Showing papers on "Phase conjugation published in 2003"
TL;DR: A fully phase encryption system, using fractional Fourier transform to encrypt and decrypt a 2-D phase image obtained from an amplitude image, and experimental results in support of the proposed idea are presented.
Abstract: We implement a fully phase encryption system, using fractional Fourier transform to encrypt and decrypt a 2-D phase image obtained from an amplitude image. The encrypted image is holographically recorded in a barium titanate crystal and is then decrypted by generating through phase conjugation, a conjugate of the encrypted image. The decrypted phase image is converted into an amplitude image by the phase contrast technique using an electrically addressed spatial light modulator. Experimental results in support of the proposed idea are presented.
117 citations
TL;DR: Noise-induced phase jitter, which is mediated by self-phase modulation, can be reduced significantly by a small number of in-line phase conjugators.
Abstract: The main impairment of differential-phase-shift-keyed communication systems is phase jitter. Noise-induced phase jitter, which is mediated by self-phase modulation, can be reduced significantly by a small number of in-line phase conjugators.
54 citations
TL;DR: In this paper, a photorefractive brown Sn2P2S6 crystal was grown by the vapor-transport technique with SnI2 as the transport agent and showed that the measured reflectivity represents the limit given by the transmission of the ring-cavity arrangement.
Abstract: A significant improvement of the ring-cavity self-pumped phase conjugation response time in the near-infrared cw regime with a photorefractive brown Sn2P2S6 crystal is reported. Brown Sn2P2S6 is grown by the vapor-transport technique with SnI2 as the transport agent. With our Sn2P2S6 samples response times below 50 ms and phase-conjugate reflectivities of 25% can be achieved at a wavelength of 780 nm with a moderate light intensity of 1 W/cm2. We show that the measured reflectivity represents the limit given by the transmission of the ring-cavity arrangement. Reaching this limit is possible because of the large two-wave mixing gain of 18 cm-1 measured in this crystal.
46 citations
TL;DR: A scanning laser Doppler vibrometer is used to record two-dimensional ultrasound fields in air and digital reconstruction by use of phase conjugation (time reversal) of the object sound field is performed.
Abstract: A scanning laser Doppler vibrometer is used to record two-dimensional ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction by use of phase conjugation (time reversal) of the object sound field is then performed, and the original object field intensity and phase is reconstructed.
39 citations
TL;DR: The four-sideband model of parametric instabilities driven by orthogonal pump waves in birefringent fibers is developed and validated by numerical simulations and facilitates the design ofparametric amplifiers driven by two pump waves with different frequencies and polarizations.
Abstract: The four-sideband model of parametric instabilities driven by orthogonal pump waves in birefringent fibers is developed and validated by numerical simulations. A polynomial eigenvalue equation is derived and used to determine how the spatial growth rates and frequency bandwidths of various instabilities depend on the system parameters. The maximal growth rate is associated with a group-speed matched four-sideband process (coupled modulation instability), whereas broad-bandwidth gain is associated primarily with a two-sideband process (phase conjugation). This four-sideband model facilitates the design of parametric amplifiers driven by two pump waves with different frequencies and polarizations.
27 citations
TL;DR: Spectral phase conjugation is used to compensate for dispersion of all orders, self-phase modulation, and self-steepening of an optical pulse in a fiber if high-order dispersion is a main source of distortion.
Abstract: We propose the use of spectral phase conjugation to compensate for dispersion of all orders, self-phase modulation, and self-steepening of an optical pulse in a fiber. Although this method cannot compensate for loss and intrapulse Raman scattering, it is superior to the previously suggested midway temporal phase conjugation method if high-order dispersion is a main source of distortion. The reshaping performance of our proposed scheme and a combined temporal and spectral phase conjugation scheme in the presence of uncompensated effects is studied numerically.
26 citations
TL;DR: In this paper, a noncollinear interaction among three amplitude-modulated plane waves in a uniaxial crystal under type I phase-matching conditions was considered and a general method to calculate the holographic wave front generated by a nonplane object wave front and a plane reference wave front was developed.
Abstract: We consider noncollinear interaction among three amplitude-modulated plane waves in a uniaxial crystal under type I phase-matching conditions. If one among the interacting fields can be taken as undepleted during the interaction, the remaining two fields are holographic replicas of each other: the undepleted field acts as the reference field in holography. We develop a general method to calculate the holographic wave front generated by a nonplane object wave front and a plane reference wave front. We present experiments in which a holographic image of an object consisting of a pointlike light source is obtained by choosing the object- and reference-field frequencies among ω1,ω2, and ω3 (with ω3=ω1+ω2) in any of the possible combinations.
