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We present a numerical study on efficient mid-infrared Raman soliton generation in a tellurite microstructured optical fiber with femtosecond Tm-doped fiber laser pulses as the pump source. A tunable soliton exhibits a wavelength shift of up to 3.54 µm and a power conversion efficiency of up to 74.2% while consuming a pump peak power of no more than 1 kW at 1.96 µm, owing to the proper design of the dispersion and nonlinearity of the tellurite fiber. We investigated the effects of pump parameters on soliton properties and found that adjusting the pump pulse duration allows for a broader tuning range of up to 3.63 µm or a higher conversion efficiency of 94.5%. The study describes an effective means of constructing compact and efficient femtosecond tunable mid-infrared laser sources with low operation power, which will boost potential applications in the important region of above 2 µm. [ABSTRACT FROM AUTHOR]

We present a random Raman fiber laser pumped by a continuous-wave 1480 nm source. The backward pumping feedback loop allows a single direction of 1584 nm wave propagation under tighter confinement of dispersion compensating fiber (DCF). This geometry that implies a stronger Kerr-lensing effect supports two types of nonlinear broadening that were achieved in the stable output power generation. The first that agrees well to wave kinetics theory favors 1.76–3.37 nm spectral progress. Against this flow, another type of wider broadening begun at 4.88 nm before reducing gradually to 4.05 nm with the increase in pump power. The former corresponds to a maximum of 6.3 times broadening ratio with respect to the pump linewidth. In contrast without the tighter confinement geometry, fluctuations in the nonlinearity growth from 1.58 to 3.53 nm bandwidth was realized. These ascertain the double roles of DCF as a stabilizing factor as well as for dispersion management. [ABSTRACT FROM AUTHOR]

Recent research in Phase-Sensitive Optical Time Doman Reflectometry (ϕ-OTDR) has been focused, among others, on performing spatially resolved measurements with various methods including the use of frequency modulated probes. However, conventional schemes either rely on phase-coded sequences, involve inflexible generation of the probe frequency modulation or mostly employ simple linear frequency modulated (LFM) pulses which suffer from elevated sidelobes introducing degradation in range resolution. In this contribution, we propose and experimentally demonstrate a novel ϕ-OTDR scheme which employs a readily adaptable Direct Digital Synthesis (DDS) of pulses with custom frequency modulation formats and demonstrate advanced optical pulse compression with a nonlinear frequency modulated (NLFM) waveform containing a complex, rigorously defined modulation law optimized for bandwidth-limited synthesis and sidelobe suppression. The proposed method offers high fidelity chirped waveforms, and when employed in resolving a 50-cm event at ∼1.13 km using a 1.2-µs probe pulse, matched filtering with the DDS-generated NLFM waveform results in a significant reduction in range ambiguity owing to autocorrelation sidelobe suppression of ∼20 dB with no averages and windowing functions, for an improvement of ∼16 dB compared to conventional linear chirping. Experimental results also show that the contribution of autocorrelation sidelobes to the power in the compressed backscattering responses around localized events is suppressed by up to ∼18 dB when advanced pulse compression with an optical NLFM pulse is employed.

We review recent advances in distributed fiber optic sensing (DFOS) and their applications. The scattering mechanisms in glass, which are exploited for reflectometry-based DFOS, are Rayleigh, Brillouin, and Raman scatterings. These are sensitive to either strain and/or temperature, allowing optical fiber cables to monitor their ambient environment in addition to their conventional role as a medium for telecommunications. Recently, DFOS leveraged technologies developed for telecommunications, such as coherent detection, digital signal processing, coding, and spatial/frequency diversity, to achieve improved performance in terms of measurand resolution, reach, spatial resolution, and bandwidth. We review the theory and architecture of commonly used DFOS methods. We provide recent experimental and field trial results where DFOS was used in wide-ranging applications, such as geohazard monitoring, seismic monitoring, traffic monitoring, and infrastructure health monitoring. Events of interest often have unique signatures either in the spatial, temporal, frequency, or wavenumber domains. Based on the temperature and strain raw data obtained from DFOS, downstream postprocessing allows the detection, classification, and localization of events. Combining DFOS with machine learning methods, it is possible to realize complete sensor systems that are compact, low cost, and can operate in harsh environments and difficult-to-access locations, facilitating increased public safety and smarter cities. [ABSTRACT FROM AUTHOR]

Since its early commercial deployment in the late 1980s, optical fiber has evolved to become the predominant carrier of the globe’s communications. Yet, after accommodating the world’s exponentially growing appetite for transmitted data for more than three decades, its ability to continue doing so is being challenged by fundamental factors. In this article, we review these factors and examine their consequences in terms of information capacity. In particular, we review the difficulties that are imposed by the nonlinear nature of fiber-optic transmission on the assessment of the capacity and on the definition of fundamental concepts, such as bandwidth and spectral efficiency. We discuss relevant approximations and regimes of operation in which bounds for the capacity can be effectively assessed while covering a broad range of applications ranging from interdatacenter communications to links spanning transoceanic distances. We relate to a broad variety of transmission schemes and discuss the potential benefits of spatial multiplexing with multimode and multicore fibers. State-of-the-art transmission experiments are also reviewed and compared with theoretical capacity bounds. [ABSTRACT FROM AUTHOR]

Randomly-coupled multi-core fiber (MCF) technology has come to attract lots of attention because of its strong applicability to long-haul transmission systems. Compared with weakly-coupled MCFs with independent cores, it can simultaneously realize higher spatial channel density and ultralow transmission loss using existing ultralow-loss single-mode fiber (SMF) core designs. The strong mode coupling characteristics of randomly-coupled MCFs can provide favorable optical properties, such as suppressed accumulation of modal dispersion (MD), mode-dependent loss (MDL), and nonlinear impairments. This article gives an overview of randomly-coupled MCF technology advancements. First, we describe the classification and design of randomly-coupled MCFs and explain what the randomly-coupled MCFs are and how they are designed. State-of-the-art randomly-coupled MCFs can accommodate four, seven, or 12 cores in a standard 125- $\mu \text{m}$ cladding while achieving ultralow transmission loss and/or small MD, which are very promising for long-haul transmission media. Next, we present the methods to characterize the optical properties of randomly-coupled MCFs and the difference compared to conventional SMF measurements. We also show the low-loss low-MDL connectivity of this type of MCF and the cabling that can suppress MD. A field-deployed randomly-coupled MCF cable testbed is also presented, which confirmed the favorable optical properties of randomly-coupled MCFs after deployment. Then, multi-core amplifier technologies are briefly summarized, and finally, we discuss the performance improvements in the transmissions over randomly-coupled MCFs and suitable application areas. [ABSTRACT FROM AUTHOR]

