Four-wave Mixing Gain Research Articles

Four-wave mixing with anti-parity-time symmetry in hot 85Rb vapor

We report an experimental demonstration of anti-parity-time symmetric optical four-wave mixing in thermal rubidium vapor, where the propagation of probe and stokes fields in a double-Λ scheme is governed by a non-Hermitian Hamiltonian. We are particularly interested in studying quantum intensity correlations between the two fields near the exceptional point, taking into account loss and accompanied Langevin noise. Our experimental measurements of classical four-wave mixing gain and the associated two-mode relative-intensity squeezing are in reasonable agreement with the theoretical predictions.

Perfect non-reciprocal reflection amplification in closed loop coherent gain atomic system

High-performance non-reciprocal photonic devices can improve the efficiency of optical quantum manipulation, information processing, and quantum simulation effectively. The enhanced optical signal can simultaneously amplify the weak signal output by the quantum system and isolate the sensitive quantum system from the back-scattered external noise, which is the core technology of high-performance photonic devices. In our previous work (<ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://doi.org/10.1364/OE.499738">2023 <i>Opt. Express</i> <b>31</b> 38228</ext-link>), we have achieved dynamic control of unidirectional reflection amplification based on four-wave mixing gain and the use of coupling field intensity varying linearly with position. In this work, we design a simple three-level closed loop coherent gain atomic system, setting the intensity of coupling field to be varying with position step shape to break the spatial symmetry of probe susceptibility, and achieving perfect non-reciprocal reflection light amplification. In contrast, the stepped variation of coupling field intensity is easier to adjust in experiment, greatly reducing the difficulty in the experiment. Specifically, the system introduces phase modulation. By changing the phase, the frequency region of probe gain and absorption can be switched, which makes the modulation of reflection amplification more flexible.

Third-order nonlinearity OPO: Schmidt mode decomposition and tripartite entanglement.

We investigate quantum properties of light in optical parametric oscillators (OPOs) based on four-wave mixing gain in media with third-order nonlinearities. In spite of other competing χ(3) effects such as phase modulation, bipartite and tripartite entanglement is predicted above threshold. These findings are relevant for recent implementations of complementary metal-oxide-semiconductor (CMOS)-compatible on-chip OPOs.

The X-like shaped spatiotemporal structure of the biphoton entangled state in a cold two-level atomic ensemble

We study the spatiotemporal structure of the biphoton entangled state generated by the four-wave mixing (FWM) process in a cold two-level atomic ensemble. We analyze, for the first time, the X-like shaped structure of the biphoton entangled state and the geometry of the biphoton correlation for different lengths and densities of the cold atomic ensemble. The propagation equations of the photon pairs generated from FWM process are derived in a spatiotemporal framework. By means of the input-output relations of the propagation equations, the biphoton amplitude function is obtained in a spatiotemporal domain. In the given frequency range, the biphoton amplitude displays an X-like shaped geometry, nonfactorizable in the space-time domain. Such an X-like shaped spatiotemporal structure is caused by the phase matching and the FWM gain. The former leads to the X-like shaped envelope of the biphoton correlation, while the latter gives rise to the oscillations around the X-like shaped envelope.

Optically induced transparency in a micro-cavity.

Electromagnetically induced transparency has the unique ability to optically control transparency windows with low light in atomic systems. However, its practical applications in quantum physics and information science are limited due to rigid experimental requirements. Here we demonstrate a new mechanism of optically induced transparency in a micro-cavity by introducing a four-wave mixing gain to nonlinearly couple two separated resonances of the micro-cavity in an ambient environment. A signature Fano-like resonance was observed owing to the nonlinear interference of the two coupled resonances. Moreover, we show that the unidirectional gain of the four-wave mixing can lead to the remarkable effect of non-reciprocal transmission at the transparency windows. Optically induced transparency may offer a unique platform for a compact, integrated solution to all-optical and quantum information.

Classical-to-quantum transition with broadband four-wave mixing.

