Showing papers on "Signal beam published in 2016"

Dynamic Control of the Extraordinary Optical Scattering in Semicontinuous 2D Metamaterials

Abstract: Coherent control of the reflection and refraction in semicontinuous metasurfaces is realized. Both the reflection and refraction efficiency of a single-layered metasurface can be greatly improved with this method. By controlling the relative phase between the signal beam and the control beam, the Snell's law can be dynamically manipulated. This method may open possibilities to the practical application of metasurfaces.

Linear phase encoding for holographic data storage with a single phase-only spatial light modulator.

Abstract: A linear phase encoding is presented for realizing a compact and simple holographic data storage system with a single spatial light modulator (SLM). This encoding method makes it possible to modulate a complex amplitude distribution with a single phase-only SLM in a holographic storage system. In addition, an undesired light due to the imperfection of an SLM can be removed by spatial frequency filtering with a Nyquist aperture. The linear phase encoding is introduced to coaxial holographic data storage. The generation of a signal beam using linear phase encoding is experimentally verified in an interferometer. In a coaxial holographic data storage system, single data recording, shift selectivity, and shift multiplexed recording are experimentally demonstrated.

Infrared sensitive liquid crystal light valve with semiconductor substrate.

Abstract: A liquid crystal light valve (LCLV) is an optically controlled spatial light modulator that allows recording of dynamic holograms. Almost all known LCLVs operate in the visible range of the spectrum. In the present work we demonstrate a LCLV operating in the infrared. The interaction of signal and pump waves is studied for different applied voltages, grating spacings, and intensities of the recording beams. A fourfold amplification of the weak signal beam is achieved. The amplitude of the refractive index modulation Δn=0.007 and nonlinear coupling constant n2=−1 cm2/W are estimated from the experimental results. External phase modulation of one of the recording beams is used for a further transient increase of the signal beam gain.

Fast and Chaotic Fiber-Based Nonlinear Polarization Scrambler

Abstract: We report a simple and efficient all-optical polarization scrambler based on the nonlinear interaction in an optical fiber between a signal beam and its backward replica which is generated and amplified by a reflective loop. When the amplification factor exceeds a certain threshold, the system exhibits a chaotic regime in which the evolution of the output polarization state of the signal becomes temporally chaotic and scrambled all over the surface of the Poincare sphere. We numerically derive some design rules for the scrambling performances of our device which are well confirmed by the experimental results. The polarization scrambler has been successfully tested on a 10-Gb/s On/Off Keying Telecom signal, reaching scrambling speeds up to 500-krad/s, as well as in a wavelength division multiplexing configuration. A different configuration based on a following cascade of polarization scramblers is also discussed numerically, which leads to an increase of the scrambling performances.

Direct measurement of the Goos-Hänchen shift using a scanning quadrant detector and a polarization maintaining fiber

Abstract: High precision measurements of optical beam shifts are important in various fields including sensing, atomic force microscopy, and measuring beam shifts at interfaces. Sub-micron shifts are generally measured by indirect techniques such as weak measurements. We demonstrate a straightforward and robust measurement scheme for the shift, based on a scanning quadrant photodiode (QPD) that is biased using a low noise electronic circuit. The shift is measured with respect to a reference beam that is co-propagating with the signal beam. Thus, the shift of the signal beam is readout directly as the difference between the x-intercepts of the QPD scan plot of the signal and reference beams versus the position of the detector. To measure the beam shift, we use polarization multiplexing scheme where the p-polarized signal and s-polarized reference beams are modulated at two different frequencies and co-launched into a polarization-maintaining fiber. Both the signal and reference beam positions are readout by two lock-in amplifiers simultaneously. In order to demonstrate the utility of this method, we perform a direct measurement of Goos-Hanchen shift of a beam that is reflected from a plane gold surface. Accuracy of 150 nm is achieved using this technique.

Beam on beam control: beyond the particle approximation

Abstract: The all-optical control of the trajectory of a nonlinear optical beam propagating in a nematic liquid crystal cell is studied using a combination of modulation theory and full numerical solutions of the governing nematic equations. In detail, the output position of a signal beam is controlled via its interaction with a second, co-propagating control beam. The input positions of both the signal and control beams are fixed, with the output position of the signal beam determined by the input angle of the control beam. A simple modulation theory based on treating the optical beams as mechanical particles in a potential well is found to give only adequate agreement with numerical solutions. However, extending this modulation theory to include the detailed profiles of the beams, so that the beams are treated as rigid bodies moving in a potential well, leads to simple, extended equations which determine the input angle of the control beam required for a given output position of the signal beam. The predictions of this extended particle theory, or rigid body theory, are compared with full numerical solutions of the nematic equations and excellent agreement is found.

