Single-mode Fiber Link Research Articles

Enabling 4-Lane Based 400 G Client-Side Transmission Links with MultiCAP Modulation

We propose a uniform solution for a future client-side 400 G Ethernet standard based on MultiCAP advanced modulation format, intensity modulation, and direct detection. It employs 4 local area networks-wavelength division multiplexing (LAN-WDM) lanes in 1300 nm wavelength band and parallel optics links based on vertical cavity surface emitting lasers (VCSELs) in 850 nm wavelength band. Total bit rate of 432 Gbps is transmitted over unamplified 20 km standard single mode fiber link and over 40 km link with semiconductor optical amplifier. 70.4 Gb/s transmission over 100 m of OM3 multimode fiber using off-the-shelf 850 nm VCSEL with 10.1 GHz 3 dB bandwidth is demonstrated indicating the feasibility of achieving 100 Gb/s per lane with a single 25 GHz VCSEL. In this review paper we introduce and present in one place the benefits of MultiCAP as versatile scheme for use in a number of client-side scenarios: short range, long range, and extended range.

Coherent ultra dense wavelength division multiplexing passive optical networks

In this paper, we firstly review the progress in ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON), by making use of the key attributes of this technology in the context of optical access and metro networks. Besides the inherit properties of coherent technology, we explore different modulation formats and pulse shaping. The performance is experimentally demonstrated through a 12×10Gb/s bidirectional UDWDM-PON over hybrid 80km standard single mode fiber (SSMF) and optical wireless link. High density, 6.25GHz grid, Nyquist shaped 16-ary quadrature amplitude modulation (16QAM) and digital frequency shifting are some of the properties exploited together in the tests. Also, bidirectional transmission in fiber, relevant in the context, is analyzed in terms of nonlinear and back-reflection effects on receiver sensitivity. In addition, as a basis for the discussion on market readiness, we experimentally demonstrate real-time detection of a Nyquist-shaped quaternary phase-shift keying (QPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array (FPGA).

Performance Comparison of Dual-Carrier 400G With 8/16/32-QAM Modulation Formats

The performance of dual-carrier 400G solutions based on three high-order quadrature amplitude modulation (QAM) formats (8/16/32-QAM) is investigated on the same platform. We first study the benefit and penalty differences of gray and differential coding, and then experimentally compare OSNR sensitivities and transmission performance using flexible transceiver configuration and the same erbium-doped fiber amplifiers-only standard single-mode fiber link. Experimental results show the implementation penalties are 1.85 dB for 42-GBd polarization multiplexed (PM)-8QAM, which is 1 and 1.5 dB better than 32-GBd PM-16QAM and 25-GBd PM-32QAM at 5.92-dB Q <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -factor (corresponding to a bit error rate of 2.4E-2), respectively. It is also found that maximum reaches of 2460 km for 42.6-GBd PM-8QAM, 1640 km for 32-GBd 16QAM, and 820 km for 25-GBd PM-32QAM are achieved. Furthermore, the performances of cascaded multimodulus algorithm and decision-directed least mean square (DD-LMS) algorithms are also compared. The improvement by addition of one sample/symbol-based DD-LMS digital filter is investigated as well.

40 Gb/s PAM-4 Transmitter IC for Long-Wavelength VCSEL Links

Conventional 850 nm multimode fiber links deployed in warehouse-scale data centers will be limited by modal dispersion beyond 10 Gb/s when covering distances up to 1 km. This can be resolved by opting for a single-mode fiber (SMF), but typically requires the use of power-hungry edge-emitting lasers. We investigate the feasibility of a high-efficiency SMF link by reporting a 0.13 μm SiGe BiCMOS laser diode driver optimized for long-wavelength vertical-cavity surface-emitting lasers (VCSELs). Bit-error rate experiments at 28 and 40 Gb/s up to 1 km of SMF reveal that four-level pulse amplitude modulation can compete with non-return-to-zero in terms of energy efficiency and scalability. With 9.4 pJ/b, the presented transmitter paves the way for VCSEL-based SMF links in data centers.

Remote light source for silicon photonic transceivers in mobile fronthaul applications

The design and experimental characterisation of a depolarised light source for feeding a remote transceiver based on silicon photonics are presented. Since the transceiver only works in TE mode, the source is designed to deliver, over up to 10 km standard single-mode fibre links, a continuous-wave light with almost constant power along this polarisation direction, whatever be the random polarisation rotation because of the fibre link. The depolarised light source is realised by combining the output of two independent distributed feedback lasers, having orthogonal polarisation and controlled frequency difference. The transmission performance and stability of the remote light source are successfully tested.

