All-optical Switching Research Articles

Ultrafast spin dynamics: From femtosecond magnetism to attosecond magnetism

Ultrafast spin dynamics is the study of the evolution of spin degrees of freedom on a time scale from picoseconds to attoseconds after being excited by an external field. With the development of laser technology, ultrafast spin dynamics has presented new opportunities for realizing ultrafast spintronic devices since 1996. However, despite decades of development, many aspects of femtosecond magnetism remain unclear. Understanding the parameters of these ultrafast spin dynamics processes requires experiments on an even faster timescale. Attosecond magnetism and the interaction of attosecond laser pulses with magnetic materials can reveal spin dynamics on a sub-femtosecond to attosecond time scale. In this review, we first introduce the significant research progress, including the mechanisms of ultrafast demagnetization, all-optical switching, ultrafast spin currents, and terahertz waves. Secondly, we analyze the problems in ultrafast spin dynamics, such as the unclear physical mechanisms of ultrafast demagnetization, the uncertain relationship between magnetic damping and ultrafast demagnetization time, and the unexplored anisotropic ultrafast demagnetization. Thirdly, we discuss the opportunities and challenges in attosecond magnetism. Finally, we analyze and discuss the future development and prospects of ultrafast spin dynamics.

Innovative triazine-core octupolar chromophores: unlocking new Frontiers in nonlinear optics

Molecular motions within functionalized octupolar NLO chromophore, with photosensitive chains comprising dual-constructed azo/stilbene units. All-optical switching is initiated by linearly polarized UV light and monitored using red-light laser line.

Anomalous spectral shift of localized surface plasmon resonance.

We report the first observation of spectral blue shift of plasmon resonance of synthesized silver nanoparticles (AgNPs) due to a negative optical nonlinearity of a local ambient medium, i.e., indigo carmine (IC) solution at around 420 nm wavelength. The blue shift occurred at a larger concentration of AgNPs or at a larger concentration of IC solution, being in obvious contrast to spectral red shift which was widely witnessed in plasmon spectral shift in a linear regime. Plasmon-enhanced local fields could excite the third-order optical nonlinearity for blue shift even under continuous (non-pulsed) light illumination. We also found that the plasmon-excited nonlinearity could allow for differential nonlinear response of the IC solution to be even greater than its differential linear response, though appearing to be somewhat inconsistent with what was generally known in light-matter interaction. The demonstrated properties of such anomalous shift of plasmon spectral peaks and its accompanying properties indicated that plasmon technologies could be exploited not only in linear but also in nonlinear aspects for critical optimization in plasmon-energy harvesting systems such as in surface enhanced spectroscopy/microscopy, biomedical imaging/sensing, laser frequency conversion, ultrashort pulse generation, and all-optical switching.

Ultrafast Plasmonics for All-Optical Switching and Pulsed Lasers

Surface plasmon resonances (SPRs) are often regarded as the collective oscillations of charge carriers localized at the dielectric–metal interface that display an ultrafast response upon light excitation. The recent developments in the fabrication and characterization of plasmonic nanostructures have stimulated continuous effects in the search for their potential applications in the photonic fields. Concentrating on the role of plasmonics in photonics, this review covers recent advances in ultrafast plasmonic materials with a prime focus on all-optical switching. Fundamental phenomena of plasmonic light–matter interaction and plasmon dynamics are discussed by elaborating on the ultrafast processes unraveled by both experimental and theoretical methods, along with a comprehensive illustration of leveraging ultrafast plasmonics for all-optical switching and pulse laser generation with a focus on device design and performance. This review is concluded with a brief highlight of the current progress and the potential future directions in ultrafast plasmonics.

Heat accumulation and phase transition induction in a VO2 thin film by a femtosecond pulse-periodic radiation.

The kinetics of optical switching due to the insulator-metal phase transition in a VO2 thin film is studied experimentally at different laser pulse repetition frequencies (PRFs) in the NIR range and compared with temperature kinetics obtained through the thermal conductance calculations. Two switching processes have been found with characteristic times <2 ms and <15 ms depending on the PRF; the former is explained by the accumulation of metallic domains remaining after a single-pulse phase transition, and the latter is referred to the heat accumulation in the film. Consequently, the dynamics of the microscopic domains is leading in the initiation of phase transition under pulse-periodic conditions compared to the macroscopic heat transfer. The reverse transition at the radiation turn-off depends on the PRF with a time coefficient of 17.5 µs/kHz and is determined by the metallic domains' decay in the film. The results are important for understanding the nature of the insulator-metal transition in thin films of VO2 as well as using them in all-optical switches of pulse-periodic laser radiation.

