Nonlinear Mixing Process Research Articles

Broadband quasi-phase-matching in dispersion-engineered all-optically poled silicon nitride waveguides

Quasi-phase-matching (QPM) has become one of the most common approaches for increasing the efficiency of nonlinear three-wave mixing processes in integrated photonic circuits. Here, we provide a study of dispersion engineering of QPM second-harmonic (SH) generation in stoichiometric silicon nitride ( Si 3 N 4 ) waveguides. We apply waveguide design and lithographic control in combination with the all-optical poling technique to study the QPM properties and shape the waveguide dispersion for broadband spectral conversion efficiency inside Si 3 N 4 waveguides. By meeting the requirements for maximal bandwidth of the conversion efficiency spectrum, we demonstrate that group-velocity matching of the pump and SH is simultaneously satisfied, resulting in efficient SH generation from ultrashort optical pulses. The latter is employed for retrieving a carrier-envelope-offset frequency of a frequency comb by using an f − 2 f interferometric technique, where supercontinuum and SH of a femtosecond pulse are generated in Si 3 N 4 waveguides. Finally, we show that the waveguide dispersion determines the QPM wavelength variation magnitude and sign due to the thermo-optic effect.

PT -symmetry-breaking-enhanced cavity optomechanical magnetometry

$\mathcal{PT}$-symmetry-breaking enhanced cavity optomechanical magnetometer is proposed, which is achieved by monitoring the change of intensity of a nonlinear four-wave mixing (FWM) process in a gain-cavity-assisted cavity optomechanical system (COMS). Compared with the traditional single loss COMS, the FWM intensity can be enhanced by two orders of magnitude when the gain-cavity-assisted COMS operates at the $\mathcal{PT}$-symmetry-breaking phase. Meanwhile, the sensitivity of magnetic field sensing can be increased from $10^{-9}$T to $10^{-11}$T. This originally comes from the fact that the effective detuning and decay of loss-cavity can be effectively modified in the $\mathcal{PT}$-symmetry-breaking phase. Our work shows that an ultrahigh-sensitivity magnetometer can be achieved in the $\mathcal{PT}$-symmetry-breaking COMS, which will have wide applications in the field of quantum sensing.

Up-Conversion Sensing of 2D Spatially-Modulated Infrared Information-Carrying Beams with Si-Based Cameras.

Up-conversion sensing based on optical heterodyning of an IR (infrared) image with a local oscillator laser wave in a nonlinear optical sum-frequency mixing (SFM) process is a practical solution to circumvent some limitations of IR image sensors in terms of signal-to-noise ratio, speed, resolution, or cooling needs in some demanding applications. In this way, the spectral content of an IR image can become spectrally shifted to the visible/near infrared (VIS/NWIR) and then detected with silicon focal plane arrayed sensors (Si-FPA), such as CCD/CMOS (charge-coupled and complementary metal-oxide-semiconductor devices). This work is an extension of a previous study where we recently introduced this technique in the context of optical communications, in particular in FSOC (free-space optical communications). Herein, we present an image up-conversion system based on a 1064 nm Nd3+: YVO4 solid-state laser with a KTP (potassium titanyl phosphate) nonlinear crystal located intra-cavity where a laser beam at 1550 nm 2D spatially-modulated with a binary Quick Response (QR) code is mixed, giving an up-converted code image at 631 nm that is detected with an Si-based camera. The underlying technology allows for the extension of other IR spectral allocations, construction of compact receivers at low cost, and provides a natural way for increased protection against eavesdropping.

The dynamics of coherent modes of gradient drift instabilities in a small magnetron discharge plasma

We report on the dynamic behavior of gradient-driven drift waves in a strongly obstructed magnetron discharge. The magnetron has a magnetic topology that results in a toroidal plasma within the gap and supports the development of very coherent modes of rotating plasma structures. The modes and their rotation are present over a wide range of conditions, and the rotation is retrograde to the usual externally imposed E×B direction. This feature seems to be unique to this device and is attributed to a field reversal due to the strong anode-directed electron diffusion that arises from large axial plasma density gradients. A multi-fluid model is proposed, and a Fourier analysis of the linearized equations results in the identification of conditions that support the growth of these instabilities and their transitions across mode symmetries, controlled experimentally by varying the discharge voltage. The model also provides insight on the possible mechanism driving cross-field particle transport. Experiments are carried out with a segmented anode to confirm the localized current flow concomitant with the presence of a coherent structure. These segment currents together with high speed videography unambiguously confirm the direction of plasma rotation and reveal the existence of a stochastic regime between voltage-controlled mode transitions. An analysis of the segment currents in this regime indicates that the lower frequency state decays into a spectrum of coherent higher frequency states that exhibit features consistent with a three-wave nonlinear parametric mixing process.