22 citations
TL;DR: In this paper, the use of an electrically addressed liquid crystal spatial light modulator (EALCSLM) operating in the phase mode as a phase-contrast filter (PCF) was proposed.
22 citations
TL;DR: In this paper, an improvement of the output energy of a multistage YAG laser system by using a stimulated Brillouin scattering (SBS) phase conjugation mirror (PCM) was achieved.
Abstract: An improvement of the output energy of a multistage YAG laser system by using a stimulated Brillouin scattering (SBS) phase conjugation mirror (PCM) was achieved. The phase conjugation of the optically nonlinear SBS process in a liquid material effectively compensated thermal degradation at an average/peak power amplifier, resulting in an average power increase from 1.5 J at 30 Hz repetition rate to 2.6 J at 50 Hz drive. The beam quality was also recovered without wave front deformation and depolarization resulting in a transfer-limited divergence with a good flat-top pattern in a near field.
16 citations
TL;DR: In this article, a scheme for simultaneous suppression of both TOD and SI in OPC systems using a periodic higher order dispersion-managed link consisting of standard singlemode fibers (SMFs) and reverse dispersion fibers (RDFs).
Abstract: In optical phase conjugation (OPC) systems, the third-order dispersion (TOD) of optical fibers and the nonlinear resonance at well-defined signal sideband frequencies called sideband instability (SI) mainly limit the transmission performance. We propose, for the first time, a scheme for simultaneous suppression of both TOD and SI in OPC systems using a periodic higher order dispersion-managed link consisting of standard single-mode fibers (SMFs) and reverse dispersion fibers (RDFs). Computer simulation results demonstrate the possibility of 200-Gb/s data transmission over 10 000 km in the higher order dispersion-managed OPC system, where the dispersion map is optimized by our system design strategies.
15 citations
TL;DR: In this paper, phase conjugation driven by orthogonal pump waves in birefringent polarization-maintaining fibers is studied analytically and numerically.
Abstract: Phase conjugation driven by orthogonal pump waves in birefringent polarization-maintaining fibers is studied analytically and numerically. For typical parameters, the gain bandwidths and polarization sensitivities associated with orthogonal-pump waves are comparable to those associated with parallel-pump waves. However, the maximal gains are significantly lower.
TL;DR: Fused-quartz glass is found to be an ideal medium for high-power stimulated Brillouin-scattering experiments, because it gives a high reflectivity of over 95% at an incident energy of 2.3 J, has pulse duration of 16 ns, and has excellent fidelity in phase conjugation as discussed by the authors.
TL;DR: A scheme for designing fiber amplifiers as SBS phase conjugators the power requirements can be decreased by orders of magnitude; yet only low coherence is required, and high fidelity is reached.
Abstract: Phase-conjugating stimulated Brillouin scattering (SBS) mirrors are frequently used to improve the brightness of solid-state lasers. With a scheme for designing fiber amplifiers as SBS phase conjugators the power requirements can be decreased by orders of magnitude; yet only low coherence is required, and high fidelity is reached. A peak power of 5 W was demonstrated to be sufficient for optical SBS phase conjugation.
TL;DR: In this article, the authors present a theoretical treatment of difference-frequency generation in conditions of phase mismatch for seed and generated fields that propagate at different angles to the pump and experiments performed with seed fields strongly phase and amplitude modulated show that the pump-field wave fronts behave as efficient phaseconjugating mirrors.
Abstract: We present a theoretical treatment of difference-frequency generation in conditions of phase mismatch for seed and generated fields that propagate at different angles to the pump. The analytical solution in the case of nondepleted plane-wave pump and experiments performed with seed fields strongly phase and amplitude modulated show that the pump-field wave fronts behave as efficient phase-conjugating mirrors.
TL;DR: In this article, a fully phase encrypted memory system using cascaded extended fractional Fourier transform (FRT) was implemented, where a two-dimensional image obtained from an amplitude image was encrypted and decrypted using phase contrast technique.
