Showing papers on "Four-wave mixing published in 1991"

Observation of squeezed states generated by four-wave mixing in an optical cavity

Abstract: Squeezed states of the electromagnetic field have been generated by nondegenerate four-wave mixing due to Na atoms in an optical cavity. The optical noise in the cavity, comprised of primarily vacuum fluctuations and a small component of spontaneous emission from the pumped Na atoms, is amplified in one quadrature of the optical field and deamplified in the other quadrature. These quadrature components are measured with a balanced homodyne detector. The total noise level in the deamplified quadrature drops below the vacuum noise level.

Third-order three-wave mixing in single-mode fibers: exact solutions and spatial instability effects

Abstract: Exact solutions are presented to the steady-state coupled-mode equations that govern the nonlinear parametric interaction of a central-frequency wave with a pair of upshifted and downshifted sidebands in isotropic single-mode optical fibers. This solution accounts for pump depletion as well for as a possible phase mismatch among the waves. The existence is predicted of eigensolutions propagating unchanged along the fiber, which may be either spatially stable or spatially unstable, depending on the total power and the propagation-constant mismatch. The presence of spatially unstable eigensolutions dramatically affects the power exchange among the three waves. The physical implications of this instability for the frequency-conversion process, as well as its potential application to all-optical switching, are discussed.

16 Gbit/s all-optical demultiplexing using four-wave mixing

Abstract: A novel, purely optical technique for demultiplexing high-speed time-division multiplexed data is proposed and demonstrated. The technique uses optical fibre nonlinearity induced four-wave mixing with a data signal and a probe signal located at different wavelengths. Using only semiconductor laser light sources, 1:4 demultiplexing of 20 ps long, subpicojoule, 2/sup 15/-1 RZ pulses at a data rate of 16 Gbit/s with less than 1 dB penalty is demonstrated.

Third‐order nonlinearity and two‐photon‐induced molecular dynamics: Femtosecond time‐resolved transient absorption, Kerr gate, and degenerate four‐wave mixing studies in poly (p‐phenylene vinylene)/sol‐gel silica film

Abstract: Femtosecond response and relaxation of the third‐order optical nonlinearity in a newly developed poly (p‐phenylene vinylene)/sol‐gel silica composite are investigated by time‐resolved forward wave degenerate four‐wave mixing, Kerr gate, and transient absorption techniques using 60 fs pulses at 620 nm. Using a theoretical description of two‐ and four‐wave mixing in optically nonlinear media, it is shown that the results obtained from simultaneous use of these techniques yield valuable information on the real and imaginary components of the third‐order susceptibility. In the composite material investigated here, the imaginary component is derived from the presence of a two‐photon resonance at the wavelength of 620 nm used for the present study. This two‐photon resonance is observed as transient absorption of the probe beam induced by the presence of a strong pump beam. It also provides fifth‐order nonlinear response both in transient absorption and in degenerate four‐wave mixing. The fifth‐order contributions are derived from the two‐photon generated excited species which can absorb at the measurement wavelength and therefore modify both the absorption coefficient and the refractive index of the medium.

Effects of nonlinear gain on four‐wave mixing and asymmetric gain saturation in a semiconductor laser amplifier

Abstract: Nearly degenerate four‐wave mixing (NDFWM) and asymmetric gain saturation were studied in a 1.5 μm InGaAsP semiconductor laser amplifier at highly saturated conditions (Pout ≫ Psat) and frequency separations up to 500 GHz. Apart from modulation of the carrier density the data reveal a new mechanism of NDFWM with a characteristic time of about 650 fs which takes over when the frequency separation exceeds 100 GHz.

Optical amplification in a nonlinear fibre interferometer

Abstract: A report is made on the observation of optical amplification in a nonlinear fibre interferometer, based on degenerate four-wave mixing (DFWM). The results are in agreement with a classical derivation for the nonlinear phase shift and gain.

Picosecond optical sampling using four-wave mixing in fibre

Abstract: An all-optical sampling system with 20 ps resolution realised by employing four-wave mixing in a fibre is demonstrated. Using only semiconductor laser sources, picosecond pulses are displayed on a microsecond time scale with a low speed receiver.

THz optical-frequency conversion of 1 Gb/s-signals using highly nondegenerate four-wave mixing in an InGaAsP semiconductor laser

Abstract: The authors report the application of the highly nondegenerate four-wave mixing (HNDFWM) process to a 1.5- mu m InGaAsP semiconductor laser in optical-frequency conversion experiments on 1-Gb/s intensity-modulated signals in a 1-THz conversion range. This conversion is based on a subpicosecond ultrafast nonlinear gain process in the laser. The HNDFWM was generated through the use of an injection-locking technique. The possibility of applying this phenomenon to an optical fiber dispersion compensator is also discussed. >

Radiation-matter oscillations and spectral line narrowing in field-correlated four-wave mixing. I. Theory.

