Space Division Multiplexing Technique Research Articles

The efficient employment of the space division multiplexing technique with OADMs for more flexibility and scalability in optical systems

Abstract The optical add drop multiplexers (OADMs) to be modeled and analyzed depends up on the simulation variables are demonstrated. Transmitted power per channel variations are studied against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. Received power from each channel variations are demonstrated against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. The bit error rate variations are clarified against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. The optical link map through fiber cable core is clarified. Total pulse broadening variations are illustrated against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. The lighted signal/noise ratio variations are demonstrated against both receiver bandwidth and number of transmitted channels at transmission distance of 200 km and temperature of 25 °C. Channel capacity variations are also demonstrated against both receiver bandwidth and number of transmitted channels at transmission distance of 200 km and temperature of 25 °C.

Ultrafast double motion-picture recording technique for propagating light pulses with an ultrashort time difference.

Ultrafast imaging techniques involving light propagation, which can record light-pulse propagation as a motion picture, are commonly applied in various fields. However, conventional ultrafast imaging techniques cannot obtain multiple motion- pictures with an ultrashort time difference. In this Letter, we propose an imaging technique to obtain double motion-pictures of propagating light pulses with an ultrashort time difference. To record double motion-pictures of propagating light pulses without superposition of the motion pictures, we employ a space-division multiplexing technique for recording holograms. Also, we construct and introduce an optical delay setup for generating light pulses with an ultrashort time difference. In the experimental demonstration of the proposed technique, we observe the first and second light propagations for a duration of 6.9 ps with a 1.78-ps time difference.

Reconfigurable Microwave Photonic Filter Based on Space-Division Multiplexing Powered by Artificial Neural Networks

Space-division multiplexing (SDM) techniques bring new approaches for various applications in microwave photonic signal processing. In this work, an all-fiber reconfigurable microwave photonic filter (MPF) is realized based on SDM techniques using multicore fiber (MCF) and multimode fiber (MMF). The multimode interference (MMI) generated from the proposed MCF-MMF-MCF structure can be manipulated in dimensions of space and wavelength simultaneously, thus configuring the power distribution in all the taps of the MPF. The trained artificial neural network can accurately predict the operating wavelength and spatial input core for a target power distribution. In a low-cost, light-weight, and compact way, SDM fibers combined with MMI allow for greater flexibility and diversity in the response of the reconfigurable MPF.

Dynamic deformation measurement of dual-wavelength arbitrary phase-shifting digital holography with automatic phase-shift detection

Dual-wavelength arbitrary phase-shifting digital holography with automatic phase-shift detection is first proposed in this study. Holograms with two wavelengths and the interference fringes used to detect the phase-shifting amount for each wavelength were simultaneously recorded in one image using the space-division multiplexing technique. Compared with conventional methods, the proposed approach can achieve simultaneous phase shifting of the reference beams of two wavelengths, which substantially reduces recording time and does not require excessive phase-shifting device precision. The proposed and conventional methods were quantitatively evaluated with numerical simulations, and a dynamic deformation measurement was obtained using the system. In the quantitative evaluation of the simulation, the root-mean-square errors of amplitude and phase images reconstructed by the proposed method were reduced by 12% and 19% compared to the conventional method, respectively. Both numerical simulations and experiments verified the effectiveness of the proposed method.

Numerical investigation of dual guided elliptical ring core few-mode fiber for space division multiplexing applications

In this article, dual elliptical ring core few-mode fiber (DE-RCF-FMF) profile with assisting dual cladding is investigated. By this approach, it is possible to combine the performance behavior two separate ring core fiber (RCF). Of course, elliptically core region is constructed for polarization maintaining properties. In this way, the maximum number of linearly polarized (LP) modes up to 20 can be generated. As dual channel separation, inner elliptical core region generates maximum of 8 L P modes and identified as LP01, LP11a, LP11b, LP21 for both X - and Y- polarizations. Similarly, outer elliptical core is supposed to generate maximum of 12 L P modes and identified as LP01, LP11, LP11, LP21, LP31, LP41, and LP51 for both x- and y- polarizations. Using finite element method (FEM), each mode characteristics is numerically simulated and the performance studies are compared with other LP modes. It is obviously well known as mode converter property and the conversion is only possible due to the mutual energy sharing between the neighborhood modes. In this design, LP01 mode is converted to LP11 and LP11 converted as LP21. The conversion region may happen for either ellipticity or wavelength variation. Anyhow, the property of mode conversion in the transverse direction is also considered as essential property of Space division multiplexing techniques.

