Multiplexing Modulation Research Articles

Thin-film lithium niobate polarization-independent modulators for mode and polarization multiplexing

We demonstrated a high-order mode modulator based on thin-film lithium niobate (TFLN). By introducing a mode converter and a polarization splitter-rotator (PSR), the modulator can achieve dual-mode modulation. Additionally, we designed a periodic capacitively loaded traveling-wave electrode on TFLN to enhance modulation efficiency and bandwidth. The modulator exhibits a polarization extinction ratio greater than 20 dB at a wavelength of 1550 nm, a modulation efficiency of V π LTE0=2.541V⋅cm and V π LTM0=2.570V⋅cm, and a 3 dB bandwidth exceeding 60 GHz. This not only meets the requirements for polarization-independent modulators but also supports on-chip multimode applications such as mode and polarization multiplexing.

Unlocking mode programming with multi-plane light conversion using computer-generated hologram optimisation

Abstract Programmable optical devices provide performance enhancement and flexibility to spatial multiplexing systems enabling transmission of tributaries in high-order eigenmodes of spatially-diverse transmission media, like multimode fibre (MMF). Wavefront shaping with spatial light modulators (SLMs) facilitates scalability of the transmission media by allowing for channel diagonalization and quasi-single-input single-output operation. Programmable mode multiplexing configurations like multi-plane light conversion (MPLC) utilise the SLM and offer the potential to simultaneously launch an arbitrary subset of spatial tributaries in any N -mode MMF. Such programmable optical processor would enable the throughput of space-division multiplexing (SDM) systems to be progressively increased by addressing a growing number of tributaries over one MMF and in this way meet a growing traffic demand – similarly to the wavelength-division multiplexing evolution path. Conventionally, MPLC phasemasks are calculated using the wavefront matching algorithm (WMA). However, this method does not exploit the full potential of programmable mode multiplexers. We show, that computer-generated hologram algorithms like direct search enable significant improvement compared to the traditional WMA-approach. Such gains are enabled by tailored cost functions with dynamic constraints concerning insertion loss as wellas mode extinction ratio. We show that average mode extinction ratio can be greatly improved by as much as ≈ 15 dB at the expense of a small insertion loss35
deterioration of < 3 dB. One particular feature of programmable mode multiplexers is the adaptability to optimised transmission functions. Besides conventional LP modes transmission, we employ our approach on Schmidt modes, which are spatial eigenchannels with minimum crosstalk derived from a measured transmission matrix

Off-axis dispersion-managed metasurface for routing orbital angular momentum mode and wavelength multiplexing channels

Off-axis dispersion-managed metasurface for routing orbital angular momentum mode and wavelength multiplexing channels

Analysis of methods for reducing the signal PAPR under the influence of the Doppler effect in hybrid communication networks

Background. For further development of communication networks, it is planned to use hybrid satellite networks for traffic transmission. However, satellite communication channels have features such as distortion caused by the Doppler effect and increased energy efficiency requirements. Aim of this study is to analyze variants of orthogonal frequency multiplexing methods and modulation methods in order to choose the most stable technology, taking into account destabilizing factors. Method. Comparing different signal processing technologies and studying their resistance to bit errors is the imitation modeling of the communication channel in the Matlab environment. This approach allows creating a model of the communication network, taking into account the main parameters of communication channels, such as the Doppler effect, energy deficiency and destabilizing factors. Results. The distribution of the bit error coefficient for various signal processing technologies, depending on the signal-to-noise ratio, is compared. The method of frequency multiplexing is defined, providing the minimum peak factor and the most resistant to bit error. It is also noted that the effectiveness of all the studied technologies depends on the spacing and modulation constellations, and that it is necessary to adjust the characteristics of the system for each case. Conclusion. The results of this study can be used to improve the quality of communication in difficult interference conditions of hybrid mobile networks of 5 and 6 generations using the satellite segment.

Utilization of Optical OFDM Modulation on Blue LED VLC Datacom Without Equalization for 4 m Wireless Link

To achieve higher visible light communication (VLC) traffic capacity, using the wide bandwidth light-emitting diode (LED) and spectral efficiency modulation signal, is currently the most commonly used method. In this demonstration, we apply the orthogonal frequency division multiplexing quadrature amplitude modulation (OFDM-QAM) with bit- and power-loading algorithm on single blue LED to achieve >1 Gbit/s VLC capacity, when a 400 MHz bandwidth avalanche photodiode (APD)-based receiver (Rx) is exploited for decoding. Here, the higher sensitivity APD can be applied to compensate for the wireless VLC link length in the proposed LED VLC system, and due to the lower LED illumination (255 to 40 lux), is used for the indoor access network after passing the wireless link length of 1 to 4 m. As a result, using single blue LED can achieve 0.962 to 1.057 Gbit/s OFDM rate with available 400 MHz bandwidth APD in poorly illuminated condition indoors without applying analogy equalization.

