Fiber Transmission Distance Research Articles

Simplified adaptive polarization controller controlled by an alpha-beta filter for the self-coherent communication system.

An adaptive polarization controller (APC) is crucial in mitigating carrier fading in a self-homodyne coherent detection (SHCD) system. In this paper, we propose a simplified APC design based on the X-cut, Y-propagating lithium niobate platform. Meanwhile, the alpha-beta filter is used to control the designed APC. The designed APC only needs one phase shifter to perform reset-free polarization stabilization. At the same time, it is the first time the alpha-beta filter has been used in the polarization control area. The results demonstrate that the alpha-beta filter outperforms the traditional greedy linear descent (GLD) algorithm in terms of both tracking limit and stability. Over a fiber transmission distance of 10 km, the designed APC enables the system to withstand a rotation of the state of polarization (RSOP) of 100 krad/s while maintaining a bit error rate (BER) below the forward error correction (FEC) threshold.

Frequency-octupled millimeter-wave ROF system without bit walk-off effect by polarization modulators

A novel, to the best of our knowledge, frequency-octupled millimeter-wave (MMW) radio over fiber (ROF) system without bit walk-off effect, based on two polarization modulators (PoIM) connected in parallel, is proposed. At the central station, the downlink data signal is split into two beams; one beam modulates the radio frequency (RF) carrier through an electrical phase modulator (PM), the other beam is amplified by an electrical amplifier (EA), and the two beams are combined into one, which is used as the RF driving signal of the PoIM. By adjusting the modulation index of the PoIMs, the phase shift of the phase shifter, and the polarization angle of the polarizer (Pol), the main components of the output signal from the PoIMs are ±4th-order sidebands. By adjusting the phase modulation index of the PM and the amplification of the EA, the downlink data signal is modulated only on the +4th-order sideband. At the base station, a part of the −4th-order sidebands are reflected by a fiber Bragg grating (FBG) and used as the optical carrier for uplink for carrier reuse; the ±4th-order sidebands passing the FBG are injected into the photodetector (PD) for photoelectrical conversion, and the frequency-octupled MMW with the downlink data signal is generated. The main innovation of the scheme proposed in this paper is that the data of the uplink and the downlink is modulated on ±4th-order sidebands separately, which eliminates the periodic fading effect and bit walk-off effect due to fiber dispersion and greatly improves the fiber transmission distance of the system, and also avoids the problems of DC bias drift and extinction ratio limitation of the Mach–Zehnder modulator.

A novel frequency 32-tupling ROF system without bit walk-off effect based on MZM with inserting pilot

A novel scheme for a frequency 32-tupling millimeter wave (MMW) radio over fiber(ROF) system without the bit walk-off effect is proposed. The operation principle and feasibility of our proposed scheme are theoretically analyzed and verified with simulation experiments. The main part of our scheme is a ±16th order sidebands generator (SG) which is constructed by eight Mach-Zehnder modulators (MZM) connected in parallel. In the back-to-back(BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±16th order sidebands are generated by the SG. In the data transmission case, the data signal is split into two beams first, one of which modulates the RF drive signal with an electrical phase modulator (PM), and the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can be modulated only to the +16th order sideband of the output of the SG. The optical carrier from the CW laser is split into two paths, one is sent into the SG, and the other is used as a pilot. The output signal of SG is combined with the pilot signal and is transmitted to the base station(BS) via optical fiber. In BS, the pilot signal is filtered out by an FBG and used as the carrier for uplink for carrier reuse. After filtering out the pilot, the signal from the FBG which is ±16th order sidebands is injected into the photodetector, and a frequency 32-tupling MMW with downlink data is generated. The influence on the bit error rate (BER) and Q factor by the key parameters in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion, greatly increase the fiber transmission distance, but also effectively improve the performance of the downlink, it has important application prospects in ROF systems.

