Search Results (8)

A fixed-frequency beam-scanning leaky-wave antenna (LWA) array with three switchable dual-polarized beams is proposed and experimentally demonstrated. The proposed LWA array consists of three groups of spoof surface plasmon polaritons (SPPs) LWAs with different modulation period lengths and a control circuit. Each group of SPPs LWAs can independently control the beam steering at a fixed frequency by loading varactor diodes. The proposed antenna can be configured in both multi-beam mode and single-beam mode, where the multi-beam mode with optional two or three dual-polarized beams. The beam width can be flexibly adjusted from narrow to wide by switching between multi-beam and single-beam states. The prototype of the proposed LWA array is fabricated and measured, and both simulation and experimental results show that the antenna can accomplish a fixed frequency beam scanning at an operating frequency of 3.3 to 3.8 GHz with a maximum scanning range of about 35° in multi-beam mode and about 55° in single-beam mode. It could be a promising candidate for application in the space–air–ground integrated network scenario in satellite communication and future 6G communication systems. Full article

This paper presents a model and experimental study of a chaotic spike oscillator based on a leaky integrate-and-fire (LIF) neuron, which has a switching element with an S-type current-voltage characteristic (S-switch). The oscillator generates spikes of the S-switch in the form of chaotic pulse position modulation driven by the feedback with rate coding instability of LIF neuron. The oscillator model with piecewise function of the S-switch has resistive feedback using a second order filter. The oscillator circuit is built on four operational amplifiers and two field-effect transistors (MOSFETs) that form an S-switch based on a Schmitt trigger, an active RC filter and a matching amplifier. We investigate the bifurcation diagrams of the model and the circuit and calculate the entropy of oscillations. For the analog circuit, the “regular oscillation-chaos” transition is analysed in a series of tests initiated by a step voltage in the matching amplifier. Entropy values are used to estimate the average time for the transition of oscillations to chaos and the degree of signal correlation of the transition mode of different tests. Study results can be applied in various reservoir computing applications, for example, in choosing and configuring the LogNNet network reservoir circuits. Full article

We proposed a novel sensor based on an ultracompact leaky-guided liquid core fiber Mach–Zehnder interferometer (LLCFMZI) for high modulation of an interference spectrum. The sensor structure is based on a micro-sized hollow-core fiber (HCF) splicing a tilt end face single-mode fiber (SMF) to create a miniature oblique gap for the effective access of different liquids. The liquid core with a relatively lower refractive index (RI) than the cladding can achieve a leaky-mode optical waveguide (LMOW) mechanism, and its volume is only approximately 7.85 pL. In addition, the utilized micro-length HCF can reduce the energy loss of core in the LMOW to obtain an acceptable extinction ratio (>30 dB) with high temperature (T) sensitivity in the interference spectra. Experimental results show that the interference spectra can be highly modulated within the wide measurement range of 1250–1650 nm with a steadily linear response for thermal effect. The measured temperature sensitivities (T-sensitivities) of various liquids of DI water, ethanol, and Cargille-liquid (n_D = 1.305) are 0.8869, 4.4754, and 4.8229 nm/°C, and the corresponding measured thermal optics coefficient (TOC) are −4.16 × 10⁻⁵, −2.11 × 10⁻⁴, and −3.6 × 10⁻⁴ °C⁻¹, respectively. Measurement results demonstrate that the used liquids with a higher TOC can obtain better T-sensitivity modulation. The highest experimental sensitivity of the liquid-core filled with Cargille-liquid (n_D = 1.40) is up to +13.87 nm/°C with a corresponding TOC of −4.07 × 10⁻⁴ °C⁻¹. Furthermore, the experimental and theoretical values are in good agreement according to FSR the measuring scheme that investigates the effectiveness of the proposed LLCFMZI. Full article

Twin-field quantum key distribution (TF-QKD) has attracted considerable attention and developed rapidly due to its ability to surpass the fundamental rate-distance limit of QKD. However, the device imperfections may compromise its practical implementations. The goal of this paper is to make it robust against the state preparation flaws (SPFs) and side channels at the light source. We adopt the sending or not-sending (SNS) TF-QKD protocol to accommodate the SPFs and multiple optical modes in the emitted states. We analyze that the flaws of the phase modulation can be overcome by regarding the deviation of the phase as phase noise and eliminating it with the post-selection of phase. To overcome the side channels, we extend the generalized loss-tolerant (GLT) method to the four-intensity decoy-state SNS protocol. Remarkably, by decomposing of the two-mode single-photon states, the phase error rate can be estimated with only four parameters. The practical security of the SNS protocol with flawed and leaky source can be guaranteed. Our results might constitute a crucial step towards guaranteeing the practical implementation of the SNS protocol. Full article

