Optical Multiplexing Technique Research Articles

Eigen-function division multiplexed coherent optical transmission in time domain by using higher-order Hermite-Gaussian pulses.

We describe a new multiplexing technique and its application to demultiplexing in the time domain by using higher-order Hermite-Gaussian (HG) pulses, which are solutions of the Schrödinger equation. We call this technique eigen-function division multiplexing (EDM). This method enables us to further increase the total transmission capacity by superimposing many different HG pulses in the same time slot. This technique is different from a conventional optical time domain multiplexing (OTDM) technique using interleaving, where one pulse exists only in one time slot. The transmitted EDM HG pulses can be demultiplexed by adopting the time-domain orthogonality of the HG pulses (eigen-function orthogonality). The information carried by the mth-order HG pulse (HGm pulse) can be coherently detected by a photo detector, where photo-mixing with a phase-locked HGm pulse generated by a local oscillator can realize demultiplexing. The overlap integral with a different HG pulse becomes zero due to the time domain orthogonality. First, we show numerically that such a new EDM transmission scheme in the time domain is possible. We then show experimentally that we could successfully carry out an EDM HG coherent pulse transmission with four different HG pulses (HG0, HG1, HG2, and HG3), where we report a 400∼480 Gbit/s (10 Gbaud x 4 eigen-functions x 2 pol-mux.) 32∼64 QAM EDM transmission over 300∼450 km.

Multiplexing in photonics as a resource for optical ternary content-addressable memory functionality

Abstract In this paper, we combine a Content-Addressable Memory (CAM) encoding scheme previously proposed for analog electronic CAMs (E-CAMs) with optical multiplexing techniques to create two new photonic CAM architectures—wavelength-division multiplexing (WDM) optical ternary CAM (O-TCAM) and time-division multiplexing (TDM) O-TCAM. As an example, we show how these two O-TCAM schemes can be implemented by performing minor modifications in microring-based silicon photonic (SiPh) circuits originally optimized for exascale interconnects. Here, our SiPh O-TCAM designs include not only the actual search engine, but also the transmitter circuits. For the first time, we experimentally demonstrate O-TCAM functionality in SiPh up to ∼ 4 Gbps ${\sim} 4\,\,\text{Gbps}$ and we prove in simulation feasibility for speeds up to 10 Gbps, 10 times faster than typical E-TCAMs at the expense of higher energy consumption per symbol of our O-TCAM Search Engine circuits than the corresponding E-TCAMs. Finally, we identify which hardware and architecture modifications are required to improve the O-CAM’s energy efficiency towards the level of E-CAMs.

Photonic reservoir computing enabled by stimulated Brillouin scattering.

Artificial intelligence (AI) drives the creation of future technologies that disrupt the way humans live and work, creating new solutions that change the way we approach tasks and activities, but it requires a lot of data processing, large amounts of data transfer, and computing speed. It has led to a growing interest of research in developing a new type of computing platform which is inspired by the architecture of the brain specifically those that exploit the benefits offered by photonic technologies, fast, low-power, and larger bandwidth. Here, a new computing platform based on the photonic reservoir computing architecture exploiting the non-linear wave-optical dynamics of the stimulated Brillouin scattering is reported. The kernel of the new photonic reservoir computing system is constructed of an entirely passive optical system. Moreover, it is readily suited for use in conjunction with high performance optical multiplexing techniques to enable real-time artificial intelligence. Here, a methodology to optimise the operational condition of the new photonic reservoir computing is described which is found to be strongly dependent on the dynamics of the stimulated Brillouin scattering system. The new architecture described here offers a new way of realising AI-hardware which highlight the application of photonics for AI.

