Showing papers on "Four-wave mixing published in 2006"

Generation of correlated photons in nanoscale silicon waveguides.

Abstract: .We experimentally study the generation of correlated pairs of photons through four-wave mixing (FWM) in embedded silicon waveguides. The waveguides, which are designed to exhibit anomalous group-velocity dispersion at wavelengths near 1555 nm, allow phase matched FWM and thus efficient pair-wise generation of non-degenerate signal and idler photons. Photon counting measurements yield a coincidence-to-accidental ratio (CAR) of around 25 for a signal (idler) photon production rate of about 0.05 per pulse. We characterize the variation in CAR as a function of pump power and pump-to-sideband wavelength detuning. These measurements represent a first step towards the development of tools for quantum information processing which are based on CMOS-compatible, silicon-on-insulator technology.

Zero-dispersion wavelength decreasing photonic crystal fibers for ultraviolet-extended supercontinuum generation

Abstract: We report the fabrication of photonic crystal fibers with a continuously-decreasing zero-dispersion wavelength along their length. These tapered fibers are designed to extend the generation of supercontinuum spectra from the visible into the ultraviolet. We report on their performance when pumped with both nanosecond and picosecond sources at 1.064 microm. The supercontinuum spectra have a spectral width (measured at the 10 dB points) extending from 0.372 microm to beyond 1.75 microm. In an optimal configuration a flat (3 dB) spectrum from 395 to 850 nm, with a minimum spectral power density of 2 mW/nm was achieved, with a total continuum output power of 3.5 W. We believe that the shortest wavelengths were generated by cascaded four-wave mixing: the continuous decrease of the zero dispersion wavelength along the fiber length enables the phase-matching condition to be satisfied for a wide range of wavelengths into the ultraviolet, while simultaneously increasing the nonlinear coefficient of the fiber.

Performance of Cavity-Parametric Amplifiers, Employing Kerr Nonlinearites, in the Presence of Two-Photon Loss

Abstract: Two-photon loss mechanisms often accompany a Kerr nonlinearity. The kinetic inductance exhibited by superconducting transmission lines provides an example of a Kerr-like nonlinearity that is accompanied by a nonlinear resistance of the two-photon absorptive type. Such nonlinear dissipation can degrade the performance of amplifiers and mixers employing a Kerr-like nonlinearity as the gain or mixing medium. As an aid for parametric-amplifier design, the authors provide a quantum analysis of a cavity parametric amplifier employing a Kerr nonlinearity that is accompanied by a two-photon absorptive loss. Because of their usefulness in diagnostics, we obtain expressions for the pump amplitude within the cavity, the reflection coefficient for the pump amplitude reflected off of the cavity, the parametric gain, and the intermodulation gain. Expressions by which the degree of squeezing can be computed are also presented. Although the focus here is on providing aids for the design of kinetic-inductance parametric amplifiers, much of what is presented is directly applicable to analogous optical and mechanical amplifiers

20-GHz-to-1-THz Repetition Rate Pulse Sources Based on Multiple Four-Wave Mixing in Optical Fibers

Abstract: In this paper, we theoretically and experimentally study the generation of very high-repetition-rate pulse sources based on multiple four-wave mixing in optical fibers. More precisely, we described the generation of nearly transform-limited pulses at repetition rates of 20, 40, 80, 160, 320, 640 GHz, and 1 THz with a wavelength tunability close to 20 nm around 1555nm. In particular, frequency resolved optical gating analyses show that 170-fs transform-limited pulses have been generated at 1 THz

Four-wave mixing of solitons with radiation and quasi-nondispersive wave packets at the short-wavelength edge of a supercontinuum

Abstract: We apply the recently developed theory of frequency generation by mixing of solitons and dispersive waves [Phys. Rev. E 72, 016619 (2005)] to explain the observed formation, quasi-trapping and frequency shift of the spectral peaks at the blue edge of supercontinua generated in silica-core photonic crystal fibers.

