Spatial Division Multiplexing Research Articles

Scalability analysis of machine learning QoT estimators for a cloud-native SDN controller on a WDM over SDM network

Maintaining a good quality of transmission (QoT) in optical transport networks is key to maintaining the service level agreement between the user and the service provider. QoT prediction techniques have been used to assure the quality of new lightpaths as well as that of the previously provisioned ones. Traditionally, two different approaches have been used: analytical methods, which take into account most physical impairments that are accurate but complex, and high margin formulas, which require much less computational resources at the cost of high margins. With the recent progress of machine learning (ML) together with software defined networking (SDN), ML has been considered as another option that could be both accurate and that does not consume as many resources as analytical methods. SDN architectures are difficult to scale because they are usually centralized; this is even worse with QoT predictors using ML. In this paper, a solution to this issue is presented using a cloud-native architecture, and its scalability is evaluated using three different ML QoT predictors and experimentally validated in a real wavelength-division multiplexing (WDM) over spatial-division multiplexing (SDM) testbed.

Matched Filtering for MIMO Coherent Optical Communications with Mode-Dependent Loss Channels.

The use of digital signal processors (DSP) to equalize coherent optical communication systems based on spatial division multiplexing (SDM) techniques is widespread in current optical receivers. However, most of DSP implementation approaches found in the literature assume a negligible mode-dependent loss (MDL). This paper is focused on the linear multiple-input multiple-output (MIMO) receiver designed to optimize the minimum mean square error (MMSE) for a coherent SDM optical communication system, without previous assumptions on receiver oversampling or analog front-end realizations. The influence of the roll-off factor of a generic pulse-amplitude modulation (PAM) transmitter on system performance is studied as well. As a main result of the proposed approach, the ability of a simple match filter (MF) based MIMO receiver to completely eliminate inter-symbol interference (ISI) and crosstalk for SDM systems under the assumption of negligible MDL is demonstrated. The performance of the linear MIMO fractionally-spaced equalizer (FSE) receiver for an SDM system with a MDL-impaired channel is then evaluated by numerical simulations using novel system performance indicators, in the form of signal to noise and distortion ratio (SNDR) loss, with respect to the case without MDL. System performance improvements by increasing the transmitter roll-off factor are also quantified.

Improved Performance Analysis of FSO Communication Link under the effect of Moderate Haze Phenomena and Heavy Haze Phenomena in SDM based on EDFA Pre-amplifier

Free Space Optics is of high bandwidth medium, having extreme rate of data. The need for enormous capacity of data speed has exponentially risen up because of the immense internet services widely reached. Thus, by means of the increasing rate of transmission and necessity in the area communication that is optical has turned into costing too much. The primary limitation of the system FSO is environment phenomena which probably indicate to maximum bit error rate (BER) of the system and makes the communication link impractical. However, the environment phenomena such as (moderate haze phenomena and heavy haze phenomena) cause attenuation thus will decrease the distance of communication system. In this paper, different combinations have been apply to improves the strength of weak signal in the free space optics (FSO) communication link under the effect of environment phenomena in spatial division multiplexing (SDM) based on erbium-doped fiber amplifiers (EDFA) Pre-amplifier.

3 × 40 Gbit/s All-Optical Logic Operation Based on Low-Loss Triple-Mode Silicon Waveguide.

Information capacity of single-mode fiber communication systems face fundamental limitations imposed by optical nonlinearities. Spatial division multiplexing (SDM) offers a new dimension for upgrading fiber communication systems. Many enabling integrated devices, such as mode multiplexers and multimode bending with low crosstalk, have been developed. On the other hand, all-optical signal processing (AOSP) can avoid optical to electrical to optical (O–E–O) conversion, which may potentially allow for a low cost and green operation for large-scale signal processing applications. In this paper, we show that the system performance of AOSP can be pushed further by benefiting from the existing technologies developed in spatial mode multiplexing (SDM). By identifying key technologies to balance the impacts from mode-dependent loss, crosstalk and nonlinearities, three-channel 40 Gbit/s optical logic operations are demonstrated using the first three spatial modes in a single multimode waveguide. The fabricated device has a broadband four-wave mixing operation bandwidth (>20 nm) as well as high conversion efficiency (>−20 dB) for all spatial modes, showing the potential for a large-scale signal processing capacity with the combination of wavelength division multiplexing (WDM) and SDM in the future.

