Km Of Standard Single-mode Fiber Research Articles

DSP-Free and Real-Time NRZ Transmission of 50 Gb/s Over 15-km SSMF and 64 Gb/s Back-to-Back With a 1.3-μm VCSEL

We demonstrate and analyze 50 Gb/s non-return-to-zero (NRZ) transmission over 15 km of standard single-mode fiber (SSMF), 60-Gb/s NRZ transmission over 5 km of SSMF and up to 64-Gb/s NRZ back-to-back using a directly modulated short-cavity long-wavelength single-mode vertical-cavity surface-emitting laser (VCSEL) emitting at 1326 nm. Owing to an analog 6-tap transmit feedforward equalizer, the link can operate without digital signal processing. In all three cases, real-time bit error ratio measurements below the 7% overhead hard-decision forward error correction threshold are demonstrated when transmitting a pseudo-random bit sequence with a period of $2^7-1$ bits. In addition, we analyze the interplay between the residual fiber chromatic dispersion at the operating wavelength of the VCSEL and the chirp due to direct modulation. These results demonstrate how O-band, short-cavity long-wavelength single-mode VCSELs can be used in intradata center networks, as well as in interdata center networks at reaches below 15 km.

On the Complexity Reduction of the Second-Order Volterra Nonlinear Equalizer for IM/DD Systems

To cope with the various nonlinear signal distortions in intensity-modulation/direct-detection transmission systems, a theoretical analysis on the Volterra nonlinear equalizer (VNLE) is provided, focusing on computational complexity aspects. The analysis yields a simple reduced-complexity scheme for the second-order VNLE (R2-VNLE) based on a performance-complexity tradeoff. An experimental verification is performed with single-sideband 28-GBaud PAM-4 signals, generated by an electroabsorption modulated distributed-feedback laser, over transmission distances of up to 80 km of standard single-mode fiber in the C-band. A comparison of the results for different equalization schemes, including a signal-signal beat interference mitigation technique, shows superior performance for the R2-VNLE.

Amplifierless PAM-4/PAM-8 transmissions in O-band using a directly modulated laser for optical data-center interconnects.

Toward the realization of low-cost, long-, and extended-reach 400GbE data-center applications, the performance of pulse amplitude modulated (PAM) signals is studied using a state-of-the-art, high-performance 1.3-μm distributed feedback directly modulated laser, without any optical amplification or complex digital processing. Amplifierless PAM-4 transmissions of up to 64-Gb/s are achieved over 40km of standard single-mode fiber (SSMF) for standard KP4-FEC, while 84-Gb/s PAM-8 signals are evaluated over 10km SSMF.

Aerosol-Jet Printed Interconnects for 60-Gb/s CMOS Driver and Microring Modulator Transmitter Assembly

We developed an aerosol-jet printing technique to realize an optical transmitter assembly of a microring modulator and a high-speed CMOS driver in which the bonding wires are replaced by aerosol-jet printed silver interconnects. First, the technology is characterized by printing coplanar waveguides (CPWs) test structures on glass and epoxy in order to fully investigate the electro-magnetic behavior of the aerosol-jet printed interconnects. The printed CPWs on glass and epoxy showed a low attenuation of 0.57 and 0.76 dB/mm at 50 GHz, respectively. Then, the aerosol-jet printed interconnects were benchmarked with conventional bonding wires while separately interconnecting the ring modulator without the CMOS driver. The measured reflection coefficient ( $S_{11}$ ) of the aerosol-jet printed interconnects showed an increase in a resonance frequency of 20 GHz compared with Al bonding wires. Furthermore, the optical transmitter was successfully demonstrated at 60 Gb/s and the measured optical eye diagrams were clearly open even after 2 km of standard single-mode fiber. An extinction ratio of 4.63 dB was achieved while applying a drive voltage of 1 $\text{V}_{\mathrm{ pp}}$ .