Multipath Quasi-Distributed Acoustic Sensing Based on Space Division Multiplexing and Time-Gated OFDR

Quasi-distributed optic sensing system has been widely utilized in various applications for its simple configuration, high sensing resolution, and long sensing range. In large sensing network, multipath sensing arrays are needed to be monitored simultaneously. This paper proposes a multi-path quasi-distributed acoustic sensing system based on time-gated digital optical frequency domain reflectometry (TGD-OFDR) and spatial division multiplexing (SDM) technique. The single mode fiber segment between weak reflectors is efficiently used. In experiments, vibrations on two weak reflectors array are detected simultaneously, and crosstalk between pathes is analyzed. This multi-path system does not require additional hardware equipment and the bandwidth of the system is not sacrificed, which has great potential in large-scale sensing network.

Line-wise scanning-based super-resolution imaging.

In this Letter, we present a novel, to the best of our knowledge, line-wise scanning-based super-resolution (LSSR) imaging method. To reduce point spread functions overlapping among pixels, we specifically present a super-resolution (SR) imaging architecture to capture a series of low-resolution images using a line-based optical multiplexing technique, which is able to achieve a good balance between imaging quality and speed. In addition, we propose an efficient joint reconstruction algorithm based on total variation and low-rank constraints to generate a high-resolution image from these low-resolution images that contain different spatial details. Meanwhile, existing stripe noises are efficiently suppressed. Experiments on real data show that LSSR imaging has significant advantages over other state-of-the-art methods in terms of visual quality and quantitative measurement.

Optical multiplexing techniques and their marriage for on-chip and optical fiber communication: a review

Herein, an attention-grabbing and up-to-date review related to major multiplexing techniques is presented which includes wavelength division multiplexing (WDM), polarization division multiplexing (PDM), space division multiplexing (SDM), mode division multiplexing (MDM) and orbital angular momentum multiplexing (OAMM). Multiplexing is a mechanism by which multiple signals are combined into a shared channel used to showcase the maximum capacity of the optical links. However, it is critical to develop hybrid multiplexing methods to allow enhanced channel numbers. In this review, we have also included hybrid multiplexing techniques such as WDM-PDM, WDM-MDM and PDM-MDM. It is probable to attain <italic>N</italic>×<italic>M</italic> channels by utilizing <italic>N</italic> wavelengths and <italic>M</italic> guided-modes by simply utilizing hybrid WDM-MDM (de)multiplexers. To the best of our knowledge, this review paper is one of its kind which has highlighted the most prominent and recent signs of progress in multiplexing techniques in one place.

Experimental demonstration of all-optical PolMux RoF system with multiservice transmission

In this paper, a Radio-over-Fiber (RoF) system is proposed by combining optical carrier suppression (OCS) and polarization multiplexing (PolMux) techniques in all-optical mode to enable multi-service transmission. Previous studies on RoF system only exploited multi-service transmission over low radio frequency (RF) oscillator-based PolMux, subcarrier multiplexing (SCM) and wavelength division multiplexing (WDM) techniques. Hence, herein, PolMux jointly with OCS techniques are exploited as a new medium of multiplexing in RoF system. Essentially, two contributions are unveiled, firstly the combination of all optical OCS and PolMux for RoF technology to enable multi-service transmission, and secondly an end-to-end all-optical transmission with the inclusion of wireless medium at millimeter wave (mmWave) frequency. The results indicate a highly reliable OCS-PolMux topology, where the EVM deterioration due to polarization leakage factor was only ∼1% to ∼2% for both services transmitted at the same frequency. Most importantly, the proposed system demonstrated an end-to-end system transmission with optical receiver power budget of up to ∼6 dB.

