Showing papers on "Signal beam published in 1999"

Nonlinear vibrational microscopy

Abstract: The present invention is a method and apparatus for microscopic vibrational imaging using coherent Anti-Stokes Raman Scattering or Sum Frequency Generation. The spatial resolution is attained by minimizing the spot size of the optical interrogation beams on the sample. Minimizing the spot size relies upon a) directing at least two substantially co-axial laser beams (interrogation beams) through a microscope objective providing a focal spot on the sample; b) collecting a signal beam together with a residual beam from the at least two co-axial laser beams after passing through the sample; c) removing the residual beam; and d) detecting the signal beam thereby creating said pixel. The method has significantly higher spatial resolution than IR microscopy and higher sensitivity than spontaneous Raman microscopy with much lower average excitation powers.

Swept continuous wave cavity ring-down spectroscopy

Abstract: An ring-down spectroscopy instrument comprising a ring-down cavity (RDC) and CW light source (CWLS). The CWLS produces light having components with different polarizations. The ring-down cavity is optically isolated from the light source so that light reflected from the cavity is precluded from perturbing the light source. A frequency shifter shifts a mean frequency of the first component of input light with respect to a mean frequency of the second component of input light by a frequency shift Δν. A first detector measures a signal beam with the a polarization. A second detector measures a tracking beam having a second polarization. The frequency shift Δν is equal to a difference between a resonant frequency of a first cavity mode with the first polarization and a resonant frequency of a second cavity mode having the second polarization. A threshold detector delivers a trigger pulse to the frequency shifter when an intensity of the signal beam reaches a predetermined value. The trigger pulse causes the frequency shifter to temporarily change the frequency shift Δν, thereby temporarily decoupling the first component of input light from the ring-down cavity. An embodiment of the invention includes a ring down spectroscopy method. Radiation coupled into a ring-down cavity is swept in frequency by to excite one or more resonant modes of the cavity. When a fundamental mode of the cavity reaches a predetermined threshold value a digitizer produces a ring-down decay curve. An absorption spectrum is determined by extrapolating a decay constant from a logarithm of the decay curve.

Single-Point Thermometry in High-Pressure, Sooting, Premixed Combustion Environments

Abstract: We have performed nonintrusive thermometry in the burnt gases of rich, pressurized ethylene/air flames using a frequency measurement based on laser-induced gratings. Light from a continuous-wav e probe beam is coherently scattered from a thermal or electrostrictive grating induced by a pair of crossed, pulsed pump beams. The measured Doppler shift of the signal beam is a function of the local speed of sound from which a temperature can be extracted. At equivalence ratios of 1.6, the transient grating temperature agreed with a corrected thermocouple temperature. At higher soot loading, it is necessary to account for the change in local gas composition caused by soot particle vaporization. Soot particles, acting as blackbody absorbers, were observed to generate thermal gratings of diagnostic value.

Volume holographic memory apparatus having a reference beam and a signal beam with opposite intensity distributions

Abstract: A volume holographic memory-based optical information-recording/reproducing apparatus is capable of enhancing density of spatial multiple recording. A recording medium is mounted in the apparatus for recording a three-dimensional optical interference pattern formed by at least two coherent light beams as spatial changes in refractive index of the recording medium. A signal beam optical system supplies a coherent signal beam to the recording medium through a Fourier transform lens. A reference beam optical system supplies a coherent reference beam to the recording medium. The reference beam is caused to intersect with the signal beam within the recording medium and an angle of intersection between the reference beam and the signal beam is changed. Diffracted light of the reference beam diffracted from the recording medium is detected. Spatial beam modulating means is arranged in the optical path of the reference beam optical system for limiting light intensity of the reference beam in a manner such that a cross section of the reference beam in the recording medium has a light intensity distribution opposite to a light intensity distribution of the signal beam in the recording medium.

