Km Of Standard Single-mode Fiber Research Articles

Electronic Dispersion Precompensation of Direct-Detected NRZ Using Analog Filtering

We demonstrate (in real-time) electrical dispersion compensation in direct detection links using analog transmit side filtering techniques. By this means, we extend the fiber reach using a low complexity solution while avoiding digital preprocessing and digital-to-analog converters (DACs) which are commonly used nowadays. Modulation is done using an IQ Mach-Zehnder modulator (MZM) which allows straightforward compensation of the complex impulse response caused by chromatic dispersion in the fiber. A SiGe BiCMOS 5-tap analog complex finite impulse response (FIR) filter chip and/or a delay between both driving signals of the MZMs is proposed for the filter implementation. Several link experiments are conducted in C-band where transmission up to 60 km of standard single-mode fiber (SSMF) of direct detected 28 Gb/s NRZ/OOK is demonstrated. The presented technique can be used in applications where low power consumption is critical.

Complexity Reduction With a Simplified MIMO Volterra Filter for PDM-Twin-SSB PAM-4 Transmission

We propose and experimentally demonstrate a simplified multiple-input multiple-output Volterra filter (MIMO-VF) in a polarization division multiplexed (PDM) twin single side-band (SSB) scheme based on two offset carriers. The right side-band (RSB) and left side-band (LSB) signals of the twin-SSB in each polarization are separated by an optical filter, and the crosstalk between the RSB and LSB is mitigated in the receiver digital signal processing (DSP) by the proposed simplified MIMO-VF, which is combined with one two-stage equalizer, i.e., a linear 2 × 2 butterfly MIMO equalizer and two independent VFs. With the proposed simplified MIMO-VF, we experimentally demonstrate a 400-Gb/s four-level pulse amplitude modulation (PAM-4) signal transmission over an 80-km standard single mode fiber (SSMF). Compared with the traditional MIMO-VF, the proposed simplified MIMO-VF can retain the same transmission performance and reduce the computational complexity by approximately 57.9%.

Comb-based WDM transmission at 10 Tbit/s using a DC-driven quantum-dash mode-locked laser diode.

Chip-scale frequency comb generators have the potential to become key building blocks of compact wavelength-division multiplexing (WDM) transceivers in future metropolitan or campus-area networks. Among the various comb generator concepts, quantum-dash (QD) mode-locked laser diodes (MLLD) stand out as a particularly promising option, combining small footprint with simple operation by a DC current and offering flat broadband comb spectra. However, the data transmission performance achieved with QD-MLLD was so far limited by strong phase noise of the individual comb tones, restricting experiments to rather simple modulation formats such as quadrature phase shift keying (QPSK) or requiring hardware-based compensation schemes. Here we demonstrate that these limitations can be overcome by digital symbol-wise blind phase search (BPS) techniques, avoiding any hardware-based phase-noise compensation. We demonstrate 16QAM dual-polarization WDM transmission on 38 channels at an aggregate net data rate of 10.68 Tbit/s over 75 km of standard single-mode fiber. To the best of our knowledge, this corresponds to the highest data rate achieved through a DC-driven chip-scale comb generator without any hardware-based phase-noise reduction schemes.

103 nm Ultra-Wideband Hybrid Raman/SOA Transmission Over 3 × 100 km SSMF

We report on the ultra-wideband (UWB) transmission of a 103 nm signal over 3 × 100 km of standard single mode fiber (SSMF), a widely-deployed fiber in terrestrial transmission networks. In such UWB systems, nonlinear effects such as stimulated Raman scattering (SRS) must be taken into account in the system design. We characterize the SRS impact in high power regime for this UWB spectrum. We study the evolution of SRS over the bandwidth when tilting the input spectrum to counter the inter-band power transition. We transmit 254 probabilistically constellation shaped (PCS)-64QAM channels over 300 km of SSMF and demonstrate a 107-Tb/s transmission throughput over a continuous 103 nm optical bandwidth using backward Raman pumping and SOA technology.