A Novel Inserting Pilot Radio over Fiber System without the Bit Walk-Off Effect for the Generation and Distribution of Frequency 16-Tupling Millimeter Waves by Mach–Zehnder Modulators

A novel inserting pilot scheme to generate and distribute a frequency 16-tupling millimeter wave (MMW) radio over fiber (ROF) system without the bit walk-off effect via Mach–Zehnder modulators (MZMs) is proposed. The operation principle is analyzed and the feasibility of our proposed scheme is verified by simulation test. The main part of our scheme is a ±8th-order sidebands generator (SG), which is constructed by four MZMs connected in parallel. In the back-to-back (BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±8th-order sidebands are generated by the SG. In the data transmission case, the data signal is first split into two beams, one of which modulates the RF drive signal with an electrical phase modulator (PM) while the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the composite RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can only be modulated to the +8th-order sideband of the output of the SG. The optical carrier from the continuous wave (CW) laser is split into two paths: one is sent into the SG, and the other is used as a pilot signal. The output signal of SG is combined with the pilot signal and is transmitted to the base station (BS) via optical fiber. At the BS, the pilot signal is filtered out by a fiber Bragg grating (FBG) and used as the carrier for the uplink for carrier reuse. After filtering out the pilot, the signal from the FBG, which is composed of ±8th-order sidebands, is injected into a photodetector, and a frequency 16-tupling MMW with downlink data is generated. The key parameters’ influence on the bit error rate (BER) and Q factor in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion and greatly increase the fiber transmission distance but can also effectively improve the performance and the tunability of system. Therefore, it has important application prospects in ROF systems.

Optimizing High Data Rate Up to 2.5 Tbps Transmission using 64-Channel DWDM System with DCF and NRZ Modulation

Objectives: This study aims to enhance and optimize a modern communication system for high data rate transmission using Dense Wavelength Division Multiplexing (DWDM). The objectives include employing a 64-channel DWDM system, implementing different data speeds, and utilizing a dispersion compensation method. Methods: To achieve the objectives, we simulate and analyze the effects of Dispersion Compensation Fiber (DCF) in a DWDM system with 64 channels. The system employs Non-Return-to-Zero (NRZ) modulation format at varied bit rates and multiple energy levels. We propose a method for achieving data rates of 10 to 40 Gbps using NRZ modulation and Erbium-Doped Fiber Amplifier (EDFA) over a single-mode fiber transmission distance of 40 to 160 km, along with a dispersion compensation fiber of 8 to 32 km (DCF). The performance of the developed model is evaluated based on Quality Factor, Bit Error Rate (BER), Eye Height, and Threshold. These metrics are measured at two input energy levels from an optical power source, covering a communication capacity ranging from 0.625 Tbps to 2.5 Tbps. Findings: Through the simulations and analyses, we uncover the impact of dispersion and demonstrate the effectiveness of the proposed method in compensating for dispersion effects. Performance analysis of two different input transmitter power levels, -10 dBm is more efficient compared to 0 dBm input transmitter power in terms of bit error rate and quality factor. Novelty: This study presents a novel approach to improving modern communication systems by utilizing DWDM with a dispersion compensation method. The use of a 64-channel DWDM system, combined with the proposed NRZ modulation technique and dispersion compensation fiber, provides an efficient solution for achieving high data rates over long transmission distances while minimizing the effects of dispersion. The findings contribute to the advancement of communication systems for high data rate transmission. Keywords Dispersion effect, Bit Error Rate, Q-factor, Optisystem software, Erbium doped fiber amplifier

Design of A Chaos-based Digital Radio over Fiber Transmission Link using ASK Modulation for Wireless Communication Systems

Secured broadband radio communications are becoming increasingly pivotal for high-speed connectivity in radio access networks, playing a crucial role in both mobile information systems and wireless IoT connections. This paper introduces a chaos-based two-channel digital radio communication system utilizing fiber optic radio transmission technology. The system comprises two radio channels operating at up to 1 Gbps using amplitude shift keying (ASK) modulation, followed by modulation with a chaotic sequence before conversion to the optical domain using the MZM modulator. To compensate for fiber loss, the system utilizes an Erbium Doped Fiber Amplifier (EDFA) and employs the optical links through standard ITU-G.655 optical fibers. Numerical simulation of the designed system is performed using the commercialized simulation software Optisystem V.15 to assess and characterize transmission performance. The results demonstrate the system’s effective operation on two channels with a fiber transmission distance of up to 110 km, maintaining a bit error ratio of less than 10−9. This feature ensures reliable performance for high-speed radio connections, particularly in applications such as fronthaul networks in cloud radio access and wireless sensor network connections.