Bidirectional hybrid OFDM based free-space/wireless-over-fiber transport system

We propose and demonstrate a successful application of orthogonal frequency division multiplexing (OFDM), reflective semiconductor optical amplifier and polarization multiplexing techniques to facilitate bidirectional hybrid OFDM based integrated free-space optics and wireless transport system. The downlink 12 Gbps OFDM data-stream and 79 community antenna television (CATV) channels are transmitted over 50 km single mode fiber (SMF) as well as 12 m and 10 m free-space link, respectively. The uplink 10 Gbps/5 GHz and 5 Gbps/3.5 GHz OFDM data streams are communicated over separate 50 km SMF along with 8 m wireless links. We have used 32-quadrature amplitude modulation (QAM) and 16-QAM modulation formats for downlink and uplink, correspondingly. The performance of the system is observed by evaluating carrier-to-noise ratio (CNR), composite second-order (CSO) and composite-triple-beat (CTB) for the CATV signal, and constellations diagrams, bit error rate (BER), signal-to-noise ratio (SNR), and error vector magnitude (EVM) values for the OFDM signals. After transmission over 50 km SMF as well as 10 m free-space, the resulting CNR, CSO and CTB values are > 51 dB, 23.3 dB, respectively. 4 dBm and 3.2 dBm power penalties at BER of $$10^{ - 8}$$, below 13% EVM and > 21.3 dB/ > 22.2 dB SNR values are observed for the uplink 10 Gbps/5 GHz and the 5 Gbps/3.5 GHz OFDM data signals, respectively, over 50 km SMF as well as 8 m wireless is observed.

Study of Optical MIMO Transmission Systems Using the MGDM Multiplexing Technique

In current local area networks, multimode fibers (MMFs), mainly graded index (GI) MMFs, are the main types of fibers used for data communications. Because of their high bandwidth, they are considered the main method of transmission that allows to offer multiservice broadband services using optical multiplexing techniques.&#x0D; &#x0D; The MGDM (ModeGroup Division Multiplexing) is a Multiplexing technique, which aims to improve the performance of the multimode optical fiber by spatially multiplexing the data streams to be transmitted. In this work, we study optical MIMO (multi-input multi-output) transmission systems on an MMF optical fiber, specifically the adaptation of the architecture of MIMO transmission systems. In this context, we have studied the mode group multiplexing technique (MDGM), to evaluate the transmission capacity. In fact, the latter depends on the injection conditions and the state of the optical fiber.

Fourth-generation Bidirectional Wireless Hybrid Transmission System Employing Power-Doubler-Amplifier and Data Comparator

Abstract An innovative cost-effective fourth-generation bidirectional wireless hybrid transport system, employing optical add-drop multiplexing technique, power doubler amplifier and data comparator, is proposed and experimentally demonstrated. The proposed system can transmits, downlink 80 community antenna television (CATV) channels, two different wireless-over-fiber (WoF) data signals (1.5-Gbps/2.4-GHz, 2.5-Gbps/3.5-GHz) at two different base stations over 40 km and 80 km single-mode fiber (SMF), respectively, and an uplink 5-Gbps baseband (BB) signal at central station over 40 km SMF, using a single optical carrier. The good carrier-to-noise ratio, composite-second order and composite-triple bit are achieved for CATV channels, and small BER and open eye-diagrams are achieved for WoF and BB signals.

Colour 3D holographic display based on a quantum-dot-doped liquid crystal

ABSTRACTLiquid crystals (LCs) doped with photo-sensitive materials exhibit large optical nonlinearity, which makes them attractive for holographic display. In this paper, we present a 3D holographic display based on a nematic LC doped with quantum dots (QDs). With this QD-doped LC, a fast response time of 8.46 ms is achieved. Using this fast-updated recording material, a video-rate 3D holographic display system is implemented, which provides vivid RGB colours and high brightness, and offers all depth cues correctly. In combination with optical multiplexing techniques, the presented system is capable of realising large-sized holographic display.

Multi-point fiber refractometer using Fresnel reflection and a coherent optical frequency-domain multiplexing technique.

We demonstrate a simple multi-point refractometer based on the coherent optical frequency-domain multiplexing technique. As local refractive index sensors, interferometers of different lengths formed between cleaved fiber tips and reference weak reflectors are employed. Referent reflectors were fabricated by splicing into lead SMF-28 fiber a very short section of hollow optical fiber using a standard fiber splicer and a cleaver with an optical microscope. Despite the very simple configuration and manufacturing of the sensor, the refractive index resolution of 6×10-4 was demonstrated during proof-of-concept experiments.

