Four-wave Mixing Research Articles

Extracting doubly excited state lifetimes in helium directly in the time domain with attosecond noncollinear four-wave-mixing spectroscopy

The helium atom, with one nucleus and two electrons, is a prototypical system to study quantum many-body dynamics. Doubly excited states, or quantum states in which both electrons are excited by one photon, showcase electronic-correlation mediated effects. In this paper, the natural lifetimes of the doubly excited 1Po2snp Rydberg series and the 1Se2p2 dark state in helium in the 60–65 eV region are measured directly in the time domain with extreme-ultraviolet/near-infrared noncollinear attosecond four-wave-mixing (FWM) spectroscopy. The measured lifetimes agree with lifetimes deduced from spectral linewidths and theoretical predictions, and the roles of specific decay mechanisms are considered. While complex spectral line shapes in the form of Fano resonances are common in absorption spectroscopy of autoionizing states, the background-free and thus homodyned character of noncollinear FWM results exclusively in Lorentzian spectral features in the absence of strong-field effects. The onset of strong-field effects that would affect the extraction of accurate natural lifetimes in helium by FWM is determined to be approximately 0.3 Rabi cycles. This study provides a systematic understanding of the FWM parameters necessary to enable accurate lifetime extractions, which can be utilized in more complex quantum systems in the future. Published by the American Physical Society 2024

Turning four-wave mixing on and off in elliptically birefringent fibers via narrow frequency detuning

Controlling four-wave mixing (FWM) is vital for several applications, including fiber optical communication, optical signal processing, optical amplification, and frequency generation. This paper presents a novel, to our knowledge, approach to control unidirectional FWM in elliptically birefringent fibers. By leveraging the frequency-dependent polarization eigenmodes of these fibers and detuning the optical frequency of one of the pump fields by a few megahertz, we can turn the FWM interaction on and off, thus controlling the generation of signal and idler fields. Moreover, this approach allows us to turn off the FWM interaction at any desired frequency, enabling all-optical switching and narrowband filtering applications.

Tunable silicon integrated quantum light source with on-chip FSR-free filters

In this work, we design and fabricate a telecom band quantum light source (QLS) on a silicon photonic chip, which integrates a piece of a long silicon waveguide as the nonlinear medium for spontaneous four-wave mixing (SFWM) and five narrow FSR-free bandpass filters based on a grating-assisted contra-directional coupler (GACDC). Two optical filtering functions of the silicon integrated QLS have been demonstrated. First, the QLS supports two tunable outputs of photon pair generations by four GACDC filters. A wavelength tunable range of 6 nm is demonstrated. Second, one GACDC bandpass filter is designed as an on-chip pump filter before the silicon waveguide. The performances of the QLSs with and without the on-chip pump filter are measured and compared. It shows that the on-chip pump filter has the effect to enhance the performance of the QLS by suppressing the Raman noise photons generated when a pump light propagated in optical fibers before it is injected into the chip. These results show that FSR-free filters would play important roles in developing silicon integrated QLSs.

Coherent control of dressing interaction of sequential-doubly-dressed four-wave mixing

Abstract We investigate the coherent control of dressing interaction in four-wave mixing (FWM) in a Y-type four-level atomic system based on the dressed states theory. We study the density matrix equation acted by two dressing fields simultaneously governing FWM signal intensity and the eigenvalues under the dressed state formalism. It is shown that the peak position and intensity of Autler–Townes splitting both originate from the dressing interaction as the detuning of the probe field is scanned. Moreover, it is observed that the interaction could be controlled by the dressing fields. Such flexibly controlled nonlinear signal has potential applications in optical communication and quantum information processing.

Four-Wave Mixing Bragg Scattering for small frequency shift from Silicon Coupled Microrings

Abstract Frequency conversion is pivotal in nonlinear optics and quantum optics for manipulating and translating light signals across different wavelength regimes. Achieving frequency conversion between two light beams with small frequency interval is a central challenge. In this work, we design a pair of coupled silicon microrings wherein coupled-induced mode-splitting exists to achieve a small frequency shift by the process of four-wavemixing Bragg scattering. As an example, the signal can be up or down converted to the idler which is 15.5 GHz spaced when two pumps align with another pair of splitted resonances. The results unveil the potential of coupled microring resonators for small interval frequency conversion in the fields of high-fidelity all-optical signal processing quantum frequency interface.

