• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-04
Nicolas Dupuis; Fuad Doany; Russell A. Budd; Laurent Schares; Christian W. Baks; Daniel M. Kuchta; Takako Hirokawa; Benjamin G. Lee

We present a strictly nonblocking $4$ × $4$ electrooptic silicon photonic switch fabric with on-chip gain. The switch integrates 12 Mach-Zehnder cells in a 3-stage topology equipped with fast electrooptic phase shifters, and thermooptic phase trimmers. To compensate for the losses of the fabric, a 4-channel GaInAsP/InP semiconductor optical amplifier array is flip-chip attached into an etched cavity in the silicon photonic chip with butt-coupled waveguide interfaces. The chip is wirebonded to a CMOS driver that provides push-pull drive to each elementary Mach-Zehnder cell. We demonstrate an optical switch assembly with net neutral insertion loss in the C-band together with nanosecond-scale reconfiguration time.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-30
Jiao Zhang; Jianjun Yu; Jun Shan Wey; Xinying Li; Li Zhao; Kaihui Wang; Miao Kong; Wen Zhou; Jiangnan Xiao; Xiangjun Xin; Feng Zhao

We experimentally demonstrate the downstream transmission of a 100 Gb/s/λ time division multiplexed passive optical network (TDM-PON) based on four-level pulsed amplitude modulation (PAM-4) in the O-band using 10 Gbps transmitters with semiconductor optical amplifier (SOA) and digital signal processing (DSP) at the receiver. Considering the soft-decision FEC (SD-FEC) threshold (1 × 10 −2 ), power budget of 30.3 dB and 29.3 dB have been achieved after 22 km and 50 km fiber transmission, respectively. There is no observable dispersion penalty after 22 km and 50 km transmission. The possibility of 100 Gb/s/λ PON is first investigated using intensity modulation and direct detection (IM/DD) schemes rather than coherent detection schemes.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-07
Yishen Huang; Qixiang Cheng; Yu-Han Hung; Hang Guan; Xiang Meng; Ari Novack; Matthew Streshinsky; Michael Hochberg; Keren Bergman

We demonstrate the first multi-stage 8 × 8 silicon photonic switch with switching elements based on dual add-drop microrings with a compact footprint of 4 mm 2 . This device leverages co-design of the switch architecture and the switching elements with a well-balanced set of performance metrics. The switching elements are designed to have a 3-dB optical passband of 165 GHz, exhibiting off- and on-resonance losses of 0.67 dB and 2 dB, respectively. Full characterization of all switch paths shows an end-to-end on-chip loss between 4.4 and 9.6 dB, with worst-case crosstalk leakage averaged at −16 dB. Owing to the efficient doped waveguide thermo-optic phase shifters, the device features a tuning efficiency of 48.85 GHz/mW. The reconfiguration time of the switch fabric is measured to be 1.2 μs and 0.5 μs at the rise and fall edge, respectively. The dual-microring switching element together with the multi-stage architecture preserves an end-to-end passband over 55 GHz. We validate the switch performance with optical paths of varying numbers of on- and off-resonance switching elements – less than 2 dB power penalties are obtained for all data routings at 32 Gbps.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-19
Jianping Yao; Weifeng Zhang

Fiber Bragg gratings have been invented for over three decades now and have been intensively employed in optical communication and sensor systems. The key limitation of a fiber Bragg grating is that once fabricated, it is hard to be tuned or with very limited tunability via thermal or mechanical tuning. Recently, great efforts have been directed into the study of realizing Bragg gratings on silicon-on-insulator (SOI) platform. The key advantage of Bragg gratings based on SOI is that the gratings can be fast and electrically reconfigured with the use of free-carrier plasma dispersion effect in silicon, which can be employed for fast programmable photonic signal processing. In this article, Bragg gratings based on SOI that are electrically programmable will be reviewed and their use for advanced programmable optical and microwave signal processing will be discussed.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-08
Yong Zhang; Ruihuan Zhang; Qingming Zhu; Yuan Yuan; Yikai Su

Switching can be performed with multiple physical dimensions of an optical signal. Previously optical switching was mainly focused in the wavelength domain. In this paper we discuss the general architecture of integrated silicon photonic switches by exploiting multi-dimensions in wavelength, polarization, and mode. To route a data channel from one input port to an arbitrary output port in a network node, three basic functions are required: de-multiplexing, switching, and multiplexing. The multiplexing and de-multiplexing processes can be realized in any one physical dimension. The capacity of a switch can be effectively scaled by using joint physical dimensions. As two examples, we first present a wavelength switch based on dual-nanobeam cavities with high quality factors, a low power consumption, and a compact footprint. We then propose a design of a mode-polarization-wavelength selective switch by leveraging three physical dimensions, and experimentally demonstrate the building blocks and key functionalities.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-12
Keijiro Suzuki; Ryotaro Konoike; Nobuyuki Yokoyama; Miyoshi Seki; Minoru Ohtsuka; Shigeru Saitoh; Satoshi Suda; Hiroyuki Matsuura; Koji Yamada; Shu Namiki; Hitoshi Kawashima; Kazuhiro Ikeda

We fabricate and characterize a polarization-diversity 32 × 32 silicon photonics switch by newly introducing SiN overpass waveguides onto our nonduplicate polarization-diversity path-independent insertion-loss switch. The SiN overpass waveguides are used to simplify the optical paths with a uniform path length between the edge couplers and the switch matrix and significantly reduce the number of waveguide intersections. The switch chip is fabricated using a 300-mm silicon-on-insulator wafer pilot line. The fabricated switch comprises more than 7,600 components, making this the largest ever complementary-metal-oxide-semiconductor-based silicon photonics circuit. The switch chip is electrically and optically packaged and evaluated for a sampled port connection with 32 paths, with an average on-chip loss of ∼35 dB and an average polarization-dependent loss of 3.2 dB where 75% of the measured paths exhibit a loss of less than 3 dB. The differential group delay is measured to be 1.7 ps. The performance can be further improved by optimizing the device design.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-12
Keijiro Suzuki; Ryotaro Konoike; Satoshi Suda; Hiroyuki Matsuura; Shu Namiki; Hitoshi Kawashima; Kazuhiro Ikeda

We review the research progress of strictly nonblocking optical switches based on silicon photonics. We have developed a switch chip fabrication process based on a complementary metal-oxide-semiconductor pilot line and optical and electrical packaging technologies. We demonstrated all-paths transmission and switching of up to 32 input ports × 32 output ports with an average fiber-to-fiber insertion loss of 10.8 dB. Furthermore, we demonstrated an operating bandwidth wider than 100 nm for −30 dB crosstalk with double-Mach–Zehnder element switches in an 8 × 8 switch. For polarization-insensitive operation, we adopted a polarization diversity scheme and fabricated an 8 × 8 switch with fiber-based polarization-beam-splitters and two switch chips. The 8 × 8 switch exhibited a polarization-dependent loss of less than 0.5 dB. Moreover, an on-chip polarization diversity 8 × 8 switch integrated with polarization splitter rotators and two switch matrices on a single chip demonstrated a differential group delay less than 1 ps. Based on current technologies, we discuss the prospects for further port count expansion and remaining challenges for commercial deployment.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-06-27
Zizhuo Liu; Constanze Hantschmann; Mingchu Tang; Ying Lu; Jae-Seong Park; Mengya Liao; Shujie Pan; Ana Sanchez; Richard Beanland; Mickael Martin; Thierry Baron; Siming Chen; Alwyn Seeds; Richard Penty; Ian White; Huiyun Liu

