Division Multiplexing Modulation Research Articles

Wideband and Channel Switchable Mode Division Multiplexing (MDM) Optical Power Divider Supporting 7.682 Tbit/s for On-Chip Optical Interconnects.

Silicon photonics (SiPh) are considered a promising technology for increasing interconnect speed and capacity while decreasing power consumption. Mode division multiplexing (MDM) enables signals to be transmitted in different orthogonal modes in a single waveguide core. Wideband MDM components simultaneously supporting wavelength division multiplexing (WDM) and orthogonal frequency-division multiplexing (OFDM) can significantly increase the transmission capacity for optical interconnects. In this work, we propose, fabricate and demonstrate a wideband and channel switchable MDM optical power divider on an SOI platform, supporting single, dual and triple modes. The switchable MDM power divider consists of two parts. The first part is a cascaded Mach-Zehnder interferometer (MZI) for switching the data from their original TE0, TE1 and TE2 modes to different modes among themselves. After the target modes are identified, mode up-conversion and Y-branch are utilized in the second part for the MDM power division. Here, 48 WDM wavelength channels carrying OFDM data are successfully switched and power divided. An aggregated capacity of 7.682 Tbit/s is achieved, satisfying the pre-forward error correction (pre-FEC) threshold (bit-error-rate, BER = 3.8 × 10-3). Although up to three MDM modes are presented in the proof-of-concept demonstration here, the proposed scheme can be scaled to higher order modes operation.

Micro-electro-mechanically tunable optical phase matching and mode conversion.

Mode-division multiplexing (MDM) enables a large increase in the information-carrying capacity of an optical network. Recently, chip-scale MDM devices that can switch different mode orders to different output waveguides have been demonstrated. However, an important milestone showing dynamically tunable mode-order conversion in a single compact device has so far not been reported. In this work, we demonstrate via simulation and measurement a new, to the best of our knowledge, approach for reconfigurable mode conversion using optical micro-electro-mechanical systems (MEMS) to locally modify the effective index in an asymmetric coupler. Modeling shows that dynamic tuning to increase or decrease the mode order is possible. Measurements on fabricated devices are consistent with simulations of reconfigurable mode conversion based on tunable phase matching. Our experimental results demonstrate reconfigurable TE0-TE2 to TE0-TE1 conversion and validate this new tunable phase-matching approach for mode-division multiplexing.

On-Chip Optical Switching Network Architecture Based on Hybrid Wavelength and Mode Division Multiplexing

On-Chip Optical Switching Network Architecture Based on Hybrid Wavelength and Mode Division Multiplexing

Machine Learning-based Inverse Model for Few-Mode Fiber Designs

The medium for next-generation communication is considered as fiber for fast, secure communication and switching capability. Mode division and space division multiplexing provide an excellent switching capability with high data transmission rate. In this work, the authors have approached an inverse modeling technique using regression-based machine learning to design a weakly coupled few-mode fiber for facilitating mode division multiplexing. The technique is adapted to predict the accurate profile parameters for the proposed few-mode fiber to obtain the maximum number of modes. It is for a three-ring-core few-mode fiber for guiding five, ten, fifteen, and twenty modes. Three types of regression models namely ordinary least-square linear multi-output regression, k-nearest neighbors of multi-output regression, and ID3 algorithm-based decision trees for multi-output regression are used for predicting the multiple profile parameters. It is observed that the ID3-based decision tree for multioutput regression is the robust, highly-accurate machine learning model for fast modeling of FMFs. The proposed fiber claims to be an efficient candidate for the next-generation 5G and 6G backhaul networks using mode division multiplexing.