Improving Interference Cancellation in Spatial Division Multiplexing Using a Combination of the Channel Coding and QR-Successive Interference Cancellation

This paper introduces QR-SIC detector to minimize the probability of error comparing to SDM system. Spatial-division-multiplexing (SDM) system is a multiple-inputs-multiple-outputs (MIMO) system used to increase data transmission rate in modern communication systems. The major disadvantage of SDM system is the interference between the received symbols. In this paper, a new trans-receiver architecture for SDM system is introduced. This receiver uses a Successive-Interference-Cancellation (SIC) detector based on QR-decomposition of the channel matrix and a Forward-Error- Correction (FEC) channel code. The proposed architecture merges the interference cancellation process in QR-SIC detector and the forward error correction process in the channel decoder. The feedback symbols in the QR-SIC detector are the output symbols from the channel decoder after they are re-encoded and re-modulated and more robust. The new architecture minimizes the probability of error in the demodulated symbols more than the conventional SDM receiver. If the conventional SDM receiver needs 100 MWATT transmitted power the proposed system needs only 64 MWATT transmitted power. So The new architecture of the SDM receiver can save up to 36% of the transmitted signal power used with the conventional SDM receiver. At BER of 10-4, the convolution codes of code rates 3/4, 1/2, and 1/4 achieve coding gains of 15 dB, 24 dB, and 30 dB with respect to the uncoded 4-antennas SDM receiver. the proposed SDM receiver at BER of 10-4 is 2dB, 1.5 dB, and 0.9 dB better than the BER performance of the conventional coded SDM receiver at the same code rates and the same number of antenna. The enhancement in the BER performance of the proposed SDM receiver increases as the code gain of the used code. This increase in the power efficiency and bandwidth comes at the expense of an increase in the receiver complexity and latency

Anycast Transmission in Routing Modulation Level Spectrum Assignment (RMLSA) Problem on Space Division Multiplexing (SDM) Elastic Optical Networks (EON)

With the rise of cloud computing in recent years, a large number of streaming media has yielded an exponential growth in network traffic. With the now present 5G and future 6G, the development of the Internet of Things (IoT), social networks, video on demand, and mobile multimedia platforms, the backbone network is bound to bear more traffic. The transmission capacity of Single Core Fiber (SCFs) may be limited in the future and Spatial Division Multiplexing (SDM) leveraging multi-core fibers promises to be one of the solutions for the future. Currently, Elastic optical networks (EONs) with multi-core fibers (MCFs) are a kind of SDM-enabled EONs (SDM-EON) used to enhance the capacity of transmission. The resource assignment in MCFs, however, will be subject to Inter-Core Crosstalk (IC-XT), hence, reducing the effectiveness of transmission. This research highlights the routing, modulation level, and spectrum assignment (RMLSA) problems with anycast traffic mode in SDM-EON. A multipath routing scheme is used to reduce the blocking rate of anycast traffic in SDM-EON with the limit of inter-core crosstalk. Hence, an integer linear programming (ILP) problem is formulated and a heuristic algorithm is proposed. Two core-assignment strategies: First-Fit (FF) and Random-Fit (RF) are used and their performance is evaluated through simulations. The simulation results show that the multipath routing method is better than the single-path routing method in terms of blocking ratio and spectrum utilization ratio. Moreover, the FF is better than the RF in low traffic load in terms of blocking ratio (BR), and the opposite in high traffic load. The FF is better than the RF in terms of a spectrum utilization ratio. In an anycast protection problem, the proposed algorithm has a lower BR than previous works.

