Next-generation Communication Research Articles

Indium Phosphide Semiconductor Technology for Next-Generation Communication Systems: Sustainability and Material Considerations

Indium phosphide (InP) semiconductor technology is being explored for radiofrequency (RF) applications, targeting frequencies exceeding 100 GHz, to support the next generation of 6G communication systems. When taking into account sustainability in designing this future generation, growing concerns are emerging regarding the environmental impact of communication networks and the reliance on raw materials for the production of Information and Communication Technologies (ICTs). The extraction, processing, and manufacturing of such materials and semiconductor technologies result in environmental impacts, but these impacts remain insufficiently documented. Firstly, this study evaluates the environmental impacts of manufacturing indium phosphide (InP) wafers based on industrial data and those of InP-based heterojunction bipolar transistors (HBTs) based on early-stage research data. Secondly, this study attempts to highlight the challenges posed by the increasing demand for high-tech solutions, involving raw materials, by evaluating the potential demand for indium for RF 6G applications, with a deployment scenario.

Enhancing Free Space Optical System Performance through Fog and Atmospheric Turbulence using Power Optimization

Free Space Optical (FSO) communication is gaining traction as a pivotal technology for next-generation communication systems, offering extremely high data rates, unlicensed bandwidth, and rapid transmission capabilities. However, its performance is significantly hindered by atmospheric factors such as turbulence and fog. This paper presents a comprehensive model for FSO communication designed to optimize performance under various atmospheric conditions. We assess channel capacity across a spectrum of weak to strong atmospheric turbulence using a Gamma-Gamma channel distribution. To mitigate channel losses, our system employs Wavelength Division Multiplexing (WDM) and multi-beam Multiple Input Multiple Output (MIMO) technologies. Results indicate that the integration of diversity techniques and WDM substantially enhances system performance in adverse weather conditions. Furthermore, power optimization is achieved through the implementation of optical amplifiers and feedback mechanisms from the receiver to the transmitter to adjust the transmitter power in accordance with received Bit Error Rate (BER). The proposed power-optimized WDM MIMO system demonstrates a remarkable BER of 1.48884e-15, while extending the transmission link distance to 2500 meters with a Q factor of 21.5 even under strong atmospheric turbulence conditions.

Flexible multi-access scheme for indoor VLC using multiband N-dimensional CAP and a wide field-of-view white laser transmitter

Visible light communication (VLC) has emerged as a crucial technology for next-generation (6 G) communication, integrating illumination and data transmission. However, the modulation bandwidths of light-emitting diodes (LEDs) are relatively limited, which restricts communication capacity. In contrast, laser diodes (LDs) offer distinct advantages, including high luminous flux, compact size, and large modulation bandwidth. Notably, white LDs with a wide field-of-view (FOV) are particularly suitable for indoor VLC applications, as they can cover a broad range. To meet the diverse requirements of indoor access devices, we propose a multiband N-dimensional carrierless amplitude and phase (multiband N-D CAP) modulation technique. In multiband N-D CAP, N users are distributed across multiple sub-bands, where frequency division multiplexing is applied between sub-bands and code division multiplexing is adopted within each sub-band. This structure enables adaptable configurations of sub-band numbers, user counts, and data rates, providing superior flexibility and compatibility compared to traditional multiband CAP or N-D CAP techniques. In our VLC system with a wide FOV white laser transmitter, we tested four configurations for 12 users with different user distributions or data rates. Results show total data rates ranging from 3.45 Gbps to 2.75 Gbps at 1.0 m, and from 1.35 Gbps to 1.00 Gbps at 2.5 m, with an effective FOV angle of approximately 25°. These results underscore the potential of multiband N-D CAP modulation for flexible and efficient indoor VLC access.

Vector mode division multiplexing in terahertz wireless link enabled by multifunction metasurfaces

Terahertz (THz) wireless links have attracted significant attention due to their pivotal role in next-generation communication systems. Multiplexing is one of the key techniques used to expand channel capacity for high-speed data transmission in point-to-point wireless communication. Using a pair of multifunction metasurfaces, we construct mode division multiplexing (MDM) in THz wireless link with cylindrical vector beams (CVBs) as orthogonal channels. The proposed metasurfaces integrate the functions of CVB generation and vector mode multiplexing, greatly simplifying MDM links. The simulated and measured results show that the multiplexer/demultiplexers are broadband in the frequency range of concern (from 0.36 to 0.44 THz) and compatible with frequency-division-multiplexing and polarization-division-multiplexing. Importantly, we experimentally accomplished a two-channel MDM in a direct modulation THz communication system at 0.36 THz in which the maximum modulation speed is 5 GHz (isolation>20dB). This study will lay the groundwork for CVB-based multidimensional multiplexing in the THz spectrum, potentially enhancing high-capacity THz communication.