Machine Learning Techniques for Optical Performance Monitoring and Modulation Format Identification: A Survey

The trade-off between more user bandwidth and quality of service requirements introduces unprecedented challenges to the next generation smart optical networks. In this regard, the use of optical performance monitoring (OPM) and modulation format identification (MFI) techniques becomes a common need to enable the development of next-generation autonomous optical networks, with ultra-low latency and self-adaptability. Recently, machine learning (ML)-based techniques have emerged as a vital solution to many challenging aspects of OPM and MFI in terms of reliability, quality, and implementation efficiency. This article surveys ML-based OPM and MFI techniques proposed in the literature. First, we address the key advantages of employing ML algorithms in optical networks. Then, we review the main optical impairments and modulation formats being monitored and classified, respectively, using ML algorithms. Additionally, we discuss the current status of optical networks in terms of MFI and OPM. This includes standards, monitoring parameters, and the available commercial products with their limitations. Second, we provide a comprehensive review of the available ML-based techniques for MFI, OPM, and joint MFI/OPM, describing their performance, advantages, and limitations. Third, we give an overview of the exiting ML-based OPM and MFI techniques for the emerging optical networks such as the new fiber-based networks that use future space division multiplexing techniques (e.g., few-mode fiber), the hybrid radio-over-fiber networks, and the free space optical networks. Finally, we discuss the open issues, potential future research directions, and recommendations for the potential implementation of ML-based OPM and MFI techniques. Some lessons learned are presented after each section throughout the paper to help the reader identifying the gaps, weaknesses, and strengths in this field.

Space division multiplexing in standard multi-mode optical fibers based on speckle pattern classification

In optical communications the transmission bandwidth of single mode optical fibers is almost fully exploited. To further increase the capacity of a telecommunication link, multiplexing techniques can be applied across 5 physical dimensions: amplitude, quadrature, polarization, frequency and space, with all but the latter being nearly exhausted. We experimentally demonstrate the feasibility of an original space division multiplexing technique based on the classification of speckle patterns measured at the fiber’s output. By coupling multiple optical signals into a standard multimode optical fiber, speckle patterns arise at the fiber’s end facet. This is due to quasi-random interference between the excited modes of propagation. We show how these patterns depend on the parameters of the optical signal beams and the fiber length. Classification of the speckle patterns allows the detection of the independent signals: we can detect the state (i.e. on or off ) of different beams that are multiplexed in the fiber. Our results show that the proposed space division multiplexing on standard multimode fibers is robust to mode-mixing and polarization scrambling effects.

Advanced DSP for Coherent Optical Fiber Communication

In this paper, we provide an overview of recent progress on advanced digital signal processing (DSP) techniques for high-capacity long-haul coherent optical fiber transmission systems. Not only the linear impairments existing in optical transmission links need to be compensated, but also, the nonlinear impairments require proper algorithms for mitigation because they become major limiting factors for long-haul large-capacity optical transmission systems. Besides the time domain equalization (TDE), the frequency domain equalization (FDE) DSP also provides a similar performance, with a much-reduced computational complexity. Advanced DSP also plays an important role for the realization of space division multiplexing (SDM). SDM techniques have been developed recently to enhance the system capacity by at least one order of magnitude. Some impressive results have been reported and have outperformed the nonlinear Shannon limit of the single-mode fiber (SMF). SDM introduces the space dimension to the optical fiber communication. The few-mode fiber (FMF) and multi-core fiber (MCF) have been manufactured for novel multiplexing techniques such as mode-division multiplexing (MDM) and multi-core multiplexing (MCM). Each mode or core can be considered as an independent degree of freedom, but unfortunately, signals will suffer serious coupling during the propagation. Multi-input–multi-output (MIMO) DSP can equalize the signal coupling and makes SDM transmission feasible. The machine learning (ML) technique has attracted worldwide attention and has been explored for advanced DSP. In this paper, we firstly introduce the principle and scheme of coherent detection to explain why the DSP techniques can compensate for transmission impairments. Then corresponding technologies related to the DSP, such as nonlinearity compensation, FDE, SDM and ML will be discussed. Relevant techniques will be analyzed, and representational results and experimental verifications will be demonstrated. In the end, a brief conclusion and perspective will be provided.

Extending recordable time of light-in-flight recording by holography with double reference light pulses.

