Showing papers on "Signal beam published in 2006"

Collinear technology for a holographic versatile disk

Abstract: A novel reading and writing technology for a holographic versatile disk (HVD) system called collinear technology is developed. With this method a two-dimensional data page can be recorded as volumetric holograms generated by a reference beam and a signal beam that are bundled on the same axis and that are irradiated on the recording medium through a single objective lens. The multiplex recording and reconstruction process is demonstrated, and it is shown that the optical configuration and the dichroic medium disk structure are suitable for a compact system. With the HVD's special structure, the system can use a servo to focus, track, and locate the reading and writing addresses. A unique selectable-capacity recording format of a HVD and its standardization activity are also introduced. This method will enable us to construct a small HVD system with CD and DVD upper compatibilities.

Formation of photovoltaic bright spatial soliton in photorefractive LiNbO3 crystal by a defocused laser beam induced by a background laser beam

Abstract: We have shown, for the first time to our knowledge, both theoretically and experimentally that a bright photovoltaic (PV) spatial soliton (SS) can be formed in a photorefractive crystal with large Glass constant and negative refractive index perturbation, provided that the Glass constant of the background beam is larger than that of the self-trapped (signal) beam. The ratio of the effective Glass constants of the self-trapped beam and the background beam is the key parameter that determines whether the PV SS is bright or dark. We have demonstrated experimentally that bright SSs can be formed in LiNbO3 crystals using all four combinations of polarizations of the signal beam and the background beam.

Broadband radio-frequency spectrum analysis in spectral-hole-burning media

Abstract: We demonstrate a 20 GHz spectrum analyzer with 1 MHz resolution and >40 dB dynamic range using spectral-hole-burning (SHB) crystals, which are cryogenically cooled crystal hosts lightly doped with rare-earth ions. We modulate a rf signal onto an optical carrier using an electro-optic intensity modulator to produce a signal beam modulated with upper and lower rf sidebands. Illuminating SHB crystals with modulated beams excites only those ions resonant with corresponding modulation frequencies, leaving holes in the crystal's absorption profile that mimic the modulation power spectrum and persist for up to 10 ms. We determine the spectral hole locations by probing the crystal with a chirped laser and detecting the transmitted intensity. The transmitted intensity is a blurred-out copy of the power spectrum of the original illumination as mapped into a time-varying signal. Scaling the time series associated with the transmitted intensity by the instantaneous chirp rate yields the modulated beam's rf power spectrum. The homogeneous linewidth of the rare-earth ions, which can be 20 GHz, determines the spectral bandwidth.

All-Optical Switching in Pharaonis Phoborhodopsin Protein Molecules

Abstract: Low-power all-optical switching with pharaonis phoborhodopsin (ppR) protein is demonstrated based on nonlinear excited-state absorption at different wavelengths. A modulating pulsed 532-nm laser beam is shown to switch the transmission of a continuous-wave signal light beam at: 1) 390 nm; 2) 500 nm; 3) 560 nm; and 4) 600 nm, respectively. Simulations based on the rate equation approach considering all seven states in the ppR photocycle are in good agreement with experimental results. It is shown that the switching characteristics at 560 and 600 nm, respectively, can exhibit negative to positive switching. The switching characteristics at 500 nm can be inverted by increasing the signal beam intensity. The profile of switched signal beam is also sensitive to the modulating pulse frequency and signal beam intensity and wavelength. The switching characteristics are also shown to be sensitive to the lifetimes of ppRM and ppRO intermediates. The results show the applicability of ppR as a low-power wavelength tunable all-optical switch

Relative intensity noise transfer of large-bandwidth pump lasers in Raman fiber amplifiers

Abstract: A theoretical analysis of the Raman amplification in optical fibers and the pump-to-signal relative intensity noise (RIN) transfer has been performed in the spectral domain. An efficient Raman amplification of a monochromatic signal beam by a large-bandwidth pump beam has been demonstrated for a pump bandwidth much smaller than the Raman linewidth. Under the same approximation the pump-to-signal RIN transfer has been calculated in both cases of copropagating and counterpropagating beams in the two limiting cases of modulated monochromatic and smooth-profile large-bandwidth pump beams. At low frequencies the excess of noise evidenced in the case of a modulated monochromatic pump beam did not exist in the case of large-bandwidth pseudoincoherent sources. As this noise reduction can be as large as 13 dB for a 40 dB net gain of the amplifier, such incoherent pumping sources must be considered for the purpose of low-noise Raman amplifiers.

