Optical Analog Research Articles

Two-dimensional optical differentiator for broadband edge detection based on dielectric metasurface.

Image edge processing has widespread adoption in a variety of scientific and industrial scenarios. To date, implementations of image edge processing have mostly been done electronically, but there are still difficulties to achieve real-time, high-throughput, and low power consumption image edge processing. The advantages of optical analog computing include low power consumption, fast transmission speed, and high parallel processing capability, and optical analog differentiators make this process possible. However, the proposed analog differentiators can hardly meet the requirements of broadband, polarization insensitive, high contrast, and high efficiency at the same time. Moreover, they are limited to one-dimensional differentiation or work in reflection mode. To be better compatible with two-dimensional image processing or image recognition systems, two-dimensional optical differentiators that integrate the above advantages are urgently needed. In this Letter, a two-dimensional analog optical differentiator with edge detection operating in transmission mode is proposed. It can cover the visible band, is polarization uncorrelated, and has a resolution that reaches 1.7 μm. The efficiency of the metasurface is higher than 88%.

Optical Analogs of Rabi Splitting in Integrated Waveguide‐Coupled Resonators

AbstractRealizing optical analogs of quantum phenomena in atomic, molecular, or condensed matter physics has underpinned a range of photonic technologies. Rabi splitting is a quantum phenomenon induced by a strong interaction between two quantum states, and its optical analogs are of fundamental importance for the manipulation of light–matter interactions with wide applications in optoelectronics and nonlinear optics. Here, purely optical analogs of Rabi splitting in integrated waveguide‐coupled resonators formed by two Sagnac interferometers are proposed and theoretically investigated. By tailoring the coherent mode interference, the spectral response of the devices is engineered to achieve optical analogs of Rabi splitting with anti‐crossing behavior in the resonances. Transitions between the Lorentzian, Fano, and Rabi splitting spectral lineshapes are achieved by simply changing the phase shift along the waveguide connecting the two Sagnac interferometers, revealing interesting physical insights about the evolution of different optical analogs of quantum phenomena. The impact of the device's structural parameters is also analyzed to facilitate device design and optimization. These results suggest a new way for realizing optical analogs of Rabi splitting based on integrated waveguide‐coupled resonators, paving the way for many potential applications that manipulate light–matter interactions in the strong coupling regime.

Generation of Longitudinal Ultrasound by Shear Strain Pulses in the Spin–Phonon Echo Regime

The possibility of generation of longitudinal ultrasonic pulses of gigahertz frequencies in the spin–phonon echo regime by acting on a magnetized isotropic paramagnet with nanosecond shear strain pulses is predicted. The frequency of generated longitudinal ultrasonic echo signals is twice as high as the frequency of pulses entered into the medium. This effect can be realized when the velocity of longitudinal ultrasound exceeds the velocity of shear strain waves by less than two times. This resonant mechanism of the pulsed regime of second harmonic generation, which is accompanied by a nonlinear transformation of transverse into longitudinal ultrasound, has no optical analog.

Dynamics of recombination in viscous electron–hole plasma in a mesoscopic GaAs channel

The recombination dynamics are studied in viscous electron–hole plasma, consisting of electrons and photo-generated heavy and light holes, formed in the high-mobility mesoscopic GaAs channel. It is shown that an increase in the pump power reduces the concentration and mobility of background electrons, which, in turn, slows down their recombination with photogenerated holes. At a critical pump power, the recombination time begins to decrease, which is a consequence of the transition of a viscous electron–hole plasma from the hydrodynamic regime to the Drude diffusive regime. The observed transition occurs when the scattering of electrons with disorder begins to dominate over electron–electron scattering, which leads to the transformation of an inhomogeneous Poiseuille charge flow into a homogeneous diffusion flow. As a result, an optical analogue of the Gurzhi effect has been found.

Optical analog to coherent population return in coupled nonlinear waveguides

In this paper, we investigate the optical analog to coherent population return (CPR) in coupled nonlinear waveguides. The nonlinearity sometimes plays a negative role in classical simulations of quantum adiabatic passages in waveguides. Nevertheless, it is interesting to note that the nonlinearity here helps simulating the adiabatic CPR technique. The CPR can still occur when the detuning (difference of the propagation constants) between the two nonlinear waveguides is moderate, which is a typical requirement of the technique. Moreover, the adiabatic process can appear when the detuning is small or zero. This is done by simply adjusting the incident light power, which is easy and of high accuracy compared with modulating the propagation constants. Therefore, the requirements towards the propagation constants of the waveguides are further relaxed in the nonlinear case. Finally, we point out that the CPR in nonlinear waveguides can be extended to design achromatic beam splitters.

