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204-GBaud On-Off Keying Transmitter for Inter-Data Center Communications
Abstract
We demonstrate an on-off keyed transmitter with direct detection, at record symbol rates of 204Gbaud and 140Gbaud, over 10km and 80km, respectively, powered by a high-speed InP-based 2:1 selector and travelling-wave electro-absorption laser-modulator.
... Multiple high-performance technologies are required to comply with this stringent requirement [4]. Several optical modulator technologies can provide low-cost and high-performance solutions for high-speed short-reach optical communications [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. High-speed silicon ring resonator modulators (RRMs) are an attractive alternative thanks to their compact size and low energy consumption. ...
... Recently, an electrically pumped laser transmitter integrated on thin-film lithium niobate has been demonstrated [12]. High-speed integrated externally modulated lasers (EMLs) [13], [14], [15], [16], [17] and directly modulated lasers (DMLs) [18], [19], [20] are, therefore, compelling alternatives enabling up to 200 Gbaud OOK transmission [17]. In an earlier demonstration, a 204 Gbaud OOK transmission over inter-Data Center distances using the C-band EML and optical dispersion compensation based on chirped fiber Bragg gratings has been shown [15]. ...
... High-speed integrated externally modulated lasers (EMLs) [13], [14], [15], [16], [17] and directly modulated lasers (DMLs) [18], [19], [20] are, therefore, compelling alternatives enabling up to 200 Gbaud OOK transmission [17]. In an earlier demonstration, a 204 Gbaud OOK transmission over inter-Data Center distances using the C-band EML and optical dispersion compensation based on chirped fiber Bragg gratings has been shown [15]. A 180 Gbaud OOK transmission over intra-Data Center distance using an EDFA was achieved with the same EML [16]. ...
The enormous traffic growth sets a stringent requirement to upgrade short-reach optical links to 1.6 TbE capacity in an economically viable way. The power consumption and latency in these links should be as low as possible, especially for high-speed computing. This is possible to achieve using high baudrate on-off keying links thanks to a better noise tolerance and a relaxed requirement on linearity for electronics and photonics. In this regard, we demonstrate a 200 Gbaud on-off keying link without any optical amplification using an externally modulated laser with 3.3 dBm of modulated output power operating at 1541.25 nm wavelength. We achieve transmission over 200 meters of single-mode fiber with performance below 6.25% overhead hard-decision forward error correction threshold for each baudrate and all selection of modulation formats. We also show 108 Gbaud on-off keying link with superior performance without decision feedback equalizer up to 400 meters of single-mode fiber. In addition, we benchmark the short-reach optical link with 112 Gbaud four-level pulse amplitude modulation and 100 Gbaud six-level pulse amplitude modulation. For 108 Gbaud on-off keying and 112 Gbaud four-level pulse amplitude modulation, we can achieve an even lower bit error rate.
... Meanwhile, EML may present smaller footprint size, lower power consumption, and lower cost than that of MZM. The application of EML had been demonstrated in various beyond 100-Gbit/s verification experiments [68][69][70][71][72][73][74][75][76][77][78] [75]. In order to achieve higher transmission rate, researchers further explored to enhance the bandwidth of EML. ...
... It can be observed that the 3-dB bandwidth was greater than 100-GHz. The applications about the monolithically integrated C-band DFB-TWEAM have been reported in 204-Gbit/s OOK [76], 200-Gbit/s PAM-4 [77], and 200-Gbit/s DMT [78] transmission systems. The recent applications of EML in beyond 100-Gbit/s per lane data transmission have been summarized as shown in Table 4. ...
According to different transmission distances, application scenarios of a data center mainly include intra- and inter-data center optical interconnects. The intra-data center optical interconnect is considered as a few kilometers optical interconnect between servers and racks inside a data center, which accounts for nearly 80% of data traffic of a data center. The other one, inter-data center optical interconnect, is mainly applied in tens of kilometers data transmission among different data centers. Since data exchange in data centers generally occurs between many servers and racks, and a lot of transmitter and receiver components are required, optical interconnects become highly sensitive to component costs. In this paper, we firstly review the development and applications of mainstream transmitter components (e.g., VCSEL, DML, EML, MZM, and monolithic integrated transmitter) and receiver components (e.g., single-end photodetector, Kramers–Kronig receiver, Stokes vector receiver, and monolithic integrated receiver), which have been widely applied in short-reach transmission systems. Then, two types of integrated solutions including simplified detection scheme and transceiver integration scheme are presented in detail. Finally, we summarize and discuss the technological and component options for different transmission distances. We believe that monolithic integrated components, especially transceiver integration, will become a powerful solution for next-generation high-speed short-reach transmission systems.