Single and entangled photon pair generation using atomic vapors for quantum communication applications

Significant progress has been achieved in leveraging atomic systems for the effective operation of quantum networks, which are essential for secure and long-distance quantum communication protocols. The key elements of such networks are quantum nodes that can store or generate both single and entangled photon pairs. The primary mechanisms leading to the production of single and entangled photon pairs revolve around established techniques such as parametric down-conversion, four-wave mixing, and stimulated Raman scattering. In contrast to solid-state platforms, atomic platforms offer a more controlled approach to the generation of single and entangled photon pairs, owing to the progress made in atom manipulation techniques such as trapping, cooling, and precise excitation schemes facilitated by the use of lasers. This review article delves into the techniques implemented for generating single and entangled photon pairs in atomic platforms, starting with a detailed discussion of the fundamental concepts associated with single and entangled photons and their characterization techniques. The aim is to evaluate the strengths and limitations of these methodologies and offer insights into potential applications. Additionally, the article will review the extent to which these atomic-based systems have been integrated into operational quantum communication networks.

Improving Optical Transmission Performance in Multi-Channel Networks Utilizing Convolutional Neural Network-Enabled Digital Signal Processing to Mitigate Four-Wave Mixing

ABSTRACT The rapid growth of online services and the global transition to digital platforms, accelerated by the COVID-19 pandemic and the emergence of AI-based services, have led to a surge in demand for high-capacity optical communication networks (OCNs). However, this transition exacerbates the issue of fiber nonlinearity, notably four-wave mixing (FWM), which can significantly impact signal integrity in long-distance OCN transmissions with multiple channels. To address this challenge, this paper presents a novel approach leveraging a convolutional neural network (CNN)-based digital signal processing (DSP) model to mitigate the nonlinear effects of FWM on signal quality. The proposed CNN model, designed with three convolutional layers and trained on a comprehensive dataset of simulated OCN transmissions, demonstrates significant improvement in reducing nonlinear distortions caused by FWM. Our method is compared with traditional compensation techniques, such as digital back-propagation and Volterra series-based equalizers, showing a reduction in power penalties by 1 dB and an enhancement in the power budget by 2 dB. Simulation results indicate that the bit error rates (BERs) remain consistently below the critical threshold of 10−9 across various transmission distances, outperforming conventional methods. The simulation analysis, conducted on a 100 km multi-channel OCN testbed, confirms the CNN equalizer’s efficacy in reducing crosstalk and improving power efficiency, with a demonstrated 15% reduction in required launch power. Moreover, the analytical models used to evaluate the CNN-based DSP model show high accuracy in predicting performance, underscoring the model’s capability to achieve high-quality transmission with lower power requirements. These findings advocate for the integration of our CNN-based DSP model into OCNs, offering a fruitful solution for managing multi-channel, long-distance, and high-data-rate optical transmissions in real-world systems.

Four-wave mixing in silicon nanophotonic waveguides and microring resonators: influence of two-photon absorption

Four-wave mixing in silicon nanophotonic waveguides and microring resonators: influence of two-photon absorption

Superspontaneous four-wave mixing in a sequence of lossy ring resonators

Superspontaneous four-wave mixing in a sequence of lossy ring resonators

Wave patterns of the coupled nonlinear Schrödinger equations in photonic crystal fibers with four-wave mixing

Abstract In this paper, we examine the behavior of modulation instability within photonic crystals. The model employed is the coherent coupled nonlinear Schrödinger equation, incorporating weak birefringence and four-wave mixing, which arises at the edge of the optical mode. The linear analysis is used to derive the modulation instability spectrum. Throughout the modulation instability spectrum, we identify both stable and unstable modes, thereby confirming the breakdown of the plane wave. For certain four-wave mixing parameters, the amplitude of the modulation instability spectrum and its bandwidths expand, creating an opening for localized structures to emerge. Another aspect of this study has been demonstrated in normal and anomalous dispersion regimes where an increasing initial amplitude of the plane wave is fulfilled. Specifically, numerical simulations highlight the occurrence of Benjamin-Feir instability, where wave patterns emerge under the influence of four-wave mixing. Additionally, solitonic waves are generated, demonstrating the presence of Akhmediev breathers and other modulated structures, confirming that photonic crystals with four-wave mixing are conducive to these formations. The findings from this study could inform future research in the development of nonlinear photonic waveguides.

Nonlinear dispersion of backward-wave four-wave mixing in a photorefractive semiconductor and its effect on group velocity

Photorefractive backward-wave four-wave mixing may be configured for the amplification of the phase conjugate output and the attenuation of the transmitted output. The nondegenerate-in-frequency interaction is studied in such a configuration, realized in a semiconductor CdTe crystal. The spectra measured at different outputs show the gain and attenuation resonances. The preliminary study of optical pulse propagation demonstrates that, due to different nonlinear dispersions at different outputs of the selected wave mixing configuration, a slowing down of light is observed at the phase conjugate output, while an acceleration of light is detected at the transmitted output for the same input pulse at the same interaction.

