Showing papers on "Signal beam published in 2008"

Quantum Illumination with Gaussian States

Abstract: An optical transmitter irradiates a target region containing a bright thermal-noise bath in which a low-reflectivity object might be embedded. The light received from this region is used to decide whether the object is present or absent. The performance achieved using a coherent-state transmitter is compared with that of a quantum-illumination transmitter, i.e., one that employs the signal beam obtained from spontaneous parametric down-conversion. By making the optimum joint measurement on the light received from the target region together with the retained spontaneous parametric down-conversion idler beam, the quantum-illumination system realizes a 6 dB advantage in the error-probability exponent over the optimum reception coherent-state system. This advantage accrues despite there being no entanglement between the light collected from the target region and the retained idler beam.

A Nonvolatile Plasmonic Switch Employing Photochromic Molecules

Abstract: We demonstrate a surface plasmon-polariton (SPP) waveguide all-optical switch that combines the unique physical properties of small molecules and metallic (plasmonic) nanostructures. The switch consists of a pair of gratings defined in an aluminum film coated with a 65 nm thick layer of photochromic (PC) molecules. The first grating couples a signal beam consisting of free space photons to SPPs that interact effectively with the PC molecules. These molecules can reversibly be switched between transparent and absorbing states using a free space optical pump. In the transparent (signal “on”) state, the SPPs freely propagate through the molecular layer, and in the absorbing (signal “off”) state, the SPPs are strongly attenuated. The second grating serves to decouple the SPPs back into a free space optical beam, enabling measurement of the modulated signal with a far-field detector. In a preliminary study, the switching behavior of the PC molecules themselves was confirmed and quantified by surface plasmon re...

New all-optical logic gates based on the local nonlinear Mach-Zehnder interferometer

Abstract: We propose new all-optical logic gates containing a local nonlinear Mach-Zehnder interferometer waveguide structure. The light-induced index changes in the Mach-Zehnder waveguide structure make the output signal beam propagate through different nonlinear output waveguides. Based on the output signal beam propagating property, various all-optical logic gates by using the local nonlinear Mach-Zehnder waveguide interferometer structure with two straight control waveguides have been proposed to perform XOR/NXOR, AND/NAND, and OR/NOR logic functions.

Beam coupling in photorefractive liquid crystal light valves

Abstract: Photorefractive liquid crystal light valves (LCLVs) are hybrid devices that combine a nematic liquid crystal layer with a thin monocrystalline Bi12SiO20 (BSO) photorefractive crystal in the form of a cell wall. The device behaves as an optically addressed spatial light modulator, where the photoconductive layer is made of the BSO crystal. Differently from conventional types of spatial light modulators, usually working in retroreflective configuration, the photorefractive light valves work in transmission, thus allowing new applications related to the coupling of the optical beams when they pass through the liquid crystal layer. Here, we review some recent experiments of beam coupling in photorefractive LCLVs. After a characterization of the device in terms of its spatial resolution, which is related to the features of pattern formation in an optical feedback configuration, we present two-beam coupling and optical amplification in single pass experiments. Then, we develop a theoretical model by taking into account the Raman–Nath diffraction of the incoming beams over the thin liquid crystal layer. By using two or more light valves in cascade, we show, both experimentally and theoretically, that the two-wave mixing gain can be enhanced by the Talbot effect related to the multi-passage of the beams through the successive layers of the nematic liquid crystal. Finally, we show that self-pumped phase conjugation can be realized by placing the light valve in a tilted feedback configuration. In this case, the four-wave mixing is spontaneously created through the scattering of the signal beam onto the feedback induced grating.

Phase-Sensitive Manipulations of a Squeezed Vacuum Field in an Optical Parametric Amplifier inside an Optical Cavity

Abstract: A squeezed vacuum field can be amplified or deamplified when it is injected, as the signal beam, into a phase-sensitive optical parametric amplifier (OPA) inside an optical cavity. The spectral features of the reflected quantized signal field are controlled by the relative phase between the injected squeezed vacuum field and the pump field for the OPA. The experimental results demonstrate coherent phenomena of OPA in the quantum regime and show phase-sensitive manipulations of quantum fluctuations for quantum information processing.

High-resolution GaP Terahertz Spectrometer and Its Application to Detect Defects in Gamma-irradiated Glucose Crystal

Abstract: We developed high-resolution GaP THz signal generator using Cr:Forsterite lasers with gratings as both a pump and a signal beam for difference-frequency generation. A line width of less than 500 MHz and a wide tunable frequency range (0.6–6.2 THz) provide sufficient resolution for measuring materials with sharp absorption bands using the generator as the light source for a THz spectrometer. This is suitable for materials such as gases or solid samples at low temperatures. We demonstrated the detection of defects in organic materials, as they appear as slight deviations in the absorption frequency in the THz region.