High-performance III–V quantum-dot lasers monolithically grown on Si substrates have been demonstrated as a promising solution to realize Si-based laser sources with very low threshold current density, high output power, and long lifetime, even with relatively high density of defects due to the material dissimilarities between III–Vs and Si. On the other hand, although conventional III–V quantum-well lasers grown on Si have been demonstrated after great efforts worldwide for more than 40 years, their practicality is still a great challenge because of their very high threshold current density and very short lifetime. However, the physical mechanisms behind the superior performance of silicon-based III–V quantum-dot lasers remain unclear. In this paper, we directly compare the performance of a quantum-well and a quantum-dot laser monolithically grown on on-axis Si (001) substrates, both experimentally and theoretically, under the impact of the same density of threading dislocations. A quantum-dot laser grown on a Si substrate with a high operating temperature (105 °C) has been demonstrated with a low threshold current density of 173 A/cm 2 and a high single facet output power >100 mW at room temperature, while there is no lasing operation for the quantum-well device at room temperature even at high injection levels. By using a rate equation travelling-wave model, the quantum-dot laser's superior performance compared with its quantum well-based counterpart on Si is theoretically explained in terms of the unique properties of quantum dots, i.e., efficient carrier capture and high thermal energy barriers preventing the carriers from migrating into defect states.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-06-24
Yoshihiro Ogiso; Josuke Ozaki; Yuta Ueda; Hitoshi Wakita; Munehiko Nagatani; Hiroshi Yamazaki; Masanori Nakamura; Takayuki Kobayashi; Shigeru Kanazawa; Yasuaki Hashizume; Hiromasa Tanobe; Nobuhiro Nunoya; Minoru Ida; Yutaka Miyamoto; Mitsuteru Ishikawa

We report a promising IQ optical modulator for beyond 100-GBd transmitter. By introducing both a new n-i-p-n heterostructure and an optimized capacitance-loaded traveling-wave electrode (CL-TWE), high-frequency electrical losses of the modulator can be drastically reduced. As a result, we extended an electro-optic (EO) bandwidth without degrading other properties, such as half-wave voltage (V π ) and optical losses. The 3-dB EO bandwidth of the 1.5-V V π modulator reaches 80 GHz. Furthermore, we demonstrated up to 128-GBd IQ modulations by co-assembling with an ultra-broadband InP-based driver IC.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-23
Sasan Zhalehpour; Mengqi Guo; Jiachuan Lin; Zhuhong Zhang; Yaojun Qiao; Wei Shi; Leslie Ann Rusch

We experimentally demonstrate the highest, to the best of our knowledge, reported net rate in a SiP IQ modulator. At 100 Gbaud 32QAM (quadrature amplitude modulation), and assuming 20% FEC (forward error correction) overhead, we achieved a dual polarization net rate of 833 Gb/s. This record was achieved by adapting digital signal processing to the challenging pattern dependent distortion encountered in the nonlinear and bandwidth limited regime. First the Mach Zehnder modulator (MZM) operating point (trading off modulation efficiency and 3 dB bandwidth) and linear compensation (electrical and optical) are jointly optimized. Next, the key application of nonlinear pre- and post-compensation are explored. We show that nonlinear processing at the transmitter, in our case an iterative learning control (ILC) method, is essential as post-processing alone could not achieve reliable communications at 100 Gbaud. Nonlinear post-compensation algorithms pushed the performance under the FEC threshold with the introduction of structured intersymbol interference in post processing and a simple one-step maximum likelihood sequence detector. We provide detailed descriptions of our methodology and results.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-10
Yongkang Gao; Jiann-Chang Lo; Shing Lee; Ronak Patel; Likai Zhu; Jocelyn Nee; Diana Tsou; Rob Carney; Jibin Sun

We have demonstrated a hybrid-integrated silicon photonic (SiPh) tunable laser in a miniaturized package suitable for coherent modules in small form factors such as OSFP and QSFP-DD. Through the integration of an in-house-designed high-power semiconductor optical amplifier (SOA), the developed SiPh laser has achieved a record-high output power of 21.5 dBm across the C-band. Also, this laser exhibits narrow linewidths down to 60 kHz, SMSR larger than 50 dB, low relative intensity noise below −150 dB/Hz, and a broad tuning range of 65 nm. These performance parameters are preferable for 400 Gb/s and beyond coherent communications using advanced high-order modulation formats. Moreover, an on-chip integrated sensor technology was developed for accurate laser frequency control. We have achieved 1 GHz frequency stability of SiPh laser against SOA current changes or package temperature variations between 10 °C and 80 °C. We further show the feasibility of this developed SiPh laser for 64 Gbaud, 16/64 QAM coherent transmission by integrating with an in-house InP-PLC hybrid coherent optical subassembly (COSA).

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-05
Jianying Zhou; Jian Wang; Likai Zhu; Qun Zhang

We achieved high performance high speed silicon photonics carrier-depletion Mach-Zehnder modulation with commercial foundry by co-optimization of doping and device design assisted with an accurate electro-optical (EO) model. We demonstrated high performance IQ modulators operating at 85 Gbaud 16 QAM and 64 Gbaud 64 QAM with extinction ratio of over 25 dB. For the design of the high performance all-silicon carrier depletion modulator, we developed modeling and design tools to provide not only accuracy, but also efficiency in the simulation of distributed optical and electronic characteristics of travelling waveguides with different designs of optical and microwave waveguides under various doping conditions, which allow the co-design of velocity phase match between optical and microwave waveguides and the impedance match between microwave travelling waveguide and terminal impedance. Our experimental characterization test data agreed well with the model simulation data. More recently, with practical Nyquist filter and linear compensation in commercial arbitrary wave generator (AWG) and optical modulation analyzer (OMA), we demonstrated 100 Gbaud 32 QAM with an all-silicon IQ modulator, which has 6 dB electro-optical bandwidth of 50 GHz and BER achieving FEC threshold with a modern FEC, showing the potential for Tb/s applications.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-29
Rubab Amin; Rishi Maiti; Jonathan K. George; Xiaoxuan Ma; Zhizhen Ma; Hamed Dalir; Mario Miscuglio; Volker J. Sorger

Here, we experimentally demonstrate an Indium Tin Oxide (ITO) Mach—Zehnder interferometer heterogeneously integrated in silicon photonics. The phase shifter section is realized in a novel lateral MOS configuration, which, due to favorable electrostatic overlap, leads to efficient modulation (V π L = 63 V . μm). This is achieved by (i) selecting a strong index changing material (ITO) and (ii) improving the field-overlap as verified by the electrostatic field lines. Furthermore, we show that this platform serves as a building block in an end-fire silicon photonics optical phased array (OPA) with a half-wavelength pitch within the waveguides with anticipated performance, including narrow main beam lobe (<3°) and >10 dB suppression of the side lobes, while electrostatically steering the emission profile up to ±80°, and if further engineered, can lead not only towards nanosecond-fast beam steering capabilities in LiDAR systems but also in holographic display, free-space optical communications, and optical switches.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-07
Georg Rademacher; Ruben S. Luís; Benjamin J. Puttnam; Yoshinari Awaji; Naoya Wada

Crosstalk-power in homogenous single-mode multi-core fibers can vary by more than 20 dB over time and frequency. The extend of these fluctuations depends on the interacting cores’ propagation parameters and the transmitted modulation format. Furthermore, the polarizations of signal and crosstalk can change randomly during transmission. In this paper, we describe the effect of random crosstalk-power variations and the relative signal-crosstalk polarization fluctuations when transmitting single-polarization, intensity-modulated signals such as on-off-keying. We show experimentally that the polarization of a signal fluctuates slower than the polarization of crosstalk, indicating uncorrelated processes. We further investigate the system impact of both, crosstalk-power fluctuations and the relative signal-crosstalk polarization variations on a 10 Gb/s on-off-keying transmission system employing a 10.1 km 19-core multi-core fiber. We show that the two-dimensional space of random fluctuations that is spanned by crosstalk power and relative signal-crosstalk polarization can vary the system's bit error rate by more than five orders of magnitude.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-05
Scott R. Bickham; Marlene A. Marro; James A. Derick; Wen-Lung Kuang; Ximao Feng; Yan Hua

Data centers are continually striving to meet the challenge of delivering more bandwidth, and this will require higher capacity optical switches and servers. One proposal for achieving this higher bandwidth density is to use embedded optical transceivers, which have arrays of VCSEL or silicon-photonic lasers integrated into on-board and co-packaged optics. The capacities of these transceivers are limited by the densities of the arrays, which in turn depend on the physical dimensions of the optical fibers that are coupled to the chip. This size constraint is motivating component manufacturers to consider using optical fibers with reduced cladding (RC) and coating diameters to enable higher density interconnects. In this paper, we introduce bend-insensitive single-mode and multimode RC fibers that have low attenuation, low bend loss, and are backward-compatible with the installed base of standard optical fibers. We also discuss how these RC fibers can be integrated into fiber array units to create a high-density fiber-chip connectivity solution.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-02
Darli A. A. Mello; Hrishikesh Srinivas; Karthik Choutagunta; Joseph M. Kahn

