Space Division Multiplexing Research Articles

Towards More Energy Efficient VLC Networks: A Study on Space Division Multiplexing and Smart Lighting

Towards More Energy Efficient VLC Networks: A Study on Space Division Multiplexing and Smart Lighting

Spatial-photonic Ising machine by space-division multiplexing with physically tunable coefficients of a multi-component model.

This paper proposes a space-division multiplexed spatial-photonic Ising machine (SDM-SPIM) that physically calculates the weighted sum of the Ising Hamiltonians for individual components in a multi-component model. Space-division multiplexing enables tuning a set of weight coefficients as an optical parameter and obtaining the desired Ising Hamiltonian at a time. We solved knapsack problems to verify the system's validity, demonstrating that optical parameters impact the search property. We also investigated a new dynamic coefficient search algorithm to enhance search performance. The SDM-SPIM would physically calculate the Hamiltonian and a part of the optimization with an electronics process.

Demonstration of an 800G CDM-SDM coherent PON utilizing weakly coupled multicore fibers with CDM tributary manipulation

In this Letter, we present an experimental demonstration of downstream signaling in a 16 × 50 Gbit/s coherent passive optical network (CPON) using the code and space division multiplexing (CDM-SDM) approach. We realize optical SDM through the utilization of a 4-core weakly coupled multicore fiber (WC-MCF), enhancing the total available optical launch power at the optical line terminal (OLT). This enhancement significantly improves the power budget for CPONs that connect with a large number of optical network units (ONUs). At the second stage of the CPON, four CDM-assigned ONUs are connected to individual cores of the WC-MCF, thereby supporting the connectivity of up to 16 ONUs. Through experiments, we have noted substantial disparities in the downstream signaling performance among individual CDM-assigned ONUs, particularly as the capacity is increased to 800 Gbit/s. To address this issue, we have employed an innovative approach by leveraging space–time coding techniques to manipulate the CDM tributaries, to achieve a balanced reception performance for all ONUs within the CPON. We believe that the proposed CDM-SDM CPON scheme, complemented by the advanced DSP flow chart, holds significant promise for future PON systems characterized by substantial capacity and extensive connectivity.

Fragmentation-Aware with core classification algorithms for spectrum allocation in Elastic Optical Networks-Space Division Multiplexing (SDM-EON)

The new technology to improve the capacity of transmission in optical networks is Elastic Optical Networking with Space Division Multiplexing (SDM-EON). However, fragmentation is one of the critical issues in EON that is created by dynamically establishing and releasing lightpaths over the time, thus increasing connection blocking probability. In this research, two new algorithms are proposed in SDM-EON to improve the fragmentation problem and improve blocking probability, called Priority Select Frequency (P-S-F) and Priority Select Core (P-S-CO). We assume that connection demands have three priorities as high-priority, mid-priority, and low-priority. Here, the requested bandwidth of a connection demand is divided into smaller sizes to be setup in multiple cores. By providing this opportunity in spectrum allocation and assignment, connection blocking probability is reduced as our performance evaluation results prove. For instance, P-S-CO and P-S-F reduce bandwidth blocking probability, respectively, at least by 6.8% and 4.5% compared to existing methods. In the best case, P-S-CO and P-S-F can improve bandwidth blocking probability, respectively, by 25% and 17.8% compared to existing methods.

Dense Space-Division Multiplexing Exploiting Multi-Ring Perfect Vortex

Vortex beams carrying orbital angular momentum (OAM) have gained much interest in optical communications because they can be used to expand the number of multiplexing channels and greatly improve the transmission capacity. However, the number of states used for OAM-based communication is generally limited by the imperfect OAM generation, transmission, and demultiplexing methods. In this work, we proposed a dense space-division multiplexing (DSDM) scheme to further increase the transmission capacity and transmission capacity density of free space optical communications with a small range of OAM modes exploiting a multi-ring perfect vortex (MRPV). The proposed MRPV is generated using a pixel checkerboard complex amplitude modulation method that simultaneously encodes amplitude and phase information in a phase-only hologram. The four rings of the MRPV are mutually independent channels that transmit OAM beams under the condition of occupying only one spatial position, and the OAM mode transmitted in these spatial channels can be efficiently demodulated using a multilayer annular aperture. The effect of atmospheric turbulence on the MRPV was also analyzed, and the results showed that the four channels of the MRPV can be effectively separated under weak turbulence conditions. Under the condition of limited available space and OAM states, the proposed DSDM strategy exploiting MRPV might inspire wide optical communication applications exploiting the space dimension of light beams.