Spatial solitons in chiral nematics

Abstract: In this work we present for the first time experimental results of measurements of spatial solitons (nematicons) in chiral nematic liquid crystalline film. We measured the propagation of light beam at the distance of a few millimeters and the nonlinear self-focusing was observed for a light power of order of a few tenths of milliwats. Additional, in a waveguide induced by the nematicon, other low-power light beam (signal beam) with different wavelength was trapped. There were also observed the changes of the nematicon direction by changing the position across the nematics layer. The experimental results are in a good agreement with theoretical predictions.

Semiconductor Raman ring amplifier

Abstract: A semiconductor-based Raman ring amplifier is disclosed. A method according to aspects of the present invention includes directing a pump optical beam having a pump wavelength and an input pump power level from an optical waveguide into a ring resonator. The optical waveguide and ring resonator are comprised in semiconductor material. A signal optical beam having a signal encoded thereon at a signal wavelength is directed from the optical waveguide into the ring resonator. The pump optical beam is resonated within the ring resonator to increase a power level of the pump optical beam to a power level sufficient to amplify the signal optical beam via stimulated Raman scattering (SRS) within the ring resonator. A free carrier concentration in the optical waveguide and the ring resonator is reduced to reduce attenuation of the pump optical beam and the signal beam.

Method and optical arrangement for generating a nonlinear optical signal on a material which is excited by an excitation field, and use of the method and of the optical arrangement

Abstract: The invention relates to a method and an optical arrangement (10) for generating a nonlinear optical signal (17) on a material (16) which is excited by an excitation field (2). With the excitation field, coherent fields of first and second optical pulses of different frequencies are overlapped in the material (16) both temporally and spatially. The first pulse of a first frequency is generated in a first beam (3) of a first optical generator unit (1), and the second pulse of a second frequency is generated in a second beam (8) of a second optical generator unit which is synchronously pumped by the first optical generator unit (1). With the first pulses of the first frequency as the fundamental frequency pulse (5) of a higher harmonic frequency, the same is generated, and the second optical generator unit (7) is pumped with the pulses of the higher harmonic frequency. According to the concept of the invention, the method proposes that the second optical generator unit (7), as an optical parametric generator unit, generates pulses of an idler frequency in an idler beam for producing the second pulse of the second frequency in the second beam (8), wherein the second frequency is smaller than the first frequency, and the second optical generator unit generates pulses of a signal frequency in a signal beam (9), wherein the second frequency is smaller than the signal frequency.

Parametric reflection upon cascade interaction of focused optical beams

Abstract: The parametric reflection of a signal beam in the waist of the reference pump beam upon mismatched three-frequency interaction in a quadratically nonlinear medium is discussed The critical angle of total internal reflection from the induced defocusing channel is found as a function of the beam waist parameters It is shown that when the reference beam is focused, this angle increases and some distortions are introduced into the reflected wave due to a finite length of the waist The modification of the cross section of a wave reflected from a convex parametric mirror is analysed The optimal beam focusing geometry is found at which the distortions of the shape and divergence of the reflected wave are minimal Under certain conditions, the signal wave also flows around a cylindrical inhomogeneity produced by the axially symmetric pump beam The results of theoretical analysis and numerical simulation are in good agreement

A phase feature extraction technique for terahertz reflection spectroscopy

Abstract: We present a phase feature extraction technique for weakly polarized organic compounds in THz-RTDS by taking the second derivative of the phase of the signal beam with respect to frequency. In nitrogen purged environment this method doesn't require any reference. In real scenarios, a reference beam is applied only to remove the influence of atmospheric attenuation. This method offers a straightforward and speedy way to retrieve the absorption features in the reflection spectrum without the presence of the amplitude of the THz pulse or the settlement of a reference surface. It opens the pathways for the application of a more un-conventional THz emission mechanism and extends the capability of THz sensing technology into more practical sensing and imaging situations.

Nonlinear gain amplification due to two-wave mixing in a broad-area semiconductor amplifier with moving gratings.