Photon pair generation using four-wave mixing in a microstructured fibre: theory versus experiment

Abstract: We develop a theoretical analysis of four-wave mixing used to generate photon pairs useful for quantum information processing. The analysis applies to a single mode microstructured fibre pumped by an ultra-short coherent pulse in the normal dispersion region. Given the values of the optical propagation constant inside the fibre, we can estimate the created number of photon pairs per pulse, their central wavelength and their respective bandwidth. We use the experimental results from a picosecond source of correlated photon pairs using a micro-structured fibre to validate the model. The fibre is pumped in the normal dispersion regime at 708 nm and phase matching is satisfied for widely spaced parametric wavelengths of 586 and 894 nm. We measure the number of photons per pulse using a loss-independent coincidence scheme and compare the results with the theoretical expectation. We show a good agreement between the theoretical expectations and the experimental results for various fibre lengths and pump powers.

Generation and characterization of phase and amplitude shaped femtosecond mid-IR pulses

Abstract: A germanium acousto-optic modulator was recently reported (Shim et al., Optics Letters, 31, 838, 2006) that is capable of generating phase and amplitude shaped femtosecond pulses directly in the mid-infrared. In this paper, the design, implementation and performance of this novel mid-IR shaper is described in detail as is the sub-50 fs optical parametric amplifier that provides large bandwidth for generation of complex pulse shapes. These details include the acoustic power and wavelength dependence of the deflection efficiency, the phase stability of the shaper, the synchronization of electronics, and a study on how the mid-IR bandwidth of the optical parametric amplifier depends on its optical configuration. With these details quantified, the accuracy of the device is tested by creating a series of shaped pulses that are characterized by cross-correlation with well-known mid-IR reference pulses and by simulations. Test waveforms include optimally compressed, phase-chirped and amplitude-modulated mid-IR pulses. The shaped pulses are of sufficient quality that they will enable new experiments in 2D IR spectroscopy and in the coherent control of vibrations in ground electronic states.

Millimeter-Wave Frequency Tripling Based on Four-Wave Mixing in a Semiconductor Optical Amplifier

Abstract: An approach to generating a frequency-tripled millimeter-wave (mm-wave) signal based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) is experimentally demonstrated. In the proposed system, two phase-correlated optical wavelengths generated by an optical phase-locked loop (OPLL) are used as two pumps to generate the FWM process in the SOA. Two idlers with a wavelength spacing three times that of the two pump wavelengths are obtained. The two pump wavelengths are then removed by two cascaded fiber Bragg gratings serving as an optical notch filter. By beating the two idlers at a photodetector, an mm-wave with a frequency that is three times that of the OPLL reference source is generated

Simultaneous four-wave mixing and cross-gain modulation for implementing an all-optical XNOR logic gate using a single SOA.

Abstract: We report on an all-optical XNOR-gate using simultaneous Four-Wave Mixing (FWM) and Cross-Gain Modulation (XGM) in a semiconductor optical amplifier (SOA). FWM generates the bitwise AND output corresponding to the two input data streams while XGM is used to generate the NOR output. These two outputs are combined using a coupler to obtain the final XNOR output. Error-free operation for RZ data with <2dB power-penalty is reported.

Spectral broadening in Raman fiber lasers.

Abstract: We present an analytical theory based on wave kinetic equations that describes a Raman fiber laser (RFL) generation spectrum. It is shown both theoretically and experimentally that the quasi-degenerate four-wave mixing between different longitudinal modes is the main broadening mechanism in the one-stage RFL at high powers. The shape and power dependence of the intracavity Stokes wave spectrum are in excellent quantitative agreement with predictions of the theory.