... The C-band enables proportional efficiency in bidirectional bandwidth for intra-datacentres thanks to mature and efficient wavelength division multiplexing technology. On-off keying (OOK) is the simplest way to modulate information, allowing for ultra-high speed and power-and cost-effective electronics 7 . This path is possible thanks to indium phosphide (InP) ultra-high-speed components with bandwidth beyond 70 GHz [8][9][10][11] enabling beyond 100 Gbaud per lane transmitters 7 for inter-datacentre links. ...
... High speed electrical signal generation is realized by a compact packaged high-speed InP-based 2:1-Selector. In addition, we extend our previous demonstration 7 by transmitting with MZM over 5500 meters of standard single mode fibre (SSMF) without amplification and dispersion compensation. Figure 1 shows the experimental setup for 9 . ...
We demonstrate 140 Gbaud intensity modulated direct detection dispersion-uncompensated links with Mach Zehnder modulator and distributed feedback travelling-wave electro-absorption modulator over 5500 and 960 meters of standard single mode fibre, respectively, enabled by compact packaged ultra-high speed InP-based 2:1-Selector.
... Nevertheless, all these multiple-sectional DMLs appear to require monolithic integration techniques such as butt-joint regrowth or selective area growth, which makes them less appealing on cost-effectiveness and reliability compared to externally modulated lasers (EMLs) [27], [28], [29], [30], [31], [32], [33], [34]. ...
Conventional push-pull modulated (PPM) distributed feedback (DFB) lasers exploit structures with symmetry, which wastes a significant amount of the optical power output from the rear facet. To improve the power efficiency, PPM DFB lasers with asymmetrically coated facets can be considered. However, the resulted imbalanced push-pull modulation causes a dip in device small-signal intensity modulation response near the carrier-photon resonance (CPR) frequency, which distorts the waveform and even cuts off the bandwidth. This work proposes an asymmetric section length design in conjunction with the asymmetric facet coating to offset the aforementioned effect on device intensity modulation response. With a delayed push-pull modulation (DPPM) scheme further incorporated, our simulation result shows that the PPM DFB laser with optimized asymmetric structure can enhance the power efficiency and maintain a smooth modulation bandwidth up to around 50 GHz.
... Cost-effective light sources are highly demanded for the broad deployment of highspeed datalinks, telecommunication access networks and wireless communication systems in their front-and middle-haul links [1][2][3][4][5]. Directly modulated lasers (DMLs), as opposed to the externally modulated lasers (EMLs) [6][7][8][9][10], are preferred for their low fabrication cost and high yield since there are no complicated monolithic integration technologies, such as butt-joint regrowth or selective area growth, involved [11,12]. To accommodate the high-speed modulation requirement in the aforementioned applications, a significant amount of effort has been devoted to extending the modulation bandwidth of the distributed feedback (DFB) DMLs mainly by raising their relaxation oscillation frequency caused by the carrier-photon resonance (CPR) [13][14][15]. ...
The bandwidth of a distributed feedback (DFB) directly modulated laser (DML) is limited by its carrier–photon resonance (CPR) frequency. A viable approach to break the bottleneck is to introduce a photon–photon resonance (PPR), since the PPR can happen at a much higher frequency than the CPR. Among the many structures that can possibly generate the PPR, the dual-sectional push–pull modulated (PPM) DFB is of particular interest for its fabrication cost-effectiveness as no regrowth is required. The PPR in the PPM DFB, however, usually shows a rapid roll-off on both edges, which brings in an indentation on the lower frequency side of the PPR peak and, consequently, cuts off the bandwidth. To compensate for this dip, we introduce a detuned PPR and restart the CPR response by exploiting a time delay between the differential signals applied to the PPM DFB. Our simulation result shows that the broadened PPR peak and the restarted CPR response indeed mitigate the dip and effectively expand the PPM-DFB’s bandwidth to approximately 50 GHz, a value double that of the conventional (single-sectional) DFB DML.
