Optical Multiplexing Research Articles

Optical single carrier-interleaved frequency division multiplexing for visible light communication systems

In this paper, a novel optical single carrier-interleaved frequency division multiplexing (OSC-IFDM) signaling scheme for an intensity modulation and direct detection (IM/DD) based visible light communications (VLC) system is presented. We show that, OSC-IFDM significantly improves the peak-to-average-power ratio (PAPR) of the DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM). The reduction in the PAPR value is achieved by exploiting the symmetrical characteristics of the single carrier-interleaved frequency division multiple access (SC-IFDMA) time domain symbol, whereby the imaginary and real parts of the SC-IFDMA samples are separated and transmitted through two sub-symbols. Simulation results show that, the PAPR of OSC-IFDM is 10 dB lower than that of the DCO-OFDM scheme. We also show that the proposed scheme offers higher spectral efficiency compared to our previous work.

Timing synchronization algorithm based on FH sequence for coherent optical OFDM systems with carrier frequency offset

A novel symbol timing synchronization algorithm based on Frank-Hermiller (FH) sequence is proposed for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems with carrier frequency offset. The timing synchronization is realized by using only one training symbol which is composed of conjugated symmetric sequences. The timing estimation of the proposed algorithm is robust to poor frequency offset. The proposed algorithm is shown to eliminate the timing sidelobes of Park’s algorithm and has a more accurate timing estimation. In the condition of frequency offset, the timing metric of the proposed method still maintains its peak value at the correct timing point, while the values are almost zero at all other positions.

Application of nonlinear photonic crystal ring resonators in realizing all optical OR/NOT/AND gates

Arithmetic logic unit (ALU) is the core of any digital processing systems. For creating an all optical ALU one needs basic logic gates such as optical NOT, OR and AND gates along with an optical full adder and optical multiplexer. In this paper we aim to design and propose these three basic logic gates using nonlinear photonic crystal ring resonators. The simulations will be done using plane wave expansion and finite difference time domain methods. The proposed structures work based on controlling the optical behavior of the nonlinear resonators using optical power. The simulation results show that the switching threshold for this resonant ring is about 15 mW/μm2. Reduced delay times and switching optical power are the main advantages of the proposed structures. Also by adding two resonant rings in input ports we reduced the cross reflection between the input ports.

White Beam Lasing from a Hybrid Microcavity with Slab-Capillary Mode Coupling

Creating a multicolor laser on a single microchip has become a subject of great interest, with white-light lasers as the ultimate goal. This requires a high-quality-factor, multichannel cavity structure supporting the lasing of all elementary colors simultaneously, with strongly enhanced ultralow-threshold emission. The authors present a hybrid microcavity that eliminates background noise and integrates multiple capillaries on a slab, achieving multiwavelength lasing. This broadly tunable multichannel laser should find use in $e.g.$ optical interconnects and multiplexing, multiagent chemical and biological detection, solid-state lighting, solar cells, and superbright microdisplays.

Optical Information Multiplexing with Nonlinear Coding Metasurfaces

AbstractCoding metasurfaces, as a new type of design concept, have provided many attractive functionalities for manipulating the wave fronts of light. Previous research only focused on linear coding metasurfaces; however, with the increasing demand for highly integrated and compact multifunctional chips, the drawbacks of linear coding metasurfaces, the constraints on information capacity and operating frequency are becoming more and more obvious. Here, Pancharatnam–Berry‐phase‐based nonlinear coding metasurfaces are proposed, in which convenient digital signal processing is employed to design multidimensional information channels in nonlinear optical processes to achieve optical information multiplexing. In order to confirm the feasibility of this methodology, by encoding various focusing functionalities and image information into nonlinear metasurfaces, a multifocal metalens and a multifunctional metasurface are theoretically designed, and their excellent performances are experimentally demonstrated. The proposed nonlinear coding metasurfaces may provide a promising platform for information encryption, multi‐channel optical data storage, and real space encoding imaging.

