High Modulation Efficiency Research Articles

Highly Efficient Slow‐Light Mach–Zehnder Modulator Achieving 0.21 V cm Efficiency with Bandwidth Surpassing 110 GHz

AbstractHigh‐speed electro‐optic modulators are key components in modern communication networks and various applications that require chip‐scale modulation with large bandwidth, high modulation efficiency, and compact footprint. However, fundamental trade‐offs make it challenging to achieve these metrics simultaneously, and thus new methodologies must be explored. To this end, a Mach–Zehnder modulator harnessing slow‐light waveguides and capacitively loaded slow‐wave electrodes are presented on silicon‐nitride‐loaded lithium niobate on an insulator platform. The increased group index and reduced microwave loss significantly improve the modulation efficiency. With the 1‐mm‐length modulation section, a low half‐wave voltage length product Vπ·L of 0.21 V cm is obtained, which is one order of magnitude smaller than that of conventional thin film lithium niobate Mach–Zehnder modulators, and a modulation bandwidth of surpassing 110 GHz is achieved. The digital signal processor‐free non‐return‐to‐zero signal and eight‐level pulse amplitude modulation signal of up to 180 and 300 Gbps, respectively, are generated by the modulator, which provides ultra‐large bandwidth, ultra‐high efficiency, and a compact solution for next‐generation electro‐optic systems.

Unipolar quantum optoelectronics for high speed direct modulation and transmission in 8–14 µm atmospheric window

The large mid-infrared (MIR) spectral region, ranging from 2.5 µm to 25 µm, has remained under-exploited in the electromagnetic spectrum, primarily due to the absence of viable transceiver technologies. Notably, the 8–14 µm long-wave infrared (LWIR) atmospheric transmission window is particularly suitable for free-space optical (FSO) communication, owing to its combination of low atmospheric propagation loss and relatively high resilience to turbulence and other atmospheric disturbances. Here, we demonstrate a direct modulation and direct detection LWIR FSO communication system at 9.1 µm wavelength based on unipolar quantum optoelectronic devices with a unprecedented net bitrate exceeding 55 Gbit s−1. A directly modulated distributed feedback quantum cascade laser (DFB-QCL) with high modulation efficiency and improved RF-design was used as a transmitter while two high speed detectors utilizing meta-materials to enhance their responsivity are employed as receivers; a quantum cascade detector (QCD) and a quantum-well infrared photodetector (QWIP). We investigate system tradeoffs and constraints, and indicate pathways forward for this technology beyond 100 Gbit s−1 communication.

Energy harvesting potential for 3 EVs equipped with PV for the area of Graz in Austria

Vehicle-integrated photovoltaics present a plausible solution to address electric vehicle barriers of limited charging access and driving ranges. This work demonstrates a simulation tool that encompasses influencing factors on a vehicle's PV yield by comparing geographical areas, vehicle classes, vehicle surfaces, weather conditions, driving/parking cycles, shading scenarios, and electric configurations. The results quantify the increase in battery energy and vehicle mileage. Extensive simulations show the roof is the primary zone for PV integration, whereas the doors contribute greatly in winter. Using high-efficiency PV modules on the roof can supply over 20 % of monthly mileage from March to September. On average, 25 % of 1000 km monthly mileage can be covered with full-vehicle PV coverage. This drops to 16 % when excluding PV doors. This technology's success centers on lightweight vehicles with large surfaces and high-efficiency modules exceeding 20 %. Simulations show that a 10 % increase in efficiency reduces charging energy needs by 12–16 %.

High modulation efficiency sinusoidal vertical PN junction phase shifter in silicon-on-insulator

