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We introduce a pioneering strategy to enhance the environmental stability of perovskite thin films, a critical step forward in advancing their application in optoelectronics. Through the innovative application of matrix encapsulation techniques, we focus on the stabilization of methylammonium lead iodide (MAPbI3) and methylammonium lead bromide (MAPbBr3) films. These films are meticulously prepared via a two-step solution deposition method under controlled ambient conditions. Our approach involves the application of poly(methyl methacrylate) (PMMA) and AZ5214 photoresist layers through spin-coating, aimed at singularly encapsulating the perovskite films. This encapsulation acts as a robust hydrophobic barrier, significantly mitigating moisture ingress and simultaneously addressing the challenge of pinhole presence within the perovskite structure. Through a series of detailed characterizations-spanning scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy-we demonstrate that, despite the thicker nature of the AZ5214 photoresist compared to the PMMA layer, it exhibits markedly enhanced stability. Notably, the integrity and optical properties of the perovskite films are preserved for extended periods of up to 960 hours under environmental exposure. This breakthrough highlights the superior performance of AZ5214 photoresist over PMMA in prolonging the operational life of perovskite thin films, thereby offering a promising avenue for their deployment in a wide range of optoelectronic devices.

Quantum state discrimination plays an essential role in quantum technology, crucial for quantum error correction, metrology, and sensing. While conventional methods rely on integrating readout signals or classifying raw signals, we developed a method to extract information about state transitions during readout, based on the path signature method, a tool for analyzing stochastic time series. The hardware experiments demonstrate an improvement in transmon qutrit state readout fidelity from 85.9 $\pm$ 1.0% to 91.0 $\pm$ 0.5%, without the need for additional hardware. This method has the potential to become a foundational tool for quantum technology.

Recently, nonreciprocal phase shifters have attracted a surge of interest thanks to the advent of nonreciprocal electromagnetic systems, such as nonreciprocal metasurfaces, nonreciprocal-beam antennas, and invisibility cloaks. To overcome the limitations associated with conventional technologies for realizing nonreciprocal phase shifters and gyrators, here we propose a low-noise, lightweight, low-profile, and linear magnetless nonreciprocal phase shifter formed by two temporal loops. The proposed temporal apparatus operates based on the generation of time-harmonic signals and destructive and constructive interferences for the undesired and desired time harmonics, respectively, at different locations of the structure. An external time-harmonic modulation signal injects an effective electronic angular momentum to the system to control the phase and frequency of the two loops. Such a temporal nonreciprocal phase shifter offers low insertion loss, and a large return loss (input matching) of greater than 28.1 dB. Additionally, this nonreciprocal phase shifter possesses a reconfigurable architecture and can be directly embedded in integrated circuit (IC) technology to create high power handling and linear IC-based nonreciprocal phase shifters., Comment: arXiv admin note: text overlap with arXiv:2107.09788

The quest for efficient and versatile microwave and optical isolators has recently spawned several novel space-time-modulated isolator structures. However, such space-time isolators suffer from a large profile and complex architecture caused by progressive nonreciprocal space-time coupling properties. To overcome these limitations, we propose a nonmagnetic phase-engineered temporal-loop-based isolator featuring large isolation levels, weak undesired time harmonics, and a low profile. The proposed isolator is composed of two temporal loops that provide desired constructive and destructive interferences of different time harmonics. Furthermore, these two loops are designed in a way to assure that the circulation and reflection of different time harmonics strengthen a low insertion loss unidirectional signal transmission. An experimental demonstration of the proposed time-modulated isolator at microwave frequencies is provided, featuring strong unidirectional wave transmission through the isolator with more than 27 dB contrast between the forward and backward waves across a fractional bandwidth of 14.3%. The proposed isolator outperforms the nonlinear-based and transistor-based isolators by featuring a highly linear response with OP1dB of higher than 31 dBm, high power rating of more than 47 dBm, and a low noise figure of 3.4 dB.