High gain distributed Raman amplifier for orbital angular momentum mode-division multiplexing and wavelength-division multiplexing in a 104-km ring-core fiber over the C + L band

Mode-division multiplexing (MDM) and wavelength-division multiplexing (WDM) are regarded as effective solutions for enhancing the communication capacity of fiber-optic transmission systems. To extend the transmission distance, a suitable amplification technique is required to amplify the signal light, with distributed Raman amplifier (DRA) offering a high-flat gain. In this paper, we experimentally demonstrate the transmission of 3 orbital angular momentum (OAM) mode-division multiplexing and 9 wavelength-division multiplexing ranging from 1530 nm to 1610 nm over a 104-km self-designed ring-core fiber (RCF) with the assistance of DRA. The homemade all-fiber mode selective couplers (MSCs) can (de)multiplex OAM modes (OAM01, OAM11, OAM21) efficiently in long-distance MDM + WDM fiber-optic transmission systems. The OAM-DRA provides high gain (with an on-off gain greater than 10 dB) as well as flat gain (with a differential wavelength gain of less than 0.88 dB and a differential mode gain of less than 0.28 dB) over the C + L band.

Multi-Plane Light Conversion (MPLC) LP mode multiplexer based on grayscale maskless lithography

Multi-Plane Light Conversion (MPLC) LP mode multiplexer based on grayscale maskless lithography

Time Evolution of Orbital Angular Momentum Modes for Deep-Routing Multiplexing Channels

Optical orbital angular momentum (OAM) mode multiplexing has emerged as a promising technique for boosting communication capacity. However, most existing studies have concentrated on channel (de)multiplexing, overlooking the critical aspect of channel routing. This challenge involves the reallocation of multiplexed OAM modes across both spatial and temporal domains—a vital step for developing versatile communication networks. To address this gap, we introduce a novel approach based on the time evolution of OAM modes, utilizing the orthogonal conversion and diffractive modulation capabilities of unitary transformations. This approach facilitates high-dimensional orthogonal transformations of OAM mode vectors, altering both the propagation direction and the spatial location. Using Fresnel diffraction matrices as unitary operators, it manipulates the spatial locations of light beams during transmission, breaking the propagation invariance and enabling temporal evolution. As a demonstration, we have experimentally implemented the deep routing of four OAM modes within two distinct time sequences. Achieving an average diffraction efficiency above 78.31%, we have successfully deep-routed 4.69 Tbit·s−1 quadrature phase-shift keying (QPSK) signals carried by four multiplexed OAM channels, with a bit error rate below 10–6. These results underscore the efficacy of our routing strategy and its promising prospects for practical applications.

Compact and low-crosstalk multimode waveguide crossing utilizing subwavelength holey metamaterial waveguides

To further increase the transmission capacity of on-chip optical communication systems, hybrid division multiplexing technology has emerged as a crucial alternative solution, in which multimode waveguide crossings are highly desired. In this paper, we propose and experimentally demonstrate a compact multimode (i.e., three different modes) waveguide crossing that employs subwavelength holey metamaterial waveguides (SHMWs). The used SHMW, formed by inserting subwavelength periodic holes into a multimode interference (MMI) coupler, deservedly exhibits synergetic advantages of the two kinds of structures, enabling an attractive three-mode (e.g., TE0, TM0, and TM1) waveguide crossing with flexible design, small size, and good performance. Simulation results show that the realized device has a low insertion loss (< 0.74 dB), low reflection loss (<−13.1 dB), and low crosstalk (<−31.6 dB) at a central wavelength of 1550 nm for all the modes with a compact footprint of 27.4 µm × 27.4 µm. The experimental results prove that insertion losses are as low as 0.72 dB, 0.27 dB, and 0.90 dB for TE0, TM0, and TM1 mode, respectively, with the corresponding crosstalk below −38 dB at 1550 nm. The proposed device can be widely applied in photonic integrated circuits to construct photonic systems with the abilities of mode control and multiplexing.

Enhancing Security of Telemedicine Data: A Multi-Scroll Chaotic System for ECG Signal Encryption and RF Transmission.

