Showing papers on "Phase conjugation published in 1993"

Polarisation-independent phase conjugation of lightwave signals

Abstract: The authors propose and demonstrate a technique for phase conjugation of lightwave signals with an efficiency that is independent of the signal polarisation Using either optical fibre or a semiconductor optical amplifier as the nonlinear element, a signal-polarisation dependence of about ±ldB in the conjugation efficiency was obtained

Oscillator-shuttle-circuit (OSC) networks for conditioning energy in higher-order symmetry algebraic topological forms and RF phase conjugation

Abstract: The present invention provides passive networks which act as the host to nonlinear and parametric interactions, with energy inputs to said networks being caused to "bleed off" auxiliary, and time-delayed conditioning flows resulting in phase modulations to the main input and which achieve, e.g., RF phase conjugation with cancellation of the noise modulation after two-way passage of beams between transmitter and receiver and when used in duplex arrangements. Also, passive networks for noise reduction in communications transmission due to conditioning of electromagnetic fields in higher order group symmetry form. Because a transmitted wave from a network of the present invention is in higher-order group symmetry form, and fields of such higher-order symmetry have a low probability of occurrence naturally, then environmental noise, which is of lower group symmetry form (usually, U(1) symmetry) and has a high probably of natural occurrence, will be excluded from a receiver matched to higher-order symmetry waves. Therefore in the case of communications, less noise will be processed statistically at a receiver designed for SU(2) or higher group symmetry operation, resulting in enhanced signal-to-noise. Also disclosed are passive networks for power transmission resulting in decreased loss in transmission. Higher-order group symmetry matched "receivers" will have enhanced signal-to-noise reception over lower-order symmetry receivers, i.e., leakage to ground will be less.

Compensation of pulse shape distortion due to chromatic dispersion and Kerr effect by optical phase conjugation

Abstract: Pulse shape distortion due to chromatic dispersion and self-phase modulation in a single-mode fiber was effectively compensated for by using an optical phase-conjugate wave generated by nondegenerate forward four-wave mixing in a zero-dispersion single-mode fiber. Using optical phase conjugation at the midpoint of a 100-km standard single-mode fiber compensates for the distortion of 10-Gb/s intensity-modulated NRZ pulse at an input power level exceeding +10 dBm with a resultant power penalty of less than 1.2 dB. >

Compensation fibre chromatic dispersion by optical phase conjugation in a semiconductor laser amplifier

Abstract: Spectral inversion in a semiconductor laser amplifier has been used, for the first time to the authors' knowledge, to achieve compensation of the chromatic dispersion in singlemode fibre. This was demonstrated by transmission of a directly modulated, highly chirped 2.5 Gbit/s signal at 1.5 μm across 100 km of normal dispersion fibre

Compensation of fibre chromatic dispersion by spectral inversion

Abstract: A chromatic dispersion compensation technique employing phase conjugation is used to transmit a directly-modulated 2.5 Gbit/s signal at 1.5 μm wavelength through 400km of normal-dispersion fibre.

Nonlinear optics in signal processing

Abstract: Nonlinear Optics in Signal Processing: This covers the applications of nonlinear optics to optical processing in a range of areas including switching, computing, and telecommunications. Each chapter presents the physics behind optical interactions between light and a range of materials and then examines the applications of the effects discussed. The book provides a comprehensive review of this expanding area and discusses the likely direction of future research. Contents: Introduction. Nonlinearities in organic solids. Semiconductors. The photorefractive effect. Optical bistability. Optical processing using phase conjugation. Architectures for optical neural networks. Third order nonlinear guided-wave optical devices. Nonlinearity in optical fibre communications. Ultrashort pulses for nonlinear optical techniques.

Self‐pumped phase conjugation with a new mechanism in KTa1−xNbxO3:Fe crystals

Abstract: A new model is proposed to explain the origin of the self‐pumped phase conjugation (SPPC) that we have observed in KTa1−xNbxO3:Fe crystals. In this model SPPC is generated by both four‐wave mixing and backscattering processes rather than by only one of them. The advantage of this kind of phase conjugator is also discussed.