Four-Channel WDM 640 Gb/s 256 QAM Transmission Utilizing Kramers-Kronig Receiver

Direct detection (DD) systems based on high-order quadrature amplitude modulation (QAM) is promising to provide high spectrum efficiency (SE) for future short-reach data-center applications with next generation standardization of 800 GbE or even 1.6 TbE considering bandwidth limitation. Kramers-Kronig (KK) receiver is recently proposed as an effective method to inherently remove signal-signal beat interference (SSBI) by reconstructing complex optical field in single-sideband (SSB) DD systems. In this paper, we make a detailed system performance assessment of applying a KK receiver in 128, 256 and 512 QAM systems through simulations and experimental demonstrations. 25 GHz-spaced 4 × 140 Gb/s wavelength division multiplexing (WDM) 128 QAM and 4 × 160 Gb/s WDM 256 QAM SSB KK transmissions over 20 km of standard single-mode fiber (SSMF) are successfully achieved. As far as we know, this is the first time that a constellation size as high as 256 QAM with a net SE of 5.12 b/s/Hz is experimentally demonstrated in a WDM system with KK receiver, and the effect of adjusting carrier-to-signal power ratio (CSPR) on the performance of 128, 256 and 512 QAM systems is also investigated with simulation and experimental results.

C-band 56-Gb/s PAM4 transmission over 80-km SSMF with electrical equalization at receiver.

In this paper, a memory polynomial equalizer combined with decision feedback equalizer (MPE-DFE) is proposed to eliminate channel distortions for intensity modulation and direct detection (IM/DD) systems. Compared with traditional feedforward equalizer and decision feedback equalizer (FFE-DFE), the proposed MPE-DFE introduces extra square terms and cubic terms to jointly equalize chromatic dispersion and nonlinear distortions. We demonstrated a C-band 56-Gb/s four-level pulse-amplitude modulation (PAM4) system over 80-km standard single mode fiber (SSMF) transmission. Experimental results show that the proposed MPE-DFE achieved up to 6.2 dB higher SNR than traditional FFE-DFE. Moreover, the achieved bit error ratio (BER) with MPE-DFE reaches 3.1 × 10-3, which is below 7% feedforward error correction (FEC) threshold of 3.8 × 10-3. To the best of our knowledge, we achieved a record transmission distance for C-band 56-Gb/s PAM4 signal with only electrical equalization at the receiver.

Numerical study on nonlinear and chaotic effects in standard fibre using RK4IP method

In this paper, we carry out a numerical study on nonlinear and chaotic effects produced by the propagation of hyperbolic secant optical pulse in standard fibre. We use the fourth-order Runge–Kutta in the interaction picture (RK4IP) method to analyse the pulse interaction in the fibre medium, this method was employed due to its potential to reduce the numerical error while simultaneously allow increasing the step size. During the study, the input peak power was varied up hundreds of kW trough 1 km of standard single-mode fibre (SMF-28); as a consequence, it was possible to observe the generation of nonlinear and chaotic effects on the final spectrum. These numerical results show the spectral and temporal evolution of energy in a 3D rendering, here, it was possible to demonstrated break frequencies and fragmentation of packets of energy by changing the pump power. Finally, we show that this analysis can be used in subsequent studies employing complex dynamic pulses (noise-like pulses, NLPs).

Performance Enhanced 256-QAM BIPCM-DMT System Enabled by CAZAC Precoding

In the paper, bit-interleaved polar-coded modulation discrete multi-tone (DMT) (BIPCM-DMT) with 256-QAM enabled by constant amplitude zero auto-correlation (CAZAC) precoding is proposed and experimentally demonstrated in a low-cost intensity-modulation and direct-detection (IM-DD) system. In order to conquer the fading effect on mapped bit-levels, two types of interleaver including quadratic polynomial permutation (QPP) interleaver and random interleaver are compared to optimize the system performance. However, for 256-QAM BIPCM-DMT system, the signal-to-noise ratio (SNR) fades dramatically as the data subcarrier index increases, it is difficult to match the well-designed operating point of Monte Carlo in the process of polar code construction. Thus, the precoding schemes including CAZAC and orthogonal circulant transform (OCT) are proposed to equalize the uneven SNRs in BIPCM-DMT system. Compared with the bit / power loading and pre-equalization schemes, it will greatly reduce the cost and complexity of the system because channel information obtained by the transmitter via round-trip feedback is not considered. In addition, CAZAC precoding is selected to optimize the BIPCM-DMT system because it is superior to OCT precoding in reducing PAPR. The experimental results show that aided by CAZAC precoding, 20.63 Gb/s BIPCM-DMT signal can be received with an error-free over 50-km standard single-mode fiber (SSMF). Furthermore, compared with BIPCM-free, only CAZAC precoding, and only random interleaver schemes, the proposed scheme can achieve Q-factor enhancement of 4.82 dB, 2.46 and 1.78 dB, respectively, at the received optical power (ROP) of −5 dBm.