Optical relay for pixel-based holographic storage and retrieval

Abstract: A holographic storage and retrieval system for use in co-propagating or counter-propagating geometries having a common optical relay for guiding a signal beam and a reference beam along a common optical axis to a holographic medium to write a hologram therein. The optical relay has an object region imaging quality such that at least 65% and preferably at least 80% of the nominal luminous energy from object pixels is encompassed or "ensquared" by the corresponding image pixels. Additionally, the optical relay has a high total numerical aperture (N.A.) of about 0.83, a pixel N.A. of approximately 0.04 for the signal beam. The system of the invention can be used with holographic storage media in the form of disks, tapes or bulk holographic crystals.

Volume holographic memory-based optical information-recording/reproducing apparatus

Abstract: A volume holographic memory-based optical information-recording/reproducing apparatus being capable of controlling an interference area formed by a reference beam and a signal beam within a recording medium more easily than by waveform shaping using a lens. A recording medium is installed in the apparatus for recording a three-dimensional optical interference pattern formed by at least two coherent light beams as spatial changes in refractive index of the recording medium. A signal beam optical system transmits a coherent signal beam to the recording medium through a Fourier transform lens. A reference beam optical system transmits a coherent reference beam to the recording medium. The reference beam intersects the signal beam within the recording medium, and an angle of intersection between the reference beam and the signal beam is changed. Diffracted light of the reference beam diffracted from the recording medium is detected. Light intensity distribution-offset element is arranged in both of optical paths of the signal and reference beam optical systems, for controlling a distribution of a light intensity of the signal beam and a light intensity of the reference beam, respectively, within an area in the recording medium in which the signal beam and the reference beam intersect with each other.

Method and device for measuring the thickness of thin films near a sample's edge and in a damascene-type structure

Abstract: A method for measuring a structure that contains overlying and underlying films in a region where the overlying film's thickness rapidly decreases until the underlying film is exposed (e.g., an edge-exclusion structure). The method includes the steps of: (1) exciting acoustic modes in a first portion of the region with at least one excitation laser beam; (2) detecting the acoustic modes with a probe laser beam that is either reflected or diffracted to generate a signal beam; (3) analyzing the signal beam to determine a property of the structure (e.g., the thickness of the overlying layer) in the first portion of the region; (4) translating the structure or the excitation and probe laser beams; and (5) repeating the exciting, detecting, and analyzing steps to determine a property of the structure in a second portion of the region.

Methods and system for optically correlating ultrashort optical waveforms

Abstract: The invention features methods and systems for optical correlation of ultrashort optical waveforms, e.g., pulses. The optical waveform passes through a diffractive optic, e.g., a mask or grating, to generate multiple sub-beams corresponding to different diffractive orders. At least two of the sub-beams are then imaged onto the sample to produce a desired crossing pattern. To perform the correlation, the diffracted sub-beams are variably delayed relative to one another prior to overlapping on the sample. The sample generates a signal beam in response to the overlapping sub-beams, the signal beam providing a correlation between the sub-beams for each of the variable delays.

Radio base station

Abstract: PROBLEM TO BE SOLVED: To decide the phase and amplitude weights to be given to an outgoing signal in an easy and optimum way in regard to a radio base station in a cellular mobile communication system where the different phase and amplitude weights are given to the transmitting signals which are inputted to plural antenna elements and an outgoing signal beam having high directional gain is transmitted to a user mobile station being an object of communication. SOLUTION: An incoming signal arrival angle extraction means 6 is prepared to extract the arrival angle information from the phase information on the signals received by every antenna element that receives the incoming signal from a mobile station together with a weight coefficient calculation means 5 which calculates the phase and amplitude weight coefficients to be multiplied by the outgoing signal that is inputted to every antenna element to form a beam pattern where a main beam is turned toward the mobile station being an object of communication and the low side lobe levels set in the directions of other mobile stations respectively based on the arrival angle information on the up signal and a weight coefficient multiplying part 4-1 which multiplies an outgoing signal by the weight coefficients calculated by the means 5. COPYRIGHT: (C)2000,JPO