Low complexity MIMO equalization for long-haul SDM systems

Space-division multiplexing (SDM) has been expected to support the continuous growth of transmission capacity. However, it suffers from high computation complexity that limits its physical implementations. In this paper, we propose and experimentally demonstrate a low-complexity MIMO equalization method to leverage the sparsity of weights and reduce the complexity by L1&L2-regularization in long-haul space-division multiplexing (SDM) systems. The L1-regularization finds the sparse solution of equalizer filters and substitutes it for optimal solution, reducing the complexity with performance degradation. On the other hand, the L2-regularization tends to produce a smoother estimation than L1 regularization and is therefore more robust to large variance. We conduct a 39.87-GBaud QPSK coherent optical transmission experiment based on a 4-core coupled-core fiber with the transmission distance from 1206-km to 7236-km. Comparisons on the equalization performance and computational complexity show that the sparse equalizer using L1&L2-regularization achieves a 30% reduction in complexity at the similar system performance, compared with the traditional time-domain MIMO.

Absolute phase retrieval based on fringe amplitude encoding without any additional auxiliary pattern

An absolute phase retrieval method based on fringe amplitude encoding is proposed. Different from the conventional intensity coding methods which are based on time division multiplexing with multiple additional auxiliary patterns, the proposed fringe order encoding strategy is codeword overlapping interaction based on space division multiplexing. It just directly encodes different fringe amplitudes for different periods in corresponding sinusoidal phase-shifting patterns to generate space division multiplexing composite sinusoidal phase-shifting patterns and quantifies the fringe amplitudes into four levels as encoding strategy, so it can retrieve absolute phase without any additional auxiliary patterns. To improve the anti-interference capability of the proposed method, a codeword extraction method based on image morphological processing is proposed to segment the grayscale. Consequently, both the phase-shifting sinusoidal deformed patterns and the single frame space division multiplexing four gray-level codewords for fringe order recognition can be extracted respectively from the captured composite deformed patterns. Then, a half-period single-connected domain correction method is also proposed to correct the codewords. Moreover, in order to suppress the effect of jump errors, the phase zero points are constructed to segment the positive and negative ranges of the phase, making the phase unwrapping process segmented. The experimental results demonstrate the feasibility and effectivity of the proposed method.

Distributed multi-parameter sensor based on Brillouin scattering in an etched few-mode multi-core fiber

We theoretically propose a unique distributed multi-parameter sensor based on an etched few-mode multi-core fiber (FM-MCF) for simultaneous sensing of temperature, strain, and sample refractive index (SRI). These three parameters can be sensed simultaneously by combining space division multiplexing (SDM) and stimulated Brillouin scattering (SBS). FM-MCF naturally contains an inner core and an outer core, and it is etched until the outer core is exposed. Therefore, the inner core can be employed to calculate the Brillouin gain spectrum (BGS) of LP01 and LP11 through distributed temperature and strain, and the outer core can be used to sense SRI through the BGS of LP01. Note that due to the high corrosion of the outer core, the higher order mode is cut off, so only the LP01 mode can be observed in the outer core. By demodulating the Brillouin frequency shift (BFS) of the BGS in the outer core and the inner core, the proposed sensor has a maximum temperature sensitivity of 1.7220 MHz/°C, a maximum strain sensitivity of 0.0783 MHz/με, and an SRI sensitivity of 274.3245 MHz/RIU around 1.440 RI unit (RIU). Therefore, we show a new perspective for discriminative sensing of multi-parameter in Brillouin distributed sensors based on SDM. The developed multifunctional fiber sensor could find application in the field of environmental sensing, materials science, biomedical applications, and structural health monitoring.