Engineering of Zeno Dynamics in Integrated Photonics

Frequent observations to a quantum system modify its coherent evolution through the Zeno effect and Zeno dynamics. Generally, the measurement process destroys the evolution environment of the monitored system, making repeated observations remain a challenge. Here, using the quantum analogy experiments, we realize and engineer the Zeno effect and Zeno dynamics in optical waveguide arrays, where the optical modes correspond to distinct quantum states, and the temporal evolution is mapped into the spatial propagation. We propose a new, extensible experimental strategy for realizing an optical analog of stroboscopic measurements, which are performed by the build-in, on-demand segmented waveguide portions. The weak-to-strong stroboscopic measurements are realized, where the monitored system undergoes a transition from free evolution to optical Zeno freezing. Setting the measurements in the strong regime, the optical Zeno effect and optical Zeno dynamics are successfully generated, and their relationship is demonstrated in optics. We then propose a novel quantum Zeno slicing approach, which allows us to dynamically engineer the Hilbert space of the monitored system. This generic approach is verified by generating a series of Zeno subspaces with different measurement projectors, based on the quantum-optical analogy. The complexity of light dynamics is largely increased, providing full control of the propagation via steering Zeno dynamics. Our results pave the way for manipulation of quantum states by harnessing Zeno dynamics in integrated photonics.

Theoretical research on the transverse spin of structured optical fields inside a waveguide

Structured optical fields inside a waveguide possess the transverse spin, i.e., the spin angular momentum perpendicular to the direction of the waveguide. The physical origin of the transverse spin can be attributed to the presence of an effective rest mass of photons in guided waves, or equivalently, to the existence of a longitudinal field component, such that the transverse and longitudinal fields together form an elliptical polarization plane. In contrary to the traditional viewpoint, the transverse spin of photons in guided waves is also quantized, and its quantization form is related to the ellipticity of the polarization ellipse. The direction of the transverse spin depends on the propagation direction of electromagnetic waves along the waveguide, such a spin-momentum locking may have important applications in spin-dependent unidirectional optical interfaces. By means of a coupling between the transverse spin of guided waves and some physical degrees of freedom, one can develop an optical analogy of spintronics, i.e., spinoptics.

Optical differentiation in a polar coordinate system

Optical analog computing prevails over digital computing in several aspects, such as processing speed and power consumption. Optical differentiation, as a main branch, can be particularly significant in image recognition. Various differentiators have been developed to realize the two-dimensional differentiation in Cartesian coordinates. Here, we propose the optical differentiation in a polar coordinate system, which can be factorized into the radial differentiation and the angular differentiation. Experimental results demonstrate that the variations along radial and angular directions can be, respectively, highlighted by the two kinds of differentiation, which suggests that employing polar coordinates may be more intuitive and informative in practical use. This work is probable to enrich the content of optical differentiation and extend potential applications in image recognition.

Sagnac interference in integrated photonics

As a fundamental optical approach to interferometry, Sagnac interference has been widely used for reflection manipulation, precision measurements, and spectral engineering in optical systems. Compared to other interferometry configurations, it offers attractive advantages by yielding a reduced system complexity without the need for phase control between different pathways, thus offering a high degree of stability against external disturbance and a low wavelength dependence. The advance of integration fabrication techniques has enabled chip-scale Sagnac interferometers with greatly reduced footprint and improved scalability compared to more conventional approaches implemented by spatial light or optical fiber devices. This facilitates a variety of integrated photonic devices with bidirectional light propagation, showing new features and capabilities compared to unidirectional-light-propagation devices, such as Mach–Zehnder interferometers (MZIs) and ring resonators (RRs). This paper reviews functional integrated photonic devices based on Sagnac interference. First, the basic theory of integrated Sagnac interference devices is introduced, together with comparisons to other integrated photonic building blocks, such as MZIs, RRs, photonic crystal cavities, and Bragg gratings. Next, the applications of Sagnac interference in integrated photonics, including reflection mirrors, optical gyroscopes, basic filters, wavelength (de)interleavers, optical analogues of quantum physics, and others, are systematically reviewed. Finally, the open challenges and future perspectives are discussed.

Bistable All‐Optical Devices Based on Nonlinear Epsilon‐Near‐Zero (ENZ) Materials

AbstractNonlinear and bistable optical systems are a key enabling technology for the next generation optical networks and photonic neural systems with many potential applications in optical logic and information processing. Here, a novel bistable resonator‐free all‐optical waveguide device based on indium tin oxide as nonlinear epsilon‐near‐zero material providing a cost‐efficient and high‐performance binarity photonic platform is proposed. The salient features of the proposed device are compatibility with silicon photonics, enabling sub‐picosecond operation speeds with moderate switching power. The device can act as an optical analogue of memristor or thyristor and can become an enabling element of photonic neural networks not requiring OEO conversions.

