Showing papers on "Signal beam published in 2005"

Development of injection-seeded, pulsed optical parametric generator/oscillator systems for high-resolution spectroscopy

Abstract: We report the development and application of pulsed optical parametric generator (OPG) and optical parametric oscillator (OPO) systems that are injection seeded with near-infrared distributed feedback diode lasers. The OPG is injection seeded at the idler wavelength without the use of a resonant cavity. Two counter-rotating, beta-barium-borate (β-BBO) crystals are used in the OPG. These crystals are pumped by the third harmonic, 355-nm output of an injection-seeded Nd:YAG laser. An OPO version of the system has also been developed by placing two flat mirrors around the two β-BBO crystals to form a feedback cavity at the signal wavelength. The OPO cavity length is not actively controlled. The output signal beam from the OPG or OPO is amplified using an optical parametric amplifier (OPA) stage with four β-BBO crystals. The frequency bandwidths of the signal and idler laser radiation from OPG/OPA and OPO/OPA systems have been determined to be slightly greater than 200 MHz. The temporal pulses from each system are smooth and near-Gaussian. High-resolution optical absorption measurements of acetylene (C2H2) were performed as another check of the frequency spectrum of the idler beam. The frequency-doubled signal output of the OPO/OPA system was used to perform high-resolution, single-photon, laser-induced fluorescence (LIF) spectroscopic studies of the (0,0) vibrational band of the A 2Σ+−X 2Π electronic transition of nitric oxide (NO) at low pressure. Excellent agreement was obtained between the theory and the experiment. The signal output of the OPG/OPA system was also used for sub-Doppler, two-photon LIF spectroscopic studies of the same vibration–rotation manifold of NO.

High-repetition-rate, intracavity-pumped KTP OPO at 1572 nm

Abstract: An efficient, eye-safe, high-repetition-rate, intracavity optical parametric oscillator (IOPO) inside an acousto-optically Q-switched Nd:YVO4 laser end pumped by a 30-W fiber-coupled diode laser was demonstrated The pumping, acousto-optically Q-switched Nd:YVO4 laser gives 3-W average output power at 1064-nm wavelength at 40-kHz repetition rate An additional separating mirror, ‘x-cut’ KTP crystal and output coupler highly reflective at 1064-nm and partially transparent at 1572-nm wavelengths form a flat–flat IOPO resonator of 35-mm length We have achieved 3-ns-duration pulses for 20-mm-long KTP and 4-ns-duration pulses for 30-mm-long KTP, respectively More than 8-kW-peak-power pulses with an average power of 15 W at the signal wavelength for 40-kHz repetition rate were demonstrated Due to the intracavity spatial cleaning effect, a near diffraction limited signal beam was achieved despite a relatively worse beam quality of the pumping beam Conversion efficiencies of 50% with respect to Q-switched output at 1064-nm wavelength and 11% with respect to diode pump power were achieved

Hologram recording device

Abstract: A hologram recording device records hologram in a hologram recording medium by splitting a coherent beam outputted from a beam source into a signal beam and a reference beam, irradiating the hologram recording medium with the signal beam by modulating the signal beam by a spatial light modulator, and by irradiating the hologram recording medium with the other reference beam to have the reference beam overlap the signal beam. The hologram recording device is provided with a plurality of optical elements (20p, 20p’) which can be in two statuses, i.e., in on-mode wherein the reference beam is transmitted or reflected in a prescribed direction toward the hologram recording medium, and in off-mode where the reference beam is guided outside the prescribed direction or blocked. Each of the optical elements (20p, 20p’) is provided with an optical phase modulating means which generates prescribed phase differences (0, π), and a phase modulation control means which controls each of the optical elements (20p, 20p’) to be in the on-mode or off-mode and modulates the reference beam to a beam having a prescribed phase pattern.

Holographically encoded elements for microarray and other tagging labeling applications, and method and apparatus for making and reading the same

Abstract: A method and apparatus is provided for writing a code on an optical element, wherein the code is written on the optical element in the form of a holographic image of an n-dimensional code generated by an interference pattern between a reference beam and a signal beam reflected off a spatial light modulation device having the n-dimensional code configured thereon. The method includes steps of generating the interference pattern between the reference beam and the signal beam reflected off the spatial light modulation device having the n-dimensional code thereon; as well as writing the interference pattern on the optical element as a holographic image of the n-dimensional code.