140/180/204-Gbaud OOK Transceiver for Inter- and Intra-Data Center Connectivity

We report on an on – off keying intensity-modulation and direct-detection C-band optical transceiver capable of addressing all datacenter interconnect environments at well beyond 100 Gbaud. For this, the transmitter makes the use of two key InP technologies: a 2:1 double heterojunction bipolar transistor selector multiplexer and a monolithically integrated distributed-feedback laser traveling-wave electro-absorption modulator, both exceeding 100-GHz of 3-dB analog bandwidth. A preamplified 110-GHz PIN photodiode prior to a 100-GHz analog-to-digital converter complete the ultrahigh bandwidth transceiver module; the device under study. In the experimental work, which discriminates between intra- and inter-data center scenarios (dispersion unmanaged 120, 560, and 960 m; and dispersion-managed 10 and 80 km of standard single-mode fiber), we evaluate the bit-error rate evolution against the received optical power at 140, 180, and 204 Gbaud on – off keying for different equalization configurations (adaptive linear filter with and without the help of short-memory sequence estimation) and forward error correction schemes (hard-decision codes with 7% and 20% overhead); drawing conclusions from the observed system-level limitations of the respective environments at this ultrahigh baudrate, as well as from the operation margins and sensitivity metrics. From the demonstration, we highlight three results: successful operation with >6-dB sensitivity margin below the 7% error-correction at 140 Gbaud over the entire 100 m–80 km range with only linear feed-forward equalization. Then, the transmission of a 180-Gbaud on – off keying carrier over 80 km considering 20% error-correction overhead. Finally, a 10-km communication at 204 Gbaud on – off keying with up to 6 dB sensitivity margin, and regular 7% overhead error-correction.

120 Gbaud PAM-4 transmission over 80-km SSMF using optical band interleaving and Kramers-Kronig detection.

We demonstrate generation and detection of 120-Gbaud PAM-4 signals using an I/Q modulator based on optical band interleaving (OBI) technique. The spectral components of target PAM signals are split and pre-processed before being sent to two digital-to-analog convertors (sub-DACs) whose outputs are imprinted to an optical carrier by an optical I/Q modulator forming a carrier-suppressed tandem single side-band (SSB) signal. The PAM signals can be recovered after photo-detection provided that an optical beating tone is added at the edge of the signal spectrum along with the modulator output. The proposed method requires only half of the Nyquist bandwidth of the target PAM signal for the transmitter and has the advantage of a simple implementation. Using Kramers-Kronig (K-K) detection, a 120 Gbaud PAM-4 transmission over 80-km standard single mode fiber (SSMF) is successfully demonstrated. The proposed scheme entails a simple implementation and a much lower bandwidth requirement at the transmitter compared with conventional all-electronic high baud rate signal generation schemes.

A full-duplex 100-GHz radio-over-fiber communication system based on frequency quadrupling

We have experimentally demonstrated an effectively full-duplex radio-over-fiber (ROF) system, which only used a single light source at central station (CS). Frequency quadrupling modulation scheme was employed to generating 100-GHz optical millimeter wave (mm-wave) for downlink transmission while the central optical carrier was reused at base station (BS) for uplink connection. Using this proposed system design, 2.5-Gb/s OOK data was successfully transmitted over 10-km dispersion shifted fiber (DSF) and 3-m wireless link for downstream channel with about 3.5-dB power penalty, and 2.5-Gb/s OOK data was transmitted over 50-km standard single-mode fiber (SMF) for upstream channel with power penalty less than 0.5-dB.This system shows good performance in long distance transmission and provides an efficient solution for high frequency mm-wave communication.

Enhanced Performance Utilizing Joint Processing Algorithm for CAP Signals

In this paper, we propose a joint processing algorithm for carrierless amplitude and phase modulation (CAP) signal to improve the system performance in both short-reach and metro network. Utilizing our proposed method, 112 Gb/s/λ CAP-64 quadrature amplitude modulation (QAM)-based transmission over 50 km of standard single mode fiber (SSMF) is experimentally achieved with a bandwidth-limited direct-detection receiver under the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10–3. Furthermore, we experimentally demonstrate 112 Gb/s/λ CAP-16 QAM transmission over 480 km of SSMF with direct detection. With our proposed joint processing algorithm, both nonlinearity and In-phase/quadrature (IQ) imbalance can be mitigated. More than 3 dB receiver sensitivity gain is achieved at the HD-FEC threshold after 400-km transmission compared with the result using traditional nonlinear compensation.

