All-optical Scheme Research Articles

Generation of high-energy electron-positron pairs in the collision of a laser-accelerated electron beam with a multipetawatt laser

Generation of electron-positron pairs via the multiphoton Breit-Wheeler process in an all-optical scheme will be made possible on forthcoming high-power laser facilities through the collision of wakefield-accelerated GeV electrons with a counter-propagating laser pulse of 1022–1023 W cm-2 peak intensity. By means of integrated 3D particle-in-cell simulations, we show that the production of high-density sources of ultrarelativistic electron-positron pairs is within the reach of soon-to-be-available laser systems. Under physical conditions accessible to the dual-beam CILEX-Apollon facility, we find that the generated positrons can carry a total charge of 0.05–1 nC, with a mean energy of 100–400 MeV and an angular divergence of 0.01–0.1 rad. The variations of the positron source’s properties with respect to the laser parameters are also examined.

Intensity dependences of the nonlinear optical excitation of plasmons in graphene.

Recently, we demonstrated an all-optical coupling scheme for plasmons, which takes advantage of the intrinsic nonlinear optical response of graphene. Frequency mixing using free-space, visible light pulses generates surface plasmons in a planar graphene sample, where the phase matching condition can define both the wavevector and energy of surface waves and intraband transitions. Here, we also show that the plasmon generation process is strongly intensity-dependent, with resonance features washed out for absorbed pulse fluences greater than 0.1 J m-2 This implies a subtle interplay between the nonlinear generation process and sample heating. We discuss these effects in terms of a non-equilibrium charge distribution using a two-temperature model.This article is part of the themed issue 'New horizons for nanophotonics'.

Manipulation of slow and superluminal light based on a graphene nanoribbon resonator

We theoretically investigate the phenomena of slow and superluminal light based on a doubly clamped Z-shaped graphene nanoribbon (GNR) nanomechanical resonator driven by two-tone fields. Superluminal and ultraslow probe light without absorption can be obtained via manipulating the pump laser on- and off-resonant with the exciton frequency, respectively. The results indicate that the above phenomena cannot occur without the coupling between graphene resonator and excition in the system. Further, the all-optical schemes for determining the graphene resonator frequency and the coupling strength of excition-resonator in the Z-shaped GNR system are also proposed. The all-optical device based on graphene resonator may have potential application in optical networks and engineering in nanoscale.

Dense pair plasma generation by two laser pulses colliding in a cylinder channel**Project supported by the National Natural Science Foundation (Grant Nos. 11475260, 11305264, 11622547, 11375265, and 11474360), the National Basic Research Program of China (Grant No. 2013CBA01504), the Research Project of National University of Defense Technology, China (Contract No. JC14-02-02), and the Science Challenge Program, China (Grant No. JCKY2016212A505).

An all-optical scheme for high-density pair plasmas generation is proposed by two laser pulses colliding in a cylinder channel. Two dimensional particle-in-cell simulations show that, when the first laser pulse propagates in the cylinder, electrons are extracted out of the cylinder inner wall and accelerated to high energies. These energetic electrons later run into the second counter-propagating laser pulse, radiating a large amount of high-energy gamma photons via the Compton back-scattering process. The emitted gamma photons then collide with the second laser pulse to initiate the Breit–Wheeler process for pairs production. Due to the strong self-generated fields in the cylinder, positrons are confined in the channel to form dense pair plasmas. Totally, the maximum density of pair plasmas can be , for lasers with an intensity of . Both the positron yield and density are tunable by changing the cylinder radius and the laser parameters. The generated dense pair plasmas can further facilitate investigations related to astrophysics and particle physics.

Dense GeV electron-positron pairs generated by lasers in near-critical-density plasmas.

Pair production can be triggered by high-intensity lasers via the Breit–Wheeler process. However, the straightforward laser–laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-critical-density plasmas at only ∼1022 W cm−2. In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit–Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 1011) overdense (4 × 1022 cm−3) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron–positron colliders.

Plasmonic Photothermal Fluorescence Modulation for Homogeneous Biosensing

Fluorescence readout is uniquely powerful for biological assays and imaging because it combines the detection of specific biotargets with high spatial and temporal resolution. Recently, several strategies for the modulation in time of fluorescence emission have been proven useful to separate the target signal from constant background contributions. Here, we investigate the emission modulation of organic fluorophores located in the nanometric vicinity of plasmonically heated gold nanorods and apply it to a novel, all-optical homogeneous biosensing scheme. The combination of plasmonic heating and temperature sensitive molecular fluorescence enables the robust quantification of surface reactions.

Ultrafast Long-Distance Quantum Communication with Static Linear Optics.