Conventional circulators are made of magnetic ferrites and suffer from a cumbersome architecture, incompatibility with integrated circuit technology and inability for high frequency applications. To overcome these limitations, here we propose a lightweight low-profile non-magnetic circulator comprising a nonreciprocal time-varying phase shifter. This circulator is composing a nonreciprocal temporal phase shifter and two reciprocal delay-line-based phase shifters. The proposed nonreciprocal temporal phase shifter is based on the generation of time-harmonic signals, enforcing destructive interference for undesired time harmonics and constructive interference for desired time harmonics at different locations of the structure. Such a unique task is accomplished through two phase-engineered temporal loops. The phase and frequency of these two loops are governed by external signals with different phases, imparting an effective electronic angular momentum to the system. We observe large isolation level of greater than 32 dB, a P1dB of +31.7 dBm and IIP3 of +42.4 dBm. Furthermore, this circulator is endowed with a reconfigurable architecture and can be directly embedded in a conventional integrated circuit (IC) technology to realize a class of high power handling and linear IC circulators., Comment: arXiv admin note: text overlap with arXiv:2107.09157

The limited radio-frequency spectrum is a fundamental factor in the design of wireless communication systems. The ever increasing number of wireless devices and systems has led to a crowded spectrum and increased the demand for versatile and multi-functional full-duplex wireless apparatuses. Recently, dynamic and intelligent metasurfaces are explored as a prominent technological solution to the current paradigm of spectrum scarcity by opportunistically sharing the spectrum with various users. In general, intelligent metasurfaces are dynamic, ultra-compact, multi-functional and programmable structures which are capable of both reciprocal and nonreciprocal signal wave transmissions in a full-duplex manner. The controllability and programmability of such metasurfaces are governed through the dc bias and occasionally a radio-frequency (RF) modulation applied to the the active components of the unit cells of the metasurface, e.g., diodes and transistors. This article shows that such intelligent metasurfaces can enhance the performance of wireless communications systems thanks to their unique features such as real-time signal coding, nonreciprocal-beam radiation, nonreciprocal beamsteering amplification, and advanced pattern-coding multiple access communication.

Metasurfaces are ultrathin structures which are constituted by an array of subwavelength scatterers with designable scattering responses. They have opened up unprecedented exciting opportunities for extraordinary wave engineering processes. On the other hand, frequency converters have drawn wide attention due to their vital applications in telecommunication systems, health care devices, radio astronomy, military radars and biological sensing systems. Here, we show that a spurious-free and linear frequency converter metasurface can be realized by leveraging unique properties of engineered transmissive temporal supercells. Such a metasurface is formed by time-modulated supercells; themselves are composed of temporal and static patch resonators and phase shifters. This represents the first frequency converter metasurface possessing large frequency conversion ratio with controllable frequency bands and transmission magnitude. In contrast to conventional nonlinear mixers, the proposed temporal frequency converter offers a linear response. In addition, by taking advantage of the proposed surface-interconnector-phaser-surface (SIPS) architecture, a spurious-free and linear frequency conversion is achievable, where all undesired mixing products are strongly suppressed. The proposed metasurface may be digitally controlled and programmed through a field programmable gate array. This makes the spurious-free and linear frequency converter metasurface a prominent solution for wireless and satellite telecommunication systems, as well as invisibility cloaks and radars. This study opens a way to realize more complicated and enhanced-efficiency spectrum-changing metasurface.

Nonreciprocal radiation refers to electromagnetic wave radiation in which a structure provides different responses under the change of the direction of the incident field. Modern wireless telecommunication systems demand versatile apparatuses which are capable of full-duplex nonreciprocal wave processing and amplification, especially in the reflective state. To realize such a unique, extraordinary and versatile functionality, we propose an architecture in which a chain of series cascaded radiating patches are integrated with nonreciprocal phase shifters, providing an original and efficient apparatus for full-duplex reflective beamsteering. Such an ultrathin reflective metasurface can provide directive and diverse radiation beams, large wave amplification, steerable beams by simply changing the bias of the gradient active nonmagnetic nonreciprocal phase shifters, and is immune to undesired time harmonics. Having accomplished all these functionalities in the reflective state, the metasurface represents a conspicuous apparatus for efficient, controllable and programmable wave engineering.