... However, there are issues such as small output power and phase control difficulty. EADFB lasers [11,12] are also attractive 200 Gbit/s/λ transmitter devices because of their simple controllability and high bandwidth. There are two issues to fabricate a high-speed and high-output power optical transmitter module using the EADFB laser. ...
We previously developed a semiconductor optical amplifier (SOA) assisted extended reach electroabsorption modulator integrated distributed feedback (EADFB) laser (AXEL) to increase the optical modulation output power and a high-frequency integrated design based on the flip-chip interconnection technique (Hi-FIT) to obtain a high modulation bandwidth. We achieved a high-output power 224-Gbit/s 4-level pulse-amplitude-modulation (4-PAM) operation of a Hi-FIT AXEL module. In this paper, we developed a compact DC block circuit integrated into Hi-FIT AXEL module to decrease chip-power consumption without increasing the sub-assembly size and degrading the modulation bandwidth. We designed a Hi-FIT AXEL sub-assembly, that include a flip-chip interconnection board with a DC block circuit that affects the modulation bandwidth. We achieved a 3-dB bandwidth of up to 64 GHz for this designed sub-assembly. The fabricated Hi-FIT AXEL module has a 3-dB bandwidth of more than 62 GHz and a flat frequency response up to 50 GHz. For the 224-Gbit/s 4-PAM operation, the fabricated Hi-FIT AXEL module has a chip-out average output power of +10.0 dBm with a transmitter eye-closure quaternary (TECQ) of 1.9 dB. The integrated compact DC block circuit can reduce chip power consumption by up to 17%.
... Also, certain low latency applications require some data centers to be closer to the user [89], but infrastructural limitations force other datacentres to be further off. There has been a demonstration of IMDD DCI working at 204 Gbaud and 140 Gbaud over 10 km and 80 km DCIs, respectively [90]. Several implementations are using wideband WDM (which seems to be the future for DCI) and many proposals for using optical amplifiers (using different optical amplifiers to amplify different bands) in such links [84], [91]- [93]. ...
We propose and demonstrate a generalized framework for performance limit evaluation and comparison of multihop optical repeated and regenerated links. The model developed is implementation agnostic and applies to multihop optical links of varied forms, including fiber, free space, and underwater links. The framework estimates the best-case performance gains of deploying an all-regenerative link over an all-repeater link for any given implementation. The implementation-independent technique is then illustrated using guided and free-space optical links. An abstract model is developed first with the evolution of signal, noise power, and bit error rate down the link compared and contrasted for both cases. The model is then evaluated using physical parameters for a typical fiber optic intensity-modulated direct detection link, and the obtained all-regenerator link performance advantage is translated to extra reach and lower transmission power requirements. Further, certain approximations are provided to reduce computational complexity and improve the analytical tractability of the procedure, which could be particularly helpful when employed in specialized hardware or for dynamic reconfiguration networks. Finally, the framework’s versatility is established by employing it in analyzing an ideal free-space link and comparing amplify and forward links against decode and forward counterparts. Similar results are also reproduced on a commercial optical link simulation suite. Detailed literature on link analysis is provided for fiber, free space, and underwater links, bringing out their similarities. We conclude by elaborating on various current and emerging application domains and certain limitations of the proposed technique.
... In 2018, NTT reported a 100 GBaud-level InP-based IQ modulator with a bandwidth of more than 3 dB 67 GHz and a gain response of more than 60 GHz, and generation 112 GBaud 16QAM and 120GBaud QPSK optical signals [5]. In 2018, the 2:1 high-speed selector and traveling wave electro-absorption laser modulator (TW-EAM) based on InP achieved a record symbol rate of 204 Gbaud and 140 Gbaud OOK to transmit SSMF over 10 km and 80 km, respectively [6]. ...