Forward-scattering degenerate four-wave mixing as a simple sub-attomole-sensitive nonlinear laser analytical spectrometric method.

Abstract: Optical phase conjugation by "forward-scattering" degenerate four-wave mixing in an absorbing liquid analyte solution is reported as a sensitive and simple nonlinear laser spectroscopic method. Since only two input laser beams are used in this nonlinear four-wave mixing setup, it offers important advantages including ease of optical alignment, efficient use of input photon density, low laser power requirements, and high wave-mixing efficiency. In addition, since the phase-conjugate signal is a laser beam, optical signal detection is very efficient and the signal-to-noise is excellent. Important characteristics of this novel nonlinear laser technique, including signal dependence on analyte concentration, individual input beam power, and modulation frequencies, are examined. Excellent detection sensitivity, small detection volume, and convenient sample introduction promise many applications for this nonlinear laser spectroscopic method. Preliminary detection limits of 0.7 amol of eosin B and 45 amol of iodine inside a probe volume of 98 pL are reported using a forward-scattering degenerate four-wave mixing setup.

Self-starting optical phase conjugation in dyed nematic liquid crystals with a stimulated thermal-scattering effect.

Abstract: We have observed a stimulated thermal-scattering-mediated self-starting phase-conjugation effect in dye-doped nematic liquid crystal. The buildup time was observed to be in the millisecond range for an input laser power of the order of 0.4 W. Because of the broadband birefringence of nematic liquid crystals, it is expected that the effect could be realized over the spectral regime from the visible to the infrared.

Speckle resistant method and apparatus with chirped laser beam

Abstract: Laser beam speckle effects are mitigated by frequency chirping a single-mode laser beam, reflecting it off a speckling surface, and then integrating the reflected beam over at least one chirp period. The speckle reduction is comparable to the use of a multi-longitudinal mode beam having a bandwidth similar to the chirped frequency excursion, while leaving the beam compatible with nonlinear optical processes that are not compatible with multi-longitudinal mode beams. Where the nonlinear process is stimulated Brillouin scattering (SBS) phase conjugation, the beam can be chirped at a rate up to the order of ##EQU1## where ΔνB is the gain bandwidth and L is the effective SBS interaction length of the phase conjugator, and C is the speed of light. Other nonlinear processes with which the beam may be used include harmonic generation and Raman-based beam cleanup or wavelength conversion.

Self-pumped phase conjugation of 18°-cut Ce-doped KNSBN crystal at 632.8 nm

Abstract: We report the self-pumped phase conjugation of an 18°-cut Ce-doped (KyNa1−y)2m(SrxBa1−x)1−m Nb2O6 crystal at a 632.8-nm He–Ne laser wavelength. A maximum phase-conjugation reflectivity of 84.3% has been measured. In addition, its incident angular response and time response are measured.

Temporal evolution of photorefractive double phase-conjugate mirrors.

Abstract: We present wave-optics calculations of the temporal and spatial evolution from random noise of a double phase-conjugate mirror in photorefractive media that show its image exchange and phase-reversal properties. The calculations show that for values of coupling coefficient times length greater than two the process exhibits excellent conjugation fidelity, behaves as an oscillator, and continues to operate even when the noise required for starting it is set to zero. For values less than two, the double phase-conjugation process exhibits poor fidelity and disappears when the noise is set to zero.

Ultrasonic imaging apparatus

Abstract: PURPOSE:To improve the phase-conjugation-wave generating efficiency of a phase-conjugation-wave generating means in an ultrasonic imaging apparatus using phase conjugation waves. CONSTITUTION:In an ultrasonic imaging apparatus for obtaining the data of a body under test by scanning with ultrasonic waves, the parts performing the following functions are provided. An ultrasonic-wave transmitting means 104 projects the ultrasonic waves on a body under test 101. A magnetic body 108 receives the ultrasonic waves through the body under test 101. A phase- conjugation-wave generating means comprises magnetic-field applying means 105, 110, 111, 112 and 109, which apply the specified external magnetic field on the magnetic body 108. A receiving means 114 receives the phase conjugation waves of the ultrasonic waves generated with the phase-conjugation-wave generating means through the body under test 101 again. The ultrasonic imaging apparatus is constituted in this way.