High-Capacity 5G Fronthaul Networks Based on Optical Space Division Multiplexing

The introduction of 5G mobile networks, bringing multi-Gbit/s user data rates and reduced latency, opens new opportunities for media generation, transport and distribution, as well as for new immersive media applications. The expected use of millimeter-wave carriers and the strong network densification resulting from a much reduced cell size—which enable the expected performance of 5G—pose major challenges to the fronthaul network. Space division multiplexing (SDM) in the optical domain has been suggested for ultra-high capacity fronthaul networks that naturally support different classes of fronthaul traffic and further enable the use of analog radio-over-fiber and advanced technologies, such as optical beamforming. This paper discusses the introduction of SDM with multi-core fibers in the fronthaul network as suggested by the blueSPACE project, regarding both digitized and analog radio-over-fiber fronthaul transport as well as the introduction of optical beamforming for high-capacity millimeter-wave radio access. Analog and digitized radio-over-fiber are discussed in a scenario featuring parallel fronthaul for different radio access technologies, showcasing their differences and potential when combined with SDM.

OCDMA System Using Two Code Keying Encryption Introducing a SOA Based CMUX And CDEMUX Over a WDM System

This paper introduces an Optical Code Division multiplexing (OCDMA) system using two code keying encryptions. In this paper proposed OCDMA system is designed using Semiconductor optical amplifiers (SOAs) which has nonlinear character and can implementor different logic functions. SOA based 2 × 1 Codeword Multiplexer (CMUX) is designed to multiplex the user data and a 1 × 2 Codeword DE Multiplexer (CDEMUX) to demodulate the user data. Then a multiple user access is provided using WDM system to design the whole OCDMA system. Transmission distance of 70 km is achieved with acceptable bit error rate and Q factor. Open eye diagram is also verified at the receiving end.

Fine particulate matter monitoring via a visible light communication in DCT-based optical OFDM.

An electromagnetic interference (EMI)-free wide-range indoor dust monitoring system that employs the optical orthogonal frequency-division multiplexing (OFDM)-based visible-light communication (VLC) is proposed. For the long-term transmission of dust information, VLC can be utilized even in EMI-restricted areas, such as medical centers, emergency rooms, and nursing homes. Discrete cosine transform-based optical OFDM is adopted to transmit a large amount of dust information. For robust light detection from eliminate ambient light and low-frequency noise, an average voltage-tracking technique is utilized and as a result LED illumination is detected over 18 m distance with reliable error rate. Wide-range dust information from multiple dust sensors are clearly displayed through the designed user interface. Users can then monitor the air quality in real-time, improving the environmental awareness of individuals.

MEMS tunable SOI waveguide Bragg grating filter with 1.3 THz tuning range for C-band 100 GHz DWDM optical network

A MEMS tunable integrated waveguide Bragg grating-based filter for C-band optical dense wavelength-division multiplexing (DWDM) network is presented and analyzed in this work. Waveguide Bragg grating being a notch filter in the transmission spectrum is used to realize a tunable filter by varying the applied voltages to the fixed–fixed beam loaded with this grating. The strain across the grating is enhanced by choosing MEMS beam configuration such that the metal electrode is the bottom-most layer of the composite fixed–fixed beam. Device dimensions are chosen to achieve a narrow full width half maximum of 0.77 nm, allowing filtering of adjacent channels of 100 GHz DWDM network. A large Bragg wavelength shift of 10.4 nm (1552.52–1562.92 nm) was achieved at 45.8 V actuation providing tuning for 14 DWDM channels with inter-channel cross talk below − 21 dB, with tuning range of 1.3 THz.