Protecting sensitive patient data, such as electrocardiogram (ECG) signals, during RF wireless transmission is essential due to the increasing demand for secure telemedicine communications. This paper presents an innovative chaotic-based encryption system designed to enhance the security and integrity of telemedicine data transmission. The proposed system utilizes a multi-scroll chaotic system for ECG signal encryption based on master-slave synchronization. The ECG signal is encrypted by a master system and securely transmitted to a remote location, where it is decrypted by a slave system using an extended state observer. Synchronization between the master and slave is achieved through the Lyapunov criteria, which ensures system stability. The system also supports Orthogonal Frequency Division Multiplexing (OFDM) and adaptive n-quadrature amplitude modulation (n-QAM) schemes to optimize signal discretization. Experimental validations with a custom transceiver scheme confirmed the system's effectiveness in preventing channel overlap during 2.5 GHz transmissions. Additionally, a commercial RF Power Amplifier (RF-PA) for LTE applications and a development board were integrated to monitor transmission quality. The proposed encryption system ensures robust and efficient RF transmission of ECG data, addressing critical challenges in the wireless communication of sensitive medical information. This approach demonstrates the potential for broader applications in modern telemedicine environments, providing a reliable and efficient solution for the secure transmission of healthcare data.

Polar coded SCMA-OCDM based on chaotic scrambled SLM

In this work, the polar coded sparse code multiple access (SCMA) scheme based on chaotic scrambled selective mapping (CS_SLM) is proposed for future passive optical networks (PONs). The original bits are coded by polar and mapped into constellation symbols by sparse code. Then orthogonal chirp division multiplexing (OCDM) modulation is adopted which has better anti-interference ability than orthogonal frequency division multiplexing (OFDM). At the receiver, the joint iterative detection and decoding for polar and SCMA is used to further improve the BER performance. The CS_SLM is helpful to improve the reliability and security, while keeping high spectral efficiency of SCMA-OCDM modulation. A 49.42 Gb/s coded SCMA-OCDM PON over 2 km seven-core fiber is demonstrated in the experiment. The results show that the SCMA-OCDM scheme gets a receiver sensitivity of 0.8 dB at a bit error rate (BER) of 3.8 × 10−3, compared with SCMA-OFDM. Because of peak to average power ratio (PAPR), the polar coded SCMA-OCDM based on CS_SLM is compared with clipping and filtering (CAF) method, about 2.08 dB receiver sensitivity gain is obtained when BER is lower than 10−5. The polar coded SCMA-OCDM based on CS_SLM also takes security into the consideration, due to the downlink broadcasting of PON. It can be a promising candidate for the next generation PONs.

Aggregation Induced Emission-Based Covalent Organic Frameworks for High-Performance Optical Wireless Communication.

Here, we report the first utilization of covalent organic frameworks (COFs) in optical wireless communication (OWC) applications. In the solid form, aggregation-induced emission (AIE) luminogen often shows promising emissive characteristics that augment radiative decays and improve fluorescence. We have synthesized an AIE-COF through the Knoevenagel condensation reaction by taking advantage of the ability to carefully design and alter the COF structure by integrating an AIE luminogen with linear building blocks. The synthesized AIE-COF exhibited a high solid-state photoluminescence quantum yield (∼39%) and a short photoluminescence lifetime (∼1 ns), crucial for achieving modulation bandwidth for high-speed OWC applications. For comparison, we constructed an aggregation-caused quenching based COF, showing a similar lifetime but almost insignificant quantum yield. The orthogonal frequency-division multiplexing modulation strategy employed by the AIE-COF demonstrates remarkable high-rate data transmission, with a wide -3 dB modulation bandwidth of nearly 200 MHz and achieving high net data rates of 825 Mb/s, outperforming traditional materials. These results open new avenues for the ability to design and finetune new COF materials for their utilization as color converters in developing cutting-edge OWC components, enabling faster and more efficient data transfer.

Ultra-Broadband Mode (De)Multiplexer on Thin-Film Lithium Niobate Platform Adopting Phase Control Theory.

Mode (de)multiplexers (MDMs) serve as critical foundational elements within systems for facilitating high-capacity communication, relying on mode conversions achieved through directional coupler (DC) structures. However, DC structures are challenged by dispersion issues for broadband mode coupling, particularly for high-order modes. In this work, based on the principles of phase control theory, we have devised an approach to mitigate the dispersion challenges, focusing on a thin-film lithium niobate-on-onsulator (LNOI) platform. This solution involves integrating a customized inverse-dispersion section into the device architecture, offsetting minor phase shifts encountered during the mode coupling process. By employing this approach, we have achieved broadband mode conversion from TE0 to TE1 and TE0 to TE2 within a 300 nm wavelength range, and the maximum deviations were maintained below -0.68 dB and -0.78 dB, respectively. Furthermore, the device exhibited remarkably low crosstalk, reaching down to -26 dB.