52 km-Long Transmission Link Using a 50 Gb/s O-Band Silicon Microring Modulator Co-Packaged With a 1V-CMOS Driver

We present an O -band silicon microring modulator with up to 50 Gb/s modulation rates, co-packaged with a 1V-CMOS driver in a dispersion un-compensated, transmission experiment through 52 km of standard single-mode fiber. The experimental results show 10−9 error-rate operation with a negligible power penalty of 0.2 dB for 40 Gb/s and wide-open eye diagrams for 50 Gb/s data, corresponding to a record high bandwidth-distance product of 2600 Gb·km/s. A comparative analysis between the proposed transmitter assembly and a commercial LiNbO3 modulator revealed a moderate increase of 3.8 dB in power penalty, requiring only 20% of the driving voltage level used by the commercial modulator.

Complexity Analysis of the Kramers–Kronig Receiver

We propose a low-complexity digital implementation of the Kramers–Kronig receiver and analyze its performance and complexity. In simulations and experiments, we find that a relatively small number of filter taps is sufficient to achieve a reasonably high accuracy for the phase retrieval and for the reconstruction of the complex field. We show that the Kramers–Kronig receiver performance strongly depends on details of the system design. Unnecessarily broad optical filters decrease the reception quality, because additional noise makes the violation of the minimum-phase condition more likely. Narrow optical filters, however, impose high local oscillator laser stability and reduce the flexibility of this kind of receiver architecture. Further, we demonstrate Kramers–Kronig reception of 16 QAM signals at a net data rate of 267 Gbit/s after transmission over 300 km of standard single-mode fiber. We compare the performance with a conventional intradyne receiver. In a back-to-back setting, we increase the net data rate to 300 Gbit/s.

112 Gb/s 16-QAM OFDM for 80-km Data Center Interconnects Using Silicon Photonic Integrated Circuits and Kramers–Kronig Detection

In this paper, we report the first demonstration of using silicon photonic integrated circuits for 62 Gb/s 4-quadrature-amplitude-modulation (4-QAM) orthogonal frequency-division multiplexing (OFDM) and 112 Gb/s 16-QAM OFDM over an 80-km standard single-mode fiber (SSMF) transmission with the Kramers–Kronig (KK) direct detection. Single sideband optical signals are generated by two silicon micro-ring modulators, and directly detected by a single integrated germanium-on-silicon waveguide photodiode fabricated in a multi-project wafer run. The complex optical field can be fully re-constructed by KK detection after an 80-km SSMF transmission. The integrated transceivers with KK detection are suitable for future low-cost, low-power, and small-footprint data center interconnects in the short and medium reach.

Digital Radio Frequency Transport over Optical Fiber for 5G Fronthaul Links

Abstract Radio over fiber (RoF) is an empowering technology for the next-generation wireless networks including fifth generation cloud radio access networks. In this paper, we propose a new fronthaul interface which has been demonstrated for a 20-MHz LTE signal having 64-Quadrature amplitude modulation (QAM) modulation over 50 km of standard single-mode fiber. The proposed methodology potentially reduces the overall bandwidth requirement of the link. The performance analysis has been demonstrated for conventional analog RoF (A-RoF) and proposed digital RoF (D-RoF). As a figure of merit, the performance evaluation of the two architectures is reported by analyzing error vector magnitude (EVM), signal-to-noise ratio and eye-opening penalty. It is shown that digital optical links can mitigate the impairments present in A-RoF links and can support the transmission up to 50 km. Moreover, it is shown that efficient D-RoF links can be obtained with a relatively low amount of analog-to–digital-converter resolution bits. For the D-RoF link, the EVM was measured to be less than 2 % at 50 km. This is within the LTE specifications, proving it as a cost and power effective solution for next-generation wireless networks.