EML based real-time 112 Gbit/s (2 × 56.25 Gbit/s) PAM-4 signal transmission in C-band over 80 km SSMF for inter DCI applications

Abstract We report on an electro-absorption modulator (EAM) integrated laser (EML) based real-time 112 Gbit/s (2 × 56.25 Gbit/s) 4-level pulse amplitude modulation (PAM-4) signal transmission in the C-band over 80 km of standard single-mode fiber (SSMF). Various operating conditions of the EAM were investigated to find the optimum driving conditions for PAM-4 modulation. When the EAM reverse bias was set to the inflection point of the transfer curve, which was −2.35 V, we obtained a bit error ratio (BER) of 4 × 10−8, which is well below the forward error correction (FEC) limit. The results demonstrate the feasibility of using EMLs for implementation in PAM-4 transceivers for inter-datacenter interconnection (inter-DCI) applications.

Multiflow Transmitter With Full Format and Rate Flexibility for Next Generation Networks

We extend our proof-of-concept demonstration of a novel multiflow transmitter for next generation optical metro networks. The multiflow concept is based on the combination of spectrum and polarization sliceability, and its implementation on the combination of a polymer photonic integration platform with high-speed IQ modulators. In this paper, we replace the static scheme of our previous demonstration for the definition of the optical flows and the generation of the driving signals, and we unveil the true potential of the transmitter in terms of programmability and network flexibility. Using a software-defined optics (SDO) platform for the configuration of the digital and optical parts of the transmitter, and the configuration of the optical switch inside the node, we demonstrate operation with flexible selection of the number and type of the optical flows, and flexible selection of the modulation format, symbol rate, emission wavelength, and destination of each flow. We focus on 16 specific cases accommodating one or two optical flows with modulation format up to 64-quadrature amplitude modulation, and symbol rate up to 25 Gbaud. Through transmission experiments over 100 km of standard single-mode fiber, we validate the possibility of the transmitter to interchange its configuration within this range of operation cases with bit-error rate performance below the forward error correction limit. Future plans for transmitter miniaturization and extension of our SDO platform in order to interface with the software-defined networking hierarchy of true networks are also outlined.

A 7-D Hyperchaotic System-Based Encryption Scheme for Secure Fast-OFDM-PON

In this paper, we propose and experimentally demonstrate a novel two-step I/Q-encryption scheme for improving physical layer security in fast orthogonal frequency division multiplexing passive optical network (fast-OFDM-PON). To meet the requirement of this encryption scheme and further enhance the security, a seven-dimensional hyperchaotic system with five positive Lyapunov exponents is designed. In this system, Walsh–Hadamard transform and discrete cosine transform are chosen to reduce the computation complexity and increase the key space simultaneously. An optional discrete Fourier transform spread is required to achieve the maximum scrambling degree. Encryption of 9.4-Gb/s 16-quadrature amplitude modulation fast-OFDM signals with a total key space of ∼10788 against the exhaustive trial has been successfully implemented over 50-km standard single mode fiber in a fast-OFDM-PON, which shows good resistance against illegal access to optical network units. All the results indicate that this proposed encryption scheme has improved security performance with relatively low computation complexity.

10 Tb/s PM-64QAM Self-Homodyne Comb-Based Superchannel Transmission With 4% Shared Pilot Tone Overhead

We demonstrate transmission of a comb-based 10 Tb/s 50 $\times$ 20 Gbaud PM-64QAM superchannel using frequency comb regeneration to reduce carrier offsets and allow for self-homodyne detection. The regeneration is enabled by transmitting two optical pilot tones which are filtered and recovered in the receiver using optical injection locking and an electrical phase-locked loop. We show that by utilizing frequency combs together with optical pilot tones, self-homodyne detection similar to systems using one pilot tone per wavelength channel, can be achieved. Sharing the overhead for pilot tones reduces the complexity and limits the overhead to 4%. This enabled a total superchannel spectral efficiency of 7.7 b/s/Hz. To evaluate the performance, we perform both back-to-back measurements and transmission over 80 km of standard single-mode fiber. Successful self-homodyne detection of all 50 data channels in the 10-nm-wide superchannel demonstrates that the spectral coherence from frequency combs, combined with the use of optical pilots, can overcome limitations arising from frequency offset and phase noise in high-order QAM transmission while keeping the pilot overhead low.