Homodyne detection of ultrasonic surface displacements using two-wave mixing in photorefractive polymers

Abstract: Summary form only given. Laser-based ultrasound is a promising technique for remote ultrasonic inspection. One approach for the measurement of small ultrasonic surface displacements uses dynamic holography in a photorefractive material to combine a distorted signal beam with a plane-wave reference beam and match their wavefronts for homodyne detection. Slow variations in the wavefront of the signal beam are compensated by the real-time hologram and thus do not produce noise or interfere with the quality of the wavefront overlap in the output beams.

Light-amplification competition between fanning noise and the signal beam in doped lithium niobate crystals

Abstract: Based on a multi-three-wave interaction model, we theoretically analyze the intense amplification competition between fanning noise and the signal beam in doped lithium niobate crystals. Our results show that the signal beam can be most effectively amplified for a specific value of the photovoltaic field because of the amplification competition between fanning noise and the signal beam. When the threshold effect of incident-light intensity for photorefractive light-induced scattering is taken into account in LiNbO3:Fe, M(M=Mg2+, Zn2+, In3+, Sc3+) crystals, the signal beam can be most effectively amplified for a specific pump intensity.

Method and apparatus for switching optical signals within an optoelectric computer network

Abstract: A method and apparatus for switching optical signals within an optoelectric computer network is disclosed. The optoelectric computer network includes multiple computers. Each of the computers includes a first fiber optic cable for sending optical signal beams and a second fiber optic cable for receiving optical signal beams. In accordance with a preferred embodiment of the present invention, an apparatus for broadcasting optical signals within the optoelectric computer network includes a prism and a mirror array. The prism is capable of splitting an optical signal beam from a first fiber optic cable of one of the computers into multiple optical signal beams. Each of the optical signal beams is of an unique frequency within a light spectrum. The mirror array, which is formed by an array of deformable mirrors, then individually directs each of the optical signal beams to a respective second fiber optic cable of the rest of the computers.

Sensitive laser spectroscopic detection based on three-dimensional nonlinear four-wave mixing

Abstract: Devices and techniques for performing highly-sensitive spectroscopic measurements in a sample vapor by using a four-wave-mixing optical system and an atomizer chamber. One embodiment of a spectrometer comprises a gas-phase atomizer having an atomizer chamber operable to vaporize a sample solution to produce a sample vapor, first and second alignment templates having apertures to align a probe beam, first and second pump beams to form a four-wave mixing configuration, a laser tunable to generate a laser beam at a desired wavelength corresponding to an absorption line in the sample vapor, and a set of optical elements disposed relative to the laser and the atomizer to split the laser beam into the probe beam, the first pump beam, and the second pump beam. The probe beam, the first and second pump beams are directed to overlap with one another in the sample vapor to produce a signal beam through a four-wave mixing process.

Propagation of transient quantum coherence

Abstract: We perform a time-resolved quantum interference experiment based on the effect of induced coherence without induced emission using two pulsed parametric down-conversion sources. We periodically vary the transmission of the first source's idler beam and measure the time-dependent visibility of fringes in the interference between the two signal beams. The visibility is found to be correlated with the transmissivity with a time delay corresponding to a combined path of the first idler and the second signal beam. The experiment is discussed in the context of the delayed choice experiments.

Wavelength detecting device

Abstract: A wavelength detecting device is used for a wavelength multiplexing optical communication system, is simple and inexpensive, and can strictly control the wavelengths of signal beams that are close to one another. The device has a path splitter and a wavelength selector. The path splitter splits a beam into at least three beams having different path angles. The wavelength selector filters the split beams into beams having predetermined wavelengths. One of the filtered beams is provided as a signal beam and the other beams are provided as monitor beams used to detect the wavelength of the signal beam.