Abstract: In this paper, we implement a fully phase encrypted memory system using cascaded extended fractional Fourier transform (FRT). We encrypt and decrypt a two-dimensional image obtained from an amplitude image. The fully phase image to be encrypted is fractional Fourier transformed three times and random phase masks are placed in the two intermediate planes. Performing the FRT three times increases the key size, at an added complexity of one more lens. The encrypted image is holographically recorded in a photorefractive crystal and is then decrypted by generating through phase conjugation, conjugate of encrypted image. The decrypted phase image is converted into an amplitude image by using phase contrast technique. A lithium niobate crystal has been used as a phase contrast filter to reconstruct the phase image, alleviating the need of alignment in the Fourier plane, thereby making the system rugged.
27 Mar 2003
TL;DR: In this article, an analysis was performed on the base of numeric experiment methods of a laser beam propagation in a turbulent atmosphere and comparison of efficiency was carried out of phase and amplitude-phase adaptive control algorithms.
Abstract: In the paper an analysis was performed on the base of numeric experiment methods of a laser beam propagation in a turbulent atmosphere. Comparison of efficiency was carried out of phase and amplitude-phase adaptive control algorithms. It was noted that only wavefront reversion insures the absolute compensation for turbulent distortions of laser beams. It is also shown that wavefront reversion is possible to realize in two-mirror adaptive optics system. The mirrors should be divided by a gap where a beam propagates under conditions of free diffraction.
TL;DR: In this paper, a double phase-conjugate mirror was obtained in seconds for beam intensities on the order of the tenth of a milliwatt, achieving 30% and stable within 3% for hours.
Abstract: Photorefractive simple and double phase-conjugate mirrors very often exhibit strong instabilities in their reflectivities. One of their possible origins can be the competition between phase conjugation and its generating process, photorefractive beam fanning. However, by suitably choosing the incident beam widths and directions, we suppressed this competition and replaced it by the enhancement of each process by the other. This technique allows to obtain a double phase-conjugate mirror in BaTiO{sub 3} that establishes itself in seconds for beam intensities on the order of the tenth of a milliwatt. The reflectivities reached are on the order of 30% and stable within 3% for hours.
Patent•
15 Dec 2003TL;DR: In this article, an optical transmission system consisting of first and second lines of optical fiber, each line including first, second, and third optical fiber portions, and an optical phase conjugator optically coupling the first two lines is provided.
Abstract: An optical transmission system is provided. The system includes first and second lines of optical fiber, each line including first, second, and third optical fiber portions, and an optical phase conjugator optically coupling the first and second lines. The first and third optical fiber portions have a local dispersion of like sign to each other, and opposite to the sign of the second optical fiber portion.
TL;DR: It is shown that at the parameters of the experimentally studied laser the noise strongly affects the temporal dependence of amplitudes of the counter-propagating waves and the regular phase jumps appear during intervals between adjacent chaotic pulses.
Abstract: We present results on experimental and theoretical studies of chaos in a solid-state ring laser with periodic pump modulation. We show that the synchronized chaos in the counter-propagating waves is observed for the values of pump modulation frequency fp satisfying the inequality f1 < fp < f2. The boundaries of this region, f1 and f2, depend on the pump-modulation depth. Inside the region of synchronized chaos we study not only dynamics of amplitudes of the counter-propagating waves but also the optical phases of them by mixing the fields of the counter-propagating waves and recording the intensity of the mixed signal. We demonstrate experimentally that in the regime of synchronized chaos the regular phase jumps appear during intervals between adjacent chaotic pulses. We improve the standard semi-classical model of a SSRL and consider an effect of spontaneous emission noise on the temporal evolution of intensities and phase dynamics in the regime of synchronized chaos. It is shown that at the parameters of the experimentally studied laser the noise strongly affects the temporal dependence of amplitudes of the counter-propagating waves.
TL;DR: In this paper, the formation of holographic gratings in nematic liquid crystals by laser beams in the telecommunications wavelength region around 1500 nm through a thermal mechanism has been demonstrated, and the gratings have been observed in a four-wave mixing experiment with millisecond-long writing pulses in 5CB liquid crystal.
Abstract: The formation of holographic gratings in nematic liquid crystals by laser beams in the telecommunications wavelength region around 1500 nm through a thermal mechanism has been demonstrated. The gratings have been observed in a four-wave mixing experiment with millisecond-long writing pulses in 5CB liquid crystal. The relatively low absorption of the crystal was compensated by the absorption in the coating of the experimental cell wall. Optimization of the liquid crystal temperature near the phase transition point allowed a diffraction efficiency of about 1% to be reached. Holographic liquid crystal devices can be used in all-optical switching, beam routing, automatic wavefront correction, phase conjugation, etc.