Evaluation of a high-speed hybrid OAM-OFDM-MDM multiplexed coherent FSO system under desert conditions

To meet the needs of future wireless optical networks, this paper introduces a high-speed, hybrid multiplexed, coherent free-space optical (FSO) communication system that integrates an orbital angular momentum (OAM) multiplexed signal with an orthogonal frequency division multiplexing (OFDM) technique. Two independent QAM polarized beams, each carrying in-phase and quadrature (I/Q) phase 16-QAM-OFDM modulated data, are combined using mode division multiplexing (MDM) to increase the capacity of the proposed system. The reason of choosing OFDM is its capability to support higher data rate, and mitigating intersymbol interference (ISI). The signal is detected using a coherent detection-based digital signal processing (DSP) algorithm at the receiver end. The proposed hybrid FSO system is evaluated in low and heavy dust environments using bit error rate (BER), link distance, optical signal-to-noise ratio (OSNR), and received optical power performance matrices. The simulation results demonstrate the successful transmission of a 120 Gb/s single carrier over the longest link ranges of 1.5 and 0.40 km, respectively, under low and heavy dust weather environments below the signal degradation threshold value (forward error correction (FEC) limit) of BER 2.2 × 10–3 in strong turbulent conditions.

Three-channel Integrated Device for Graphene Electro-optic Modulation and Mode Division Multiplexing

Three-channel Integrated Device for Graphene Electro-optic Modulation and Mode Division Multiplexing

A novel multi-granularity flexible-grid switching optical-node architecture

A novel multi-granularity flexible-grid switching optical-node architecture is proposed in this paper. In our system, the photonic lanterns are used as mode division multiplexing/demultiplexing (MD-Mux/MD-Demux) for selecting mode. The wavelength division multiplexer/demultiplexer (WD-Mux/WD-Demux) and the fiber bragg gratings (FBGs) are used to select wavelength channels with the various grid. The experimental results show that the transmission bandwidth covers the C+L band, the average transmission loss is −13.4 dB, and the average crosstalk is −30.5 dB. The optical-node architecture is suit for mode division multiplexing (MDM) optical communication system.

Multi-stream receive-spatial modulation based cell-free MIMO downlink transmission method

Multi-stream receive-spatial modulation (MSR-SM) technology is applied to the cell-free multiple-input multiple-output (MIMO) downlink transmission, where both users and access points (APs) are multi-antenna, providing a new idea for green and energy-saving wireless communication. The power control coefficients of each AP are obtained using the sequential convex approximation (SCA) algorithm to optimize energy efficiency (EE) under the constraints of the highest transmitting power of the AP and the lowest signal interference-to-noise ratio of the user. This paper proposes an access point selection scheme based on a water-filling algorithm to reduce the number of unnecessary service APs and the total power consumption of the system. The simulation results show that the proposed power allocation algorithm outperforms the max-min power control algorithm in terms of energy efficiency. The MSR-SM-based downlink transmission mode is more energy efficient than the traditional space division multiplexing MIMO digital modulation mode. Furthermore, the SCA algorithm based on AP selection can improve energy efficiency performance compared with the power control algorithm without AP selection.

High Speed MIMO-free Transmission Experiment of Mode Division Multiplexing System with Photonic Lanterns

High Speed MIMO-free Transmission Experiment of Mode Division Multiplexing System with Photonic Lanterns

MIMO Pre‑Equalization Based Mode Crosstalk Mitigation Method in Mode Division Multiplexing Passive Optical Network

MIMO Pre‑Equalization Based Mode Crosstalk Mitigation Method in Mode Division Multiplexing Passive Optical Network

Low Power Consuming Mode Switch Based on Hybrid-Core Vertical Directional Couplers with Graphene Electrode-Embedded Polymer Waveguides

We propose a mode switch based on hybrid-core vertical directional couplers with an embedded graphene electrode to realize the switching function with low power consumption. We designed the device with Norland Optical Adhesive (NOA) material as the guide wave cores and epoxy polymer material as cladding to achieve a thermo-optic switching for the E11, E21 and E12 modes, where monolayer graphene served as electrode heaters. The device, with a length of 21 mm, had extinction ratios (ERs) of 20.5 dB, 10.4 dB and 15.7 dB for the E21, E12 and E11 modes, respectively, over the C-band. The power consumptions of three electric heaters were reduced to only 3.19 mW, 3.09 mW and 2.97 mW, respectively, and the response times were less than 495 µs, 486 µs and 498 µs. Additionally, we applied such a device into a mode division multiplexing (MDM) transmission system to achieve an application of gain equalization of few-mode amplification among guided modes. The differential modal gain (DMG) could be optimized from 5.39 dB to 0.92 dB over the C-band, together with the characteristic of polarization insensitivity. The proposed mode switch can be further developed to switch or manipulate the attenuation of the arbitrary guided mode arising in the few-mode waveguide.