Optimization of the liquid crystal light valve for signal beam amplification

Abstract: A liquid crystal light valve is an optically controlled spatial light modulator made as a cell with liquid crystal on a photoconductive substrate Dynamic holograms recorded in such a hybrid device may give rise to the amplification of one of the recording beams at the expense of the other In the present work, liquid crystal light valves with different thicknesses of the liquid crystal layer are studied at various conditions of the dynamic grating recording aiming to maximize the signal beam amplification in the infrared A seventeen-fold gain is achieved in the improved cell for optimal recording conditions

Nonlinear negative refraction by difference frequency generation

Abstract: Negative refraction has attracted much interest for its promising capability in imaging applications. Such an effect can be implemented by negative index meta-materials, however, which are usually accompanied by high loss and demanding fabrication processes. Recently, alternative nonlinear approaches like phase conjugation and four wave mixing have shown advantages of low-loss and easy-to-implement, but associated problems like narrow accepting angles can still halt their practical applications. Here, we demonstrate theoretically and experimentally a scheme to realize negative refraction by nonlinear difference frequency generation with wide tunability, where a thin Beta barium borate slice serves as a negative refraction layer bending the input signal beam to the idler beam at a negative angle. Furthermore, we realize optical focusing effect using such nonlinear negative refraction, which may enable many potential applications in imaging science.

Large signal beam-wave interaction analysis of folded waveguide traveling wave tube

Abstract: A cavity cascade model is presented for the large signal beam-interaction analysis of folded waveguide (FWG) traveling wave tube (TWT). We use an equivalent circuit to describe the FWG and the parameters of the circuit are provided. A large signal simulation code was build based on this model and the calculating results show this model is well agree with the experimental data.

High efficiency coherent imager

Abstract: An extended field heterodyne detection apparatus comprises a local signal oscillator, a micro-lens array set in optical relation to the local signal oscillator to multiplex a beam from the local signal oscillator, a local oscillator injection lens in the optical path of the local oscillator and the micro-lens array, a semi-reflective beam splitter at the telecentric stop of the local oscillator injection lens to reflect the beam of the local oscillator in parallel to a signal beam passing through the semi-reflective beam splitter, an objective lens, with a stop, located at the semi-reflective beam splitter, and a focal plane array, situated to receive the source beam. The extended field heterodyne detection apparatus solves the problem of creating a local oscillator beam that is mode-matched for an incoming signal beam, for the eventual process of mixing both the signal beam and the local oscillator using a conventional, square-law detector.

Nano-vibration measurements using the photoelectromotive force effect in the GaAs crystal

Abstract: A broadband, nano-vibration measuring method based on the photoelectromotive force (photo-EMF) effect of semiconductor crystal is presented. A He-Ne-laser homodyne interferometer system is used as a light source and a GaAs crystal is used as a photodetector. The signal beam, which is modulated by the vibration, interferes with the reference beam, and a vibrating interference pattern is created on the surface of the GaAs crystal. Due to the photo-EMF effect, an alternating current signal, which relates to the vibration, is produced. We found the optimum parameters for the measurements by adjustments of the intensity ratio of the two beams, the angle between the beams and the interelectrode spacing on the GaAs crystal. The system can detect the vibration amplitude about several nanometers. The results of measurements of the vibrations of the PZT sample are well coincided with those obtained by TEMPO200 (Bossa Nova Technologies, America) system.

Biodynamic microscopes and methods of use thereof

Abstract: An apparatus for viewing a biological sample that functions as both a microscope and an interferometer. A short-coherence light source directs light onto the sample. A Fourier transform lens and a pixel-array detector are positioned to collect light scattered by the sample. An optic fiber assembly conveys a reference beam from the short-coherence light source. The detector collects the reference beam and the signal beam and uses coherence gating to acquire interferometric image data. In some embodiments the axis of the incident light striking the sample and the axis of collected scattered signal light form an angle of less than 180 degrees and advantageously an angle between 120 and 150 degrees. A method of converting a microscope into an interferometer is also disclosed.

Apparatus and method for manufacturing holographic optical element

Abstract: Provided are an apparatus and a method for manufacturing a holographic optical element which are capable of displaying a two- or three-dimensional image. The apparatus for manufacturing a holographic optical element includes a light radiation unit; a beam splitter for dividing a laser beam from the light radiation unit into a signal beam and a reference beam; a reference beam optical system for irradiating the reference beam to a holographic material; a lens array including a plurality of elemental lenses; and a signal beam optical system for radiating the signal beam to the lens array. An interference fringe of the signal beam, which is modified through the reference beam and the lens array, is recorded on the holographic material.