Performance analysis of 2D-OCDMA system in long-reach passive optical network

In this paper, a performance analysis is reported for optical code division multiplexing (OCDM) system for long-reach passive optical network (LR-PON) systems by taking into account multiple access interference (MAI), single-mode fiber (SMF) channel effects and receiver noise. The mathematical model representing the 2-D optical code parameters for different receiver structures used in optical code division multiplexing access (OCDMA) are developed, optimized and implemented using Matlab simulations, where channel imperfections, such as attenuation losses and chromatic dispersion have been considered. In the proposed system configuration, we have investigated the probability of error for Back-to-Back (B2B) with conventional correlation receiver (CCR), SMF with CCR receiver and SMF channel with successive interference cancelation (SIC) receiver. Additionally, SMF channel with SIC receiver system performance has been addressed by taking into account two key metrics, such as BER and Q-factor as function of simultaneous users, and fiber length, respectively. We have managed to substantially improve simultaneous multiuser data transmission over significant fiber lengths without use of amplification, where Q-factor of 6 at fiber length of 190 and 120 km, while a SIC receiver using 5 stages cancelation is employed for 2D prime hop system (2D-PHS) and for 2D hybrid codes (2D-HC), respectively.

Improved Optical Multiplexing with Temporal DNA Barcodes.

Many biochemical events of importance are complex and dynamic. Fluorescence microscopy offers a versatile solution to study the dynamics of biology at the mesoscale. An important challenge in the field is the simultaneous study of several objects of interest, referred to as optical multiplexing. For improved multiplexing, some prior techniques used repeated reporter washing or the geometry of nanostructures; however, these techniques require complex nanostructure assembly, multiple reporters, or advanced multistep drift correction. Here we propose a time-based approach, for improved optical multiplexing, that uses readily available inexpensive reporters and requires minimal preparation efforts. We program short DNA strands, referred hereby as DNA devices, such that they undergo unique conformation changes in the presence of the dye-labeled reporters. The universal fluorescent reporter transiently binds with the devices to report their activity. Since each device is programmed to exhibit different hybridization kinetics, their fluorescent time trace, referred to as the temporal barcode, will be unique. We model our devices using continuous-time Markov chains and use stochastic simulation algorithm to generate their temporal patterns. We first ran simulation experiments with a small number of DNA devices, demonstrating several distinct temporal barcodes, all of which use a single dye color. Later, using nanostructure-based devices, we designed a much larger pool of temporal barcodes and used machine learning for classification of these barcodes. Our simulation experiments and design principles can aid in the experimental demonstration of the DNA devices.

Impairment Aware Routing, Bit Loading, and Spectrum Allocation in Elastic Optical Networks

The exponential growth of Internet traffic due to bandwidth hungry applications has led to the design of spectrum efficient, flexible, and scalable elastic optical networks. The scope of high spectral-efficient modulation formats and optical orthogonal frequency-division multiplexing (OFDM) in coherent optical communication systems appears to be significant in catering to the heterogeneous bandwidth demands. Furthermore, OFDM enables each subcarrier to be modulated independently to enhance the spectrum efficiency known as bit loading in OFDM. On the other hand, spectral efficiency and the optical reach of a signal are limited by the transmission impairments such as shot noise, amplified spontaneous emission noise, beat noises due to coherent detection, crosstalk in cross-connect, nonlinear and filter narrowing effects, etc. In this paper, we propose a novel impairment-aware routing, bit loading, and spectrum allocation scheme through a mixed-integer linear programming optimization framework. Within our optimization framework, we ensure that a minimum end-to-end bit error rate for each demand is provisioned in the presence of impairments. We also propose a novel heuristic for realistic networks and compare the performance with existing schemes. Through simulation, we demonstrate the benefits of our approach in terms of achieving lower blocking probability and the spectral fragmentation compared to other existing studies.

Increased Performance of Single-Channel Analog Photonic Links Enabled by Optical Wavelength-Division Multiplexing

Laser-intensity noise often sets the limitation to the performance of an analog photonic link. In particular, optimization of the all-important noise figure requires reduction of the laser’s relative-intensity noise (RIN) in the spectral band of interest. In this paper, we build on earlier work and analyze an approach for RIN reduction using multiple wavelengths. We extend the analysis and calculate all the important link parameters with no assumptions on modulator bias, RIN spectra, or signal power strength. We then impose constraints that conform with various practical situations and we calculate the performance tradeoffs among the three link parameters: 1) direct current photocurrent; 2) number of wavelengths; and 3) ratio of RIN-to-non-RIN noise. An experiment was performed with five lasers, and the results are in excellent agreement with theory.

