Ultrafast Optical Switching Research Articles

Room Temperature Weak-to-Strong Coupling and the Emergence of Collective Emission from Quantum Dots Coupled to Plasmonic Arrays.

Colloidal quantum dot (CQD) assemblies exhibit interesting optoelectronic properties when coupled to optical resonators ranging from Purcell-enhanced emission to the emergence of hybrid electronic and photonic polariton states in the weak and strong coupling limits, respectively. Here, experiments exploring the weak-to-strong coupling transition in CQD-plasmonic lattice hybrid devices at room temperature are presented for varying CQD concentrations. To interpret these results, generalized retarded Fano-Anderson and effective medium models are developed. Individual CQDs are found to interact locally with the lattice yielding Purcell-enhanced emission. At high CQD densities, polariton states emerge as two-peak structures in the photoluminescence, with a third polariton peak, due to collective CQD emission, appearing at still higher CQD concentrations. Our results demonstrate that CQD-lattice plasmon devices represent a highly flexible platform for the manipulation of collective spontaneous emission using lattice plasmons, which could find applications in optoelectronics, ultrafast optical switches, and quantum information science.

Nonlinear Optics in Dielectric Guided-Mode Resonant Structures and Resonant Metasurfaces.

Nonlinear optics is an important area of photonics research for realizing active optical functionalities such as light emission, frequency conversion, and ultrafast optical switching for applications in optical communication, material processing, precision measurements, spectroscopic sensing and label-free biological imaging. An emerging topic in nonlinear optics research is to realize high efficiency optical functionalities in ultra-small, sub-wavelength length scale structures by leveraging interesting optical resonances in surface relief metasurfaces. Such artificial surfaces can be engineered to support high quality factor resonances for enhanced nonlinear optical interaction by leveraging interesting physical mechanisms. The aim of this review article is to give an overview of the emerging field of nonlinear optics in dielectric based sub-wavelength periodic structures to realize efficient harmonic generators, wavelength mixers, optical switches etc. Dielectric metasurfaces support the realization of high quality-factor resonances with electric field concentrated either inside or in the vicinity of the dielectric media, while at the same time operate at high optical intensities without damage. The periodic dielectric structures considered here are broadly classified into guided-mode resonant structures and resonant metasurfaces. The basic physical mechanisms behind guided-mode resonances, electromagnetically-induced transparency like resonances and bound-states in continuum resonances in periodic photonic structures are discussed. Various nonlinear optical processes studied in such structures with example implementations are also reviewed. Finally, some future directions of interest in terms of realizing large-area metasurfaces, techniques for enhancing the efficiency of the nonlinear processes, heterogenous integration, and extension to non-conventional wavelength ranges in the ultra-violet and infrared region are discussed.

Atomic Carbon Spraying: Direct Growth of Graphene on Customized 3D Surfaces of Ultrafast Optical Devices

AbstractDespite the long‐standing efforts to develop 3D graphene, which is critical for practical electronic, optoelectronic, and optical devices, the lack of synthetic methods and the use of conventional transfer approaches have limited its realization. Herein, a metal‐free, etching‐free, transfer‐free, direct synthesis of functional graphene is introduced that contours 3D‐structured surfaces of nonlinear optical devices, thereby maximizing the nonlinear interaction of graphene with guided light. Central to this method is the use of γ‐Al2O3, a ceramic catalyst, which generates carbon atoms from the precursor molecules and supplies them for the graphene synthesis on the 3D structures located near the catalyst through spatial diffusion, described as atomic carbon spraying (ACS). The optical nonlinearity facilitated by ACS‐processed 3D graphene is experimentally verified by realizing both passively mode‐locked laser with a pulse width of 770 fs and ultrafast optical switching with 67% enhancement in nonlinear effect over 6 mm interaction length.