We propose a projection measurement onto encoded Bell states with a static network of linear optical elements. By increasing the size of the quantum error correction code, both Bell measurement efficiency and photon-loss tolerance can be made arbitrarily high at the same time. As a main application, we show that all-optical quantum communication over large distances with communication rates similar to those of classical communication is possible solely based on local state teleportations using optical sources of encoded Bell states, fixed arrays of beam splitters, and photon detectors. As another application, generalizing state teleportation to gate teleportation for quantum computation, we find that in order to achieve universality the intrinsic loss tolerance must be sacrificed and a minimal amount of feedforward has to be added.

Elastic all-optical multi-hop interconnection in data centers with adaptive spectrum allocation

In this paper, a novel flex-grid all-optical interconnect scheme that supports transparent multi-hop connections in data centers is proposed. An inter-rack all-optical multi-hop connection is realized with an optical loop employed at flex-grid wavelength selective switches (WSSs) in an intermediate rack rather than by relaying through optical-electric-optical (O-E-O) conversions. Compared with the conventional O-E-O based approach, the proposed all-optical scheme is able to off-load the traffic at intermediate racks, leading to a reduction of the power consumption and cost. The transmission performance of the proposed flex-grid multi-hop all-optical interconnect scheme with various modulation formats, including both coherently detected and directly detected approaches, are investigated by Monte-Carlo simulations. To enhance the spectrum efficiency (SE), number-of-hop adaptive bandwidth allocation is introduced. Numerical results show that the SE can be improved by up to 33.3% at 40Gbps, and by up to 25% at 100Gbps. The impact of parameters, such as targeted bit error rate (BER) level and insertion loss of components, on the transmission performance of the proposed approach are also explored. The results show that the maximum SE improvement of the adaptive approach over the non-adaptive one is enhanced with the decrease of the targeted BER levels and the component insertion loss.

Time Lens-Based Optical Fourier Transformation for All-Optical Signal Processing of Spectrally-Efficient Data

We review recent progress in the use of time lens-based optical Fourier transformation for advanced all-optical signal processing. A novel time lens-based complete optical Fourier transformation (OFT) technique is introduced. This complete OFT is based on two quadratic phase-modulation stages using four-wave mixing, separated by a dispersive medium, which enables time-to-frequency and frequency-to-time conversions simultaneously, thus performing an exchange between the temporal and spectral profiles of the input signal. Using the proposed complete OFT, several advanced all-optical signal processing schemes for spectrally-efficient systems and networks have been achieved, including all-optical generation, detection and format conversion of spectrally-efficient signals. The spectrally-efficient signals in this paper mainly refer to efficiently multiplexed signals with a high symbol rate per Hz, such as orthogonal frequency division multiplexing, Nyquist wavelength-division multiplexing (Nyquist-WDM), and Nyquist optical time division multiplexing (Nyquist-OTDM) signals.

Picometer-resolution dual-comb spectroscopy with a free-running fiber laser.

Dual-comb spectroscopy holds the promise as real-time, high-resolution spectroscopy tools. However, in its conventional schemes, the stringent requirement on the coherence between two lasers requires sophisticated control systems. By replacing control electronics with an all-optical dual-comb lasing scheme, a simplified dual-comb spectroscopy scheme is demonstrated using one dual-wavelength, passively mode-locked fiber laser. Pulses with a intracavity-dispersion-determined repetition-frequency difference are shown to have good mutual coherence and stability. Capability to resolve the comb teeth and a picometer-wide optical spectral resolution are demonstrated using a simple data acquisition system. Energy-efficient, free-running fiber lasers with a small comb-tooth-spacing could enable low-cost dual-comb systems.

Performance analysis of an all-optical logic gate based on a single I/Q modulator with direct detection.

This paper investigates the performance of an all-optical logic gate scheme based on a single in-phase and quadrature (I/Q) modulator with direct detection. The proposed scheme of an all-optical logic gate is simple, high speed, and easily reconfigured to realize 24 logic states by adjusting bias voltages, peak-to-peak voltages of the driven RF signals, and the phase shift. As the scheme to realize logic gates is based on the irregular use of a commercially available I/Q modulator and laser source, a specialized logic gate system including a laser, I/Q modulator, and driven RF module should be optimally designed to obtain the best performance. With the system's extinction ratio (ER) and Q-factor as metrics, the performance of the proposed logic gate scheme is analyzed theoretically and numerically in this paper. We first give a new theoretical model of the I/Q modulator. Next, taking the OR gate as an example, the simulations are carried out to analyze performance under the influence of some key factors in the system. Results show that the extinction ratio of the whole system is affected by the phase shift between the two arms of the I/Q modulator and the extinction ratios of two Mach-Zehnder modulators (MZMs), while Q-factor is further influenced by the output power of the laser and the insertion loss of the MZMs in the I/Q modulator. For an I/Q modulator with MZMs having an extinction ratio of 20 dB, the minimum laser output power to obtain a system's ER higher than 16 dB is 3 dBm, while in order to obtain a Q-factor higher than 6, the output power of the laser must not be <10 dBm.