Apparatus and method for measuring a property of a structure

Abstract: A method and apparatus for measuring a property of a structure that includes at least one layer (10) is described. The apparatus comprises a laser (52) that generates an optical pulse (12), a beam splitter (62) for splitting the optical pulse in at least two excitation pulses (12', 12''), an optical system (70) for spatially and temporally overlapping the excitation pulses on or in the structure to form an excitation pattern (15) that launches an acoustic wave which modulates a property of the structure, for example generates a time dependent surface ripple (17a, 17b), and a light source (54) for producing a probe beam (20) to generate a signal beam (20'). By using a diffractive element as the beam splitter, imaging this element on the structure and using the probe beam reflected by the structure as the signal beam an accurate and reliable measurement can be performed.

Active phase-shift control in optical-hybrid etalons

Abstract: Active phase-shift control is achieved in a hybrid etalon by selecting appropriate elements in the photodiode array 22, 22' of FIG. 2 for a prescribed phase-shift. A negative lens 20, (20") is used to expand the beam spot of the output beams P 2 16, (P 1 18) to the line length of the photodiode array 22, (22'). The signal beam 14 and the LO (local oscillator) beam 12 are angularly misaligned by the incident beam angle δ 26 to the 2-face 8 and δ' 26' to the 1-face 10 (δ'≠δ), thus resulting in the misaligned signal and LO beamlets inside the etalon 6. The beamlets from the 2-face 8 comprise the P 2 beam 16 and the beamlets from the 1-face 10 comprise the P 1 beam 18. The photodiode array 22, 22' detects an interference fringe pattern in the output beams P 1 18 and P 2 16 due to the misaligned input beams. The beamlets from the 2-face 8 and the 1-face 10 have been expanded for illustrative purposes in FIG. 2 lie within the initial beam diameters of the signal 14 and LO 12 beams. Both input beams 12, 14 are linearly polarized, and the signal beam 14 has a variable polarization angle. For a conventional etalon 6 the polarization angle of the LO beam 12 bisects the crystal axes of the input quarter-waveplate 24. The input quarter-waveplate 24 in the signal channel allows the polarization angle of the signal beam to combine into the overall phase angle of the output beams of the hybrid and thereby makes possible to have simultaneous phase- and polarization-diversity properties in the hybrid.

Undersea object detection and recognition: the use of spatially and temporally varying coherent illumination

Abstract: Increased optical range of target detection and recognition is always a problem in the marine environment. Methods for the formation of images in scattering media generally rely upon temporal or spatial methodologies. Time gating is a temporal example of image formation whereby a light source is time pulse projected toward a target and the detector is time gated to accept image-forming illumination from a specific range. To be successful at eliminating much of the backscatter, this method requires exacting range information and loses the simplicity of a continuous light source. Holography is one example of an image formation method requiring specific spatial relationships, i.e. mutual coherence between a reference beam and a signal beam. The coherence allows the formation of an interference pattern that carries the signal information on a "spatial carrier". In order for the method to be of use, the medium in which the beams are carried must preserve the coherence or phase spatially across the beams and in relation to the reference beam. In water, the distance over which the phase may be preserved is dependent upon many factors. Generally, the demands of maintaining a spatially coherent beam at optical frequencies is difficult over a long range thereby limiting the usefulness of the technique for image formation in turbid media. A paper submitted by the authors at the OCEANS '98 describes a variation of the spatial interferometric technique that relies upon projected spatial gratings with subsequent detection against a quasi-coherent return signal. The method is advantageous in not requiring temporal coherence between reference and signal beams and may use a continuous illumination source. Coherency of the spatial beam allows detection of the direct return, while scattered light appears as a noncoherent noise term. The theoretical foundation of the method and the initial results for turbid media were developed. This paper presents the latest ongoing research results.