Adiabatic geometric phase in fully nonlinear three-wave mixing

In a nonlinear three-wave mixing process, the interacting waves can accumulate an adiabatic geometric phase (AGP) if the nonlinear coefficient of the crystal is modulated in a proper manner along the nonlinear crystal. This concept was studied so far only for the case in which the pump wave is much stronger than the two other waves, hence can be assumed to be constant. Here we extend this analysis for the fully nonlinear process, in which all three waves can be depleted and we show that the sign and magnitude of the AGP can be controlled by the period, phase and duty cycle of the nonlinear modulation pattern. In this fully nonlinear interaction, all the states of the system can be mapped onto a closed surface. Specifically, we study a process in which the eigenstate of the system follows a circular rotation on the surface. Our analysis reveals that the AGP equals to the difference between the total phase accumulated along the circular trajectory and that along its vertical projection, which is universal for the undepleted (linear) and depleted (nonlinear) cases. Moreover, the analysis reveals that the AGPs in the processes of sum-frequency generation and difference-frequency generation have opposite chirality. Finally, we utilize the AGP in the fully nonlinear case for splitting the beam into different diffraction orders in the far field.

Experimental Implementation of a Raman-Assisted Eight-Wave Mixing Process

Engineering higher-order nonlinear interactions is vital in autonomous protection of quantum systems against errors. Such interactions are often not directly available, though, or are slow compared to error rates of the system. The authors present a nonlinear eight-wave mixing process that exchanges four photons of a harmonic oscillator with two excitations of a transmon-qubit mode and two pump photons, by combining more accessible lower-order interactions via a sort of Raman transition. Surprisingly, this technique produces a stronger interaction than a six-wave mixing process in the same system. This eight-wave mixing process is expected to become a key component of autonomous continuous-variable quantum error correction.

All-optical field-free three-dimensional orientation of asymmetric-top molecules

Orientation and alignment of molecules by ultrashort laser pulses is crucial for a variety of applications and has long been of interest in physics and chemistry, with the special emphasis on stereodynamics in chemical reactions and molecular orbitals imaging. As compared to the laser-induced molecular alignment, which has been extensively studied and demonstrated, achieving molecular orientation is a much more challenging task, especially in the case of asymmetric-top molecules. Here, we report the experimental demonstration of all-optical field-free three-dimensional orientation of asymmetric-top molecules by means of phase-locked cross-polarized two-color laser pulse. This approach is based on nonlinear optical mixing process caused by the off-diagonal elements of the molecular hyperpolarizability tensor. It is demonstrated on SO2 molecules and is applicable to a variety of complex nonlinear molecules.

High-Quality-Factor AlGaAs-on-Sapphire Microring Resonators

We realize an AlGaAs-on-sapphire platform through Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -assisted direct wafer bonding and substrate removal processes. The direct wafer bonding process is optimized concerning the intermediate layer deposition and annealing temperature to obtain a high bonding strength between the AlGaAs and sapphire wafers. High quality-factor (Q) microring resonators are fabricated using electron-beam lithography in which the charging effect is mitigated by applying a thin aluminum layer, and a smooth pattern sidewall definition is obtained using a multi-pass (exposure) process. We achieve an intrinsic Q of up to ~460,000 which is the highest Q for AlGaAs microring resonators. Taking advantage of such high Q resonators, we demonstrate an ultra-efficient nonlinear four-wave mixing process in this platform and obtain a conversion efficiency of -19.8 dB with continuous-wave pumping at a power level of 380 μW. We also investigate the thermal resonance shift of microring resonators with different substrate layouts and observe superior temperature stability for devices in the AlGaAs-on-sapphire platform. The realization of the AlGaAson-sapphire platform also opens new prospects for AlGaAs devices in nonlinear applications in the mid-infrared wavelength range.

Generation of quadripartite entanglement from a hybrid scheme with a four-wave mixing process and linear beam splitters

We theoretically propose a hybrid scheme with nonlinear four-wave mixing process and linear beam splitters to generate continuous-variable quadripartite entanglement. To expose the entanglement properties of the generated state, the coupling strength matrix is derived to reveal the interactions of the resulting modes at first. The generated state is verified to be a H-graph state with a non-full rank coupling strength matrix by using graphical calculus for Gaussian pure states. Then based on the eigenmodes for the generated state, we find that the introduction of beam splitters does not alter the deduced eigenmodes of the nonlinear four-wave mixing process, and only contributes to generate quadripartite entanglement. In the end, we quantitatively investigate the internal entanglement structure of this scheme. Our work paves the way to generate quadripartite entanglement from a hybrid scheme with nonlinear four-wave mixing process and linear beam splitters.

