Phase Matching Control Research Articles

Bio-inspired wake tracking and phase matching of two diagonal flapping swimmers

Wake interaction provides hydrodynamic gain and flow-aided navigation in fish schools. The lateral spacing Ly and phase angle Φ relative to upstream wake are two important states for downstream swimmers. In this paper, the lateral wake tracking and phase matching of two diagonal flapping swimmers are studied through experiments. Bio-inspired differential pressure (DP) sensing on the downstream swimmer is adopted to capture the wake interaction features. Two DP sensing strategies, the symmetrical differential pressure (SDP) and leading edge differential pressure (LDP), are employed to capture the wake interaction features. SDP measures the pressure difference of two symmetrical ports on the two sides of the downstream swimmer, and LDP measures the pressure difference of leading edge port against the two side ports. One-dimensional convolutional neural networks (1D CNN) with a parallel structure are trained to decode wake interaction states (Ly and Φ) based on DP signals. The 1D CNN model is trained and tested offline and is used to estimate the wake interaction states online. Three demonstrations of online lateral wake tracking and phase matching control are carried out. Compared with SDP, LDP predicts Ly and Φ more accurately. It is found that the downstream wakes are more compact after control, which is consistent with high propulsive efficiency mode.

Optical-parametric oscillation in photonic-crystal ring resonators

By-design access to laser wavelength, especially with integrated photonics, is critical to advance quantum sensors, such as optical clocks and quantum-information systems, and open opportunities in optical communication. Semiconductor-laser gain provides exemplary efficiency and integration but merely in developed wavelength bands. Alternatively, nonlinear optics requires control of phase matching, but the principle of nonlinear conversion of a pump laser to a designed wavelength is extensible. We report on laser-wavelength access by versatile customization of optical-parametric oscillation (OPO) with a photonic-crystal ring resonator (PhCR). Leveraging the exquisite control of laser propagation provided by a photonic crystal in a traveling-wave ring resonator, we enable OPO generation across a wavelength range of 1234–2093 nm with a 1550-nm pump and 1016–1110 nm with a 1064-nm pump. Moreover, our platform offers pump-to-sideband conversion efficiency of > 10 % and negligible additive optical-frequency noise across the output range. From laser design to simulation of nonlinear dynamics, we use a Lugiato–Lefever framework that predicts the system characteristics, including bidirectional OPO generation in the PhCR and conversion efficiency in agreement with our observations. Our experiments introduce broadband lasers by design with PhCR OPOs, providing critical functionalities in integrated photonics.

Optical parametric amplifier pulse cleaning driven by aperiodic frequency converter

We demonstrate temporal shape improvement of a short laser pulse using chirped aperiodic nonlinear frequency converter within an optical parametric amplifier. The aperiodic converter generated walk-off free high spatial quality pulse with ∼40% efficiency second harmonic while preserving the pump bandwidth. A <300 fs idler pulse was generated, with ∼10 nm central wavelength tunability around 1053 nm by pump generation and phase matching control. A pronounced contrast pedestal suppression of up to 40 dB was observed within a few picoseconds range around the peak. Such pedestal suppression has good scalability potential to high energies.

Phase-matching control of high-order harmonics with circular Airy-Gaussian beams.

We investigate the phase-matching of the high harmonics (HHG) driven by the circular Airy-Gaussian beams (CAiGB), which abruptly auto-focus and subsequently propagate without diffraction. The results show that the harmonics corresponding to both short and long quantum paths can be well phase-matched after the focusing point of the CAiGB. Therefore, the effective interaction length of HHG for CAiGB is much longer than that for the conventional Gaussian beams with the same size of the waist. Our numerical simulations reveal that the harmonics continuously gain up to 1 cm of the propagation distance. This work provides a route to enhance the conversion efficiency of HHG by the coherent control of abrupt auto-focusing beams.

Intermodal frequency generation in silicon-rich silicon nitride waveguides

Dispersion engineering in optical waveguides allows applications relying on the precise control of phase matching conditions to be implemented. Although extremely effective over relatively narrow band spectral regions, dispersion control becomes increasingly challenging as the bandwidth of the process of interest increases. Phase matching can also be achieved by exploiting the propagation characteristics of waves exciting different spatial modes of the same waveguide. Phase matching control in this case relies on achieving very similar propagation characteristics across two, and even more, waveguide modes over the wavelengths of interest, which may be rather far from one another. We demonstrate here that broadband (>40 nm) four-wave mixing can be achieved between pump waves and a signal located in different bands of the communications spectrum (separated by 50 nm) by exploiting interband nonlinearities. Our demonstration is carried out in the silicon-rich silicon nitride material platform, which allows flexible device engineering, allowing for strong effective nonlinearity at telecommunications wavelengths without deleterious nonlinear-loss effects.