Wavelength conversion based on four-wave mixing in high-nonlinear dispersion shifted fiber using a dual-pump configuration

Abstract: The dual-pump all-optical wavelength conversion based on a four-wave mixing (FWM) in a high-nonlinear dispersion shifted fiber (HNL-DSF) is demonstrated experimentally. The polarization sensitivity of the wavelength converter based on this dual-pump figuration is investigated experimentally and theoretically. The experimental results indicate that the wavelength-conversion configuration with copolarization pumps shows the smallest polarization sensitivity. A model of the beating-wave modulation from the dynamic wave equation is erected to explain the experimental phenomena, and the theoretical analyses agree well with the experimental results.

Four-wave-mixing cascades near the zero-dispersion frequency.

Abstract: Exact formulas are obtained for the amplitudes of light waves involved in four-wave-mixing cascades near the zero-dispersion frequency of a fiber. The cascade that is initiated by two strong pump waves is phase insensitive, whereas the cascade that is initiated by two strong pump waves and a weak signal wave is phase sensitive. In both cascades, the number of waves that have significant power increases with distance.

Ultrahigh-speed all-optical half adder based on four-wave mixing in semiconductor optical amplifier

Abstract: A novel scheme for an ultrahigh-speed all-optical half adder based on four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is proposed. This scheme is free of pattern effect, due to using the polarization-shift-keying (PolSK) modulation format. By numerical simulation, the output power level of logic "1" dependence on the operating conditions, such as two input signal powers, injection current, and input signal wavelength, are investigated in detail using the broad-band model of this all-optical half adder.

Bismuth-oxide-based nonlinear fiber with a high SBS threshold and its application to four-wave-mixing wavelength conversion using a pure continuous-wave pump

Abstract: The unique and practical benefits of the use of bismuth-oxide-based nonlinear fiber (Bi-NLF) in implementing a four-wave-mixing (FWM)-based wavelength converter for fiber-optic-communication-system applications are experimentally demonstrated. First, the Kerr-nonlinearity and stimulated-Brillouin-scattering (SBS) characteristics of our fabricated Bi-NLF are experimentally investigated. The Bi-NLF is found to have the superior advantage of a significantly high SBS threshold in addition to its ultrahigh Kerr nonlinearity /spl gamma/ of /spl sim/1100 W/sup -1//spl middot/km/sup -1/, compared to the conventional silica-based highly nonlinear fiber. Next, the authors perform an experiment for the FWM-based wavelength conversion of a non-return-to-zero (NRZ) signal within a 40-cm length of the Bi-NLF fusion spliced to standard silica fibers by using a continuous-wave (CW) high-power pump beam. Error-free tunable wavelength conversion over a 10-nm bandwidth is readily achieved. No SBS-suppression scheme is employed for the pump due to the high SBS threshold, which simplifies the system configuration and improves the quality of the wavelength-converted signal.

Photon-pair generation by four-wave mixing in optical fibers

Abstract: We present a theory to quantify a fundamental limit on correlated photon pairs generated through four-wave mixing inside optical fibers in the presence of spontaneous Raman scattering (SpRS). Our theory is able to explain current experimental data. We show that if correlated photon pairs are generated with polarization orthogonal to the pump the effect of SpRS is significantly reduced over a broad spectral region extending from 5 to 15 THz.

Analysis of four-wave mixing of high-power lasers for the detection of elastic photon-photon scattering

Abstract: We derive expressions for the coupling coefficients for electromagnetic four-wave mixing in the nonlinear quantum vacuum. An experimental setup for detection of elastic photon-photon scattering is suggested, where three incoming laser pulses collide and generate a fourth wave with a new frequency and direction of propagation. An expression for the number of scattered photons is derived and, using beam parameters for the Astra Gemini system at the Rutherford Appleton Laboratory, it is found that the signal can reach detectable levels. Problems with shot-to-shot reproducibility are reviewed, and the magnitude of the noise arising from competing scattering processes is estimated. It is found that detection of elastic photon-photon scattering may be achieved.