Misalignment Effects in Laser-Induced Grating Experiments.

Abstract: Laser-induced grating spectroscopy (LIGS) is an experimental method in which two pulsed laser beams and a continuous-wave laser beam have to be superimposed under well-defined angles to generate a coherent signal beam. In this Note, the possible effects of different forms of misalignment are examined. This includes the overlap of the pump lasers as well as the influence of the probe laser alignment on the temporal profile of the signal.

Optical Coherence Tomography Systems Integrated with Surgical Microscopes

Abstract: Some embodiments of the present inventive concept provide optical coherence tomography (OCT) systems for integration with a microscope. The OCT system includes a sample arm coupled to the imaging path of a microscope. The sample arm includes an input beam zoom assembly including at least two movable lenses configured to provide shape control for an OCT signal beam; a scan assembly including at least one scanning mirror and configured for telecentric scanning of the OCT signal beam; and a beam expander configured to set the OCT signal beam diameter incident on the microscope objective. The shape control includes separable controls for numerical aperture and focal position of the imaged OCT beam.

Dual-wavelength Nd:LGGG laser intracavity pumped simultaneous OPO and SRS processes in single KTP.

Abstract: Simultaneous optical parametric oscillation (OPO) and stimulated Raman scattering (SRS) in a single KTiOPO4 (KTP) intracavity pumped by a dual-wavelength Nd:LGGG laser were demonstrated for the first time, to the best of our knowledge. A maximum output power for the signal beam was 448 mW, while for the Stokes radiations it was 40 mW, corresponding to an overall conversion efficiency of about 4.65%. The shortest pulse durations for OPO and SRS waves were directly measured to be 850 ps and 1.526 ns, respectively. The highest peak power of 30.6 kW and the pulse energy of 26 μJ for the signal beam were also obtained. A set of coupled rate equations for the dual-wavelength pumped OPO and SRS was also established. The numerical solutions fit with the experimental results.

Optical image measuring device

Abstract: PROBLEM TO BE SOLVED: To restrain influences of reflected beams from a specific region and thereby obtain clear images of a measurement object.SOLUTION: An optical image measuring device is equipped with a beam source 301 that emits a laser beam, a beam branching unit 304 that branches the laser beam into a signal beam and a reference beam, an objective lens 306 that condenses the signal beam onto a measurement object in a container 308 and irradiates it with the condensed beam, a beam condensation point scanner 307 that scans the condensed position of the signal beam, an objective lens 311 that condenses the reference beam, a reflection mirror 314, a flat plate 313 arranged between the objective lens 311 and the reflection mirror 314, an interference optical system that multiplexes the signal beam reflected or diffused by the measurement object and the reference beam reflected by the reflection mirror and having passed the objective lens 311 and generates three or more interference beams differing from one another in phase relationship, and optical detectors 324 and 325 that detect the interference beams. Here, the objective lens 311 is the same as the objective lens 306, and the flat plate 313 has the same material and the same thickness as the signal beam transmitting part of the container 308.SELECTED DRAWING: Figure 3

Anderson Localization in the Induced Disorder System

Abstract: We propose a coherently prepared three-level atomic medium that can provide a flexible disordered scheme for realizing the Anderson localization. Different disorder levels can be attained by modulating the intensity ratio between the two control beams. Due to the real-time tunability, the localization of the signal beam is observable and controllable. The influences of the induced disorder level, atomic density and the initial waist radius of the signal beam on the Anderson localization in the medium are also discussed.

Optical fibre sensor

Abstract: The invention relates to an optical fibre sensor for detecting an energisation near an optical fibre assembly, said energisation inducing a modulation of the phase of an optical signal propagating through said optical fibre assembly, said sensor including: a laser assembly (SL) emitting at least one laser beam; an optical fibre assembly (OF); an optical system configured to: inject at least one portion of said laser beam, generate at least one portion of said laser beam, generate at least one signal laser beam originating from the laser beam injected and propagated through said fibre assembly, generate at least one reference beam (Fr) from said laser beam or said signal beam, form at least one interference area corresponding to the interference between a portion of the reference beam and a portion of the interference signal beam corresponding to the interference between a portion of the reference beam and a portion of the signal beam; a digital holography assembly including: a liquid-crystal spatial light modulator, a camera configured to receive said interference area and to transcribe same electrically onto said liquid-crystal spatial light modulator in order to create a phase hologram therein corresponding to same; and at least one optical detector configured to detect an output optical signal beam (F out ).