Integrated Communication and Measurement System with BOC-Assisted OFDM

For unmanned aerial vehicles (UAVs), high-precision measurement and high-speed communication are necessary to realize flight and operational missions. In this paper, we propose an integrated communication and measurement system in a Doppler frequency offset environment. The system combines orthogonal frequency division multiplexing (OFDM) modulation with binary offset carrier (BOC) modulation to formulate an OFDM+BOC composite signal through power control. High-precision measurement is achieved through BOC modulation, and high data transmission is achieved through OFDM modulation. Furthermore, the high-precision Doppler frequency offset tracked by the BOC signal is adopted to assist in the demodulation of the OFDM signal. This substantially decreases the impact of the Doppler frequency offset on the OFDM signal. Moreover, the ranging error is within 10−2, and the maximum Doppler frequency error is within 2 Hz.

Performance and complexity study of a neural network post-equalizer in a 638-nm laser transmission system through over 100-m plastic optical fiber

In recent years, plastic optical fiber (POF) has been considered as a promising cost-effective scheme for short-distance data communications, multimedia communication in cars, and in-house networks. However, due to the intrinsic nature of the relatively large numerical aperture of POF and the high attenuation rate, implementing high data rates over 100-m POF transmission length will be a significant challenge. We propose a scheme of high-speed 100-m POF transmission system based on a visible red laser and a cascaded neural network (NN) post-equalizer. To mitigate the nonlinear distortion induced by the POF, three different NNs, i.e., convolutional NN (CNN), long and short-term memory NN (LSTM), and cascaded NN structure consisting of convolutional layers and LSTM (CNN-LSTM), are employed as the post-equalizer. Experimental results show that using three different post-equalizers can significantly improve the system performance compared with the Volterra equalizer baseline. Among them, CNN-LSTM can outperform the others in terms of the bit error rate (BER) and the system Q-factor in the low nonlinear region. When the system operating in strong nonlinear region, CNN can achieve optimal performance at a lower system overhead of complexity. Finally, we successfully demonstrated a 100-m POF transmission system using 16 quadrature amplitude modulation discrete Fourier transform-spread orthogonal frequency division multiplexing modulation format at 1.8 Gbps with BER below 3.8 × 10 − 3 by utilizing CNN-LSTM.

Performance investigation of 2 × 20 Gb/s MDM-RoFSO link incorporating spiral-phased Hermite–Gaussian modes under strong weather conditions

This research paper presents a novel high bit rate and spectral efficient 20 Gb/s mode division multiplexed (MDM) radio over free space optical communication (MDM-RoFSO) system. 10 Gb/s MZM/QAM-16-modulated data streams, each from two distinct channels, are transported over two spiral-phased Hermite–Gaussian (HG) laser modes, HG00 and HG01, respectively. These two HG channels are multiplexed using MDM at a 10 GHz RF signal, amplified and transmitted over the atmospheric link at an optical wavelength of 1550 nm. The proposed MDM-RoFSO system is simulated for MZM modulation over two distinct HG modes in clear sky, dense haze, dense fog, and strong rain weather conditions. The performance of the system is evaluated using performance metrics such as BER, eye diagram, Q factor, and link transmission range. The simulation results show that the HG00 mode is more robust and the extended transmission range is achieved from (7 to 24.4) km for (24.4 to 2.98) Q factor for clear sky to strong rain conditions. This transmission range is further extended by the factor of (2.9 to 1.7) km when the QAM-16 modulation is incorporated in composite (HG00 + HG01) mode and then transmitted in similar weather conditions for the acceptable BER of < 10–5. Finally, the simulation results confirm that the QAM-16 modulated composite HG mode is able to mitigate the atmospheric weather conditions and travel a longer transmission distance compared to individual HG mode transmission.