Compensating Chromatic Dispersion and Phase Noise using Parallel AFB-MBPS For FBMC-OQAM Optical Communication System

Filter Bank Multi-Carrier Offset-QAM (FBMC-OQAM) is one of the hottest topics in research for 5G multi-carrier methods because of its high efficiency in the spectrum, minimal leakage in the side lobes, zero cyclic prefix (CP), and multiphase filter design. Large-scale subcarrier configurations in optical fiber networks need the use of FBMC-OQAM. Chromatic dispersion is critical in optical fiber transmission because it causes different spectral waves (color beams) to travel at different rates. Laser phase noise, which arises when the phase of the laser output drifts with time, is a major barrier that lowers throughput in fiber-optic communication systems. This deterioration may be closely related among channels that share lasers in multichannel fiber-optic systems using methods like wavelength-division multiplexing with frequency combs or space-division multiplexing. In this research, we use parallel Analysis Filter Bank (AFB) equalizers in the receiver part of the FBMC OQAM Optical Communication system to compensate for chromatic dispersion (CD) and phase noise (PN). Following the equalization of CD compensation, the phase of the carriers in the received signal is tracked and compensated using Modified Blind Phase Search (MBPS). The CD and PN compensation techniques are simulated and analyzed numerically and graphically to determine their efficacy. To evaluate the FBMC's efficiency across various equalizers, 16-OQAM is taken into account. Bit Error Rate (BER), Optical Signal-to-Noise Ratio (OSNR), Q-Factor, and Mean Square Error (MSE) were the primary metrics we utilized to evaluate performance. Single-tap equalizer, multi-tap equalizer (N=3), ISDF equalizer with suggested Parallel Analysis Filter Banks (AFBs) (K=3), and MBPS were all set aside for comparison. When compared to other forms of Nonlinear compensation (NLC), the CD and PN tolerance attained by Parallel AFB equalization with MBPS is the greatest.

Multiplexing of Holograms Based on Spatial Separation

The analysis of multiplexing methods using spatial separation has been carried out. It is shown that space division multiplexing is possible when there is no Bragg sampling action. The action of the Bragg sampling, its features for the cases of thin-layer flat holograms and in a sufficiently thick medium of volume holograms are considered separately. Among the methods of multiplexing using spatial selection, the methods of fractal type multiplexing and rotational multiplexing are considered. Fractal-type multiplexing allows, when used simultaneously with angular-type multiplexing, up to 6000 holograms to be recorded in one area, while the total volume of the storage medium remains the same. Rotational multiplexing is a special case of fractal type multiplexing. This type of multiplexing is especially effective for storing holograms in rather thin-layer media. Similar to fractal-type multiplexing, in this type of multiplexing, more than one hologram is simultaneously reconstructed by the required reference wave. However, only the result of the reconstruction of one hologram turns out to be unbiased and is fixed by the CCD matrix. The difference between this method and fractal-type multiplexing is that the offset in rotational multiplexing is the result of rotation of the storage medium.

Ultra-Reliable Deep-Reinforcement-Learning-Based Intelligent Downlink Scheduling for 5G New Radio-Vehicle to Infrastructure Scenarios.

Higher standards for reliability and efficiency apply to the connection between vehicle terminals and infrastructure by the fifth-generation mobile communication technology (5G). A vehicle-to-infrastructure system uses a communication system called NR-V2I (New Radio-Vehicle to Infrastructure), which uses Link Adaptation (LA) technology to communicate in constantly changing V2I to increase the efficacy and reliability of V2I information transmission. This paper proposes a Double Deep Q-learning (DDQL) LA scheduling algorithm for optimizing the modulation and coding scheme (MCS) of autonomous driving vehicles in V2I communication. The problem with the Doppler shift and complex fast time-varying channels reducing the reliability of information transmission in V2I scenarios is that they make it less likely that the information will be transmitted accurately. Schedules for autonomous vehicles using Space Division Multiplexing (SDM) and MCS are used in V2I communications. To address the issue of Deep Q-learning (DQL) overestimation in the Q-Network learning process, the approach integrates Deep Neural Network (DNN) and Double Q-Network (DDQN). The findings of this study demonstrate that the suggested algorithm can adapt to complex channel environments with varying vehicle speeds in V2I scenarios and by choosing the best scheduling scheme for V2I road information transmission using a combination of MCS. SDM not only increases the accuracy of the transmission of road safety information but also helps to foster cooperation and communication between vehicle terminals to realize cooperative driving.