Time- and spectrally-resolved four-wave mixing in single CdTe/ZnTe quantum dots

Abstract: We present transient four-wave mixing experiments on individual excitonic transitions in self-assembled CdTe∕ZnTe quantum dots. Using a two-dimensional femtosecond spectroscopy and heterodyne detection of the nonlinear signal we study the dephasing and mutual coherent coupling of single quantum dot states. For the homogeneous linewidth of the zero-phonon line (ZPL) values of 0.06–0.1 meV (T2=13–20 ps) are measured, and a ZPL weight in the total line shape of Z=0.9 at T=7 K is estimated. We observe two linearly polarized fine-structure split exciton transitions with transition dipole moment ratios of 1.0–1.1 deduced from the four-wave mixing (FWM) amplitude, and splitting energies of 0.2–0.35 meV deduced from the FWM spectral response or quantum beat period. Coherent coupling between excitonic states is identified by off-diagonal signals in the two-dimensional spectrally-resolved FWM. The presence of an inhomogeneous broadening caused by spectral diffusion in the time ensemble is evidenced by the formation of a photon echo in the time-resolved FWM from a single transition.

On the balance between delay, bandwidth and signal distortion in slow light systems based on stimulated Brillouin scattering in optical fibers.

Abstract: We describe systematic measurements of the gain and delay spectra in a slow light system based on stimulated Brillouin scattering in optical fibers. The measurements yield the system complex transfer function with which delays and signal distortion can be calculated for any input signal. The theoretical predictions are confirmed experimentally for single pulses as well as 50 Mb/s data streams in a system which employs pump modulation to modify the gain and delay spectra of the SBS process.

Stimulated parametric emission microscopy

Abstract: We propose a novel microscopy technique based on the four-wave mixing (FWM) process that is enhanced by two-photon electronic resonance induced by a pump pulse along with stimulated emission induced by a dump pulse. A Ti:sapphire laser and an optical parametric oscillator are used as light sources for the pump and dump pulses, respectively. We demonstrate that our proposed FWM technique can be used to obtain a one-dimensional image of ethanol-thinned Coumarin 120 solution sandwiched between a hole-slide glass and a cover slip, and a two-dimensional image of a leaf of Camellia sinensis.

Polarization modulation instability in photonic crystal fibers.

Abstract: Polarization modulation instability (PMI) in birefringent photonic crystal fibers has been observed in the normal dispersion regime with a frequency shift of 64 THz between the generated frequencies and the pump frequency. The generated sidebands are orthogonally polarized to the pump. From the observed PMI frequency shift and the measured dispersion, we determined the phase birefringence to be 5.3×10−5 at a pump wavelength of 647.1 nm. This birefringence was used to estimate the PMI gain as a function of pump wavelength. Four-wave mixing experiments in both the normal and the anomalous dispersion regimes generated PMI frequency shifts that show good agreement with the predicted values over a 70 THz range. These results could lead to amplifiers and oscillators based on PMI.

Experimental demonstration of slow and superluminal light in semiconductor optical amplifiers.

Abstract: Tunable delays in semiconductor optical amplifiers are achieved via four wave mixing between a strong pump beam and a modulated probe beam. The delay of the probe beam can be controlled both electrically, by changing the SOA bias, and optically, by varying the pump power or the pump-probe detuning. For sinusoidal modulated signal at 0.5 GHz, a tunable delay of 1.6 ns is achieved. This corresponds to a RF phase change of 1.6 pi. For 1.3 ns optical pulses propagating through the SOA a delay of 0.59 ns is achieved corresponding to a delay-bandwidth product exceeding 0.45. For both the cases, slow light and superluminal light are observed as the pump-probe detuning is varied.