... Today, the deployment of 400 Gb s −1 per fibre has already begun, and the 800 Gb Ethernet (800 GbE) and 1.6 Tb Ethernet (TbE) are soon expected to be standardized. The modulation bandwidth (BW) of electrical absorption modulators (EMLs) and Mach-Zehnder (MZ) modulators on InP or Si has taken a massive stride towards the realization of 100 Gb s −1 λ −1 or even beyond 1,2 . With such high-speed data transmission, the receiver sensitivity degrades, and a higher optical power from the transmitter, typically ~5 dBm at the receiver, is required 1 . ...
Today, in the face of ever increasing communication traffic, minimizing power consumption in data communication systems has become a challenge. Direct modulation of lasers, a technique as old as lasers themselves, is known for its high energy efficiency and low cost. However, the modulation bandwidth of directly modulated lasers has fallen behind those of external modulators. In this Article, we report wide bandwidths of 65–75 GHz for three directly modulated laser design implementations, by exploiting three bandwidth enhancement effects: detuned loading, photon–photon resonance and in-cavity frequency modulation–amplitude modulation conversion. Substantial reduction of chirp (α < 1.0) as well as isolator-free operation under a reflection of up to 40% are also realized. A fast data transmission of 294.7 Gb s⁻¹ over 15 km of a standard single-mode fibre in the O-band is demonstrated. This was achieved without an optical fibre amplifier due to a high laser output power of 13.6 dBm.
... For the next generation of data center networks (DCNs) and data center interconnections (DCIs), an 800 GE interface (i.e., four-lane 200 Gbit/s per wavelength) is potentially a competitive solution that attracts more and more attention. To realize a 200 Gbit/s per wavelength interface, simple non-return to zero-on-offkeying (NRZ-OOK) signal format may no longer be sufficient to support the speed requirements [3], because the expected bandwidth (BW) for a transmitter (TX) and receiver (RX) is more than 100 GHz [4], which could be a terrible challenge for commercial production. Advanced modulation formats, such as discrete multi-tone (DMT), carrier-less amplitude phase (CAP), or multi-level pulse amplitude modulation (PAM), which allow for increased capacity at constant BW, are considered as potential solutions and have been widely researched [3]. ...
We demonstrate the optical transmission of an 800 Gbit/s (4×200 Gbit/s) pulse amplitude modulation-4 (PAM-4) signal and a 480 Gbit/s (4×120 Gbit/s) on–off-keying (OOK) signal by using a high-bandwidth (BW) silicon photonic (SiP) transmitter with the aid of digital signal processing (DSP). In this transmitter, a four-channel SiP modulator chip is co-packaged with a four-channel driver chip, with a measured 3 dB BW of 40 GHz. DSP is applied in both the transmitter and receiver sides for pre-/post-compensation and bit error rate (BER) calculation. Back-to-back (B2B) BERs of the PAM-4 signal and OOK signal are first measured for each channel of the transmitter with respect to a variety of data rates. Similar BER performance of four channels shows good uniformity of the transmitter between different channels. The BER penalty of the PAM-4 and OOK signals for 500 m and 1 km standard single-mode fiber (SSMF) transmission is then experimentally tested by using one channel of the transmitter. For a 200 Gbit/s PAM-4 signal, the BER is below the hard-decision forward error correction (HD-FEC) threshold for B2B and below the soft-decision FEC (SD-FEC) threshold after 1 km transmission. For a 120 Gbit/s OOK signal, the BER is below SD-FEC threshold for B2B. After 500 m and 1 km transmission, the data rate of the OOK signal shrinks to 119 Gbit/s and 118 Gbit/s with the SD-FEC threshold, respectively. Finally, the 800 Gbit/s PAM-4 signal with 1 km transmission is achieved with the BER of all four channels below the SD-FEC threshold.
... A 50-Gbaud class PAM4 operation using an EA-DFB has been demonstrated by several researchers [2][3][4][5][6][7] for 400 Gbit/s interconnections. Additionally, a few interesting studies of 100-Gbaud class PAM4 using EA-DFBs have been reported recently for achieving interconnections beyond 400Gb/s [8,9]. ...