Global luminescence lifetime imaging of thermally activated delayed fluorescence on an auto-phase-locked time-gated microscope

Luminescence lifetime imaging plays an important role in time-resolved detection of luminescence decay differences in microscopic scale. However, the traditional instruments always require expensive detector such as time-correlated single photon counter, stream camera, or intensified CCDs, limiting their practical applications. Herein, a novel approach for global lifetime imaging was developed based on an auto-phase-locked time-gated luminescence microscopy. By utilizing a common color CCD to photograph a set of time-gated luminescence images at different phase differences between the exciting and detecting, a luminescence lifetime image could be obtained by exponential fitting of the gray level of each pixel to the delay time. Compare to the lifetime imaging based on point-by-point scanning, this is a global lifetime measurement of all the pixels, which consumes much less time in detecting long-lifetimes over microseconds. Besides, this method needs no expensive confocal laser scanning systems, intensified CCDs or complex electronic phase matching control, which greatly simplifies the instrument and decreases the cost. This approach was successfully used for fast luminescence lifetime imaging of two classical TADF molecules, which exhibited obvious lifetime differences in microscopic scale. The temporal resolution of the system could reach a few microseconds, suggesting its extensive applicability for many other molecules with long lifetimes.

Auto-phase-locked time-gated luminescence detection for background-free upconversion spectra measurement and true-color biological imaging

Time-resolved technique is widely used in biological detection and imaging, since this technique can eliminate the background signals from scattering and short-lived autofluorescence and greatly increase the signal-to-noise ratio. However, the relative apparatus always require pulse source, gated detector and electronic phase matching circuitry, which are expensive to implement and maintain. Herein, a simple method for time-gated upconversion luminescence spectra measurement and biological imaging was developed. By adjusting the exciting and detecting optical paths to pass through the same chopper wheel, only one mechanical chopper was needed, which simultaneously acted as pulse generator and detecting shutter. The phases of each excitation and time gate were synchronized and locked automatically as the optical paths fixed. Therefore, no complex electronic phase matching circuitry or control system was needed. By equipping with a 980 nm CW laser as exciting source, the time-gated spectra of upconversion lanthanide luminescence free from the scattering light was measured. Moreover, smart phones or the human eyes could easily detect the delayed luminescence of these materials, promising the true-color biological imaging with common cameras. This approach could be used in many other time-gated luminescence detection for long-lived luminescence materials and probes excited by other light sources.

Phase matching effects in high harmonic generation at the nanometer scale.

Plasmon resonances are known to amplify the electromagnetic fields near metallic nanostructures, providing a promising scheme to generate extreme-ultraviolet harmonics using low power drivings. During high-order harmonic generation (HHG), the driving and harmonic fields accumulate a phase difference as they propagate through the target. In a typical set-up -a laser focused into a gas jet- the propagation distances amount to several wavelengths, and the cumulative phase-mismatch affects strongly the efficiency and properties of the harmonic emission. In contrast, HHG in metallic nanostructures is considered to overcome these limitations, as the common sources of phase mismatch -optical density and focusing geometry- are negligible for subwavelength propagation distances. We demonstrate that phase matching still plays a relevant role in HHG from nanostructures due to the non-perturbative character of HHG, that links the harmonic phase to the intensity distribution of the driving field. Our computations show that widely used applications of phase matching control, such as quantum path selection and the increase of contrast in attosecond pulse generation, are also feasible at the nanoscale.

All-optical manipulation of non-degenerate FWM conversion bandwidth by gain-transparent SBS

We demonstrate all-optical manipulation of non-degenerate four-wave mixing (FWM) wavelength conversion bandwidth based on phase-matching control through gain-transparent stimulated Brillouin scattering (SBS). A 3-dB bandwidth of 26nm is achieved when the conversion efficiency is maximized, corresponding to 44% increase from the original value. The bandwidth can also be shrunk to a minimum of 15nm. The spectral dependence of conversion efficiency can potentially be synthesized randomly, leading to a large tunability in the bandwidth. The performance in bandwidth manipulation is also evaluated in the wavelength conversion of 10Gbit/s non-return-to-zero (NRZ) on-off-keying (OOK) signal.