Abstract: New radiation-matter phenomena in four-wave mixing spectroscopies, given a theoretical basis in the preceding paper [Dugan and Albrecht, Phys. Rev. A 43, 3877 (1991)], are examined experimentally here. A new class of Rabi detuning oscillations is recorded in interferometric coherent Stokes Raman scattering (CSRS). Two identical nanosecond incoherent light fields are mutually delayed, while simultaneously mixing in a nonlinear medium with a narrow-band field of a different color. Spectral filtering of the CSRS signal is essential. From such signals the frequencies and the dephasing rate constants can be a measure of the Raman-active vibrations in both the electronic ground state and the electronic excited state of the scattering chromophore. In principle, analogous probing of vibronic transitions is possible. Detuning oscillations for multimode systems are presented. It is shown how they are transformed into quantum beats, exactly those seen with femtosecond CSRS, when the narrow-band field is made broad and/or the detection is ``white.'' Finally, an example of the sub-Raman linewidth spectral feature, predicted in the preceding paper, is presented. It determines a Raman frequency, but does not carry its linewidth.

Phase and frequency resolution of picosecond optical Kerr nonlinearities

Abstract: We report on a method aimed at measuring both the real and imaginary parts of the third-order Kerr-type nonlinear-optical susceptibility of isotropic materials. It is based on Kerr ellipsometry in which analysis of the polarization state of transmitted light between a nearly crossed polarizer and an analyzer allows separation of pump-induced dichroism and birefringence. The method provides a natural measurement of nonlinear phase retardations in angle units, without any calibration procedure. By using a white-light continuum as a probe, this property is used to get a simultaneous measurement of the nonlinear dispersion in the whole visible spectrum. It is illustrated in tetramethylsilane, where stimulated Stokes and anti-Stokes Raman contributions to the nonlinearity are observed.

Degenerate four-wave mixing measurements of high order nonlinearities in semiconductors

Abstract: Degenerate four-wave mixing experiments on ZnSe and CdTe semiconductor samples with picosecond laser pulses at wavelengths below the bandgap are described. The authors identify the dominant nonlinearities in ZnSe and CdTe. They determine these to be fast third-order nonlinearities, due to the same processes which give rise to the effects of bound-electronic refraction and two-photon absorption, while higher order effects are due to free-carrier refraction. Measurements of the absolute magnitude of the combined third order susceptibilities are described. Studies of higher order effects due to free-carrier gratings are discussed. To obtain a quantitative measurement of the carrier induced nonlinearities, an expression for the diffraction efficiency of these carrier gratings was developed, and a value for the free-carrier refractive index coefficient in ZnSe was found. By measuring the angular dependence of the grating decay, the carrier diffusion coefficient was determined as a function of carrier density. >

Influence of two-photon absorption on third-order nonlinear optical processes as studied by degenerate four-wave mixing: The study of soluble didecyloxy substituted polyphenyls

Abstract: We have investigated the influence of two‐photon absorption on the third‐order nonlinear optical properties of model organic molecules using the technique of degenerate four‐wave mixing (DFWM). A theoretical formulation developed here shows that the presence of two‐photon absorption, which is related to the imaginary part of the third‐order susceptibility χ(3), leads to an enhancement of the effective third‐order nonlinearity and to the appearance of effects caused by the formation of two‐photon generated excited states. The dynamic behavior of the nonlinearity is then governed by the properties of excited molecules. The nonlinear effects also involve contributions which depend on the fifth power of the electric field. We have performed a systematic study of third‐order nonlinear optical properties of alkoxy (–C10H21OCH) substituted p‐polyphenyl oligomers using the technique of time‐resolved degenerate four‐wave mixing with subpicosecond pulses at 602 nm. Experimentally determined values of the second‐ord...

