Photonic Concept Research Articles

Relativistic free electrons based quantum physics

The light-matter interaction is one of the fundamental research fields in physics. The electron is the first discovered elementary particle that makes up matter. Therefore, the interaction between electron and light field has long been the research interest of physicists. Electrons are divided into two kinds, i.e. bounded electrons and free electrons. The quantum transition of bounded electron system is constrained by the selection rules with the discrete energy levels, while the free electron systems are not. In the last decade, the experiments of photon-induced near-field electron microscopy (PINEM) have been demonstrated. The experimental setup of PINEM is based on ultrafast electron transmission microscopy (UTEM). The thoeritcal framworks have also been developed to describe the interaction between quantum free electrons and optical fields. Within macroscopic quantum electrodynamics, the concept of photon is extended to photonic quasi-particles. Solutions of maxwell's equations in medium that satisfy certain boundary conditions are called photonic quasiparticles, such as surface plasmon polaritons, phonon polaritons, or even magnetic field. The different dispersion relations of photonic quasi-particles produce abundant phenomena in the interaction between light and matter. The underlying information about the PINEM interaction can be inferred from the electron energy loss spectrum (EELS). It has been used for implementing the near-field imaging in its infancy. By now it is capable of not only realizing time-resolved dynamic imaging, reconstructing the dispersion relation of photonics crystal and its Bloch mode, but also measuring the mode lifetime directly. The PINEM has also been used to study free electron wavepacket reshaping, free electron comb, free electron attosecond pulse train, etc. Recently, this field has entered into the era of quantum optics, and people use PINEM to study novel phenomena in quantum optics, such as entanglement between free electrons and cavity photons, entanglement between free electrons and free electrons, free electron qubits, and preparation of novel light quantum states. In this paper, the theoretical and experimental development of free-electron quantum physics are reviewed. We have disscussed the application scenarios of quantum free electron system. The current difficulties and future development are envisaged.

High-Quality Optical Hotspots with Topology-Protected Robustness

Optical hotspots underpin a wide variety of photonic devices ranging from sensing, nonlinear generation to photocatalysis, taking advantage of the strong light–matter interaction at the vicinity of photonic nanostructures. While plasmonic nanostructures have been widely used for strongly localized electromagnetic energy on surfaces, they suffer from high loss and consequently a low quality factor. Resonance-based dielectric structures provide an alternative solution with a larger quality factor, but there is a mismatch between the maximum values of the light confinement (quality factor) and the leakage (intensity in the near-field). Here, we propose to apply the concept of topological photonics to the formation of hotspots, producing them in both topological edge states and topological corner states. The topology secures strong light localization at the surface of the nanostructures where the underlying topological invariant shows a jump, generating a field hotspot with simultaneous increment of quality factor and light intensity. Meanwhile, it leverages a good robustness to fabrication imperfection including fluctuation in shape and misalignment. After a systematic investigation and comparison of the robustness between 1D and 2D topological structures, we conclude that the hotspots from 1D topological edge states promise a fertile playground for emerging applications that require both enhanced light intensity and high spectral resolution.

Single-photon microwave photonics

With the rapid development of microwave photonics technology, high-speed processing and ultra-weak signal detection capability have become the main bottlenecks in many applications. Thanks to the ultra-weak signal detection capability and the extremely low timing jitter properties of single-photon detectors, the combination of single-photon detection and classical microwave photonics technology may provide a solution to break the above bottlenecks. In this paper, we first report a novel concept of single-photon microwave photonics (SP-MWP), a SP-MWP signal processing system with phase shifting and frequency filtering functionalities is demonstrated based on a superconducting nanowire single photon detector (SNSPD) and a successive time-correlated single photon counting (TCSPC) module. Experimental results show that an ultrahigh optical sensitivity down to −100 dBm has been achieved, and the signal processing bandwidth is only limited by the timing jitter of single-photon detectors. In the meantime, the proposed system demonstrates an ultrahigh anti-interference capability, only the signal which is phase locked by the trigger signal in TCSPC can be extracted from the detected signals combining with noise and strong interference. The proposed SP-MWP concept paves a way to a novel interdisciplinary field of microwave photonics and quantum mechanism, named by quantum microwave photonics.