Abstract: The two-wave mixing in a broad-area semiconductor amplifier with moving gratings is investigated theoretically, where a pump beam and a signal beam with different frequencies are considered, thus both a moving phase grating and a moving gain grating are induced in the amplifier. The coupled-wave equations of two-wave mixing are derived based on the Maxwell’s wave equation and rate equation of the carrier density. The analytical solutions of the coupled-wave equations are obtained in the condition of small signal when the total intensity is far below the saturation intensity of the amplifier. The results show that the optical gain of the amplifier is affected by both the moving phase grating and the moving gain grating, and there is energy exchange between the pump and signal beams. Depending on the moving direction of the gratings and the anti-guiding parameter, the optical gain may increase or decrease due to the two-wave mixing.

Hologram recording apparatus and method

Abstract: A hologram recording apparatus includes a laser light source for emitting laser light, a light splitter for splitting the laser light emitted from the laser light source into a signal beam and a reference beam, a light modulator for modulating the signal beam split by the light splitter, a phase modulator for phase-modulating the reference beam split by the light splitter, an optical system for collecting the signal beam modulated by the light modulator and the reference beam phase-modulated by the phase modulator onto almost the same collecting position on a hologram recording medium, a collecting-position control mechanism for controlling the collecting position along a surface of the hologram recording medium, and a distance control mechanism for controlling the distance between the phase modulator and the hologram recording medium.

Optical pickup, optical information recording and reproducing apparatus and method for optically recording and reproducing information

Abstract: An optical pickup for recording a hologram by using an angle multiplexing method. An optical beam is separated into two beams, a signal beam and a reference beam having different convergence/divergence degrees, by using an optical component such as a diffraction lens. The signal and reference beams are made incident upon the same objective, and the optical component or the objective lens is moved in a direction perpendicular to an optical axis, to thereby realize angle multiplex recording. If an optical information recording medium is inclined, the optical component or the objective lens is moved along the direction along which the optical information recording medium moved to change an angle of the reference beam incident upon the optical information recording medium and compensate for degradation of a reproduction signal.

Recording apparatus and recording method

Abstract: A recording apparatus includes a drive unit that rotationally drives a holographic recording medium including a recording layer and a track forming layer that includes guide tracks formed at constant intervals in a radial direction, where a signal beam and a reference beam are emitted to the recording layer so that a hologram is recorded in accordance with the signal beam, a signal beam generating unit, a reference beam generating unit, a recording unit that emits the signal beam and reference beam into the medium and records the hologram, a rotation control unit that controls the drive unit so that the medium is rotationally driven at a constant rotation speed, and a recording control unit that selects some of the guide tracks so that radial-direction recording intervals of the holograms are statistically decreased towards the outer periphery and controls the recording unit to record the holograms along the selected tracks.

Apparatus for recording/reproducing holographic information

Abstract: A holographic information recording and/or reproducing apparatus, including a light source to emit light; a polarization forming optical system to form a polarized signal beam and a polarized reference beam from the light emitted from the light source, wherein the polarized signal beam and the polarized reference beam are incident on a holographic information storage medium through an identical surface; a focusing optical system to focus the polarized signal beam and the polarized reference beam onto in the holographic information storage medium so that information is recorded by an interference pattern; and an adjustment optical system to set the focal positions of the polarized signal beam and the polarized reference beam, and to adjust a difference between a path of the polarized signal beam and a path of the polarized reference beam.

Optical Information Recording and Reproducing Device

Abstract: The optical information recording and reproducing device utilizing holography requires the optical system to generate the signal beam and the reference beam to be irradiated to the holographic storage medium as well as another optical system to generate the curing light beam to be irradiated to the holographic storage medium. Furthermore, from the viewpoint of backward compatibility, if the same device is used for recording or reproduction on the conventional optical discs represented by Blu-ray Disc, another optical system adaptable to recording and reproduction on these optical disks is required. This means the optical system configurations become complicated and larger in size. One solution for downsizing is to use the reference beam also as the curing light beam. Another way is sharing of optical path for curing light beam and for the reference beam. Furthermore, it is possible to share the light source for generating the curing light beam and for generating the recording or reproducing light beam. In such way, optical system configurations become simple.

Differential-phase interferometric system

Abstract: A differential-phase interferometric system includes a polarized heterodyne interferometer for generating reference and signal beam that travel along reference and signal channels, respectively. The signal beam is directed to a specimen and contains measured information of the specimen. The interferometer further generates a first electrical signal output corresponding to first linear polarized waves of the reference and signal beams, and a second electrical signal output corresponding to second linear polarized waves of the reference and signal beams. A differential amplifier receives the first and second electrical signal outputs, and generates a differential signal output therefrom. A data acquisition unit is used to measure amplitudes of the first and second electrical signal outputs and the differential signal output. A computing unit computes the amplitudes measured by the data acquisition unit to determine a phase difference between the electrical signal outputs, which corresponds to the measured information of the specimen.