Motivated by the recent interest in single-mode semiconductor optical amplifiers and multimode erbium-doped fiber amplifiers, we present a unified, comprehensive treatment of the effect of polarization- and mode-dependent gain (PDG and MDG) on the capacity of ultra-long-haul transmission systems. We study the problem using simulations of a multisection model, including the effects of PDG or MDG and polarization mode dispersion (PMD) or modal dispersion. We also analytically derive exact expressions for the capacity distribution of PDG-impaired single-mode systems. In agreement with previous work, we find that PDG and MDG cause fluctuations in capacity, which reduces average capacity and may cause outage. We show that the multimode systems studied, with at least $D = 14$ spatial/polarization modes, have sufficient modal diversity and frequency diversity to strongly suppress capacity fluctuations and reduce outage probability so that the outage capacity approaches the average capacity. We show that single-mode systems, by contrast, inherently provide low modal and frequency diversity, making them more prone to outage. To alleviate this problem, frequency diversity can be increased by artificially inserting PMD. Finally, we quantify the PDG/MDG requirements of optical amplifiers to ensure that the average capacity is close (within a 1-2 dB effective SNR loss) to the theoretical optimum. We show that these PDG/MDG requirements are stringent, especially considering the minimum-mean-square error linear equalizers implemented in typical multiple-input multiple-output receivers.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-18
Mark Pelusi; Takashi Inoue; Shu Namiki

The limits of narrowband Brillouin gain for improving the carrier to noise ratio (CNR) of spectral lines is evaluated for 64-QAM communications. Calculations of the change in CNR for practical gain, noise, and bandwidth parameters indicate the maximum obtainable CNR enhancement factor and output CNR as being ≈25 dB and ≈40∼43 dB/0.1 nm, respectively, limited by the narrowness of the Brillouin gain bandwidth and Brillouin amplifier noise, respectively. These limits determined from the relative power suppression of out of band noise contained within a 10 GHz channel bandwidth are relevant to spectral line amplification either before data modulation at the transmitter, or for a local oscillator (LO) at the receiver for coherent detection. A calibration measurement of the bit error rate (BER) of a 48 Gb/s 64-QAM signal versus CNR of a LO loaded with ASE noise is used to extrapolate the BER from the calculated CNR for Brillouin gain. The results predict the BER being minimally degraded for an input CNR of ≈>20 dB/0.1 nm and falling below the hard decision FEC limit for an input CNR as low as ≈0 dB/0.1 nm. The estimates are found consistent with 64-QAM signal experiments of pilot tone carrier recovery by Brillouin gain for both single channel and WDM cases. The insight aids the design and estimation of achievable performance improvement for applying Brillouin amplifiers to coherent communications.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-07-23
Xingyuan Xu; Jiayang Wu; Mengxi Tan; Thach G. Nguyen; Sai T. Chu; Brent E. Little; Roberto Morandotti; Arnan Mitchell; David J. Moss

We report a broadband microwave frequency converter based on a coherent Kerr optical micro-comb generated by an integrated micro-ring resonator. The coherent micro-comb displays features that are consistent with soliton crystal dynamics with a free spectral range of 48.9 GHz. We use this to demonstrate a high-performance millimeter-wave local oscillator for microwave frequency conversion. We experimentally verify the microwave performance up to 40 GHz, achieving a ratio of −6.8 dB between output radio frequency power and intermediate frequency power and a spurious suppression ratio of >43.5 dB. The experimental results show good agreement with theory and verify the effectiveness of microwave frequency converters based on coherent optical micro-combs, with the ability to achieve reduced size, complexity, and potential cost.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-19
Qijie Xie; Honghui Zhang; Chester Shu

The programmable envelope shaping technique of high-repetition-rate optical pulse sequences with low-speed modulation is summarized in this letter. First, we reviewed our work on amplitude-only modulation approach for generating symmetric envelopes, including parabolic, step-like and binary patterns. Next, we reported our recent demonstration of asymmetric-enveloped pulse generation achieved by applying simultaneous amplitude and phase modulations. The asymmetric patterns we demonstrated include a trapezoid envelope and a random optical pattern. Finally, we analyze the influence of practical issues of the implementation on the generated optical pulse trains through numerical simulation. The newly proposed scheme provides flexibility in envelope processing and enriches the diversity of temporal pulse shapes.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-19
G. Cincotti; T. Murakawa; T. Nagashima; S. Shimizu; M. Hasegawa; K. Hattori; M. Okuno; S. Mino; A. Himeno; N. Wada; H. Uenohara; T. Kodama; T. Konishi

We present a power-efficient and reduced-complexity all-optical approach to generate high-bit rate superchannels, based on joint time-frequency multiplexing. Both optical orthogonal frequency division multiplexing (OFDM) and Nyquist-optical time division multiplexing (N-OTDM) signals are generated and processed using a wavelength-selective switch (WSS). We use the fractional Fourier transform (FrFT) to introduce the largest degree of flexibility in optical networking, and we experimentally demonstrate that the transmitted signal can be received either in parallel, as OFDM subcarriers, or in series, as an N-OTDM signal. Compared to conventional optical OFDM, we achieve peak to average power ratio (PAPR) reduction; compared to N-OTDM, we introduce flexible chromatic dispersion (CD) management. We successfully demonstrate a field trial experiment of 4-channel 40 Gb/s hybrid OFDM/N-OTDM transmission over the 89.2-km Japan gigabit network-extreme (JGN X) test bed, with 1 bit/s/Hz spectral efficiency.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-28
Sergey Turitsyn; Egor Sedov; Alexey Redyuk; Mikhail Fedoruk

The nonlinear Schrödinger equation (NLSE) is often used as a master path-average model for fiber-optic links to analyze fundamental properties of such nonlinear communication channels. Transmission of a signal in nonlinear channels is conceptually different from linear communications. We use here the NLSE channel model to explain and illustrate some new unusual features introduced by nonlinearity. In general, NLSE describes the co-existence of dispersive (continuous) waves and localized (here in time) waves: soliton pulses. The nonlinear Fourier transform method allows one to compute for any given temporal signal the so-called nonlinear spectrum that defines both continuous spectrum (analog to conventional Fourier spectral presentation) and solitonic components. Nonlinear spectrum remains invariant during signal evolution in the NLSE channel. We examine conventional orthogonal frequency-division multiplexing (OFDM) and wavelength-division multiplexing (WDM) return-to-zero signals and demonstrate that both signals at certain power levels have soliton component. We would like to stress that this effect is completely different from the soliton communications studied in the past. Applying Zakharov–Shabat spectral problem to a single WDM or OFDM symbol with multiple sub-carriers, we quantify the effect of statistical occurrence of discrete eigenvalues in such an information-bearing optical signal. Moreover, we observe that at signal powers optimal for transmission, an OFDM symbol with high probability has a soliton component.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-16
Ahmad Fallahpour; Fatemeh Alishahi; Kaiheng Zou; Yinwen Cao; Ahmed Almaiman; Arne Kordts; Maxim Karpov; Martin Hubert Peter Pfeiffer; Karapet Manukyan; Huibin Zhou; Peicheng Liao; Cong Liu; Moshe Tur; Tobias J. Kippenberg; Alan E. Willner