We study the robustness of a nonlinear frequency-division multiplexing (NFDM) system, based on the Zakharov-Shabat spectral problem (ZSSP), that is comprised of two independent quadrature phase-shift keyed (QPSK) channels modulated in the discrete spectrum associated with two distinct eigenvalues. Among the many fiber impairments that may limit this system, we focus on determining the limits due to third-order dispersion, the Raman effect, amplified spontaneous emission (ASE) noise from erbium-doped fiber amplifiers (EDFAs), and fiber losses with lumped gain from EDFAs. We examine the impact of these impairments on a 1600-km system by analyzing the Q-factor calculated from the error vector magnitude (EVM) of the received symbols. We found that the maximum launch power due to these impairments is: 13 dBm due to third-order dispersion, 11 dBm due to the Raman effect, 3 dBm due to fiber losses with lumped gain, and 2 dBm due to these three impairments combined with ASE noise. The maximum launch power due to all these impairments combined is comparable to that of a conventional wavelength-division multiplexing (WDM) system, even though WDM systems can operate over a much larger bandwidth and, consequently, have a much higher data throughput when compared with NFDM systems. We find that fiber losses in practical fiber transmission systems with lumped gain from EDFAs is the most stringent limiting factor in the performance of this NFDM system. [ABSTRACT FROM AUTHOR]

We report on a Q-switched Er-doped all-fiber laser based on a solution-processed Ti3C2Txsaturable absorber (SA). Ti3C2Tx is transferred to the fiber core region by optical deposition process through thermal effect. The Ti3C2Tx SA is clamped between two optical fiber connectors, which is flexible to integrate into the laser oscillator. The modulation depth and saturation incident fluence are measured to be ~3% and $\sim 53.31~\mu \text{J}$ /cm2 at 1550 nm wavelength region, respectively. At a threshold pump power of 190mW, we get self-started stable Q-switched operation with single-pulse energy of 22.17 nJ and pulse duration of $\sim 7.07~\mu \text{s}$. With the pump power varing from 190 to 280 mW, the repetition frequency (RF) changes from 52.8 kHz to 62.79 kHz. The maximum average output power is 2.14 mW, which corresponds to the single-pulse energy of 34.03 nJ. The short-term stability is obtained by measuring the RF and temporal sequences of output pulse for 12 hours. Moreover, the long-term stability is demonstrated by measuring the output power and repetition rate for one week, showing the highly stable operation of the Ti3C2Tx fiber laser, for the first time as far as we know. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a high-speed vestigial sideband (VSB) probability shaping 8-ary pulse amplitude modulation (PS-PAM8) system at C-Band. The strong-coupled linear and nonlinear impairments in high-speed VSB transmission systems lead to performance degradation. Neural network-based equalization has been widely adopted in the optical transmission system. However, the effective combination of linear and nonlinear impairment compensation in NN equalization has not been discussed intensively. In this experiment, we have proposed an equalizer based on the joint neural network (JNN) to compensate for the linear and nonlinear impairments. With the proposed JNN equalizer and PS technique, 92 GBaud PS-PAM8 signals can be delivered over 10 km standard single mode fiber (SSMF). Given the forward error correction (FEC) overhead and the entropy of PS-PAM8 signals, the net bit rate can reach 207 Gbit/s/ $\lambda $ , satisfying the demand for a 200 Gbit/s/ $\lambda $ data connection. [ABSTRACT FROM AUTHOR]

Chromatic dispersion enhanced spectrum aliasing, a nonlinear effect in the frequency domain, is theoretically analyzed under symbol-rate sampling conditions, and the relationship between its nonlinear strength and chromatic dispersion is investigated in detail. To address chromatic dispersion enhanced spectrum aliasing efficiently, a hardware efficient and chromatic dispersion tolerant equalization scheme is proposed to deal with inter-symbol-interference, chromatic dispersion, chromatic dispersion enhanced spectrum aliasing and phase noise simultaneously. Compared with the conventional T/2-spaced adaptive equalizer (AEQ) and symbol-rate AEQ, the proposed scheme can deal with large accumulated chromatic dispersion in a cost-efficient manner, which is extremely attractive for ultra-high baud rate and short-reach coherent optical interconnects. The experimental results also indicate that the proposed scheme can provide more than 3 dB received optical power sensitivity improvement over symbol-rate Sim-AEQ after 20 km fiber transmission links. With 7% FEC threshold, the proposed scheme with the same tap number can provide around 250 ps/nm and 90 ps/nm chromatic dispersion tolerance improvement over symbol-rate Sim-AEQ and conventional T/2-spaced equalization schemes, respectively. Additionally, compared with T/2-spaced 2 × 2 MIMO, the proposed scheme can also save around 50% real value multiplier because of the simplified equalization structure. Consequently, the proposed scheme with high chromatic dispersion tolerance and low complexity can be considered a promising DSP solution for ultra-capacity short-reach coherent optical interconnects such as datacenter interconnects and access applications. [ABSTRACT FROM AUTHOR]

A coherent optical frequency comb with a gigahertz line spacing is important in diverse fields, such as calibration of astronomical spectrographs and wavelength division multiplexing optical communications. In this paper, we realize octave-spanning 10-GHz optical combs using a directly-modulated 1.55 μm microlaser as a seeding source. A 6.4 ps transform-limited pulse is successfully generated from the directly-modulated laser output through optimal chirp compensation in a fiber. Moreover, after amplifying by an EDFA, the optical pulse width is further reduced to 140 fs by combing the self-phase modulation effect and the anomalous group velocity dispersion in commercial fibers. Finally, a coherent optical comb spanning from 900-2400 nm is produced in a home-made fluorotellurite fiber using the 140-fs pulse boosted to a few Watts as a seeding source. The experimental results demonstrate that optical combs generated from the directly-modulated microlaser have the potential for a fully stabilized frequency comb. [ABSTRACT FROM AUTHOR]