Waveband-Shift-Free Optical Phase Conjugator for Spectrally Efficient Fiber Nonlinearity Mitigation

We discuss a novel broadband, polarization-insensitive, and wavelength-shift-free optical phase conjugator (OPC). In the OPC scheme, the original input signal is inherently suppressed in a polarization-diversity loop setup. This allows for spectrally efficient, wavelength-(band)-shift-free generation of phase-conjugated idlers over a continuous operating band. The idlers are generated using four-wave mixing in nonlinear fibers using out-of-band, orthogonally polarized pump waves. The saturation characteristics of the exploited nonlinear mixing process as well as the crosstalk characteristics of the OPC diversity loop scheme are investigated. The OPC subsystem is finally utilized for fiber nonlinearity mitigation by midlink spectral inversion in 800-km transmission experiments over dispersion-managed fiber spans with lumped amplification by Erbium-doped fiber amplifiers. Q 2-factor improvements of up to 0.7 dB are obtained in transmission of a 300-GHz wide 1.6 Tb/s super channel consisting of eight 200 Gb/s polarization division multiplexed 16-ary quadrature amplitude modulation subchannels.

Hybrid interferometer with nonlinear four-wave mixing process and linear beam splitter.

Optical interferometer has played an important role in optics. Up to now, many kinds of interferometers have been realized and found their applications. In this letter, we experimentally construct an interferometer by using parametric amplifier as a wave splitter and beam splitter as a wave combiner. We make measurements of interference fringes and explore the relationships between the interference visibility of the interferometer and various system parameters, such as the gain of the parametric amplifier, the one-photon detuning and the temperature of the Rb-85 vapor cell.

Near-resonant four-wave mixing of attosecond extreme-ultraviolet pulses with near-infrared pulses in neon: Detection of electronic coherences

Coherent narrow-band extreme-ultraviolet (EUV) light is generated by a near-resonant four-wave mixing (FWM) process between attosecond pulse trains and near-infrared pulses in neon gas. The near-resonant FWM process involves one vacuum-ultraviolet (VUV) photon and two near-infrared (NIR) photons and produces new higher-energy frequency components corresponding to the $ns/nd$ to ground-state $(2{s}^{2}2{p}^{6})$ transitions in the neon atom. The EUV emission exhibits small angular divergence (2 mrad) and monotonically increasing intensity over a pressure range of 0.5--16 Torr, suggesting phase matching in the production of the narrow-bandwidth coherent EUV light. In addition, time-resolved scans of the NIR nonlinear mixing process reveal the detection of a persistent, ultrafast bound electronic wave packet based on a coherent superposition initiated by the VUV pulse in the neon atoms. This FWM process using attosecond pulses offers a means for both efficient narrow-band EUV source generation and time-resolved investigations of ultrafast dynamics.

Nonlinear mixing of Nd:YAG lasers; harmonic and sum frequency generation

Nonlinear optical materials give rise to a number of phenomena under high intensity of the incident electric field, with nonlinear mixing being a prominent example. This article discusses such nonlinear mixing processes of Nd:YAG lasers in BBO outside the more common harmonics of the 1.064 μm transition (0.532 μm, 0.366 μm and 0.266 μm). In particular, harmonics of the less common 0.946 μm transition (0.473 μm and 0.315 μm) as well as sum frequency of the 1.052 and 1.319 μm transitions (0.585 μm) and its second harmonic (0.293 μm) is discussed.

Unique Vibrational Features as a Direct Probe of Specific Antigen-Antibody Recognition at the Surface of a Solid-Supported Hybrid Lipid Bilayer.

Here, we demonstrate how sum frequency generation (SFG), a vibrational spectroscopy based on a nonlinear three-photon mixing process, may provide a direct and unique fingerprint of bio-recognition; This latter can be detected with an intrinsically discriminating unspecific adsorption, thanks to the high sensitivity of the second-order nonlinear optical (NLO) response to preferential molecular orientation and symmetry properties. As a proof of concept, we have detected the biological event at the solid/liquid interface of a model bio-active antigen platform, based on a solid-supported hybrid lipid bilayer (ss-HLB) of a 2,4-dinitrophenyl (DNP) lipid, towards a monoclonal mouse anti-DNP complementary antibody.