Amplifier-free 200-Gb/s tandem SSB doubly differential QPSK signal transmission over 80-km SSMF with simplified receiver-side DSP.

We numerically demonstrate 80-km standard single-mode fiber transmission without optical amplification, dispersion compensation or carrier recovery using 200-Gb/s tandem single sideband modulated doubly differential QPSK. Simulation results show that doubly differential encoding enables practically constant system performance for frequency offsets within ± 2.3 GHz and allows a linewidth tolerance of 2.5 × 10-3 at 1-dB receiver sensitivity penalty. Employing 2.9-MHz linewidth lasers, the receiver sensitivity penalty at 7% HD-FEC threshold for 80-km transmission is less than 0.2 dB. By adding a 12-symbol decision feedback in the 2nd differential operation of doubly differential decoding, the receiver sensitivity is improved by 3.7 dB.

Optical frequency comb generation for DWDM transmission over 25- to 50-km standard single-mode fiber

Dense wavelength division multiplexed (DWDM) transmission equal to 1.2 Tbps over 25 to 50 km across standard single-mode fiber (SSMF) in the C band is performed based on an optical frequency comb generator. Sixty-one flattened optical frequency tones were realized with 30-GHz frequency spacing, high side-mode suppression ratio over 35 dB, and minimum amplitude difference was realized using amplitude modulator for first time in cascade mode with two Mach–Zehnder modulators (MZMs) where all the modulators were tailored by RF signals. 20×61 Gbps DWDM-based differential quadrature phase shift keying modulated signals were successfully transmitted over SSMF and analyze its transmission capability for range of 25 to 50 km with acceptable power penalties and bit error rates.

DAC-Less and DSP-Free 112 Gb/s PAM-4 Transmitter Using Two Parallel Electroabsorption Modulators

Four-level pulse amplitude modulation (PAM-4) is widely regarded as the modulation format of choice for the next generation of 400 gigabit Ethernet short-reach optical transceiver. However, generating and receiving PAM-4 at line rates of 112 Gb/s has proven challenging, without relying on power-hungry tools as digital signal processing and digital-to-analog converters, as it requires linearity from the E/O-components in the link and/or predistortion techniques. Moving the binary to multilevel conversion to the optical domain would greatly relax these requirements. Electroabsorption-based transceivers would be ideally suited for this type of data center interconnects as they are capable of combining low-power and high bandwidth operation with a very compact layout, removing the need for large travelling wave structures and dedicated 50 Ω terminations. In this paper, we present a novel transmitter topology for generating PAM-4 using two binary-driven electroabsorption modulators in parallel. Using this approach, we achieve superior performance with respect to a single, but identical multilevel-driven EAM. Finally, we demonstrate the first silicon-based modulator capable of transmitting single-lane 112 Gb/s PAM-4 over 2 km of standard single-mode fiber without any electrical digital-to-analog converter, DSP, or long transmission line structures and terminations.

Simple and robust ternary pulse‐encoding and reconstruction of narrowband RF signals over low‐cost fibre‐optic links

An existing ternary pulse-coding scheme for bandpass signals, whereby a timing code specifies positive and negative rectangular pulses as well as a third zero state formed by skipping pulses, is adapted to transmission and reconstruction of narrowband RF signals over inexpensive fibre-optic links. The main feature of this technique is that reconstruction of the narrowband analog signal is particularly simple, requiring only a bandpass filter. Simulations using a complex band-limited Gaussian baseband input to represent a 20-MHz LTE-A signal establish the ideal theoretical performance, which is then compared to experimental results obtained by transmission on a 1.6-GHz carrier over a fibre-optic link consisting of an electro-absorption modulated laser, 10 km of standard single-mode fibre (SSMF), and avalanche photodiode detector. The experimental results are only slightly impaired from ideal performance, even for only 6 dB signal-to-noise ratio, thereby demonstrating the viability and robustness of the proposed technique.