Mechanism and properties of all-optical switching constructed from 1D symmetric defect ring optical waveguide network

In this paper, barium fluoride (BaF2) and bismuth doped silicon-rich silicon dioxide (Bi-doped Si-rich SiO2) are used for designing a novel pump-free ultracompact ultrahigh efficiency all-optical switching constructed from a photonic band gap (PBG) structure, the one-dimensional (1D) symmetric defect ring optical waveguide network (SDROWN) with integer-broken waveguide length ratio. The ultralow threshold control energy of our designing all-optical switching is 1.24556 × 10−25J, which makes the switching be pump-free. The transverse and longitudinal feature sizes of the switching are, respectively, 160 nm and 270 nm, which arrive at the level of the best reported results and makes the switching may realize intense integration. The ultrahigh switching efficiency arrives at 8.69565 × 107 and is more than 2 orders of magnitude larger than those of other kinds of all-optical switchings. The switching time is nearly 116fs, which arrives at the level of the best reported results. On the other hand, this technique may provide the probability for solving the four contradictions/difficulties in the designing of practical on-chip all-optical switching. It may deepen people's knowledge on PBG structures and provide new scientific bases for the designing of practical on-chip all-optical switching.

Photochromic polymers: Structural engineering driving individual NLO response

Photochromic polymers have attracted a lot of attention in the last few decades because of their useful properties related to color change and optical data storage. In this contribution we present a macromolecular structure influence on the output spectroscopic properties in the manner of all-optical switching and harmonics of light generation. Slight chemical architecture changes make significant difference if we consider generated optical anisotropy magnitude and kinetics of photoinduced process but also force diversified nonlinear optical response. We have placed a strong electron acceptor unit, fluorine atom, in a few alternate substitution patterns. One of them (1,4-) activates the phenyl unit, the other one (1,3-) works opposite. Finally, a joined form was also investigated, which led to appealing results making materials engineering field of studies a useful tool dedicated for advanced functional materials fabrication. Moreover, experimental achievements presented here indicate that investigated materials are perfect candidates for opto-electronics, photonics and spectroscopy fields and can be easily implemented into individual optical processing solutions.

Analysis of high-contrast all-optical dual-wavelength switching in asymmetric dual-core fibers.

We systematically present experimental and theoretical results for the dual-wavelength switching of 1560 nm, 75 fs signal pulses (SPs) driven by 1030 nm, and 270 fs control pulses (CPs) in a dual-core fiber (DCF). We demonstrate a switching contrast of 31.9 dB, corresponding to a propagation distance of 14 mm, achieved by launching temporally synchronized SP-CP pairs into the fast core of the DCF with moderate inter-core asymmetry. Our analysis employs a system of three coupled propagation equations to identify the compensation of the asymmetry by nonlinearity as the physical mechanism behind the efficient switching performance.

ẢNH HƯỞNG CỦA ĐỘ KẾT HỢP ĐƯỢC TẠO BỞI PHÁT XẠ TỰ PHÁT VÀ BƠM KHÔNG KẾT HỢP LÊN CHUYỂN MẠCH TOÀN QUANG TRONG MÔI TRƯỜNG NGUYÊN TỬ BA MỨC BẬC THANG KHI CÓ MẶT CỦA PHA TƯƠNG ĐỐI

This paper investigates the impact of spontaneously generated coherence (SGC) and relative phase on the propagation of a probe laser pulse in the presence of an incoherent pump field. It was discovered that when the control laser field is turned on, the medium forms an electromagnetically induced transparency (EIT) effect. Hence, the propagation of the probe laser pulse has a like-soliton form/shape. On the contrary, the probe laser field is rapidly attenuated when the control laser field is turned off. This feature allows the creation of a mechanism to turn “off” and “on” the probe laser field through “turning off” and “on” the control laser field, i.e., an all-optical switching mechanism based on EIT. Besides intensity and frequency, the laser field is also characterized by polarization and phase. The EIT has the nature of quantum interference, so it is very sensitive to changes in polarization, especially in the presence of relative phase between laser fields. Therefore, they also significantly affect pulse propagation and optical switching performance. The research results could be helpful for experimental observations or applications in photonic devices such as logic gates, quantum optical information processors, and quantum computers.

All-optical switching at the two-photon limit with interference-localized states

All-optical switching at the two-photon limit with interference-localized states

Thermo-plasmon-assisted all-optical switches based on coupled micro-cavities

Given the major applications of optical switches in the next generation electronics, plasmon assisted all-optical switch is proposed based on plasmonic micro ring arrays covered with the graphene layer. For this purpose, we use a laser writing system to fabricate micro hole arrays and cover them by plasmonic gold thin film via sputtering machine, with chemical vapor deposition method being used to produce graphene layer. After theoretically and experimentally evaluating the plasmonic substrate, we use ellipsometric method to characterize the optical modes of the samples. Furthermore, the all-optical and gated switches response is recorded for the fabricated sample. Our results show phase delay plasmon induced switching as well as thermo-plasmonic affected benefit for the proposed switching structure in the order of 0.29 s (duty cycle). The suggested switch with its low power consumption, small size, and easier and low-cost fabrication process can open new insight into plasmon-assisted all-optical switches.