Erbium-ytterbium co-doped fiber amplifier provided with auxiliary cavity for pumping

Abstract: The invention discloses an erbium-ytterbium co-doped fiber amplifier provided with an auxiliary cavity for pumping The erbium-ytterbium co-doped fiber amplifier comprises a signal input end (1), an isolator (2), pumping sources (3), a pumping/signal beam combiner (4), a forward reflection fiber grating (5), an erbium-ytterbium co-doped fiber (6), a backward reflection fiber grating (7) and an output end (8), wherein laser beams output by the pumping sources (3) are sent into the erbium-ytterbium co-doped fiber (6) after sequentially passing through the pumping/signal beam combiner (4) and the forward reflection fiber grating (5), thereby being pumped; a to-be-amplified laser signal is input by the input end (1) and enters the erbium-ytterbium co-doped fiber (6) after sequentially passing through the isolator (2), the signal end of the pumping/signal beam combiner (4) and the forward reflection fiber grating (5); and after the laser signal is amplified, the laser signal is output by the output end (8) According to the erbium-ytterbium co-doped fiber amplifier, Yb-ASE can be effectively restrained and the stability and the pumping conversion efficiency of the erbium-ytterbium co-doped fiber amplifier can be improved

Improved optical efficiency of bulk laser amplifiers with femtosecond written waveguides

Abstract: In the paper we proposed improved technique of three-dimensional waveguides writing with direct femtosecond laser inscription technology. The technique allows, for the first time of our knowledge, production of waveguides with mode field diameter larger than 200 μm. This result broadens field of application of femtosecond writing technology into bulk laser schemes and creates an opportunity to develop novel amplifiers with increased efficiency. We proposed a novel architecture of laser amplifier that combines free-space propagation of signal beam with low divergence and propagation of pump irradiation inside femtosecond written waveguide with large mode field diameter due to total internal reflection effect. Such scheme provides constant tight confinement of pump irradiation over the full length of active laser element (3-10 cm). The novel amplifier architecture was investigated numerically and experimentally in Nd:phosphate glass. Waveguides with 200 μm mode field diameter were written with high frequency femtosecond oscillator. Proposed technique of three-dimensional waveguides writing based on decreasing and compensation of spherical aberration effect due to writing in heat cumulative regime and dynamic pulse energy adjustment at different depths of writing. It was shown, that written waveguides could increase optical efficiency of amplifier up to 4 times compared with corresponding usual free-space schemes. Novelty of the results consists in technique of femtosecond writing of waveguides with large mode field diameter. Actuality of the results consists in originally proposed architecture allows to improve up to 4 times optical efficiency of conventional bulk laser schemes and especially ultrafast pulse laser amplifiers.

Analysis of Optical Properties of Off-Axis Reflective Volume Holographic Grating

Abstract: The coupled wave theory for volume holographic grating with curved interference fringes has been proposed based on the Kogelnik’s coupled wave theory with the plane interference fringes. The formula about the magnitude and directional angle of grating vector in arbitrary position of volume holographic grating with curved grating has been deduced. We found that the wavelength selectivity and angular selectivity may be different in different position of volume holographic curved stripe grating which depend on the angle between the propagation vector of reference beam and signal beam. The larger the angle, the greater the angle and wavelength selectivity, whereas the weaker.

Signal transmitting method and device

Abstract: The invention discloses a signal transmitting method and device. The method includes that a base station receives an uplink pilot signal sent by a legal user equipment and determines a direction vector parameter used for receiving confidential singles and a first channel attenuation parameter of the channel used for transmitting the confidential signals of the legal user equipment; according to the direction vector parameter and the first channel attenuation parameter, a first signal beam former parameter used for emitting the confidential signals is calculated; an artificial noise signal emitting area is determined according to the direction vector parameter and a second signal beam former parameter for emitting the artificial noise signals is calculated; the to-be-emitted signals are processed by utilizing the first signal beam former parameter and the second signal beam former parameter; the signals subjected to processing are emitted. Energy leakage of the confidential signals sent to the legal user equipment by the base station is minimized in a non-target direction and the emitted artificial noise signals are centralized in an area with comparatively high confidential signal leakage risks, and interference on signal receiving of legal user equipment in other directions is reduced.