Reinforcement learning-based automated modulation switching algorithm for an enhanced underwater acoustic communication

Acoustic communication is the preferred method for underwater communication due to its superior propagation characteristics, including longer range, lower attenuation, better penetration, and adaptability to water density. However, challenges like varying water depths, temperature gradients, noise, and multipath propagation require innovative solutions beyond fixed-data rate systems and single modulation schemes. To address these challenges, we propose a reinforcement learning (RL)-based automated modulation switching algorithm designed to enhance data transmission efficiency. This approach leverages the UNETStack software and the Frequency Hopping-Binary Frequency Shift Key (FH-BFSK) modulation, extending its capabilities by incorporating Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), and Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques. We designed a cost-effective, software-controlled acoustic modem using commercial off-the-shelf (COTS) components, enabling full-duplex underwater communication. The RL algorithm utilizes a Q-matrix guided by a greedy policy to assess network conditions, such as data volume and data rates. It continuously monitors underwater environments to select the most suitable modulation scheme dynamically. Experimental validation demonstrates a 3.648 % improvement in Received Signal Strength Indicator (RSSI), a 32 % reduction in bit error rate at a constant 7 dB Signal-to-Noise Ratio (SNR), and a 5 % increase in utility at 10 dB SNR when using OFDM selected by the reinforcement learning algorithm, compared to FH-BFSK.

Silica‐Rich Sol‐Gel Ink for Two‐Photon Direct Laser Writing of Microscale Structures and Optical Elements

AbstractInnovative materials enable two‐photon polymerization for precise additive fabrication of intricate optical components. Existing polymeric inks suffer from poor optical performance due to their high organic content. Silica‐rich sol‐gel ink (75 wt%, under ambient conditions) is presented for high‐precision three‐dimensional (3D) printing of microscale structures and optical devices. A photoinitiator with high‐efficiency nonlinear absorption is introduced to initiate two‐photon polymerization. Utilizing a commercial direct laser writing system, 3D‐printing is demonstrated including the optimization of printing parameters and ink characterization. The optical performance of the printed microscale elements using the new sol‐gel ink surpasses commercially available polymeric inks on key metrics: Printed elements exhibit extremely low surface roughness, 3nm; visible and near‐IR light transmission is greater than 90%; Printed elements present enhanced mechanical and chemical resistance to common organic solvents; Structures exhibit low isotropic shrinkage, <10%; Elements withstand continuous‐wave laser intensities exceeding 7 × 105 W cm−2. Direct writing onto an optical fiber tip with no need for surface functionalization is presented, with the demonstration of a tall waveguide taper (≈1:5 aspect ratio) with low losses and modal crosstalk, and a freestanding photonic lantern mode multiplexer. The new ink can be utilized in a variety of applications and across many materials, requiring compact, durable, and complex optical elements.

MEMS‐enabled Ultralow Power Consumption Programmable Arbitrary Order Mode Switch

AbstractMode‐division‐multiplexing (MDM) recently attracted much interest due to its ability to enhance the capacity for optical information communication. To meet growing data transmission demands and enable flexible on‐chip mode manipulation, programmable optical mode converter switches are essential. This work introduces a micro‐electromechanical‐system (MEMS)‐enabled programmable arbitrary order mode switch, capitalizing on the benefits of MEMS technology such as low power consumption, robust modulation capabilities, and seamless large‐scale integration. Employing newly developed MEMS‐tunable mode converter (MTMC) units, the system achieves high conversion efficiencies from the fundamental mode to arbitrary higher‐order modes and supports programmable power distribution among different modes by cascading multiple MTMCs. As a proof‐of‐concept, a programmable TE0–TE0/1/2 mode switch operates in the 3.64 to 3.71 µm wavelength range, achieving maximum crosstalk values of –9.56 and –9.88 dB for TE0 to TE1 and TE0 to TE2 mode conversion, respectively, and a remarkably low power consumption of 67 pW. Furthermore, a programmable mode multiplexer is developed by simultaneously actuating two MEMS actuators to modulate phase matching conditions, enabling arbitrary power splitting ratios among these modes. The demonstrated scalability and flexibility of the proposed system highlight its potential as a foundational component for MDM systems.