Evaluation of Optical Transport Unit Line-Card Integration in Spatially and Spectrally Flexible Optical Networks in Terms of Device Cost and Network Performance

The explosive growth of internet traffic has accelerated the evolution of optical transport networks, emphasizing the need to expand transmission capacity. To overcome the limitations of conventional single-core/mode fiber-based optical transmission, spatial-division multiplexing (SDM) has been proposed. Spatial and spectral superchannel (Spa <inline-formula><tex-math notation="LaTeX">$\&amp;$</tex-math></inline-formula> Spe SpCh) technology in SDM-based optical networks realizes high-capacity transmission. Such an optical transmission technology can be supported by the Spa <inline-formula><tex-math notation="LaTeX">$\&amp;$</tex-math></inline-formula> Spe SpCh transceiver and the reconfigurable optical add/drop multiplexer (ROADM), allocating optical carriers (OCs) in spatial and spectral domains simultaneously. The architectures of the manufactured transceivers and ROADMs installed in advance at each network node are fixed. This necessitates the determination of the appropriate spatial and spectral granularity combination that affects the transceiver and ROADM designs to efficiently utilize the switching capacity and reduce the implementation costs. In this paper, we focus on the performance analysis for the <inline-formula><tex-math notation="LaTeX">$N$</tex-math></inline-formula>-core MCF-based network deployment issues under different granularity combinations. Detailed evaluation of a 4-core MCF-based network reveals that the device cost and network performance are influenced by spatial and spectral granularities and can provide guidance for real-world network planning and design. In particular, the trade-off between device cost and network performance based on different granularities should be taken into account in network design.

Multicore fibers with 10 and 16 single-mode cores for the visible spectrum.

We report multicore fibers (MCFs) with 10 and 16 linearly distributed cores with single-mode operation in the visible spectrum. The average propagation loss of the cores is 0.06 dB/m at λ = 445 nm and < 0.03 dB/m at wavelengths longer than 488 nm. The low inter-core crosstalk and nearly identical performance of the cores make these MCFs suitable for spatial division multiplexing in the visible spectrum. As a proof-of-concept application, one of the MCFs was coupled to an implantable neural probe to spatially address light-emitting gratings on the probe.

Joint Spatial Division and Coaxial Multiplexing for Downlink Multi-User OAM Wireless Backhaul

Orbital angular momentum (OAM) at radio frequency (RF) provides a novel approach of multiplexing a set of orthogonal modes on the same frequency channel to achieve high spectral efficiencies (SEs). However, the existing research on OAM wireless communications is mainly focused on point-to-point transmission in the line-of-sight (LoS) scenario. In this paper, we propose an overall scheme of the downlink multi-user OAM (MU-OAM) wireless backhaul based on uniform circular arrays (UCAs) for broadcasting networks, which can achieve the joint spatial division and coaxial multiplexing (JSDCM). A salient feature of the proposed downlink MU-OAM wireless backhaul systems is that the channel matrices are completely characterized by the position of each small base station (SBS), independent of the numbers of subcarriers and antennas, which avoids estimating large channel matrices required by the traditional downlink multi-user multiple-input multiple-output (MU-MIMO) wireless backhaul systems. Thereafter, we propose an OAM-based multi-user distance and angle of arrival (AoA) estimation method, which is able to simultaneously estimate the positions of multiple SBSs with a flexible number of training symbols. With the estimated distances and AoAs, a MU-OAM preprocessing scheme is applied to eliminate the co-mode and inter-mode interferences in the downlink MU-OAM channel. At last, the proposed methods are extended to the downlink MU-OAM-MIMO wireless backhaul system equipped with uniform concentric circular arrays (UCCAs), for which much higher spectral efficiency (SE) and energy efficiency (EE) than traditional MU-MIMO systems can be achieved. Both mathematical analysis and simulation results validate that the proposed scheme can effectively eliminate both interferences of the practical downlink MU-OAM channel and approaches the performance of the ideal MU-OAM channel.

Fluorescence tuning, all-optical switching and OR gate realization of phloroglucinol derived carbon dots

Carbon dots that display unusual optical properties are promising materials for photonic applications. Surface passivation of carbon dots improves its optical properties, enabling full-colour emission and excitation dependent emission, making them ideal candidates for bio-imaging. We observed multicolour emission from phloroglucinol-derived carbon dots with surface passivation. Tuning the emission spectra from ultraviolet to visible spectra is achieved with varying surface passivation. Nonlinear optical properties of the samples were studied using spatial self-phase modulation. Power and wavelength dependent variation of nonlinear optical properties are investigated. All-optical switching is achieved from the sample using spatial cross-phase modulation. We have successfully demonstrated an all-optical OR gate with a switch laser and a signal laser. With appropriate control of the switching time, spatial division multiplexing of different signals or different typetypes of data can be encrypted using the same setup. Experimental results show that these carbon dots have better nonlinear optical properties for application in all-optical switching, OR gate and space division multiplexing.