... In [112] and [113], an in-house fabricated selector power digital-to-analog converter (SP-DAC) was used to demonstrate up to 214 Gbps generation and 200 Gbps transmission of PAM-4 over 0.5 km SMF in the C-band, with a maximum likelihood sequence detection (MLSD) at the receiver. Besides the aforementioned works, the DFB-TWEAM reported in [65] was also employed for a 204 Gbaud OOK transmission, where two 2:1 InP DHBT multiplexing selector was used to generate the high-baud rate signal [114], [115]. A maximum a posteriori (MAP) symbol detector with a look-up-table (LUT) at the receiver was used to detect the received symbols. ...
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 requirements, 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 paper, 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.
... Time Exploiting time means, substantially, increasing either the symbol rate or the number of levels. With respect to the symbol rate, there have been reported OOK symbol rates up to 204 GBaud [108], which represents a 10× improvement compared to current standard (∼ 25 GBaud). However, increasing the symbol rate requires a huge effort in terms of hardware development. ...
The main topic of this work is the application of advanced Digital Signal Processing
(DSP) techniques to high data-rate optical links. The first part of the thesis is devoted to direct-detection systems, with a specific focus on data-center (DC) communications. These links, until recently, used very simple On-Off Keying modulation. However, the strong push towards higher data-rates introduced the use of some DSP algorithms in the DC. First, this thesis introduces a novel architecture for 400-Gbit/s Intra-DC (shorter than 2 km) applications. This architecture uses each fiber pair in both directions, doubling the per-laser and per-fiber capacity. Crosstalk is reduced by using a short feed-forward adaptive equalizer and a small frequency shift between lasers transmitting over the same fiber. This system, after an initial theoretical evaluation, was successfully tested with an experiment. Then, Intra-DC links were analyzed, i.e. links interconnecting different DCs in the same region. The target distance was 80 km. For this purpose, Single Side-Band (SSB) modulation was compared with Intensity Modulation/Direct Detection schemes over dispersion-uncompensated links with single-photodiode receivers. Using, as an application example, the DMT modulation format, the comparison was carried over different span lengths. It was found that, for distances longer than 10 km, SSB has a significant advantage over IM/DD systems.
The second part of the thesis focuses on coherent systems. In particular, it studied constellation shaping techniques, which have been recently proposed for optical communications. To perform a fair analysis, shaped constellations were compared, at the same net data rates, with standard lower-cardinality QAM constellations. It was found that, over a linear channel, the gain of constellation shaping is approximately 25%. Afterwards, this thesis discusses the non-linear properties of the optical channel, which are known to be enhanced by constellation shaping. In particular, it focuses on the generation of Non-Linear Phase Noise (NLPN) at different system conditions, using both standard QAM and shaped constellations. It was found that, in some scenarios, such as low symbol rates or low dispersion fibers, NLPN significantly degrades the performance of shaped constellations. Then, this thesis proposes some compensation techniques, which are able to partially mitigate the effect of NLPN in those conditions.
... Time Exploiting time means, substantially, increasing either the symbol rate or the number of levels. With respect to the symbol rate, there have been reported OOK symbol rates up to 204 GBaud [108], which represents a 10× improvement compared to current standard (∼ 25 GBaud). However, increasing the symbol rate requires a huge effort in terms of hardware development. ...
The main topic of this thesis is the application of advanced Digital Signal Processing (DSP) techniques to high data-rate optical links. This thesis is divided in two parts: Direct-Detection systems, and Coherent systems. In the first part, it is proposed a novel bi-directional architecture for <2km Intra-DC link and a detailed analysis of self-coherent single-sideband transmission for <80km dispersion-uncompensated Inter-DC link. The second part instead focuses on Probabilistic Constellation Shaping techniques, and their impact on long-haul optical communication links.
... Alternatively, external modulators offer higher speed and better signal quality than directly modulated sources. Highest modulation bandwidths can be achieved with external modulators based on LiNbO3 photonics [31][32][33], InP photonics [34][35][36][37][38][39][40][41][42], Si photonics [43][44][45][46][47] or plasmonics [48][49][50][51][52]. However, dense integration of external modulators based on photonic solutions is challenging due to a large footprint. ...