Light-in-flight (LIF) recording by holography is a powerful technique for observing ultrashort light pulse propagation. However, the recordable time of the technique has been limited by the lateral length of the holographic plate. Then, to extend the recordable time of LIF recording by holography, we proposed a space-division multiplexing technique of holograms, which divides the holographic plate longitudinally and uses double reference light pulses. We experimentally demonstrated that the recordable time becomes twice as long as before for the first time, to the best of our knowledge, using the proposed technique. Specifically, we recorded the motion picture of the ultrashort light pulse propagation for 236ps.

Transmission of wireless signals using space division multiplexing in few mode fibers

Evolution of next generation wireless networks brings challenges to efficiently transmit a large amount of data from a base station to a remote antenna unit. We investigate a space division multiplexing technique that employs few mode fibers (FMFs) to transmit 3 × 3 MIMO wireless signals, aiming to employ a common digital signal processing (DSP) unit to equalize both the fiber and wireless channel. We optimize system parameters and obtain above 28 dB and 23 dB signal-to-interference and noise ratio (SINR) for 3 meters wireless systems with 500 m and 2 km FMF, which correspond to the transmission capacity of 578 Mb/s and 468 Mb/s using a 20 MHz bandwidth, respectively. Moreover, we analyze that the nonlinear spectrum distortion due to the combined effect of nonlinearity in the directly modulated laser and the differential mode delay in multimode fibers and validate it by simulations.

Feasibility of Space-Division-Multiplexed Transmission of IEEE 802.11 n/ac-Compliant Wireless MIMO Signals Over OM3 Multimode Fiber

In this paper, we have experimentally demonstrated the feasibility of space-division-multiplexed 3 × 3 multiple-input multiple-output (MIMO) transmission over a single OM3 multimode fiber (MMF) using commercial IEEE 802.11 n/ac access points. Throughput performance for different fiber length links under a range of fiber bending conditions was evaluated. To study the throughput improvement by MIMO technology, throughput performance of single-input single-output (SISO), 2 × 2 MIMO and 3 × 3 MIMO over separate SMF links was also measured for comparison. It is shown that, spatially-multiplexed MMF channel with 3 × 3 MIMO configuration could provide a significant throughput increase in comparison with SISO and 2 × 2 MIMO SMFs configurations, and present a comparable performance with 3 × 3 MIMO SMFs configuration. Meanwhile, the analyses of the impact of fiber bending indicate that, even under a tight fiber bending radius as low as 2 mm, the system performance could still keep at an acceptable level. With all fiber bending radii tested, within each 5-min measurement time, the fiber channel is found to be good enough to provide throughput greater than twice the average SISO value for more than 87.66% and 72.72% of the time, at the 2.4 and 5 GHz bands, respectively. These results together point out a very simple and cost-saving solution for future in-building DASs to distribute wireless MIMO signals using commercially-available MMF infrastructure by space division multiplexing technique, even though it may encounter tight bending conditions.

A 400 Gbps/100 m free-space optical link

A 400 Gbps/100 m free-space optical (FSO) link with dense-wavelength-division-multiplexing (DWDM)/space-division-multiplexing (SDM) techniques and a doublet lens scheme is proposed. To the best of our knowledge, this is the first time that a link adopting DWDM and SDM techniques and a doublet lens scheme has demonstrated a 400 Gbps/100 m FSO link. The experimental results show that the free-space transmission rate is significantly enhanced by the DWDM and SDM techniques, and the free-space transmission distance is greatly increased by the doublet lens scheme. A 16-channel FSO link with a total transmission rate of 400 Gbps (25 Gbps/λ × 16 λ = 400 Gbps) over a 100 m free-space link is successfully demonstrated. Such a 400 Gbps/100 m DWDM/SDM FSO link provides the advantages of optical wireless communications for high transmission rates and long transmission distances, which is very useful for high-speed and long-haul light-based WiFi (LiFi) applications.

Ultra-Long-Haul High-Capacity Super-Nyquist-WDM Transmission Experiment Using Multi-Core Fibers

This paper describes promising techniques for approaching the capacity-distance product over 1 Exabit/s×km in the transoceanic-class optical fiber transmission. One is the Super-Nyquist wavelength-division multiplexing (WDM) technique based on poly-binary-pulse shaping with maximum likelihood sequence estimation, in which it is possible to multiplex optical signals with WDM spacing of less than the signal baudrate. Another technique is the space-division multiplexing technique based on multi-core fibers (MCFs) with multi-core Erbium-doped fiber amplifiers (EDFAs), in which the fiber capacity can be increased when the number of cores of MCF is increased. Finally, we present a demonstration of 140.7-Tbit/s, 7 326-km transmission of 201-channel 25-GHz-spaced Super-Nyquist-WDM 100-Gbit/s optical signals using seven-core fibers and full C-band seven-core EDFAs.