In this paper, a sinusoidal vertical PN junction phase shifter on a silicon waveguide is designed, and the results demonstrate that modifying the shape of the PN junction significantly increases the area of the depletion region within the standard waveguide width of 500 nm, thereby enhancing the overlap between the depletion region and optical waveguide modes under reverse bias conditions. Furthermore, by adjusting the sinusoidal amplitude (A) of the doping contact interface, it is observed that when A=0.065µm, the resulting sinusoidal PN junction most effectively enhances the interaction between carriers and photons, leading to the highest modulation efficiency and the lowest loss. Based on this, further adjustment of the doping concentration distribution in the waveguide was conducted using a doping compensation method. It is observed that setting the doping concentration at 3×1018cm−3 in the heavily doped region and at 1×1018cm−3 in the lightly doped region enables the phase shifter to achieve high modulation efficiency while maintaining low loss. This is attributed to the highest optical intensity being concentrated in the central region of the waveguide, as well as to the positive correlation between doping concentration and modulation efficiency. The final designed device with a length of 1.5 mm successfully attained a low V π L of 0.58V⋅cm, resulting in high modulation efficiency. By employing traveling wave electrodes and ensuring that the effective refractive index of the radio frequency (RF) matches the optical group index (OGI), circuit-level simulations were conducted. The device exhibited a 3 dB bandwidth of 8.85 GHz and eye diagrams of up to 40 Gbit/s, with a maximum extinction ratio (ER) of 8.27 dB and a bit error rate (BER) of 8.83×10−6, which can be widely used in the field of high-speed silicon optical modules.

Exploring electrochromic performance via layered deposition of tungsten oxide on niobium oxide composite electrode

Previous studies examined the incorporation of several transition metal oxides into niobium oxide (Nb2O5) to enhance the electrochromic (EC) performance. The objective was to improve the durability, color neutrality, coloring efficiency, and optical characteristics because individual metal oxides often exhibit limits that might affect overall functioning. Therefore, an innovative approach, integrating mixed metal oxides, emerges. This novel approach addresses these challenges and unlocks new possibilities to enhance EC efficiency. This paper introduces a new method for synthesizing niobium oxide/tungsten oxide (Nb2O5/WO3) bilayer composite materials using a combination of facile hydrothermal synthesis with electrodeposition. The electrochromic, structural, morphological, and optical characteristics of Nb2O5 thin films were enhanced by conducting thorough investigations into different electrodeposition cycles of WO3. X-ray diffraction confirmed the amorphous nature of WO3 in combination with the crystalline orthorhombic Nb2O5 structure. Raman spectroscopy examined the vibrational modes and structural attributes in the Nb2O5/WO3 bilayer composite thin films. X-ray photoelectron spectroscopy was conducted to examine the chemical composition, elemental state, and surface characteristics. Field emission scanning electron microscopy was used to examine the impact of different WO3 electrodeposition cycles on the morphology of Nb2O5 thin films, revealing the formation of porous, clumped, and dense nanogranules on the film surface. EC investigations highlight the superior performance of the NW-20 thin film, showing efficient Li+ accommodation. The optimized NW-20 sample exhibits excellent EC performance, including high optical modulation (81.48 %), good reversibility (98.11 %), and high coloration efficiency (115.09 cm2/C) with long-term cycling stability. The NW-20 electrode incorporated into a device form exhibited functionality on a real-world scale, delivering remarkable EC performance with substantial optical modulation (78.1 %) and excellent cycling stability. These findings expand the potential applications of Nb2O5/WO3 bilayer composite materials for EC performance.

Single-drive electro-optic frequency comb source on a photonic-wire-bonded thin-film lithium niobate platform.

Stable pulse and flat-top frequency comb generation are an indispensable component of many photonic applications, from ranging to communications. Lithium niobate on insulator is an excellent electro-optic (EO) platform, exhibiting high modulation efficiency and low optical loss, making it a fitting candidate for pulse generation through electro-optic modulation of continuous-wave (CW) light, a commonly utilized method for generating ultrashort pulses. Here, we demonstrate an on-chip electro-optic comb generation module on thin-film lithium niobate (TFLN) consisting of a Mach-Zehnder interferometer (MZI) amplitude modulator (AM) and a cascaded phase modulator (PM) system driven by a single-electrode drive. We show that when operated in the correct regime, the lithium niobate chips can generate frequency combs with excellent spectral power flatness. In addition, we optically package one of the pulse generator chips via photonic wire bonding. The pulses generated by the photonic-wire-bonded device are compressed to 840 fs pulse duration using an optical fiber and show extremely stable operation.

Highly efficient silicon modulator via a slow-wave Michelson structure.

The weak free carrier dispersion effect significantly hinders the adoption of silicon modulators in low-power applications. While various structures have been demonstrated to reduce the half-wave voltage, it is always challenging to balance the trade-off between modulation efficiency and the bandwidth. Here, we demonstrated a slow-wave Michelson structure with 1-mm-long active length. The modulator was designed at the emerging 2-μm wave band which has a stronger free carrier effect. A record high modulation efficiency of 0.29 V·cm was achieved under a carrier depletion mode. The T-rail traveling wave electrodes were designed to improve the modulation bandwidth to 13.3 GHz. Up to 20 Gb/s intensity modulation was achieved at a wavelength of 1976 nm.