Optical prisms are made of glass and map temporal frequencies into spatial frequencies by decomposing incident white light into its constituent colors and refract them into different directions. Conventional prisms suffer from their volumetric bulky and heavy structure and their material parameters are dictated by the Lorentz reciprocity theorem. Considering various applications of prisms in wave engineering and their growing applications in the invisible spectrum and antenna applications, there is a demand for compact apparatuses that are capable of providing prism functionality in a reconfigurable manner, with a nonreciprocal/reciprocal response. Here, we propose a nonreciprocal metasurface-based prism constituted of an array of phase- and amplitude-gradient frequency-dependent spatially variant radiating super-cells. In conventional optical prisms, nonreciprocal devices and metamaterials, the spatial decomposition and nonreciprocity functions are fixed and noneditable. Here, we present a programmable metasurface integrated with amplifiers to realize controllable nonreciprocal spatial decomposition, where each frequency component of the incident polychromatic wave can be transmitted under an arbitrary and programmable angle of transmission with a desired transmission gain. Such a polychromatic metasurface prism is constituted of frequency-dependent spatially variant transistor-based phase shifters and amplifiers for the spatial decomposition of the wave components. Interesting features include three-dimensional prism functionality with programmable angles of refraction, power amplification, and directive and diverse radiation beams. Furthermore, the metasurface prism can be digitally controlled via a field-programmable gate array (FPGA), making the metasurface a suitable solution for radars, holography applications, and wireless telecommunication systems.

Static metasurfaces have shown to be prominent compact structures for reciprocal and frequency-invariant transformation of electromagnetic waves in space. However, incorporating temporal variation to static metasurfaces would result in dynamic apparatuses which are capable of four-dimensional tailoring of both the spatial and temporal characteristics of electromagnetic waves, leading to functionalities that are far beyond the capabilities of conventional static metasurfaces. This includes nonreciprocal full-duplex wave transmission, pure frequency conversion, parametric wave amplification, spatiotemporal decomposition, and space-time wave diffraction. This paper reviews recent progress and opportunities offered by space-time metasurfaces to break reciprocity, revealing their potential for low-energy, compact, integrated non-reciprocal devices and sub-systems, and discusses the future of this exciting research front., Comment: arXiv admin note: text overlap with arXiv:1902.09885

This study presents a nonreciprocal-beam phased-array antenna constituted of phase-gradient patch radiators integrated with transistor-based nonreciprocal phase shifters. Such an antenna exhibits different beams for transmission and reception states. The proposed phased-array antenna provides power amplification for both transmission and reception states, which is of paramount importance in most practical applications. In addition, in contrast to the recently proposed time-modulated antennas, the proposed nonreciprocal-beam phased-array antenna introduces no undesired time harmonics and unwanted frequency conversion, requires no radio frequency bias signal. Furthermore, the nonreciprocal phased-array antenna is lightweight and is amenable to integrated circuit fabrication. The transmission and reception beam angles, the beam shapes, and the power amplification level may be easily tuned by changing the direct current (dc) bias of the transistors and phase of the passive phase shifters. Such a nonreciprocal-beam phased-array antenna is expected to find military and commercial applications.

We show that a space-time-varying medium can function as a front-end transceiver, i.e., an antenna-mixer-amplifier. Such a unique functionality is endowed by space-time surface waves associated with complex space-time wave vectors in a subluminal space-time medium. The proposed structure introduces pure frequency up- and down-conversions and with very weak undesired time harmonics. In contrast to other recently proposed space-time mixers, a large frequency up-/down conversion ratio, associated with gain is achievable. Furthermore, as the structure does not operate based on progressive energy transition between the space-time modulation and the incident wave, it possesses a subwavelength thickness (metasurface). Such a multi-functional, highly efficient and compact medium is expected to find various applications in modern wireless telecommunication systems.