The feasibility of coexisting a quantum channel with carrier-grade classical optical channels over Hollow Core Nested Antiresonant Nodeless Fibre (HC-NANF) is experimentally explored for the first time in terms of achievable quantum bit error rate (QBER), secret key rate (SKR) as well as classical signal bit error rates (BER). A coexistence transmission of 1.6 Tbps is achieved for the classical channels simultaneously with a quantum channel over a 2 km-long HC-NANF with a total coexistence power of 0 dBm. To find the best and worst wavelength position for the classical channels, we simulated different classical channels bands with different spacing between the quantum and classical channels considering the crosstalk generated from both Raman scattering and four-wave-mixing (FWM) on the quantum channel. Following our simulation, we numerically estimate the best (Raman spectrum dip) and worst locations (Raman spectrum peak) of the classical channel with respect to its impact on the performance on the quantum channel in terms of SKR and QBER. We further implemented a testbed to experimentally test both single-mode fibre (SMF) and HC-NANF in the best and worst-case scenarios. In the best-case scenario, the spacing between quantum and classical is 200 GHz (1.6 nm) with 50 GHz (0.4 nm) spacing between each classical channel. The SKR was preserved without any noticeable changes when coexisting the quantum channel with eight classical channels at 0 dBm total coexistence power in HC-NANF compared to a significant drop of 73% when using SMF at $-$ 24 dBm total coexistence power which is 250 times lower than the power used in HC-NANF. In the worst-case scenario using the same powers, and with 1 THz (8 nm) spacing between quantum and classical channels, the SKR dropped 10% using the HC-NANF, whereas in the SMF the SKR plummeted to zero. [ABSTRACT FROM AUTHOR]

Direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems have been proposed as a well-suited solution for cost-sensitive applications, but also for metro/regional optical links. In this article, we experimentally demonstrate tolerance enhancements of constant-envelope OFDM (CE-OFDM) signals towards Mach–Zehnder modulator (MZM) intermodulation impairments and fiber nonlinear Kerr effects. The additional tolerance is achieved by the reduced peak-to-average power ratio (PAPR) of CE-OFDM signals, unlike conventional OFDM signals that inherently possess high PAPR values and therefore, are prone to distortions induced by the above-mentioned impairments. The experiments show that the transmission of CE-OFDM signals with PAPR $=3$ dB over 1000 km of dispersion-uncompensated standard single-mode fiber (SSMF) is successfully accomplished. The proper choice of the MZM bias point, as well as the electrical phase modulation index, provides link length enlargements at the same bit error rate. An enlargement around 320 km of SSMF was achieved with an optical launch power of 10 dBm and with a guard-band of $\approx 16\%$ of the signal bandwidth when compared to conventional DDO-OFDM systems. [ABSTRACT FROM AUTHOR]

Optical carrier recovery provides a method to increase the carrier-to-signal power ratio at the receiver side of an optical communications system. Here, we propose to use optical carrier recovery based on stimulated Brillouin scattering to help overcome performance limits of Kramers-Kronig direct detection systems that arise due to the need for a high carrier-to-signal power ratio. By transmitting a low power pilot tone along with the signal, we simplify the stimulated Brillouin scattering based optical carrier recovery subsystem, toward better compatibility with the technology demands of short-reach systems. Experimental results show that after 80 km standard single mode fibre transmission, an 8.8 dB required optical signal-to-noise ratio improvement is achieved by the proposed optical carrier recovery subsystem, when compared with the standard Kramers-Kronig direct detection system. Moreover, we measure a receiver sensitivity enhancement of more than 2.8 dB in an optically pre-amplified receiver. These results indicate the potential of the proposed optical carrier recovery subsystem to improve reach or power requirements for Kramers-Kronig direct detection systems. [ABSTRACT FROM AUTHOR]

The modeling of optical wave propagation inoptical fiber is a task of fast and accurate solving the nonlinear Schrödinger equation (NLSE), and can enable the optical system design, digital signal processing verification and fast waveform calculation. Traditional waveform modeling of full-time and full-frequency information is the split-step Fourier method (SSFM), which has long been regarded as challenging in long-haul wavelength division multiplexing (WDM) optical fiber communication systems because it is extremely time-consuming. Here we propose a linear-nonlinear feature decoupling distributed (FDD) waveform modeling scheme to model long-haul WDM fiber channel, where the channel linear effects are modelled by the NLSE-derived model-driven methods and the nonlinear effects are modelled by the data-driven deep learning methods. Meanwhile, the proposed scheme only focuses on one-span fiber distance fitting, and then recursively transmits the model to achieve the required transmission distance. The proposed modeling scheme is demonstrated to have high accuracy, high computing speeds, and robust generalization abilities for different optical launch powers, modulation formats, channel numbers and transmission distances. The total running time of FDD waveform modeling scheme for 41-channel 1040-km fiber transmission is only 3 minutes versus more than 2 hours using SSFM for each input condition, which achieves a 98% reduction in computing time. Considering the multi-round optimization by adjusting system parameters, the complexity reduction is significant. The results represent a remarkable improvement in nonlinear fiber modeling and open up novel perspectives for solution of NLSE-like partial differential equations and optical fiber physics problems. [ABSTRACT FROM AUTHOR]

Volterra equalizations (VE) have delivered significant performance improvement on optical signals, but their extremely high demands on computation complexity severely impede the possibility of large-scale deployment in resource-constrained optical interconnects. In this paper, we propose and experimentally demonstrate a novel sparsity tuned elastic net-pruned Volterra equalization (SENVE) technique to remove the redundancy in the structure of conventional VE (baseline VE) to save complexity without degrading system performance. With a three-stage configuration: pretraining, pruning, and retraining, our SENVE scheme can: (1) realize the compressed structure from a larger VE to reduce computation complexity and (2) accomplish budget-conscious and hardware- friendly structured sparsity of VE to efficiently accelerate the VE's evaluation. We experientially demonstrate the proposed scheme on an 80-Gbps four-level pulse-amplitude modulation (PAM4) signal in O-band for 40-km single-mode fiber (SMF) transmission with a 30-GHz externally modulated laser (EML). Under optimal pruning but without retraining scenarios, the experimental results show that, compared with baseline VE at the KP4-FEC limit, the proposed SENVE can achieve up to 68.7% complexity reduction without degrading performance over 40 km transmission at an received optical power (ROP) of −5 dBm. Moreover, we also find our proposed SENVE with retraining can achieve up to 90.8% and 35.8% complexity reduction, with respect to baseline VE and L1-regularization VE, without sacrificing system performance under the same over-pruning scenarios. [ABSTRACT FROM AUTHOR]