The temperature dependent performance analysis of EDFAs pumped at 1480 nm: A more accurate propagation equation

Abstract: An analytically expression for the temperature dependence of the signal gain of an erbium-doped fiber amplifier (EDFA) pumped at 1480 nm are theoretically obtained by solving the propagation equations with the amplified spontaneous emission (ASE). It is seen that the temperature dependence of the gain strongly depends on the distribution of population of Er3+-ions in the second level. In addition, the output pump power and the intrinsic saturation power of the signal beam are obtained as a function of the temperature. Numerical calculations are carried out for the temperature range from -20 to +60 °C and the various fiber lengths. But the other gain parameters, such as the pump and signal wavelengths and their powers, are taken as constants. It is shown that the gain decreases with increasing temperature within the range of L≤27 m.

Transient Grating Spectroscopy in a Hot Turbulent Compressible Free Jet

Abstract: Speed of sound profiles of an unseeded hot, supersonic, axisymmetric free air jet at atmospheric pressure are measured with 2% uncertainty using laser-induced electrostrictive gratings. Signal level and lifetime decay with increasing temperature, and no data are obtained for static temperatures above 540 K. The influence of temperature, turbulence, beam steering, and mechanical vibrations on the signal amplitude and lifetime is examined quantitatively. It is argued that electrostrictive gratings are applicable for thermometry and velocimetry in supersonic combustors by employing a powerful pulsed infrared probe beam. The significantly larger beam power raises the signal level by three orders of magnitude, whereas the longer wavelength reduces the effects of beam steering by increasing the angular separation between probe and signal beam.

Recording and reproducing method

Abstract: A hologram recording method for forming a light interference pattern in a hologram recording medium to record information thereon. The method includes a step of interfering with a reference beam a signal beam spatially modulated by an information pattern which carries the information to generate interfered beams. The method includes a step of executing a recording sequence a plurality of times, the recording sequence including steps of irradiating the interfered beams onto a recording surface of the hologram recording medium to form a group of a plurality of holograms each corresponding to the information pattern. The method includes a step of completing the recording sequence. Different modulation conditions are set for at least one of the signal beam and the reference beam in one recording sequence and the subsequent recording sequence immediately after the one recording sequence.

Prism device and combined optical and radio frequency beam steering system

Abstract: A prism device includes: a prism material having substantially the same index of refraction at first and second wavelengths; a first anti-reflection coating for reducing reflection of a first signal beam at the first wavelength; and a second anti-reflection coating for reducing reflection of a second signal beam at the second wavelength The prism material can be silicon, which has substantially the same index of refraction at IR and RF wavelengths In this case, the RF anti-reflection coating can be a layer of silicon dioxide (fused silica), which can be sandwiched between two IR anti-reflection coatings designed to minimize IR reflections between the surrounding air and the RF anti-reflection coating and between the RF anti-reflection coating and the prism material, respectively Two or more of the prism devices can be used in a beam steering system to simultaneous direct the first and second signal beams in substantially the same direction

Hologram record carrier, hologram apparatus and recording method

Abstract: A hologram record carrier capable of information recording or regeneration by beam irradiation, comprising a hologram recording layer storing in its interior optical interference patterns by coherent reference beam and signal beam components as a diffraction grating, and comprising a reflection functional layer superimposed on the hologram recording layer at its side opposite to beam incident side, in which nonreflecting zones are developed in irradiated regions in response to the intensity of irradiation beam.

Hologram retrieval method and holographic recording and reproducing apparatus

Abstract: Provided is a hologram retrieval method and a holographic recording and reproducing apparatus for preventing an increase in SNR, a decrease in retrieval accuracy, or the retrieval itself from being made impossible, which would otherwise occur because of a small size of data used for retrieval. Digital information is recorded on a holographic recording medium as data pages DP formed of a two-dimensional bit map image with each page being multiplexed. The data page DP is divided into a plurality of equal data blocks DB 11 to 13 , DB 21 to DB 23 , and DB 31 to DB 33 , and each data block DB is provided with a data image that is encoded by an encoding method for providing a certain number of ON pixels within each data block DB. A spatial light modulator allows the to-be-retrieved data image to be encoded by the encoding method and displayed as block information on a retrieval data block associated with the data block, and a signal beam to be thereby modulated. Of resulting diffracted beams, the diffracted beam of the maximum intensity is used to detect the target data image and the address of the reference beam.