A key question of quantum optics is how nonclassical biphoton correlations at low power evolve into classical coherence at high power. Direct observation of the crossover from quantum to classical behavior is desirable, but difficult due to the lack of adequate experimental techniques that cover the ultrawide dynamic range in photon flux from the single photon regime to the classical level. We investigate biphoton correlations within the spectrum of light generated by broadband four-wave mixing over a large dynamic range of ∼80 dB in photon flux across the classical-to-quantum transition using a two-photon interference effect that distinguishes between classical and quantum behavior. We explore the quantum-classical nature of the light by observing the interference contrast dependence on internal loss and demonstrate quantum collapse and revival of the interference when the four-wave mixing gain in the fiber becomes imaginary.

Wavelength conversion and parametric amplification of optical pulses via quasi-phase-matched four-wave mixing in long-period Bragg silicon waveguides.

We present a theoretical analysis supported by comprehensive numerical simulations of quasi-phase-matched four-wave mixing (FWM) of ultrashort optical pulses that propagate in weakly width-modulated silicon photonic nanowire gratings. Our study reveals that, by properly designing the optical waveguide such that the interacting pulses copropagate with the same group velocity, a conversion efficiency enhancement of more than 15 dB, as compared to a uniform waveguide, can readily be achieved. We also analyze the dependence of the conversion efficiency and FWM gain on the pulse width, time delay, walk-off parameter, and grating modulation depth.

Quasi-Phase-Matching of Four-Wave-Mixing-Based Wavelength Conversion by Phase-Mismatch Switching

We propose a novel quasi-phase-matching scheme for achieving efficient four-wave-mixing (FWM)-based wavelength conversion in the presence of a large phase-mismatch. The scheme is based on respectively increasing and decreasing the propagation lengths over which there is FWM gain and FWM loss by switching between two different phase-mismatch values. We discuss how such a phase-mismatch switching (PMS) approach can be optimized for wavelength conversion and show that it can be realized in silicon-on-insulator strip waveguides by switching adiabatically between two waveguide widths along the propagation path. By means of numerical simulations we demonstrate that, for a pump wavelength of 1550 nm, PMS wavelength converters can enable efficient conversion (> -23 dB) around a target signal wavelength situated anywhere in the entire near-infrared wavelength domain of 1300-1900 nm.

All-Optical Highly Sensitive Chromatic Dispersion Monitoring Method Utilizing Phase-Matched Four-Wave Mixing

This letter represents a highly sensitive all-optical chromatic dispersion (CD) monitoring method utilizing phase-matched four-wave mixing (FWM) in highly nonlinear optical fibers (HNLFs). The monitoring ability arises from the exponential FWM gain which provides an exponential power transfer function (PTF) mapping the CD experienced by the signals onto the average power of the output idler wave. Our method is simple and much more sensitive compared to the other PTF-based monitoring methods proposed before. The sensitivity enhancement is important for highly accurate dispersion compensation and makes the method effective for signals with high duty cycles. Furthermore, by tailoring the phase-matched wavelength range our method can be used to monitor CD in a wavelength-division-multiplexing (WDM) network.

Ultralow-Power Four-Wave Mixing with Rb in a Hollow-Core Photonic Band-Gap Fiber

We demonstrate extremely efficient four-wave mixing with gains greater than 100 at microwatt pump powers and signal-to-idler conversion of 50% in Rb vapor confined to a hollow-core photonic band-gap fiber. We present a theoretical model that demonstrates such efficiency is consistent with the dimensions of the fiber and the optical depths attained. This is, to our knowledge, the largest four-wave mixing gain observed at such low total pump powers and the first demonstrated example of four-wave mixing in an alkali-metal vapor system with a large (approximately 30 MHz) ground state decoherence rate.

Back-seeding of higher order gain processes in picosecond supercontinuum generation

In photonic crystal fibers with closely spaced zero dispersion wavelengths it is possible to have two pairs of four-wave mixing (FWM) gain peaks. Here, we demonstrate both numerically and experimentally how the outer four-wave mixing gain peaks can be used to produce a strong amplification peak in a picosecond supercontinuum. The method involves feeding back part of the output light of a SC source and time matching it with the pump light. In this way it is possible to produce a gain of over 20 dB near the FWM gain wavelengths.