Fractional Photoconduction and Nonlinear Optical Behavior in ZnO Micro and Nanostructures

A fractional description for the optically induced mechanisms responsible for conductivity and multiphotonic effects in ZnO nanomaterials is studied here. Photoconductive, electrical, and nonlinear optical phenomena exhibited by pure micro and nanostructured ZnO samples were analyzed. A hydrothermal approach was used to synthetize ZnO micro-sized crystals, while a spray pyrolysis technique was employed to prepare ZnO nanostructures. A contrast in the fractional electrical behavior and photoconductivity was identified for the samples studied. A positive nonlinear refractive index was measured on the nanoscale sample using the z-scan technique, which endows it with a dominant real part for the third-order optical nonlinearity. The absence of nonlinear optical absorption, along with a strong optical Kerr effect in the ZnO nanostructures, shows favorable perspectives for their potential use in the development of all-optical switching devices. Fractional models for predicting electronic and nonlinear interactions in nanosystems could pave the way for the development of optoelectronic circuits and ultrafast functions controlled by ZnO photo technology.

Singular optical propagation properties of two types of one-dimensional anti- PT -symmetric periodic ring optical waveguide networks

Two types of one-dimensional (1D) anti- PT -symmetric periodic ring optical waveguide networks, consisting of gain and loss materials, are constructed. The singular optical propagation properties of these networks are investigated. The results show that the system composed of gain materials exhibits characteristics of ultra-strong transmission and bidirectional reflection. Conversely, the system composed of loss materials demonstrates equal transmittance and reflectance at some frequencies. In both the systems, a new type of total reflection phenomenon is observed. When the imaginary part of the refractive indices of waveguide segments is smaller than 10−5, the system shows bidirectional transparency with the transmittance tending to be 1 and reflectivity to be smaller than 10−8 at some bands. When the refractive indices of the waveguide segments are real, the system will be bidirectional transparent at the full band. These findings may deepen the understanding of anti- PT -symmetric optical systems and optical waveguide networks, and possess potential applications in efficient optical energy storage, ultra-sensitive optical filters, ultra-sensitive all-optical switches, integrated optical chips, stealth physics, and so on.

Plasmon mediated coherent population oscillations in molecular aggregates

The strong coherent coupling of quantum emitters to vacuum fluctuations of the light field offers opportunities for manipulating the optical and transport properties of nanomaterials, with potential applications ranging from ultrasensitive all-optical switching to creating polariton condensates. Often, ubiquitous decoherence processes at ambient conditions limit these couplings to such short time scales that the quantum dynamics of the interacting system remains elusive. Prominent examples are strongly coupled exciton-plasmon systems, which, so far, have mostly been investigated by linear optical spectroscopy. Here, we use ultrafast two-dimensional electronic spectroscopy to probe the quantum dynamics of J-aggregate excitons collectively coupled to the spatially structured plasmonic fields of a gold nanoslit array. We observe rich coherent Rabi oscillation dynamics reflecting a plasmon-driven coherent exciton population transfer over mesoscopic distances at room temperature. This opens up new opportunities to manipulate the coherent transport of matter excitations by coupling to vacuum fields.

Highly efficient nonlinear vortex beam generation by using a compact nonlinear fork grating

Vortex beams with an orbital angular momentum (OAM) are extremely important in optical trapping, optical micromachining, high-capacity optical communications, and quantum optics. Nonlinear generation of such a vortex beam enables vortex beams to be obtained at new wavelengths, which opens up new possibilities for all-optical switching and manipulation of vortex beams. However, previous nonlinear vortex beam generation suffers from either low efficiency or low-level integration. Here, we use the technique of ultraviolet photolithography-assisted inductively coupled plasma (ICP) etching to realize a compact nonlinear fork grating for high-efficiency nonlinear vortex beam generation. In our experiment, the depth of such a compact nonlinear fork-grating structure can be precisely controlled by etching time. The vortex beams with a topological charge of l = ±1, ± 2, ± 3 can be generated in the far field, and the normalized nonlinear conversion efficiency of such nonlinear vortex beam is 189% W−1cm−2. Our method not only provides an efficient and compact method for nonlinear vortex beam manipulation but also suits for timesaving and large-area nonlinear functional device fabrication.