Multifrequency Vector Mm-Wave Signal Generation with No Optical Filtering Based on One Dual-Arm MZM with Phase Factor Optimization

In order to reduce the number of devices in and cost of a multifrequency vector millimeter-wave (mm-wave) signal generation system, we propose a novel scheme for multifrequency vector mm-wave signal generation based on one dual-arm Mach-Zehnder modulator (MZM) without optical filtering. This scheme utilizes the carrier suppression modulation of a single modulator, without the need for optical filtering and combines precoding technology to generate high-frequency QPSK and 16 QAM mm-wave signals. The transmitter is applied with precoding technology to make the frequency multiplying vector mm-wave signal display regular vector modulation at the receiver, and the system is optimized with a phase factor to ensure that the phase distribution of QPSK signal at the receiver is symmetrical. We demonstrated the generation of 4-Gbaud 76 GHz QPSK and 16 QAM vector mm-wave signals through simulation. The simulation results show that, at a fiber transmission distance of 12 km, when the launched optical power of the PD is greater than −20.535 dBm, the bit error ratio (BER) of the QPSK signal is lower than the hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10−3. At a fiber transmission distance of 10 km, when the launched optical power of the PD is greater than −18.637 dBm, the BER of 16 QAM signal is also lower than 3.8 × 10−3.

Dual-Channel Secure Communication Based on Wideband Optical Chaos in Semiconductor Lasers Subject to Intensity Modulation Optical Injection

Chaotic optical communication was initially proposed to provide advanced physical layer security for optical communication. Here, we propose and numerically demonstrate an optical chaos communication scheme based on semiconductor lasers subject to intensity modulation optical injection for secure transmission of quadrature amplitude modulation (QAM) messages. In this scheme, two chaotic sources were generated with different modulation parameters and acted as chaotic carriers at the transmitter side, which were subsequently used to drive two receivers in two separate channels. Numerical results demonstrate that this scheme allows for broadband chaos generation and high-quality chaos synchronization can be achieved to simultaneously encrypt two messages for secure communication; a 20 GBaud 16-QAM message was recovered correctly with a transmission distance in standard single mode fiber (SMF) over 120-km, while the other 20 GBaud 64-QAM message was limited to a 20-km fiber transmission distance. The system performance was systematically evaluated by analyzing the bit error ratio (BER) of the recovered message versus the masking coefficient and the transmission distance. Furthermore, our simulations justify the robustness against the mismatch of parameters. Therefore, we hope that this scheme can be experimentally implemented for high-speed chaos communication and secure key distribution.

Deep intelligent spectral labelling and receiver signal distribution for optical links.

A unique automatic receiver signal distribution strategy is proposed for private optical networks based on the concept of non-orthogonality. A non-orthogonal signal waveform can compress the spectral bandwidth, which not only fits a signal in a bandwidth limited scenario, but also enables the compression ratio information for labelling. Depending on a unique value of spectral compression, an end user destination can be correlated. A network edge node will rely on deep learning to intelligently identify each raw signal and forward it to corresponding end users with no sophisticated digital signal pre-processing. In this case, signal identification and distribution are faster while computationally intensive signal compensation and detection will be shifted to each end user since the receiver is highly dynamic and user-defined in private optical networks. An intelligent signal classifier will be trained considering various fiber transmission factors such as transmission distance, training dataset size and launch power. At the end, a universal classifier is obtained, which can be used to identify signals in a system for any fiber transmission distance and launch power.

Impact of fiber dispersion on the performance of entanglement-based dispersive optics quantum key distribution

Dispersive optics quantum key distribution (DO-QKD) based on energy-time entangled photon pairs is an important QKD scheme. In DO-QKD, the arrival time of photons is used in key generation and security analysis, which would be greatly affected by fiber dispersion. In this work, we established a theoretical model of the entanglement-based DO-QKD system, considering the protocol, physical processes (such as fiber transmission and single-photon detection), and the analysis of security tests. Based on this theoretical model, we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD. By analyzing the benefits and costs of dispersion compensation, the system performance under G.652 and G.655 optical fibers are shown, respectively. The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks. Whereas, it is still required in DO-QKD systems with longer fiber transmission distances.