Optical transmission apparatus, continuity testing method therein and optical transmission system

Abstract: An optical transmission apparatus comprises a preamplifier controlling unit for controlling a preamplifier so that amplified spontaneous emission including all wavelength bands of a wavelength-multiplexed signal beam is outputted toward a wavelength demultiplexing unit, with the wavelength-multiplexed signal beam not inputted, power monitors for monitoring optical powers of the amplified spontaneous emission fed from the preamplifier and wavelength-demultiplexed by the wavelength demultiplexing unit, and a determining unit for determining the continuity state of an optical propagation path of each wavelength component on the basis of a result of monitoring by the power monitors. The optical transmission apparatus allows the continuity test on optical propagation paths of channels including a channel not used at the time of a start of the operation to be made easier than the known techniques.

Holographic digital data storage system compatible with holographic and reflective medium

Abstract: In a holographic digital data storage system, a light source generates a reference beam, a holographic optical element saves a plurality of interference patterns between the reference beam and a plurality of beams of specific sizes and a beam splitter splits each reproduced beam into a holographic signal beam and a holographic reference beam. A medium records an interference pattern between the holographic reference beam and the holographic signal beam and reflecting the holographic reference beam to generate a reflective information beam and, if only the holographic reference beam is illuminated, a displaying means displays a holographic reproduced beam for the holographic signal beam and detecting the reflective information beam.

Holographic recording apparatus and method for recording holograms

Abstract: A hologram recording apparatus for carrying out holographic recording by emitting a signal beam and a reference beam onto a holographic recording medium includes a laser light source configured to output a pulsed laser beam, a splitter configured to split the laser beam into a signal beam and a reference beam, a spatial light modulator configured to modulate the signal beam or both the signal beam and the reference beam, and a controlling unit configured to control the spatial light modulator to modulate at least one of the signal beam and the reference beam with a totally dark pattern for a predetermined period of time, wherein the predetermined period begins no later than the start of the risetime of a pulse of a laser beam output from the laser light source.

Offset quadrature phase-shift-keying method and optical transmitter using the same

Abstract: Disclosed is an optical transmitter using an offset quadrature phase-shift-keying (OQPSK) method. The method includes: a first phase modulator for outputting a first signal beam generated by phase-modulating an input beam based on a first data; a second phase modulator for outputting a second signal beam generated by phase-modulating the input beam based on a second data; a phase delay unit for granting a predetermined phase difference between the first signal beam and the second signal beam; and an optical coupler for coupling the first signal beam and the second signal beam between which the phase difference exists.

Enhanced detection of acousto-photonic emissions in optically turbid media using a photo-refractive crystal-based detection system

Abstract: A system and method of detecting acousto-photonic emissions in optically turbid media that provide increased levels of detection sensitivity. The detection system includes an ultrasonic transducer, a laser, a photo-detector for detecting ultrasound-modulated laser light, and circuitry for processing the detected signals for subsequent analysis. The ultrasonic transducer generates an ultrasonic wave that propagates within an optically turbid medium. The laser generates a coherent light beam, which is split to form signal and reference beams. The signal beam is sent through the turbid medium, where it is phase modulated by the ultrasound. The ultrasound-modulated signal beam is provided to a photo-refractive crystal for subsequent interference with the reference beam to convert the phase modulation to intensity modulation. The DC offset of the signal beam intensity provides a measure of the magnitude of the mean phase shift induced by the ultrasound on the multiply scattered optical field within the turbid medium.