A tunable and reconfigurable optical aggregation system is experimentally demonstrated. Optical Nyquist pulses are generated on multiple channels using a microresonator-based Kerr optical frequency comb and insertion of uniform lines by an intensity modulator. Data are modulated on optically generated Nyquist pulses and aggregated through nonlinear wave mixing in a periodically poled lithium niobate (PPLN) waveguide. Two quadrature-phase-shift-keying (QPSK) channels are aggregated to a single 16-quadrature amplitude modulation (16-QAM) channel of Nyquist pulses. To demonstrate the system tunability, we perform aggregation over different baud rates and different modulation formats. The reconfigurability of the system is demonstrated by aggregating two binary-phase-shift-keying (BPSK) channels into a QPSK or a 2-level amplitude-shift keying and a 2-level phase-shift keying (2-ASK/2-PSK) channel by tuning the relative phase and amplitude of the inputs. Furthermore, three BPSK channels are aggregated into one 4-ASK/2-PSK channel. The quality of the aggregated channel is investigated using two different approaches for wave mixing in the PPLN waveguide.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-13
Xinying Li; Jianjun Yu; Gee-Kung Chang

To meet the enhanced-mobile-broadband (eMBB) challenges in 5G, we have systematically explored the potential of the photonics-aided millimeter-wave (mm-wave) communication in terms of the wireless transmission capacity and distance it can accommodate. Enabled by various kinds of advanced multiplexing and digital-signal-processing (DSP) techniques, we have successfully achieved the significant enhancement of the wireless mm-wave signal transmission capacity from 100 Gb/s to 400 Gb/s, even to 1 Tb/s. Since our large-capacity (>100-Gb/s) experimental demonstrations typically have a very short wireless transmission distance of several meters, we have further explored the techniques for the extension of the wireless mm-wave signal transmission distance, and successfully achieved a series of field-trial demonstrations on photonics-aided long-distance (>100-m) wireless mm-wave signal transmission. We have realized the record-breaking product of wireless transmission capacity and distance, i.e., 54 Gb/s × 2.5 km.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-21
Bernhard Schrenk; Fotini Karinou

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-07-29
Haolin Li; Michiel Verplaetse; Jochem Verbist; Joris Van Kerrebrouck; Laurens Breyne; Chia-Yi Wu; Laurens Bogaert; Bart Moeneclaey; Xin Yin; Johan Bauwelinck; Piet Demeester; Guy Torfs

All-digital radio-over-fiber (RoF) transmission has attracted a significant amount of interest in digital-centric systems or centralized networks because it greatly simplifies the front-end hardware by using digital processing. The sigma-delta modulator (SDM)-based all-digital RoF approach pushes the digital signal processing as far as possible into the transmit chain. We present a real-time 100-GS/s fourth-order single-bit SDM for all-digital RoF transmission in the high-frequency band without the aid of analog/optical up-conversion. This is the fastest sigma-delta modulator reported and this is also the first real-time demonstration of sigma-delta-modulated RoF in the frequency band above 24 GHz. 4.68 Gb/s (2.34 Gb/s) 64-QAM is transported over 10-km standard single-mode fiber in the C-band with 6.46 $\text{}\%$ (4.73 $\%$ ) error vector magnitude and 3.13 Gb/s 256-QAM can be even received in an optical back-to-back configuration. The carrier frequency can be digitally tuned at run-time, covering a wide frequency range from 22.75 to 27.5 GHz. Besides, this high-speed sigma-delta modulator introduces less than 1 μs latency in the transmit chain. Its all-digital nature enables network virtualization, making the transmitter compatible with different existing standards. The prominent performance corroborates the strong competitiveness of this SDM-based RoF approach in high-frequency RoF 5G communication.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-11
Abel Lorences-Riesgo; Fernando P. Guiomar; Artur N. Sousa; António L. Teixeira; Nelson J. Muga; Maria C. R. Medeiros; Paulo P. Monteiro

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-21
Motoharu Matsuura; Nana Tajima; Hayato Nomoto; Daisuke Kamiyama

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-20
Minkyu Sung; Joonyoung Kim; Eon-Sang Kim; Seung-Hyun Cho; Young-Jun Won; Byoung-Chul Lim; Sung-Yeop Pyun; Hoon Lee; Joon Ki Lee; Jong Hyun Lee

In this study, we report the successful demonstration of an intermediate-frequency-over-fiber (IFoF)–based radio access network (RAN) for 28 GHz millimeter-wave (mmWave)-based 5G mobile communication. In order to increase the network coverage of the mmWave-based 5G networks, we propose a distributed antenna system (DAS) that uses the IFoF technology. An IFoF-based DAS with 2 × 2 multiple-input multiple-output (MIMO) configuration was deployed in the PyeongChang area to provide 5G trial demonstration during the Winter Olympics. 5G trial services such as high-speed data transfer and autonomous vehicle driving were offered to the public through the IFoF-based DAS. A downlink throughput of ∼1 Gb/s and uplink throughput of ∼200 Mb/s were achieved in the DAS-deployed area. We also present an IFoF-based 5G mobile fronthaul that can overcome the bandwidth bottleneck in RANs. We performed real-time transmission of mmWave-based 5G wireless access networks using the IFoF-based mobile fronthaul. The real-time downlink throughput achieved per 5G terminal was approximately 9 Gb/s, when using a 4 × 4 MIMO configuration. An outdoor demonstration was performed to verify the technical feasibility of the 5G fronthaul based on IFoF technology. When moving the 5G terminal between remote radio heads at a speed less than 60 km/h, 5G mobile broadband services could be provided with real-time throughput more than 5 Gb/s. Thus, we confirmed that the IFoF technology was capable of supporting RANs for mmWave-based 5G networks and providing real-time multi-Gb mobile services.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-16
Xiaobin Sun; Chun Hong Kang; Meiwei Kong; Omar Alkhazragi; Yujian Guo; Mustapha Ouhssain; Yang Weng; Burton H. Jones; Tien Khee Ng; Boon S. Ooi

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-05
Joris Lambrecht; Jochem Verbist; Hannes Ramon; Michael Vanhoecke; Johan Bauwelinck; Xin Yin; Gunther Roelkens

As next-generation data center optical interconnects aim for 0.8 Tb/s or 1.6 Tb/s, serial rates up to 106 GBd are expected. However doubling the bandwidth of current 53 GBd 4-level pulse-amplitude modulation (PAM-4) transmitters is very challenging, and perhaps unfeasible with compact, non-travelling wave, lumped modulators or lasers. In our previous work, we presented an integrated 4:1 optical serializer with electro-absorption modulators (EAMs) in each path. Transmitter (TX) functionality was shown up to 104 GBd non-return-to-zero (NRZ) On-Off Keying (OOK) or PAM-4. However the performance for PAM-4 was limited by the distortion introduced by the EAM non-linearity. We also presented a real-time, DSP-free 128 Gb/s PAM-4 link with a silicon photonic transmitter using binary driven EAMs in a Mach-Zehnder interferometer (MZI) configuration. By combining two of such half-rate (53 GBd) transmitters in an integrated 2:1-serializer, improved 106 GBd PAM-4 performance is expected without needing to compensate the inherent modulator non-linearity and without requiring faster modulators or drivers. In this paper, we present a Silicon integrated 53 GBd PAM-4 TX as a candidate for integration into 106 GBd PAM-4 2:1 serialized TX. The presented TX consists of two EAMs in an MZI configuration, wirebonded to a low-power 55 nm 4-channel SiGe BiCMOS driver, operating at 1.5 pJ/b (excluding laser). With a reference receiver (RX), transmission at or below the KP4-FEC threshold is shown beyond 1km standard single-mode fiber (SSMF) and up to 2 km non-zero dispersion-shifted fiber (NZ-DSF) at 1565 nm. Furthermore, the integrated TX was combined with an Si-integrated RX consisting of the same EAM component, wirebonded to a 55 nm SiGe BiCMOS transimpedance amplifier (TIA). Both TX and RX were wirebonded on an RF-PCB, with electrical connectivity through transmission lines and 6-inch 50 GHz multi-coax cable connectors. With this electrically connectorized all-EAM TX and RX, PAM-4 link operation is shown up to 40 GBd at 3.9 pJ/b (excluding laser), without using DSP or equalization.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-04
Takeo Sasai; Asuka Matsushita; Masanori Nakamura; Seiji Okamoto; Fukutaro Hamaoka; Yoshiaki Kisaka