Concept of Photorefractive Connection Module by Photorefractive Four-Wave Mixing with Extraordinary Writing Beams and an Ordinary Reading Beam

Abstract: We propose a new optical network device photorefractive connection module (PRCM) which operates as optical switch, amplifier and signal distributor controlled by parallel optical signals. Simple optical control bus systems can be realized by cascade connection of PRCMs. PRCM branches off a desired channel from the spatial multiplexed optical bus line by appropriate setting of the control beam pattern. PRCM uses cross polarized four wave mixing (CPFWM) with extraordinary polarized writing beams and an ordinary polarized reading beam to achieve a high connection gain to the next PRCM stage. We analyze the phase matching angle of CPFWM in which the optical paths of two pump beams are slightly different. The phase conjugate reflectivity indicating a branching ratio of optical signal is derived and calculated in consideration of the phase mismatching Δk. The optimum pump ratio and the grating vector orientation for the largest phase conjugate reflectivity and signal amplification factor are discussed for optical design of PRCM. Since the measured signal beam power after passing through the BaTiO3 crystal is three or four times higher than its incident power, PRCM has a sufficient connection gain for optical bus and interconnection systems.

Variable sensitivity acoustic transducer

Abstract: The gauge length of an acoustic signal detector is dynamically variable by adjusting the location of an induced light reflection interface within a section of optical waveguide to which an acoustic stimulus is coupled. In an interferometer based architecture, a light beam is applied to each of an ‘acoustic signal detection’ optical waveguide and a ‘reference’ optical waveguide. The ‘acoustic signal detection’ waveguide is coupled to an acoustic energy transmission element. The acoustic input modifies the index of refraction of the optical waveguide and modulates the light passing through the waveguide. Since the index of refraction of the optical waveguide section is modified by the acoustic stimulus, the signal beam has a phase delay dependent upon the acoustic signal and the distance between one end of the signal waveguide section and an induced reflection interface. The ‘reference’ optical waveguide section also contains a reflection interface, the induced location of which is ganged with that of the signal optical waveguide section. The ‘signal’ path and ‘reference’ path beams reflected by their reflection interfaces are combined and applied to a photo-detector. The index of refraction of the material of the signal optical waveguide section is modified by the acoustic stimulus is the ‘signal path’. This ‘signal’ path light beam is combined out of phase with ‘reference’ light beam at the photo-detector.

Forward-Scattering Degenerate Four-Wave Mixing Detection in Micro-Column Liquid Chromatography Using Fused-Silica Capillary Flow Cells

Abstract: In order to have as simple a chromatographic setup as possible, laser-based forward scattering degenerate four-wave mixing (FD4WM) detection is applied directly to fused-silica capillary flow cells that can be used in micro-column liquid chromatography (mu LC). Compared to the previously used specially designed flow cells (optimized from an optical point of view), such cylindrically shaped cells have obvious disadvantages such as background scatter and signal beam distortion. However, a laser beam can be focused easily in a fused-silica capillary, yielding a laser-probed volume of less than 100 pL, which is attractive for miniaturized chromatographic systems. Parameters such as capillary dimensions (internal and outer diameters), capillary configuration in relation to eluent flow direction, flow rate, and various background suppression techniques are considered from a theoretical and a practical point of view and subsequently optimized. Interestingly, the direction of the eluent flow is critical; it should be in the plane formed by the two laser beams. mu LC/F-D4WM is used to analyze spiked river Rhine water.