Beyond 100G Single Sideband PAM-4 Transmission With Silicon Dual-Drive MZM

We experimentally demonstrate beyond 100G single sideband (SSB) 4-ary pulse amplitude modulation (PAM-4) signal generation with a silicon dual-drive Mach-Zehnder modulator (DD-MZM) operating at C-band. With Kramers-Kronig detection, a 128-Gb/s PAM-4 signal is transmitted over 80-km standard single mode fiber (SSMF) with a bit error rate (BER) below the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . In comparison, a 168-Gb/s PAM-4 signal is transmitted over 80-km SSMF with a BER below the 20% HD-FEC threshold of 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . A two-tap digital post filter and maximum likelihood sequence detection are applied to compensate for the limited system bandwidth. To the best of our knowledge, this letter reports the highest single-lane bitrate of 80-km SSB transmission with a DD-MZM and direct detection. It provides an attractive low-cost solution for inter-datacenter interconnection and metro-haul transmission.

Optimized digital radio over fiber system for medium range communication

In recent years, the demand of efficient and broadband wireless access has escalated, for which Radio over Fiber (RoF) is considered as an appropriate solution. In this paper, we present a Digitized Transmission of 20 MHz LTE signal having 64 quadrature amplitude modulation over 70 Km of Standard Single Mode Fiber (SSMF) for broadband wireless signal transportation and distribution applications. The performance analysis has been evaluated for conventional Analog Radio over Fiber (A-RoF) and proposed Digital Radio over Fiber (D-RoF). The bandpass sampling technique is discussed and employed for digitizing the RF signal. As a figure of merit, the performance evaluation of two architectures is reported by analyzing the Error Vector Magnitude (EVM), Signal to Noise Ratio and Eye-Opening Penalty. It is shown that digital optical links can mitigate the impairments present in A-RoF links and can support the transmission up to 70 Km. Moreover, it is shown that efficient D-RoF links can be obtained with a relatively low amount of analog to digital converter (ADC) resolution bits. An experimental validation of the proposed analytical D-RoF model is done for 30 Km of SSMF, whose experimental results are in line with the analytical ones. The evaluated parameters are within the LTE specifications, proving this is a cost and power effective solution for next generation wireless networks.

200 Gb/s PAM-4 transmission over 10 km of standard single-mode fiber using multiwavelength directly modulated transmitter optical subassemblies for data center

A 200-Gb / s wavelength-division multiplexing transmission system using multiwavelength directly modulated transmitter optical subassemblies for data center has been proposed and demonstrated experimentally. The 8 × 25 Gb / s PAM-4 optical transmission system over 10 km of standard single-mode fiber is tested. The penalty variation within 1 dB for eight channels indicates that colorless transmission operation in the C-band is feasible with stable performance. Clear eye openings without any distortion show a good linearity characteristic for the optical transmission system. The advantages of integration, channelization, miniaturization, and low power consumption of the proposed scheme present a promising result for data center interconnection.

Multi-Twin-SSB Modulation with Direct Detection Based on Kramers–Kronig Scheme for Long-Reach PON Downstream

As the demand for high data volumes keeps increasing in optical access networks, transmission capacities and distance are becoming bottlenecks for passive optical networks (PONs). To solve this problem, a novel scheme based on multi-twin single sideband (SSB) modulation with direct detection is proposed and investigated in this paper. At the central office, two SSB signals are generated simultaneously with the same digital-to-analog converters (DACs). The twin-SSB signal is not only robust against frequency selected power fading introduced by chromatic dispersion (CD), but also improves the spectral efficiency (SE). By combining a twin-SSB technique with multi-band carrier-less amplitude/phase modulation (multi-CAP), different optical network units (ONUs) can be supported by flexible multi-band allocation based on software-reconfigurable optical transceivers. The Kramers–Kronig (KK) scheme is adopted on the ONU side to effectively mitigate the signal–signal beat interference (SSBI) induced by the square-law detection. The proposed system is extensively studied and validated with four sub-bands using 50 Gbps 16 quadrature amplitude modulation (QAM) modulation for each sub-band using numerical simulations. Digital pre-equalization is introduced at the transmitter-side to balance the performance of different ONUs. After system optimization, a bit error rate (BER) threshold for hard decision forward error correction (HD-FEC) code with 7% redundancy ratio (BER = 3.8 × 10−3) can be reached for all ONUs over 50-km standard single-mode fiber.