By effectively suppressing the nonlinear sweep noise and random range of wavelength sweep in the optical frequency domain reflectometer, the theoretical spatial resolution and uniform sweep distribution are delivered for high sensing accuracy. A strain accuracy of ±0.51 μϵ is realised with a 5 mm sensing resolution, while the accuracy is ±5.89 μϵ with a 1 mm sensing resolution. Theoretical limitation between the strain accuracy and sensing resolution is further studied for the sub-millimetre resolution sensing. It is found that signal to noise ratio and frequency bandwidth of the calculated cross-correlation are critical factors in measuring accuracy. Increasing the sweep range can provide a better spatial frequency step for a high signal to noise ratio in the cross-correlation. With a 130 nm sweep range, the measurement accuracy is limited to ±19.31 μϵ with a 0.5 mm sensing resolution. Besides, for the long-distance sensing of 104 m, the measurement accuracy is ±8.72 μϵ with a 1 mm sensing resolution. [ABSTRACT FROM AUTHOR]

In this paper, we report a new method to generate tunable high-repetition-rate temporal cavity solitons (TCSs) in a nonlinear fiber cavity, which is driven by dual Brillouin laser pulses. This method is more feasible than generating solitons via a continuous optical-driven nonlinear cavity because of the enhanced four-wave mixing process triggered by the high peak intensity Brillouin laser pulses. The generated TCSs lock to the beating signal arriving from dual Brillouin pulses, which allows the repetition rate of the solitons to be directly tuned all- optically. The TCSs can be continuously tuned over a repetition rate range of 140∼242 GHz by controlling the external dual-wavelength spacing, and the pulse duration can be accordingly adjusted from 0.9 ps to 513 fs. Such TCSs with tunable high-repetition-rate can provide a practical solution for the low-noise controllable millimeter-wave and terahertz sources. [ABSTRACT FROM AUTHOR]

This work presents the use of a directly modulated laser (DML) in time- and wavelength division multiplexed passive optical networks (TWDM-PONs), in which an EDFA-based booster amplification and an SOA-based pre-amplification are utilized to improve the optical power budget. We experimentally demonstrate the C-band optically amplified data transmissions and compare the performance of the non-return-to-zero on-off keying (NRZ-OOK), four and eight-level pulse amplitude modulation (PAM-4/PAM-8) using a 10-G class DML. With optical amplification, the uplink and downlink power budgets of about 28 dB and 35 dB, respectively, are achieved for the PAM-4 54-Gbit/s signals at the hard-decision forward error correction (HD-FEC) limit of 3.8x10-3 after transmissions over a 25-km single-mode fiber link. To mitigate waveform distortions caused by the limited bandwidth, nonlinear dynamics, memory effects, and strong laser frequency chirp of the DML, especially during multi-level signal modulations, artificial neural network-based machine learning equalizers and low-complexity Volterra nonlinear equalizers are applied, which operate at the signal baud rate. The bit error ratio performance in conjunction with an enhanced power budget through the use of a low-complexity nonlinear equalizer can justify the validity of using a DML in the next-generation PONs. [ABSTRACT FROM AUTHOR]

We present ultra-broadband flat-topped supercontinuum laser sources with programmable repetition rate, spectral bandwidth, and wavelength regime. Supercontinuum sources with multiband coverage can be achieved by merging high-repetition-rate electro-optic frequency comb techniques with optical line-by-line pulse shaping. Because nonlinear broadening in the optical wave-breaking regime does not provide the required flatness and spectral bandwidth to the comb-based sources, we iteratively manipulate the spectral amplitude and phase of the optical pulse shaper. We implemented here a smooth flat-topped supercontinuum with a 97 nm bandwidth at 10 dB and programmable repetition rate up to 50 GHz by applying a bandwidth-limited quasi-super-Gaussian apodised pulse train to a highly nonlinear medium with programmable super-Gaussian and phase coefficients. This work opens new possibilities for generating robust and coherent multiple optical carriers with further C-bands in optical networks. We believe that the supercontinuum sources based on electro-optic frequency comb and pulse shaping techniques enable the provision of coherent flat-topped optical sources, at least from the L- to S-band with a programmable repetition rate and spectral bandwidth. [ABSTRACT FROM AUTHOR]

The optical parametric amplifier (OPA) has attractive features for optical communications, such as a wideband, high gain, and fast transient response. In addition, by using idler light, which is phase-conjugated light generated in the amplification process, various kinds of optical signal processing, such as fiber-nonlinearity mitigation, wavelength conversion, and phase-sensitive amplification, can be performed. A periodically poled LiNbO3 (PPLN) waveguide is an χ(2)-based optical parametric amplification medium, and it makes both wideband and high-gain amplification possible. We developed a 4-port PPLN module that can combine signal light and pump light into a PPLN waveguide with low loss. In this paper, we overview the applications of OPA to WDM optical fiber transmission and explain the configurations of an OPA using 4-port PPLN modules. As applications of our PPLN-based OPA, we introduce the demonstration of wideband inline amplification exceeding 5 THz. Furthermore, we demonstrate inter-band wavelength conversion between C- and S-bands using PPLN waveguides developed for multi-band optical transmission applications. [ABSTRACT FROM AUTHOR]

Pilot tone (PT) is a low frequency, small intensity modulation applied to high speed optical channel. Traditionally PT is used for channel identification and channel power monitoring. A pilot tone scheme suitable for optical performance monitoring (OPM) in coherent optical communication systems is described. Two effects, Stimulated Raman scattering (SRS) and dispersion fading, are discussed. An important enhancement, multiband pilot tone, is introduced, which provides sub-channel monitoring capability. With the advanced PT technologies, signal spectrum, and relative frequency offset between signal and optical filter can be monitored with sub-GHz resolution. PT also enables direct OSNR and fiber nonlinear noise monitoring with high accuracy and sensitivity. [ABSTRACT FROM AUTHOR]