Comparison of Optical OFDM and M-PAM for LED-Based Communication Systems

Light-emitting diode (LED)-based communications, such as visible light communications and infrared communications, are candidate techniques to provide short-range and high-speed data transmission. In this letter, $M$ -ary pulse amplitude modulation (M-PAM), used as a high bandwidth efficiency scheme, is compared with three well-known optical orthogonal frequency-division multiplexing (OFDM) schemes. Considering the bandwidth limit and constrained peak transmitted power characteristics of LEDs, a bit loading algorithm and a single-tap equalizer with an optimized modulation index are used for the optical OFDM schemes tested. To reduce the inter-symbol interference caused by the bandlimited channel, an optimized pulse shape and a minimum mean squared error equalizer are applied to the M-PAM system. From numerical results, M-PAM can provide a substantially higher data rate than OFDM for bandlimited channels. When the channel bandwidth is ample compared with the symbol rate, optical OFDM outperforms M-PAM.

Dynamic evolving neural fuzzy inference system equalization scheme in mode division multiplexer for optical fiber transmission

The performance of optical mode division multiplexer (MDM) is affected by inter-symbol interference (ISI), which arises from higher-order mode coupling and modal dispersion in multimode fiber (MMF). Existing equalization algorithms in MDM can mitigate linear channel impairments, but cannot tackle nonlinear channel impairments accurately. Therefore, mitigating the noise in the received signal of MDM in the presence of ISI to recover the transmitted signal is important issue. This paper aims at controlling the broadening of the signal from MDM and minimizing the undesirable noise among channels. A dynamic evolving neural fuzzy inference system (DENFIS) equalization scheme has been used to achieve this objective. Results illustrate that nonlinear DENFIS equalization scheme can improve the received distorted signal from an MDM with better accuracy than previous linear equalization schemes such as recursive‐least‐square (RLS) algorithm. Desirably, this effect allows faster data transmission rate in MDM. Additionally, the successful offline implementation of DENFIS equalization in MDM encourages future online implementation of DENFIS equalization in embedded optical systems.

Transmission of Higher Order Solitons Created by Optical Multiplexing

The nonlinear Fourier transform (NFT) is a promising tool to linearize the inherently nonlinear optical fiber channel. The NFT transforms a time-domain signal into the continuous and the discrete spectrum. The discrete spectrum is composed of an arbitrary number of complex valued discrete eigenvalues and their associated amplitudes. These discrete eigenvalues relate to solitons, which maintain their shape or return to it in an oscillating manner, while passing through the optical channel. Higher order solitons consisting of multiple eigenvalues are complex pulses, which are created and demodulated by sophisticated digital signal processing (DSP) leading to demanding hardware requirements. This paper shows a way to work with higher order solitons in a wavelength division multiplexing such as fashion by using optical-electrical signal processing and presents boundaries of this method. Optical-electrical signal processing decreases the required electrical and electro-optical hardware specifications substantially and enables to use a simplified DSP. The proposed creation method is subsequently employed to transmit higher order solitons consisting of five QPSK modulated eigenvalues. Furthermore, the optical-electrical processing is benchmarked against the Darboux transformation, which creates higher order solitons purely numerically. The results show that for a fifth-order soliton transmission the proposed method can significantly reduce the hardware requirements and DSP complexity.