Experimental demonstration of iterative post-equalization algorithm for 375-Gbaud PM-16QAM quad-carrier Terabit superchannel

We experimentally demonstrate a quad-carrier 1-Tb/s solution with 37.5-GBaud PM-16QAM signal over 37.5-GHz optical grid at 6.7 b/s/Hz net spectral efficiency. Digital Nyquist pulse shaping at the transmitter and post-equalization at the receiver are employed to mitigate the impairments of joint inter-symbol-interference (ISI) and inter-channel-interference (ICI) symbol degradation. The post-equalization algorithms consist of one sample/symbol based decision-directed least mean square (DD-LMS) adaptive filter, digital post filter and maximum likelihood sequence estimation (MLSE), and a positive iterative process among them. By combining these algorithms, the improvement as much as 4-dB OSNR (0.1nm) at SD-FEC limit (Q(2) = 6.25 corresponding to BER = 2.0e-2) is obtained when compared to no such post-equalization process, and transmission over 820-km EDFA-only standard single-mode fiber (SSMF) link is achieved for two 1.2-Tb/s signals with the averaged Q(2) factor larger than 6.5 dB for all sub-channels. Additionally, 50-GBaud 16QAM operating at 1.28 samples/symbol in a DAC is also investigated and successful transmission over 410-km SSMF link is achieved at 62.5-GHz optical grid.

Symbol-Rate Dependence of Dominant Nonlinearity and Reach in Coherent WDM Links

We provide simulations of the nonlinear threshold (NLT) versus per-channel symbol rate at a constant bandwidth efficiency for a 15-channel wavelength-division multiplexing long-haul coherent optical transmission over a 20 $\times$ 100 km single-mode fiber link, both dispersion-managed (DM) and dispersion-uncompensated (DU), with several popular polarization multiplexed modulation formats. We exploit the nonlinearity-decoupling method to estimate the NLT due to each individual nonlinear effect, and, thus, show how the dominant nonlinearity changes with symbol rate. Plots of the NLT normalized to the symbol rate also reveal the symbol rate achieving the longest distance. Assuming a signal-independent Gaussian nonlinear interference, we derive a new formula yielding the system reach based on knowledge of NLT measurements on a much shorter link. We finally provide reach simulations to verify the accuracy of the new reach formula for both DM and DU links.

Frequency comb-based multiple-access ultrastable frequency dissemination with 7 × 10(-17) instability.

In this letter, we demonstrate frequency-comb-based multiple-access ultrastable frequency dissemination over a 10-km single-mode fiber link. First, we synchronize optical pulse trains from an Er-fiber frequency comb to the remote site by using a simple and robust phase-conjugate stabilization method. The fractional frequency-transfer instability at the remote site is 2.6×10(-14) and 4.9×10(-17) for averaging times of 1 and 10,000 s, respectively. Then, we reproduce the harmonic of the repetition rate from the disseminated optical pulse trains at an arbitrary point along the fiber link to test comb-based multiple-access performance, and demonstrate frequency instability of 4×10(-14) and 7×10(-17) at 1 and 10,000 s averaging time, respectively. The proposed comb-based multiple-access frequency dissemination can easily achieve highly stable wideband microwave extraction along the whole link.

Kerr nonlinearity mitigation in 5 × 28-GBd PDM 16-QAM signal transmission over a dispersion-uncompensated link with backward-pumped distributed Raman amplification.

We present experimental and numerical investigations of Kerr nonlinearity compensation in a 400-km standard single-mode fiber link with distributed Raman amplification with backward pumping. A dual-pump polarization-independent fiber-based optical parametric amplifier is used for mid-link spectral inversion of 5 × 28-GBd polarization-multiplexed 16-QAM signals. Signal quality factor (Q-factor) improvements of 1.1 dB and 0.8 dB were obtained in the cases of a single-channel and a five-channel wavelength-division multiplexing (WDM) system, respectively. The experimental results are compared to numerical simulations with good agreement. It is also shown with simulations that a maximum transmission reach of 2400 km enabled by the optical phase conjugator is possible for the WDM signal.