Migration of elastic optical networks to the C + L-bands subject to a partial upgrade of the number of erbium-doped fiber amplifiers

Space division multiplexing (SDM) and band division multiplexing (BDM) are considered promising technologies to increase the capacity of optical transport networks. The progressive shortage of available dark fibers and the immaturity of multicore and multimode fibers for multichannel transmission induce network operators to postpone the process of capacity enhancement through SDM. Therefore, capacity increase revolves around BDM by lighting up at least the L-band of the already installed optical fiber infrastructure, which is a practical solution in the short to middle term. However, L-band activation requires the upgrade of network components such as erbium-doped fiber amplifiers (EDFAs). To manage the imposed cost while leveraging the L-band, a network can be partially rather than fully migrated in a single step by upgrading just a subset of the fibers and thus a subset of EDFAs to operate in the C+L-bands. In this paper, the focus is set on determining which fibers in the network should be upgraded to exploit the L-band, subject to a constraint on the maximum number of EDFAs to be upgraded, and analyzing its impact on network performance when facing dynamic traffic in terms of the blocking ratio. To this end, three heuristic algorithms, each pursuing a different objective, and two of them based on an integer linear programming (ILP) formulation, are proposed for the network planning to identify which fibers to upgrade. Simulation results demonstrate that, thanks to the use of these heuristics, the upgrade of a partial set of links to the C+L line system is a viable solution for network operators to circumvent the huge cost associated with migrating the full network. For instance, we demonstrate that a strategic partial upgrade using the proposed methods, subject to upgrading a maximum of 60% of the EDFAs, can significantly boost the supported traffic load in the examined topologies, ranging from 175% to 322%, when compared to the non-upgraded network.

Synthesizing the crosstalk between OAM modes of vortex beam by simultaneously propagating a probe vortex beam in free space

To overcome the upcoming famine of channel capacity driven by explosive increases of new applications, optical orbital angular momentum (OAM) carried by a vortex beam has been considered to be a promising candidate for space-division multiplexing (SDM) in a novel physics domain. However, owing to the inescapable disturbance induced by atmosphere turbulence (AT), the performance of OAM-based free-space optical communication (FSOC) is seriously restrained, which can be ascribed to the crosstalk among different OAM modes induced by the distorted helical phase. For promoting the development of OAM-based FSOC, a synthesizing-crosstalk method is proposed for mitigating the AT by coaxially propagating an OAM-probe beam (OPB), wherein the OAM mode of the extra OPB is identical to the OAM mode of the propagated OAM-data beam (ODB). The corresponding theory analysis of the proposed method demonstrates that the conjugated distortion of the crosstalk can be generated by a hybrid of the OPB and the ODB in a photoelectric receiver/detector (PD/PR). The generated conjugate distortion of the OPB can effectively counteract the crosstalk of ODB induced by the turbulence. To verify the feasibility of the proposed scheme, an experimental setup is built. The measured results demonstrate that the bit error rate (BER) and constellation plot (CP) of the employed two OAM channels can be significantly improved under different atmosphere turbulence (AT) by utilizing the proposed scheme. A continuous 30 min-long-BER-testing results depict that the proposed concept can stably work well. The proposed concept can be also suitable for multiplexing other OAM modes as well as the employed two OAM channels. Besides, with the increase of data speed, the proposed scheme can also effectively mitigate the crosstalk and improving the system performance. Consequently, the proposed concept is valid and feasible both in theory and practice, which can be used for compensating the distorted helical phase and improving the system performance of an OAM-based FSOC in the future.

Channel Estimation and Turbo Equalization for Coded OTFS and OFDM: A Comparison

In this letter, we study joint channel estimation and turbo equalization for coded orthogonal time frequency space (OTFS) and orthogonal frequency division multiplexing (OFDM). To the best of our knowledge, this is the first study that compares performance of OTFS and OFDM coded systems using the state-of-the-art message passing (MP) and soft minimum mean square error (MMSE) equalizers, under imperfect channel estimation. We show that the commonly used threshold-based channel estimator incurs noticeable performance loss for OTFS. Hence, we propose a basis expansion model (BEM) channel estimation technique for OTFS, which improves performance of the threshold-based channel estimator and yields a superior performance to OFDM when using small modulations of BPSK and QPSK. Our work also reveals that OTFS can perform inferior to OFDM as the modulation order increases. This is due to the increased 2D detection complexity of OTFS.

Transmission Technology for Space-division Multiplexing Supporting Next-generation High-speed, Large-capacity Communications beyond Existing Limits

Transmission Technology for Space-division Multiplexing Supporting Next-generation High-speed, Large-capacity Communications beyond Existing Limits

High-speed chaos-based secure optical communications over 130-km multi-core fiber.