A new plasmonic transmitter solution offering 0.8 Tbit/s on an ultra-compact 90 μm × 5.5 μm footprint is introduced. It comprises a densely arranged 4-channel plasmonic phase modulator array that directly interconnects an optical fiber array. Each plasmonic modulator features high-index grating couplers - for direct and efficient conversion from a fiber mode to a plasmonic slot mode and vice versa - and a plasmonic waveguide - for efficient high-speed modulation. The individual devices achieve data rates of 200 Gbit/s with a symbol rate of 100 GBd. Electrical and optical crosstalk between neighboring modulators were found to have no significant influence on the data modulation experiment. The modulator array has been tested in a 100 GBd experiment with signals at a single wavelength (mimicking a space division multiplexing scheme) and at different wavelengths (mimicking a wavelength division multiplexing experiment).
... Despite the challenges, an increase of the symbol rate would be a favored solution for DCI and has been subject of much recent research. A 204 Gb/s On-Off keying (OOK) transmitter has been demonstrated using InP platforms for both the optics and electronics in combination with offline DSP [5], [6]. Similarly, an EAM integrated with a DFB laser (EADFB) was used to demonstrate 214 Gb/s PAM-4 transmission [7]. ...
... The towering increase of traffic demand in datacenters imposes the need for solutions that, on one hand, are capable of scoping with the constantly growing bandwidth requirements 1 and, on other hand, are dealing the bandwidthdensity issues 2 . In this regard, a spatial division multiplexing (SDM) is proposed on top of highspeed and low-cost solutions of short-reach interfaces for addressing the bandwidth-density problem and for scalability improvements 2,3 . ...
We experimentally demonstrate the impact of inter-core crosstalk in multicore fibers on 56Gbaud PAM-4 signal quality after 2.5-km transmission over a weakly-coupled and uncoupled sevencore fibers, revealing the crosstalk dependence on carrier central wavelength in range of 1540-1560 nm.
Multi-lane integrated transmitter chips are key components in future compact optical modules to realize high-speed optical interconnects. Thin-film lithium niobate (TFLN) photonics have emerged as a promising platform for achieving high-performance chip-scale optical systems. Combining a coarse wavelength-division multiplexing (CWDM) devices using fabrication-tolerant angled multimode interferometer structure and high-performance electro-optical modulators, we demonstrate monolithic on-chip four-channel CWDM transmitter on the TFLN platform for the first time. The four-channel CWDM transmitter enables high-speed transmissions of 100 Gb/s data rate per wavelength channel (i.e., an aggregated date rate of 400 Gb/s).
We presenta silicon photonic based stacked die assembly (SDA) compatible with the commercial complementary metal-oxide-semiconductor process. The SDA consists of a driver die and a transimpedance amplifier die, both populated onto a photonic integrated circuit die with a dimension of 5 mm×9 mm. The SDA is designed to be an O-band optical engine for a 4×200-Gbit/s parallel single-mode fiber short-reach transmission system. Performance of several pulse amplitude modulation (PAM) formats are evaluated and compared for the feasibility of 200-Gbit/s transmission. Aided by a Volterra nonlinear equalizer, the system experiment demonstrated that PAM-8 is a promising candidate for single lane 200-Gbit/s transmission with achieved bit error rate (BER) floor of 1.4×10
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup>
. Instead of using costly optical amplifier, the system relies on the transimpedance amplifier on the SDA to boost up receiver sensitivity, which is shown to be −2.6 dBm and −2.0 dBm for 2-km and 10.5-km fiber transmissions respectively. The system impairments and noise sources are quantitatively discussed to facilitate further hardware improvement. We believe this is the first demonstration of net 200-Gbit/s transmission over 10 km without optical amplification, accomplished with silicon photonic integrated circuit and offline processing.