Optical amplification by two-wave mixing in lithium niobate waveguides

Abstract: Photorefractive Fe:LiNbO3 planar waveguides have been fabricated by proton exchange method using Fe:LiNbO3 assubstrate and benzoic acid as exchange medium. The waveguide has a much larger refractive index increment than a Tidiffused one. Through end-face coupling, a pump beam and a signal beam were injected into the waveguide and the opticalamplification properties of the waveguide have been investigated experimentally. The results showed that a hundred foldamplification gain could be obtained in a wide range of grating periods and an amplification gain of 180 was achieved easily.This scheme has potential applications in optical signal processing at not very high incident intensity.Keywords: Two-wave mixing, optical amplification, lithium niobate, proton exchange, waveguide 1. Introduction Multi-wave coupling in nonlinear media has been extensively investigated for applications in wave-front amplification, laserbeam manipulation, parallel optical processing, phase-conjugation, and real-time holography. 1-3 A lot of photorefractivecrystals (such as LiNbO3, KNbO3, and SBN), have been studied for these purposes and have exhibited attractive capabilities.Meanwhile, much attention has also been paid to the photorefractive effect in waveguides of electro-optic and nonlinearoptical crystals for their potential applications in optical integrated circuits and interconnections. In comparison with bulkcrystals, waveguides permit a large interaction length, require low power sources, and enable easy integration. Hesselink, Ito,and Kamishilin et a! have demonstrated holographic storage in the fibers of SBN, Fe:LiNbO3 and Bi12TiO20, and obtainedhigh quality reconstructed images.4 Yu has studied the application of LiNbO3 fiber holograms to interconnection, switches,and massive memories.7'8 Optical amplification by two-wave mixing in planar waveguides also has been studied. Fischerachieved optical amplification in photorefractive BaTiO3 waveguide by lateral pumping of guide wave.9 Ito et a! performedoptical amplification in a periodically polarization-reversed BaTiO3 waveguide.'°" It also has been shown by James et althat the response of two-wave mixing in ion-implanted BaTiO3 waveguide is two or three orders faster than that in bulkcrystal!2 In comparison with other crystals, iron doped LiNbO3 (Fe:LiNbO3) has higher photorefractive sensitivity and can

Measurements of quantum noise in optical phase conjugation via four-wave mixing in an atomic vapor

Abstract: We present the results of a comprehensive investigation of the quantum-noise properties of a continuous-wave phase-conjugate mirror (PCM) formed using backward-four-wave mixing in potassium vapor. We characterize the quantum-noise properties of the PCM as functions of the vapor density, pump detuning from resonance, and relative frequency detuning of the signal beam from the probe beam. We compare the noise measurements of the PCM with the predicted noise of an ideal quantum-noise-limited PCM and determine the value of the minimum signal that can be used to perform phase conjugation with unity signal-to-noise ratio. For the range of vapor densities studied, we find that the PCM operates nearest the quantum-noise limit and that the value of the minimum signal is lowest under conditions in which the reflectivity is maximized. These results demonstrate that it is possible to perform phase conjugation with signals as weak as 14 fW with near-unity reflectivity. Our measurements are in qualitative agreement with the predictions of a quantum theory of phase conjugation via nearly degenerate four-wave mixing in a two-level system.

Using multiple mutually incoherent fiber lasers to pump a coherent signal beam in an optical parametric oscillator

Abstract: Although the concept of using multiple pumps to drive an optical parametric oscillator (OPO) is old, experimental evidence bearing on this possibility has been reported only recently. Periodically poled lithium niobate (PPLN) has recently been applied to the construction of efficient CW singly resonant optical parametric oscillators with a single collinear pump beam. Here we use three-dimensional numerical modeling to study the possibility of noncollinearly pumping a PPLN OPO using N CW fiber lasers. Our results suggest that a tunable signal whose power exceeds that of a single pump laser may be possible. The modeling reported here does not take thermal lensing into account, and so is appropriate for a situation where the average pump power is reduced by a mechanical chopper or where thermal effects are mitigated by a technique such as beam scanning. The modeling also assumes the availability of 40 W polarized fiber lasers operating at /spl lambda//sub p/=1.064 /spl mu/m and of 1 mm thick PPLN, whereas 20 W polarized fiber lasers and 0.5 mm thick PPLN are the current state-of-the-art. We suppose that the nonlinear grating period in the 5 cm long PPLN is chosen to quasi-phase-match signal and idler wavelengths /spl lambda//sub s/=1.5 /spl mu/m and /spl lambda//sub i/=3.66 /spl mu/m.