We numerically and experimentally investigate the laser phase noise tolerance of probabilistically shaped (PS) and uniformly shaped (US) quadrature amplitude modulation (QAM) signals. In the simulations, we compare PS-64QAM to US-16QAM, PS-256QAM to US-64QAM, and PS-1024QAM to US-256QAM under the same information rate (IR). We confirm that a sufficient shaping gain is observed with narrow linewidth lasers, whereas degradation of the shaping gain is clearly observed when large phase noise and high order modulation formats are assumed. In our experiments, we compare polarization-division-multiplexed (PDM) 16-GBd PS-1024QAM and US-256QAM under the same IR using lasers with 0.1-kHz and 40-kHz linewidths. For carrier phase recovery (CPR), we employ a pilot-assisted digital phase locked loop. Results reveal that PS-1024QAM achieves high performance with the 0.1 kHz-laser or >5% pilot ratio, whereas US-256QAM outperforms PS-1024QAM when lasers with 40-kHz linewidth and <5% pilot ratio are used. We also evaluate the pilot ratio dependency of the required optical signal-to-noise ratio at the forward error correction limit and the achievable information rate. Additionally, we compare the performance of two types of CPR updating schemes: updating phase estimation at only the pilot symbol or at all symbols.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-11
Takuo Tanemura; Takahiro Suganuma; Yoshiaki Nakano

Direct-detection (DD) Stokes vector receiver (SVR) has rapidly gained interest for the high-speed datacenter and short-reach links, owing to its capability of recovering 3D optical signals without using expensive coherent detection. In order to reduce the size and cost of SVR, we have recently proposed and demonstrated a simple and compact device with single-ended photodetectors (S-PDs), which can be monolithically integrated on InP. In this paper, we provide comprehensive analysis on the receiver sensitivity for different SVR configurations. From rigorous theoretical investigations, we derive optimal design of SVR to maximize the sensitivity as well as explicit analytical expression of the bit-error-rate assuming an unamplified thermal-noise-limited case. From the obtained results, we find that the optimized 4-port S-PD-based SVR exhibits a moderate penalty of 2.1 dB with respect to the conventional more complicated SVR configuration based on 3-port balanced PDs. Since the proposed S-PD-based SVR can reduce the number of PDs, and requires neither a polarization-beam splitter nor precisely tuned optical interferometer, it may be an attractive candidate in realizing a low-cost and compact fully integrated DD-based receiver for the future >Tb/s short-reach systems, where the power budget is not the primary concern.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-27
Tobias Fehenberger; David S. Millar; Toshiaki Koike-Akino; Keisuke Kojima; Kieran Parsons; Helmut Griesser

In order to realize probabilistically shaped signaling within the probabilistic amplitude shaping (PAS) framework, a shaping device outputs sequences that follow a certain nonuniform distribution. In case of constant-composition (CC) distribution matching (CCDM), the sequences differ only in the ordering of their constituent symbols, whereas the number of occurrences of each symbol is constant in every output block. Recent results by Amari et al. have shown that the CCDM block length can have a considerable impact on the effective signal-to-noise ratio (SNR) after fiber transmission. So far, no explanation for this behavior has been presented. Furthermore, the block-length dependence of the SNR seems not to be fully aligned with previous results in the literature. This paper is devoted to a detailed analysis of the nonlinear fiber interactions for CC sequences. We confirm in fiber simulations the inverse proportionality of SNR with CCDM block length and present two explanations. The first one, which only holds in the short-length regime, is based on how two-dimensional symbols are generated from shaped amplitudes in the PAS framework. The second, more general explanation relates to an induced shuffling within a sequence, or equivalently a limited concentration of identical symbols, that is an inherent property for short CC blocks, yet not necessarily present in case of long blocks. This temporal property results in weaker nonlinear interactions, and thus higher SNR, for short CC sequences. For a typical multi-span fiber setup, the SNR difference is numerically demonstrated to be up to 0.7 dB. Finally, we evaluate a heuristic figure of merit that captures the number of runs of identical symbols in a concatenation of several CC sequences. For moderate block lengths up to approximately 100 symbols, this metric suggests that limiting the number identical-symbol runs can be beneficial for reducing fiber nonlinearities and thus, for increasing SNR.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-28
Shuto Yamamoto; Hiroki Taniguchi; Asuka Matsushita; Masanori Nakamura; Seiji Okamoto; Yoshiaki Kisaka

The amount of data center traffic is rapidly increasing, and it is necessary for short-reach optical transmission such as Ethernet to realize a higher capacity data link. Therefore, the next-generation Ethernet links will require the higher data rate. In such a situation, transmission distance is limited by the bandwidth limitation due to optical and electrical devices in the Ethernet transceiver. In this article, we propose a nonlinear-coded-modulation which shapes the signal spectrum in order to realize the higher tolerance to bandwidth limitation. We apply this technique to a 92-Gbaud PAM4 signal and confirm that the proposed technique achieves the 7% HD-FEC threshold in 184-Gb/s transmission with the bandwidth limitation of 20 GHz through an O-band 10-km transmission experiment. We also investigate the applicability of MLSE to the proposed technique and show that the KP4-FEC threshold can be achievable with 2-memory MLSE and 5-tap channel-shortening filter. In addition, we study the applicability of the proposed technique to a QAM signal which is conventionally utilized in coherent systems. We compare the proposed nonlinear-coded QAM to the conventional duobinary QAM and show that the performance of the proposed QAM signal is greater than that of the duobinary QAM signal with MLSE where the signal degradation is induced by additive white Gaussian noise.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-29
Xiang Zhou; Ryohei Urata; Hong Liu

We discuss technology options and challenges for scaling intra-datacenter interconnects beyond 1 Tb/s bandwidths, with focus on two possible approaches: pulse amplitude modulation (PAM)-based intensity modulation-direct detection (IM-DD) and baud-rate sampled coherent technology. In our studies, we compare the performance of various orders of PAM modulation (PAM4 to 8). In addition to these fixed PAM signaling options, a flexible PAM (FlexPAM) technique leveraging granularity in spectral efficiency (SE) is proposed to maximize link margin. For baud-rate sampled coherent technology, we propose a simplified digital signal processing (DSP) architecture to bring down power consumption of the coherent approach closer to that of IM-DD PAM. We also propose two new phase noise tolerant 2D coherent modulation formats to relax the laser linewidth requirement. In closing, a comparative study of fixed IM-DD PAM versus coherent polarization multiplexed-quadrature amplitude modulation (PM-QAM) is presented for a 1.6 Tb/s solution (200 Gb/s per dimension), with consideration of link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-18
Shaohua An; Qingming Zhu; Jingchi Li; Yikai Su

We introduce and experimentally demonstrate a modified Kramers-Kronig (KK) receiver with direct detection (DD) to realize an accurate optical field reconstruction at low carrier-to-signal power ratio (CSPR) condition. In our scheme, an exponential operation is applied to a single-sideband (SSB) signal, rather than a continuous-wave tone adding method in the conventional KK scheme. By this means, the minimum phase condition (MPC) is inherently satisfied, thus the optical field can be reconstructed accurately through KK relation at a low CSPR, leading to a high receiver sensitivity in a DD system. A proof-of-concept experiment is conducted, in which an SSB signal is generated based on an 8-GBaud 16-quadrature amplitude modulation (QAM) data stream and then is transmitted over an 80-km single mode fiber (SMF). By using the modified KK technique, 1.1- and 0.9-dB sensitivity improvements are achieved in the optical back-to-back and after the fiber transmission cases, respectively. The proposed and the conventional KK schemes show similar BER performances at the optimum CSPR value with a high received optical power. In addition, we perform numerical simulations to study the impacts of bandwidth limitation and chromatic dispersion on the proposed minimum phase signal.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-25
Xiaodan Pang; Oskars Ozolins; Rui Lin; Lu Zhang; Aleksejs Udalcovs; Lei Xue; Richard Schatz; Urban Westergren; Shilin Xiao; Weisheng Hu; Gunnar Jacobsen; Sergei Popov; Jiajia Chen