Gigahertz Harmonic Mode‐Locked Fiber Laser Based on Tunable SMS Ultrafast Optical Switch

AbstractA novel passively gigahertz harmonic mode‐locked all‐fiber laser based on hybrid fiber structure (single‐mode fiber–graded‐index multimode fiber–single‐mode fiber (SMS)) is proposed SMS, which coils on the paddles of polarization controller (PC), is demonstrated to modulate the temporal intensity for mode‐locking. The nonlinear absorption properties of the optical switch are controllable by adjusting the paddles of PC; such an ultrafast optical switch enables the wavelength switchable harmonic mode‐locking operation. Ultrafast pulses with 1.9 ps at 1558.41 nm and 0.95 ps at 1563.08 nm are generated. The maximum repetition rate of the laser up to 1.127 GHz harmonic of fundamental repetition mode‐locking at 1563.08 nm, corresponding to 880 order, and the output power is 4.2 mW. Considering its superiority in terms of low cost, easy integration, and high reliability, the findings validate that SMS can be used in harmonic mode‐locking.

Ultrafast control of vortex microlasers.

The development of classical and quantum information-processing technology calls for on-chip integrated sources of structured light. Although integrated vortex microlasers have been previously demonstrated, they remain static and possess relatively high lasing thresholds, making them unsuitable for high-speed optical communication and computing. We introduce perovskite-based vortex microlasers and demonstrate their application to ultrafast all-optical switching at room temperature. By exploiting both mode symmetry and far-field properties, we reveal that the vortex beam lasing can be switched to linearly polarized beam lasing, or vice versa, with switching times of 1 to 1.5 picoseconds and energy consumption that is orders of magnitude lower than in previously demonstrated all-optical switching. Our results provide an approach that breaks the long-standing trade-off between low energy consumption and high-speed nanophotonics, introducing vortex microlasers that are switchable at terahertz frequencies.

Ultrafast vortex microlasers

Optics For applications in ultrafast communication, all-optical switches will require low energy consumption, high speed, a strong modulation ratio, a small footprint, and on-chip integration. Although the small footprint and on-chip integration are accessible, the trade-off between low energy consumption and high speed has been challenging. Huang et al. exploited the idea of bound states in the continuum, effectively a high–quality ( Q ) cavity without the physical cavity, to design vortex lasers with highly directional output and single-mode operation. With the trade-off between low energy consumption and high speed now broken, it should be possible to realize ultrafast optical switching that meets all the requirements of modern classic and quantum information. Science , this issue p. [1018][1] [1]: /lookup/doi/10.1126/science.aba4597

Ultrafast optical switches and pulse lasers based on strong nonlinear optical response of plasmon nanostructures

Nonlinear optical (NLO) effects are ubiquitous in the interaction of light with different materials. However, the NLO responses of most materials are inherently weak due to the small NLO susceptibility and the limited interaction length with the incident light. In plasmonic nanostructures the optical field is confined near the surface of the structures, so that the electromagnetic field is greatly enhanced in a localized fashion by spectral resonance. This effect results in the enhancement of light-matter interaction and NLO response of the material. Ultrafast pulse lasers have been widely used in optical communication, precise measurement, biomedicine, military laser weapons and other important fields due to their excellent performances. Although commercial lasers become very matured, they can achieve ultra-high peak power and ultra-short pulse width and ultra-high repetition rate, but the ultra-fast pulses in the mid-to-far infrared band are seldom studied, so finding a saturable absorber material with excellent performance is of great significance for developing the pulsed lasers. In this paper, we review the recent research progress of the applications of exiton nanostructure in ultrafast optical switches and pulse lasers based on noble metal and non-noble metals. The metallic system mainly refers to gold and silver nanoparticles. For non-noble metals, we mainly introduce our researches of chalcogenide semiconductor, heavily doped oxide and titanium nitride. A variety of wide bandgap semiconductors can exhibit metal-like properties through doping. Since doping can form free carriers, when their size is reduced to a nanometer scale, they will show the characteristics of local surface plasmon resonance, thus realizing ultra-fast nonlinear optical response, and the concentration of doped carriers cannot reach the level of metal carriers, thus being able to effectively reduce the inter-band loss caused by excessively high carriers. Through pump probe detection and Z-scan testing, we found that these plasmonic nanostructures exhibit ultrafast NLO response in tunable resonance bandwidth, which has been utilized as a working material for developing the optical switch to generate the pulsed laser with duration down to a femtosecond range. These results take on their potential applications in ultrafast photonics. Finally, we make a comparison of the pros and cons among different plasmonic materials and present a perspective of the future development.