By using the generalized frequency division multiplexing (GFDM) and the machine learning algorithm for self-feedback amplitude/phase pre-distortion, the electro-absorption modulator integrated distributed-feedback semiconductor laser diode (EAM-DFBLD) is encoded with improved transmission quality and capacity. Both back-to-back (BtB) and 10-km single-mode fiber (SMF) transmissions are preliminarily demonstrated for inter-data-center applications. Optimizing the EAM-DFBLD transmitter at 1306.8 nm with a bias current of 100 mA and a bias voltage of −1.5 V can provide a 34.5-GHz bandwidth for 16-QAM discrete multitone (DMT) and GFDM formats. The parametric comparison reveals that the 16-QAM GFDM with
K
= 16 can improve its performance from BtB to 10-km SMF transmission with decoding BER slightly increasing from 1.44 × 10
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup>
to 2.82 × 10
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup>
. The EAM-DFBLD carried GFDM data also provides a better power penalty by -0.25 dB. This enables higher raw data rates of 149.6 Gbit/s under BtB case and 138 Gbit/s in 10-km SMF transmission link below the forward error correction (FEC) criterion. The GFDM format carried by the EAM-DFBLD transmitter thus becomes the more suitable candidate than the DMT to implement ultra-high-speed inter-data-center and data access link applications.
In recent years, the technology to narrow the gap between the achievable information rate and the Shannon capacity limits attracts increasing attention. In this paper, a probabilistic shaping coding method based on multi-repeat mapping is proposed. By applying block coding to the information sequences with our method, we transform the modulated constellation points from a uniform distribution to the desired distribution. Rate adaption and controllable distribution are achieved by adjusting the block length and the size of different mapping sets. The proposed algorithm has better coding efficiency, low storage and computational complexity, so is more suitable for data center optical networks. An experiment that demonstrates probabilistically shaped data transmission is successfully conducted over 10 km standard single-mode fiber (SSMF) with 16 quadrature amplitude modulation – discrete multi-tone (16-QAM-DMT). We evaluate our method for a set of code rates, i.e., 16 QAM with code rate 6/8, 7/8 and 9/12. The experimental results show that the improved signal to noise ratios (SNR) can be up to 1.1 dB at a bit error rate (BER) of 10⁻³ after using the proposed method for probabilistic shaping.
In this paper, for the first time, we propose a photonic-aided digital-to-analog converter (PADAC) to break through transmitter-side bandwidth limitation in intensity modulation and direct detection (IM-DD) systems. By this method, bandwidth of receiver-side devices can be fully utilized, and nonlinear distortions in high-data-rate electrical signals are avoided. Experimental results indicate that, with only linear equalization, 120 GBaud PAM-4 and PAM-6 signals have been successfully generated and detected below 6.25%-OH HD-FEC and 20%-OH SD-FEC limits, respectively.
The demand for transmitting optical signals with high spectral efficiency (SE) by exploiting cost-effective systems and techniques is raising an increasing interest in the area of wide or metro area networks (WAN/MAN). Recently, many different solutions, e.g., amplitude modulation formats, direct-detection schemes, line codes, and simple signal processing techniques have been investigated for wavelength division multiplexing (WDM) short haul optical links, where coherent systems turn out to be economically unfavourable. In this paper the Time-Frequency Packing technique, already successfully proposed for long-haul coherent optical links, is extended to direct-detection systems, based on pulse amplitude modulation (PAM) and differential phase-shift keying (DPSK), with the purpose of trading between detection complexity and SE, and of providing performance limits for advanced digital signal processing (DSP) at the receive side.
We report high speed electro-absorption modulators (EAMs), designed, fabricated and characterized within an open access generic foundry process. The EAM as a new building block (BB) is optimized in the existing platform, in which other BBs are established. By optimizing the EAM design layout, we show a static extinction ratio (static ER) of 18 dB, a low DC bias voltage below 1 V at increased temperature, as well as operation in a semi-cooled environment, tested in the range of
$\rm 20-60^\circ C$
. Furthermore, we improve the intrinsic S-parameter response with a co-design circuit. The intrinsic 3-dB bandwidth of a 100 μm-long EAM is 17 GHz. When measured with the EAM submount design, it is increased to 24 GHz. Simultaneously, the return loss bandwidth is improved by a factor of 2.5 staying below -10 dB up to 20 GHz. Through the realization of the EAM submount design we achieve a three time speed increase of the existing platform, from previously offered 9 GHz (using an electro-optical modulator) to 24 GHz shown in this work.