Monolithic Multiparameter Terahertz Nano/Microdetector Based on Plasmon Polariton Atomic Cavity.

Terahertz (THz) signals are crucial for ultrawideband communication and high-resolution radar, demanding miniaturized detectors that can simultaneously measure multiple parameters such as intensity, frequency, polarization, and phase. Traditional detectors fail to meet these needs. To address this, we introduce a plasmon polariton atomic cavity (PPAC) detector based on monolayer graphene, offering a multifunctional, monolithic, and miniaturized solution. With a footprint only one-tenth the size of the incoming wavelength, the PPAC achieves benchmark performance in intensity-, frequency-, and polarization-sensitive detection. Operating at room temperature across 0.22-4.24 THz, it delivers sub-diffraction detection resolution and high-speed operation. Furthermore, we demonstrate its application in free-space THz polarization-coded communication and stealth imaging for physical property analysis. The unique design of PPAC enables strong absorption with weak signal detection, within a structure just 10-5 times the excitation wavelength in thickness, an accomplishment beyond current technologies. By simultaneously resolving intensity, frequency, and polarization, this detector can replace multiple single-function devices, providing a compact and efficient solution for next-generation ultrawideband communication and high-resolution radar systems.

Realization of two-dimensional beam scanning in 0.2 THz band with the combination of frequency sweeping and phased array method

Abstract Based on terahertz (THz) waves, the realization of mobile high-speed communication and rapid high-resolution imaging through two-dimensional (2D) electronically controlled beam scanning antennas holds significant research merit. However, accomplishing 2D electronically controlled beam scanning within the THz band poses formidable challenges. This paper presents a novel design methodology for a 2D beam-scanning antenna specifically tailored for the THz frequency range. Operating effectively within 190 GHz–210 GHz, the proposed antenna demonstrates frequency-controlled beam scanning along one dimension, while leveraging phased array technology to achieve phase-controlled beam scanning in the orthogonal dimension. Based on the proposed concept of combining frequency scanning and phased array to realize 2D beam scanning, the 2D electronically controlled beam scanning in the THz band was be ultimately realized in this paper. This antenna holds pivotal application potential in enhancing the acquisition efficiency of THz imaging field of view, augmenting the capability to capture moving targets, and advancing the development of next-generation mobile communication technologies, notably 6 G.

Advancing Microscale Electromagnetic Simulations for Liquid Crystal Terahertz Phase Shifters: A Diagnostic Framework for Higher-Order Mode Analysis in Closed-Source Simulators

This work addresses a critical challenge in microscale computational electromagnetics for liquid crystal-based reconfigurable components: the inadequate capability of current software to accurately identify and simulate higher-order modes (HoMs) in complex electromagnetic structures. Specifically, commercial simulators often fail to capture modes such as Transverse Electric (TE11) beyond the fundamental transverse electromagnetic (TEM) mode in coaxial liquid crystal phase shifters operating in the terahertz (THz) regime, leading to inaccurate performance predictions and suboptimal designs for telecommunication engineering applications. To address this limitation, we propose a novel diagnostic methodology incorporating three lossless assumptions to enhance the identification and analysis of pseudo-HoMs in full-wave simulators. Our approach theoretically eliminates losses associated with metallic conductivity, dielectric dissipation, and reflection effects, enabling precise assessment of frequency-dependent HoM power propagation alongside the primary TEM mode. We validate the methodology by applying it to a coaxially filled liquid crystal variable phase shifter device structure, underscoring its effectiveness in advancing the design and characterization of THz devices. This work provides valuable insights for researchers and engineers utilizing closed-source commercial simulators in micro- and nano-electromagnetic device development. The findings are particularly relevant for microscale engineering applications, including millimeter-wave (mmW), sub-mmW, and THz systems, with potential impacts on next-generation communication technologies.