Multiple Access Techniques for Bipolar Optical Code Division in Wireless Optical Communications

In this paper, multiple access techniques for bipolar optical code division are proposed for application in wireless optical communications. First, several fiber Bragg gratings (FBGs) and optical circulators are used to encode optical signals. Then, the horizontal or vertical polarization state can be controlled using bipolar data. Experiments were conducted using two devices to determine the feasibility of using multiple access techniques for bipolar optical code division in free-space optical communication. The first experiment tested the first architecture, in which each user operates a mechanical optical switch by switching data bits to generate optical signals with specific polarization states through a collimator in a free-space channel. As the decoding components, several FBGs and optical circulators are used as primary devices. Decoded signals are sent to a balanced photodetector, which can reconstruct original data from the encoder. The second experiment involved a second architecture, in which an encoder with an erbium-doped fiber amplifier and a decoder with an attenuator are used to improve system stability. The third experiment was designed to test whether multiple access interference can be alleviated with the proposed architectures. In the final experiment, an ultrafast optical switch was used instead of the original optical switch for selecting optical signals with a specific polarization state to improve the overall transmission rate. The experimental results indicate that the proposed scheme could be successfully implemented in free-space optical communication systems. The architectures of the proposed scheme mitigate multiple access interference with a simple and cost-effective design.

Sequential insulating-metal-insulating phase transition of NbO2 by doping photoexcited carrier

A large number of free carriers are introduced in the photoexcitation process and the complex interaction between photoexcited carriers and lattice can lead to an ultrafast phase transition in the solid. Niobium dioxide is an important optical material, which exhibiting a threshold switching phenomenon that can be explained by insulating-metal phase transition. It can be used as an ultrafast optical switches for telecommunication and optoelectronic devices. Here, we investigated the effects of injecting photoexcited carriers on consecutive insulator-metal-insulator phase transition of NbO2 by applying the GGA and GGA + U energy functions on the basis of density functional theory (DFT). Compared with electron injection, the effect of hole doping on phase transition in NbO2 is significantly more effective. The length of Nb-Nb dimer (long or short) is nearly unchanged upon electron doping, while the length of Nb-Nb_l is gradual shortened from 3.366 to 3.039 Å and the Nb-Nb_s is gradual stretched from 2.733 to 3.035 Å upon hole doping below a critical level of doping 12 holes per conventional cell. The structure phase changed from a body-center tetragonal (bct) to a rutile. Upon a higher hole doping, the structure kept the rutile structure until the number of doping holes reached 28 and it began to change to bct structure. We studied the electronic properties of NbO2 at a certain carriers concentration and reported a controlled and reversible insulator-metal-insulator phase transition by carries doping. The coexistence of the strong electron correlation and the Nb-Nb dimerization due to lattice distortion obscures the nature of the phase transition in NbO2. By analyzing the evolutions of lattice parameters and electronic properties of NbO2 at different charge carrier concentration, we got a conclusion that this sequential phase transition of NbO2 is not just a Mott phase transition or Peierls phase transition, but a collaborative of Peierls-Mott phase transition. Our work confirms that the observed structural transformations are driven primarily by hole doping, and the dominant lattice distortion caused by hole doping is the off-centering of Nb atoms in NbO6 octahedral.