An Integrated High-Speed Full Duplex Coherent OFDM-PON and Visible-Light Communication System

Abstract We demonstrated a full duplex hybrid passive optical network and indoor optical wireless system employing coherent optical frequency division multiplexing. To accomplish reliable transmission in passive optical networks integrated visible-light communication (VLC), yellow light-emitting diode and infrared LED is used in downstream and upstream, respectively, for intra building network. In order to support high data rate, pulse-width reduction scheme based on dispersion compensation fiber is incorporated and system successfully covered the distance of 50 km. A data stream at the rate of 30 Gb/s is transmitted for each user out of eight users. VLC-supported users are catered with the bit rate of 1.87 Gb/s over 150 cm and in order to realize a low-cost system, visible and infrared LEDs are used in downlink and uplink, respectively.

Performance Investigation of OTDM Link at 10*4 Gbps and Link Range of 348 km Using NRZ and RZ Schemes

Abstract In Optical Time Division Multiplexing (OTDM)-based systems, several optical signals with low bit rate B share the same carrier frequency and are optically multiplexed to form a composite bit stream at the higher bit rate N*B, where N denotes the number of channels multiplexed. In this paper, the analysis and investigation of the performance of OTDM link are carried out with help of simulation. In this paper, OTDM link is designed based on four channels having data rate of each channel which is equal to 10 Gbps with the use of RZ and NRZ schemes being analyzed. The proposed optical link achieved maximum transmission distance of 348 km over single mode fiber. The system operated over a distance of 348 km with bit error rate of 1.39×10−31 and Q-value of 11.60 with RZ, and bit rate of 1.47×10−24 and Q-value of 10.13 with NRZ respectively. The results shows that the proposed link performance is better optimized using RZ modulation scheme in comparison to NRZ scheme. This simulation work is done in optisystem 7.0. Further in this proposed OTDM link the comparison of the link performance is also analyzed using different pulse shapes for RZ and NRZ. The results being presented in this paper are significantly taken at transmitted power of 0 dBm and 2 dBm.

Adaptive modulation scheme for DML-based IM/DD FOFDM systems using overlap frequency-domain equalization

Abstract To further investigate the optical fast orthogonal frequency-division multiplexing (FOFDM) with sub-channel spacing equal to half of the symbol rate, an adaptive modulation scheme for FOFDM is proposed and experimentally demonstrated in low-cost short-reach intensity-modulated and direct-detection (IM/DD) systems using a directed modulated distributed feedback laser (DML). The experimental results and analyses indicate, it is feasible to transmit an adaptively modulated optical FOFDM signal over 20-km and 50-km standard single mode fibers (SSMFs). Compared with a single modulation format of 16-PAM, after 20-km SSMF transmission, the receiver sensitivity of the adaptive modulation scheme can be improved by about 2.3 dB at the bit error ratio (BER) of 2.4 × 10−2. Moreover, after 50-km SSMF transmission, the adaptive modulation scheme can still under 2.4 × 10−2 when received optical power (ROP) is larger than −1 dBm, while the 16-PAM modulation scheme cannot. In addition, an overlap frequency-domain equalization (OFDE) scheme is employed after sub-carrier de-multiplexing at the receiver to enable the effects of inter-symbol interference (ISI) to be effectively suppressed even though a cyclic prefix (CP) is not employed. Experimental results show that the FOFDM systems employing OFDE scheme have almost no performance degradation when compared to employing conventional FDE with an additional CP, but the spectral efficiency (SE) can be significantly improved by 12.37%.

Polarization de-multiplexing using a modified Kalman filter in CO-OFDM transmissions

We propose the modified Kalman filter (MKF) using the received signal for observation and constructing an inverse process of the conventional Kalman filter (CKF) for polarization de-multiplexing in coherent optical (CO) orthogonal frequency-division multiplexing (OFDM) transmissions. The MKF can avoid the convergence error problem in CKF without matrix inverse operation and has a faster converging speed and a much larger tolerance to the process and measurement noise covariance, about two orders of magnitude more than those of CKF. We experimentally demonstrate the 12 Gbaud OFDM signal transmission over 480 km standard single-mode fiber. The performance of MKF and CKF outperforms pilot-aided polarization de-multiplexing with better accuracy and nonlinearity tolerance.