Adaptive weighted 61‐QAM based on geometric shaping in coherent optical communication utilizing K‐Means algorithm

AbstractA novel adaptive weighted geometric‐shaped (GS) 61 quadrature amplitude modulation (QAM) constellation is proposed in order to mitigate the nonlinear damage and increase the transmission distance. By introducing an adaptive weighting factor related to Kerr effect and fiber transmission distance in concentric regular hexagon constellation, the overlapping problem of the outer constellation points induced by nonlinear damage was reduced. The simulation results show that the proposed GS‐61QAM outperformed uniform 64QAM and has more obvious advantages in long‐haul optical transmission system. For a 120‐Gb/s coherent optical communication system, compared with uniform 64QAM, the proposed algorithm can obtain about 4.1 dB optical signal‐to‐noise (OSNR) gain at the BER of 10−2. Moreover, in order to further improve the system tolerance of nonlinearity, a scheme of adaptive weighted GS‐61QAM in coherent optical communication system utilizing K‐Means algorithm is proposed, the proposed scheme outperforms the traditional uniform 64QAM communication system by 5 dB in OSNR at the BER of 10−2.

PERFORMANCE EVALUATION OF RADIO OVER FIBER SYSTEM BY EMPLOYING OPTICAL AMPLIFIERS EDFA AND SOA

As per the centralized operations in a radio over fiber (RoF) system, the transmission distance can be increased between the control station and base station. The transferring of the optical signal over large distances results in transmission loss, such as attenuation, fiber tap, fiber splice, etc., which cannot be ignored after a 5 km optical fiber distance, because the transmission losses result in the degradation of signal quality at the receiver end. This creates the need for optical amplifiers to amplify the light signal. The optical amplifiers further enhance the transfer speeds and quantity of transferred data. This paper analyzes the performance of a RoF system by employing optical amplifiers, such as an erbium doped fiber amplifier (EDFA) and a semiconductor optical amplifier (SOA) over different fiber distance. The outcomes and features of an EDFA- and a SOA-based RoF system are also discussed. Finally, the comparative analysis is found by proposed model simulation in OptSIM software. The rapid increment in the undesired nonlinear terms are found over a fiber distance from 5 to 10 km by EDFA- and SOA-based RoF systems, and the obtained results play an important role for maintaining signal quality over fiber transmission distance.

Optical Signal Processing for W-Band Radio-Over-Fiber System With Tunable Frequency Response

Tunable frequency response is designed and experimentally demonstrated in this paper. The performance of frequency response in proposed radio-over-fiber (RoF) systems is investigated in terms of theoretical analysis, simulations, and experimental results with various fiber transmission distances. The notch in frequency response can be easily circumvented by changing the oriented angle of polarized lightwave in the proposed direct detection (DD) scheme. For comparison, the conventional Mach-Zehnder modulator (MZM) based DD scheme suffers from fixed frequency notch at certain frequencies, which generates forbidden frequency bands for W-band signal delivery. Our experimental results show that the proposed DD scheme exhibits a stable EVM performance of the 16-QAM signal from 83 GHz to 87 GHz via 25-km standard single-mode fiber (SSMF) and 1-m wireless transmission. On the contrary, the conventional MZM-based DD scheme encounters severe signal degradation at 85 GHz and 86 GHz. In this paper, the proposed scheme is implemented to demonstrate full bandwidth availability within a desirable frequency range by tuning the frequency response. Furthermore, a 10-Gbps 16-QAM signal located at 85 GHz is successfully transmitted by the proposed DD scheme which can provide 10-gigabit data transmission under 5G requirement.

