Four-wave mixing

About: Four-wave mixing is a research topic. Over the lifetime, 7530 publications have been published within this topic receiving 112702 citations.

Cascaded free-induction decay four-wave mixing

Abstract: We report the observation of cascaded optical free-induction decay four-wave mixing (FID-FWM) signal. This process can take place when nonlinear optical measurements are carried out with pulses that are orders of magnitude shorter than the dephasing time of the sample. Experimental observations and theoretical calculations show that the coherent emission from the first laser pulse participates as a time-delayed local electric field to yield the cascaded signal. We arrive at this conclusion based on pulse sequences of degenerate noncollinear femtosecond pulses for which three-pulse FWM is forbidden. Further confirmation was obtained from experiments where the time delay between two pulses were used to form ground or excited state populations, the signal reflected the corresponding ground or excited state dynamics. Although FID is long lived, the femtosecond resolution was found to be maintained in our measurements on gas phase molecular iodine. This is because the FID is modulated in the femtosecond time scale by the molecular dynamics of the system; its intensity and modulation were confirmed using femtosecond time-gated up-conversion measurements.

Light storage based on four-wave mixing and electromagnetically induced transparency in cold atoms

Abstract: We performed an experiment to observe the storage of an input probe field and an idler field generated through an off-axis four-wave mixing (FWM) process via a double-\ensuremath{\Lambda} configuration in a cold atomic ensemble. We analyzed the underlying physics in detail and found that the retrieved idler field came from two parts if there was no single-photon detuning for the pump pulse: Part 1 was from the collective atomic spin (the input probe field, the coupling field, and the pump field combined to generate the idler field through FWM; then the idler was stored through electromagnetically induced transparency). Part 2 was from the generated new FWM process during the retrieval process (the retrieved probe field, the coupling field, and the pump field combined to generate a new FWM signal). If there was single-photon detuning for the pump pulse, then the retrieved idler was mainly from part 2. The retrieved two fields exhibited damped oscillations with the same oscillatory period when a homogeneous external magnetic field was applied, which was caused by the Larmor spin precession. We also experimentally realized the storage and retrieval of an image of light using FWM, in which an image was added into the input signal. After the storage, the retrieved idler beams and input signal carried the same image. This image storage technique holds promise for applications in image processing, remote sensing, and quantum communication.

Tunable coupled-mode dispersion compensation and its application to on-chip resonant four-wave mixing

Abstract: We propose and demonstrate localized mode coupling as a viable dispersion engineering technique for phase-matched resonant four-wave mixing (FWM). We demonstrate a dual-cavity resonant structure that employs coupling-induced frequency splitting at one of three resonances to compensate for cavity dispersion, enabling phase-matching. Coupling strength is controlled by thermal tuning of one cavity enabling active control of the resonant frequency-matching. In a fabricated silicon microresonator, we show an 8 dB enhancement of seeded FWM efficiency over the non-compensated state. The measured four-wave mixing has a peak wavelength conversion efficiency of -37.9 dB across a free spectral range (FSR) of 3.334 THz ($\sim$27 nm). Enabled by strong counteraction of dispersion, this FSR is, to our knowledge, the largest in silicon to demonstrate FWM to date. This form of mode-coupling-based, active dispersion compensation can be beneficial for many FWM-based devices including wavelength converters, parametric amplifiers, and widely detuned correlated photon-pair sources. Apart from compensating intrinsic dispersion, the proposed mechanism can alternatively be utilized in an otherwise dispersionless resonator to counteract the detuning effect of self- and cross-phase modulation on the pump resonance during FWM, thereby addressing a fundamental issue in the performance of light sources such as broadband optical frequency combs.

Four-wave mixing of incoherent light in a dispersion-shifted fiber using a spectrum-sliced fiber amplifier light source

Abstract: We investigate the FWM efficiency of incoherent light in a dispersion-shifted fiber (DSF) using a spectrum-sliced fiber amplifier light source. A theoretical model is provided to describe the FWM mechanism of incoherent light. The FWM efficiencies of coherent and incoherent light are compared theoretically and experimentally. Unlike the FWM of coherent light, the FWM signals of incoherent light are mostly generated by nondegenerate FWM regardless of the number of input signals. Thus, when two input signals are mixed, incoherent light has about 6 dB higher mixing efficiency than coherent light due to the difference in their degeneracy factor.

Phase shifts of photorefractive gratings and phase-conjugate waves

Abstract: We present measurements of the two-wave mixing gain as a function of frequency detuning in photorefractive crystals. In many cases, this function is asymmetric, indicating that the phase shift of the photorefractive inde grating with respect to the light interference pattern is not exactly 90 degrees , as is often assumed. In four-wave mixing, the phase of the phase-conjugate wave contains the phase of the pumping and probe waves and a phase shift determined by the interaction taking place in the nonlinear medium. This second term, the phase shift of the phase conjugator, is a function of the type of grating and the phase shift of this grating. The phase shift of the grating obtained from the two-wave mixing measurements compares well with that obtained from four-wave mixing measurements of the phase of the phase conjugator.