Holgraphic recording and reading method and holographic recording and reading apparatus

Abstract: A method of holographically recording and reading information is disclosed. The method includes: recording information in a holographic recording medium by irradiating the holographic recording medium with a laser beam, wherein a transverse sectional area of the laser beam is divided into a central area for a signal beam and a ring-shaped area for a reference beam, the ring-shaped area surrounding the central area with a predetermined gap; and reading out the information from the holographic recording medium by irradiating the holographic recording medium with a ring-shaped readout beam having an area greater than that of the reference beam in at least one of directions inward of an inner diameter thereof and outward of an outer diameter thereof.

Apparatus and method for recording/reproducing holographic data and holographic data storage medium

Abstract: A method and apparatus for recording and/or reproducing holographic data and a holographic information storage medium, wherein the apparatus for recording and/or reproducing holographic information includes an optical pickup emitting light onto a holographic information storage medium and receiving the emitted light. The optical pickup includes: a light source unit emitting a signal beam and a reference beam in a recording mode; and a focusing optical system focusing the signal beam and the reference beam on one focal point in the holographic information storage medium so that information can be recorded by using an interference pattern formed along a depth direction of the holographic information storage medium in the vicinity of the focal point, wherein the numerical aperture of the focusing optical system for the signal beam is different from the numerical aperture of the focusing optical system for the reference beam.

Apparatus for recording/reproducing holographic data

Abstract: A holographic information recording and/or reproducing apparatus includes: a light source to emit light; a polarization conversion device to form a polarized signal beam and an orthogonal polarized reference beam; an optical path forming optical system to separate the optical paths of the signal beam and the reference beam; a focus adjustment optical system disposed on the optical path of at least one of the signal beam and the reference beam, and to vary a position of a focus of at least one of the signal beam and the reference beam in a depth direction of the holographic information storage medium; an objective lens to focus the signal beam and the reference beam in the holographic information storage medium, and form an interference pattern to record information; and a 4f relay system disposed on an optical path between the focus adjustment optical system and the objective lens.

The Electrooptic and Photorefractive Effects

Abstract: The electrooptic effect is the change in the refractive index of a material induced by the presence of a dc (or low-frequency) electric field. In some materials, the change in refractive index depends linearly on the strength of the applied electric field. This change is known as the linear electrooptic effect or Pockels effect. Linear electrooptic effect can occur only for materials that are noncentrosymmetric. Although the linear electrooptic effect can be described in terms of a second-order nonlinear susceptibility, a very different mathematical formalism has historically been used to describe the electrooptic effect. The photorefractive effect is the change in refractive index of an optical material that results from the optically induced redistribution of electrons and holes. The photorefractive effect is quite different from most of the other nonlinear-optical effects. The photorefractive effect tends to give rise to a strong optical nonlinearity. Moreover, under certain circumstances, two beams of light can interact in a photorefractive crystal in such a manner that energy is transferred from one beam to the other. This process, which is often known as two-beam coupling, can be used to amplify a weak, image-bearing signal beam by means of an intense pump beam.

Optical pickup, optical information recording apparatus and optical information recording and reproducing apparatus using the optical pickup

Abstract: In holographic recording, it is important to form stably an interference fringe between a reference beam and a signal beam in a holographic storage medium. To suppress factors degrading stability of the interference fringe, such as fluctuation of atmospheric air, position displacement of optical components and the like during propagation of the reference and signal beams, an optical pickup and an optical information recording/reproducing apparatus adopt an optical system structure providing a higher proportion of optical components shared by the reference and signal beams optical path than conventional optical system structure. To increase the proportion of shared optical components, the signal beam and the reference beam pass through the PBS prism as parallel beams and a concave lens is placed on a reference beam path just before the objective lens.

Higher diffraction order photorefractive optical beam splitter

Abstract: A higher diffraction order photorefractive (PR) optical beam splitter has been realized based on a PR higher diffraction order grating. In the experiments, the beam splitter was produced by two-wave coupling at a small incident angle in Fe:LiNbO3 using the output from a He–Ne laser at 632.8 nm. An incident signal beam containing three different wavelengths (632.8, 532.0 and 488.0 nm) was split into multi-output beams by the beam splitter. The size of higher diffraction order is given and the influence of crystal thickness is discussed. Results show that the higher diffraction order PR optical beam splitter provides a practical method to split a multi-wavelength signal beam.