Hologram reconstruction method and device

Abstract: There is provided a hologram reconstruction method including: onto an optical recording medium in which a hologram is recorded by simultaneously irradiating the Fourier transformed signal beam representing a digital data with a bright and dark image and removing a DC component and the Fourier transformed reference beam thereon, irradiating a first reference beam for reading out that is the same as the reference beam to generate a first diffracted light generated by the recorded hologram, and synthesizing a DC component of a predetermined phase with the generated first diffracted light to generate a first synthesized light; detecting an inverse Fourier transformed image of the first synthesized light to obtain first image data; irradiating a second reference beam for reading out that differs from the reference beam onto the hologram recorded on the optical recording medium to generate a second diffracted light from the recorded hologram, and synthesizing a DC component of a predetermined phase with the generated second diffracted light to generate a second synthesized light; detecting an inverse Fourier transformed image of the second synthesized light to obtain second image data; subtracting one of the first image data and the second image data from the other at each pixel of the light and dark image; and decoding the digital data based on the value obtained by subtraction.

Two-wavelength switching with a distributed-feedback semiconductor optical amplifier (DFBSOA)

Abstract: Switching of a signal beam by another control beam at different wavelength is demonstrated experimentally using the optical bistability occurring in a 1.55 /spl mu/m-distributed feedback semiconductor optical amplifier (DFBSOA) working in reflection. Counterclockwise (S-shaped) and reverse (clockwise) bistability are observed in the output of the control and the signal beam respectively, as the power of the input control signal is increased. With this technique an optical signal can be set in either of the optical input wavelengths by appropriate choice of the powers of the input signals. The switching properties of the DFBSOA are studied experimentally as the applied bias current is increased from below to above threshold and for different levels of optical power in the signal beam and different wavelength detunings between both input signals. Higher on-off extinction ratios, wider bistable loops and lower input power requirements for switching are obtained when the DFBSOA is operated slightly above its threshold value.

Two-wavelength switching with a distributed-feed back semiconductor optical amplifier (DFBSOA)

Abstract: Switching of a signal beam by another control beam at different wavelength is demonstrated experimentally using the optical bistability occurring in a 1.55 mm-distributed feedback semiconductor optical amplifier (DFBSOA) working in reflection. Counterclockwise (S-shaped) and reverse (clockwise) bistability are observed in the output of the control and the signal beam respectively, as the power of the input control signal is increased. With this technique an optical signal can be set in either of the optical input wavelengths by appropriate choice of the powers of the input signals. The switching properties of the DFBSOA are studied experimentally as the applied bias current is increased from below to above threshold and for different levels of optical power in the signal beam and different wavelength detunings between both input signals. Higher on-off extinction ratios, wider bistable loops and lower input power requirements for switching are obtained when the DFBSOA is operated slightly above its threshold value.

Holographic recording and reconstructing apparatus and holographic recording and reconstructing method

Abstract: A holographic recording and reconstructing apparatus includes a laser light source for emitting a laser beam, a beam splitting element for splitting the emitted laser beam into a signal beam and a reference beam, a light modulating element for modulating the signal beam, an optical system for collecting the modulated signal beam and the reference beam onto a reflection hologram recording medium at substantially the same location, a light detection element for detecting a reconstructed light beam from the hologram recording medium, and wavelength shifting means for shifting the wavelength of the laser beam used during reconstruction from the wavelength used during recording.

Holographic optical information recording/reproducing device and holographic optical information recording/reproducing method

Abstract: A holographic optical information recording/reproducing device is provided with a laser light source (1) and a polarizing beam splitter (8) which splits a light from the laser light source (1). At the time of recording information, one of the optical beams split by the polarizing beam splitter (8) is modulated by a spatial light modulating element (2) to form arranged beam rows and the beam rows become a signal beam (25), the other split optical beam becomes a reference beam (22), and an interference fringe made by the signal beam (25) and the reference beam (22) is recorded in a hologram disc (5) as hologram. At the time of reproducing the information, only the reference beam (22) is applied on the hologram disc (5) and its diffracted light is detected. At this time, the holographic optical information recording/reproducing device permits the power of the reference beam (22) in the hologram disc (5) for information reproduction to be larger than the sum of the power of the reference beam (22) in the hologram disc (5) for information recording and the power of the signal beam (25).