Hologram recording device, hologram reproduction device, hologram recording method, and hologram reproducing method

Abstract: In recording of an interference fringe of a reference beam and a signal beam in a hologram recording medium, at the time of multiple recording of holograms in the same recording region by varying the angle of incidence of the reference beam on the hologram recording medium, the angular pitch of the incidence angle of the reference beam is varied according to the incidence angle of the reference beam in the manner of Δθ1, Δθ2, . . . , Δθm−1, and is thereby set to a minimum in such a range as not to worsen crosstalk. This makes it possible to increase the degree of multiplexing when the movable angle of the reference beam is the same, and to narrow the movable angle of the reference beam when the degree of multiplexing is the same, as compared with the related art.

Holographic digital data storage system

Abstract: In a holographic digital data storage system, a light source generates a reference beam, a holographic optical element saves a plurality of interference patterns between the reference beam and a plurality of beams of specific sizes and a beam splitter splits each reproduced beam into a holographic signal beam and a holographic reference beam. A medium records an interference pattern between the holographic reference beam and the holographic signal beam and reflecting the holographic reference beam to generate a reflective information beam and, if only the holographic reference beam is illuminated, a displaying means displays a holographic reproduced beam for the holographic signal beam and detecting the reflective information beam.

Optical fiber amplifier

Abstract: PROBLEM TO BE SOLVED: To obtain an optical fiber amplifier which can control the wavelength characteristic of a gain so as not to be varied from an initial condition even when the wavelength of signal light beam is varied. SOLUTION: An excited light beam is inputted from the signal beam output side of a fiber 6 for amplification, an output light beam l1 to the signal beam input side from the fiber 6 for amplification is branched, and wavelength adjusting information d2a to d2n for keeping the optical level of the branched light beam l2 to a constant level are supplied to the wavelength adjusting means 3a to 3n. Therefore, the signal beam is not almost included in the output light beam l1 to the signal beam input side from the fiber 6 for amplification. It is also possible from the optical level of the naturally radiated light beam and the excited light beam to control so that the wavelength characteristic of a gain is kept within the initial condition. Accordingly, the optical fiber amplifier having excellent expandability can be obtained even when the wavelength of the signal beam is varied without taking into account the wavelength of the signal beam in the control of the wavelength characteristic of the gain. COPYRIGHT: (C)2005,JPO&NCIPI

Data read/write device for holographic storage medium and method thereof

Abstract: An apparatus writes and reads data with respect to a holographic storage medium. The holographic data writing apparatus includes a laser beam irradiating device irradiating a laser beam onto a storage medium which is capable of writing a holographic data thereon; and a reflective data mask arranged adjacent to the storage medium and storing data for copy thereon, and when the laser beam is transmitted through the storage medium and is incident on the reflective data mask, the reflective data mask reflects the incident laser beam in the form of a signal beam corresponding to the data, and irradiates the signal beam onto the storage medium, such that interference patterns of the laser beam and the signal beam are written in the storage medium.

Hologram apparatus and hologram recording method

Abstract: The present invention provides a hologram apparatus for recording an interference fringe of a signal beam and a reference beam having a speckle pattern in a recording area of a hologram recording material. The hologram apparatus includes a speckle pattern generating unit for generating the speckle pattern so that the speckle pattern is different in form in the track direction and the cross-track direction of the recording area. With this configuration, it is possible to perform recording under an increased tolerance in the cross-track direction while securing the shift selectivity necessary in the track direction, and, hence, to easily and stably perform the tracking servo at the time of reproduction.

Holographic data recording apparatus and method

Abstract: A holographic data recording apparatus includes: a signal beam patterning unit (48) for irradiating a signal beam onto a holographic medium (50), the signal beam including a data pattern to be recorded; a cylindrical optical body (102) including a cylindrical reflective surface, by which a first and a second reference beams alternatively incident thereto at incident angles are reflected toward the holographic medium, alternatively; and an incident angle control unit for controlling the incident angles of the first and the second reference beams incident on the cylindrical optical body, wherein the data pattern is recorded on the holographic medium by interfering the signal beam with the first and the second reference beams on the holographic medium. The holographic data recording apparatus do not require the replacement of the conventional conical mirrors while recording a plurality of data on a holographic medium, thereby increasing the recording speed and reducing the manufacturing cost thereof.