An Optical Content Addressable Memory Cell for Address Look-Up at 10 Gb/s

We propose and experimentally demonstrate the first all-optical content addressable memory (CAM) cell that comprises an all-optical monolithically integrated InP flip-flop and an optical XOR gate. The experimental results reveal error-free operation at 10 Gb/s for both content addressing and content writing operations. The potential of these memory architectures to allow for up to 40-Gb/s operation could presumably lead to fast CAM-based routing applications by enabling all-optical address look-up schemes.

All-optical bright γ-ray and dense positron source by laser driven plasmas-filled cone.

An all-optical scheme for bright γ-rays and dense e-e+ pair source is proposed by irradiating a 1022 W/cm2 laser onto a near-critical-density plasmas filled Al cone. Two-dimensional (2D) QED particle-in-cell (PIC) simulations show that, a dense electron bunch is confined in the laser field due to the radiation reaction and the trapped electrons oscillate transversely, emitting bright γ-rays forward in two ways: (1) nonlinear Compton scattering due to oscillation of electrons in the laser field, and (2) Compton backwardscattering resulting from the bunch colliding with the reflected laser by the cone tip. Finally, the multi-photon Breit-Wheeler process is initiated, producing abundant e-e+ pairs with a density of ∼ 1027m-3. The scheme is further demonstrated by full 3D PIC simulations, which indicates a positron number up to 2 × 109. This compact γ-rays and e-e+ pair source may have many potential applications, such as the laboratory study of astrophysics and nuclear physics.

All-Optical Fiber Hanbury Brown &Twiss Interferometer to study 1300 nm single photon emission of a metamorphic InAs Quantum Dot.

New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 μeV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown & Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths.

Polarization-tunable terahertz radiation in the high-field regime.

Polarization control of terahertz (THz) pulses in the high-field regime is a challenging subject. Here we propose and numerically demonstrate an all-optical scheme to generate a polarization-tunable high-field THz source based on relativistic laser plasma interactions. By adjusting the polarization state of the driving laser, collective oscillation of the plasmas can be steered. Phase difference between the laser field components is inherited in the plasma dynamics, as well as in the resulting THz generation process. Single-cycle extremely intense THz pulses with field strength ∼ GV/cm can be generated. The THz polarization state can be tuned from linear through elliptical to circular by changing the polarization state of the driving laser.

Quasi-phase matching via femtosecond laser-induced domain inversion in lithium niobate waveguides.

We demonstrate an all-optical fabrication method of quasi-phase matching structures in lithium niobate (LiNbO3) waveguides using a tightly focused femtosecond near-infrared laser beam (wavelength of 800nm). In contrast to other all-optical schemes that utilize a periodic lowering of the nonlinear coefficient χ(2) by material modification, here the illumination of femtosecond pulses directly reverses the sign of χ(2) through the process of ferroelectric domain inversion. The resulting quasi-phase matching structures, therefore, lead to more efficient nonlinear interactions. As an experimental demonstration, we fabricate a structure with the period of 2.74μm to frequency double 815nm light. A maximum conversion efficiency of 17.45% is obtained for a 10mm long waveguide.

Stimulated Brillouin Scattering in Photonic Integrated Circuits: Novel Applications and Devices

The last few years have seen major progress in harnessing on-chip photon-phonon interactions, leading to a wide range of demonstrations of new functionalities. Utilizing not only the optical response of a nonlinear waveguide-but also acoustic resonances-enables the realization of microwave devices with unprecedented performance, otherwise hard to achieve in all-optical processing schemes or electronically. Here, we overview on-chip stimulated Brillouin scattering (SBS) with special emphasis on microwave sources and microwave signal processing schemes. We review the different material platforms and structures for on-chip SBS, ranging from chalcogenide rib waveguides to hybrid silicon/silicon-nitride structures, high-Q photonic-phononic silica microresonators, and suspended silicon nanowires. We show that the paradigm shift in SBS research-from long length of fibers to chip-scale devices-is now moving toward fully integrated photonic-phononic CMOS chips.

All-optical feedforward automatic gain control scheme for pump power shared erbium-doped fiber amplifiers

All-optical feedforward automatic gain control scheme for pump power shared erbium-doped fiber amplifiers

An all-optical scheme for implementing a NAND logic by dibit representation of squeezed state of light

Squeezed state of light can present a promising world of quantum communication breaking the quantum limit of noise. We report an all-optical NAND logic operation by dibit representation of squeezed light for a highly noise reduced communication.

All-optical generation of surface plasmons in graphene

Here we present an all-optical plasmon coupling scheme, utilising the intrinsic nonlinear optical response of graphene. We demonstrate coupling of free-space, visible light pulses to the surface plasmons in a planar, un-patterned graphene sheet by using nonlinear wave mixing to match both the wavevector and energy of the surface wave. By carefully controlling the phase-matching conditions, we show that one can excite surface plasmons with a defined wavevector and direction across a large frequency range, with an estimated photon efficiency in our experiments approaching $10^{-5}$.