Design and analysis of heptagonal cladding with rotated-hexa elliptical core based PCF for the applications of communication sectors in the THz region

Photonic crystal fiber-based heptagonal cladding with the elliptical rotated-Hexa core is reported in the terahertz waveguide for the applications of communication area in this paper. By utilizing the photonic crystal fiber concept, all numerical results have been obtained by the finite element method with perfectly matched layers based on the COMSOL Multiphysics computer software tool. This H-PCF fiber shows a low effective material loss of 0.0076 cm−1, with a larger effective area of 5.95 × 10–8 m2, power flows within the core area of 90%, confinement loss of 3.35 × 10–16 cm−1, and scattering loss of 1.24 × 10–10 cm−1 at 1 THz. Besides, other optical properties like confinement loss, scattering loss, power fraction, V-parameter, and effective area have also been considered briefly. So, it is expected that the mentioned H-PCF structure-based waveguide will significantly improve many kinds of communication fields of the THz technology.

Architecture of photonics correlation for infrared heterodyne interferometry: demonstration of amplitude-modulation based correlation

In the context of mid-infrared astronomical aperture synthesis, heterodyne interferometry has been identified as a potential solution to combine a large number of telescopes in the 10 µm–20 µm wavelength regime. In search of an alternative to costly and technologically difficult digital correlation, we have proposed to correlate wide bandwidth radio-frequency signals in the analog domain, using photonics components developed in the frame of telecommunication applications. In this paper, we propose an extension to amplitude modulation of our initial proposition, in which the encoding of the heterodyne signal was performed through phase modulation. Both schemes are compared, and an experimental demonstration of correlation between two signals using amplitude modulation is presented. Our experiment shows that this concept has important advantages over phase modulation, in particular with regard to the requirements on phase stabilization. The possibility to scale-up the photonics concept to the recombination of a large number of telescopes, and a large number of spectral channels to increase the instantaneous bandwidth coverage of infrared heterodyne interferometry, is discussed. This study shows that the necessary technological building blocks of a pathfinder instrument adaptable to existing astronomical facilities are available.

Reservoir Computing Assisted Ultrafast User Localization in Beam Steering Optical Wireless System

A novel approach to achieving ultrafast real-time user localization in optically controlled beam-steering wireless communications (OWC) is proposed and demonstrated in this letter. Ultrafast wavelength encoded user localization at 50 MHz rate is achieved based on photonic time stretch concept and a passive beam scanner using a 45° tilted fibre grating (TFG). Not only the angular separation but also the linear distance from the access point can be determined simultaneously. More importantly, challenging instantaneous optical wavelength identification within nanosecond range is successfully achieved through chirped microwave frequency encoding and reservoir computing (RC) based frequency identification. A proof-of-concept experiment was carried out to verify the proposed approach. The results show that RC is more efficient in frequency chirp identification than the conventional short-time Fourier transform approach.