We provided a feasible solution for 800-Gb/s per carrier long-distance wavelength division multiplexing (WDM) coherent optical fibre transmission based on offline DSP. We experimentally demonstrate 5-carrier 125-GHz-spacing WDM coherent optical fibre transmission achieving 2000-km transmission distance and 800-Gb/s net bit rate per carrier. We utilized 100-Gbaud truncated probabilistically shaped (TPS) polarization-multiplexed 64QAM format in this work. In terms of advanced components, the high-speed digital-to-analog converter with 35-GHz 3 dB-bandwidth and Raman-amplified ultra-large-area fibre were utilized to achieve higher baud-rate and longer transmission distance. In terms of modulation format, we changed PS to TPS to obtain a more suitable shaping depth, and make the shaped signal better suited to the DSP process of coherent optical communication, including constant modulus algorithm (CMA) equalizer. Besides, our results show that the TPS-64QAM signal with 5-bit/symbol/polarization entropy outperforms the standard-32QAM with a same bit rate by around 1 dB sensitivity gain. Furthermore, we proposed a multiple-input multiple-output (MIMO) Volterra equalizer (VE), which consists of a 1st-order 2 × 2 MIMO complex-valued widely linear (WL) equalizer and a 2nd-order real-valued nonlinear equalizer. Our proposed MIMO VE can effectively resolve the impact of In-phase/quadrature (IQ) imbalance and IQ skew, and compensate linear and nonlinear impairments at the same time. We also utilized partial kernel VE to reduce the complexity by retaining part of the 2nd-order kernels. [ABSTRACT FROM AUTHOR]

We introduce the concept of the universal virtual lab, an extension to the virtual lab platform of [Golani et al. 2016], enabling a fast and accurate simulation of wideband nonlinear DWDM systems. The universal virtual lab is compliant with non-ideal transmitter and receiver architectures, distributed optical filters in the optical link, inter-channel stimulated Raman scattering, and it provides accurate performance predictions even when adaptive equalization methods are applied. In comparison with the conventional full-bandwidth split step Fourier transform method, we show with different test scenarios that the universal virtual lab provides accuracy errors below 0.1 dBQ and 0.09 bit/4D-symb in Q-factor and GMI assessments respectively, with runtime speedup factors exceeding 1000. We also report performance assessments in an ultra-wideband (11 THz) C+L system and discuss equalization gain under different compensation scenarios. The estimated speedup factor with respect to the full-bandwidth split step Fourier transform method is assessed to be greater than 35,000. [ABSTRACT FROM AUTHOR]

Fiber Kerr nonlinearity is a fundamental limitation to the achievable capacity of long-distance optical fiber communication. Digital back-propagation (DBP) is a primary methodology to mitigate both linear and nonlinear impairments by solving the inverse-propagating nonlinear Schrödinger equation (NLSE), which requires detailed link information. Recently, the paradigms based on neural network (NN) were proposed to mitigate nonlinear transmission impairments in optical communication systems. However, almost all neural network-based equalization schemes yield high computation complexity, which prevents the practical implementation in commercial transmission systems. In this paper, we propose a center-oriented long short-term memory network (Co-LSTM) incorporating a simplified mode with a recycling mechanism in the equalization operation, which can mitigate fiber nonlinearity in coherent optical communication systems with ultralow complexity. To validate the proposed methodology, we carry out an experiment of ten-channel wavelength division multiplexing (WDM) transmission over 1600 km standard single-mode fiber (SSMF) with 64 Gbaud polarization-division-multiplexed 16-ary quadrature amplitude modulation (16-QAM) signals. A 0.51 dB Q2 factor gain is observed with the Co-LSTM equalization, which is comparable to that of DBP. The complexity of the Co-LSTM equalization is only 5.2% of that of the conventional bi-directional LSTM, and 28.4% of that of the DBP method with a single step per span. In principle, the complexity of the Co-LSTM with a simplified mode is almost independent of the transmission distance, which shows an essential benefit over the DBP method that determined by the optical signal evolution along the fiber link. The proposed Co-LSTM methodology presents an attractive approach for low complexity nonlinearity mitigation with neural networks. [ABSTRACT FROM AUTHOR]

Opening new wavelength bands is the most economic step for further increasing the capacity of optical transmission links. Characteristics of different amplifier technologies for signal amplification in different wavelength bands are detailed. In particular, the suitability of these technologies for short–term and mid–term implementation is considered. An important criterion is the availability of qualified components, notably the required pump laser diodes. On this basis, solutions for the near–term and the mid–term are discussed. [ABSTRACT FROM AUTHOR]

A CS2-filled Er-doped fiber, which can provide high nonlinearity and gain, low and flat all-normal dispersion profile, low loss and single-mode operation in the wavelength range of 1500-2500 nm, is proposed and analyzed by numerical simulation. When the 1900-nm 0.1-ps initial pulse with a peak power of 30 kW is injected into the active fiber, the generated supercontinuum (SC) spectrum has a double-hump structure in the 1550-nm window and covers about 800-nm wavelength range spanning from 1400 to 2200 nm at -20 dB level. Furthermore, the 1550-nm pulse can be obtained synchronously with the 1900-nm initial pulse when the amplified pulse with a temporal double-peak shape is passed through a band-pass filter with its center wavelength at 1550 nm.

The generation and evolution process of red shifting in a ultrafast fiber laser with the soliton self-frequency shift are investigated by numerical simulation. And the effect of different parameters including the pump strength, the length of dispersion shift fiber, the modulation depth of saturable absorber and the initial field on the red shifting are analyzed for the first time to our knowledge. By optimizing these parameters, a soliton with the maximum red shifting beyond the laser's gain bandwidth is obtained. In addition, within a narrow parameter range, we have also achieved a novel red-shift period-doubling bifurcated soliton with a periodic switching central wavelength.

The expected spatial resolution of the optical frequency domain reflectometry (OFDR) system is hugely degraded by nonlinearity in the lightwave-frequency sweep of the tunable laser source (TLS). We proposed a phase-domain-interpolation-based resampling (PDIR) method to solve this problem, which significantly enhances the spatial resolution. Due to the corresponding relationship between the phase of the beat signal generated from the auxiliary interferometer and sweeping time, the Hilbert transformation was used to obtain the instantaneous phase of the beat signal for coordinate transformation. Theoretical analysis shows that the tuning frequency rate of the TLS is approximately proportional to its phase variation. So the PDIR method can implement even-phase interpolation directly on the beat signal waveform in the new coordinate system. The relationship between the spatial resolution and the interpolation interval was investigated, which guides the choice of the optimum interpolation interval. To verify the feasibility and accuracy of the PDIR approach, we carried out experiments on an OFDR system. A spatial resolution of around 0.15 mm over a 302 m single-mode fiber was achieved with our proposed method. Compared with conventional compensation methods, PDIR possesses a better nonlinearity compensation adequate. Besides, the proposed method is also convenient to operate by interpolating in the phase domain directly. [ABSTRACT FROM AUTHOR]