Optical noise reduction by reconstructing positive and negative images from Fourier holograms in coaxial holographic storage systems

Abstract: A technique for reconstructing positive and negative images from an identical intensity-modulated hologram is demonstrated theoretically and experimentally by use of a coaxial holographic storage system. Negative images are obtained by adding a phase-modulated dc component of signal beam on reading. By comparing positive and negative images, the bit error rate (BER) is improved by two orders of magnitude. This technique can reduce optical noise of reconstructed images to attain low BERs.

Coaxial holographic data storage without recording the dc components.

Abstract: A technique of recovering the data pages from Fourier holograms recorded without the dc components is demonstrated theoretically and experimentally by use of a coaxial holographic storage system. A reconstructed image is obtained by adding a phase-modulated dc component of the signal beam on reading. The bit error rate of the reconstructed image is comparable with that for the hologram recorded with the dc component as well. Since high intensities of the dc components are not recorded in this technique, the dynamic range of the recording media can be saved, which potentially contributes to increasing the number of multiplexed holograms.

Pulsed coherent fiber array and method

Abstract: A pulsed coherent fiber array laser system that includes a beam generating sub-system that provides a signal pulse beam having pulses of the desired duration that is split into several fiber channels. Optical leakage between the pulses in each split beam is measured and locked to a reference beam by a phase sensing circuit and phase adjusters so that the phase of each fiber pulsed beam is aligned with the phase of the reference beam. A pulse clipper or filter is employed to remove the pulses in the fiber beams so that they do not saturate the phase sensing circuit. The beam generating sub-system can employ any suitable combination of devices to generate the signal beam and the reference beam, including continuous wave master oscillators, amplitude modulators, frequency shifters, injection seed oscillators, Q-switched lasers, reference oscillators, frequency lockers, wavelength division multiplexers, time gated switches, etc.

Holographic memory medium, holographic memory device and holographic recording device

Abstract: Even when a tilt error is caused in a holographic memory in a direction perpendicular to a surface including optical axes of a signal beam and a reference beam, the signal beam and the reference beam are allowed to enter the holographic memory at adequate angles relative thereto at all times by suppression of the tilt error. During recording and reproducing operations, the reference incident angle of the reference beam in the radial tilt direction is detected based on a received light state. A tilt actuator for displacing the holographic memory medium in the radial tilt direction is driven to adjust an incident angle of the reference beam in the radial tilt direction to the reference angle Sr. Then, the signal beam and the reference beam are emitted to the holographic memory medium to execute the recording and reproducing operations.

System and method for holographic storage

Abstract: A system and a method for holographic storage mainly involve forming a holographic interference pattern in a holographic recording medium. The holographic storage system utilizes a light source to emit a coherent beam. The coherent beam is irradiated to a first reflector to form a divergent beam. The divergent beam is then irradiated to a second reflector to form collimating beams (a signal beam and a reference beam). The signal beam goes through a spatial light modulator (SLM) and is modulated by the SLM. After that, the reference beam and the modulated signal beam are irradiated to a convergent unit, and are directed to the holographic recording medium for forming the holographic interference pattern. The holographic storage system that the light source is split into a signal beam and a reference beam by a set of reflectors according to the reflection principle without involving refraction may employ wavelength multiplexing.

Qubit degradation due to cross-phase-modulation photon-number measurement

Abstract: Kerr effect cross-phase-modulation between signal and probe beams has been proposed and demonstrated as a means for quantum nondemolition (QND) measurement of the signal beam's photon number by homodyne detection of the probe beam. Recently, such QND measurements have been suggested as providing a new route to photonic quantum computation. For a signal-beam qubit, whose computational basis is the vacuum and one-photon states, the QND detector's error probability is shown to be determined by the qubit fidelity after the cross-phase-modulation interaction, with the former increasing from 0 to $\frac{1}{2}$ as the latter increases from $\frac{2}{3}$ to 1. This relationship is shown to hold regardless of the probe beam's input state. It also applies, without modification, when the cross-phase-modulation interaction is replaced with a more general unitary transformation.