Selective spectral filtering of molecular modes of β‐carotene in solution using optimal control in four‐wave‐mixing spectroscopy

Abstract: Femtosecond laser pulses are spectrally broad and therefore coherently excite several molecular modes. While the temporal resolution is high, usually no mode-selective excitation is possible. In this work, we demonstrate that, by phase shaping one of the two pulses, which excite the vibrational modes of β-carotene within a coherent anti-Stokes Raman scattering (CARS) process, specific modes can be enhanced or suppressed. Using the pulse shaper setup in a feedback-controlled closed-loop optimizes this mode selection. Here, the ratio of signal intensities observed in the CARS spectrum serves as a feedback function for an evolutionary algorithm responsible for the optimization. The optimized phase structure of the femtosecond pulse is characterized using the frequency resolved optical gating (FROG) technique to get an insight into the optimization process. Furthermore, it is shown that the temporal resolution after optimization is still high enough to investigate the ultrafast molecular dynamics. The suppression or relative enhancement of vibrational modes persists over the entire coherence time. Copyright © 2006 John Wiley & Sons, Ltd.

Blue extended super continuum light source

Abstract: A new blue extended super continuum light source is claimed. When pulses of partly coherent monochromatic 'pump' radiation of essentially constant amplitude is 5 propagating through a microstructure fibre medium within a region of anomalous dispersion of the medium, then, provided the medium has a finite nonlinear coefficient of the index of refraction, the pump pulse is subject to a modulation instability. This instability results in the generation and exponential growth of sidebands, the two closest to the 'pump' frequency being the dominant ones. The 10 modulation frequency is proportional to the square root of the power in the carrier wave. In the time domain this leads to that the interaction between the medium and the radiation results in contraction of the width of the amplitude peaks, which results in formation of a train of narrow pulses with Tera Hertz repetition rate. 15 Phase match between red shifted Raman solitons generated by the pump pulse and energy shed by the pump pulse at all frequencies with a group velocity below the pump pulse group velocity will lead to the formation of Cherenkov radiation. The solitons or 'light bullets' will seed Cherenkov radiation in the near infrared, visible or at UV wavelengths depending on the actual fibre parameters. This extends the 20 generated super continuum light beyond the four wave mixing limit usually experienced when applying picoseconds or nanoseconds pump pulses.

Mixed frequency/time domain optical analogues of heteronuclear multidimensional NMR.

Abstract: Ultrafast spectroscopy is dominated by time domain methods such as pump-probe and, more recently, 2D-IR spectroscopies. In this paper, we demonstrate that a mixed frequency/time domain ultrafast four wave mixing (FWM) approach not only provides similar capabilities, but it also provides optical analogues of multiple- and zero-quantum heteronuclear nuclear magnetic resonance (NMR). The method requires phase coherence between the excitation pulses only over the dephasing time of the coherences. It uses twelve coherence pathways that include four with populations, four with zero-quantum coherences, and four with double-quantum coherences. Each pathway provides different capabilities. The population pathways correspond to those of two-dimensional (2D) time domain spectroscopies, while the double- and zero-quantum coherence pathways access the coherent dynamics of coupled quantum states. The three spectral and two temporal dimensions enable the isolation and characterization of the spectral correlations between different vibrational and/or electronic states, coherence and population relaxation rates, and coupling strengths. Quantum-level interference between the direct and free-induction decay components gives a spectral resolution that exceeds that of the excitation pulses. Appropriate parameter choices allow isolation of individual coherence pathways. The mixed frequency/time domain approach allows one to access any set of quantum states with coherent multidimensional spectroscopy.

Waveband converters based on four-wave mixing in SOAs

Abstract: Four wave mixing (FWM) is distinguished from other wavelength conversion techniques by its ability to simultaneously convert a number of input wavelength channels. In this case, optical signal-to-noise ratio (OSNR) is insufficient to describe the performance of the device as many effects are involved. A multiwavelength FWM model is used here to simulate a waveband converter (WBC). The numerical model predicts the waveform of the FWM product. Based on that output, the Q factor of the signal and the power penalty induced to the signal can be calculated to evaluate the performance of such a device. Meanwhile, an analytical model is used for the calculation of the signal power levels and the standard deviation of the fluctuation; hence, it describes the constituent effects-namely, the extinction ratio (ER) degradation, the OSNR degradation, the gain modulation (GM) related crosstalk, and interference. The model's validity is tested against the numerical results. To the best of the authors' knowledge, this is the first time that a numerical model and an analytical model are used to systematically investigate a WBC and to identify the specific effects and derive the design rules. These rules are tested in the experiment. Finally, a tunable WBC (TWBC) based on the dual-pump configuration is described and implemented experimentally