Application of an adaptive two-wave mixing interferometer for detection of surface defects

Abstract: The technology of non-contact and non-destructive detection of acoustic and ultrasound waveforms play an importance role in industrial application which make it possible to measure acoustic and ultrasonic in hostile environments, such as high temperature circumstance or long distance from test structure. The conventional Optical interferometer cannot detect rough surfaces accurately due to the noise caused by serious scattering. And the environmental noise (low-frequency) arise from machine vibration can also affect the measuring result. Thus, a kind of nonlinear interferometer based on photorefractive effective of photorefractive crystal (BSO) has been proposed to solve these problems. When signal beam (carrying vibration information) and reference beam incident on the photorefractive crystal, A holographic grating is formed due to the photorefractive effect, and the grating diffracts the signal beam and reference beam then the information of the ultrasonic vibration can be demodulated. Meanwhile, the low frequency noise caused by the environmental perturbation can be filtered by the dynamic holographic grating. It is demonstrated that this kind of nonlinear interferometer has the advantages of highly sensitive, low cut-off frequency, simple structure and high resolution. In this paper, we use this nonlinear interferometer to detect the surface defects of the aluminum sheet and get the information of defect location successfully. Samples of aluminum sheet with different size and location of defects are divided into groups to study. Finally we compare with the result concluded from ultrasonic flaw detector. The research findings conclude that this technology provide a potential application for testing surface-breaking cracks and ultrasonic vibration detection in industrial production.

Optical source for coherent transceiver

Abstract: An optical source that implements a wavelength tunable laser diode (t-LD) and a Mach-Zehnder (MZ) modulator within a single package is disclosed. The optical source, which outputs a modulated signal beam and a local beam of a continuous wave (CW), accompanies a control circuit mounted on several circuit boards. Only one of the circuit boards is rigidly mounted on the housing of the optical source. Rest of the circuit boards is moderately fixed to the housing through the rigidly fixed circuit board to suppress stresses caused in the housing and the circuit boards when the optical source is rigidly installed in the host system

Virtual interferogram-generation algorithm for robust complex amplitude measurement using two interferograms.

Abstract: We propose a virtual interferogram-generation algorithm using two interferograms. This algorithm can measure a complex amplitude of a signal beam with high accuracy even when its intensity is greater than the intensity of a reference beam. Unlike the conventional algorithm that uses two interferograms, our algorithm can compute measurements when the phase shift of interferograms in not equal to π/2. Our method generates two phase-shifted holograms in a computer by capturing the intensities of two signal beams, two reference beams, and two interferograms. The complex amplitude of a signal beam is calculated by four interference patterns, two holograms, and two interferograms. The proposed algorithm can drastically suppress the calculation error caused by the smaller value between the intensity of the reference beam and can choose the most suitable phase shift.

Numerical evaluation of shift multiplexing using a spherical wave in a holographic memory based on a computer-generated hologram

Abstract: Shift multiplexing method using a spherical wave is proposed for a holographic memory system based on a computer-generated hologram (CGH). In the proposed method, a propagated signal beam along an optical axis is generated by a CGH. The zero order beam of the CGH is obtained as a point source in the Fourier plane. This point source becomes a spherical reference beam on a recording medium by displacing a Fourier transform lens. The use of the spherical reference beam allows us to implement shift multiplexing in the holographic memory based on a CGH. Shift selectivity of the proposed method is numerically evaluated. In addition, shift multiplexing with the proposed method is numerically demonstrated.

Device, method, and system for imaging laser amplifier

Abstract: An optical image amplifier device capable of amplifying low-intensity backscattered illumination includes an optical port having an input, an output, and a controller having an ON state and an OFF state, the controller connecting the input and the output to form an optical loop in the ON state and disconnecting the input and the output in the OFF state, and an optical relay housing the optical loop and connected to the optical port having a gain medium configured for amplifying a signal beam propagating inside the optical loop in the ON state.

To catch a photon nondestructively

Abstract: Quantum Optics With several techniques now available for generating single photons, coupled with their relative robustness and ability to be transmitted long distances, photons are ideal carriers of quantum information. However, determining the best methodol-ogy for detecting a single propagating photon without absorbing it (and destroying it) remains a work in progress. Xia et al. propose a cavity-free approach based on an induced nonlinear interaction. By co-propagating a weak probe beam with the signal beam containing the single photon in a nonlinear medium, they show theoretically that the phase of the probe beam should be shifted, conditional on the presence of the single photon. The proposed technique could offer a simpler route for implementing such quantum non-demolition detection strategies necessary for successful quantum information processing. Phys. Rev. Lett. 116 , 023601 (2016).