Integrated phase-sensitive photonic sensors: a system design tutorial

Photonic integration has seen tremendous progress over the previous decade, and several integration platforms have reached industrial maturity. This evolution has prepared the ground for miniaturized photonic sensors that lend themselves to efficient analysis of gaseous and liquid media, exploiting large interactions lengths of guided light with surrounding analytes, possibly mediated by chemically functionalized waveguide surfaces. Among the various sensor concepts, phase-sensitive approaches are particularly attractive: offering a flexible choice of the operation wavelength, these schemes are amenable to large-scale integration on mature technology platforms such as silicon photonics or silicon nitride ( S i 3 N 4 ) that have been developed in the context of tele- and data-communication applications. This paves the path toward miniaturized and robust sensor systems that offer outstanding scalability and that are perfectly suited for high-volume applications in life sciences, industrial process analytics, or consumer products. However, as the maturity of the underlying photonic integrated circuits (PICs) increases, system-level aspects of mass-deployable sensors gain importance. These aspects include, e.g., robust system concepts that can be operated outside controlled laboratory environments as well as readout schemes that can be implemented based on low-cost light sources, without the need for benchtop-type tunable lasers as typically used in scientific demonstrations. It is, thus, the goal of this tutorial to provide a holistic system model that allows us to better understand and to quantitatively benchmark the viability and performance of different phase-sensitive photonic sensor concepts under the stringent limitations of mass-deployable miniaturized systems. Specifically, we explain and formulate a generally applicable theoretical framework that allows for a quantitatively reliable end-to-end analysis of the overall signal chain. Building upon this framework, we identify and explain the most important technical parameters of the system, comprising the photonic sensor circuit, the light source, and the detector, as well as the readout and control scheme. We quantify and compare the achievable performance and the limitations that are associated with specific sensor structures based on Mach–Zehnder interferometers (MZIs) or high-Q optical ring resonators (RRs), and we condense our findings by formulating design guidelines both for sensor concepts. As a particularly attractive example, we discuss an MZI-based sensor implementation, relying on a vertical-cavity surface-emitting laser (VCSEL) as a power-efficient low-cost light source in combination with a simple and robust readout and control scheme. In contrast to RR-based sensor implementations, MZIs can be resilient to laser frequency noise, at the cost of a slightly lower sensitivity and a moderately increased footprint. To facilitate the application of our model, we provide a MATLAB-based application that visualizes the underlying physical principles and that can be readily used to estimate the achievable performance of a specific sensor system. The system-level design considerations are complemented by an overview of additional aspects that are important for successful sensor system implementation such as the design of the underlying waveguides, photonic system assembly concepts, and schemes for analyte handling.

Plasmonic topological metasurface by encircling an exceptional point.

Resonant scattering, guided mode propagation phase, and/or orientation-dependent phase retardations are the three main mechanisms used to date to conceive optical metasurfaces. Here, we introduce an additional degree of freedom to address optical phase engineering by exploiting the topological features of non-Hermitian matrices operating near their singular points. Choosing metasurface building blocks to encircle a singularity following an arbitrarily closed trajectory in parameter space, we engineered a topologically protected full 2π-phase on a specific reflected polarization channel. The ease of implementation together with its compatibility with other phase-addressing mechanisms bring topological properties into the realm of industrial applications at optical frequencies and prove that metasurface technology represents a convenient test bench to study and validate topological photonic concepts.

The MorphoColor Concept for Colored Photovoltaic Modules

We introduce a photonic color concept for integrated photovoltaic modules. Taking up the inspiration from the Morpho butterfly with its brightly colored wings, we developed this photonic concept further to achieve an improved angular independent color effect, suitability for module integration, and compatibility with industrial production processes, while maintaining high module efficiencies. We demonstrate the steps that lead to the optimized photonic structure and explain the underlying optical effects. Using the data from demonstrator modules, we show the outstanding performance in terms of module efficiency and color stability. A power output for the MorphoColor modules of more than 94% compared to the reference module power is shown.

Photocontrolled Strain in Polycrystalline Ferroelectrics via Domain Engineering Strategy.

The use of photonic concepts to achieve nanoactuation based on light triggering requires complex architectures to obtain the desired effect. In this context, the recent discovery of reversible optical control of the domain configuration in ferroelectrics offers a light-ferroic interplay that can be easily controlled. To date, however, the optical control of ferroelectric domains has been explored in single crystals, although polycrystals are technologically more desirable because they can be manufactured in a scalable and reproducible fashion. Here we report experimental evidence for a large photostrain response in polycrystalline BaTiO3 that is comparable to their electrostrain values. Domains engineering is performed through grain size control, thereby evidencing that charged domain walls appear to be the functional interfaces for the light-driven domain switching. The findings shed light on the design of high-performance photoactuators based on ferroelectric ceramics, providing a feasible alternative to conventional voltage-driven nanoactuators.