Laser-diode phase-shifting interferometry with a self-pumped phase-conjugate mirror.

Abstract: A laser-diode phase-measuring interferometer with a BaTiO3 self-pumped phase-conjugate mirror is presented that is based on a phase-shifting technique with a stepwise wavelength change by variation of the laser-diode current. The phase is shifted to produce a spatially uniform phase difference uncanceled by a phase conjugator between the beams in the two arms of the interferometer. The dc light buildup phase-conjugate reflectivities with a maximum of 60% versus time are measured for different incident angles to the crystal. The visibility of the interferograms is estimated by varying the pump-beam frequency of the laser diode. Experimental results of the phase measurement with a four-step method are shown.

BaTiO3 waveguide self-pumped phase conjugator.

Abstract: For the first time to our knowledge, self-pumped phase conjugation is reported in a planar waveguide structure in a BaTiO3 single crystal. The waveguide was fabricated by the technique of ion implantation, with 1.5-MeV H+ ions at a dose of 1016 ions/cm2. Phase-conjugate reflectivities >20% have been measured for waveguide self-pumped phase conjugation, and, for a given input power, an order-of-magnitude reduction in the response time is observed in the waveguide compared with the bulk. The fidelity of phase conjugation in the guide is also discussed.

Excited-state absorption and pump propagation effects on optical phase conjugation in a saturable absorber

Abstract: Phase conjugation by degenerate four-wave mixing in a saturable absorbing medium with a relatively long-lived excited state is analyzed; the analytical results are compared with experimental results. We propose a four-level model and take into account the effects of both excited-state absorption and pump propagation to explain the experimental results, which could not be explained by the models proposed previously. The numerical result predicts that the value of the phase-conjugate reflectivity as a function of the pump intensity is maximum at a certain absorbance (as absorbance increases) that is dependent on the cross section of the excited-state absorption. The present analysis explains most observations in the experiment, which was performed with a saturable-dye-doped polymer film as the saturable absorbing medium.

Time-resolved measurements of stimulated-Brillouin-scattering phase jumps

Abstract: In the absence of feedback, stimulated-Brillouin-scattering (SBS) generators typically rely on random acoustic noise to initiate and sustain the stimulated-scattering process. Phase jumps in the Stokes signal are the well-known macroscopic consequence of the noiselike origin of the Stokes seed. Phase jumps are abrupt reversals of the Stokes phase that occur simultaneously with dramatic variations in the Stokes intensity. We report what we believe to be the first time-resolved measurements of phase jumps in the Stokes beam produced by an SBS generator. Our experimental results1 are in excellent agreement with the results of simple theoretical models.3 These experiments also led to the identification of slow phase drifts and distinct frequency shifts in the Stokes beam. Phase jumps, phase drifts, and frequency shifts are properties common to oscillators that develop, without feedback, from noise.

Polarization Properties in Phase Conjugation with Bacteriorhodopsin

Abstract: Polarization properties of the phase conjugate beam in biological photochrome bacteriorhodopsin with photoinduced anisotropic nonlinearity are studied. We derived the polarization state and reflectivity of the phase conjugate beam in degenerate four-wave mixing (DFWM) where two pump beams have the same or orthogonal polarization and a probe beam has arbitrary polarization. Theoretical results are proved by experiments.

Theoretical description of two-photon phase conjugation in polar molecules

Abstract: Degenerate four-wave-mixing phase conjugation is analyzed in the case of two-photon transitions between levels having unequal dipole moments. The theoretical treatment is based upon a nonperturbative solution of the density matrix and does not require the rotating-wave approximation. We give an analytical expression for the polarization component oscillating at the field frequency for a medium excited by stationary waves. In the weak-probe-beam limit, the contributions in the direction of the probe and conjugated beams are evaluated. For instance, by using this two-photon process, instead of the usual single-photon one which is independent of the permanent dipole moments even in the strong-field limit, it is shown that lower intensities are sufficient to reach higher reflectivities. The influences of the permanent dipole moments, relaxation rates, and field frequency are also discussed.