Application of Machine Learning to Next-Generation Communication Protocols for IoT and 5G Network

Application of Machine Learning to Next-Generation Communication Protocols for IoT and 5G Network

A Comprehensive Review and Analysis of the Design Aspects, Structure, and Applications of Flexible Wearable Antennas

This review provides a comprehensive analysis of the design, materials, fabrication techniques, and applications of flexible wearable antennas, with a primary focus on their roles in Wireless Body Area Networks (WBANs) and healthcare technologies. Wearable antennas are increasingly vital for applications that require seamless integration with the human body while maintaining optimal performance under deformation and environmental stress. Return loss, gain, bandwidth, efficiency, and the SAR are some of the most important parameters that define the performance of an antenna. Their interactions with human tissues are also studied in greater detail. Such studies are essential to ensure that wearable and body-centric communication systems perform optimally, remain safe, and are in compliance with regulatory standards. Advanced materials, including textiles, polymers, and conductive composites, are analyzed for their electromagnetic properties and mechanical resilience. This study also explores innovative fabrication techniques, such as inkjet printing, screen printing, and embroidery, which enable scalable and cost-effective production. Additionally, solutions for SAR optimization, including the use of metamaterials, electromagnetic band gap (EBG) structures, and frequency-selective surfaces (FSSs), are discussed. This review highlights the transformative potential of wearable antennas in healthcare, the IoT, and next-generation communication systems, emphasizing their adaptability for real-time monitoring and advanced wireless technologies, such as 5G and 6G. The integration of energy harvesting, biocompatible materials, and sustainable manufacturing processes is identified as a future direction, paving the way for wearable antennas to become integral to the evolution of smart healthcare and connected systems.

Source-independent quantum random number generators with integrated silicon photonics

Random numbers play a crucial role in numerous scientific applications. Source-independent quantum random number generators (SI-QRNGs) can offer true randomness by leveraging the fundamental principles of quantum mechanics, eliminating the need for a trusted source. Silicon photonics demonstrates significant promise for QRNG due to its benefits in miniaturization, cost-effective device manufacturing, and compatibility with CMOS microelectronics. This study experimentally demonstrates a silicon-based discrete variable SI-QRNG. Our SI-QRNG system achieves a low error rate of only 0.21%, thanks to the inherent stability of the silicon-based decoder chip and its excellent polarization extinction ratio. Additionally, by using a laser with a higher repetition rate and a robust simulation model, we achieve the highest quantum random number generation rate of 9.49 Mbits per second. Our research paves the way for integrated SI-QRNGs, providing a cost-effective and robust secure QRNG module for next-generation communications.

Reflective metasurface for 5G & beyond Wireless communications

This paper presents a scalable reflective metasurface design optimized for 5G and beyond (B5G) wireless communications, featuring a unique combination of passive metasurface elements. The proposed design emphasizes a less complex structural configuration, facilitating easy scalability and cost-effective fabrication. By implementing a single-layer structure, the metasurface enables straightforward integration with existing B5G infrastructure and demonstrates compatibility with emerging intelligent surface technologies, such as Reconfigurable Intelligent Surfaces (RIS). The dual-polarization capabilities of the metasurface ensure angular stability in reflection, enhancing signal reliability and performance in diverse communication environments. Theoretical analyses, supported by experimental validation, showcase the metasurface’s effectiveness in addressing the challenges of modern wireless communication systems, paving the way for its practical application in next-generation communication.

Signal Transmission and Feedback Control in Wearable Devices: Review

Wearable devices have become a critical driving force in areas such as smart health management, sports tracking, smart homes, and remote healthcare, thanks to advancements in signal transmission and feedback control technologies. This paper systematically reviews the key technologies involved in signal acquisition, transmission, and feedback control in wearable devices, focusing on how closed-loop control enhances user experience and health management through real-time monitoring and dynamic adjustment. By utilizing sensor technology, wearable devices can gather various physiological signals and collaborate with smart systems to provide personalized health and environmental adjustment solutions. The paper also discusses the technical challenges related to latency, energy management, and data security in wearable devices. Additionally, it explores the potential of 5G, artificial intelligence, and next-generation communication technologies to improve device performance. The integration of feedback transmission and closed-loop control offers more intelligent and personalized solutions for future applications in health management, sports tracking, and smart living.

