Single-mode Transmission Research Articles

Robust terahertz on-chip topological pathway with single-mode and linear dispersion.

Terahertz on-chip pathway is crucial for next-generation wireless communication, terahertz integrated circuits, and high-speed chip interconnections, yet its development is impeded by issues like channel crosstalk and disordered scattering. In this study, we propose and experimentally demonstrate a terahertz on-chip topological pathway that exhibits exceptional transmission robustness, unaffected by structural curvature. The pathway is constructed using a subwavelength structure that combines the benefits of topological properties, such as broadband single-mode transmission and linear dispersion, with the field localization effects of periodic metal structures. By integrating topological protection into radio frequency circuits through metal microstructures, the device maintains efficient terahertz wave transmission even in the presence of scattering or structural defects while minimizing signal interference. These findings hold significant potential for applications in radio frequency device transmission and chip interconnection, particularly within the terahertz frequency range.

Dynamic switching of transmission modes hydroacoustic communication MAC protocols

In recent years, the hydroacoustic communication MAC (Medium Access Control) protocol has attracted wide attention. Hydroacoustic communication networks suffer from issues such as long propagation delays and rapid dynamic changes in network load, which prevent the maximization of network performance through the use of a single transmission mode. In this paper, we propose a Dynamic Switching Transmission MAC protocol called the DSTM-MAC protocol. Firstly, the protocol realizes the design of dynamic switching transmission mode by adapting to changes in network load, introduces a more accurate model for total system delay, and computes parameters such as the switching threshold L and the optimal fixed contention window. Secondly, it carries out parameter design for different transmission modes and realizes dynamic concurrent transmission based on these modes, ultimately achieving the goal of maximizing network performance improvement. Finally, experiments demonstrate that the DSTM-MAC protocol surpasses the traditional DCF protocol in terms of end-to-end delay and system throughput.

A Modified Regular Perturbation Model for the Single-Span Fiber Transmission Using Learnable Methods

In fiber optic communication systems, the dispersion and nonlinear interaction of optical signals are critical to modeling fiber optic communication, and the regular perturbation (RP) model is a simplified modeling method composed of parallel branches, which has obvious advantages in deep learning backpropagation. In this paper, we propose a simplified single-mode fiber signal transmission model based on the RP model, which significantly improves the fitting accuracy of the model for dispersion and nonlinear interactions at the same complexity by adding trainable parameters to the standard RP model. We explain in the paper that this improvement is applicable to dual-polarization systems and still effective under the conditions of large launch power, without dispersion management, and containing amplified spontaneous emission (ASE) noise. The model uses the standard split-step Fourier method (SSFM) to generate labels and updates parameters through gradient descent method. When transmitting a dual-polarization signal with a launch power of 13 dBm, the modified regular perturbation (MRP) model proposed in the paper can reduce the fitting errors by more than 75% compared to the standard RP model after transmitting through a 120 km standard single-mode fiber.

Single-mode chirped high-contrast metastructure VCSEL for 106 Gbps PAM4 transmission

Short-reach optical interconnects, employing an 850 nm wavelength multimode vertical cavity surface emitting laser (VCSEL) and multimode fiber (MMF), are confronted with transmission distance limitation as the transmission speed increases. Achieving higher speeds over the same transmission distance necessitates a significant enhancement in the fiber’s effective bandwidth, resulting in substantial costs. Employing single-mode VCSEL with single-mode fiber transmission presents as a more economically viable solution. Here we report, to our knowledge, the first demonstration of an 850 nm single-mode VCSEL using a chirped high-contrast metastructure (HCM) as the top mirror with spatially graded reflectivity to suppress higher-order modes. The chirped HCM top reflector is designed to favor lasing of the fundamental mode. We show stable single-mode lasing with a >40dB side mode suppression ratio (SMSR) up to 15 times threshold current and an open eye through a short single-mode fiber SM800 transmission at 106 Gbps PAM4 modulation. This study highlights the potential for scalable single-mode VCSEL in advanced optical interconnects, providing a cost-effective pathway for high-speed applications.

A Wireless Bi-Directional Brain-Computer Interface Supporting Both Bluetooth and Wi-Fi Transmission.