Closed-form formula for unequal channel allocation to reduce FWM crosstalk in DWDM long-haul networks

Dense wavelength division multiplexing (DWDM) is considered as a mainstream solution for 5G optical transmission networks to confront increasing bandwidth demand. In such a dense multiwavelength system, the four wave mixing (FWM) non-linear effect limits the achievable transmission distance and channel capacity. For this reason, and to the best of our knowledge, a new unequal channel allocation (UCA) has been introduced in this paper based on new closed-form equations to reduce the FWM crosstalk in the DWDM optical long-haul network. The proposed channel allocation has been investigated based on several design parameters that affect FWM nonlinear crosstalk, such as total transmission distance, channel frequency spacing, the number of WDM channels, and the input power per channel. The suggested technique has further been compared with a previous model proposed by other authors to prove the effectiveness of this work. The simulation results have been examined and validated by analysing the optical spectrum analyser and the power of the FWM spectral products. Results demonstrate the reliability and the efficiency of the developed method.

Multi-wavelength generation in UV and green bands through SRS and parametric processes in silica fibers.

We report on multi-wavelength generation through simultaneous second-order and third-order nonlinear parametric processes following cascaded stimulated Raman scattering (SRS) in silica fibers. The fiber system consists of a short standard step-index silica fiber and a microfiber tapered from it. When this system is pumped with a 130 ps laser at 1040 nm, multiple new wavelengths in the UV (340-370 nm) and green (507-547 nm) bands arise through four-wave mixing (FWM)/sum-frequency generation (SFG) from the pump and its Raman signals. The evolution of these wavelengths with pump power is demonstrated in detail. Matching of frequencies and propagation constants in the involved processes is verified. This work provides a compact and simple method of multi-wavelength generation with fibers.

Comparison of non-Hermitian three-dimensional quantization line shape in ion-doped microcrystals

In this paper, we studied the relationship between non-Hermitian quantization and line shape in ion-doped microcrystals. We depict the Eu3+: BiPO4 exhibited a broad line shape in contrast to Eu3+: NaYF4, and Dy3+: BiPO4. The line shape is controlled through angle quantization (constructive and destructive quantization) and phonon detuning effects. The Eu3+: BiPO4 and Eu3+: NaYF4 exhibits less sensitivity to line shape as compared to Dy3+: BiPO4. The more sensitivity of Dy3+: BiPO4 is supported by the presence of multiple levels, which disrupt the transition from destructive (out of phase de-phase rate Г) to constructive (in phase dressing Rabi frequency G) three-dimensional quantization. The line shape evolution from out of phase to in phase could be tuned by changing time gate position (the ratio of G and Г regulated largely) and time gate width (the ratio of G and Г regulated on a small scale). We observed that the line shape ratio in Dy3+: BiPO4 is significantly smallest (13.63 %) as compared to Eu3+: NaYF4 (61.29 %) and Eu3+: BiPO4 (85.18 %). Furthermore, the angle quantization affects the line shape evolution of fluorescence and Autler-Townes. However, spontaneous four-wave mixing line shape evolution can not be controlled by the angle quantization. Such results hold significant potential for applications in long band stop filter.

Dual-comb source with a reconfigurable repetition frequency difference using intracavity Brillouin lasers

A Brillouin-assisted 80-GHz-spaced dual-comb source with a reconfigurable repetition frequency difference ranging from 48 MHz to 1.486 GHz is demonstrated. Two pairs of dual-pump seeds with an interval offset produce the corresponding dual Brillouin lasers in two fiber loops, and then the Brillouin lasers give rise to dual combs via the cavity-enhanced cascaded four-wave mixing effect. The repetition frequency difference is determined by the interval offset of the dual-pump seeds, which is induced by the Brillouin frequency shift difference between different fibers in a frequency shifter. Each comb provides 22 lasing lines, and the central 10 lines in a 20-dB power deviation feature high optical signal-to-noise ratios exceeding 50 dB. The linewidths of the dual-comb beating signals are less than 300 Hz, and the absolute linewidths of the comb lines are around 1.5 kHz. The dual-comb source enables substantial repetition frequency differences from 48 MHz to 1.486 GHz by changing the pluggable fibers in the frequency shifter.

Improving phase sensitivity of a hybrid interferometer with the two-mode squeezed coherent state

We investigate the enhancement of phase sensitivity of a nonlinear-linear hybrid interferometer with the input of the two-mode squeezed coherent state (TMSCS). With the TMSCS produced by four-wave mixing, the quantum Cramér-Rao bounds (QCRB) can beat the Heisenberg limit (HL). Under the phase matched conditions, the optimal phase sensitivity with the balanced homodyne detection measurement can beat the HL and approach QCRB. The effects of internal and external losses on the measurement accuracy are also discussed. The results demonstrate that the scheme is robustness against to internal losses and this protocol can resist external detection loss which is up to 39%. Our results improve the performance of hybrid interferometers and this scheme can find important practical applications in quantum metrology.