Novel insights into high-order dispersion and soliton dynamics in optical fibers via the perturbed Schrödinger–Hirota equation

This study offers a comprehensive analysis of the Perturbed Schrödinger -Hirota Equation (PSHE), crucial for understanding soliton dynamics in modern optical communication systems. We extended the traditional Nonlinear Schrödinger Equation (NLSE) to include higher-order nonlinearities and spatiotemporal dispersion, capturing the complexities of light pulse propagation. Employing the modified auxiliary equation method and Adomian Decomposition Method (ADM), we derived a spectrum of exact traveling wave solutions, encompassing exponential, rational, trigonometric, and hyperbolic functions. These solutions provide insights into soliton behaviors across diverse parameters, essential for optimizing fiber optic systems. The precision of our analytical solutions was validated through numerical solutions, and we explored modulation instability, revealing conditions for soliton formation and evolution. The findings have significant implications for the design and optimization of next-generation optical communication technologies.

Innovative MIM diplexer with neural network enhanced refractive index detection for advanced photonic applications

This study introduces a high-performance 4-channel Metal-Insulator-Metal (MIM) diplexer, employing silver and Teflon, optimized for advanced photonic applications. The proposed diplexer, configured with two novel band-pass filters (BPFs), operates across four distinct wavelength bands (843 nm, 1090 nm, 1452 nm, 1675 nm) by precisely manipulating the passband dimensions. Utilizing Finite-Difference Time-Domain (FDTD) simulations, the designed diplexer achieves exceptional sensitivity values of 3500 nm/RIU, 4250 nm/RIU, 3375 nm/RIU, and 4003 nm/RIU, along with high figures of merit (FOM) ranging from 113.4 to 124.7 1/RIU. Also, the compact design (400 nm × 830 nm) underscores its suitability for integrated photonic circuits and advanced sensing applications. Furthermore, to further enhance accuracy in detecting refractive index (RI) changes, a multilayer perceptron (MLP) neural network was employed, ensuring the highest sensor accuracy. The accuracy of the MIM diplexer’s RI measurements was statistically validated through a one-sample t-test, confirming the sensor’s reliability. Comparative analysis with existing sensors highlights the diplexer’s superior sensitivity and efficiency, setting a new benchmark in optical communication and photonic sensing technologies. This work paves the way for future advancements in miniaturized, high-sensitivity optical devices, offering robust solutions for next-generation communication and sensing systems.

Graphene-Oxide-Assisted Electroless Cu Plating on a Glass Substrate.

In recent years, the advancement of high-frequency communication systems, particularly 5G and future 6G technologies, has increased the need for substrates that minimize signal loss and electromagnetic interference. Glass substrates are highly desirable for these applications due to their low dielectric constant and excellent surface smoothness. However, conventional electroless Cu plating methods struggle to achieve strong adhesion between Cu and the smooth, low-polarity surface of glass, making this an important challenge to address. To overcome this issue, this study presents a novel electroless Cu plating method that employs graphene oxide (GO) as an intermediary layer on amino-functionalized glass substrates. During a preheating process at 150 °C, the GO layer forms covalent C-N bonds with the amino-modified glass, significantly enhancing adhesion while preserving the surface smoothness required for high-frequency applications (Ra = 6.6 nm). This GO-based approach eliminates the need for traditional surface roughening techniques. Additionally, by incorporating silver nanoparticles (Ag NPs) as a catalyst, this method provides a cost-effective alternative to conventional palladium-based processes for Cu electroless plating. The resulting Cu film exhibits excellent adhesion, as confirmed by tape peel tests and a low volume resistivity of 2.4 μΩ·cm, making it well-suited for applications that require minimal signal loss at high frequencies.This innovative technique not only enhances the adhesion of the conductive layer but also maintains the surface smoothness crucial for high-frequency signal transmission, positioning it as a promising solution for the fabrication of advanced substrates in next-generation communication technologies.

Spatial-division multiplexing self-homodyne coherent transmission over 19-/24-core fibers assisted by homemade fan-in/fan-out 3D photonic devices.