It will soon be a decade since leaky mode waveguide devices were presented as a solution for holographic video displays. This paper seeks to provide a brief, topical review of advances made during that time. Specifically, we review the new methods and architectures that have been developed over this period. This work draws primarily from papers seeking to present dynamic holographic patterns using mode coupling from indiffused waveguides on lithium niobate. The primary participants during this time period have been groups from the Massachusetts Institute of Technology, Brigham Young University, and Draper. We also describe the challenges that remain. The body of work reviewed speaks to the need for further development, but it also reaffirms that leaky mode waveguides continue to hold a unique place within spatial light modulation for holographic video displays. Full article

Platinum (Pt) gratings on langasite (LGS) substrates are a widely used structures in high temperature surface acoustic wave (SAW) devices. Multiple modes can be excited in Pt$/$LGS SAW devices owing to the heavy weight of the Pt electrode and leaky waves in the LGS substrate. In this work, we report on a detailed mode analysis of Pt$/$LGS SAW devices, where three commonly used LGS cuts are considered. A three-dimensional (3D) finite element method (FEM) numerical model was developed, and the simulation and experiment results were compared. The experiment and simulation results showed that there are two modes excited in the Pt$/$LGS SAW devices with Euler angle (0$°$, 138.5$°$, 27$°$) and (0$°$, 138.5$°$, 117$°$), which are Rayleigh-type SAW and SH-type leaky wave, respectively. Only the Rayleigh-type mode was observed in the Pt$/$LGS SAW devices with Euler angle (0$°$, 138.5$°$, 72$°$). It was found that the acoustic velocities are dependent on the wavelength, which is attributed to the change of wave penetration depth in interdigital transducers (IDTs) and the velocity dispersion can be modulated by the thickness of the Pt electrode. We also demonstrated that addition of an Al₂O₃ passivation layer has no effect on the wave modes, but can increase the resonant frequencies. This paper provides a better understanding of the acoustic modes of Pt$/$LGS SAW devices, as well as useful guidance for device design. It is believed that the Rayleigh-type SAW and SH-type leaky waves are potentially useful for dual-mode sensing applications in harsh environments, to achieve multi-parameter monitoring or temperature-compensation on a single chip. Full article

This paper proposes an efficient transmission line modulation by using the bending technique to realize low profile leaky wave antennas in the Ku-band for frequency scanning and sensor applications. The paper focuses mainly on the bending effects of the transmission line in terms of the sharpness of edges. The right-hand/left-hand transmission line can be designed in the form of zig-zag pattern with sharp corners and only the right-hand transmission line in the form of sinusoidal patterns with smooth corners. In this presentation, we demonstrate that transmission lines of this kind can be used to realize highly efficient leaky wave antennas with broadband impedance matching and high gain characteristics in the Ku-band. Dispersion analysis and ladder network analysis have been performed for investigating the performance of the proposed designs. The sharpness of the bends periodically distributed along the body of the antenna has been used to our advantage for frequency scanning in the left-hand and right-hand quadrants at different frequencies. The proposed bending technique has been proven to be instrumental in achieving the desired characteristics of low profile leaky wave antennas. Full article

In this work, we suggest a new method of expanding the field of view in bottom-exit, leaky mode devices for transparent, monolithic, holographic, near-eye display. In this approach, we propose the use of static, laser-induced, grating structures within the device substrate to break the leaky mode light into diffracted orders. We then propose to use carefully timed illumination pulses to select which diffracted order is visible to the eye at every display refresh interval (up to 100 kHz). Each of these orders becomes a view for a different image point. To describe this new method, we use K-vector analysis. We give the relevant equations and a list of parameters which lead to a near-eye geometry with little or no overlap in higher-order view zones. We conclude that it should be possible to increase the field of view of our bottom-exit, leaky mode devices by as much as one order of magnitude by simply adding a laser-induced grating structure to the substrate and by carefully timing the device illumination. If successful, this method would make possible a transparent, holographic, near-eye display that is simple to fabricate, relative to pixelated approaches, and which has a wide field-of-view relative to our current bottom-exit displays. Full article