Two-level encryption for physical-layer security in OFDM-PON based on multi-scrolls system

The security of orthogonal frequency division multiplexing-based passive optical network (OFDM-PON) system has been an important and hot problem recently. In this paper, a two-level encryption method based on multi-scrolls system for physical-layer security is proposed and experimentally demonstrated in an OFDM-PON system. The proposed scheme is based on a four-order grid multi-scrolls and it can generate chaotic sequences for IQ encryption and row–column chaotic permutation. A huge key space can be achieved in the proposed scheme. Furthermore, a DFT precoding method can be applied to improve the PAPR performance of the system. In the experiment, a secure transmission of 8.9-Gb/s encrypted OFDM signal has been experimentally demonstrated over 50-km standard single-mode fiber (SSMF). The results show that the proposed method can effectively enhance the physical layer security and simultaneously improve the bit-error-rate (BER) performance of the system.

Increasing the Spectral Efficiency of DDO-CE-OFDM Systems by Multi-Objective Optimization

A multi-objective optimization was implemented to increase the spectral efficiency of direct-detection optical orthogonal frequency division multiplexing (OFDM) systems with constant-envelope (CE) signals. Based on a genetic algorithm, the optimization procedure evaluates the impact of fiber injection power in the reduction of the guard band between the optical carrier and the CE-OFDM signals, optimizing important parameters such as electrical phase modulation and optical modulation indices of the denominated DDO-CE-OFDM system. Simulation results show that a guard-band reduction around 40% was achieved in a 4 Gbps optimized DDO-CE-OFDM system with 16-QAM subcarrier mapping and -7 dBm fiber input power. Results obtained in an experimental proof-of-concept conducted to validate the optimization procedure show that this reduction can reach 66% according to a power penalty of ≈2 dB demanded by the inherent spectral broadening of CE-OFDM signals, after propagation over 40 km of standard single-mode fiber.

50-km C-Band Transmission of 50-Gb/s PAM4 Using 10-G EML and Complexity-Reduced Adaptive Equalization

In this paper, we experimentally demonstrate the transmission of 50-Gb/s four-level pulse-amplitude modulation (PAM4) signal over 50-km standard single mode fiber (SSMF) in C-band using electroabsorption modulated laser and PIN/APD detector with 8.5/6 GHz bandwidth. A simplified Volterra-DFE filter is proposed, which reduces the required tap number by ∼70% compared with traditional DFE and Volterra filtering. Experimental results show that by using 86-tap equalization, a sensitivity of –15 and –14 dBm can be achieved at the FEC limit of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> in back to back (BtB) and 50-km SSMF transmission cases. In addition, by replacing the PIN-TIA with a 10-Gb/s APD-ROSA for detection, the sensitivity can be further increased by 5.5 and 3 dB for BtB and 50-km SSMF transmission cases, respectively.

Single-Sideband OFDM Transmission via a Silicon Microring IQ Modulator

We experimentally demonstrate the generation of a single-sideband orthogonal frequency division multiplexed (OFDM) signal using an on-chip silicon photonics microring-based IQ modulator. Over 18-dB sideband suppression ratio is achieved for the wideband OFDM: 15.7-GHz data band and 2.7-GHz guard band. The 31.4-Gb/s signal was transmitted over 20 km of standard single-mode fiber with a bit error rate below the forward error correction threshold. While single-sideband continuous-wave signals have been produced with such hardware, this is the first demonstration of stable data transmission on the single sideband carrier.