Holographic pump coupler and laser grating reflector

Abstract: In the present invention, a volume holographic optical element is used as a pump coupler. The holographic coupler allows at least one pump wavelength to be coupled into the laser medium. The direction of the pump beam onto the coupler is not co-linear with the direction of the signal beam out of the coupler. The invention further provides the coupling of more than one pump wavelengths using a single holographic coupler element while maintaining the high isolation between pump and signal beam. The invention further provides a narrow-band reflection grating of various efficiencies for the signal beam (as part of the laser cavity).

Phase sensitive parametric amplification of optical vortex beams

Abstract: This work deals with the experimental parametric amplification of optical vortex beams (OVB) in a degenerate type I optical parametric amplifier (OPA). Results show that in a degenerate type I OPA, the amplification gain in the transverse plane depends on the pump beam profile as well as the relative phase between interacting beams. It leads to amplification or de-amplification that reshapes the signal beam in its transverse plane and preserves the orbital angular momentum when an optical vortex is carried by the signal beam. Then, new various patterns are obtained depending on phase matching condition, topological charge of the vortex and wave front of the pump beam.

Experiment on PR SEW of SBN crystal

Abstract: Photorefractive surface electromagnetic wave (PR SEW) at the interface between SBN crystal and air based on drift and diffusion mechanism was observed experimentally for the first time. PR SEW can be formed when laser beam was incident at an angle of 55° in proper ratio of signal beam to background beam, and the intensity of PR SEW increases along with the increasing of additional electric field.

Pickup module with coating layer

Abstract: A pickup module comprises a plurality of optical components along an optical path, wherein at least two of the optical components are provided with coating layers to change a polarization of a light beam and collectively circularly polarize the light beam. The circularly-polarized beam is projected on an optical storage medium and converted to a signal beam received by an optical detector. A quarter wavelength plate (QWP) or the other phase retarded plate for required purpose (½λ, ¼λ, ⅛λ . . . ) is not included in the optical component set.

Gain monitor in a distributed raman amplifier

Abstract: In order to determine the actual on-off gain of a Roman amplifier (RA) in a fiber optical communication system, a low frequency signal modulation is applied to the Raman pump beam. A corresponding intensity modulation is then measured at the signal beam and the on-off Raman gain is determined from this detected intensity modulation. The Roman optical amplifier (RA) contains a pump light source (LD) coupled to a fiber (F) of the communication system to launch a pump light signal into said fiber for amplifying an optical signal traversing said fiber (F) by stimulated Roman amplification. A low-frequency modulator (MO) is coupled to said pump light source (LD) for applying a low frequency intensity modulation to said pump light signal. A detector (PD) detects a corresponding low frequency amplitude modulation in said signal traversing said optical fiber (F). A controller dynamically determines a parameter of amplification of said optical amplifier (RA).

Difference frequency mixing of strongly focused Gaussian beams in periodically poled LiNbO3

Abstract: Difference frequency mixing of strongly focused Gaussian beams in periodically poled LiNbO3 was investigated. The beams were focused inside the crystal without damage. Mixing of cw and pulsed laser systems was employed to minimize the thermal lensing effects inside this crystal. A low-power cw 1.064‐μm Nd:YAG laser beam was used as the pump, whereas the signal beam came from a picosecond optical parametric oscillator. The two independently focused beams were made to overlap inside the crystal. The focusing parameters of the two beams were about the same. The focusing function developed by Boyd and Kleinman for tightly focused beams was extended to periodically poled crystals in order to fit the temperature-tuning curve. A 0.66%∕W efficiency was obtained for the difference frequency mixing process.

Phase-sensitive lock-in detection of semiconductor waveguide intensity profiles

Abstract: A phase-sensitive lock-in detection scheme is employed in the measurement of transverse intensity distributions in semiconductor waveguide structures. A modulated (chopped) sampling beam is scanned across the waveguide, and the photocurrent signal from a 1550-nm signal beam in the waveguide is monitored through phase-sensitive lock-in detection (referenced to the sampling beam chopping frequency). It is determined that the photoinjected free-carrier perturbation by the scanning beam can be successfully mapped onto the local signal intensity, and the transverse intensity profile of the signal beam in the waveguide can be extracted. For the 3-μm-wide waveguide and the 2-μm sampling spot size employed in this investigation, the spatial resolution was limited mainly by the 1.7-μm carrier diffusion length in the semiconductor.