Integrated device for electro-optic modulation and wavelength-mode division hybrid multiplexing based on graphene and photonic crystal

An integrated device for graphene electro-optic (EO) modulation and wavelength-mode division hybrid multiplexing (WMDM) is proposed. The device is composed of three parts: EO modulator, wavelength division multiplexer (WDM), and mode division multiplexer (MDM). The EO modulator and WDM consist of a one-dimensional photonic crystal nanobeam cavity coupled with a nanowire waveguide. The modulation of a certain wavelength can be achieved by utilizing the characteristic that the chemical potential of graphene can be adjusted with voltage. The MDM adopts nanowire waveguides to realize mode conversion. The performance parameters of the integrated device are analyzed using the three-dimensional finite-difference time-domain method of numerical analysis. The results show that the integrated device can simultaneously complete the modulation and WMDM of the fundamental transverse electric (TE0) modes and first-order TE (TE1) modes at 1570.0 and 1573.2 nm, respectively. The extinction ratio is greater than 23.2 dB, the insertion loss is <0.36 dB, and the channel crosstalk is < − 22.7 dB. In addition, the modulation speed reaches 18 GHz.

Improving MDM–WDM optical network performance via optimized power allocation using Gaussian noise model

The few-mode fiber nonlinearity has been well modeled by an additive Gaussian Noise (GN) source. The available GN models in Mode Division Multiplexing–Wavelength Division Multiplexing (MDM–WDM) systems are incoherent and neglect the dispersion slope. The incoherent GN model assumes that the Nonlinear Interference (NLI) noise created at each span is summed up in power incoherently at the receiver and leads to underestimating the NLI noise power. In the first part of this paper, a coherent GN model is derived by taking into account the dispersion slope and verified through Split-Step Fourier Method (SSFM) simulations. In the second part of this paper, the total capacity maximization, as well as the minimum Signal to Noise Ratio (SNR) margin maximization problems are presented and solved based on the obtained GN model. MDM–WDM multi-node nonlinear network under different scenarios including Equal/Non-Equal Required SNR (ERS/NERS), and Flat/Non-Flat Amplifier Gain (FG/NFG) are considered in the numerical simulations. Considering 200 different sets of randomized traffic demands (random channel-mode distributions) the cumulative distribution function of minimum SNR margin improvement in optimized power allocation compared with the best flat power allocation is in 99% more than 1 dB, 1.2 dB, 2.4 dB, and 2.8 dB, for ERS-FG, ERS-NFG, NERS-FG, and NERS-NFG scenarios, respectively.

The channel WDM system incorporates of Optical Wireless Communication (OWC) hybrid MDM-PDM for higher capacity (LEO-GEO) inter satellite link

The rising demand for exponential growth in data rate and effectiveness of satellite communication systems has drawn the attention of several researchers recently. The Inter Satellite OWC (Is-OWC) technology, which combines Optical Wireless Communication (OWC) and Inter Satellite Link (ISL), is critical for achieving high data rate transport around the world. The challenge in ISL's transmission range is limited for a variety of reasons, including the appropriate modulation format, pointing error, and space turbulence. As a result, this paper designs and implements a high-capacity 8-channel Wavelength Division Multiplexing (WDM) system that uses the Orthogonal Frequency Division Multiplexing (OFDM) technique to support high data rates by implementing multiple low-data rate subcarriers and achieves high tolerance to dispersion and Inter Symbol Interference (ISI). Additionally, by using a hybrid scheme for Mode Division Multiplexing (MDM) and Polarization Division Multiplexing (PDM) for cost-effectiveness requirements and transmit eight independent channels over a 48,000 km Is-OWC link. Each channel is capable of carrying 320 Gbps of data rate, and by using the novel hybrid MDM-PDM scheme, the data rate for each channel is raised to 640 Gbps. The simulation analysis achieved a maximum data rate of 5.12 Tbps using the 8-channel Is-OWC WDM OFDM. The maximum distance achieved was 48,000 km at a log BER of − 3.1101 and the average received power of − 70.14 dBm. The proposed system shall prop the transfer of high data rates and meet the requirements for reliable satellite connectivity links.