Superchannel Multicasting Module Placement Algorithm Applied to Elastic Optical Networks

The spectral fragmentation problem in elastic optical networks decreases the spectral usage provided by this technology. One way to tackle this problem is by the use of the optical inverse multiplexing technique based on superchannel multicasting (SM). This technique allows to fill the fragments presented in the network with requests, by either modifying the original central frequency of the request or by dividing the original request superchannel into discontiguous sets of slots, in part of the route. These two forms of SM usage are investigated in this paper, in order to evaluate the advantage of applying descontiguity. An algorithm for an efficient superchannel multicasting module distribution among the network nodes with this capability is the main subject of this article. The effectiveness of the heuristics is assessed by comparing its call request blocking probability with that provided by the uniform SM module distribution. We analyze three distinct topologies under multiple network loads and amount of SM modules. In all cases, our proposed module distribution provides reductions of 25% to 48% in the call request blocking probability when compared to the uniform SM module distribution.

Ultrafast Fully Photonic Random Bit Generator

To achieve complete security of communication, there is a need for “ real-time ” ultrafast physical random bit generators (RBGs). In the available physical RBGs, random bit extraction is effected in the electrical domain and, therefore, cannot directly function beyond the frequencies of 10 GHz or so in real time . Here, we present a fully photonic strategy for real-time random number generation and report a proof-of-concept experimental demonstration of an integrated 10 Gb/s RBG system (prototype) based on laser chaos. The use of an ultrastable mode-locked laser, together with ultrafast optical interactions, gives our method the capability to develop super-high-speed RBGs in practice. The photonic implementation is fully compatible with optical communications so that well-established optical multiplexing techniques can be used to realize Tb/s real-time random bit generation.

Pulse patterning effect in optical pulse division multiplexing for flexible single wavelength multiple access optical network

Abstract A demand for high spectral efficiency requires multiple access within a single wavelength, but the uplink signals are significantly degraded because of optical beat interference (OBI) in intensity modulation/direct detection system. An optical pulse division multiplexing (OPDM) technique was proposed that could effectively reduce the OBI via a simple method as long as near-orthogonality is satisfied, but the condition was strict, and thus, the number of multiplexing units was very limited. We propose pulse pattern enhanced OPDM (e-OPDM) to reduce the OBI and improve the flexibility in multiple access within a single wavelength. The performance of the e-OPDM and patterning effect are experimentally verified after 23-km single mode fiber transmission. By employing pulse patterning in OPDM, the tight requirement was relaxed by extending the optical delay dynamic range. This could support more number of access with reduced OBI, which could eventually enhance a multiple access function.

Hadamard Matrix Design for a Low-Cost Indoor Positioning System in Visible Light Communication

A positioning system based on visible light communication (VLC) utilizes illuminating indoor lights to identify the location of objects. The complexity and the cost of VLC are largely affected by limited bandwidths on optical emitters and detectors. In this paper, we present an optical signaling and multiplexing technique, which employs Hadamard matrices to implement a multiple-input multiple-output (MIMO) system. Fundamental conditions to create nonnegative optical signals and brightness control are defined in conjunction with multiplexing different sources and receiving messages. By using two design methods $n-1$ and $M$ constructions, Hadamard matrices can be used to implement MIMO VLC without considering bandwidth limits for emitters or receivers. Eventually, the presented model and the method generalize multiplexing techniques with orthogonality from a view of orthogonal matrices. Experiments show that the proposed positioning system has 0.02-m standard errors of identification due to the noise component in a slow optical receiver.