Three-dimensional optical recording medium

Abstract: PROBLEM TO BE SOLVED: To prevent energy loss and recording of an erroneous information due to reflection of coherent light on an interface and to improve the recording accuracy by forming an antireflection layer on at least one of the surfaces of a transparent substrate and interfaces of layers. SOLUTION: When a signal beam 10 and a referential beam 11 enter one transparent substrate 3, both of the signal beam 10 and the referential beam 11 reach the surface of the transparent substrate 3 (interface with air) and further reach the interface between the transparent substrate 3 and a recording layer 2. Since antireflection layers 7, 5 are formed on the interfaces in the hologram memory 1, an energy loss by reflection of the signal beam 10 and the referential beam 11 can be prevented. Further, when the signal beam 10 and the referential beam 11 entering the recording layer 2 transmit through the recording layer 2 to outgo from the transparent substrate 4 to the outside, both of the beams are not reflected by the interfaces owing to the antireflection layers 6, 8 on the respective interface, but outgo from the transparent substrate 4.

Volume horographic memory and optical information recording/reproducing apparatus utilizing the same

Abstract: PROBLEM TO BE SOLVED: To reduce the size of apparatus by forming a column type holographic memory for recording three-dimensional distribution of interference fringes. SOLUTION: An optical modulator SLM12 of two-dimensional plane converts, depending on the data supplied from an encoder 25, the beam from a beam expander 14 to a signal beam and then condenses such signal beam to a volume holographic memory medium 10. The other beam from a beam splitter 16 is incident to a medium 10 as the reference beam and interferes with signal beam to form the interference fringes. The medium 10 is moved in the direction of the arrow mark A to realize space multiple recording by shifting the recording position of interference fringes. Moreover, the medium 10 is rotated in the direction of the arrow mark B to realize angular multiple recording by rotating the recording surface of interference pattern. At the time of reproducing operation, only the reference beam from a mirror 18 is incident to the medium 10. The diffraction beam from the interference fringes passes through a lens 21 and is then incident to a CCD 22 having the light receiving surface of two-dimensional plane. CCD 22 converts the reproduced beam into an electrical signal and then outputs such electrical signal to a decoder 26.

Two-wave-mixing induced self-focusing in an active photorefractive oscillator

Abstract: We derive a nonlinear wave equation for a signal beam which is coupled to a pump beam by two-wave-mixing in a photorefractive crystal. This equation describes self-focusing of the signal beam. We compare two-wave-mixing induced spatial self-focusing of single-pass experiments in a diffusion-type photorefractive crystal and of a photorefractive oscillator using the same crystal. We observe that the nonlinear refractive index change in the oscillator is decreased while increasing resonator losses.

Beam path monitoring system

Abstract: PROBLEM TO BE SOLVED: To provide an inexpensive monitoring system capable of monitoring even an entire beam path which contains a repeater or an optical amplifier with a single test device. SOLUTION: A test beam, having a wavelength different from that of a main signal beam propagates to a beam path 1 and this beam is observed to monitor the state of the path 1. In a beam path monitoring system, of such a constitution, a bypass line 2 of the test beam is prepared at a test disable area of the path 1. Then the main signal beam and the test beam are propagated to the path 1. The line 2 is provided with a transmissive filter which transmits the test beam but does not transmit the main signal beam. Then the line 2 is constituted of an optical coupler isolator 3.

Proposition of all-optical switch with photorefractive crystal and analysis of the influence of the phase mismatching

Abstract: We propose an all-optical switch controlled by the phase difference of the two control beams with photorefractive effect that induce strong nonlinear effect by relatively low beam power. We explain the concept of this switch, and calculate intensity of signal beam at each output port, then show that the switch can work. We also analyze the influence of phase mismatching in order to operate the switch efficiently.