Comparison of VSB PAM4 and OOK Signal in an EML-Based 80-km Transmission System

A comparison between 51.84-Gb/s vestigial sideband 4-level pulse amplitude modulation (PAM4) and ON–OFF keying (OOK) signals at a transmission distance of 80 km is experimentally demonstrated for the first time. An electro-absorption modulated laser-based intensity-modulation and direct-detection 80-km transmission is achieved using both modulation formats without dispersion compensating fiber. The relative frequency between single sideband filter and signal is adjusted to find an optimized condition for both carrier to signal power ratio and sideband suppression ratio. The experimental results show that with linear equalization and without bandwidth limitation, the OOK signal has a 4-dB better sensitivity compared with PAM4 after 80-km standard single-mode fiber transmission.

Real-Time 100 Gb/s NRZ and EDB Transmission With a GeSi Electroabsorption Modulator for Short-Reach Optical Interconnects

Transceivers based on electroabsorption modulators (EAM) are considered as a promising candidate for the next generation 400 GbE short-reach optical networks. They are capable of combining high bandwidth and low-power operation with a very compact layout, removing the need for traveling wave electrodes and dedicated 50 $\Omega$ termination. In this paper, we demonstrate the first silicon-based EAM, in combination with an in-house developed SiGe BiCMOS transceiver chipset, capable of transmitting single-lane 100 Gb/s non-return-to-zero in real-time. Transmission over 500 m of standard single mode fiber and 2 km of nonzero dispersion shifted fiber is demonstrated, assuming a forward-error coding scheme is used with a bit-error ratio limit of $3.8\times 10^{-3}$ . Due to the high line rate, transmission over longer fiber spans was limited by the chromatic distortion in the fiber. As a possible solution, electrical duobinary modulation is proposed as it is more resilient to this type of fiber distortion by reducing the required optical bandwidth. We show improved performance for longer fiber spans with a 100 Gb/s electrical duobinary link, resulting in real-time sub-forward error coding operation over more than 2 km of standard single-mode fiber without any digital signal processing. Finally, the possibility of a 100 Gb/s EAM-to-EAM link is investigated.

Single Carrier 400G Transmission With Single-Ended Heterodyne Detection

We demonstrate single channel 448 Gb/s (56 GBaud) and wavelength division multiplexed (WDM) 1.792-Tb/s transmission of Nyquist polarization division multiplexed 16-ary quadrature amplitude modulation (16-QAM) signal by employing heterodyne detection with single-ended photodiodes. The signal-signal beat interference induced by square-law detection of the single-ended photodiodes is overcome by the Kramers-Kronig scheme. For both single channel 160-km standard single mode fiber (SSMF) transmission and WDM 80-km SSMF transmission, the bit-error rates are below the 7% hard-decision forward error correction threshold of $4.5\times 10^{-3}$ . To the best of our knowledge, this letter is the first experiment of single carrier 400G optical transport with heterodyne detection. For WDM operation of high symbol rate heterodyne system, a record net spectral efficiency of 5.71 b/s/Hz is achieved.

100-Gb/s 80-km transmission of PIM-SSB-OFDM at C-band using a single-end photodetector

Polarization-interleave-multiplexed (PIM) with single-sideband orthogonal frequency-division multiplexing (SSB-OFDM) based on direct detection is proposed for short-reach applications transmitted up to 80 km in which the guard band can be shared for the two SSB signals with interleave electrical center frequencies. Based on two dual-drive Mach–Zehnder modulators with one single-end photodetector (PD), 100-Gb/s PIM-SSB-OFDM transmission over a 80-km standard single-mode fiber is successfully demonstrated. After 80-km transmission, the optical signal-to-noise ratio requirement is 29.1 dB with respect to the bit error rate threshold of 7% hard decision-forward error correction overhead.