21 Oct 2003
TL;DR: Using two beam coupling geometry, high order copropagating and contra-propagating isotropic and anisotropic self-diffraction are demonstrated using photorefractive cerium doped barium titanate.
Abstract: Using two beam coupling geometry, high order copropagating and contrapropagating isotropic and copropagating anisotropic self-diffraction are demonstrated using photorefractive cerium doped barium titanate. At small incident angles, typically less than 0.015 radians, both codirectional isotropic self-diffraction (CODIS) and contradirectional isotropic self-diffraction (CONDIS) orders are generated simultaneously. At larger incident angles, typically approximately more than 0.2094 radians, only codirectional anisotropic-self diffraction (CODAS) orders are generated. Ongoing work on image auto/cross correlation results are also shown.
TL;DR: In this article, a phase conjugate mirror based on stimulated Brillouin scattering (SBS) in a multimode fiber amplifier is presented, where optical amplification leads to a drastic reduction of the SBS threshold.
Abstract: A new phase conjugate mirror based on stimulated Brillouin scattering (SBS) in a multimode fiber amplifier is presented The optical amplification leads to a drastic reduction of the SBS threshold A peak power threshold of 5 W was detected for a 10 m long Ytterbium doped fiber amplifier The experimental examinations include the measurements of the phase conjugate fidelity, the temporal behavior of the Stokes pulse and the spectra of the back scattered light
Patent•
05 Sep 2003
TL;DR: The phase conjugate generating device is applicable to various optical systems as discussed by the authors, such as optical communication, optical measurement, optical information processing, and other fields, and it can be used in any nonlinear optical medium.
Abstract: PROBLEM TO BE SOLVED: To provide a new device which is applicable to use in which phase conjugation optics is applied to optical communication, optical measurement, optical information processing, and other fields. SOLUTION: A nonlinear optical medium (1) is supplied with exciting light and input signal light to generate output signal light and phase conjugate light in the nonlinear optical medium (1). The output signal light and the phase conjugate light are extracted by a signal light/phase conjugate light extracting means (7) and outputted from output ports (5) and (6), respectively. The phase conjugate generating device is applicable to various optical systems. COPYRIGHT: (C)2003,JPO
01 Jan 2003
TL;DR: In this paper, the formation of steady-state spatial solitons by laser beam propagation through photorefractive crystals (PRC) with optical activity and absorption is theoretically and experimentally described.
Abstract: This chapter is an overview of the photorefractive effect, the important photorefractive nonlinear processes and common photorefractive materials. In Section 2, the formation of steady-state spatial solitons by laser beam propagation through photorefractive crystals (PRC) with optical activity and absorption is theoretically and experimentally described. The spatial soliton features, which characterize the dynamic waveguide built in PRC, are analyzed. The soliton polarisation dynamics reaches a stable behavior under high external electric fields. Two-wave mixing and self-diffraction in dynamic harmonic and inharmonic gratings, induced by lasers in PRC, are presented in Section 3. The diffraction efficiency and beam amplification can reach high values, with promising potential in optical interconnections and storage. Dynamic and adaptive gratings by double phase conjugation (DPC) in PRC are discussed in Section 4. High phase conjugated reflectivity, high coupling transmission efficiency and robust interconnections of mutually incoherent lasers are achieved in DPC using Rh:BaTiO3 crystals.
TL;DR: This work presents what to their knowledge is the first demonstration of self-pumped phase conjugation in a laser- pumped solid-state Rhodamine-6G dye saturable amplifier.
Abstract: We present what to our knowledge is the first demonstration of self-pumped phase conjugation in a laser-pumped solid-state Rhodamine-6G dye saturable amplifier. Phase-conjugate energy reflectivity of as much as 2100% at 557 nm has been obtained.
TL;DR: In this paper, the effect of phase conjugation for the second harmonic of a focused ultrasonic beam was investigated experimentally and by numerical simulation, and it was shown that the field of a conjugate wave adequately reproduces the field field of the incident wave.