Coherence in single photon emission from droplet epitaxy and Stranski–Krastanov quantum dots in the telecom C-band

The ability of two photons to interfere lies at the heart of many photonic quantum networking concepts and requires that the photons are indistinguishable with sufficient coherence times to resolve the interference signals. However, for solid-state quantum light sources, this can be challenging to achieve as they are in constant interaction with noise sources in their environment. Here, we investigate the noise sources that affect InAs/InP quantum dots emitting in the telecom C-band by comparing their behavior on a wetting layer for Stranski–Krastanov grown quantum dots with a nearly wetting layer-free environment achieved with the droplet epitaxy growth mode. We show that the droplet epitaxy growth mode is beneficial for a quiet environment, leading to 96% of exciton transitions having a coherence time longer than the typical detector resolution of 100 ps, even under non-resonant excitation. We also show that the decay profile indicates the presence of slow dephasing processes, which can be compensated for experimentally. We finally conduct Hong–Ou–Mandel interference measurements between subsequently emitted photons and find a corrected two-photon interference visibility of 98.6 ± 1.6% for droplet-epitaxy grown quantum dots. The understanding of the influence of their surroundings on the quantum optical properties of these emitters is important for their optimization and use in future quantum networking applications.

Electronic Bottleneck Suppression in Next‐Generation Networks with Integrated Photonic Digital‐to‐Analog Converters

Digital‐to‐analog converters (DAC) are indispensable functional units in signal processing instrumentation and wide‐band telecommunication links for both civil and military applications. As photonic systems are capable of high data throughput and low latency, an increasingly found system limitation stems from the required domain crossing such as digital to analog and electronic to optical. A photonic DAC implementation, in contrast, enables a seamless signal conversion with respect to both energy efficiency and short signal delay, often requiring bulky discrete optical components and electric–optic transformation, hence introducing inefficiencies. Herein, a novel coherent parallel photonic DAC concept along with a 4‐bit experimental prototype capable of performing this DAC without optic–electric–optic domain crossing is introduced. This new paradigm guarantees a linear intensity weighting among bits when operating at high sampling rates (50 GHz), featuring an exceptional sampling efficiency (> 100 GS ) and small footprint (≈1 mm2) in an 8‐bit implementation. Importantly, this photonic DAC enables seamless interfaces of next‐generation data processing hardware with high relevance in data centers, task‐specific compute accelerators such as neuromorphic engines, and network edge processing applications.

Photonic Antenna Design for Long Term Evolution Application

Radio over fiber (RoF) technology is an appropriate solution of transmission media a new fiber optic and cable development very high cost. The photonic antenna can crack this problem. This paper focuses on the development of the photonic antenna concept in order to integrate the antenna for long term evolution application. The proposed operating frequency range is 1.7 to 2.4 GHz which supports most of the spectrum used. The simulation of the designed an antenna by using FR-4 the substrate is analyzed by using the Microwave studio (CST). This project presents a proposed design for the Long-Term Evolution application in the close area by analyzes from the S-parameter characteristics.

Chromatic Dispersion Induced Semi Optical Pulse Stretching Approach to Beam Steering Applications of Phase Array Antenna

A semi optical technique based on chromatic dispersion induced pulse stretching effect of single mode optical fiber has been utilized to demonstrate the beam steering of phase array antenna. In the proposed study $$1 \times 4$$ antenna array has been fabricated at desired specifications before applying the photonic feeding concept. In the beginning of the paper detail, fabrication process of antenna array has been demonstrated followed with establishing relationships between the phase shifts introduced between two consecutive antenna elements. The purpose of this paper is to design and fabricate a novel Rectangular Microstrip antenna array. The Resonant frequency of antenna is 13 GHz. The proposed rectangular patch antenna has been designed using FR4 with dielectric constant (er = 4.4), loss tangent (tanδ) equal to 0.02. The individual rectangular patch antenna is coaxially feeded using photonic excitation. Various important parameters like return loss, gain, VSWR, radiation pattern etc are measured and compared with simulated results. High frequency Structure simulator (HFSS) is used for simulation. A concept of pulse stretching in beam steering has been experimentally validated.