Client-side optics are facing an ever-increasing upgrading pace, driven by upcoming 5G related services and datacenter applications. The demand for a single lane data rate is soon approaching 200 Gbps. To meet such high-speed requirement, all segments of traditional intensity modulation direct detection (IM/DD) technologies are being challenged. The characteristics of electrical and optoelectronic components and the performance of modulation, coding, and digital signal processing (DSP) techniques are being stretched to their limits. In this context, we witnessed technological breakthroughs in several aspects, including development of broadband devices, novel modulation formats and coding, and high-performance DSP algorithms for the past few years. A great momentum has been accumulated to overcome the aforementioned challenges. In this article, we focus on IM/DD transmissions, and provide an overview of recent research and development efforts on key enabling technologies for 200 Gbps per lane and beyond. Our recent demonstrations of 200 Gbps short-reach transmissions with 4-level pulse amplitude modulation (PAM) and discrete multitone signals are also presented as examples to show the system requirements in terms of device characteristics and DSP performance. Apart from digital coherent technologies and advanced direct detection systems, such as Stokes–vector and Kramers–Kronig schemes, we expect high-speed IM/DD systems will remain advantageous in terms of system cost, power consumption, and footprint for short reach applications in the short- to mid- term perspective.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-10
Aymeric Arnould; Amirhossein Ghazisaeidi; Dylan Le Gac; Patrick Brindel; Mathilde Makhsiyan; Karim Mekhazni; Fabrice Blache; Nicolas Fontaine; David Neilson; Roland Ryf; Haoshuo Chen; Mohand Achouche; Jérémie Renaudier

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.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-28
Aymeric Arnould; Amirhossein Ghazisaeidi; Dylan Le Gac; Patrick Brindel; Mathilde Makhsiyan; Karim Mekhazni; Fabrice Blache; Mohand Achouche; Jérémie Renaudier

This article presents an experimental characterization of the impact of nonlinear impairments induced by semiconductor optical amplifiers (SOA) in a wavelength division multiplexed (WDM) coherent communication system. Motivated by a ceaseless traffic growth in optical transport systems, extending the bandwidth of the fiber link is a promising way to increase the throughput in optical networks. Using specific design, SOA can provide ultra-wideband (UWB) and continuous amplification spreading from S to L bands. For both off-the-shelf C-band SOA and UWB SOA devices, we show that SOA nonlinear impairments are not critical in the WDM regime. We report on the impact of the WDM channel count on the nonlinear distortions induced by an UWB SOA. We also demonstrate that besides having a wider bandwidth, our custom UWB SOA devices have superior performance compared to off-the shelf components even for C-band only transmission, and are well suited for wideband WDM signal amplification.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-30
Kohki Shibahara; Takayuki Mizuno; Hiroto Kawakami; Takayuki Kobayashi; Masanori Nakamura; Kota Shikama; Kazuhide Nakajima; Yutaka Miyamoto

We have achieved the longest three mode-multiplexed full C-band transmission yet attained over 3060 km. In wideband mode-multiplexed transmission over weakly-coupled fewmode fibers (FMFs), the width of signal impulse responses is dependent on wavelength, and also exhibits a linear growth with increased transmission distance because of the presence of differential mode delay (DMD). Those properties are technically challenging issues for future deployable space division multiplexing (SDM) transport systems since they make a system design complicated, especially for terrestrial FMF transmission links. In this article, we describe how we applied a cyclic mode permutation (CMP) technique to achieve wideband long-haul FMF transmission where spatial channels are cyclically interchanged in each span to suppress DMD-induced pulse broadening. The CMP technique enabled DMD-unmanaged long-haul transmission across 4.4-THz optical bandwidth over two-mode FMF whose DMD varied in the range from 33.7–44.3 ps/km, resulting in 3060-km FMF transmission with a net capacity of 40.2 Tb/s.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-09
Jian Xu; Shujuan Sun; Qianggao Hu; Jiekui Yu; Jiasheng Liu; Qing Luo; Wenzhong Wang; Liyan Huang; Min Xiang; Jianjun Wu; Fusheng Zheng; Weihua Li; Li Deng; Hongyan Zhou; Lei Zhang; Shugang Jia; Xiaohong Zhang; Haitao Chen

We report the results of 50G, 100G, 200G, 400G un- repeatered transmission aimed at achieving the longest distance without any inline active elements, this system realizes record single-carrier 50 Gb/s (PM-BPSK), 100 Gb/s (PS-QPSK), 200 Gb/s (PM-8QAM) and 400 Gb/s (PM-64QAM) unrepeatered transmission over 670.64 km with 103.95 dB span loss, 653.35 km with 101.27 dB span loss, 601.93 km with 93.3 dB span loss, and 502.13 km with 77.83 dB span loss, respectively. This is achieved using optimized high-order Raman pumps, cascaded RGUs and coherent modulation format with concatenated FEC. G.654.E fiber with ultra-low loss & 130 μm 2 effective area is used as span fiber.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-19
Maria Ionescu; Domaniç Lavery; Adrian Edwards; Eric Sillekens; Daniel Semrau; Lidia Galdino; Robert I. Killey; Wayne Pelouch; Stuart Barnes; Polina Bayvel

Ultrawide-bandwidth optical amplification over almost 90 nm, covering the C+L bands, is described. Complemented by system-tailored geometrical constellation shaping and nonlinearity compensation, it enabled a record capacity transmission of 74.38 Tb/s over 6,300 km of G.654 single-mode fibre. The hybrid scheme, combining backward Raman pre-amplification with EDFA, significantly improves the average effective noise figure across the entire bandwidth, allowing the use of span lengths of 70 km. The system-tailored GS-64QAM constellation was optimised to both linear link impairments and transceiver nonlinearities, improving the gap to the AWGN channel capacity relative to square 64QAM from 0.6 bit/symbol to 0.35 bit/symbol. We experimentally evaluated the system performance using the bit-wise achievable information rate (AIR) and signal-to-noise ratio (SNR) at the end of transmission, as well as post SD-FEC BER.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-16
Son Thai Le; Karsten Schuh; Roman Dischler; Fred Buchali; Laurent Schmalen; Henning Buelow

Due to the growing demand for cloud services with high availability, high connection speed and low latency, distributed data-centers have emerged as a key architecture for future optical networks. This architecture relies on power and cost-efficient solutions for 400 Gb/s client interfaces over distances up to 80 km which can be densely wavelength-division multiplexed (WDM) in the C-band. Recently, single side band (SSB) direct detection (DD) has been considered as an attractive transmission scheme for achieving data rates beyond 100 Gb/s per channel due to its capability of electronic dispersion compensation. However, as SSB DD schemes utilize only a single polarization for data transmission, achieving 400 Gb/s per channel requires a baudrate beyond 80 Gbaud, which might reduce the effectiveness of the commonly used signal-signal beat interference (SSBI) cancellation techniques such as iterative SSBI cancellation or Kramers-Kronig algorithm due to the imperfection of Tx drivers, modulator and Rx front-end. In this paper, through effective Tx calibration and Rx DSP, we have achieved for the first time a net data rate per channel above 400 Gb/s with a 64 QAM signal at 85 Gbaud using a single photodetector (PD) at the receiver. In addition, a WDM transmission consisting of 5 channels at 100 GHz spacing was successfully conducted. This result indicates that SSB DD is an effective transmission technique for high capacity data center interconnect (DCI) applications.

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-13
A. Mayoral; V. López; M. López-Bravo; D. García-Montes; O. Gonzalez-de-Dios; A. Aguado; R. Szwedowski; K. Mrówka; F. Marques; Z. Stevkovski; D. Verchere; Q. Pham-Van; L. Tancevski; J.-P. Fernandez-Palacios

The need of introducing interoperability in the transport network segment has motivated the emergence of several open initiatives and standardization efforts for the development of different interfaces to allow Software Defined Network (SDN) controllers manage and control the network devices. Optical disaggregation in particular aims the introduction of standard device-level interfaces in the optical terminals and line-systems to ‘open’ them from vendor lock-in situations, allowing an interoperable ecosystem in the optical network's transport segment. In this article, it is firstly presented the Software Defined Transport Network (SDTN) architecture, as the control and management framework to build a L0-L3 multi-layer, multi-technology transport network, enabling end-to-end network service delivery. Later, we introduce the partially disaggregated network architecture proposed, including the technical assessment of the topology discovery and resilience service provisioning use cases, by providing a low-level description of the information models employed and the translation between models. To conclude, a proof-of-concept of multi-layer service provisioning over resilient disaggregated multi-vendor testbed is presented, including the results obtained in the experimental demonstration presented in last 2019 Optical Fiber Conference (OFC).