Performance Limits of Inhomogeneous Fiber Optic Parametric Amplifiers Operated in Saturated Regime

Performance limits of saturated parametric amplifiers with very high nonlinear figure of merit were investigated. While such devices can be constructed using high confinement fiber, they also require localized phase matching control over hundreds of meters of interaction length. The limit on signal-induced pump depletion imposed by stochastic dispersion fluctuations in physical fibers is studied for a case of high-gain parametric amplifiers. We show that nanometer-scale fluctuations in fiber transverse geometry can lead to qualitatively different saturation characteristics in very efficient parametric devices. In contrast to a pump-undepleted parametric amplifier, an inhomogeneous parametric amplifier operated in saturation regime is found to possess truly nonreciprocal transfer characteristic.

Effects of Phase Matching Pattern on Pulse Laser-Arc Hybrid Welding Process

This paper proposed a method on accurate phase matching control between the pulse laser and the AC TIG arc in real time, and a pulse laser-arc hybrid heat source phase matching control system is developed as well. With the utilization of this system in two typical matching cases that the pulse laser acts on the peak and the trough of the arc welding current waveform, effect regulations on weld formation, weld penetration depth and hybrid plasma shape are studied during welding on magnesium alloy AZ61. Results indicate that, when the pulse laser acting on the peak of arc welding current waveform, the weld formation is better than that of on the trough. However, when pulse laser act on the arc trough the weld penetration depth is deeper than that of on the peak.

Quantum memory based on phase matching control**We dedicate this paper to the memory of Professor Igor Yevseyev, the internationally renowned scientist, one of the pioneers of the field of quantum coherence effects. We have warm memories of many fruitful and pleasant communications with Professor Yevseyev during the International Laser Physics Workshops, which he so successfully organized and hosted.

We discuss a class of quantum memory (QM) scheme based on phase matching control (PMC). A single-photon wave packet can be mapped into and retrieved on demand from a long-lived spin grating in the presence of a control field, forming along with the signal field a Raman configuration, when the wave vector of the control field is continuously changed in time. Such mapping and retrieval takes place due to the phase matching condition and requires neither a variation of the amplitude of the control field nor inhomogeneous broadening of the medium. We discuss the general model of PMC QM and its specific implementation via (i) modulation of the refractive index, (ii) angular scanning of the control field, and (iii) its frequency chirp. We show that the performance of the PMC QM protocol may be as good as those realized in the gradient echo memory (GEM) but achieved with less stringent requirements on the medium. We suggest the experimental realization of PMC QM in nitrogen vacancies (NV) and silicon vacancies (SiV) in diamond as well as in rare-earth doped crystals.

Multimode cavity-assisted quantum storage via continuous phase-matching control

A scheme for spatial multimode quantum memory is developed such that spatial-temporal structure of a weak signal pulse can be stored and recalled via cavity-assisted off-resonant Raman interaction with a strong angular-modulated control field in an extended $\ensuremath{\Lambda}$-type atomic ensemble. It is shown that effective multimode storage is possible when the Raman coherence spatial grating involves wave vectors with different longitudinal components relative to the paraxial signal field. The possibilities of implementing the scheme in the solid-state materials are discussed.

Dynamic Control of Phase Matching in Four-Wave Mixing Wavelength Conversion of Amplitude- and Phase- Modulated Signals

We propose and experimentally demonstrate dynamic control of phase-matching in fiber-based four-wave mixing (FWM) for wavelength conversion of communication signals. By introducing self-compensation of optical gain/loss with stimulated Brillouin scattering (SBS) pump and Stokes waves, the FWM phase-matching condition and hence the conversion efficiency (CE) can be flexibly controlled. The phase difference between the interplaying fields is manipulated by modifying the refractive index through SBS without disturbing the initial parameters of the FWM process. The scheme is first applied to wavelength conversion of 10 Gbit/s non-return-to-zero (NRZ) on-off-keying (OOK) signal. Its performance on phase-transparent wavelength conversion is subsequently examined using 10 Gbit/s NRZ differential-phase-shift-keying (DPSK) signal. Eye diagrams, FWM spectra and bit-error rate (BER) performances for the converted signals without SBS, with gain-transparent SBS for maximum CE and for minimum CE are analyzed. In the OOK/DPSK wavelength conversion with gain-transparent SBS, the CE has been reduced by 10.7/11.4 dB at a signal-pump spectral spacing of 1.9/1.94 nm; while it has been enhanced by 8.8/7.4 dB at a signal-pump spectral spacing of 4.1/4.07 nm. The pronounced enhancement of the CE at large signal-pump spectral spacing results in enlargement of the 3-dB FWM conversion bandwidth. Limitations in the extent of bandwidth enlargement and noise performance are discussed. Potential use of the scheme in other applications is also described.