The self-homodyne detection (SHD) is a promising solution to achieve low-cost and low-power-consumption fiber-optic communications. In this work, we propose and demonstrate a high-capacity spatial-division multiplexing (SDM) system with SHD technology by employing single-mode multi-core fibers (SM-MCFs), where the fan-in/fan-out (FIFO) 3D photonic devices are designed and fabricated based on the femtosecond laser direct writing technique, enabling high-efficiency coupling between single-mode fibers (SMFs) and SM-MCFs. The FIFO 3D photonic devices, serving as the SDM (de)multiplexer, facilitate superior performance of low insertion loss and low inter-channel crosstalk. Using a low-cost MHz linewidth distributed feedback (DFB) laser, we experimentally demonstrate the SDM-SHD transmission system of 102-Gbaud dual-polarization (DP) 16-ary quadrature amplitude modulation (16QAM) signals per channel over a 2.7-km 24-core SM-MCF and 22-Gbaud DP-64QAM signals per channel over a 1-km 19-core SM-MCF. Without using wavelength-division multiplexing (WDM), the total data rate per channel reaches 816 Gbit/s, with an aggregate data throughput of 18.7 Tbit/s. The obtained results indicate that, by extending SHD technology to SDM communication systems, one can achieve low-cost, low-power-consumption, and scalable high-capacity data transmission in next-generation fiber-optic communication networks.

Revolutionizing Free-Space Optics: A Survey of Enabling Technologies, Challenges, Trends, and Prospects of Beyond 5G Free-Space Optical (FSO) Communication Systems.

As the demand for high-speed, low-latency communication continues to grow, free-space optical (FSO) communication has gained prominence as a promising solution for supporting the next generation of wireless networks, especially in the context of the 5G and beyond era. It offers high-speed, low-latency data transmission over long distances without the need for a physical infrastructure. However, the deployment of FSO systems faces significant challenges, such as atmospheric turbulence, weather-induced signal degradation, and alignment issues, all of which can impair performance. This paper offers a comprehensive survey of the enabling technologies, challenges, trends, and future prospects for FSO communication in next-generation networks, while also providing insights into the current mitigation strategies. The survey explores the critical enabling technologies such as adaptive optics, modulation schemes, and error correction codes that are revolutionizing FSO communication and addressing the unique challenges of FSO links. Also, the integration of FSO with radio frequency, millimeter-wave, and Terahertz technologies is explored, emphasizing hybrid solutions that enhance reliability and coverage. Additionally, the paper highlights emerging trends, such as the integration of FSO with artificial intelligence-driven optimization techniques and the growing role of machine learning in enhancing FSO system performance for dynamic environments. By analyzing the current trends and identifying key challenges, this paper emphasizes the prospects of FSO communication in the evolving landscape of 5G and future networks. In this regard, it assesses the potential of FSO to meet the demands for high-speed, low-latency communication and offers insights into its scalability, reliability, and deployment strategies for 5G and beyond. The paper concludes by identifying the open challenges and future research directions critical to realizing the full potential of FSO in next-generation communication systems.

Interleaving based SCMA Codebook Design Using Arnold’s Cat Chaotic Map

Non-orthogonal multiple access (NOMA) technology is a significant topic of the present 5G investigation. A possible NOMA approach is Sparse Code Multiple Access (SCMA), increasing next-generation communication's ability to handle multiple users. In SCMA, codebook designing and optimization are crucial components that define the performance of multiple access systems. In this work, the complete design procedure of the SCMA codebook based on interleaving is explained and simulated. Furthermore, a chaotic interleaving based onArnold’sCat map is proposed to reduce the computational complexity. The performance of the SCMA codebook based on interleaving is evaluated through comparison with selected codebooks for SCMA multiplexing. The measures used for performance evaluation include Bit Error rate (BER), Peak to Average Power Ratio(PAPR), and minimum EuclidianDistance(MED). The results show that the proposed codebook with chaotic interleaving achieves comparable performance to the traditional codebook based on interleaving and less MED and higher BER compared to computer-generated and 16-star QAM codebook design methods but with reduced complexity.

A Dynamic Load Modulation Power Amplifier with Ferroelectric-Based Tunable Matching Network.