Wireless neural signal transmission is essential for both neuroscience research and neural disorder therapies. However, conventional wireless systems are often constrained by low sampling rates, limited channel counts, and their support of only a single transmission mode. Here, we developed a wireless bi-directional brain-computer interface system featuring dual transmission modes. This system supports both low-power Bluetooth transmission and high-sampling-rate Wi-Fi transmission, providing flexibility for various application scenarios. The Bluetooth mode, with a maximum sampling rate of 14.4 kS/s, is well suited for detecting low-frequency signals, as demonstrated by both in vitro recordings of signals from 10 to 50 Hz and in vivo recordings of 16-channel local field potentials in mice. More importantly, the Wi-Fi mode, offering a maximum sampling rate of 56.8 kS/s, is optimized for recording high-frequency signals. This capability was validated through in vitro recordings of signals from 500 to 2000 Hz and in vivo recordings of single-neuron spike firings with amplitudes reaching hundreds of microvolts and high signal-to-noise ratios. Additionally, the system incorporates a wireless stimulation function capable of delivering current pulses up to 2.55 mA, with adjustable pulse width and polarity. Overall, this dual-mode system provides an efficient and flexible solution for both neural recording and stimulation applications.

Broadband and tunable fiber polarizer based on a graphene photonic crystal fiber.

The recent flourishing development of two-dimensional (2D) graphene has sparked considerable interest and extensive research on graphene-based optical fiber polarizers. However, studies on graphene-optical fiber polarizers focused on the structure with graphene films attached to side-polished fibers, which face challenges such as low birefringence of 10-6, low polarization extinction ratio (PER), and narrow polarizing window of tens of nanometers. Here, a fiber polarizer based on a graphene-photonic crystal fiber (Gr-PCF) is proposed firstly, which exhibits high birefringence of ∼2.5 × 10-3, high PER of ∼111 dB/mm, broad polarizing window of >400 nm, and tunable polarization states. Graphene or graphene/hBN/graphene (Gr/hBN/Gr) heterojunctions are attached to the surface of two square holes in the PCF to make one of the polarizing modes attenuate significantly. The tunability of the Fermi level (EF) in Gr/hBN/Gr enables the proposed device to function as a polarizer or a polarization-maintaining fiber. The combination of PCF's endless single-mode feature and graphene's broadband optical response feature enables the fiber polarizer to exhibit a wide spectrum range with single-mode transmission characteristics.

Integrated Optical Waveguide Electric Field Sensors Based on Bismuth Germanate.

Bismuth germanate (Bi4Ge3O12, BGO) is a widely used optical sensing material with a high electro-optic coefficient, ideal for optical electric field sensors. Achieving high precision in electric field sensing requires fabricating optical waveguides on BGO. Traditional waveguide writing methods face challenges with this material. This study explores using femtosecond laser writing technology for preparing waveguides on BGO, leveraging ultrafast optical fields for superior material modification. Our experimental analysis shows that a cladding-type waveguide, written with a femtosecond laser at 200 kHz repetition frequency and 10.15 mW average power (pulse energy of 50.8 nJ), exhibits excellent light-guiding characteristics. Simulations of near-field optical intensity distribution and refractive index variations using the refractive index reconstruction method demonstrate that the refractive index modulation ensures single-mode transmission and effectively confines light to the core layer. In situ refractive index characterization confirms the feasibility of fabricating a waveguide with a refractive index reduction on BGO. The resulting waveguide has a loss per unit length of approximately 1.2 dB/cm, marking a successful fabrication. Additionally, we design an antenna electrode, analyze sensor performance indicators, and integrate a preparation process plan for the antenna electrode. This achievement establishes a solid experimental foundation for future studies on BGO crystal waveguides in electric field measurement applications.

Single vector mode transmission in hollow-core photonic bandgap fiber based on surface mode coupling effect

Single vector mode transmission in hollow-core photonic bandgap fiber based on surface mode coupling effect

Theoretical probability distribution model and reduction techniques based on an interleaved DFT spread for PAPR in a digital sub-carrier multiplexing system.