Wavelength independency of spatially multiplexed communication channels in standard multimode optical fibers

Spatial domain multiplexing (SDM), also known as space division multiplexing, adds a new degree of photon freedom to existing optical fiber multiplexing techniques by allocating separate radial locations to different channels of the same wavelength as a function of the input launch angle. These independent MIMO channels remain confined to their designated locations while traversing the length of the carrier fiber owing to helical propagation of light inside the fiber core. As a result, multiple channels of the same wavelength can be supported inside a single optical fiber core, thereby allowing spatial reuse of optical frequencies and multiplication of fiber bandwidth. It also shows that SDM channels of different operating wavelengths continue to follow an output pattern that is based on the input launch angle. As a result, the SDM technique can be used in tandem with wavelength division multiplexing (WDM), to achieve higher optical fiber bandwidth through increased photon efficiency and added degrees of photon freedom. This endeavor presents the feasibility of a hybrid optical fiber communication architecture in which the spectral efficiency of the combined system increases by a factor of “n” when each channel of an “ n ” channel SDM system carries the entire range of WDM spectra.

Time division multiplexed orbital angular momentum access system

We propose and experimentally demonstrate time division multiplexed orbital angular momentum (OAM) access system to increase transmission capacity and spectral efficiency. In this system, data carried on different time tributaries share the same OAM mode. Multiple time division multiplexed OAM modes are multiplexed to realize two-dimensional (time dimension and OAM dimension) multiplexing. Therefore, the capacity and spectral efficiency of the access system will increase. The orthogonality between optical time division multiplexing (OTDM) and OAM techniques is also verified in our experiment. In a proof-of-concept experiment, 2×5-Gbps return-to-zero signal over OAM mode +4 is transmitted and investigated. The bit error ratio performance after transmission in this system can be smaller than 1×10−9. Results show that the proposed time division multiplexed OAM access system is suitable for future broadband access network.

Combined Optical and Electrical Spectrum Shaping for High-Baud-Rate Nyquist-WDM Transceivers

We discuss the benefits and limitations of optical time-division multiplexing (OTDM) techniques based on the optical generation of a periodic train of sinc pulses for wavelength-division multiplexing (WDM) transmission at high baud rates. It is shown how the modulated OTDM spectrum bandwidth is related to the optical comb parameters and the pulse shaping of the modulating waveforms in the electrical domain. Such dependence may result in broadening of the modulated spectra, which can degrade the performance of Nyquist-WDM systems due to interchannel crosstalk penalties. However, it is shown and experimentally demonstrated that the same technique of optical pulse train generation can be allied with digital pulse shaping to improve the confinement of the modulated spectrum toward the Nyquist limit independently of the number of OTDM tributaries used. To investigate the benefits of the proposed approach, we demonstrate the first WDM Nyquist-OTDM signal generation based on the periodic train of sinc pulses and electrical spectrum shaping. Straight line transmission of five 112.5-Gbd Nyquist-OTDM dual-polarization quadrature phase-shift keying (QPSK) channels is demonstrated over a dispersion uncompensated link up to 640 km, with full-field coherent detection at the receiver. It is shown that such a design strategy effectively improves the spectral confinement of the modulated OTDM signal, providing a minimum intercarrier crosstalk penalty of 1.5 dB in baud-rate-spaced Nyquist-WDM systems.

Novel Method for Improving the Capacity of Optical MIMO System Using MGDM

In current local area networks, multimode fibers (MMFs), primarily graded index (GI) MMFs, are the main types of fibers employed for data communications. Due to their enormous bandwidth, it is considered that they are the main channel medium that can offer broadband multiservices using optical multiplexing techniques. Amongst these, mode group diversity multiplexing (MGDM) has been proposed as a way to integrate various services over an MMF network by exciting different groups of modes that can be used as independent and parallel communication channels. In this paper, we study optical multiple-input–multiple-output (O-MIMO) systems using MGDM techniques while also optimizing the launching conditions of light at the fiber inputs and the spot size, radial offset, angular offset, wavelength, and the radii of the segment areas of the detectors. We propose a new approach based on the optimization of launching and detection conditions in order to increase the capacity of an O-MIMO link using the MGDM technique. We propose a (3 $\times$ 3) O-MIMO system, where our simulation results show significant improvement in GI MMFs' capacity compared with existing O-MIMO systems.