Nanoengineering of photonic crystal fibers for supercontinuum spectral shaping

Supercontinuum generation using picosecond pulses pumped into cobweb photonic crystal fibers is investigated. Dispersion profiles are calculated for several fiber designs and used to analytically investigate the influence of the fiber structural parameters (core size and wall thickness) on the location of the Stokes and anti-Stokes bands and gain bandwidth. An analysis shows that the Raman effect is responsible for reducing the four-wave mixing gain and a slight reduction in the corresponding frequency shift from the pump, when the frequency shift is much larger than the Raman shift. Using numerical simulations we find that four-wave mixing is the dominant physical mechanism for the pumping scheme considered, and that there is a trade-off between the spectral width and the spectral flatness of the supercontinuum. The balance of this trade-off is determined by nanometer-scale design of the fiber structural parameters. It is also shown that the relatively high loss of the nonlinear fiber does not significantly affect the supercontinuum generation.

Amplification of broadband noise pumped by two lasers in optical fibers

A theoretical and experimental investigation of catastrophic amplification of broadband noise in optical fibers near the zero-dispersion frequency (ν0) pumped by two lasers with frequencies that are symmetrically tuned relative to ν0 is presented. The effect is due to a four-wave mixing (FWM) process, phase matched up to third-order dispersion, between the spectral components of noise and the lasers. We observed a FWM gain of 16 dB (10-dB net gain) over a 22-nm bandwidth (limited by fourth-order dispersion) for 18-dBm power lasers at ±1 THz (8 nm) from ν0 in a 25-km-long dispersion-shifted fiber. A simple analytical model is proposed that will permit us to investigate this effect numerically in amplified links with concatenated amplifiers and consider random fluctuations of ν0 along the fiber.

Sensitive detection of sodium in a flame using parametric four-wave mixing and seeded parametric four-wave mixing

Two-photon resonant parametric four-wave mixing and a newly developed variant called seeded parametric four-wave mixing are used to detect trace quantities of sodium in a flame. Both techniques are simple, requiring only a single laser to generate a signal beam at a different wavelength which propagates collinearly with the pump beam, allowing efficient signal recovery. A comparison of the two techniques reveals that seeded parametric four-wave mixing is more than two orders of magnitude more sensitive than parametric four-wave mixing, with an estimated detection sensitivity of 5 x 10(9) atoms/cm(3). Seeded parametric four-wave mixing is achieved by cascading two parametric four-wave mixing media such that one of the parametric fields generated in the first high-density medium is then used to seed the same four-wave mixing process in a second medium in order to increase the four-wave mixing gain. The behavior of this seeded parametric four-wave mixing is described using semiclassical perturbation theory. A simplified small-signal theory is found to model most of the data satisfactorily. However, an anomalous saturationlike behavior is observed in the large signal regime. The full perturbation treatment, which includes the competition between two different four-wave mixing processes coupled via the signal field, accounts for this apparently anomalous behavior.

Active optical pulse compression with a gain of 29.0 dB by using four-wave mixing in an optical fiber

The four-wave mixing gain in an optical fiber strongly depends on the nonlinear phase mismatch when the pump power itself causes a nonlinear index change. The peak of the pump pulse has a much higher gain than its wings, and so this process can be used to obtain efficient pulse compression. A 93-ps signal pulse at 1569.9 nm is compressed to as short as 20 ps with a gain of 29.0 dB. The wavelength-converted signal at 1559.9 nm is simultaneously compressed to 21 ps and amplified by 28.9 dB as compared with the original signal.

Nearly-degenerate frequency technique for simultaneous measurement of n(2) and α(2), and four-wave mixing gain coefficients in waveguides

We describe an experimental technique that allows the simultaneous measurement of the nonlinear refractive index n (2) and the nonlinear absorption coefficient α (2) in waveguides. With minor modifications in the experimental setup, the four-wave mixing gain coefficient can also be measured. Measurements are demonstrated in AlGaAs waveguides.

Scale factor and optical bias in a ring four-wave mixing gyro

The expression of the beat frequency between the counterpropagating beams in a ring four-wave mixing oscillator is determined. In the case where the four-wave mixing gain occurs in a collisionally-broadened vapor, a more complete expression of the variation of the scale factor versus the buffer gas pressure is presented. The bias associated with purely radiative effects (three-photon scattering) is also considered. It is shown that these calculations can explain preceeding experimental observations and put very severe constraints on the quality of the pump lasers to obtain a reliable gyro.