All-Optical Switches for Optical Soliton Interactions in a Birefringent Fiber

Interactions among optical solitons can be used to develop photonic information processing devices such as all-optical switches and all-optical logic gates. It is the key to achieve high-speed, high-capacity all-optical networks and optical computers, which is also important in academy. We study the properties of all-optical switches of optical solitons in birefringent fibers, based on the coupled nonlinear Schrödinger equations. It is found that under different initial conditions we can achieve all-optical switching functions. We also study the influence of different physical parameters of birefringent fibers on all-optical soliton switching. The relevant conclusions are conducive to achieving the all-optical switching function of optical solitons in birefringent fibers, providing useful guidance for widespread applications of optical soliton all-optical switches in birefringent fibers of communications.

Polaronic Nonlinear Optical Response and All-Optical Switching Based on an Ionic Metal Oxide.

It has been well-established that light-matter interactions, as manifested by diverse linear and nonlinear optical (NLO) processes, are mediated by real and virtual particles, such as electrons, phonons, and excitons. Polarons, often regarded as electrons dressed by phonons, are known to contribute to exotic behaviors of solids, from superconductivity to photocatalysis, while their role in materials' NLO response remains largely unexplored. Here, the NLO response mediated by polarons supported by a model ionic metal oxide, TiO2, is examined. It is observed that the formation of polaronic states within the bandgap results in a dramatic enhancement of NLO absorption coefficient by over 130 times for photon energies in the sub-bandgap regions, characterized by a 100fs scale ultrafast response that is typical for thermalized electrons in metals. The ultrafast polaronic NLO response is then exploited for the development of all-optical switches for ultrafast pulse generation in near-infrared (NIR) fiber lasers and modulation of optical signal in the telecommunication band based on evanescent interaction on a planar waveguide chip. These results suggest that the polarons supported by dielectric ionic oxides can fill the gaps left by dielectric and metallic materials and serve as a novel platform for nonlinear photonic applications.

Dynamics of twin pulse propagation and dual-optical switching in a Λ + Ξ atomic medium

Optical bistability (OB) and optical multistability (OM) as well as optical soliton and all-optical switching have been successfully established in a lambda + cascade-type five-level atomic medium under electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) regimes. For this configuration, three laser fields are required to excite atomic transitions. The probe laser field with two circularly left- and right-polarized components excites atoms in a lambda-type configuration. Meanwhile, two coupling laser fields excite atoms in a ladder-type configuration. In this way, the above optical phenomena can occur with two frequency channels corresponding to the circularly left- and right-polarized light components. By adjusting the strength/direction of the static magnetic field in the presence of the driving field, the EIT and EIA effects can be swapped, at the same time, OB and OM effects can also be converted. In the EIT regime, the propagation of the probe pulse easily achieves the soliton state, whereas it can be completely extinguished in the EIA regime. This makes it easy to create an all-optical switching mechanism. Especially, both components of the probe field (cw) can be modulated into a synchronous or asynchronous square pulse according to the modulation of the driving field. The results obtained from the investigated model may provide merits of the applications for optical storage and all-optical switching for multi-channel optical communications.

Transient Non-Collinear Magnetic State for All-Optical Magnetization Switching.

Resonant absorption of a photon by bound electrons in a solid can promote an electron to another orbital state or transfer it to a neighboring atomic site. Such a transition in a magnetically ordered material could affect the magnetic order. While this process is an obvious road map for optical control of magnetization, experimental demonstration of such a process remains challenging. Exciting a significant fraction of magnetic ions requires a very intense incoming light beam, as orbital resonances are often weak compared to above-band-gap excitations. In the latter case, a sizeable reduction of the magnetization occurs as the absorbed energy increases the spin temperature, masking the non-thermal optical effects. Here, using ultrafast X-ray spectroscopy, this work is able to resolve changes in the magnetization state induced by resonant absorption of infrared photons in Co-doped yttrium iron garnet, with negligible thermal effects. This work finds that the optical excitation of the Co ions affects the two distinct magnetic Fe sublattices differently, resulting in a transient non-collinear magnetic state. The present results indicate that the all-optical magnetization switching (AOS) most likely occurs due to the creation of a transient, non-collinear magnetic state followed by coherent spin rotations of the Fe moments.

Multipole engineering by displacement resonance: a new degree of freedom of Mie resonance

The canonical studies on Mie scattering unravel strong electric/magnetic optical responses in nanostructures, laying foundation for emerging meta-photonic applications. Conventionally, the morphology-sensitive resonances hinge on the normalized frequency, i.e. particle size over wavelength, but non-paraxial incidence symmetry is overlooked. Here, through confocal reflection microscopy with a tight focus scanning over silicon nanostructures, the scattering point spread functions unveil distinctive spatial patterns featuring that linear scattering efficiency is maximal when the focus is misaligned. The underlying physical mechanism is the excitation of higher-order multipolar modes, not accessible by plane wave irradiation, via displacement resonance, which showcases a significant reduction of nonlinear response threshold, sign flip in all-optical switching, and spatial resolution enhancement. Our result fundamentally extends the century-old light scattering theory, and suggests new dimensions to tailor Mie resonances.