Colorless Amplified WDM-PON Employing Broadband Light Source Seeded Optical Sources and Channel-by-Channel Dispersion Compensators for &gt;100 km Reach

We have demonstrated an amplified wavelength-division multiplexed (WDM) passive optical network (PON) by using broadband light source (BLS) seeded optical sources and chirped fiber Bragg gratings (FBGs) based dispersion compensators. Chirped FBGs located at central office (CO) were fabricated and used as channel-by-channel dispersion compensators in order to mitigate the dispersion-induced distortion of both downstream and upstream signals. Owing to a low insertion loss of chirped FBG based dispersion compensator, the optical signal-to-noise ratio (OSNR) of the downstream signal could be improved to be ~28 dB. Thus, we re-confirmed that an error-free transmission of 1.25 Gb/s signals over a 100 km single-mode fiber (SMF) link could be achieved with a proposed amplified WDM-PON architecture. We have also evaluated the impact of various noises on the system's performance, and found that the low OSNR of the downstream signal would be a main limiting factor on the maximum reach of the proposed amplified WDM-PON architecture. From the measured ~13 dB improvement in OSNR of the downstream signal compared to our previously-proposed dispersion compensating module based scheme, we believe that the proposed architecture can accommodate a reach of longer than 100 km SMF link easily.

A novel approach for simultaneous millimeter wave generation and high bit rate data transmission for Radio over Fiber (RoF) systems

We propose a novel method for simultaneous transmission of OC-192 (9.95328Gbps) digital data and 60GHz RF generation in a Standard Single Mode Fiber (SSMF) link utilizing Stimulated Brillouin Scattering (SBS). The system comprises of a 1550nm DFB Laser diode, Mach Zehnder modulator (MZM), 50km SSMF and Optical receiver. The receiver includes laser diode for optical pump, a regenerator for data retrieval and a RF bandpass filter for RF generation. This system requires minimum number of RF and optical components for the generation of 60GHz RF. The remotely generated 60GHz RF signal may be used for wireless transmission of data. The entire link is simulated in Optisystem software to analyze the system performance.

Terabit Nyquist PDM-32QAM signal transmission with training sequence based time domain channel estimation.

We propose a time domain structure of channel estimation for coherent optical communication systems, which employs training sequence based equalizer and is transparent to arbitrary quadrature amplitude modulation (QAM) formats. Enabled with this methodology, 1.02 Tb/s polarization division multiplexed 32 QAM Nyquist pulse shaping signal with a net spectral efficiency of 7.46 b/s/Hz is transmitted over standard single-mode fiber link with Erbium-doped fiber amplifier only amplification. After 1190 km transmission, the average bit-error rate is lower than the 20% hard-decision forward error correction threshold of 1.5 × 10(-2). The transmission distance can be extended to 1428 km by employing intra-subchannel nonlinear compensation with the digital back-propagation method.

Long-haul dual-channel bidirectional chaos communication based on polarization-resolved chaos synchronization between twin 1550 nM VCSELs subject to variable-polarization optical injection

Based on the polarization-resolved chaos synchronization between twin 1550nm vertical-cavity surface-emitting lasers (VCSELs), a novel long-haul dual-channel bidirectional chaos communication system is proposed. In this system, a time delay signature (TDS)-suppressed chaotic signal, generated by a driving VCSEL (D-VCSEL) under double external cavity feedbacks (DECFs), simultaneously injects into twin VCSELs by variable-polarization optical injection (VPOI) to synchronize them and enhance the chaos output bandwidth of the two VCSELs. The simulated results show that, under proper injection parameters, high-quality polarization-resolved chaos synchronization between the twin VCSELs can be achieved; meanwhile the bandwidths of chaotic signals output from the twin VCSELs have been enhanced in comparison with that of the driven chaotic signal. Based on the high-quality polarization-resolved chaos synchronization, after adopting polarization-division-multiplexing (PDM) and chaos masking (CM) techniques, four 10Gb/s messages hidden respectively in four chaotic carriers can be decrypted effectively after propagating 15km in single-mode fiber (SMF) links. After adopting dispersion-shifted fibers (DSFs) as fiber links, the dual-channel bidirectional chaos communication distance can be extended to 140km.