A modulation format identification method based signal amplitude sorting and ratio calculation

Modulation format identification (MFI) is an indispensable part of next generation optical networks such as elastic optical networks (EON). We propose a simple MFI method based on signal amplitude sorting and ratio calculation. After sorting the amplitude of signals, three MFI feature values are extracted to identify polarization division multiplexing (PDM) quadrature phase shift keying (PDM-QPSK) and three commonly used quadrature amplitude modulation (QAM) signals (PDM-16QAM, PDM-32QAM and PDM-64QAM). Numerical simulations verify the effectiveness of proposed MFI method with the required optical signal noise ratio (OSNR) lower than 7% forward error correction (FEC) threshold. Proof-of-concept experiments using QPSK, 16QAM, 32QAM and 64QAM signals with 100 km fiber transmission demonstrate the feasibility of proposed MFI method. We also investigate the influence of fiber transmission distance, fiber nonlinearity and symbol numbers on the proposed method and the results show that the proposed MFI methods can achieve accurate identification at different fiber transmission length, a range of fiber nonlinearity and small requirement of symbol number. The method is simple and insensitive to phase impairments caused by laser phase noise and frequency offset (FO), which will bring convenience into future EONs.

Wideband and Dispersion Immune Microwave Photonic Phase Shifter With Tunable Optical Carrier to Sideband Ratio

A wideband microwave photonic phase shifter (MPPS) based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) is proposed and experimentally demonstrated. The proposed system has the features of chromatic dispersion (CD) immunity and tunable optical carrier to sideband ratio (OCSR), which can realize long fiber transmission distance with improved power efficiency. It is realized by carrier suppress double sideband (CS-DSB) plus optical carrier (OC) modulation at two orthogonal polarization states. The phases of output RF signals can be tuned continuously and independently by controlling the phases of the OCs. The experiment results show that the continuous 360° phase shifts of output RF signal over 5–25 GHz are both realized in the cases of back-to-back and fiber transmission. No CD-induced power fading and phase severe shaking of the RF signals appear after the dispersion compensating fiber (DCF) of −331 ps/nm at 1545 nm transmission. By optimizing the OCSR of the system, the output RF power efficiency of the proposed scheme realizes significantly improvement when input RF powers and output optical powers are both fixed. The possibility of generating frequency doubling signal is also verified.

Computational complexity comparison of feedforward/radial basis function/recurrent neural network-based equalizer for a 50-Gb/s PAM4 direct-detection optical link.

The computational complexity and system bit-error-rate (BER) performance of four types of neural-network-based nonlinear equalizers are analyzed for a 50-Gb/s pulse amplitude modulation (PAM)-4 direct-detection (DD) optical link. The four types are feedforward neural networks (F-NN), radial basis function neural networks (RBF-NN), auto-regressive recurrent neural networks (AR-RNN) and layer-recurrent neural networks (L-RNN). Numerical results show that, for a fixed BER threshold, the AR-RNN-based equalizers have the lowest computational complexity. Amongst all the nonlinear NN-based equalizers with the same number of inputs and hidden neurons, F-NN-based equalizers have the lowest computational complexity while the AR-RNN-based equalizers exhibit the best BER performance. Compared with F-NN or RNN, RBF-NN tends to require more hidden neurons with the increase of the number of inputs, making it not suitable for long fiber transmission distance. We also demonstrate that only a few tens of multiplications per symbol are needed for NN-based equalizers to guarantee a good BER performance. This relatively low computational complexity signifies that various NN-based equalizers can be potentially implemented in real time. More broadly, this paper provides guidelines for selecting a suitable NN-based equalizer based on BER and computational complexity requirements.