Research of space curve fitting based on FBG sensor technology

Based on the principle of fiber bragg grating sensors, orthogonal multipoint curvature information can be detected by space division multiplexing technique (SDM) and wavelength division multiplexing technique (WDM). This paper discusses the space curve fitting based on this orthogonal discrete curvature information. To realize space curve fitting, the curvature information interpolation method and the curve fitting method are discussed. The visualization reconstruction software combined with VC++ and OpenGL technology was developed for simulation and experiment. Simulation results show that the interpolation method and fitting method can reflect the curved shape of space curve more accurately. And experiment results shows the curved shape perception and visualization reconstruction of experiment model with implantable distributed FBG sensor network exactly, dynamically based on FBG detection technology.

OPTICAL ADD DROP MULTIPLEXERS (OADMS) IN UW-WDM OPTICAL PASSIVE COMMUNICATION NETWORKS

In the present paper, we have been modeled numerically and parametrically the high and best performance functions of optical add drop multiplexers (OADMs) for ultra wide wavelength division multiplexing technique with ultra wide space division multiplexing technique in advanced optical communication networks and photonic networking over the assumed set of parameters. Moreover, we have analyzed and investigated the maximum time division multiplexing (MTDM) and soliton transmission techniques to be processed to handle bit rate either per link or per channel for cables of multi-links (20-120 links/core). Where maximum number of transmitted channels in the range of 1000-4800 channels are processed to handle the product of bit rate either per channel or per link for cables of multilinks of silica cable core fabrication material. The MTDM or soliton transmission bit rates either per link or per channel are also treated over wide range of the affecting parameters under the ambient temperature variations. Also, the performance characteristics of the OADMs are taken as the major interest in optical networks to handle maximum transmission bit rates for the supported subscribers.

Parallel phase-shifting color digital holographic microscopy

We propose parallel phase-shifting color digital holographic microscopy (PPSCDHM) which is capable of both color imaging and three-dimensional (3-D) motion measurement by using space-division multiplexing technique. By the PPSCDHM, instantaneous information of not only the 3-D structure of specimens but also the spectral image can be simultaneously acquired with a single-shot exposure. The PPSCDHM can be implemented by using a micro-polarizer array, a micro-wavelength-filter array, and more than two wavelengths of lasers. We conducted a preliminary experiment using three wavelengths of lasers, and then much clearer image was reconstructed by the PPSCDHM than that by Fresnel transform alone for each wavelength. Thus, the effectiveness of the PPSCDHM was verified.

Parallel phase-shifting digital holographic microscopy.

We propose parallel phase-shifting digital holographic microscopy (PPSDHM) which has the ability of three-dimensional (3-D) motion measurement using space-division multiplexing technique. By the PPSDHM, instantaneous information of both the 3-D structure and the phase distributions of specimens can be simultaneously acquired with a single-shot exposure. We constructed a parallel phase-shifting digital holographic microscope consisting of an optical interferometer and an image sensor on which micro polarizers are attached pixel by pixel. The validity of the PPSDHM was experimentally verified by demonstrating the single-shot 3-D imaging and phase-imaging ability of the constructed microscope.

Simplified Fair Scheduling and Antenna Selection Algorithms for Multiuser MIMO Orthogonal Space-Division Multiplexing Downlink

We consider the downlink of a multiuser multiple-input multiple-output (MIMO) system, where the base station and the mobile receivers are equipped with multiple antennas. We propose simplified algorithms for channel-aware multiuser scheduling in conjunction with receive antenna selection for two downlink multiuser orthogonal space-division multiplexing techniques: block diagonalization and successive optimization. The algorithms greedily maximize the weighted sum rate. The algorithms add the best user at a time from the set of users that are not selected yet to the set of selected users until the desired number of users has been selected. To apply the proportional fairness criterion, simplified user scheduling metrics are proposed for block diagonalization and successive optimization. Two receive antenna selection algorithms are also proposed, which further enhance the power gain of the equivalent single-user channel after orthogonal precoding by selecting a subset of the receive antennas that contributes the most toward the total power gain of the channel. A user grouping technique is used to further lower the complexity of the selection algorithms. We compare various multiuser MIMO scheduling strategies that are applied to block diagonalization and successive optimization transmission techniques through simulation. Simulation results demonstrate the effectiveness of the proposed algorithms in ensuring throughput fairness among users. Results also show that when the number of users is large, the proposed scheduling algorithms perform close to the exhaustive search algorithms and previously proposed greedy scheduling algorithms, but with much lower complexity.