Optical delay lines are vital for the development of all optical telecommunications, optical computers and for many nonlinear and quantum optics processes. Periodic structures such as coupled resonator optical waveguides (CROW) achieve high delays in a compact manner and with a large bandwidth. Wedge disk resonators have demonstrated high quality factors compared to rectangular disks and rings while remaining integrable on chip. Vertical coupling is needed since the optical mode is pushed toward the disk center by the wedge. We propose an optical delay line made of wedge disks arranged in two overlapping layers. Disks are made of silicon dioxide on silicon pillars. Numerical calculations of the device performance and an experimental proof of concept are presented. A maximum delay of 85 ps for eleven disks is achieved with a loss per cavity of 3.91 dB. This is a first proof of concept of a CROW structure made of wedge disk coupled vertically. [ABSTRACT FROM AUTHOR]

The traditional optical frequency domain reflectometry usually requires a separate auxiliary interferometer to compensate for laser nonlinear tuning effect. In order to break through this limitation, this paper proposes a simplified optical frequency domain reflectometry system by integrating an in-fiber auxiliary interferometer before the sensing fiber. We experimentally characterized the laser nonlinear tuning effect, and then verified the feasibility of the proposed system in compensating the laser nonlinear tuning effect by both simulation and experiment. Finally, the capabilities of the distributed sensing of our proposed system was confirmed by the temperature and strain sensing experiments. [ABSTRACT FROM AUTHOR]

Single-sideband (SSB) signaling is a promising technology for short and medium reach optical transmission. We propose a novel architecture of linear network-assisted long short-term memory network (LN-LSTM) to mitigate optical transmission impairments in SSB systems. With a combination of a linear network and an input-pruned LSTM network, LN-LSTM achieves better performance and lower computation complexity compared with conventional LSTM equalization. With LN-LSTM, we achieve 6.4 Tb/s ($32\times 200$ Gb/s) wavelength division multiplexing (WDM) SSB transmission over 320km standard single-mode fiber (SSMF) with a bit error rate (BER) below the 20% soft-decision forward error-correction (SD-FEC) threshold of $2.4\times 10^{-2}$. [ABSTRACT FROM AUTHOR]

The optical single sideband (OSSB) modulation with tunable optical carrier to sideband ratio (OCSR) is a promising and popular technique in wideband analog signal transmission and microwave signal processing, which can improve modulation efficiency and combat the fiber chromatic dispersion. However, in all reported schemes for achieving OSSB modulation with tunable OCSR, the spurious free dynamic ranges (SFDR) of the systems are all limited by the third-order intermodulation distortion (IMD3). In this paper, our object is to improve the SFDR and suppress the IMD3 in a novel OSSB modulation with tunable OCSR. The proposed system consists of a primary channel and a secondary channel. In primary channel, an OSSB modulation with tunable OCSR is implemented. In secondary channel, the optical carrier and first-order sidebands are perfectly cancelled out, which can suppress the IMD3 without gain penalty at the same received optical power. In this way, a large-SFDR OSSB modulation with tunable OCSR is realized. Experimental results exhibit that the IMD3 gets effective cancellations without gain penalty under unchanged total received power, and the output microwave signal power obtains about 11-dB improvement by optimizing the OCSR. A greatly increased SFDR of over 128 dB·Hz4/5 is achieved in the proposed system. [ABSTRACT FROM AUTHOR]

In this work we experimentally demonstrate the compensation of nonlinearities introduced by a semiconductor optical amplifier (SOA) operating as a power booster in a field-modulated direct detection fiber-optic system transmitter. We show that a combination of digital pre-compensation to deal with SOA nonlinearities, and digital post-compensation after Kramers-Kronig receiver for mitigating the impacts of chromatic dispersion and signal-signal beat interference (SSBI) is an effective scheme to gain ∼3dB in ROSNR in presence of SOA nonlinearity at 3dB of gain compression. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate spatial beam self-cleaning in an Yb-doped graded-index multimode fiber taper, both in passive and active configurations. The input laser beam at 1064 nm was injected for propagation from the small to the large core side of the taper, with laser diode pumping in a counterdirectional configuration. The Kerr effect permits to obtain high-beam quality amplification with no accompanying frequency conversions. As a result, our nonlinear taper amplifier may provide an important building block for multimode fiber lasers and amplifiers.

The inter-modal four-wave mixing (IM-FWM) and transversal mode instabilities (TMI) are experimentally studied in high-power distributed side-pumped fiber amplifiers. To the best of our knowledge, we have made the first demonstration of TMI and IM-FWM which can be suppressed simultaneously by increasing the bending diameter. Besides, the experimental results show that the counter-pumping scheme is beneficial to suppress both of IM-FWM and TMI, when comparing with co-pumping scheme. Furthermore, these two effects cannot be observed when the M2 factor is lower than 1.3, which can give a condition to estimate whether these two effects should be considered or not. The pertinent study can provide some guidance for understanding TMI and IM-FWM in the high-power fiber laser and amplifier.

The effect of tens-of-Watt seed light on the stimulated Raman scattering (SRS) in a distributed side-pumped Yb-doped fiber amplifier is studied. By using two sorts of seed sources with the power smaller than 70 W, it is observed in experiment that the SRS can be enhanced by lowering the seed power. To the best of our knowledge, this is the first observation of the weak-seed enhancement of SRS in the distributed side-pumped Yb-doped fiber amplifier. In order to reveal the physical mechanism of the phenomenon, the numerical study is carried out. It is found that the Yb-gain at Raman wavelength, although much smaller than that at signal wavelength (i.e., 1080 nm), plays an important role in the phenomenon. It is also revealed that the weak-seed enhancement of SRS can only be presented when the dopant concentration is large enough (e.g., larger than 3 × 1025 in our numerical calculation). Besides, with more effective suppression of Raman seed, the weak-seed induced enhancement of SRS could be observed in a larger seed power range. The pertinent results and conclusion can provide significant guidance for designing high-power fiber lasers and amplifiers.

The three-core photonic crystal fiber (TC-PCF) is proposed to obtain large group-velocity dispersion (GVD) because of the coupling effects between the fundamental modes (FMs) of the central core and higher-order modes (HOMs) of the two side cores. The supermodes of the TC-PCF can provide concave anomalous- and normal-GVD profiles with large peak values at the maximum dispersion wavelengths (MDWs), which can be shifted in three wavelength windows of 1030 nm, 1550 nm and 1900 nm by properly tuning the refractive indexes of the cores or the air-hole diameters. Furthermore, the numerical results show that two segments of the TC-PCFs with large anomalous GVDs and opposite values of the third-order dispersion (TOD) can provide much higher efficiency of pulse compression than one segment of the TC-PCF. Additionally, the TC-PCFs with large normal GVDs can be used to stretch pulses due to their low nonlinearities and short fiber lengths.