更新日期：2020-01-24
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-11-01
Jun Shan Wey 魏君珊

In light of the 5G deployments, edge computing, and future high bandwidth services, the industry is rethinking the optical access network architecture design. Passive optical network (PON) with its efficient fiber infrastructure plays an essential role in this design transformation. This article reviews the driving forces shaping the new generations of PON systems in the coming years; and discusses the course of action in the FSAN Group, ITU-T, and IEEE standards bodies to address the impending requirements.

更新日期：2020-01-07
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-31

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-12-31

The papers in this special section were presented at the Optical Fiber Communications Conference (OFC)2019 that was held in San Diego, CA, March of 2019. The papers document the state of the art in optical fiber technology and networks in greater depth than is possible in the limited format of the conference technical digest.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-23
Min Teng; Amirmahdi Honardoost; Yousef Alahmadi; Sajad Saghaye Polkoo; Keisuke Kojima; He Wen; C. Kyle Renshaw; Patrick LiKamWa; Guifang Li; Sasan Fathpour; Reza Safian; Leimeng Zhuang

Integrated optical signal processors, in combination with conventional electrical signal processors, are envisioned to open a path to a new generation of signal processing hardware platform that allows for significant improvement in processing bandwidth, latency, and power efficiency. With its well-known features and potential, silicon photonics is considered as a favorable candidate for the device implementation, particularly with high circuit complexity, and hence has been the focus of the study. As an outlook from the previous discussions on such processors, we are considering new building blocks in the silicon photonics platform for further extending the processor capabilities and adding practical features, particularly the miniaturized devices that enable ultra-dense integration of complex circuits into such processor chips. As enlightening examples, we review here our recent contribution together with representative works from other groups of compact designs of silicon photonics devices that enrich functionalities of processor building blocks such as multiplexing, polarization handling, and optical I/Os. The results shown in this review reflect the significance and maturity of the state-of-the-art photonic fabrication technology and contribute to the implementation of high-capacity, general-purpose optical signal processing functionalities on the chip scale.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-19
Lu Zhang; Jiajia Chen; Erik Agrell; Rui Lin; Lena Wosinska

With the continuously growing popularity of cloud services, the traffic volume inside the data centers is dramatically increasing. As a result, a scalable and efficient infrastructure for data center networks (DCNs) is required. The current optical DCNs using either individual fibers or fiber ribbons are costly, bulky, hard to manage, and not scalable. Spatial division multiplexing (SDM) based on multicore or multimode (few-mode) fibers is recognized as a promising technology to increase the spatial efficiency for optical DCNs, which opens a new way towards high capacity and scalability. This tutorial provides an overview of the components, transmission options, and interconnect architectures for SDM-based DCNs, as well as potential technical challenges and future directions. It also covers the co-existence of SDM and other multiplexing techniques, such as wavelength-division multiplexing and flexible spectrum multiplexing, in optical DCNs.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-04

This paper reviews optical injection locking (OIL) of semiconductor lasers and its application in optical communications and signal processing. Despite complex OIL dynamics, we attempt to explain the operational principle and main features of the OIL in an intuitive way, aiming at a wide understanding of the OIL phenomenon and its associated techniques in the optic and photonic communities. We review and compare different control techniques that enable robust OIL in practical systems. The applications are reviewed with a focus on new developments in the past decade, under the categories of ‘High Speed Directly Modulated Lasers’ and ‘Optical Carrier Recovery’. Finally, we draw our vision for future research directions.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-23
Ryota Tanomura; Rui Tang; Samir Ghosh; Takuo Tanemura; Yoshiaki Nakano

An integrated optical unitary converter (OUC), which can realize arbitrary N × N unitary transformation on chip, is promising for widespread applications in various areas, such as optical communication, quantum information processing, and optical neural networks. Most of the integrated OUCs demonstrated to date comprise cascaded 2 × 2 Mach-Zehnder interferometers (MZIs) based on Reck's scheme or its variation, or cascaded multimode interference (MMI) couplers based on multi-plane light conversion (MPLC). However, these schemes are sensitive to fabrication errors, making it difficult to realize high-performance large-scale OUCs. In this work, we experimentally demonstrate a silicon photonic 4 × 4 OUC that is inherently robust to fabrication errors, based on a novel structure. The proposed structure consists of cascaded multiport directional couplers (DCs) and phase shifter arrays. In this scheme, the multiport DC assures unitary transformation with inherent robustness against fabrication errors. By optimizing all the phase shifters using a simulated annealing algorithm, we experimentally demonstrate reconfigurable 4-mode demultiplexing and error-free demultiplexing of 40-Gb/s non-return-to-zero (NRZ) signals.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-09-30
Yixiao Zhu; Fan Zhang; Fan Yang; Lei Zhang; Xiaoke Ruan; Yanping Li; Zhangyuan Chen

In this work, based on a conventional silicon photonic travelling-wave Mach-Zehnder modulator (MZM) with a 3-dB bandwidth of 22.5 GHz, we experimentally demonstrate ultra-high speed optical interconnects with Nyquist shaped pulse amplitude modulation (PAM) signals. For bandwidth-limited systems, a two-tap digital post filter is employed to suppress the equalization-enhanced high frequency noise. The post filter induced inter-symbol interference (ISI) is subsequently eliminated by maximum likelihood sequence detection (MLSD). Enabled by the post filter and MLSD, we achieve 200 Gb/s (80 Gbaud) PAM-6 signal direct detection (DD) transmission over 1 km standard single-mode fiber (SSMF) with a bit-error rate (BER) below the 20% hard-decision forward error correction (HD-FEC) threshold of 1.5 × 10 −2 . For PAM-4 format, we successfully transmit 192 Gb/s (96 Gbaud) and 176 Gb/s (88 Gbaud) signals over 1 km and 2 km SSMF, respectively, with BERs lower than the 20% HD-FEC threshold. For PAM-8 format, 192 Gb/s (64 Gbaud) and 168 Gb/s (56 Gbaud) signals are generated at back-to-back (BTB) and transmitted over 1 km SSMF, respectively. To our best knowledge, we achieve the highest single lane bitrates ever reported for single polarization PAM-4/6/8 signal generation and DD transmission with all-silicon MZM. The flexible receiver-side digital signal processing (DSP) can significantly enhance the performance of silicon MZM, which provides a promising solution for future single lane 200 G data-center interconnects.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-14
Ming-Fang Huang; Milad Salemi; Yuheng Chen; Jingnan Zhao; Tiejun J. Xia; Glenn A. Wellbrock; Yue-Kai Huang; Giovanni Milione; Ezra Ip; Philip Ji; Ting Wang; Yoshiaki Aono

To the best of our knowledge, we present the first field trial of distributed fiber optical sensing (DFOS) and high-speed communication, comprising a coexisting system, over an operation telecom network. Using probabilistic-shaped (PS) DP-144QAM, a 36.8 Tb/s with an 8.28-b/s/Hz spectral efficiency (SE) (48-Gbaud channels, 50-GHz channel spacing) was achieved. Employing DFOS technology, road traffic, i.e., vehicle speed and vehicle density, were sensed with 98.5% and 94.5% accuracies, respectively, as compared to video analytics. Additionally, road conditions, i.e., roughness level was sensed with >85% accuracy via a machine learning based classifier.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-06
Haoqian Song; Hao Song; Runzhou Zhang; Karapet Manukyan; Long Li; Zhe Zhao; Kai Pang; Cong Liu; Ahmed Almaiman; Robert Bock; Brittany Lynn; Moshe Tur; Alan E. Willner