Parallel interconnection through an optical fiber using phase conjugation mirror acceptable for optical data pattern

Abstract: A class of optical parallel interconnections is proposed in which a two-dimensional data pattern is directly transmitted through a multimode fiber. It is demonstrated using an optically addressed spatial light modulator that functions as a data input port and a phase conjugation mirror. The interconnection technology is shown to be effective for two-dimensional data transmission between optical processors and memories. >

Mutually pumped phase conjugator for remote identification

Abstract: A universal IFF technique and system utilizes a real-time communication l established between both parties allowing the approximate immediate transferral of digital information with positive direction and identification of both parties achieved. A pump laser emits a first signal at a first position and a remote laser beacon emits a second signal at a second position, both signals at nominally the same wavelength. A MPPCM receives the first signal which establishes a beam fan. The MPPCM and first signal scans about a region of interest to intercept the second signal. The second signal provides a second input signal into the MPPCM so that a two-way phase conjugation signal builds up and lock-on is established.

Overthreshold Nonlinearity of Parametric Sound Wave Phase Conjugation in Solids

Abstract: The nonlinear stage of acoustic wave phase conjugation over the threshold of absolute parametric instability is considered with respect to magnetic active media. The common case of nonlinear, nonstationary and spatially inhomogeneous parametric interaction is studied. Theoretical results are compared with experimental data on phase conjugate wave gain measurements in ferrite. It is shown that the pumping exhaustion mechanism of nonlinearity provides a reproduction of incident wave field distribution in the output of the active zone by parametric phase conjugation in the overthreshold regime of giant amplification in ferrite. The signal and fluctuation mode competition is shown to be essential for overthreshold limitation of phase conjugate wave amplitude.

Potentiality of photorefractive CdTe

Abstract: For optical telecommunication networks, optical switching is now being studied. Different solutions have been proposed (integrated optics, free space switching, etc.), and reconfigurable optical interconnects, based on phase conjugation, should be one interesting method. For example, some results have been obtained with a double-phase conjugated mirror configuration, allowing reconfigurable connection between single-mode optical fibres. These phase-conjugated optics use photorefractive crystals and the first demonstration has been given using Bi12 TiO20 photorefractive crystals. In a telecommunication network, semiconductive crystals with a good efficiency in the near-IR wavelength are needed. Our first experiments were carried out with InP:Fe crystals at 1.3 μm. However, it is well known, from published studies, that II–VI materials are, in principle, more interesting for the following reasons. The electro-optic coefficient is higher (and therefore the figure of merit is higher). The solubility of dopants is higher (and therefore the space charge electric field, which modulates the refractive index of the material, may be higher). Next we tested a CdTe:V crystal and, in a two-wave mixing experiment without an external electric field, an amplification gain was observed and a high photosensitivity demonstrated at 1.3 μm. In this paper, we shall describe the photorefractive effect and explain our choice of the CdTe:V crystal, taking into account the parameters of this photorefractive effect and some other parameters required by the applications in the optical beam steering field. Next the results will be given, and finally an optical configuration using phase conjugation will be presented as an example of application.

Self-pumped phase conjugation and four-wave mixing in 0 degrees - and 45 degrees -cut n-type BaTiO(3):Co.

Abstract: Relatively fast self-pumped phase-conjugate and four-wave-mixing rise times are reported in n-type cobalt-doped barium titanate. With the crystal oriented in a 45-deg cut as compared with the same crystal in a 0-deg cut we find a factor of 3 decrease in the 0-90-percent rise time to 800 ms with 25-mW input power at 514.5 nm. Also, the self-pumped phase-conjugate reflectivity increases from 20 to 40 percent. We deduce that the phase conjugation is from internally seeded stimulated photorefractive backscattering. The four-wave-mixing rise time of the 45-deg-cut crystal is 4 ms with a reflectivity of 48 percent when the pumping beams are derived from self-pumped phase conjugation that has an input power of 25 mW.