Ultrafast Plasmonic Optical Switching Structures and Devices

[This submission is based on the contacts with Prof. Pavesi by code JMDC(100%.2019.FPHY.832).] Plasmonic structures possess rich physics related to the sensitivity of plasmon resonance to the change in the environmental dielectric constant, the enhanced light scattering and optical extinction, and the local field enhancement enabled strong light-matter interactions, which have been applied in refractive-index sensors, optical feedback in various micro- or nano-cavity lasers, surface enhanced Raman scattering spectroscopy, and high-sensitivity molecular detection. However, ultrafast optical response is another important aspect of plasmons, which can be utilized to achieve switching of optical signals in different spectral bands. These optical switching designs are very important for applications in optical logic circuits and optical communication system. In this review, we summarize a series of reports on ultrafast plasmonic optical switches, where we focus our discussions on the structural and device designs, instead of on their physics. By categorizing the designs of optical switches into different groups by their featured performances, we intend to propose the development trend and the commonly interested mechanisms of such ultrafast optical switches. We hope this review will supply helpful concepts and technical information for further development and new applications of ultrafast optical switching devices.

Ultra-fast optical switch with reconfigurable wavelength reuse functionality for dynamic flexible spectrum networks

ABSTRACTCurrent optical interconnects are dominated by electrical wavelength converter module technologies which are not only power consuming but also bandwidth limited. We experimentally demonstrate a technique to maximize network robustness, flexibility and efficiency through combined adoption of energy-efficient VCSELs, distributed forward Raman, all-optical wavelength conversion and reuse. The precise wavelength selectivity of a fibre Bragg grating (FBG) is exploited to realize all-optical wavelength switch at 10 Gbps directly modulated 1549.60 nm VCSEL channel. The 6.2 dB flat gain of a forward Raman amplifier is exploited to achieve a 25.25 km downstream transmission of the switched channel incurring a 1.23 dB transmission penalty. Gain saturation of an Erbium-doped fibre amplifier (EDFA) is incorporated to achieve real-time all-optical data erase/rewrite. The 1549.62 nm VCSEL channel is further reused for upstream transmission of 8.5 Gbps data incurring a maximum penalty of 0.83 dB. Our concept is key for adoption in dynamic wavelength routing for spectral utilization in optical interconnect.

Ultrafast Nano-scale Optical Switching in a Plasmonic Interferometer with Enhanced Tunability

An all-optical switch based on plasmonic metal–insulator–metal (MIM) waveguides and the Mach–Zehnder (MZ) interferometer is designed. In order to realize an all-optical and active switch, a nonlinear material with intensity-dependent refractive index is introduced in one arm. Other than studying a typical MZ structure, we also investigate the asymmetric case where unequal thicknesses and distances for MZ arms are proposed. The finite element method (FEM) with a refined triangle mesh is employed for simulations. Results for ON and OFF states are provided with or without employing the pump field. Investigation of the geometrical dispersion reveals tunability of the structure for specific frequencies in the terahertz region. Finally, we show that introducing asymmetric arms provides better tunability in the designed ultrafast nano-scale switch and suggests its potential applications in integrated optical circuits.