Research on multiple-image encryption mechanism based on Radon transform and ghost imaging

In the process of multiple-image encryption, there are some problems such as low reconstruction accuracy, easy cross-talk, and poor robust performance. To solve these problems, a multiple-image encryption algorithm based on Radon transform and ghost imaging is proposed. Radon transform is applied to the encryption system of ghost imaging. The Cartesian coordinates of the two-dimensional images are firstly converted to the polar coordinates. Then, the Radon transform is fully used to obtain the projection of digital images at arbitrarily given angles. By adjusting the projecting angle interval, the spatial division multiplexing is used to realize the multiple-image encryption. By the numerical simulations and optical experiments, the feasibility of the proposed encryption system is verified. The results show that the proposed system not only reduces the amount of data transmission, but also improves the precision of the reconstructed image and the robustness of the encryption system.

Enhancing the flexibility and functionality of SCNs: demonstration of evolution toward any-core-access, nondirectional, and contentionless spatial channel cross-connects [Invited

A spatial channel network (SCN) was recently proposed toward the forthcoming spatial division multiplexing (SDM) era, in which the optical layer is explicitly evolved to the hierarchical SDM and wavelength division multiplexing layers, and an optical node is decoupled into a spatial cross-connect (SXC) and wavelength cross-connect to achieve an ultrahigh-capacity optical network in a highly economical manner. In this paper, we report feasibility demonstrations of an evolution scenario regarding the SCN architecture to enhance the flexibility and functionality of spatial channel networking from a simple fixed-core-access and directional spatial channel ring network to a multidegree, any-core-access, nondirectional, and core-contentionless mesh SCN. As key building blocks of SXCs, we introduce what we believe to be novel optical devices: a 1 × 2 multicore fiber (MCF) splitter, a core selector (CS), and a core and port selector (CPS). We construct free-space optics-based prototypes of these devices using five-core MCFs. Detailed performance evaluations of the prototypes in terms of the insertion loss (IL), polarization-dependent loss (PDL), and intercore cross talk (XT) are conducted. The results show that the prototypes provide satisfactorily low levels of IL, PDL, and XT. We construct a wide variety of reconfigurable spatial add/drop multiplexers (RSADMs) and SXCs in terms of node degree, interport cross-connection architecture, and add/drop port connectivity flexibilities. Such RSADMs/SXCs include a fixed-core-access and directional RSADM using a 1 × 2 MCF splitter; an any-core-access, nondirectional SXC with core-contention using a CS; and an any-core-access, nondirectional SXC without core-contention using a CPS. Bit error rate performance measurements for SDM signals that traverse the RSADMs/SXCs confirm that there is no or a very slight optical signal-to-noise-ratio penalty from back-to-back performance. We also experimentally show that the flexibilities in the add/drop port of the SXCs allow us to recover from a single or concurrent double link failure with a wide variety of options in terms of availability and cost-effectiveness.

Comb Type Pilot Based Channel Estimation using Dft Based Interpolation for Spatial Modulated OFDM Systems

An integration of Spatial Modulation with Orthogonal Frequency Division Multiplexing (SM OFDM) is a recently evolved transmission technique. In practical scenarios, channel estimation is significant for detecting transmitted data coherently. Impulse response based interpolation technique that provides channel frequency response estimate with reduction in noise error is proposed for comb type pilot based channel estimation of SM OFDM system along with 1D interpolation techniques under frequency selective channel. This scheme focus on carrying out smoothing and estimation in time domain and transforming output back to the frequency domain. BER performance is investigated for Rayleigh channel employing COST 207 project model on two test urban environments (Typical and Bad) for 4 and 16 QAM SM OFDM systems. Results show that the Least Square estimator with DFT interpolation performs finer compared to all one dimensional interpolation methods with less computational complexity by employing FFT algorithms.