Multifractality of light in photonic arrays based on algebraic number theory

Many natural patterns and shapes, such as meandering coastlines, clouds, or turbulent flows, exhibit a characteristic complexity that is mathematically described by fractal geometry. Here, we extend the reach of fractal concepts in photonics by experimentally demonstrating multifractality of light in arrays of dielectric nanoparticles that are based on fundamental structures of algebraic number theory. Specifically, we engineered novel deterministic photonic platforms based on the aperiodic distributions of primes and irreducible elements in complex quadratic and quaternions rings. Our findings stimulate fundamental questions on the nature of transport and localization of wave excitations in deterministic media with multi-scale fluctuations beyond what is possible in traditional fractal systems. Moreover, our approach establishes structure–property relationships that can readily be transferred to planar semiconductor electronics and to artificial atomic lattices, enabling the exploration of novel quantum phases and many-body effects.

Absorption Engineering in an Ultrasubwavelength Quantum System.

Many photonic and plasmonic structures have been proposed to achieve ultrasubwavelength light confinement across the electromagnetic spectrum. Notwithstanding this effort, however, the efficient funneling of external radiation into nanoscale volumes remains problematic. Here, we demonstrate a photonic concept that fulfills the seemingly incompatible requirements for both strong electromagnetic confinement and impedance matching to free space. Our architecture consists of antenna-coupled meta-atom resonators that funnel up to 90% of the incident radiation into an ultrasubwavelength semiconductor quantum well absorber of volume V = λ310-6. A significant fraction of the coupled electromagnetic energy is used to excite the electronic transitions in the quantum well, with a photon absorption efficiency 550 times larger than the intrinsic value of the electronic dipole. This system opens important perspectives for ultralow dark current quantum detectors and for the study of light-matter interaction in the extreme regimes of electronic and photonic confinement.

Electric Field-Induced Linear Electro-Optic Effect Observed in Silicon-Organic Hybrid Ring Resonator

In this work, we report on the observation of the electric field-induced linear electro-optical effect in a silicon-based slot waveguide ring resonator covered by the nonlinear optical polymer Poly[(methyl methacrylate)-co-(Disperse Red 1 methacrylate)]. The device is fabricated in a photonic integrated circuit technology and intensity modulation is demonstrated to work in a direct-detection setup. As unique feature, the electric field-induced linear electro-optical effect allows to modulate the optical carrier wave with a time-varying electric field, while a static electric field can control its amplitude with no need for additional photonic components. Here, a linear tuning of the modulation-amplitude as function of the applied static electric field is demonstrated. This work paves a way toward novel integrated photonic device concepts.

Demonstration of Automated Adjustment and Coupling of Fiber Array to PICs Based on the Detection of Edges

ABSTRACTProgress in integrated photonics enables development of photonics integrated circuits (PIC) with new unique properties and overcomes current limits in information and communication technologies. The effective coupling of optical radiation between telecom optical fiber and photonic integrated circuits is necessary. To address these challenges, we present our concept of photonics integrated circuit (PIC) fully customized packaging with microwave, direct current, and fiber array ports with automated active alignment system. Automated adjustment and coupling of single-mode fiber (SMF) arrays with 8 fibers to PIC based on the detection of edges and markers on PIC and SMF arrays were successfully realized.