Time-dependent behavior of photorefractive two- and four-wave mixing

Abstract: A theoretical and experimental study of the temporal response of photorefractive two- and four-wave mixing processes is given We examine the buildup and the decay of the output signal and the gratings when the input signal beam is turned on and off For two-wave mixing we have performed an analysis that includes the depleted-pump regime The experiment was done with a BaTiO3 crystal The buildup-and-decay behavior is strongly dependent on the coupling constant and the ratio of the signal and pump intensities From these measurements we obtain the crystal time constant, which was found to have an intensity dependence with a power of −07 The coupling constant is extracted from the data of the whole dynamic process of buildup and erasure and not only from the steady-state point, as is usually done This is the first analytic study, to the best of our knowledge, for the four-wave mixing decay and buildup We find that the solution for time-dependent four-wave mixing processes (the phase-conjugate mirror and the double phase-conjugate mirror) with undepleted pumps is identical to that for two-wave mixing with unidirectional optical feedback circuits This similarity provides a direct way to study the stability properties of the devices We find, for example, that in the unstable regime of four-wave mixing a self-pulsation of the output corresponds to the frequency detuning of the unidirectional two-wave mixing oscillator

Molecular, multiresonant coherent four-wave mixing spectroscopy

Abstract: Recent research has expanded the capabilities of four-wave mixing by providing it with component selectivity, site selectivity, and mode selectivity. The selectivity is achieved by taking advantage of the three resonance enhancements that occur in a four-wave mixing process. New spectral scanning strategies allow one to scan a single resonance while maintaining the other two resonances at constant values. The constant resonances can be used to select a specific component, a specific site within an inhomogeneously broadened envelope of a component, and/or a specific vibrational or vibronic mode of that site. The scanned resonance will then contain enhanced features corresponding to the particular component, site, and/or mode that was chosen by the constant resonances. These component and site selective capabilities of the four-wave mixing complement the single vibronic level fluorescence methods. The relative transition intensities from a specific component or site reflect the mode coupling betwee...

Observation of highly nondegenerate four‐wave mixing (≳1 THz) in an InGaAsP multiple quantum well laser

Abstract: Highly nondegenerate four‐wave mixing (NDFWM) in the pump‐probe detuning region of more than 1 THz has been observed in an InGaAsP multiple quantum well laser for the first time. Each of the probe and signal frequencies is closed to cavity resonance modes for the pump laser and those outputs are enhanced. The highly NDFWM process is based on a mechanism whose response time is less than 0.2 ps.

Multiple Stokes wavelength generation in H 2 , D 2 , and CH 4 for lidar aerosol measurements

Abstract: Experimental results are reported of multiple Stokes generation of a frequency-doubled Nd:YAG laser in H2, D2, and CH4 in a focusing geometry. The energies at four Stokes orders were measured as functions of pump energy and gas pressure. The characteristics of the Stokes radiation generated in these gases are compared for optical production of multiple wavelengths. The competition between Raman components is analyzed in terms of cascade Raman scattering and four-wave mixing. The results indicate the possibility of using these generation processes for atmospheric aerosol measurements by means of multiwavelength lidar systems. Also, this study distinguishes between the gases, as regards the tendency to produce several wavelengths (H2,D2) versus the preference to produce mainly first Stokes radiation (CH4).

Performance degradation due to four-wave mixing in multichannel coherent optical communications systems

Abstract: Bit-error rate (BER) degradation due to four-wave mixing (FWM), in multichannel coherent optical communications systems, is studied. In particular, analytic expressions for the BER are derived for ASK, PSK, and FSK modulation schemes. The effects of input power, fiber chromatic dispersion, number of channels, and inter-channel spacing on the BER degradation is explicitly shown. The results show that, on the basis of equal peak power per channel, the ASK noncoherent detection scheme has the best performance, while the PSK coherent detection scheme has the poorest performance. For 1.55 μηι 100 channels transmission systems, having 5 GHz inter-channel spacing, the analysis predicts a maximum allowable input power per channel to be 2 dBm for 100 km of conventional single-mode fibers, and only — 9 dBm for 100 km of dispersion-shifted fibers. Finally, these analytical results are found to be in good agreement with recent experimental results.

Arrangement of orthogonal polarized signals for suppressing fiber four-wave mixing in optical multichannel transmission systems

Abstract: The arrangement of signal polarization states for suppressing fiber four-wave mixing (FWM) in optical multichannel transmission is described. Experiments show that light power generated through fiber FWM becomes 0 or 1/4 of the maximum value when signals are orthogonal. Based on the experimental results, power reduction of FWM light is evaluated for various arrangements of signal polarizations, and the optimum arrangements is shown to efficiently suppress fiber FWM in a multichannel system. >

Effect of amplifier spacing on four-wave mixing in multichannel coherent communications

Abstract: The buildup of four-wave mixing (FWM) is studied for the case of a multichannel coherent system using cascaded optical fibre amplifiers. It is shown, both analytically and numerically, that FW interactions can be either reduced or resonantly enhanced depending on the choice of the amplifier spacing. An example is given of a three channel phase modulated system with a channel separation of 12.5 GHz transmitted over 1000km. For this example, resonance of FWM occurred at an amplifier spacing of 53 km.