This paper presents a theoretical probability distribution model for peak-to-average power ratio (PAPR) in the digital sub-carrier multiplexing (DSCM) system, which has not previously been proposed in the literature. To reduce PAPR, an interleaved discrete Fourier transform spread DSCM (I-DFT-S-DSCM) scheme is proposed, which introduces reversible correlations between subcarriers. To investigate the effectiveness of the proposed schemes, a 64-GBaud 16 quadrature amplitude modulation (16-QAM) DSCM system with 4, 8, and 16 sub-carriers was constructed. In the digital domain, the results demonstrate that the proposed theoretical PAPR probability distribution model exhibits mean squared errors (MSE) below 10-5 for the observed and model-predicted complementary cumulative distribution functions (CCDF) in both DSCM and I-DFT-S-DSCM schemes. Regarding PAPR reduction, the I-DFT-S-DSCM scheme demonstrated a reduction in PAPR of up to 1.44 dB compared to the conventional DSCM scheme. To further investigate the impact of PAPR on the bit error rate (BER) performance of the DSCM system, the I-DFT-S-DSCM scheme is implemented with 8 subcarriers transmitted over a 100-km standard single-mode fiber (SSMF). A comparative analysis with DSCM indicates that I-DFT-S-DSCM achieves a PAPR reduction of approximately 1.1 dB and improves receiver sensitivity by approximately 0.7 dB at a 7% hard-decision forward error correction (HD-FEC) threshold, in 100-km single-mode fiber SSMF transmissions.

Nested hollow-core anti-resonant fiber with elliptical cladding for 2 µm laser transmission.

In this work, a nested hollow-core anti-resonant fiber (HC-ARF) with an elliptical cladding for high-power lasers for 2 µm laser transmission was proposed and theoretically investigated. The dual-layer elliptical tubes nested within the fiber enable the low-loss single-mode transmission. The finite element method (FEM) was employed to analyze and optimize the structure of fiber, with a total loss of less than 5 × 10-4 dB/m across the wavelength range of 1920nm to 2040nm. An extremely low loss of 1.22 × 10-5 dB/m at 1948nm was realized. A high-order mode extinction ratio (HOMER) exceeding 3 × 104 was maintained across a significant bandwidth and a size tolerance ratio under 15%. Furthermore, a low loss of 5 × 10-5 dB/m at 1948nm with a bending radius over 15 cm was obtained, indicating high bending resistance. It was demonstrated that the proposed fiber has exceptional transmission performance for 2 µm laser transmission.

Stress-Induced Polarization-Maintaining Large-Mode-Area Photonic Crystal Fibers With Deviation of the Single-Mode Transmission Band and Delocalization of Higher-Order Modes

Stress-Induced Polarization-Maintaining Large-Mode-Area Photonic Crystal Fibers With Deviation of the Single-Mode Transmission Band and Delocalization of Higher-Order Modes

Fabry–Perot interference temperature sensor integrated high-power-laser optical fiber probe for laser ablation

In this study, an optical fiber probe with an extremely short integrated temperature sensor for high-power laser ablation was proposed and successfully fabricated. Both optical mode and wavelength multiplication were performed simultaneously using a double-clad fiber with a wavelength-division multiplication technique. The wavelength shift with temperature showed a linear relationship with a sensitivity of 10 pm/°C. High-power laser irradiation of 1000 mW or more using multimode transmission and fine temperature monitoring using single-mode transmission were performed simultaneously with a system response time of a few seconds. The laser wavelength selection and power variation can increase the variability of the heating region required for medical applications.

Design and Analysis of a Narrow Linewidth Laser Based on a Triple Euler Gradient Resonant Ring

We designed a narrow-linewidth external-cavity hybrid laser leveraging a silicon-on-insulator triple Euler gradient resonant ring. The laser’s outer cavity incorporates a compact, high-Q resonant ring with low loss. The straight waveguide part of the resonant ring adopts a width of 1.6 μm to ensure low loss transmission. The curved section is designed as an Euler gradient curved waveguide, which is beneficial for low loss and stable single-mode transmission. The design features an effective bending radius of only 26.35 μm, which significantly improves the compactness of the resonant ring and, in turn, reduces the overall footprint of the outer cavity chip. To bolster the laser power and cater to the varying shapes of semiconductor optical amplifier (SOA) spots, we designed a multi-tip edge coupler. Theoretical analysis indicates that this edge coupler can achieve an optical coupling efficiency of 85%. It also reveals that the edge coupler provides 3 dB vertical and horizontal alignment tolerances of 0.76 μm and 2.4 μm, respectively, for a spot with a beam waist radius of 1.98 μm × 0.99 μm. The outer cavity, designed with an Euler gradient micro-ring, can achieve a side-mode suppression ratio (SMSR) of 30 dB within a tuning range of 100 nm, with a round-trip loss of the entire cavity at 1.12 dB, and an expected theoretical laser linewidth of 300 Hz.