Klein tunneling through a rectangular potential barrier in a binary waveguide array

We analytically and numerically investigate the optical analog of the quantum relativistic Klein tunneling of a particle through a large repulsive rectangular potential barrier. This quantum relativistic model can be mimicked and analyzed by studying the propagation of a Dirac soliton in a binary waveguide array (BWA). The rectangular potential step in this platform is created by introducing a certain offset for waveguides’ refractive indices. We analytically derive the transmission coefficients of plane waves through the rectangular potential step in BWAs and also in the continuous model in free space. We demonstrate that the analytical transmission coefficient in the discrete model with BWAs is in strikingly perfect agreement with the simulations-based results.

An Analog EIC-PIC Receiver With Carrier Phase Recovery for Self-Homodyne Coherent DCIs

Coherent techniques, used for high-capacity optical links, conventionally use high-speed ADCs and digital signal processing, which make them power hungry. For short-reach coherent links such as data center interconnects, power consumption, form factor, cost, and latency have to be greatly reduced. Co-designed photonic and electronic integrated circuits, in the optical and electrical analog domains, respectively, can achieve these goals. In this brief, for the first time, we present integration of a silicon photonic integrated coherent receiver (ICR) front-end with an electronic carrier phase recovery chip, as a part of a complete coherent receiver solution. A phase shifter in the ICR (fabricated in a 220 nm silicon-on-insulator technology) receives feedback from the CPR chip, and the combination compensates for the time varying phase offset between the modulated signal and the unmodulated carrier in the closed loop configuration. In this proof-of-concept demonstration, we present experimental results obtained from the stand-alone ICR, and its system level integration with CPR chip, for QPSK signals. The technique can be extended to a higher-order modulation formats, such as 16-QAM, for capacity scaling. The proposed scheme is suitable for carrier-forwarded coherent links, such as polarization multiplexed carrier based self-homodyne links.

Selectively reflective edge detection system based on cholesteric liquid crystal.

Optical analog computing has attracted extensive interest in image processing and optical engineering in recent decades. Here, we propose a reflective optical analog computing system based on a cholesteric liquid crystal (CLC), which simplifies the traditional optical analog computing system by taking advantage of the CLC reflecting the light with specified circular polarization and provides a new, to the best of our knowledge, idea for the integration of optical analog computing systems. Meanwhile, we present results in which a section of an insect foot is observed using the reflective optical analog computing system, which may develop valuable applications in biomedical imaging.

High-NA polarization-independent isotropic spatial differential metasurface

Metasurface-based optical computing has been a topic of interest for many researchers, aimed at implementing high-speed and efficient image processing in small equipment. However, the existing designs cannot work well in the aspects of spatial resolution, polarization and azimuth angle simultaneously. Here, we present a 2D differential metasurface with a honeycomb photonic structure as the basic unit, which not only satisfies isotropy and polarization independence, but also has a NA as high as 0.44. Through numerical verification, the proposed metasurface can produce the result of second-order differential operation of Gaussian functions in 1D space, and can be used to implement edge detection of objects in an image as well. Our results provide new opportunities for optical analog computing and computer vision applications.

Pursuing excitonic energy transfer with programmable DNA-based optical breadboards.

DNA nanotechnology has now enabled the self-assembly of almost any prescribed 3-dimensional nanoscale structure in large numbers and with high fidelity. These structures are also amenable to site-specific modification with a variety of small molecules ranging from drugs to reporter dyes. Beyond obvious application in biotechnology, such DNA structures are being pursued as programmable nanoscale optical breadboards where multiple different/identical fluorophores can be positioned with sub-nanometer resolution in a manner designed to allow them to engage in multistep excitonic energy-transfer (ET) via Förster resonance energy transfer (FRET) or other related processes. Not only is the ability to create such complex optical structures unique, more importantly, the ability to rapidly redesign and prototype almost all structural and optical analogues in a massively parallel format allows for deep insight into the underlying photophysical processes. Dynamic DNA structures further provide the unparalleled capability to reconfigure a DNA scaffold on the fly in situ and thus switch between ET pathways within a given assembly, actively change its properties, and even repeatedly toggle between two states such as on/off. Here, we review progress in developing these composite materials for potential applications that include artificial light harvesting, smart sensors, nanoactuators, optical barcoding, bioprobes, cryptography, computing, charge conversion, and theranostics to even new forms of optical data storage. Along with an introduction into the DNA scaffolding itself, the diverse fluorophores utilized in these structures, their incorporation chemistry, and the photophysical processes they are designed to exploit, we highlight the evolution of DNA architectures implemented in the pursuit of increased transfer efficiency and the key lessons about ET learned from each iteration. We also focus on recent and growing efforts to exploit DNA as a scaffold for assembling molecular dye aggregates that host delocalized excitons as a test bed for creating excitonic circuits and accessing other quantum-like optical phenomena. We conclude with an outlook on what is still required to transition these materials from a research pursuit to application specific prototypes and beyond.