Temperature dependence of degenerate four wave mixing in azo dye doped polymer films

Abstract: Experimental results of the temperature dependence of the nonlinear optical response of disperse red 1 and methyl red doped in polystyrene film in the range 90–290 K are reported. It is found that the phase conjugate signal intensity resulting from degenerate four wave mixing is decreased by an order of magnitude at low temperature. The decay time of the recorded grating at fixed pump intensity also decreases with decreasing temperature.

Stable isotope ratio analysis at trace concentrations using degenerate four-wave mixing with a circularly polarized pulsed probe beam.

Abstract: Stable isotope analysis based on vectorial optical-phase conjugation by resonant degenerate four-wave mixing (D4WM) is reported by using a D4WM method with vertically polarized pump beams and a circularly polarized probe beam. Since the polarization of the signal beam is different from that of the pump beams, the background radiation is suppressed more effectively. Excellent sensitivity, high spectral resolution, and efficient optical detection make this an effective and unusually convenient nonlinear spectrometric method for the analysis of trace amounts of stable isotopes. Using an excimer-pumped pulsed dye laser, the fine structures of lithium are examined. A detection limit of 2.5 ng/mL lithium is observed while a Doppler-free resolution is maintained by using transient "coherent-grating" based D4WM spectroscopy.

Origin of picosecond‐pulse‐induced, degenerate four‐wave‐mixing signals in KTa1−xNbxO3 crystals

Abstract: Transient gratings have been produced in KTa1−xNbxO3 by picosecond‐pulse, two‐photon excitation using degenerate four‐wave‐mixing techniques The excitation process has been characterized through fluorescence studies, and the fluorescence is attributed to the transition between an excited state and the ground state of B4+ ions that are produced in ABO3 perovskite crystals Strong electron‐phonon coupling gives rise to the luminescence quenching The observed degenerate four‐wave‐mixing signal is shown to be due predominantly to a phase grating caused by a change in the susceptibility associated with the formation of Nb4+ or Ta4+ ions in the peak region of the grating The grating signal intensity was found to be dependent on the concentration of niobium ions and the crossing angle of the two laser write beams

Nondegenerate multiwave mixing in polydiacetylene: phase conjugation with frequency conversion

Abstract: We present an analysis of optical phase conjugation with frequency doubling in terms of nondegenerate six-wave mixing fifth-order nonlinear susceptibility. We show how the Bragg phase-matching condition is achieved at small angles. The process under picosecond-pulse conditions in a polydiacetylene solution pumped at two-photon resonance and probed at one-photon resonance is experimentally demonstrated. Results are discussed in terms of a one-dimensional quantum three-level system. The proximity of one- and two-photon resonance in conjugated polymers makes these polymers efficient nonlinear-optical materials for this original application. The experiment permits artifact-free measurement of the two-photon state recovery time of the red form of polydiacetylene.

Studies of resonant and preresonant femtosecond degenerate four-wave mixing in unoriented conducting polymers

Abstract: Degenerate four‐wave mixing with femtosecond time resolution is used to measure the magnitude and transient response of the third‐order nonlinear optical susceptibility χ(3) (ω;ω,−ω,ω) at 620 nm in nonoriented conducting polymers including polydiacetylene, polyacetylene, polyaniline, polydiethynylsilane, polythiophene, and polythiophene derivatives. Resonant and nonresonant excitations influence the magnitude and transient response of χ(3). The electronic response is instantaneous for preresonant excitation, but for resonant excitation it has ultrafast and slow components which illustrate photoexcitation dynamics. The magnitude of χ(3) for all of the polymers is in the range from 10−10 to 5×10−8 esu depending on the energy difference between the laser excitation and the polymer absorption maximum.

Efficient anti-Stokes Raman conversion by four-wave mixing in gases

Abstract: We describe a means for efficient, energy-scalable generation of first-order anti-Stokes light by four-wave mixing, using collimated pump and first-order Stokes seed beams. We performed a one-dimensional, plane-wave analysis of the process, assuming steady-state conditions and monochromatic beams. A prescription for designing the optimum anti-Stokes converter with this technique is derived from this analysis, and we show that energy conversion efficiencies from pump light to anti-Stokes light of ~30% might be possible. We also report an unoptimized, proof-of-concept experiment that produced 40 mJ of anti-Stokes-shifted light at 432 nm from 1.2 J of 527-nm pump light in a 60-cm-long hydrogen cell.