Millimetre Wave Communication with Spatial Division Multiplexing for 5G systems

The point of this paper is to combination of spatial division multiplexing (SDMA) along with NOMA improves the performance of the system. This paper is done with multibeam forming for performance enhancement, Analog beam forming is done along with the digital beam forming to increase the spectral efficiency and also the user count increases so that we could able to achieve high throughput. In this paper the design problems of mm wave NOMA due to beamforming is focused so that achievable data rate is high. This is due to the number of RF chains. We analyses the demanding joint plan of the intertwined power distribution and client matching for mm Wave-SDMA. Some problems are talked about and a few arrangements are proposed in detail in mm Wave communications.

Fiber Vector Eigenmode Multiplexing Based High Capacity Transmission Over 5-km FMF With Kramers-Kronig Receiver

Vector modes (VMs) with spatially nonhomogeneous polarization patterns, combining polarization and spatial-mode degrees of freedom together, are regarded as the eigenmodes of optical fiber. Such eigenmodes have potential to be used to implement the high capacity spatial division multiplexing (SDM)/mode division multiplexing (MDM) based optical fiber communication systems. Here, we respectively demonstrate 2 VMs of the same order (l = +2, EH11o and EH11e modes) and 2 VMs of different orders (l = 0, HE11o mode and l = +2, EH11e mode) multiplexing transmissions over 5-km few-mode fiber (FMF). The mode crosstalk after FMF transmission has been minimized to prepare high capacity signal transmission without multiple-input-multiple-output (MIMO) digital signal processing (DSP). To increase the transmission capacity and decrease the system cost, the Kramers-Kronig (KK) receiver has been employed and the single-wavelength two sets of eigenmodes multiplexed 360 Gbit/s and 400 Gbit/s signal transmissions over 5-km FMF link are realized, respectively. Then, to further burst the transmission capacity, 2 vector-mode-division-multiplexing channels (HE11o and EH11e modes) in combination of 5 wavelength-division-multiplexing (WDM) channels with a total of 10 parallel channels have been demonstrated. A total data rate of 1.12 Tbit/s with 28 GBaud 16-state quadrature amplitude modulation (QAM) signal has been realized over the 5-km FMF. In all data-carrying experimental demonstrations, the bit-error rate (BER) performance of each VM channel is below the 7% hard decision forward error correction threshold (FEC) at 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 experimental results highlight that the VMDM-based optical transmission technology could find enormous potential in huge-capacity short-reach optical interconnects.

High Data Transfer Rate Spatial Division Multiplexing for Short Range non-Line-of-Sight Ultraviolet Optical Transmission

To overcome the inherent bandwidth limitation of non-line-of-sight (NLOS) ultraviolet communication (UVC) channel, a novel space division multiplexing (SDM) framework based on non-coplanar rotation angle is established. The influence of SDM structure parameters on inter-channel interference (ICI) is studied to obtain the optimal antenna configuration. And a Gaussian approximate distribution (GAD) signal detection model is presented, which simplifies the calculation of the Bit error rate (BER) of the Photon multiplier tube (PMT) reception and is suitable for complex ICI analysis. Furthermore, a low ICI scheme based on the relationship between BER and the interference factor is proposed to increase the data transmission rate or reduce the alignment configuration. As a result, the maximum data rate increases to 34 Mbps, or the alignment demand decreases by 33.33% at most. Moreover, these analysis results and techniques can be applied to other NLOS scattering optical wireless communication systems.

Power control strategies and network performance assessment for C+L+S multiband optical transport

Spatial-division multiplexing (SDM) and band-division multiplexing (BDM) have emerged as solutions to expand the capacity of existing C-band wavelength-division multiplexing (WDM) optical systems and to deal with increasing traffic demands. An important difference between these two approaches is that BDM solutions enable data transmission over unused spectral bands of already-deployed optical fibers, whereas SDM solutions require the availability of additional fibers to replicate C-band WDM transmission. On the other hand, to properly design a multiband optical line system (OLS), the following fiber propagation effects have been taken into account in the analysis: (i) stimulated Raman scattering (SRS), which induces considerable power transfer among bands; (ii) frequency dependence of fiber parameters such as attenuation, dispersion, and nonlinear coefficients; and (iii) utilization of optical amplifiers with different doping materials, thus leading to different characteristics, e.g., in terms of noise figures. This work follows a two-step approach: First, we aim at maximizing and flattening the quality of transmission (QoT) when adding L- and -bands to a traditional WDM OLS where only the C-band is deployed. This is achieved by applying a multiband optimized optical power control for BDM upgrades, which consists of setting a pre-tilt and power offset in the line amplifiers, thus achieving a considerable increase in QoT, both in average value and flatness. Second, the SDM approach is used as a benchmark for the BDM approach by assessing network performance on three network topologies with different geographical footprints. We show that, with optical power properly optimized, BDM may enable an increase in network traffic, slightly less than an SDM upgrade but still comparable, without requiring additional fiber cables.