Optical pickup apparatus and hologram recording and reproducing system

Abstract: An optical pickup apparatus includes a light source for generating a coherent beam, a spatial light modulator having a central region arranged on an optical axis of the coherent beam and an annular region arranged in a manner surrounding the central region, to spatially separate a transmission component of the coherent beam through the central region and a transmission component through the annular region thereby producing a reference beam and a signal beam and propagating those coaxially in a same direction, an objective lens optical system arranged on the optical axis and for illuminating the signal beam and the reference beam coaxially toward the hologram record layer and causing the reference beam and the signal beam to focus on focal points different from each other, image detecting means arranged on the optical axis and for receiving a beam returning from the hologram record layer through the objective lens optical system when the reference beam is illuminated to the hologram record layer; and a polarization-plane rotating device having a central polarizing region arranged on the optical axis and an annular polarizing region arranged in a manner surrounding the central polarizing region and for making transmission components through the central and annular polarizing regions different in rotation angle on the polarization plane from each other.

Mid-infrared all solid state DIAL for remote sensing of hazardous chemical agents

Abstract: We describe all solid state differential absorption lidar (DIAL) based on the mid-infrared (IR) tunable Optical Parametric Oscillator (OPO). Generation of tunable mid-infrared laser radiation using a two stage tandem OPO was demonstrated. The first stage was based on the nonlinear KTP crystal and produced up to 45 mJ of 1.57 m radiation, while pumped by a commercial Q-switched Nd:YAG laser. The quality of signal beam was improved by the use of unstable resonator. The AgGaSe2 crystal was used in the second stage OPO. Idler energies up to 1 mJ were generated at this stage within tuning range from 6 to 12 m. The receiver consisted of a 250 mm gold mirror telescope, two channel detection system and control electronics. We have designed a photoacoustic cell for wavelength calibration of lidar. Preliminary lidar field test results are presented.

Optical information processing apparatus and optical information recording and reproducing methods

Abstract: An optical information processing apparatus includes: a light source; a reference beam guiding optical system guiding a reproducing reference beam emitted from the light source to an optical information storage medium in which optical information is recorded at multiplexing angles; a signal beam guiding optical system guiding a reproduced signal beam, which is reproduced from the optical information storage medium in the coaxial line with the reproducing reference beam and in the opposite direction of the traveling direction of the reproducing reference beam and is a phase-conjugation wave of a recording signal beam used at the time of recording the optical information; and an optical information detector detecting the reproduced signal beam guided by the signal beam guiding optical system. Accordingly, it is possible to reduce the manufacturing cost, to enhance the multiplexing density of optical information, and to simplify and miniaturize the entire optical information processing apparatus.

Hologram reconstructing apparatus and hologram reconstructing method

Abstract: A hologram reconstructing apparatus configured to irradiate a hologram recording medium that stores an interference pattern of a signal beam spatially modulated by data displayed on a spatial modulator and a reference beam emitted simultaneously with the signal beam with a reconstructing reference beam and to reconstruct data by capturing a reconstruction signal beam generated at the hologram recording medium being irradiated includes an image pickup unit that receives a partial reconstruction signal beam that constitutes part of the reconstruction signal beam by a full light-receiving plane; and a moving unit that relatively move the light-receiving surface of the image pickup means within an irradiation range of the reconstruction signal beam. All information included in the reconstruction signal beam is reconstructed by receiving the reconstruction signal beam corresponding to the entire irradiation range by relatively moving the image pickup means within the irradiation range of the reconstruction signal beam.

Optical recording method, optical reproducing method, and optical reproducing apparatus

Abstract: An optical recording method includes providing an optical recording medium capable of forming both a refractive index grating and an absorption grating by light irradiation; Fourier transforming with the same lens a signal beam that represents binary digital data with a brightness image and a reference beam such that they are focused at a point outside the optical recording medium; irradiating the Fourier transformed signal beam and reference beam simultaneously onto the optical recording medium and forming a diffraction grating at the optical recording medium according to an interference fringe between the signal beam and the reference beam, or according to an interference fringe within the signal beam itself, and recording the signal beam as a hologram.