We present the concept, theoretical model and experimental implementation of a full-duplex nonreciprocal-beam-steering transmissive phase-gradient metasurface. Such a metasurface is realized by exploiting the unique properties of the frequency-phase transition in coupled time-modulated twin meta-atoms. The metasurface may be placed on top of a source antenna to transform the radiation pattern of the source antenna, and introduce different radiation patterns for the transmit and receive states. In contrast to the recently proposed applications of time modulation, here the incident and transmitted waves share the same frequency. The metasurface is endowed with directive, diverse and asymmetric transmission and reception radiation beams, and tunable beam shapes. Furthermore, these beams can be steered by simply changing the modulation phase. The proposed coupled meta-atoms inherently suppress undesired time harmonics, leading to a high conversion efficiency which is of paramount importance for practical applications such as point to point full-duplex communications.

This paper overviews the principles, theoretical analysis and numerical simulation of STM media and their applications in communication systems. We first present a global perspective on the principles of ST modulation, naturally and artificially created STM media and their applications in communication systems. Next, the interaction of artificial STM media with electromagnetic waves is analyzed, and numerical simulation of electromagnetic wave propagation and scattering from these media is provided. Then, the dispersion diagram of the STM medium is studied for the characterization of subluminal, luminal and superluminal ST modulations. In addition, we investigate the effect of length, modulation velocity, modulation frequency, and equilibrium on wave scattering from the STM medium. The extraordinary interaction of the STM medium with electromagnetic waves leads to unidirectional frequency generation and amplification, which are leveraged for the realization of various enhanced-efficiency broadband microwave components that are integrable with circuit technology, lightweight, tunable, and low cost. These applications include, but are not limited to, magnet-free isolators, magnet-free circulators, transceiver front-ends, and pure frequency mixers.

This paper studies the theory and applications of the diffraction of electromagnetic waves by space-time periodic (STP) diffraction gratings. We show that, in contrast with conventional spatially periodic grating, a STP diffraction grating produces spatial diffraction orders, each of which is formed by an infinite set of temporal diffraction orders. Such spatiotemporally periodic gratings are endowed with enhanced functionalities and exotic characteristics, such as asymmetric diffraction pattern, nonreciprocal and asymmetric transmission and reflection, and an enhanced diffraction efficiency. The theory of the wave diffraction by STP gratings is formulated through satisfying the conservation of both momentum and energy, and rigorous Floquet mode analysis. Furthermore, the theoretical analysis of the structure is supported by time and frequency domain FDTD numerical simulations for both transmissive and reflective STP diffraction gratings. Additionally, we provide the conditions for Bragg and Raman-Nath diffraction regimes for STP gratings. Finally, as a particular example of a practical application of the STP diffraction gratings to communication systems, we propose an original multiple access communication system featuring full-duplex operation. STP diffraction gratings are expected to find exotic practical applications in communication systems, especially for the realization of enhanced-efficiency or full-duplex beam coders, nonreciprocal beam splitters, nonreciprocal and enhanced-resolution holograms, and illusion cloaks.

This article demonstrates the realization of an extraordinary beam splitter based on nonreciprocal and synchronized photonic transitions in obliquely illuminated space-time-modulated (STM) slabs which impart the coherent temporal frequency and spatial frequency shifts. As a consequence of such unusual photonic transitions, a one-way beam splitting and amplification is exhibited by the STM slab. Beam splitting is a vital operation for various optical and photonic systems, ranging from quantum computation to fluorescence spectroscopy and microscopy. Despite the beam splitting is conceptually a simple operation, the performance characteristics of beam splitters significantly influence the repeatability and accuracy of the entire optical system. As of today, there has been no approach exhibiting a nonreciprocal beam splitting accompanied with transmission gain and an arbitrary splitting angle. Here, we show that oblique illumination of a periodic and semi-coherent dynamically-modulated slab results in coherent photonic transitions between the incident light beam and its counterpart space-time harmonic (STH). Such photonic transitions introduce a unidirectional synchronization and momentum exchange between two STHs with same temporal frequencies, but opposite spatial frequencies. Such a beam splitting technique offers high isolation, transmission gain and zero beam tilting, and is expected to drastically decrease the resource and isolation requirements in optical and photonic systems. In addition to the analytical solution, we provide a closed-form solution for the electromagnetic fields in STM structures, and accordingly, investigate the properties of the wave isolation and amplification in subluminal, superluminal and luminal ST modulations.