Probabilistic neural network equalizer for nonlinear mitigation in OAM mode division multiplexed optical fiber communication.

Orbital angular momentum (OAM) mode-division multiplexing (MDM) is a key technique to achieve ultra-high-capacity optical fiber communications. However, the high nonlinear impairment from optoelectronic devices, such as spatial light modulators, modulators, and photodiodes, is a long-standing challenge for OAM-MDM. In this paper, an equalizer based on a probabilistic neural network (PNN) is presented to mitigate the nonlinear impairment for an OAM-MDM fiber communication system with 32 GBaud Nyquist pulse amplitude modulation-8 (PAM8) intensity-modulation direct-detection (IM-DD) signals. PNN equalizer can calculate the distribution of the nonlinearity using Bayesian decision theory and thus mitigate the stochastic nonlinear impairment of the received signal. Experimental results show that compared with the convolutional neural network (CNN) equalizer, the PNN equalizer improves the receiver sensitivity by 0.6dB and 2dB for two OAM modes with l = + 3 and l = + 4 at the 20% FEC limit, respectively. Moreover, compared with Volterra or CNN equalizers, the PNN equalizer can reduce the computation complexity significantly, which has great potential to mitigate the nonlinear signal distortions in high-speed IM-DD OAM-MDM fiber communication systems.

Enhanced Atmospheric Turbulence Resiliency With Successive Interference Cancellation DSP in Mode Division Multiplexing Free-Space Optical Links

We experimentally demonstrate the enhanced atmospheric turbulence resiliency in a 137.8 Gbit/s/mode mode-division multiplexing free-space optical communication link through the application of a successive interference cancellation digital signal processing algorithm. The turbulence resiliency is further enhanced through redundant receive channels in the mode-division multiplexing link. The proof of concept demonstration is performed using commercially available mode-selective photonic lanterns, a commercial transponder, and a spatial light modulator based turbulence emulator. In this link, 5 spatial modes with each mode carrying 34.46 GBaud dual-polarization quadrature phase shift keying signals are successfully transmitted with an average bit error rate lower than the hard-decision forward error correction limit. As a result, we achieved a record-high mode- and polarization-division multiplexing channel number of 10, a record-high line rate of 689.23 Gbit/s, and a record-high net spectral efficiency of 13.9 b/s/Hz in emulated turbulent links in a mode-division multiplexing free-space optical system.

A reach enhanced hybrid OCDMA-MDM multiplexing based IsOWC system incorporating EDFA, SOA, and RFA

Abstract Reach enhancement in inter-satellite optical wireless communication systems (IsOWC) is an utmost requirement due to ever-increasing internet usage all over the globe. Optical code division multiplexing is prominently incorporated for security enhancement in IsOWC systems, however, limited in terms of total reach. Therefore, in this work, a 120 Gbps capacity-based hybrid OCDMA and mode division multiplexed (MDM) IsOWC is presented using different optical amplifiers such as semiconductor optical amplifier (SOA), erbium-doped fiber amplifier (EDFA), and Raman fiber amplifier (RFA). Moreover, the combined effects of Laguerre–Gaussian (LG) with EDFA/SOA/RFA and Hermite–Gaussian (HG) modes with EDFA/SOA/RFA amplifiers are investigated. Results revealed that the proposed system can cover 5000 km IsOWC link within acceptable BER limits and EDFA with LG modes is found to be the best technique.