Modelling Li-V2O5 Batteries Using Galvanostatic Intermittent Titration Technique and Electrochemical Impedance Spectroscopy: Towards Final Applications

Given the relevance of lithium and post-lithium batteries as electrochemical energy storage systems, the peculiar crystalline structure of V2O5 and its doping capacity play key roles in lithium-ion battery technology. To integrate them in high-efficiency modules, systematic methodologies are required to estimate the state of charge in a reliable way and predict the Li-V2O5 battery’s performance according to their electrochemical phenomena, including two plateaus in the galvanostatic cycling curves and the dynamic behavior governed by the energy demand. Most state of charge estimation and battery modeling procedures are focused on conventional Li-batteries that show a unique plateau. In this work, we propose a systematic methodology based on the galvanostatic intermittent titration technique and electrochemical impedance spectroscopy to study battery performance in the time and frequency domains, respectively. The proposed methodology, with a time–frequency correlation, promotes a deeper understanding of the electrochemical phenomena and general behavior of Li-V2O5 batteries, allowing for its subsequent extrapolation to more complex and higher-capacity lithium and post-lithium batteries used in high-power applications with a minimum error.

High performance deep-ultraviolet light-emitting diodes with transverse electron injection

Conventional structure deep-ultraviolet light-emitting diodes (DUV-LEDs) at short wavelengths typically suffer from electron overflow and low light-emitting efficiency. For solar-blind communication application, conventional DUV-LEDs are struggling to simultaneously implement high external quantum efficiency (EQE) and high modulation bandwidth. In this paper, we report that transverse structure LEDs can overcome abovementioned problems and achieve high EQE and high modulation bandwidth. The n-AlGaN free transverse structure LEDs have been demonstrated to yield high crystal quality multiple quantum wells (MQWs). Due to the transverse electron injection, transverse structure LEDs can confine electrons well within the MQWs and avoid electron overflow. To enhance the electron injection and light extraction characteristics, the narrow and long mesa designs were optimized by both experimental and theoretical-fit results. Finite-difference time domain simulation indicates that the n+-GaN layer of the transverse LEDs with the transverse MQWs mesa design does not degrade light extraction. The transverse structure LEDs attain the maximum light output power and EQE recorded to date for DUV-LEDs below 250 nm, respectively 14 mW and 1.72 %. Furthermore, the −3 dB modulation bandwidth can be achieved up to 416 MHz.

Efficient and high-speed coupling modulation of silicon racetrack ring resonators at 2 µm waveband.

Significantly increased interests have been witnessed for the 2 µm waveband which is considered to be a promising alternative window for fiber and free-space optical communications. However, the less mature device technology at this wavelength range is one of the primary obstacles toward practical applications. In this work, we demonstrate an efficient and high-speed silicon modulator based on carrier depletion in a coupling tunable resonator. A benchmark high modulation efficiency of 0.75 V·cm is achieved. The 3-dB electro-optic bandwidth is measured to be 26 GHz allowing for up to 34 Gbit/s on-off keying modulation with a low energy consumption of ∼0.24 pJ/bit. It provides a solution for the silicon modulator with high-speed and low power consumption in the 2-µm waveband.

High spectral efficiency modulation scheme based on joint interaction of orthogonal compressed chirp division multiplexing and power superimposed code.

In this paper, we propose a high spectral efficiency modulation scheme based on joint interaction of orthogonal compressed chirp division multiplexing (OCCDM) and power superimposed code (PSC) under the intensity modulation and direct detection (IM/DD) system. OCCDM is a novel orthogonal chirp division multiplexing technology featuring spectral compression through the implementation of processing similar to a discrete Fourier transform, enhancing the spectral efficiency (SE) through bandwidth savings without loss of orthogonality of each chirp. Meanwhile, PSC technology enables multiple code words being transmitted superimposed on the same chirp. This technique involves allocating varying power levels to different users, thereby distinguishing them, increasing the transmission's net bit rate and substantially boosting the SE. The transmission has been performed experimentally using a 2 km 7-core fiber span. The impact of the above-mentioned technologies on the bit error rate (BER) performance is assessed in the power, frequency, and joint domain. The BER and enhancements in the SE can be balanced when the spectral bandwidth compression factor (α) and power distribution ratio are equal to 0.9 and 4, respectively. The observed outcome leads to the transmission's SE increase to more than double the baseline value, at 2.22 times. Based on the above analysis, we believe this structure is expected to become a potential for developing next-generation PON.