Two-dimensional thin film lithium niobate photonic crystal waveguide for integrated photonic chips

The photonic crystal waveguide (PCW) possesses remarkable capabilities in manipulating light beams and light–matter interactions within the subwavelength range. This property renders it a highly promising structure for the miniaturization of optical devices. We delve into the mode characteristics in two-dimensional PCWs on thin film lithium niobate, establish the correlation between the single-mode region in the PCW and its photonic crystal duty cycle, and observe mode hybridization in the waveguide. A lithium niobate PCW with sidewall angles can realize single-mode transmission or mode conversion by adjusting the width of its defective waveguides, and it is theoretically and experimentally verified that a change in the width of the waveguide shifts the operating wavelength. The results of the mode analysis are useful in the design of waveguide structures for photonic crystal-based electro-optical modulators and optical sensors.

Mode-entangled resonance for lamb waves in a plate

We report a novel resonance phenomenon called the mode-entangled resonance. It can occur at a specific frequency in a plate carrying both symmetric and antisymmetric Lamb wave modes. We show that at this resonance, a symmetric or antisymmetric Lamb wave can be fully transmitted with its mode preserved from one plate to another through a matching plate geometrically misaligned with the two base plates. This phenomenon appears to be counter-intuitive because both symmetric and antisymmetric waves are generally formed in the reflected and transmitted wave fields when the misaligned plate is used as a matching plate. Our analysis shows that if both symmetric and antisymmetric Lamb wave modes at the resonance are entangled in the misaligned matching plate to satisfy the established phase matching condition, the matching plate fully transmits any wave mode across the two base plates. The discovered phenomenon is related to the classical Fabry-Perot resonance (FPR), but FPR is only applicable for single-mode transmission through a matching plate aligned with two base plates. Numerical and experimental results were presented to validate the discovered mode-entangled resonance phenomenon. Furthermore, we show that the discovered phenomenon can be used for super-amplification of the amplitude of the antisymmetric Lamb wave when it is excited by plate-surface-mounted patch transducers.

A design method for multi-mode power-split hybrid electric transmission considering mode continuity

Compared with single-mode power-split hybrid electric transmission, multi-mode power-split hybrid electric transmission can achieve high power, wide speed range, and high efficiency, which is the most suitable hybrid electric transmission scheme for heavy vehicles. Mode switching quality is the key factor restricting the application of multi-mode power-split hybrid electric transmission. Therefore, a design method for multi-mode power-split hybrid electric transmission which can ensure mode switching without speed difference is proposed. Firstly, based on the lever analogy method and analysis on characteristics of mechanical points, three conditions of mode continuity and methods to satisfy these conditions on function level are obtained. Then the design method can be divided into three steps: (1) design the function model of each mode scheme to achieve the conditions of mode continuity; (2) design the configuration of each mode scheme according to the function model and comprehensive consideration of mode continuity, structural simplification and operation logic, and combine the configuration of each mode into an integral scheme by arranging clutches/brakes; (3) inversely convert the lever model in the configuration scheme to planetary gear set to obtain specific transmission scheme. Finally, to demonstrate the feasibility of the design method, one of the design results is taken as an example to carry out mechanical structure design, kinematics and power flow analysis.

Designing an Electro-Optical Tunable Racetrack Microring Resonator on a Diamond–Lithium Niobate Thin-Film Hybrid Platform

This study proposes and simulates a numerical analysis of a diamond racetrack microring resonator on a lithium niobate thin film, operating at a 1.55 µm wavelength. The single-mode conditions, transmission losses, and waveguide dispersions are systematically examined. The microring resonator’s radius and gap size are computed and optimized. The designed racetrack microring resonator exhibits a high quality factor (Q-factor) and a high coupling efficiency of approximately 6100 and 95%, respectively, for the transverse TE mode in the C-band. This study achieves a resonant tunability of 1.84 pm/V near the 1.55 μm wavelength by harnessing the electro-optical effect of lithium niobate.