Simulation of Optical Microfiber Strain Sensors Based on Four-Wave Mixing

We investigate the performance of a microfiber strain sensor based on the nonlinear four-wave mixing process. This simple sensor of only an elliptical microfiber has considerable advantages, such as sensing directly by microfiber inherent nonlinearity in the telecommunication range and being compatible with the existing fiber network. Dispersion, nonlinearity, and strain effect are analyzed to find optimum sensing performance. The numerical simulations reveal that the strain can cause a marked wavelength shift of the signal wave. The wavelength shift range can be more than 74 nm within a reasonable strain range. To the ultimate strain range of 30 $\text{m}\varepsilon $ , the average strain sensitivity of 2.46 pm/ $\mu \varepsilon $ can be obtained when the pump wavelength is 1550 nm and the peak power is 100 W. In addition to the range of 5 $\text{m}\varepsilon $ , it could achieve 9.86 pm/ $\mu \varepsilon $ by optimizing the fiber size and highly birefringent characteristic. This strain sensor with high sensitivity, simple configuration, light, and portable performance has wide applications in mechanical detection and fault diagnosis and is of intensified interest for a great deal of wavelength selected devices in quantum information process.

Broadband second-harmonic phase-matching in dispersion engineered slot waveguides.

Parametric optical nonlinearities are usually weak and require both high optical field intensity and phase-matching. Micro/nanophotonics, with strong confinement of light in waveguides of nanometer-scale cross-sections, can provide high field intensity, but is still in need of a solution for phase-matching across a broad bandwidth. In this article, we show that mode-coupling in slot waveguides can engineer the waveguide modal dispersion, and with proper choice of materials, can achieve on-chip broadband second-harmonic phase-matching. A phase-matching bandwidth in the range of 220 nm at mid-infrared can occur for a hetero-slot waveguide consisting of aluminum nitride (AlN) and silicon nitride (SiN). With a high-nonlinearity polymer as cladding material, about 1.76 W(-1)cm(-2) of normalized conversion efficiency in second-harmonic-generation (SHG) and about 23 dB signal gain in degenerate optical parametric amplification (DOPA) can be achieved over a broad bandwidth. An asymmetric-slot waveguide configuration and a thermal tuning scheme are proposed to reduce the fabrication difficulty. This concept of broadband second-harmonic phase-matching can be extended to other nonlinear optical frequency mixing processes, thus expanding the scope of on-chip nonlinear optical applications.

Revealing carrier-envelope phase through frequency mixing and interference in frequency resolved optical gating.

We demonstrate that full temporal characterisation of few-cycle electromagnetic pulses, including retrieval of the carrier envelope phase (CEP), can be directly obtained from Frequency Resolved Optical Gating (FROG) techniques in which the interference between non-linear frequency mixing processes is resolved. We derive a framework for this scheme, defined Real Domain FROG (ReD-FROG), for the cases of interference between sum and difference frequency components and between fundamental and sum / difference frequency components. A successful numerical demonstration of ReD-FROG as applied to the case of a self-referenced measurement is provided. A proof-of-principle experiment is performed in which the CEP of a single-cycle THz pulse is accurately obtained and demonstrates the possibility for THz detection beyond optical probe duration limitations inherent to electro-optic sampling.

Electromagnetically induced transparency-assisted four-wave mixing process in the diamond-type four-level atomic system

With electromagnetically induced transparency (EIT)-assisted configuration, we study the third-order nonlinear four-wave mixing (FWM) process in a diamond-type four-level atomic system both theoretically and experimentally. Following the proposal by the recent study (Willis et al., 2009), we introduce EIT contribution to the theoretical model which will enhance the conversion efficiency of the nonlinear process and narrow the linewidth of the FWM signal. By means of the coherent EIT effect, we get higher conversion efficiency at lower power level of incident beam in such atomic system. Compare to our previous models, the conversion efficiency in such diamond-type atomic system is much smaller which needs higher threshold temperature. In addition, the frequency dependences on incident beams reveal that the dipole transition of one-photon and two-photon processes affect this nonlinear process.

Cascaded Four-Wave Mixing in Nonlinear Yb-Doped Fiber Amplifiers

We experimentally demonstrated high-power yellow and near-infrared laser emissions by cascaded four-wave mixing in a nonlinear Yb-doped multimode fiber amplifier, generating 2.0 W at 830 nm and 0.35 W at 594 nm. Moreover, multiple cascaded four-wave mixing processes which generated supercontinuum covering more than four octaves from 398 to 1700 nm was also investigated in Q-switched mode-locking regime. The group velocity matching for pump and parametric waves as well as multimode fiber amplification promoted the cascaded nonlinear frequency mixing processes.

Multiwavelength generation in a random distributed feedback fiber laser using an all fiber Lyot filter

Multiwavelength lasing in the random distributed feedback fiber laser is demonstrated by employing an all fiber Lyot filter. Stable multiwavelength generation is obtained, with each line exhibiting sub-nanometer line-widths. A flat power distribution over multiple lines is obtained, which indicates that the power between lines is redistributed in nonlinear mixing processes. The multiwavelength generation is observed both in first and second Stokes waves.