Temperature-dependent synergistic antioxidants for high-efficiency modulation of anti-scorch performance and crosslinking degree in peroxide-initiated low-density polyethylene

The contradiction between anti-scorch performance and crosslinking degree severely limits further development of cable insulation. To address this issue, synergistic antioxidants are proposed to modulate crosslinking reactions in peroxide-initiated low-density polyethylene (PLDPE). The results demonstrate that the combination of antioxidant 300 and antioxidant 736 achieves an extraordinarily excellent anti-scorch performance in a highly crosslinked PLDPE. The infrared spectroscopy and molecular simulation provide evidences for the existing hydrogen bond and proton transfer effects between the two antioxidants. The reactivity activity of antioxidants determined by these temperature-dependent synergistic effects effectively modulates crosslinking reactions under different temperatures, contributing to excellent anti-scorch performance and crosslinking degree in PLDPE.

Deep-ultraviolet LEDs with an Al-graded p-AlGaN layer exhibiting high wall-plug efficiency and high modulation bandwidth simultaneously

This work demonstrated a deep-ultraviolet (DUV) LED with an Al-graded p-AlGaN contact layer above the electron blocking layer to alleviate p-type contact resistance, the asymmetry of carriers transport, and the polarization effect. The fitting results from the ABC + f(n) model revealed that the LED has a higher radiative recombination coefficient than the conventional structures ever reported, which contributes to a lower carrier lifetime. The light output power of the LED at 350 mA is 44.71 mW, the peak external quantum efficiency (EQE) at 22.5 mA is 5.12%, the wall-plug efficiency at 9 mA is 4.40%. The 3 dB electrical-to-optical modulation bandwidth of the graded p-AlGaN contact layer LED is 390 MHz after impedance matching. In short, this study provides an in-depth analysis of the physical mechanism of the enhanced EQE and decreased carrier lifetime of DUV LEDs with Al-graded AlGaN as a p-type contact layer.

Liner multimode fibers with high distributed optical amplification system based high efficient quadrature modulation system for reliable high capacity local area network

Abstract This paper clarified the liner multimode fibers with high optical amplification system based high efficient quadrature modulation system for high capacity local area optical networks. The clarified the lighted QPSK transmitter system based linear multimode fiber profile is clarified under modal bandwidth effects. The optimum power variations are studied with spectral base band wavelength variations for various modal bandwidths based linear multimode fiber. Optimum power is clarified with time variations for various modal bandwidths based linear multimode fiber. Total power for 1500 and 1700 MHz km modal bandwidth is demonstrated based linear multimode fiber. The Max-Min signal base band amplitude based QAM pulse generator is clarified after photo-detector by using electrical constellation visualizer. The optimum Q Factor form with Min BER is demonstrated after photo-detector for 1300, 1500, and 1700 MHz km modal bandwidth based linear multimode fiber. The base band lighted SNR is clarified and simulated with the modal bandwidth variations based linear multimode fiber. Optimum Q form factor through photo-detector is demonstrated with the modal bandwidth variations based linear multimode fiber. The electrical SNR through photo-detector is studied and simulated with the modal bandwidth variations based linear multimode fiber.

Sub-volt high-speed silicon MOSCAP microring modulator driven by high-mobility conductive oxide

Silicon microring modulator plays a critical role in energy-efficient optical interconnect and optical computing owing to its ultra-compact footprint and capability for on-chip wavelength-division multiplexing. However, existing silicon microring modulators usually require more than 2 V of driving voltage (Vpp), which is limited by both material properties and device structures. Here, we present a metal-oxide-semiconductor capacitor microring modulator through heterogeneous integration between silicon photonics and titanium-doped indium oxide, which is a high-mobility transparent conductive oxide (TCO) with a strong plasma dispersion effect. The device is co-fabricated by Intel’s photonics fab and our in-house TCO patterning processes, which exhibits a high modulation efficiency of 117 pm/V and consequently can be driven by a very low Vpp of 0.8 V. At a 11 GHz modulation bandwidth where the modulator is limited by the RC bandwidth, we obtained 25 Gb/s clear eye diagrams with energy efficiency of 53 fJ/bit.