Multiplexing hologram recording and reconstructing apparatus and method therefor

Abstract: A hologram recording and reconstructing apparatus (100A) includes a rotating mirror (16), a rectangular aperture (12) and a medium drive unit (38A), records interference fringes of a reference beam (RL) and a signal beam (SL) in a hologram recording medium (30) and reconstructs the hologram recorded in the hologram recording medium (30). The rotating mirror (16) changes the angle of incidence of the reference beam (RL) incident on the hologram recording medium (30) such that multiple data is recorded in the same recording region of the hologram recording medium (30). The rectangular aperture (12) blocks a reconstructed beam from a hologram adjacent to the hologram to be reconstructed. The medium drive unit (38A) drives the hologram recording medium (30) such that the angle of incidence of the signal beam (SL) and the reference beam (RL) incident on the hologram recording medium (30) is changed.

Difference phase demodulation interference system

Abstract: A differential-phase interferometric system includes a polarized heterodyne interferometer for generating reference and signal beam that travel along reference and signal channels, respectively. The signal beam is directed to a specimen and contains measured information of the specimen. The interferometer further generates a first electrical signal output corresponding to first linear polarized waves of the reference and signal beams, and a second electrical signal output corresponding to second linear polarized waves of the reference and signal beams. A differential amplifier receives the first and second electrical signal outputs, and generates a differential signal output therefrom. A data acquisition unit is used to measure amplitudes of the first and second electrical signal outputs and the differential signal output. A computing unit computes the amplitudes measured by the data acquisition unit to determine a phase difference between the electrical signal outputs, which corresponds to the measured information of the specimen. The invention can satisfy the demands of amplitude adjustment, has rapid response and feasibility of phase difference measuring sensitivity and can be arranged in wide and various applications.

Recording and reproducing device, recording and reproducing method, recording device, recording method, reproducing device and reproducing method

Abstract: A recording technique for performing data recording onto a hologram recording medium in accordance with information on phases by performing spatial light phase modulation as spatial light modulation corresponding to recording data, and a reproducing technique for reproducing recorded data by properly reading information on phases recorded as described above are suggested. A signal beam having a phase modulation pattern provided thereto corresponding to recording data and a reference beam having a specific phase modulation pattern provided thereto are applied to the hologram recording medium. Thus, recording data can be recorded onto the hologram recording medium in accordance with information on phases. In addition, at the time of reproduction, a reference beam and a DC beam having the entire phase whose phase difference with respect to a reference phase within the reference beam is π/2 are applied to the hologram recording medium. By providing a phase difference based on π/2 as described above, the phase of a reproduction beam obtained from the hologram recording medium in accordance with application of the reference beam and the phase of the DC beam can be set to be the same. Thus, the DC beam can be added as a component of an amplitude of "1" to the reproduction beam. By reading the reproduction beam to which the DC beam is added as described above, recorded information on phases can be correctly read, and recorded data can be reproduced in accordance with the phase information.

Attenuated total reflection spectrometry and device at terahertz frequency

Abstract: PROBLEM TO BE SOLVED: To provide a terahertz spectroscopy and device that can measure the spectrum of a sample existing near a prism for totally reflecting terahertz electromagnetic waves and a sample interface and can measure complex refractive index of a sample, even in a terahertz region. SOLUTION: The attenuated total reflection spectrometry and device at terahertz frequency utilize surface waves (evanescent waves), having the terahertz frequency occurring, when the terahertz electromagnetic waves are totally reflected. This device comprises a terahertz electromagnetic wave light source that emits two exciting lasers of a pump beam and signal beam to an optical crystal for generating terahertz electromagnetic waves and generating the terahertz electromagnetic waves, and a prism for receiving the terahertz electromagnetic waves and generating the evanescent waves. COPYRIGHT: (C)2009,JPO&INPIT

Optical beam transmission channel switching device for optical fiber network

Abstract: The invention discloses a device for switching a beam transmission channel in a fiber network, which can be applied for integrating to a fiber-type network system such as an LAN or a telephone network system. The invention is used for providing a switching function of the beam transmission channel for the fiber-type network system. The invention is characterized by providing a monitoring function of a reserve channel for the fiber type network system by adopting two double to double (2*2 type) optical path switchers and a beam transmission. The characteristic enables the monitoring beam and the signal beam move in different paths so that the monitoring beam and the signal beam can not interface mutually. Thus the data transmission of the fiber type network system can be more reliable with higher safety.