Enhanced ultraviolet pulse generation via dual-color filament interaction induced phase-matching control

We demonstrated efficient generation of intense vacuum ultraviolet pulses at 133 nm directly from a 400-nm filament in argon gas. The conversion efficiency was significantly enhanced by adding a coaxial 267-nm pump pulse to dramatically ameliorate the phase matching conditions, as the dispersion originated from neutral atoms was compensated by additional free electrons stemmed from enhanced ionization induced by dual-color fields. Such a robust all-optical phase-matching control was shown to be dependent upon the pump intensity and temporal delay between the dual-color fields.

High-Q surface-plasmon-polariton whispering-gallery microcavity

Surface plasmon polaritons (SPPs) are electron density waves excited at the interfaces between metals and dielectric materials. Owing to their highly localized electromagnetic fields, they may be used for the transport and manipulation of photons on subwavelength scales. In particular, plasmonic resonant cavities represent an application that could exploit this field compression to create ultrasmall-mode-volume devices. A key figure of merit in this regard is the ratio of cavity quality factor, Q (related to the dissipation rate of photons confined to the cavity), to cavity mode volume, V (refs 10, 11). However, plasmonic cavity Q factors have so far been limited to values less than 100 both for visible and near-infrared wavelengths. Significantly, such values are far below the theoretically achievable Q factors for plasmonic resonant structures. Here we demonstrate a high-Q SPP whispering-gallery microcavity that is made by coating the surface of a high-Q silica microresonator with a thin layer of a noble metal. Using this structure, Q factors of 1,376 +/- 65 can be achieved in the near infrared for surface-plasmonic whispering-gallery modes at room temperature. This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method. The SPP eigenmodes, as well as the dielectric eigenmodes, are confined within the whispering-gallery microcavity and accessed evanescently using a single strand of low-loss, tapered optical waveguide. This coupling scheme provides a convenient way of selectively exciting and probing confined SPP eigenmodes. Up to 49.7 per cent of input power is coupled by phase-matching control between the microcavity SPP and the tapered fibre eigenmodes.

Phase-matching control of high-order harmonic generation in a two-color laser field

The phase-matching condition of high-order harmonic generation driven by intense few-cycle pulses could be controlled by adding second-harmonic pulses to change the ionization fraction of the gaseous medium. The harmonic generation efficiency could be improved by moving the phase-matching point with an all-optical control of the ionization fraction or a proper change of the confocal parameter. A specific order of harmonics could be easily controlled to reach phase matching at a fixed higher gas pressure by adding second-harmonic pulses with a suitable intensity. Such an all-optical phase-matching control was demonstrated to be dependent upon the temporal delay between the fundamental-wave and second harmonic pulses.

Spatial Four Wave Mixing in Nonlinear Periodic Structures

We present the first experimental study of spatial four-wave mixing in photonic lattices, demonstrating universal aspects of nonlinear processes in periodic media, such as engineered phase matching, Bloch-wave folding, and continuous control over the band at which the interaction products emerge.

High-order-harmonic generation: towards laser-induced phase-matching control and relativistic effects

We present a review of some recent results on high-order-harmonic generation, aiming at optimizing the photon flux to allow for future applications in extreme-ultra-violet non-linear optics. We first present new schemes to control phase matching of high harmonics in gases, by using the effect of the spatially varying atomic phase displayed by the high harmonics. An enhancement by a factor of 50 is observed in neon in conditions for which the gradient of the atomic dispersion balances the electronic dispersion. A new scheme to manipulate the laser field was demonstrated, and shown to improve phase matching. We then turn to high-harmonic generation by solid targets, and show that high harmonics generated by an intense 30-fs laser pulse remain collimated even at the threshold of the relativistic regime.

Pressure control of phase matching in high-order harmonic generation in hollow fibers filled with an absorbing weakly ionizing gas

High-order harmonic generation in a hollow fiber filled with a weakly ionizing gas is theoretically analyzed within the framework of the slowly varying envelope approximation. The gas pressure that corresponds to maximum efficiency of frequency conversion, the absorption coefficient, the phase mismatch owing to gas dispersion, and the enhancement of harmonic-generation efficiency owing to waveguide phase matching are estimated for 27th-harmonic generation in hollow fibers filled with helium, neon, argon, krypton, or xenon. As a result of the ionization-induced self-phase modulation of the pump pulse in a hollow fiber filled with a weakly ionizing gas, the phase mismatch changes within the pump pulse, decreasing the overall efficiency of harmonic generation and making the harmonic-generation efficiency less sensitive to the gas pressure in the hollow fiber.