Lightscaping

A collaboration of German researchers presents the first instance of two-photon polymerisation induced by a mode-locked diode laser system, with a pulse length of 440 fs. Two-photon polymerisation allows for the production of complex microstructures, usually using an expensive laser system, such as Ti:sapphire. The development presented here works using a much cheaper diode laser, significantly reducing the cost of the process. Around the turn of the millennium, the research area of multiphoton polymerisation became well established; in particular, a technique known as direct laser writing (DLW) was developed to more easily produce photonic crystals with a range of uses, from thin-film optics to colour changing paints to photonic circuits. DLW requires a photoresist (a light sensitive material) to be illuminated by laser light of a frequency below its single-photon polymerisation threshold. When the laser light is tightly focused inside the photoresist, the light intensity may exceed the threshold for initiating multiphoton polymerisation. Authors Gordon Zyla (left) and Nils Surkamp (right) in their lab. SEM overview image of the ‘winding tower’ structure. Two-photon polymerisation manufacturing process.The oil immersion objective focusses the incident laser beam into the photoresist. Three-dimensional structuring can be obtained by moving the focal spot relative to the droplet. The smallest polymerisation is defined by the voxel size, which depends on the structuring speed and intensity of the focal spot. The SEM image in A. shows the fabricated lines structures between two cuboids. The SEM image in B. shows the ‘winding tower’ structure. In the past 10 years this area of research has seen a resurgence in interest, primarily due to the increased capabilities of diode lasers. One of the main drawbacks of multiphoton polymerisation is that it requires a high-frequency laser that can operate in the femtosecond range. Traditionally, appropriate laser systems of this type are expensive, such as Ti:sapphire lasers or fibre lasers. However, we are now starting to see diode lasers that can reliably operate in the femtosecond range for a fraction of the operating costs of conventional systems. Surkamp et al., in their work published in Electronics Letters, propose using a mode-locked diode laser, capable of producing ultrashort laser pulses 440 fs in length. In their design, the laser outputs an impressive 160 mW per pulse. The mode-locked nature of the laser is what allows pulses to reach the 440 fs pulse length. A key characteristic of two-photon polymerisation is that it has a high resolution, in the order of sub-100 nm. The resolution depends on the ‘voxel size’ – voxels being a 3D analogue of pixels. Therefore, with a small voxel size, very fine structures can be produced. The structures are produced layer-by-layer, in a manner similar to conventional 3D printing techniques. The size of the voxel is dependent on the structuring velocity (the speed at which the structure is produced) and the focus intensity. Surkamp et al. produced two structures, the first being two cuboids, 4 micrometres apart, connected by a number of lines. The lines were produced at increasing velocities to test how the technique's resolution would cope at different speeds. The second structure was much more complex, a winding ‘tower’ with additional embellishment in the structure. The tower has a roof, with two angled supports, and a central post containing a winding ‘staircase’ running up it. The two structures were analysed using a scanning electron microscope and look fantastic. The results clearly show the suitability of two-photon polymerisation as a way of producing structure at the micrometer scale. Diode lasers are much cheaper, meaning that the technique is accessible to a broader audience, not just those in well-funded laboratories. In addition, the work highlights the competitiveness of femtosecond optical pulse generation using diode lasers compared to fibre lasers – the current most compact femtosecond laser systems. With some additional tweaking, the technique could be used in the field of nanorobotics, where robots on the micro and sub-micro scale have the potential to be used in vivo. There are also obvious applications for producing ever smaller and more intricate circuitry components. Moreover, photonic integration concepts will further promote this development and promise to deliver ever more compact and cost-effective femtosecond diode laser systems in the coming decade.

Floquet topological insulator laser

We introduce a class of topological lasers based on the photonic Floquet topological insulator concept. The proposed system is realized as a truncated array of lasing helical waveguides, where the pseudomagnetic field arises due to twisting of the waveguides along the propagation direction that breaks the time-reversal symmetry and opens up a topological gap. When sufficient gain is provided in the edge channels of the array, the system lases into topological edge states. Topological lasing is stable only in certain intervals of the Bloch momenta that ensure a dynamic, but stable balance between the linear amplification and nonlinear absorption leading to the formation of breathing edge states. We also illustrate topological robustness of the edge currents by simulating lattice defects and triangular arrangements of the waveguides.