance over which the phase may be preserved is dependent upon many factors, including turbulence induced refractive index variations, thermal gradient structure, and relative motion. If pathlength differences exceed the temporal coherence length of the beam, interference is not obtained and the method breaks down. Generally, the demands of maintaining a spatially coherent beam at optical frequencies is difficult over long range thereby limiting the usefulness of the technique for image formation in turbid media. This paper describes a variation of the spatial interferometric technique that relies upon projected spatial gratings with subsequent detection against a quasi-coherent return signal.

One-way image transmission through a thick dynamic distorter without a reference beam

Abstract: We demonstrated a method to perform one-way image transmission through a dynamic distorter without a reference beam. In this method, a photorefractive four-wave mixing configuration was used to pick up the reconstructed image from the image-bearing signal beam, which acted as an erase beam. The fluctuation period of the dynamic distorter must be much shorter than the response time of the nonlinear material. Reconstructed images with high-fidelity have been obtained. Because use of a reference beam is unnecessary this method is simpler and more effective.

Volume holographic data storage system using a beam pattern from a tapered optical fiber

Abstract: A volume holographic data storage(VHDS) system incorporates therein a tapered optical fiber for generating a speckle beam pattern from the tapered optical fiber for increasing the amount of holograms to be stored into a photorefractive crystal. The VHDS system includes a light source for generating a coherent light beam, a beam splitter for splitting the coherent light beam into a reference and a signal beams, a storage medium for storing the multiple holograms thereinto, a mirror for directing the signal beam to the storage medium, a coupler for coupling the reference beam to the tapered optical fiber, wherein one end of the tapered optical fiber has a tapered structure to give perturbation in the form of a speckle pattern to the reference beam from the tapered optical fiber and the reference beam containing the speckle pattern travels to the storage medium after being transmitted through the tapered structure, thereby the speckle pattern reference beam interfering with the signal beam in the storage medium.

Volume holographic storage using rotated signal beam encoder

Abstract: The data encoder (e.g. an amplitude spatial light modulator, ASLM) in a volume holographic storage system is rotated by 45° relative to the normal to the plane of the reference and signal beams, such that the near-Fourier transform pattern of the encoder at the medium has an X-shape. The encoder rotation allows tight packing of spatial multiplexing subvolumes in a rectangular array, and provides for uniform spatial frequency filtering in a perpendicular geometry.

Coherent imaging in turbid media

Abstract: A system for forming an image of an object in a turbid medium comprises a light source for producing a coherent light beam of a selected frequency that is divided by a beamsplitter into a reference beam directed along a first optical path and a signal beam directed along a second optical path where the object to be imaged is located. The signal beam impinges upon the object and reflects back toward the beamsplitter. The reference beam is modulated to shift its frequency. A mirror reflects the reference beam back toward the beamsplitter for combination with the signal beam to produce an output optical signal. A photodetector receives the output optical signal from the beamsplitter and produces an electrical signal having a frequency related to shifts in frequency between the reference beam and the signal beam and having an amplitude proportional to the image intensity. A heterodyne detector connected to the photodetector produces a beat signal when the first and second optical paths have matching lengths so that the location of the point on the object where the signal beam reflected can be determined. By scanning the signal beam across the object, the system determines locations of a number of points on the object sufficient to form its image.

Phase conjugation of depolarized light with a loop PCM

Abstract: The loop phase conjugate mirror (PCM) has attracted much of attention recently for application to high power solid state lasers. We suggest an idea how to modify the basic loop PCM optical scheme in order to work with depolarized radiation. In this paper we present experimental results showing near 100% polarization conjugation fidelity, in combination with compensation of phase distortions and high reflectivity. Basically, loop PCM is a laser that is seeded and triggered by an external signal beam, which we want to be phase conjugated.

Optimum signal profile in longitudinally pumped three-level amplifiers

Abstract: The increase of signal power through an optical amplifier generally depends on the shape of the input signal. The optimum signal beam profile in three-level amplifiers is analytically determined using a variational approach. For a Gaussian pump distribution, it is demonstrated that a highorder super-Gaussian signal is nearly optimum for a wide range of the signal to pump width ratio.

Photonic applications of bacteriorhodopsin

Abstract: The photochromic protein bR is receiving much attention as an interesting alternative to conventional inorganic semiconductor based materials for a variety of applications in optical recording and information processing. Recent advances in genetic engineering techniques for tailoring molecular properties without degrading of its inherent mechanical and thermal stability make it an outstanding photonic material. Some of the photonic applications already demonstrated by our group are reviewed. We exploit the parallel processing of optics and the real-time nature of bR films for the implementation of several photonic applications. We reported a convenient method to obtain all-optical light modulation in bacteriorhodopsin films using a degenerate four-wave mixing geometry. Chemically stabilized films of bacteriorhodopsin in a polymer matrix for which the life time of the excited M state is tens of seconds are used to demonstrate all-optical light intensity modulation. Small intensities of order mW/cm2 are used in the modulation experiments. The fast photochemical transition from M to B permits reasonably fast modulation speeds independent of the slow thermal M to B relaxation time. The experimental system can also be viewed as an all-optical switch, that uses molecular states in a bacteriorhodopsin thin film, where a low power blue pulse turns on a signal red beam. All-optical logic gates are implemented with wild- type and chemically stabilized films of bacteriorhodopsin using a two-color backward degenerate four- wave mixing geometry. The sensitivity of each bR film is markedly different due to the large differences in the saturation intensity. Red light is used to form a grating due to the B to M transition and blue light is used to form a grating due to the fast photochemical transition from M to B. Each of the two wavelengths in the experimental system acts as an input to the all-optical gate and the phase conjugate signal beam bears the output of the gate. To establish the origin of the nonlinearity we studied the intensity dependence of the self-focusing and self-defocusing properties of wild-type bR in water solution using the Z-scan technique with low power cw lasers at two wavelengths on either side of the absorption band. Our measurements indicate that the sign of the nonlinearity depends on the wavelength and the magnitude depends on the fluence of the incident laser beam. The observed self-defocusing and focusing is not due to the intrinsic electronic nonlinearity. The observations can be explained in terms of the Kramers-Kronig dispersion relation that relates the real and imaginary parts of the complex index of refraction to the absorption spectrum.We developed an optical pattern recognition system using Optical Fourier Transform with bR films. The photoinduced dichroism and its dependence on light intensity allows one to use the bR film as a real-time self-adaptive spatial filter at the FT plane. We also demonstrate flow disturbance visualization and beam shaping.

Optical element, optical control method and apparatus using the optical element, and method of manufacturing the optical element

Abstract: An optical element, an optical control method and an optical control apparatus, wherein use is made of a low-power laser beam as a control beam to yield a light response of sufficient magnitude and speed. A control beam is projected from a light source (1), while a signal beam is from a light source (2). The control beam and the signal beam are converged by a condenser lens (7) and thrown onto an optical element (8). These beams pass through a light receiving lens (9) and a wavelength selection filter (20), and only the signal beam is detected with a photodetector (22). By turning the control beam on and off, a thermal lens is reversibly formed in the optical element, realizing the modulation of the signal beam intensity. The optical element may be formed in a laminated structure comprising, for example, a heat transfer layer, a heat retaining layer, and a heat transfer layer, and the thickness of the light absorbing layer is adjusted so as not to exceed two times the confocal distance of the converged control beam, thereby providing a light response of sufficient magnitude and speed by the use of a low-power laser beam as a control beam.