The synthesis and nonlinear optical properties of NiS2/MoS2 composites

NiS2/MoS2 composites were synthesized by a hydrothermal method. The scanning electron microscope, energy dispersive spectrometer analyses, and transmission electron microscopy confirmed that the NiS2 particles were distributed on the basal surface of MoS2 nanosheets. Then, the NiS2/MoS2 composites were dispersed in methyl methacrylate (MMA) which was polymerized to poly(methyl methacrylate) (PMMA) to prepare NiS2/MoS2/PMMA organic glass. The nonlinear optical (NLO) and optical limiting (OL) properties of the NiS2/MoS2/PMMA organic glass were studied via an open-aperture (OA) Z-scan technique. As the input energy varies from 20 to 70 μJ, the NiS2/MoS2/PMMA organic glass changes from saturable absorption (SA) to reverse saturable absorption (RSA). Compared to the NiS2/PMMA and MoS2/PMMA organic glasses, the NiS2/MoS2/PMMA organic glass is observed with enhanced NLO and OL properties, which were attributed to the interfacial charge transfer between NiS2 particles and MoS2 nanosheets, the unique band gap structure of NiS2 particles, and the layered structure of MoS2 nanosheets. The nonlinear absorption coefficient of the NiS2/MoS2/PMMA organic glass could be up to 5.03 × 10−9 mW−1. Thus the NiS2/MoS2/PMMA organic glass have a broad vision of application in ultrafast optical switches, optical shutters and optical limiters.

Phase-matching-free pulse retrieval based on transient absorption in solids.

In this paper, we introduce a pulse characterization technique that is free of phase-matching constraints, exploiting transient absorption in solids as an ultrafast optical switch. Based on a pump-probe setup, this technique uses pump pulses of sufficient intensity to induce the switch, while the pulses to characterize are probing the transmissivity drop of the photoexcited material. This enables the characterization of low-intensity ultra-broadband pulses at the detection limit of the spectrometer and within the transparency range of the solid. For example, by using zinc selenide (ZnSe), pulses with wavelengths from 0.5 to 20 μm can be characterized, denoting five octaves of spectral range. Using ptychography, we retrieve the temporal profiles of both the probe pulse and the switch. To demonstrate this approach, we measure ultrashort pulses from a titanium-sapphire (Ti-Sa) amplifier, which are compressed using a hollow core fiber setup, as well as infrared to mid-infrared pulses generated from an optical parametric amplifier (OPA). The characterized pulses are centered at wavelengths of 0.77, 1.53, 1.75, 4, and 10 μm, down to sub-two optical cycles duration, exceeding an octave of bandwidth, and with energy as low as a few nanojoules.

Orbital angular momentum bistability in a microlaser.

Light's orbital angular momentum (OAM) is an unbounded degree of freedom emerging in helical beams that appears very advantageous technologically. Using chiral microlasers, i.e., integrated devices that allow generating an emission carrying a net OAM, we demonstrate a regime of bistability involving two modes presenting distinct OAM (ℓ=0 and ℓ=2). Furthermore, thanks to an engineered spin-orbit coupling of light in these devices, these modes also exhibit distinct polarization patterns, i.e., circular and azimuthal polarizations. Using a dynamical model of rate equations, we show that this bistability arises from polarization-dependent saturation of the gain medium. Such a bistable regime appears very promising for implementing ultrafast optical switches based on the OAM of light. As well, it paves the way for the exploration of dynamical processes involving phase and polarization vortices.

Light Polarization-Controlled Conversion of Ultrafast Coherent-Incoherent Exciton Dynamics in Few-Layer ReS2.

Coherent light-matter interaction can transiently modulate the quantum states of matter under nonresonant laser excitation. This phenomenon, called the optical Stark effect, is one of the promising candidates for realizing ultrafast optical switches. However, the ultrafast modulations induced by the coherent light-matter interactions usually involve unwanted incoherent responses, significantly reducing the overall operation speed. Here, by using ultrafast pump-probe spectroscopy, we suppress the incoherent response and modulate the coherent-to-incoherent ratio in the two-dimensional semiconductor ReS2. We selectively convert the coherent and incoherent responses of an anisotropic exciton state by solely using photon polarizations, improving the control ratio by 3 orders of magnitude. The efficient modulation was enabled by transient superpositions of differential spectra from two nondegenerate exciton states due to the light polarization dependencies. This work provides a valuable contribution toward realizing ideal ultrafast optical switches.