In this paper, we experimentally demonstrate the mitigation of atmospheric turbulence effects using phase patterns that apply the inverse transmission matrix for pre-compensation in the 200-Gbit/s free-space orbital angular momentum (OAM) multiplexed optical link. In this link, two OAM channels are multiplexed, each carrying a 100-Gbit/s quadrature-phase shift keying (QPSK) signal. In the uni-directional (forward) link, a combination of two OAM modes is generated using a designed phase pattern in each of the two channels. After the two channels are multiplexed, each OAM mode will carry the combination of signals from both channels. Such beams could perform the inverse function of turbulence-induced crosstalk. We explore the link performances including crosstalk and bit error rate (BER) under 6 different turbulence realizations with a Fried parameter of 1-mm. We find the following: (a) the inter-channel crosstalk is reduced by up to 21 dB; (b) the inter-channel crosstalk is below −10 dB for the 6 turbulence realizations when the compensation is applied; (c) a BER below the FEC limit could be realized for the 6 turbulence realizations with an optical signal-to-noise ratio (OSNR) of 16.8 dB for the uni-directional link with the compensation. Moreover, the post-compensation is also investigated for the two 100-Gbit/s OAM-multiplexed backward channels in the bi-directional link. For the backward channels, the phase patterns are used to mitigate turbulence-induced crosstalk at the receiver for backward channels, and the inter-channel crosstalk is reduced by up to 16 dB.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-14
Yuki Yoshida; Toshimasa Umezawa; Atsushi Kanno; Naokatsu Yamamoto

To achieve an ultra-compact and flexible coherent transceiver solution, a carrier-less coherent detection technique using a two-dimensional (2-D) photodetector array (PDA) is proposed based on the idea of phase retrieval (PR). In the proposed PR-based coherent receiver, the optical phase information is digitally reconstructed from multiple intensity-only measurements acquired by arrayed photodetectors; neither local light sources, optical hybrids, nor spatial demultiplexers are needed. We develop a robust and low-complexity PR algorithm, which exploits prior knowledge on the optical modulation format, for the proposed PR receiver. As a proof-of-concept, the coherent detection of 10-Gbaud optical phase-modulated signals, including QPSK, 16-QAM, coherent optical OFDM, and polarization-multiplexed QPSK signals, using only a 2-D PDA is demonstrated experimentally.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-07-26
Joonyoung Kim; Minkyu Sung; Seung-Hyun Cho; Young-Jun Won; Byoung-Chul Lim; Sung-Yeop Pyun; Joon-Ki Lee; Jong Hyun Lee

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-10
Atsushi Kanno; Pham Tien Dat; Naokatsu Yamamoto; Tetsuya Kawanishi; Nagateru Iwasawa; Nariya Iwaki; Kazuki Nakamura; Kunihiro Kawasaki; Naoki Kanada; Naruto Yonemoto; Yosuke Sato; Masato Fujii; Katsuya Yanatori; Nobuhiko Shibagaki; Kenichi Kashima

A linear-cell-based radio-over-fiber (LC-RoF) system is proposed and demonstrated for efficient mobile communication in high-speed trains without hard handover processes. The configuration of the LC-RoF network and possible router architectures are discussed for the field trial test of the proposed system and for advanced systems in the future. Via the LC-RoF network, 90-GHz, millimeter-wave radio access between the ground and a train car is operated in a centralized manner. The resulting throughput of 1.5 Gbit/s is achieved in the field trial test, which is comprised of 250-Mbaud four-subcarrier differential quadrature phase-shift keying with a forward-error correction code implemented in field-programmable gate arrays to the Shinkansen train traveling at 240 km/h without any interruptions in the connections at the change of radio access units.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-14
Benjamin J. Puttnam; Georg Rademacher; Ruben S. Luís; Tobias A. Eriksson; Werner Klaus; Yoshinari Awaji; Naoya Wada; Koichi Maeda; Shigehiro Takasaka; Ryuichi Sugizaki

We describe a series of optical transmission experiments based around single-mode, multi-core fiber (MCF) amplified with 19-core, C+L band erbium-doped fiber amplifier (EDFA). The cladding-pumped amplifier uses two multi-mode pumps in each of C and L band to provide gain bandwidth over more than 75 nm. For recirculating transmission of PDM-16QAM signals on 345 wavelength carriers between 1530.52 nm and 1605.52 nm, we measure 0.715 Pb/s transmission over a distance of 2009 km (64 recirculations), equivalent to a throughput-distance product of 1.44 exabit/s x km. Next, using PDM-QPSK modulation, we investigate trans-oceanic transmission distances, measuring throughputs of 18.6 Tb/s and 14.5 Tb/s in 2 cores after 255 recirculations, a distance of 8007 km. Further, we evaluate the combined EDFA and fiber crosstalk penalties showing a core and wavelength dependence in agreement with previous MCF crosstalk measurements. These results demonstrate the potential of high core-count EDFAs to combine both high capacity transmission over transoceanic distances with benefits of SDM integration.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-08-30
Hao Li; Ganesh Balamurugan; Meer Sakib; Jie Sun; Jeffery Driscoll; Ranjeet Kumar; Hasitha Jayatilleka; Haisheng Rong; James Jaussi; Bryan Casper

Microring modulators (MRMs) with CMOS electronics enable compact low power transmitter solutions for 400G Ethernet and future on-package optical transceivers. In this paper, we present a 112 Gb/s PAM4 transmitter using silicon photonic MRM, on-chip laser and co-packaged 28 nm CMOS driver. We describe the impact of static and dynamic MRM nonlinearity on PAM4 signaling and present a dual path nonlinear pre-distortion technique to compensate both effects. PAM4 measurement results of our transmitter at 112 Gb/s show that TDECQ <0.7 dB is achieved from 30 °C to 60 °C while dissipating 6 pJ/bit. We also present link level measurements at 112 Gb/s PAM4 obtained by coupling this transmitter with our previously published CMOS TIA-based receiver, to demonstrate the feasibility of low cost optical transceivers through CMOS integration of optical interface circuits.

更新日期：2020-01-04
• J. Lightw. Technol. (IF 4.162) Pub Date : 2019-10-28
Rui Wang; Rodrigo S. Tessinari; Emilio Hugues-Salas; Anderson Bravalheri; Navdeep Uniyal; Abubakar S. Muqaddas; Rafael S. Guimaraes; Thierno Diallo; Shadi Moazzeni; Qibing Wang; George T. Kanellos; Reza Nejabati; Dimitra Simeonidou

Dynamic and flexible optical networking combined with virtualization and softwarisation enabled by network function virtualization (NFV) and software defined networking (SDN) are the key technology enablers for supporting the dynamicity, bandwidth, and latency requirements of emerging 5G network services. To achieve the end-to-end connectivity objective of 5G, network services (NSes) must be often deployed transparently over multiple administrative and technological domains. Such scenario often presents security risks since a typical NS 1 1 Network service is a combination of multiple virtual and physical network functions created to realise a desired network functionality. may comprise a chain of network functions, each executed in different remote locations, and tampering within the network infrastructure may compromise their communication. To avoid such threats, quantum key distribution (QKD) has been identified and proposed as a future-proof method immune to any algorithmic cryptanalysis based on fundamental quantum-physics mechanisms to distribute symmetric keys. The maturity of QKD has enabled the research and development of quantum networks with gradual coexistence with classical optical networks using carrier-grade telecom equipment. This makes the QKD technology a suitable candidate for security of distributed and virtualised network services. In this article, for the first time, we propose a dynamic quantum-secured optical network for supporting network services that are dynamically created by chaining virtual network functions (VNFs) 2 2 Hardware network functions when implemented in software and deployed as VMs or containers are called VNFs. over multiple network domains. This work includes a new flex-grid quantum-switched reconfigurable optical add drop multiplexer (q-ROADM), extensions to SDN-enabled optical control plane, and extensions to NFV orchestration to achieve quantum-aware, on-demand chaining of VNFs. The experimental results verify the capability of routing quantum and classical data channels both individually and dynamically over shared fibre links. Moreover, quantum secured chaining of VNFs in 5G networks is experimentally demonstrated via interconnecting four autonomous 5G islands simultaneously through the q-ROADM with eight optical channels using the 5GUK Exchange orchestration platform. The experimental scenarios and results confirm the benefit of the proposed data plane architecture and control/management plane framework.

更新日期：2020-01-04
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