Performance enhanced down-stream signalling for next generation long-reach 10 Gbit/s passive optical networks

In this paper, we have analyzed the signal processing methods both in digital and optical domain to enhance the transmission performance of downstream signalling in long reach passive optical networks (LR-PONs). The impact of non-linear (NL) equalization through signal processing, i.e. Volterra Equalization (VE), Digital Backpropagation (BP) and Optical Phase Conjugation with Non-linearity Module (OPC-NM) is investigated, in 10Gbit/s (XG) DP-QPSK long-reach wavelength division multiplexed (WDM) PONs without midspan repeaters over 120km standard single mode fibre (SMF) link for down-stream signals. Due to the compensation of optical Kerr effects, the sensitivity penalty is reduced to 2dB by BP algorithm, 1.5dB by VE algorithm and 2.69dB by OPC-NM. Moreover, with the implementation of NL equalization technique we are able to get the transmission distance of 126.6km SMF for the 1:1024 split-ratio at 5GHz channel spacing in the non-linear region. Furthermore, the concept of super passive optical network (S-PON) is also evaluated, which involves a repeater stage consisting of optical amplifiers, to study the feasibility for receiver side signal processing and simplification.

Transmission and demodulation of multi-polarization-multiplexed signals

We propose the configuration of signal multiplexing with four polarization states and investigate its transmission performance over single-mode fiber links. Using coherent detection and digital signal processing, a demodulation scheme for four-polarization-multiplexed (4PM) system is presented. We discuss the impact of crosstalk from polarization mode dispersion and polarization beam splitter misalignment on the proposed 4PM system. Furthermore, the transmission distance could be doubled to ~50 km by employing feedback decision equalizers.

Signal Processing Algorithms for Down-Stream Traffic in Next Generation 10 Gbit/s Fixed-Grid Passive Optical Networks

We have analyzed the impact of digital and optical signal processing algorithms, that is, Volterra equalization (VE), digital backpropagation (BP), and optical phase conjugation with nonlinearity module (OPC-NM), in next generation 10 Gbit/s (also referred to as XG) DP-QPSK long haul WDM (fixed-grid) passive optical network (PON) without midspan repeaters over 120 km standard single mode fiber (SMF) link for downstream signals. Due to the compensation of optical Kerr effects, the sensitivity penalty is improved by 2 dB by implementing BP algorithm, 1.5 dB by VE algorithm, and 2.69 dB by OPC-NM. Moreover, with the implementation of NL equalization technique, we are able to get the transmission distance of 126.6 km SMF for the 1 : 1024 split ratio at 5 GHz channel spacing in the nonlinear region.

Experimental evaluation of the BER performance in optical OFDM system based on discrete Hartley transform precoding

We experimentally assess the bit error rate (BER) performance of an intensity modulation/direct detection (IM/DD) optical orthogonal frequency division multiplexing (OFDM) system based on discrete Hartley transform (DHT) precoding in single-mode fiber (SMF) link for 2.5 Gbit/s quadrature phase shift keying (QPSK) OFDM symbol rate. The experimental results show that for the optical OFDM system based on DHT-precoding, the receiver sensitivity at the BER of 10−4 after 100 km SMF transmission is about 1.5 dBm better than that of the original QPSK OFDM signal, and the DHT-precoded OFDM QPSK signal can achieve approximately 1.3 dB of peak-to-average power ratio (PAPR) reduction.

System performance enhancement with pre-distorted OOFDM signal waveforms in DM/DD systems

In this work we propose a pre-distortion technique for the mitigation of the nonlinear distortion present in directly modulated/detected OOFDM systems and explore the system performance achieved under varying system parameters. Simulation results show that the proposed pre-distortion technique efficiently mitigates the nonlinear distortion, achieving transmission information rates around 40 Gbits/s and 18.5 Gbits/s over 40 km and 100 km of single mode fiber links, respectively, under optimum operating conditions. Moreover, the proposed pre-distortion technique can potentially provide higher system performance to that obtained with nonlinear equalization at the receiver.

Field demonstration of mode-division multiplexing upgrade scenarios on commercial networks

We demonstrate three possible scenarios for upgrading current single-mode transmission networks with high capacity few-mode fiber technology using mode-division multiplexing (MDM). The results were obtained from measurements over a number of field-deployed single-mode fiber links with an additional experimental in-line amplified few-mode fiber link. The results confirm the viability of employing MDM using few-mode fiber technology to gradually replace legacy optical systems.

Counteracting 16-QAM Optical Fiber Transmission Impairments With Iterative Turbo Equalization

A turbo equalization (TE) scheme based on convolutional code and normalized least mean square equalizer for coherent optical communication links is proposed and experimentally demonstrated. The proposed iterative TE technique is proved effective for counteracting polarization-division-multiplexing 16 quadrature amplitude modulation impairments in dispersion uncompensated coherent transmission links. Gains exceeding one order of magnitude in terms of bit error rate are obtained in experimental validation up to 497 km-standard single mode fiber link transmission.