Black phosphorus quantum dot based all-optical signal processing: ultrafast optical switching and wavelength converting

As a unique two-dimensional material, few-layered black phosphorus (BP) nanosheets have shown promising applications in electronics and optoelectronics. Black phosphorus quantum dots (BPQDs) have attracted attention due to the unique properties of BP combined with the edge effects. In this paper, we report on the all-optical application of BPQD based on its nonlinear Kerr effect. BPQDs were synthesized using a liquid exfoliation method combined with probe sonication and bath sonication. BPQD deposited on the microfiber as an optical device was demonstrated as the Kerr switcher with extinction ratio of 20 dB and four-wave mixing based wavelength converter with −40 dB conversion efficiency. These findings suggest that BPQD-based novel nonlinear photonics devices could be further developed in the applications of next generation high-speed optical communication.

InAs-Nanowire-Based Broadband Ultrafast Optical Switch.

Due to their tunable optical properties with various shapes, sizes, and compositions, nanowires (NWs) have been regarded as a class of semiconductor nanostructures with great potential for photodetectors, light-emitting diodes, gas sensors, microcavity lasers, optical modulators, and converters. Indium arsenide (InAs), an attractive III-V semiconductor NW with the advantages of narrow bandgap and large electron mobility, has attracted considerable interest in infrared optoelectronic and photonic devices. Here, we studied the ultrafast carrier dynamics and nonlinear optical responses of InAs NWs ranging from 1.0 to 2.8 μm and demonstrated the InAs-NW-based ultrafast broadband optical switch for passively Q-switching in all-solid-state laser systems. Furthermore, we achieved ultrafast optical modulation for laser mode-locking at 1.0 μm, paving the way for their applications in the field of ultrafast optics. These exotic optical properties indicate that InAs NWs have significant potential for various optoelectronic and photonic devices, especially in the mid-infrared wavelength range.

Characterization of 20-fs VUV pulses by plasma-mirror frequency-resolved optical gating.

We demonstrate that vacuum ultraviolet (VUV) pulses (λ∼160 nm) with 20-fs duration can be fully characterized by plasma-mirror frequency-resolved optical gating. Plasma is formed as an ultrafast optical switch on a fused silica surface by irradiation of an intense near-infrared (NIR) femtosecond laser pulse. We measure the spectra of the VUV pulses reflected off plasma as a function of the delay with respect to the NIR pulse and reconstruct it to simultaneously extract a nearly Fourier-transform limited VUV pulse shape and a time-dependent reflectivity of plasma using the least-squares generalized projections algorithm. We show that there is almost no spatial dependence of the VUV pulse shape, whereas the plasma mirror reflectivity strongly depends on the spatial region.

Nonlinear optics in all-dielectric nanoantennas and metasurfaces: a review

Freed from phase-matching constraints, plasmonic metasurfaces have contributed significantly to the control of the optical nonlinearity and enhancing the nonlinear generation efficiency by engineering subwavelength meta-atoms. However, the high dissipative losses and the inevitable thermal heating limit their applicability in nonlinear nanophotonics. All-dielectric metasurfaces, supporting both electric and magnetic Mie-type resonances in their nanostructures, have appeared as a promising alternative to nonlinear plasmonics. High-index dielectric nanostructures, allowing additional magnetic resonances, can induce magnetic nonlinear effects, which along with electric nonlinearities increase the nonlinear conversion efficiency. In addition, low dissipative losses and high damage thresholds provide an extra degree of freedom for operating at high pump intensities, resulting in a considerable enhancement of the nonlinear processes. In this review, we discuss the current state-of-the-art in the intensely developing area of all-dielectric nonlinear nanostructures and metasurfaces, including the role of Mie modes, Fano resonances and anapole moments for harmonic generation, wave mixing, and ultrafast optical switching. Furthermore, we review the recent progress in the nonlinear phase and wavefront control using all-dielectric metasurfaces. We discuss techniques to realize all-dielectric metasurfaces for multifunctional applications and generation of second-order nonlinear processes from CMOS compatible materials.