Chaotic optical communication is of great significance for secure data transmission. Despite rapid development over the decades, high-speed (>100 Gbps) and long-distance (>100 km) chaotic optical communication in a single fiber is still full of challenges. Here, we propose and experimentally demonstrate high-speed and long-distance chaos-based secure optical communications using mutual injection of semiconductor lasers and space-division multiplexing (SDM) techniques. The encrypted signals are transmitted through all seven core channels of the multi-core fiber (MCF), which effectively expands the aggregate transmission capacity of a single fiber. A pair of source and synchronization devices based on mutual injection of semiconductor lasers are employed to effectively encrypt and decrypt signals. Chaos-based secure optical communications with 70-Gbps on-off keying (OOK) and 140-Gbps quadrature phase-shift keying (QPSK) signals over a 130-km MCF are successfully demonstrated in the experiment with favorable performance. The demonstration may pave the way for future ultrahigh capacity and ultra-long distance chaotic optical communications by fully exploiting multi-dimensional resources of light waves, including the spatial dimension.

OCDM-SDM Optical Communication System Utilizing Four-Dimensional Constellation Mapping

In this paper, an orthogonal chirp division multiplexing (OCDM) Space division multiplexing (SDM) optical communication utilizing four-dimensional constellation mapping is proposed. A new 16-point four-dimensional constellation is designed, and its constellation figure of merit (CFM) can reach 1.17. A direct detection orthogonal chirp division multiplexing (DD-OCDM) transmission scheme based on four-dimensional constellation mapping is designed, and 32.8 Gb/s OCDM signal transmission is performed across 2 km seven core fiber through experiments, which verifies the performance of the proposed constellation. Under the condition of multi-core multiplexing and the bit error rate (BER) of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , the receiver sensitivity of the OCDM signal, which is based on the proposed four-dimensional constellation mapping based on associated constellation mapping (16ACM-4D), has a gain of 0.59 dB, 3.26 dB, and 5.73 dB compared with the OCDM signals based on QPSK, 16QAM, and 16PSK, respectively. The results show that the proposed OCDM short-reach optical communication scheme based on four-dimensional constellation mapping has good bit error performance and anti-interference ability, and has broad application prospects in the future short-reach optical communication.

3.61 Pbit/s S, C, and L-Band Transmission With 19-Core Single-Mode Fiber

We experimentally demonstrate a 3.61 Pbit/s generalized mutual information (GMI) estimated throughput by space division multiplexing (SDM) and wavelength division multiplexing (WDM) combined transmission over 19-core single-mode fiber. Covering 17 THz bandwidth with a 25-GHz grid in S, C, and L band, 680 wavelength channels are used to deliver 24.5 GBaud probabilistically constellation-shaped (PCS) 256 quadrature amplitude modulation (QAM) and PCS-64QAM signals. The measured data rate shows a great potential for S/C/L-band transmission to dramatically enhance the achievable data rate in multi-core fibers.

10.51-Tbit/s multi-channel IF-over-fiber transmission with SDM/WDM/SCM for beyond-5G mobile fronthaul accommodating ultra-high-density antennas

In beyond-5G and 6G mobile communication systems, it is expected that massive numbers of antennas are densely deployed to provide a stable and high-speed communication environment. To efficiently accommodate high-density antennas, high-capacity mobile fronthaul (MFH) is also required. Intermediate-frequency-over-fiber (IFoF) is considered as one of the attractive solutions for realizing high-capacity MFH due to its high spectral efficiency and multi-channel transmission capability. In this paper, we demonstrate the highest-capacity IFoF transmission with combinations of space division multiplexing, wavelength division multiplexing, and subcarrier multiplexing; 4608 channels of 64-quadrature amplitude modulation orthogonal frequency division multiplexing signals with a total net bit rate of 10.51 Tbit/s (4608×380.16MHz/ch×6bit/s/Hz) are successfully transmitted over a 10.1-km uncoupled 12-core multi-core fiber.

Design of silica-PLC LP11 mode rotator based on adiabatic mode conversion.

A silica-based LP11 mode rotator, which is one of the basic and indispensable optical components for space division multiplexing, with multiple tapered trenches is proposed. Compared with the conventional interference-based LP11 mode rotator with a simple L-shape waveguide, the proposed LP11 mode rotator has many advantages in a mode conversion efficiency, an insertion loss, and a fabrication tolerance because the operation principle is based on the adiabatic mode conversion. By using an approach of the shortcut to adiabaticity, the proposed device is effectively miniaturized rather than the standard tapered structures. Among the LP11 mode rotators in the silica-based mode multi/demultiplexers, the proposed type will be a considerably promising candidate.