Frequency tunable polarization and intermodal modulation instability in high birefringence holey fiber

Abstract: We present an experimental analysis of polarization and intermodal noise-seeded parametric amplification, in which dispersion is phase matched by group velocity mismatch between either polarization or spatial modes in birefringent holey fiber with elliptical core composed of a triple defect. By injecting quasi-CW intense linearly polarized pump pulses either parallel or at 45 degrees with respect to the fiber polarization axes, we observed the simultaneous generation of polarization or intermodal modulation instability sidebands. Furthermore, by shifting the pump wavelength from 532 to 625 nm, we observed a shift of polarization sidebands from 3 to 8 THz, whereas intermodal sidebands shifted from 33 to 63 THz. These observations are in excellent agreement with the experimental characterization and theoretical estimates of phase and group velocities for the respective fiber modes.

Dynamic behavior of wavelength converters based on FWM in SOAs

Abstract: As wavelength converters based on four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) attract more attention, dynamic effects and wavelength dependent performance become key aspects to be investigated. Such issues are particularly important, as complex configurations are likely to be used to overcome challenges like tunability and polarization dependence. In this paper a numerical model is used to predict the dynamic performance of three FWM configurations and an analytical model is used to derive design rules. First, the wavelength dependent behavior of a wavelength converter is investigated and the requirement for a widely tunable converter is identified. Secondly, a configuration for extinction ratio (ER) improvement is studied and novel design rules are obtained analytically, tested experimentally and explained by the numerical model; experimental results with ER improvement at 10 Gb/s were achieved for the first time. The third configuration studied is a dual-pump arrangement enabling wide tunability. Fixed input/tunable output and tunable input/fixed output configurations are discussed in terms of optical signal-to-noise ratio and tunability. Design rules are extracted and verified for all three configurations that are likely to be deployed: simple wavelength converters, regenerating converters and tunable wavelength converters.

Generation of few-cycle pulses directly from a MHz-NOPA.

Abstract: We demonstrate the generation of 10-fs-pulses from a noncollinear optical parametric amplifier (NOPA). The NOPA is driven by microjoule pulses from a directly diode pumped Yb:KYW oscillator with cavity-dumping.

Matched ultraslow propagation of highly efficient four-wave mixing in a closely cycled double-ladder system

Abstract: We present a fully time dependent, adiabatic solution, and steady-state analysis for the ultraslow propagation of the nondegenerate four-wave mixing (NDFWM) signal and the weak probe beam in a closely-cycled double-ladder system. Under appropriate (especially power balance) conditions, the two-mode probe and phase-matched NDFWM pulses, after a characteristic propagation length, evolve into a pair of amplitude and group velocity matched pulses. Double transparency for the probe and NDFWM beams can be achieved owing to an efficient one- and three-photon destructive interference involving the NDFWM beam and its back reaction to the probe beam. The forward and backward configurations are investigated in this double-ladder system, and their efficiencies are calculated and compared.

Self-Pumping Wavelength Conversion for DPSK Signals and DQPSK Generation Through Four-Wave Mixing in Highly Nonlinear Optical Fiber

Abstract: A novel scheme is proposed to achieve self-pumping wavelength conversion for two differential phase-shift keying (DPSK) signals at different wavelengths through four-wave mixing (FWM) effect in a highly nonlinear optical fiber. By changing the phase modulation depths to pi/2 for both of the DPSK signals, the two signals can be multiplexed to generate a differential quadrature phase-shift keying signal. The simulations and experimental results demonstrate the feasibility of phase manipulations for phase-shift keying signals through the FWM process