Scattering of obliquely incident electromagnetic waves from periodically space-time modulated slabs is investigated. It is shown that such structures operate as nonreciprocal harmonic generators and spatial-frequency filters. For oblique incidences, low-frequency harmonics are filtered out in the form of surface waves, while high-frequency harmonics are transmitted as space waves. In the quasisonic regime, where the velocity of the space-time modulation is close to the velocity of the electromagnetic waves in the background medium, the incident wave is strongly coupled to space-time harmonics in the forward direction, while in the backward direction it exhibits low coupling to other harmonics. This nonreciprocity is leveraged for the realization of an electromagnetic isolator in the quasisonic regime and is experimentally demonstrated at microwave frequencies.

Nonreciprocal electromagnetic devices play an important role in modern optical and microwave technologies. Conventional methods for realizing such systems are incompatible with integrated circuits. With recent advances in integrated photonics, the need for efficient on-chip magnetless nonreciprocal devices is more urgent than ever. This paper leverages space-time engineered asymmetric photonic bandgaps to generate optical isolation. It is shown that a properly designed space-time modulated slab is highly reflective/transparent for opposite directions of propagation. The proposed method requires a low modulation frequency, is magnetless and can achieve very high isolation levels. Experimental proof of concept at microwave frequencies is provided.

We introduce a nonreciprocal nongyrotropic magnetless metasurface. In contrast to previous nonreciprocal structures, this metasurface does not require a biasing magnet, and is therefore lightweight and amenable to integrated circuit fabrication. Moreover, it does not induce Faraday rotation, and hence does not alter the polarization of waves, which is a desirable feature in many nonreciprocal devices. The metasurface is designed according to a Surface-Circuit-Surface (SCS) architecture and leverages the inherent unidirectionality of transistors for breaking time reversal symmetry. Interesting features include transmission gain as well as broad operating bandwidth and angular sector operation. It is finally shown that the metasurface is bianisotropic in nature, with nonreciprocity due to the electric-magnetic coupling parameters, and structurally equivalent to a moving uniaxial metasurface.

We present a mixer-duplexer-antenna leaky-wave system based on periodic space-time modulation. This system operates as a full transceiver, where the upconversion and downconversion mixing operations are accomplished via space-time transitions, the duplexing operation is induced by the nonreciprocal nature of the structure, and the radiation operation is provided by the leaky-wave nature of the wave. A rigorous electromagnetic solution is derived for the dispersion relation and field distributions. The system is implemented in the form of a spatio-temporally modulated microstrip leaky-wave structure incorporating an array of sub-wavelengthly spaced varactors modulated by a harmonic wave. In addition to the overall mixer-duplexer-antenna operation, frequency beam scanning at fixed input frequency is demonstrated as one of the interesting features of the system. A prototype is realized and demonstrated by full-wave and experimental results.

We show that a continuously nonuniform coupled line C-section phaser, as the limiting case of the step discontinuous coupled-line multisection commensurate and non-commensurate phasers, provides enhanced bandwidth and diversity in real-time analog signal processing (R-ASP). The phenomenology of the component is explained in comparison with the step-discontinuous using multiple-reflection theory and a simple synthesis procedure is provided. The bandwidth enhancement results from the suppression of spurious group delay harmonics or quasi-harmonics, while the diversity enhancement results from the greater level of freedom provided by the continuous nature of the nonuniform profile of the phaser. These statements are supported by theoretical and experimental results.