High Efficiency and Low Complexity Dual-Reference Voltage-Based Pulse Width Modulation for Three-Phase Five-Level HANPC Inverters

High Efficiency and Low Complexity Dual-Reference Voltage-Based Pulse Width Modulation for Three-Phase Five-Level HANPC Inverters

Perovskite Topological Lasers: A Brand New Combination.

Nanolasers are the essential components of modern photonic chips due to their low power consumption, high energy efficiency and fast modulation. As nanotechnology has advanced, researchers have proposed a number of nanolasers operating at both wavelength and sub-wavelength scales for application as light sources in photonic chips. Despite the advances in chip technology, the quality of the optical cavity, the operating threshold and the mode of operation of the light source still limit its advanced development. Ensuring high-performance laser operation has become a challenge as device size has been significantly reduced. A potential solution to this problem is the emergence of a novel optical confinement mechanism using photonic topological insulator lasers. In addition, gain media materials with perovskite-like properties have shown great potential for lasers, a role that many other gain materials cannot fulfil. When combined with topological laser modes, perovskite materials offer new possibilities for the operation and emission mechanism of nanolasers. This study introduces the operating mechanism of topological lasers and the optical properties of perovskite materials. It then outlines the key features of their combination and discusses the principles, structures, applications and prospects of perovskite topological lasers, including the scientific hurdles they face. Finally, the future development of low-dimensional perovskite topological lasers is explored.

Transient-liquid-phase bonding for Skutterudite-based thermoelectric modules

Thermoelectric (TE) generators are an option for waste heat recovery in a large diversity of applications, such as automotive, aerospace or high temperature industrial processes with high energy throughput. Skutterudite materials are among the most interesting candidates for high efficiency modules in the high-temperature range up to 500 °C. However, Skutterudite-based TE modules still lack published results on reliable solutions for electrical and thermal contacts between the semiconducting TE pellets and metallic bridges and their stability under thermal treatment, leaving room for suggestions on durable joining and assembly technology.In this article we will present contacting schemes for TE couples using different diffusion barriers and a transient liquid phase (TLP) joining process. The joints have been investigated concerning their microstructure, diffusion effects and electrical contact resistivities. CrSi2 has shown suitable as anti-diffusion layer with good adhesion and electrical properties leading to contact resistivities as low as 5 μΩ cm2.

A Design of High-Efficiency: Vertical Accumulation Modulators Based on Silicon Photonics.

On-chip optical modulators, which are capable of converting electrical signals into optical signals, constitute the foundational components of photonic devices. Photonics modulators exhibiting high modulation efficiency and low insertion loss are highly sought after in numerous critical applications, such as optical phase steering, optical coherent imaging, and optical computing. This paper introduces a novel accumulation-type vertical modulator structure based on a silicon photonics platform. By incorporating a high-K dielectric layer of ZrO2, we have observed an increase in modulation efficiency while maintaining relatively low levels of modulation loss. Through meticulous study and optimization, the simulation results of the final device structure demonstrate a modulation efficiency of 0.16 V·cm, with a mere efficiency-loss product of 8.24 dB·V.

Playdough-like carbon electrode: A promising strategy for high efficiency perovskite solar cells and modules

Carbon-based perovskite solar cells (C-PSCs) are promising candidates for large-scale photovoltaic applications due to their theoretical low cost and high stability. However, the fabrication of high-performance C-PSCs with large-area electrodes remains challenging. In this work, we propose a novel playdough-like graphite putty as top electrode in the perovskite devices. This electrode with soft nature can form good contact with the hole-transporting layer and the conductive substrate at room temperature by a simple pressing technique, which facilitates the fabrication of both small-area devices and perovskite solar modules. In this preliminary research, the corresponding small devices and modules can achieve efficiencies of 20.29% (∼0.15 ​cm2) and 16.01% (∼10 ​cm2), respectively. Moreover, we analyze the limitations of the optical and electrical properties of this playdough-like graphite electrode on the device performance, suggesting a direction for further improvement of C-PSCs in the future.