Power amplifiers are crucial components that significantly influence the linearity and energy efficiency of next-generation communication system radio units. A key challenge in designing power amplifiers is managing high peak-to-average power ratio (PAPR) in order to achieve both high linearity and energy efficiency during back-off conditions. This paper presents simulation and measurement results for a dynamic load modulation power amplifier based on a ferroelectric tunable matching network to operate at 2.5 GHz. Experimental studies on a power amplifier with the tunable output matching network confirm its performance at 8 dB back-off while varying the control voltage applied to the ferroelectric element. Additionally, a bias modulator to adjust the transistor's load in relation to input power was designed. Measurement studies of the dynamic load modulation power amplifier have demonstrated an efficiency of at least 50% at 8 dB back-off and more than 60% at peak power at 2.5 GHz. Furthermore, it was found that the modulator output voltage adjustment function on input power of the bias modulator affects the linearity of the output power. Different bias responses were studied and, as a result, the optimal output voltage response was found. The proposed load modulation power amplifier is promising for operation with high PAPR digital signals.

Simple Contact-Less Photo-Electrochemical (CL-PEC) Etching for AlGaN/GaN Heterostructures

AlGaN/GaN high electron mobility transistors (HEMTs) are expected to become high-frequency power devices required for next-generation communication systems because of the high breakdown voltage characteristics of GaN-based materials and the high channel density and high electron mobility of the two-dimensional electron gas (2DEG) induced at the AlGaN/GaN hetero-interface. Etching is an important process for transistors using 2DEGs at the AlGaN/GaN hetero-interface as a channel, as it provides isolation to electrically separate the neighboring devices by deep etching from the AlGaN layer to the GaN layer, and also controls the threshold voltage by the thickness of the AlGaN layer. Contactless photo-electrochemical (CL-PEC) etching is performed by immersing a sample with a cathode pad in a solution containing an oxidant and irradiating it with ultra-violet (UV) light. It is very simple set-up and is one of the most promising wet etching techniques for nitride semiconductors such as GaN [1] and AlGaN [2]. In this study, we have demonstrated the deep and shallow etching of AlGaN/GaN structures by optimizing the CL-PEC conditions.The AlGaN/GaN samples with a cathode pad were immersed into the K2S2O8-based solution, where the UV-light was irradiated to the top surface. In the CL-PEC etching, the hole concentration at the anode area to be etched and the efficiency of electron extraction at the cathode area are key parameters to control the etching rate. To demonstrate to realize both the deep and shallow etching by CL-PEC technique, the UV-light power, P in, and the ratio of the cathode area to the anode area, C/A, was changed.We have compared the etching rate of the samples having different cathode pads. The etching depth was linearly controlled by the time for the sample having a Ti/Al/Ti/Au ohmic cathode. On the other hand, the etching rate was very slow, and the etching was saturated for the sample having a Ti Schottky cathode. The results indicate that the deep and shallow etching can be switched by changing the cathode pad, where their conductivity plays an important role.The effect of changes in P in and C/A ratio on etching rate was investigated for the case of deep etching with Ti/Al/Ti/Au ohmic cathodes. The etching rate was found to be strongly dependent on P in and independent of C/A. These results suggest that the hole concentration produced by light irradiation is the dominant factor in determining the etching rate for the sample having a Ti/Al/Ti/Au ohmic cathode. We have demonstrated that such deep CL-PEC etching is useful for separating devices fabricated on AlGaN/GaN heterostructures. Evaluation of the current-voltage characteristics between two ohmic electrodes placed across the insulating region formed by CL-PEC etching showed that deep CL-PEC etching increased the resistance between the electrodes by a factor of 108. Despite being a very simple method, this is comparable to device separation by dry etching or ion implantation.The Shallow etching with a Ti Schottky cathode was then evaluated by AFM for etching depth and surface morphology after CL-PEC etching. Under optimum conditions, the etching rate of the AlGaN layer was very slow (<1.0 nm/min) and the residual thickness of the AlGaN layer could be accurately controlled. The etched surface was very smooth, with a root mean square (RMS) value of 0.4 nm for roughness. This shallow etching was applied to the gate recess fabrication of AlGaN/GaN HEMTs. The drain current-voltage (I DS-V DS) characteristics of the recess-gate HEMTs showed good pinch-off behavior, with a decrease in drain leakage current under the reverse bias and a positive shift in Vth from -3.4V (planar gate device) to 0V. The subthreshold slope (SS) values obtained from the transfer characteristics were smaller than those obtained for the planar-gate HEMTs.The CL-PEC etching enabled device separation and threshold voltage control of AlGaN/GaN HEMTs by optimizing its conditions. We believe that the CL-PEC etching is a promising alternative to dry etching and other processes that cause processing damage.Acknowledgements: This work was supported by JSPS KAKENHI- JP23K26131.