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

Abstract: PROBLEM TO BE SOLVED: To provide a modulation scheme capable of realizing the advantages of a QPSK scheme and minimizing performance deterioration, even if an optical signal beam passes through an optical filter having a narrow bandwidth, and to provide an optical transmitter that uses the same. SOLUTION: The optical transmitter, using the offset quadrature phase-shift-keying modulation scheme, includes a first phase modulator for outputting a first optical signal beam generated by phase-modulating an input optical beam based on a first data, a second phase modulator for outputting a second optical signal beam generated by phase-modulating the input optical beam based on a second data, a phase delay unit for granting a predetermined phase difference between the first optical signal beam and the second optical signal beam, and an optical coupler for coupling the first optical signal beam and the second optical signal beam, between which a phase difference exists. COPYRIGHT: (C)2006,JPO&NCIPI

Method and device for recording/reproducing hologram

Abstract: A hologram recording method by which a hologram recording device records information by forming diffraction grating by irradiating a hologram record carrier with a signal beam and a reference beam from opposing sides. The hologram recording method includes a step of collecting the reference beams from a first effective aperture at a first numerical aperture by a reference beam objective lens of a reference beam optical system; a step of splitting the reference beam on an optical axis and a part of the beam in the vicinity of the reference beam, generating a recording reference beam, which passes through the hologram recording carrier from a second effective aperture smaller than the first effective aperture at a second numerical aperture less than the first numerical aperture by a reference beam objective lens of the reference beam optical system and projecting the recording reference beam coaxially with the reference beam; and a step of preventing only the recording reference beam from being projected to the hologram recording carrier by a signal beam optical system.

Optical information processing apparatus and optical information recording and reproducing methods using the same

Abstract: There is provided an optical information recording apparatus comprising: a light source; a light modulator in which a reference beam pattern for converting a beam emitted from the light source into a reference beam and a signal beam pattern for converting the beam into a signal beam are formed and varies the reference beam pattern at the time of multiplexing and recording optical information; and a lens allowing optical information to be recorded in an optical information storage medium by means of interference between the reference beam and the signal beam when the signal beam and the reference beam emitted from the light modulator are irradiated to the optical information storage medium. Accordingly, in an optical information processing apparatus using a coaxial optical system, it is possible to more efficiently multiplex optical information and to enhance a storage density of holographic optical information.

Method for Recording and Reproducing a Hologram and Apparatus Therefor

Abstract: A hologram recording method is a method of recording a hologram, on a hologram recording apparatus that records information by forming a diffraction grating through oppositely irradiating the signal beam and the reference beam to the hologram record carrier. The hologram recording method includes a step of focusing the reference beam at a first numerical aperture from a first effective diameter by means of the reference-beam objective lens, a step of separating the reference beam in a part on the optical axis and a neighborhood thereof to thereby produce from the reference beam a recording reference beam to passes through the hologram record carrier at a second numerical aperture smaller than the first numerical aperture from a second effective diameter smaller than the first effective diameter by means of the reference-beam objective lens of the reference-beam optical system, and allowing the recording reference beam to exit coaxially to the reference beam, and a step of not allowing only the recording reference beam to exit toward the hologram record carrier by means of the signal-beam optical system.

Optical receiver corresponding to differential M-phase shift keying system

Abstract: A small size and low cost optical receiving apparatus, which can stably demodulate the signal, lights in accordance with the differential M-phase shift keying (DMPSK) system. An optical receiving apparatus comprises a light branching unit for branching the differential M-phase shift keying signal beam into four signal light beams, a delay adjusting unit giving a delay time difference of one symbol between a first signal light beam and a second signal light beam and between a third signal light beam and a fourth signal light beam, a demodulating unit for outputting a least two demodulated light signals through respective interferences between the first signal light beam and the second signal light beam, and between the third signal light beam and the fourth signal light beam on one plane which is not parallel to any signal light beam, and at least two optical detectors for converting at least two light signals into electrical signals.