Compact implementation of an all-optical 1-bit full adder by coherent excitation of a single 3-µm2 plasmonic cavity

In contrast to the high performances of long-range, high-speed optical information transfer, optical information processing remains outperformed by electronic microprocessing. The two mains reasons are the lack of gain medium that hampers the development of an optical analogue of the transistor and the lack of compactness of the approaches proposed so far. Here, we demonstrate a new concept of the design of all-optical elementary computing units based on the shaping of plasmonic modal landscape in micrometric on-chip 2D cavities to realize reconfigurable Arithmetic and Logic Units (ALU). Our interconnect-free devices perform multi-bit logic gate functions in a single cavity without ALU cascading, therefore obviating loss in vias and so the need for gain to restore the binary signal. Moreover, an astute cavity design allows to reconfigure a single cavity into multiple logic functions, including a first full adder. The main challenge on the way to increasing the functional Boolean complexity is the design of the cavity shape and of the excitation/detection parameters for which an approach based on artificial intelligence will be implemented.

Development and Applications of Spatial Optical Analog Computing

Development and Applications of Spatial Optical Analog Computing

A Novel Microstructure of 2‐Bit Optical Analog to Digital Converter Based on Kerr Effect Nonlinear Nanocavities in 2D Photonic Crystal

In this paper, an all‐optical analog‐to‐digital converter based on nonlinear with silicon materials is designed and simulated. The proposed structure consists of three nonlinear nanocavity that control the optical signal power intensity. The nonlinear material used is aluminum gallium arsenide (AlGaAs). Aluminum gallium arsenide (AlGaAs) with a linear refractive index of n0 = 1.4 and a nonlinear refractive index of n2 = 1.5 × 10−17. Due to the small path length of the waveguides, the optical signals move a short distance and as a result, the power optical losses along the path are reduced and on the other hand, the speed of the structure is increased. The transmission percentage is between 90% and 100%. The overall dimensions of the structure are 324 μm2. The plane wave expansion (PWE) method is used to calculate the band structure. The two‐dimensional finite difference time domain (2D‐FDTD) method is used to calculate the transmission power spectrum and the simulation results.

New cross-coupled resonator induced shifted absorption (CRISA) in double microring resonators using a cross-coupling-structure technique

We report, for the first time to the best of our knowledge, a technique that employs ′cross-coupling structure’ in the cascaded microring resonators (MRRs) to bring new optical analogues of quantum coherence phenomena. The new configuration resembles a standard double resonator (SDR) but uses cross-coupled–based directional couplers (DCs) instead of the typical direct-coupled–based DCs. One of its unique features is that it does not exhibit the typical SDR’s signature quantum coherence analogue effects like coupled-resonator induced transparency (CRIT) or coupled-resonator induced absorption (CRIA). On the contrary, it produces a new very narrow reflection dip positioned at single-pass phase shift θ = − π/2 which we refer to as cross-coupled resonator induced shifted absorption (CRISA). We compare extensively CRISA’s characteristics with the CRIT, CRIA, and Autler-Townes splitting (ATS) found in SDR. The technique opens up new configurations with richer optical behaviours that could find potentially still unexplored applications.

The lens of theory: seeing better or differently?

PurposeThis article explicates the notion of using a “theoretical lens” to interpret research data, which has grown increasingly common in recent decades, often without a second thought about the implications of use of a mere metaphor in the pursuit of truth. Poets may not question that metaphors reveal truths, but should social scientists accept that?Design/methodology/approachIt looks first at what theory means, then – and in greater detail – what the metaphor of a lens entails.FindingsDrawing on the base analogy in optics, it identifies four mechanisms through which theory might act as a lens – adjustment, correction, distortion and augmentation-suppression, with examples based on theories of business strategy and organisation studies.Research limitations/implicationsThese four mechanisms involve two different ways of seeing – better and differently. With adjustment and correction see better what is, or perhaps what was. With distortion and especially augmentation-suppression, we see differently, which helps us imagine what might be, or what we might have overlooked. They help us escape narrow silos of thinking. Researchers and students alike need to be aware of all four lenses of theory and be ready to experiment.Originality/valueIt argues that if some theories try to help us see better, others push us to see differently, with implications for the practice and teaching of research methods.