Abstract: The effect of phase conjugation for the second harmonic of a focused ultrasonic beam was investigated experimentally and by numerical simulation. An ultrasonic pulse with the carrier frequency f=3 MHz was emitted into water and focused at a point between the source and the phase conjugating system. The phase conjugation for the second harmonic of the incident wave (2f=6 MHz) was performed in a magnetostrictive ceramic as a result of the parametric interaction of the incident wave with the pumping magnetic field (the pumping frequency was f
p=4f=12 MHz). The axial and focal distributions of sound pressure in the incident and conjugated beams were measured using a broadband PVDF membrane hydrophone. The corresponding calculations were performed by solving numerically the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation allowing for the nonlinearity, diffraction, and thermoviscous absorption. The results of measurements agreed well with the calculations and showed that the field of a conjugate wave adequately reproduces the field of the second harmonic of the incident wave. A certain advantage of focusing with the phase conjugation for the second harmonic was demonstrated in comparison with the operation at the doubled frequency of the incident wave. The results of this study can serve as a basis for the utilization of the phase conjugation of harmonics in ultrasonic tomography and nondestructive testing.
Proceedings Article•
06 Jun 2003TL;DR: In this article, the authors demonstrate a straightforward technique for complete prepulse elimination in chirped pulse amplification systems, using two cascaded optical parametric amplifiers, and demonstrate for the first time how to eliminate prepulse in a chirping pulse amplification system.
Abstract: We demonstrate for the first time a straightforward technique for complete prepulse elimination in chirped pulse amplification systems, using two cascaded optical parametric amplifiers.
TL;DR: The possibility of realizing an optical phase conjugation in an excited semiconductor medium was shown theoretically and experimentally in this paper, where the photon energy equal to half the energy of the radiative recombination of excitons in CuI films pumped by a nitrogen laser at room temperature was revealed.
Abstract: The possibility of realizing an optical phase conjugation in an excited semiconductor medium is shown theoretically and experimentally. A phase conjugation is revealed for the photon energy equal to half the energy of the radiative recombination of excitons in CuI films pumped by a nitrogen laser at room temperature. The dependences of the phase-conjugation signal intensity on its spectral composition are investigated. The quadratic interaction of light and exciton electromagnetic oscillations in the semiconductor medium is suggested as an explanation of this effect.
09 Apr 2003
TL;DR: In this article, phase conjugators are used to compensate for phase distortions in master oscillator power amplifier systems (MOPA) to achieve high output power while preserving a diffraction limited beam quality.
Abstract: Solid-state laser sources are required for numerous applications in industry and science. High output power while preserving a diffraction limited beam quality results in high brightness operation. However, conventional laser systems suffer from thermally induced phase distortions in the active medium, which considerably reduce the beam quality. Proper cooling, diode pumping, as well as active media with high quantum efficiency reduce the thermal load. But the still remaining phase distortions result in a reduction of beam quality. Phase cojugate mirrors are suitable to compensate for phase distortions in master oscillator power amplifier systems (MOPA). Stimulated Brillouin scattering (SBS) in commercial multimode silica fibers leads to reliable and stable phase conjugation. A further advantage is, that the fiber core diameter can be select in respect of the systems pulse energy to obtain the necessary intensity for high reflectivity SBS. Three systems with phase conjugators have been investigated. A pulse pumped, passively q-switched Nd:YAP System which delivers an average output power of 315 W with M 2 = 2.6. The pulse energy is about 160 mJ with a pulse width of 140 ns at 2 kHz repetition rate. Another pulse pumped MOPA system based on Nd:YAG with depolarization compensation delivers an average output power up to 124 W with M 2 = 2.2. Due to active q-switching the pulse repetition rate and peak power of this system are variable in a wide range. Furthermore a continuously pumped amplifier arrangement with nearly diffraction limited output of 120 W average power has been achieved at 10 kHz repetition rate.
Patent•
14 Feb 2003
TL;DR: In this article, a laser processing unit which is capable of correcting the deterioration of a laser beam caused by an optical fiber, an amplifier or the like and reducing its processing head in size and weight is provided.
Abstract: PROBLEM TO BE SOLVED: To provide a laser processing unit which is capable of surely correcting the deterioration of a laser beam caused by an optical fiber, an amplifier or the like and reducing its processing head in size and weight. SOLUTION: A laser amplifier 13 equipped with an amplifying unit 17 and a phase conjugation mirror 18 is connected to a laser oscillator 12 through the intermediary of a first multi-mode optical fiber 19 to form an incident system on a unit body 11 side, and a condensing lens system 26 on a processing head 24 side is connected to the laser amplifier 13 through the intermediary of a beam splitter 20 and a second multi-mode optical fiber 27 to form a projection system.