Extreme Learning Machines to Combat Phase Noise in RoF-OFDM Schemes

Radio-over-fiber (RoF) orthogonal frequency division multiplexing (OFDM) systems have been revealed as the solution to support secure, cost-effective, and high-capacity wireless access for the future telecommunication systems. Unfortunately, the bandwidth-distance product in these schemes is mainly limited by phase noise that comes from the laser linewidth, as well as the chromatic fiber dispersion. On the other hand, the single-hidden layer feedforward neural network subject to the extreme learning machine (ELM) algorithm has been widely studied in regression and classification problems for different research fields, because of its good generalization performance and extremely fast learning speed. In this work, ELMs in the real and complex domains for direct-detection OFDM-based RoF schemes are proposed for the first time. These artificial neural networks are based on the use of pilot subcarriers as training samples and data subcarriers as testing samples, and consequently, their learning stages occur in real-time without decreasing the effective transmission rate. Regarding the feasible pilot-assisted equalization method, the effectiveness and simplicity of the ELM algorithm in the complex domain are highlighted by evaluation of a QPSK-OFDM signal over an additive white Gaussian noise channel at diverse laser linewidths and chromatic fiber dispersion effects and taking into account several OFDM symbol periods. Considering diverse relationships between the fiber transmission distance and the radio frequency (for practical design purposes) and the duration of a single OFDM symbol equal to 64 ns, the fully-complex ELM followed by the real ELM outperform the pilot-based correction channel in terms of the system performance tolerance against the signal-to-noise ratio and the laser linewidth.

PAM-4 Transmission at 1550 nm Using Photonic Reservoir Computing Post-Processing

The efficacy of data decoding in contemporary ultrafast fiber transmission systems is greatly determined by the capabilities of the signal processing tools that are used. The received signal must not exceed a certain level of complexity, beyond which the applied signal processing solutions become insufficient or slow. Moreover, the required signal-to-noise ratio of the received signal can be challenging, especially when adopting modulation formats with multi-level encoding. Lately, photonic reservoir computing (RC) - a hardware machine learning technique with recurrent connectivity - has been proposed as a post-processing tool that deals with deterministic distortions from fiber transmission. Here we show that RC post-processing is remarkably efficient for multilevel encoding and for the use of very high launched optical peak power for fiber transmission up to 14dBm. Higher power levels provide the desired high signal-to-noise ratio (SNR) values at the receiver end, at the expense of a complex nonlinear transformation of the transmission signal. Our demonstration evaluates a direct fiber communication link with 4-level pulse amplitude modulation (PAM-4) encoding and direct detection, without including optical amplification, dispersion compensation, pulse shaping or other digital signal processing (DSP) techniques. By applying RC post-processing on the distorted signal, we numerically estimate fiber transmission distances of 27km at 56Gb/s and of 5.5 km at 112Gb/s data encoding rates, while fulfilling the hard-decision forward error correction (HD-FEC) bit-error-rate (BER) limit for data recovery. In an experimental equivalent demonstration of our photonic reservoir, the achieved distances are 21km and 4.6km respectively.

Adaptive millimeter-wave radio generation and transmission of phase shift-keying signal based on radio over fiber system

A scheme to realize the flexible photonic frequency multiplication at millimeter-wave (mm-wave) and radio over fiber (RoF) transmission has been proposed and demonstrated. To enable the generated multiple-frequency signal to have a better performance of phase preserving, we theoretically investigated the phase change during the generation and transmission and proposed an adaptive coding algorithm to reduce the impact of phase fluctuation. The coding algorithm brings the frequency multiplication and fiber transmission distance together into consideration and adjusts the phase of the signal consequently. Due to the proposed coding algorithm, the system not only realizes the flexible frequency multiplication but also eliminates the phase deviation induced by the modulation and fiber dispersion, which effectively increases the transmission distance of fiber link. In addition, it also reduces the complexity of phase retrieval at receiver side. A 50-GHz to 100-GHz RoF system with 1 Gbit / s radio signal has been implemented by numerical simulation, and the result shows that the adaptive mm-wave RoF system could realize arbitrary multiple-frequency of quadrature phase shift-keying signal from double to decuple and reliable transmission of the tenfold signal at least 50 km.

Smart architecture for stable multipoint fiber Bragg grating sensor system

In this work, we propose and investigate an intelligent fiber Bragg grating (FBG)-based sensor system in which the proposed stabilized and wavelength-tunable single-longitudinal-mode erbium-doped fiber laser can improve the sensing accuracy of wavelength-division-multiplexing multiple FBG sensors in a longer fiber transmission distance. Moreover, we also demonstrate the proposed sensor architecture to enhance the FBG capacity for sensing strain and temperature, simultaneously.