Frequency conversion of an entangled state

Abstract: The quantum characteristics of sum-frequency process in an optical cavity with an input signal optical beam, which is a half of entangled optical beams, are analyzed. The calculated results show that the quantum properties of the signal beam can be maintained after its frequency is conversed during the intracavity nonlinear optical interaction. The frequency-conversed output signal beam is still in an entangled state with the retained other half of the initial entangled beams. The resultant quantum correlation spectra and the parametric dependences of the correlations on the initial squeezing factor, the optical losses and the pump power of the sum-frequency cavity are calculated. The proposed system for the frequency conversion of the entangled state can be used in quantum communication network and the calculated results can provide direct references for the design of experimental systems.

Hologram recording and reproducing system

Abstract: A hologram recording and reproducing system for recording or reproducing information to or from a hologram record carrier that stores an optical interference pattern of a reference beam and a signal beam therein as a diffraction grating, includes: light producing means that generates a reference beam and a signal beam based on a coherent beam in which the coherent beam is modulated into the signal beam according to information to be recorded; interference means that allows one of the reference and signal beams to propagate axially on an optical axis as a central region light flux and allows the other of the reference and signal beams to propagate coaxially and annularly in section as an annular region light flux surrounding the one spatially separated from the other in a same direction and converges both the reference beam and the signal beam on different focal points in the optical axis respectively through an objective lens optical system to cause interference between the reference beam and the signal beam; a hologram record carrier having a hologram record layer located on a side of a near one of the different focal points to the objective lens optical system and a reflection layer located on a side of a distant one of the different focal points from the objective lens optical system; and image detecting means arranged on the optical axis and for receiving a beam returning from the hologram record layer through the objective lens optical system when the reference beam is illuminated to the hologram record layer; wherein the hologram record carrier further comprising a servo guide layer which is placed at a position either nearer to the objective lens optical system than the hologram record layer or farther than the reflection layer from the objective lens optical system. The hologram recording and reproducing system further includes a servo control system for focusing a servo beam onto the servo guide layer and for receiving a reflection light returning from the servo guide layer to photoelectrically convert it to a signal and for driving the objective lens optical system in accordance with the signal photoelectrically converted, wherein the servo beam has a wavelength different from the coherent beam wavelength and passes through the central region coaxially with the central region light flux including the optical axis.

Optical switch based on parametric interaction

Abstract: A method and apparatus for switching at least one wavelength component of an optical signal beam from a first state to a second state. The phase characterizing the optical signal component is incremented by interaction with one or more escort beams in a non-linear medium thereby switching the state of the optical signal component on the basis of its incremented phase. Multiple escort beams may also be employed to switch different wavelength components of the signal. The method may be employed to achieve high speed, and substantially transparent, switching of phase, intensity or polarization of a signal.

Direct Nonlinear Optics Measurements Of Raman Gain In Bulk Glasses And Estimates Of Fiber Performance

Abstract: The need for more bandwidth in communications has stimulated the search for new fiberizable materials with properties superior to fused silica which is the current state-of-the-art. One of the key properties is Raman gain by which a pump beam amplifies a signal beam of longer wavelength. An apparatus capable of directly measuring the spectral dependence and absolute magnitude of the material Raman gain coefficient using nonlinear optics techniques has been built. Using radiation from a 1064 nm Nd:YAG laser as the pump and from a tunable Optical Parametric Generator and Amplifier as the signal, the Raman gain spectrum was measured for different families of glass samples with millimeter thickness. A number of glass families were investigated. Tellurites with added oxides of tungsten, niobium, and thallium produced the largest Raman gain coefficients of any oxide family reported to date, typically 30-50 times higher than that of fused silica. On the other hand, phosphate families were found with spectrally broad Raman gain response, 5 times broader than fused silica and flat to [plus or minus] dB over the full spectral range in some compositions. Although the chalcogenides were found to photodamage easily, coefficients 50 - 80 times that of fused silica were measured. Finally, a numerical study was undertaken to predict the theoretical performance and noise properties of tellurite fibers for communications. Included in the computer modeling were linear loss; the interaction among multiple pumps and signals; forward and/or backward propagating pump beams; forward, backward and double Rayleigh scattering; noise properties of amplifiers; excess noise, etc. This led to a comparison of the optical signal-to-noise characteristics for Raman gain in a tellurite versus a silica fiber.