A cost-effective chromatic dispersion (CD) estimation method is proposed, which is based on the delay-tap sampling (DTS) technique in combination with periodic training sequences (PTS). By performing equivalent sampling of PTS, DTS-based CD estimation at ultra-low sampling rate can be realized, significantly reducing the cost and high-speed requirements of analog to digital converters (ADCs). In contrast to the existing Nyquist DTS-based CD estimation method, we construct the CD lookup table in the CD over-compensated region, which can be suitable for a dynamic range of OSNR conditions. The CD lookup table built from the simulation can be used in the experimental system with similar configurations directly, indicating that the suggested method is reasonable and highly feasible. Besides, with only 1.25 GSa/s sampling rate of ADCs (about 1/30 of the Nyquist sampling rate which is 40.28 GSa/s), both 20.14 GBaud quadrature-phase-shift-keying (QPSK) simulation and experimental systems demonstrate the feasibility of the method, with a 28 ps/nm maximum CD estimation error for the simulation and a 35 ps/nm maximum CD estimation error for the experiment when OSNR is fixed to 18 dB. Furthermore, we also investigate the robustness of our method under the condition of different amplifier spontaneous emission (ASE) noise and nonlinear noise. The proposed method shows great potential for making a remarkable cost reduction in CD monitoring.

Achieving multi-wavelength synchronous ultra-short pulses with arbitrary wavelength intervals is a difficult problem for fiber lasers. Herein, a laser based on multi-stage cascaded Mamyshev regenerators is proposed as a solution. The regenerators are cascaded to form a single laser cavity, each at a different position within the cavity and corresponding to a different output wavelength. A single pulse oscillating in the cavity has its wavelength sequentially switched by the regenerators. Synchronous multi-wavelength pulsed lasers with 5 nm and 0.01 nm output center-wavelength intervals are realized through numerical simulation; the output pulses have 10 nm spectral widths, peak powers of ~0.7 kW, and durations of ~0.4 ps. Design principles, system stability, and the effects of the filter bandwidth, length of single mode fiber and wavelength ordering in the cavity are discussed.

A wavelength-interval switchable wide-band multi-wavelength Brillouin-erbium fiber laser with a half-open cavity is proposed and experimentally demonstrated, which is constructed by random distributed feedback (RDFB) mirrors provided by Rayleigh backscattering in a 1-km-long highly nonlinear fiber (HNLF) and a fiber loop mirror (FLM) incorporated a high-power erbium-doped fiber amplifier (HP-EDFA). A strong RDFB and high stimulated Brillouin scattering (SBS) gain are provided by the HNLF. The HP-EDFA is incorporated into the FLM to boost power of the Brillouin pump and feedback Stokes, enhanced SBS and multiple four-wave mixing are stimulated in the HNLF. Using the presented scheme, up to 118 stable Stokes laser lines with a power deviation of less than 15 dB, 70 stable Stokes laser lines with a power deviation of less than 5 dB and a fix wavelength spacing of 0.075 nm are obtained. Peak power fluctuations of arbitrarily chosen 27 Brillouin comb lines are less than 1.95 dB during a 60-minute measurement period, indicates that the proposed laser has a good stability. The effect of pump power of the HP-EDFA on Stokes generating in the laser is also investigated. Furthermore, when a polarization-maintaining fiber loop mirror is cascaded with the free end of the HNLF via an optical isolator, wavelength-interval switchable laser can be conveniently achieved.

The monitoring of ionizing radiation is critical for the safe operation of nuclear and other high-power plants. Fiber-optic sensing of radiation has been pursued for over 45 years. Most protocols rely on radiation effects on the optical properties of the fiber. Here we propose a new concept, in which the opto-mechanics of standard fibers coated by thin layers of fluoroacrylate polymer are observed instead. The time-of-flight of radial acoustic waves through the coating is evaluated by forward stimulated Brillouin scattering measurements. The time-of-flight is seen to decrease monotonically with the overall dosage of gamma radiation from a cobalt source. Variations reach 15% of the initial value for 180 Mrad dose and remain stable for at least several weeks following exposure. The faster times-of-flight are consistent with a radiation-induced increase in the coating stiffness, observed in offline analysis. The effects on the coating are independent of possible changes in the optical parameters of the fiber. The combination of opto-mechanical analysis together with established fiber sensing protocols may help disambiguate the evaluation of multiple radiation metrics and reduce environmental cross-sensitivities. The technique is suitable for online monitoring and may be extended to spatially distributed measurements. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated a photoelectric nonlinear compensation scheme of optical phase conjugation (OPC) with complex-valued deep neural network (CVDNN) to mitigate fiber nonlinearity in wavelength division multiplexing (WDM) 64-QAM coherent optical transmission system. The factors to affect the performance of OPC and CVDNN are comprehensively considered. OPC in WDM system is experimentally optimized to alleviate the deployment requirements of strict symmetrical distributed power and chromatic dispersion. The performance penalty caused by the simplification of the OPC is further compensated by the CVDNN. The selections of the input neurons’ number and the optimization algorithm are also considered to design a simple two-hidden-layer-structure CVDNN. The proposed method is experimentally verified and evaluated in a 12.5-GBd 4-channel WDM 64-QAM 160-km standard single-mode fiber (SSMF) transmission system with channel spacing of 50-GHz. The experimental results show that the proposed nonlinear equalizer based on the OPC with CDVNN has a strong robustness to the input signal power and wavelength, which can not only improve the Q factor of the signal by 1.5-dB, but also greatly increase the total launched signal power. [ABSTRACT FROM AUTHOR]

The per-sample zero-dispersion channel model of the optical fiber is considered. It is shown that capacity is uniquely achieved by an input probability distribution that has continuous uniform phase and discrete amplitude that takes on finitely many values. This result holds when the channel is subject to general input cost constraints, that include a peak amplitude constraint and a joint average and peak amplitude constraint. [ABSTRACT FROM AUTHOR]