Squeezing enhancement by suppression of noise through a resonant interferometric coupler

We propose an integrated resonant structure to enhance squeezing by dual-pump spontaneous four-wave mixing (SFWM) while simultaneously suppressing parametric noise due to parasitic processes. The structure relies on a resonant interferometric coupler that allows one to engineer the field enhancement on-demand in the spectral region of interest. We analyze the different configurations in which the structure can operate, and we calculate the generated squeezing. We show that our device can overcome the intrinsic squeezing limit of a single-ring resonator.

A Brief Look Into Nonlinear Optical Properties Of MXenes (M2X) Ti2C, Nb2C, And V2C Through Four Wave Mixing Generation In 2 µm Fiber Laser

Generation of four wave mixing (FWM) effect in MXenes with chemical ratio of M2X, particularly Ti2C, Nb2C, and V2C were reported in this work. The setup was operated at 2 µm wavelength region with tapered fiber as the material host. The experiment managed to show conversion efficiencies of −43.93 dB, −42.60 dB, and −41.20 dB and idlers’ SNR of 7.73 dB, 9.10 dB, and 9.80 dB for Ti2C, Nb2C, and V2C, respectively. The relation of nonlinear optical properties such as nonlinear absorption coefficient and nonlinear refractive index to FWM generation were explored. The result of the investigation successfully showed the relationship of third order nonlinear optical properties and FWM effect in the specified MXenes with comparisons.

Tracing the Background‐Suppressed Vibrational Decay Time of a Molecular Monolayer with Time‐Resolved Surface‐Enhanced Broadband Coherent Anti‐Stokes Raman Scattering

AbstractThe sensitivity of molecular spectroscopy based on surface‐enhanced coherent anti‐Stokes Raman scattering (SECARS) is limited by the spectrally overlapping background from nonresonant four‐wave mixing (FWM). While the SECARS signal is mediated by the molecular vibrational eigenstates and exhibits long lifetime (a few picoseconds), the FWM background stems from the instantaneous electronic polarization and decays rapidly with the vanishment of excitation. Therefore, CARS and FWM can be separated by time‐resolved CARS (trCARS) using ultrashort pulsed lasers. The broad spectral bandwidth also enables broadband CARS (BCARS) for simultaneous identification of multiple vibrational signatures. This work combines trCARS and BCARS with an optimized plasmonic system to demonstrate time‐resolved surface‐enhanced BCARS) and show its capability in obtaining background‐suppressed broadband vibrational spectra from a monolayer of 4‐Aminothiophenol (4‐ATP) molecules self‐assembled on a gold grating. The vibrational dephasing time of the ring‐breathing mode for the 4‐ATP monolayer on the gold grating (≈1.00 ± 0.17 ps) is significantly shortened compared to that for 4‐ATP powder on a glass substrate (2.10 ± 0.05 ps). This work presents an effective method to suppress FWM background and investigate the vibrational dynamics of molecules in the vicinity of plasmonic nanostructures.

Decoherence-induced formation of sub-poissonian entangled and steerable states of collective fields

The decoherence process has a tendency to yield the evolution of a pure state into a mixed one and to cause the quantum-to-classical transition by the coupling of a system of interest to the reservoir with infinitely many degrees of freedom. This is the major obstacle to the implementation of quantum computation and hence the realization of quantum computers. We propose a scheme to create unconditionally sub-Poissonian entangled and steerable states of the collective cavity field modes by use of the dissipation process. Based on the suitable choice of combination modes, the scheme uses the inherent, efficient and controllable two-mode squeezed vacuum reservoir coupled to the combination modes of concern rather than the original cavity modes in the two-level quantum beat laser. The decoherence is shown to pull the collective modes into the sub-Poissonian entangled and steerable states in the stationary regime, while the job of the dissipation of the individual cavity fields is to give rise to the degradation of the bipartite entanglement of the two individual modes and to inhibit the occurrence of the quantum steering from one cavity mode to the other. In particular for the case that the external driving field is close to the exact resonance with the atom, the collective fields are eventually prepared asymptotically in the stationary Einstein–Podolsky–Rosen state, while the two individual cavity modes are pulled into the vacuum states and reach steady state. The disappearance of the decoherence disables the nonclassical states of the collective modes, while the ignorance of the dissipation process of the cavity field modes guarantees the generation of the entanglement between the pair of individual modes. The decoherence-induced formation of a nonclassical source is ascribed to the four-wave mixing process together with the intrinsic amplitude and phase locking.