A Novel Waveform Optimization Method for Orthogonal-Frequency Multiple-Input Multiple-Output Radar Based on Dual-Channel Neural Networks.

The orthogonal frequency-division multiplexing (OFDM) mode with a linear frequency modulation (LFM) signal as the baseband waveform has been widely studied and applied in multiple-input multiple-output (MIMO) radar systems. However, its high sidelobe levels after pulse compression affect the target detection of radar systems. For this paper, theoretical analysis was performed, to investigate the causes of high sidelobe levels in OFDM-LFM waveforms, and a novel waveform optimization design method based on deep neural networks is proposed. This method utilizes the classic ResNeXt network to construct dual-channel neural networks, and a new loss function is employed to design the phase and bandwidth of the OFDM-LFM waveforms. Meanwhile, the optimization factor is exploited, to address the optimization problem of the peak sidelobe levels (PSLs) and integral sidelobe levels (ISLs). Our numerical results verified the correctness of the theoretical analysis and the effectiveness of the proposed method. The designed OFDM-LFM waveforms exhibited outstanding performance in pulse compression and improved the detection performance of the radar.

Broadband and low-cross talk mode multiplexer based on subwavelength-assisted phase matching.

Integrated mode multiplexers are key components in photonic networks and are crucial to achieving higher data density. Asymmetric directional couplers represent one of the most common multiplexing architectures, owing to their low losses and scalability, but further bandwidth enhancements are sought after. In this Letter, we demonstrate a multiplexer/demultiplexer link based on asymmetric directional couplers assisted by subwavelength grating metamaterials. Through subwavelength-assisted phase matching, low losses and cross talk are achieved on a small form factor over a broad bandwidth. Experimental measurements show insertion losses under 0.8 dB and cross talk under -19.8 dB in a 170 nm bandwidth (1500 nm to 1670 nm) for a full multiplexer/demultiplexer link.

Cascaded partitioned phase modulation for cross-connection of orbital angular momentum mode and polarization multiplexing channels.

Multi-dimensional orbital angular momentum (OAM) mode multiplexing provides a promising route for enlarging communication capacity and establishing comprehensive networks. While multi-dimensional multiplexing has gained advancements, the cross-connection of these multiplexed channels, especially involving modes and polarizations, remains challenging due to the needs for multi-mode interconversion and on-demand polarization control. Herein, we propose an OAM mode-polarization cross-transformation solution via cascaded partitioned phase modulation, which enables the divergently separated OAM modes to be independently phase-imposed within distinct spatial regions, leading to the synergistic conversion operation of mode and polarization channels. In demonstrations, we implemented the cross-connection of three OAM modes and two polarization multiplexed channels, achieving the mode purity that exceeds 0.951 and polarization contrast up to 0.947. The measured mode insertion losses and polarization conversion losses are below 3.42 and 3.54 dB, respectively. Consequently, 1.2 Tbit/s quadrature phase shift keying signals were successfully exchanged, yielding the bit-error-rates close to 10-6. Incorporating with increased partitioned phase treatments, this approach shows promise in accommodating massive mode-polarization multiplexed channels, which hold the potential to augment networking capability of large-scale OAM mode multiplexing communication networks.

Photonic crystal-connected bidirectional micro-ring resonator array for duplex mode and wavelength channel (de)multiplexing

The progress of on-chip optical communication relies on integrated multi-dimensional mode (de)multiplexers to enhance communication capacity and establish comprehensive networks. However, existing multi-dimensional (de)multiplexers, involving modes and wavelengths, face limitations due to their reliance on single-directional total internal reflection and multi-level mode conversion based on directional coupling principles. These constraints restrict their potential for full-duplex functionality and highly integrated communication. We solve these problems by introducing a photonic-like crystal-connected bidirectional micro-ring resonator array (PBMRA) and apply it to duplex mode-wavelength multiplexing communication. The directional independence of total internal reflection and the cumulative effect of the subwavelength-scale pillar within the single-level photonic crystal enable bidirectional mode and wavelength multiplexed signals to transmit among multi-pair nodes without interference, improving on-chip integration in single-level mode conversion. As a proof of concept, we fabricated a nine-channel bidirectional multi-dimensional (de)multiplexer, featuring three wavelengths and three TE modes, compactly housed within a footprint of 80 μm×80 μm, which efficiently transmits QPSK-OFDM signals at a rate of 216 Gbit/s, achieving a bit error rate lower than 10−4. Leveraging the co-ring transmission characteristic and the orthogonality of the mode-wavelength channel, this (de)multiplexer also enables a doubling of communication capacity using two physical transmission channels.