The ever-increasing demand for data rates by mobile users can be fulfilled by radio over fiber (RoF) combined with spectrally-efficient modulation techniques. Thus, RoF is critical to the design of the fronthaul for 5th generation (5G) mobile communication networks. We propose and experimentally demonstrate a low-cost directly modulated laser (DML)-based wavelength division multiplexing (WDM)-RoF transmission system for use in next-generation 5G networks. The proposed architecture provides flexible resource allocation as well, under low and high traffic loads at the remote radio heads (RRHs). We also present robust analytical models of the proposed DML-based WDM-RoF network with spectrally-efficient M-ary-quadrature amplitude modulation (M-QAM), beneficial for system designers. In OptiSystem software, we evaluate the error vector magnitudes (EVM) as a function of the optical link lengths, input optical power, and the received optical power with 4/16/64-QAM over the optical link. The EVMs of the link for 4/16/64-QAM are below the 3GPP standards for 5G. We find good agreement between the simulations and the analytical results. We also experimentally demonstrate a small scale model of this network with resource allocation. Such a flexible architecture is suitable for meeting the demands of femtocells in 5G fronthaul networks. [ABSTRACT FROM AUTHOR]

We study the robustness of a nonlinear frequency-division multiplexing (NFDM) system, based on the Zakharov-Shabat spectral problem (ZSSP), that is comprised of two independent quadrature phase-shift keyed (QPSK) channels modulated in the discrete spectrum associated with two distinct eigenvalues. Among the many fiber impairments that may limit this system, we focus on determining the limits due to third-order dispersion, the Raman effect, amplified spontaneous emission (ASE) noise from erbium-doped fiber amplifiers (EDFAs), and fiber losses with lumped gain from EDFAs. We examine the impact of these impairments on a 1600-km system by analyzing the Q-factor calculated from the error vector magnitude (EVM) of the received symbols. We found that the maximum launch power due to these impairments is: 13 dBm due to third-order dispersion, 11 dBm due to the Raman effect, 3 dBm due to fiber losses with lumped gain, and 2 dBm due to these three impairments combined with ASE noise. The maximum launch power due to all these impairments combined is comparable to that of a conventional wavelength-division multiplexing (WDM) system, even though WDM systems can operate over a much larger bandwidth and, consequently, have a much higher data throughput when compared with NFDM systems. We find that fiber losses in practical fiber transmission systems with lumped gain from EDFAs is the most stringent limiting factor in the performance of this NFDM system.

Power over fiber (PoF) with sleep mode operation in centralized radio access networks (C-RAN) of low power Remote Radio Heads (RRH) helps to reduce power consumption. This proposal includes bundles of single mode optical fibers (SMF) as part of the 5G C-RAN front-haul solution for providing control on power consumption by selectively activating some parts of the RRH. We experimentally demonstrate a PoF system based on 14.43 km of SMF feed by 2.24 W giving 226 mW electrical power at the RRH for control, battery charge, load operation and communication purposes. A bidirectional control channel is integrated in the central office and the RRH for providing the capability of entering in sleep mode operation and to provide information about the status of the battery and sensing elements at RRH. The optical data uplink/downlink operates over separate optical fibers shared by various RRHs and achieves low power consumption below 33 mW with low data rates. The measured PV cells conversion efficiency is above 30%. The RRH has two sleep modes of operation with a minimum power consumption of 5.8 mW. [ABSTRACT FROM AUTHOR]

We analyze theoretically and verify experimentally an effective approach to detect slight wavelength shift based on stimulated Brillouin scattering (SBS) effect. The concerned wavelength variation in an actively mode-locked fiber laser (MLFL) is caused by a π-phase-shifted fiber Bragg grating (π-PSFBG) under different temperatures. Based on the microwave photonics technology, the weak variations of the MLFL wavelength are converted into the amplitude changes of the beat signal generated by the mode-locked fiber laser. With the aid of the SBS effect, the beat signal is amplified larger than 20 dB, enhancing the measurement sensitivity. Through seeking the maximum beat signal, approximately 359.6 MHz modulation frequency shift of pump light with 0.2 °C temperature raise, corresponding to 2.876 pm wavelength shift in the 1550 nm band, is experimentally realized. Our proposed scheme achieves detection of minute wavelength shift with ultrahigh accuracy and convenient operation, which has potential applications for optical spectrum analysis of silicon-based integrated chips, biomedical fields and high sensitive optical sensing. [ABSTRACT FROM AUTHOR]

Optical eigenvalue communication is a promising technique for overcoming the Kerr nonlinear limit in optical communication systems. The optical eigenvalue associated with the nonlinear Schrödinger equation remains invariant during fiber-based nonlinear dispersive transmission. However, practical applications involving use of such systems are limited by the occurrence of fiber loss and amplified noise that induce eigenvalue distortion. Thus, several time-domain neural-network-based approaches have been proposed and demonstrated to enhance receiver sensitivity toward eigenvalue-modulated signals. However, despite the substantial improvement in power margin realized using time-domain neural-network-based demodulators compared to their conventional counterparts, these devices require rigorous training for each transmission distance owing to changes in time-domain pulses during transmission. This paper presents a method for demodulation of eigenvalue-modulated signals using an eigenvalue-domain neural network and demonstrates its utility through simulation and experimental results. Simulation results obtained in this study reveal that the proposed demodulator demonstrates superior generalization performance compared to its time-domain counterpart with regard to the transmission distance. Moreover, experimental results demonstrate successful demodulation over distances from zero to 3000 km without training for each distance. [ABSTRACT FROM AUTHOR]

Radio-over-fiber (RoF)-based front haul architecture has attracted considerable attention for fifth-generation (5G) cellular systems because of its cost effectiveness, however, it is susceptible to harmonic frequency distortion and intermodulation products (IMs) arising from the nonlinearity of the laser diode. To overcome this limitation, an asymmetric electrical predistortion method, using a single Schottky diode with nonlinear characteristics similar to those of a laser diode, was previously proposed. However, its asymmetric structure causes a phase mismatch, which limits the system bandwidth. In this study, we propose an enhanced electrical predistortion technique using dual-parallel Schottky diode blocks. The proposed technique was validated by experiments involving an IM3 drop of approximately 27 dB, and by using identical dual Schottky diode blocks, the phase mismatch in the previously proposed method is completely eliminated. Thus, the applicable bandwidth is extended to 1.8 GHz. This technique can be used to improve the linearity and increase the bandwidth of RoF systems. Additionally, the simple structure is attractive for low-power applications. [ABSTRACT FROM AUTHOR]