Single-shot multi-depth full-field optical coherence tomography using spatial frequency division multiplexing.

Fast 3D volumetric imaging has been essential for biology, medicine and industrial inspections, and various optical coherence tomography (OCT) methods have been developed to meet such needs. Point-scanning based approaches, such as swept-source OCT and spectral domain OCT, can obtain a depth information at once, but they require lateral scan for full 3D imaging. On the contrary, full-field OCT needs the scanning of imaging depth while it records a full lateral information at once. Here, we present a full-field OCT system that can obtain multi-depth information at once by a single-shot recording. We combine a 2D diffraction grating and a custom-made echelon to prepare multiple reference beams having different pathlengths and propagating angles. By recording a single interference image between the reflected wave from a sample and these multiple reference beams, we reconstruct full-field images at multiple depths associated with the pathlengths of the individual reference beams. We demonstrated the single-shot recording of 7 different depth images at 10 µm for biological tissues. Our method can potentially be useful for applications where high-speed recording of multiple en-face images is crucial.

Repeater Power Conversion Efficiency in Submarine Optical Communication Systems

In power-limited trans-oceanic submarine systems, the electrical-to-optical (E/O) power conversion efficiency determines the amount of optical signal power generated by repeaters, which governs the cable capacity. In contrast to conventional submarine systems, recent single mode fiber spatial division multiplexing (SDM) systems operate at a lower channel power and support a larger number of optical fibers. Moreover, pump sharing technology is used in SDM systems to enhance cable capacity and system reliability, where a group of pump lasers are combined to feed a group of fiber pairs. The repeater E/O power conversion efficiency is directly related with cable capacity, as well as capacity per power and cost per capacity analysis. Therefore, it is important to understand the characteristics of repeater E/O efficiency. We developed a model to analyze the repeater E/O efficiency in submarine SDM systems. Experimental measurement data of pump lasers and numerical simulation results of Erbium doped fiber amplifiers (EDFAs) were used as input information to the model to analyze repeater E/O efficiency in various system designs. Based on the E/O efficiency model results, we investigated cable capacity using the Gaussian noise (GN) model. Moreover, cable capacity per power was calculated and compared based on three different power metrics: (i) electrical supply power, (ii) pump optical power and (iii) EDFA output power. With the aid of the repeater E/O efficiency model, one can analyze the efficiency of submarine systems using the direct metric of cable capacity per electrical supply power.

Multi-Gigabit Spatial-Division Multiplexing Transmission Over Multicore Plastic Optical Fiber

Today, we are evident to the revolution of the automotive industry and its demand for high bandwidth sensor fusion. Multiple high bandwidth sensors are connected, generating tremendous amount of data to be transferred in real-time in harsh environment, i.e., multi-gigabit intra-vehicle networks. Plastic optical fiber (POF) is an attractive medium for these multi-gigabit intra-vehicle networks due to its inherent EM compatibility, galvanic isolation, low weight, high tolerance to mechanical vibrations, low bending loss, and easy handling. However, commercial off-the-shelf PMMA based POFs are bandwidth-length product limited. Here, we suggest increasing the spectral efficiency using spatial-division multiplexing (SDM). In this article, we have experimentally demonstrated a low cost and eye-safe 3 × 3 multiple-input multiple-output (MIMO) SDM system over a 15 meters multicore (MC) POF using commercial optical components, e.g., RC-LEDs and Si-PIN photodiodes. A 3 × 1 spot-based cores coupler spatial multiplexer was developed to couple the optical components with the MC-POF. This system achieved raw data rates of 1.5 Gb/s and 2.4 Gb/s using offline-processed MIMO equalization. The proposed system enables a flexible and scalable optical MIMO system that can meet the requirements of the automotive industry.