Single-polarization single-mode broadband ultra-low loss hollow-core anti-resonant fiber with nested double C-type cladding tubes

A novel five-tube nested double C-type single-polarization hollow-core anti-resonant fiber (HC-ARF) is proposed for single-polarization single-mode, ultra-low loss, and broadband characteristics. Different tube thicknesses are introduced along the orthogonal direction to couple the x-polarized fundamental mode (FM) to the silica modes (SMs). At the same time, the y-polarized FM is tightly bound in the core, achieving a high polarization extinction ratio (PER). In order to achieve large bandwidth, a layer of high-refractive-index silicon material is coated on the inner surface of the cladding tube. To the best of our knowledge, the proposed single-polarization HC-ARF has the highest PER at 1.55μm with a remarkable value of 162486 so far, while the y-polarized FM loss is only 1.4 × 10-3 dB/km. However, the single-polarization bandwidth remains limited. By optimizing the structural parameters on single-polarization bandwidth, the HC-ARF at 1.55μm for single-polarization single-mode transmission is obtained with a high-order mode extinction ratio (HOMER) and PER of 2891, 9531, respectively. In addition, a remarkably high single-polarization bandwidth of up to 150 nm is achieved with ultra-low confinement loss (CL) as low as 2.8 × 10-3 dB/km. Furthermore, the proposed fiber exhibits good bending characteristics, with a bending loss of 6.7 dB/km at the bending radius of 5 cm in the x-direction.

MIMO-free OAM-MDM transmission with a ring-core fiber recirculation loop

We experimentally demonstrate the record long-haul orbital angular momentum (OAM) mode-division multiplexed (MDM) transmission over 300-km assisted by a ring-core fiber (RCF) recirculating loop. The recirculation loop consisting of 50-km RCF is controlled mainly by two acousto-optic switches with opposite states, and the signals are cyclically transmitted in the single-span 50-km RCF to achieve long-haul transmission. The RCF features largely separated OAM mode groups, where the effective refractive index difference between adjacent high-order OAM mode groups is larger than 1.0 × 10-3. Due to the low-crosstalk feature of RCF incorporated into fiber optic links, multiple-input multiple-output (MIMO) equalization technology is not used in the OAM MDM system. We transmit 20-Gbit/s quadrature phase-shift keying signals over two high-order OAM modes, and the transmission performance is characterized. The measured average optical signal-to-noise ratio penalties at a bit-error rate of 1.5 × 10-2 are about 2 dB between single OAM mode transmission and OAM modes multiplexing transmission. The obtained experimental results indicate favorable OAM-based MDM transmission performance in a 300-km recirculating loop link.

A high-order TE50 mode waveguide with single mode transmission property and its application in slot array antenna

Conventional array antenna techniques contain various feeding networks, such as T-junction power dividers, phase dividers, and baluns. To feed a relatively large array, one can cascade the traditional T-junction power dividers, resulting in the increase of design complexity. In this paper, an overmoded waveguide supporting the single mode propagation of TE50 mode, is presented. Since TE50 mode can be separated into five TE10 modes with equi-amplitude and opposite phase properties, it is advisable to distribute the input signal flexibly and decrease the cascading of the T-junctions for the traditional feeding networks. To actualize a TE50 mode waveguide, several rows of metallic blocks acting as metamaterial are periodically loaded inside an overmoded waveguide to tailor the dispersion of the waveguide modes and yield the proposed mode bandgaps. Considering the Bloch theory, parts of the undesired waveguide modes are not supported inside the metamaterial and will be removed by these bandgaps. In addition, central feeding method is used to suppress the unwanted modes further in light of mode mismatch. As a proof-of-concept, we drilled the slot array on the top of the overmoded waveguide directly and give rise to a pencil beam radiation along the broadside with 15–17 dBi realized gain among 9.4–10.6 GHz, which demonstrates the stable feeding ability of TE50 mode.