A low complexity digital signal processing architecture for dual-polarization coherent detection is presented. It synchronizes impairments in the frequency domain and uses synergies between the filtering processing stages to minimize overall complexity. We show how chromatic dispersion, skew, carrier frequency offset, timing error, and state of polarization can be mitigated with a single filtering stage in the frequency domain. The error estimation in the frequency domain is based on the modified Godard algorithm, which calculates the clock tone with less than 2 samples per symbol and small timing jitter. The synchronization in the frequency domain is independent of the modulation format and therefore a good candidate for higher order modulation formats and so the synchronization of probabilistic shaped (PS) signals based on a high cardinality rectangular QAM format. We show the synchronization of PS polarization-division multiplexed (PDM)-64QAM signals with a symbol rate of 42.7 GBd in the frequency domain. Simulative results for the influence of the FFT size and the number of FFT blocks used for the error estimation are shown. Finally, we show experimental results for 4 different probabilistic shapings in back-to-back and transmission over 300 km which are synchronized with the introduced digital signal processing (DSP).
In response to the ever-growing challenge of using conventional direct-modulation/direct-detection transceivers for upgrading passive optical networks, there has recently been a surge in interest in alternative transceiver technologies. Candidate systems include (simplified) coherent receivers, and digital signal processing in combination with direct detection. Beyond these mainstream solutions, other, more esoteric, system designs have been proposed, including networks based on general purpose signal processing hardware, split carrier transmitters, and ultra-wide bandwidth coherent receivers. Herein, we review these techniques and detail an experimental investigation of an ultra-wide bandwidth coherent receiver. It is found that the use of a dual-local oscillator receiver in an ultra-dense wavelength division multiplexed passive optical network (UDWDM-PON) enables the simultaneous detection of multiple upstream channels while efficiently using the complete receiver optoelectronic bandwidth.
As optical transceivers evolve towards 200G per lane, the comparatively low bandwidth and sampling speed of the commercially available high-speed DACs and ADCs increasingly become the dominating obstacle towards success. On the other hand, DACs and ADCs are essential to make use of digital signal processing for impairment compensation and error correction; altogether driving systems engineers to a hard design dilemma. With the purpose of alleviating this compromise, we propose a transceiver structure - encompassing both hardware and software - enabling the generation, transmission, and detection of strongly over-filtered data signals whose baudrate exceeds the sampling rates of (potentially) both the DAC and ADC. We call this approach sub-baudrate sampling, a technique which does not increase the processing complexity at the transmitter side and does not even require the information about the channel state for pre-distortion or pre-coding purposes. We experimentally assess the performance of sub-baudrate sampled signals in two blocks of experiments: first the proof of concept in back-to-back configuration, including up to 112Gbaud on-off keying at 0.785 samples per symbol in ~25-GHz aggregate bandwidth. And then the C-band transmission demonstration, showing up to 100Gbaud quaternary pulse-amplitude modulation (0.92 samples per symbol) and 125Gbaud on-off keying (0.736 samples per symbol) over 1 and 80-km of singlemode fiber respectively with more than 3-dB receiver sensitivity margin at the 7%-overhead hard-decision bit error-rate limit.
We report on an on-off keying intensity-modulation and direct-detection C-band optical transceiver capable of addressing all datacenter interconnect environments at well-beyond 100Gbaud. For this, the transmitter makes use of two key InP technologies: a 2:1 double heterojunction bipolar transistor selector multiplexer and a monolithically integrated distributed-feedback laser traveling-wave electro-absorption modulator, both exceeding 100-GHz of 3-dB analog bandwidth. A pre-amplified 110-GHz PIN photodiode prior to a 100-GHz analog-to-digital converter complete the ultra-high bandwidth transceiver module; the device under study. In the experimental work, which discriminates between intra- and inter-data center scenarios (dispersion unmanaged 120, 560, 960m; and dispersion-managed 10, and 80km of standard singlemode fiber), we evaluate the bit-error rate evolution against the received optical power at 140, 180, and 204Gbaud on-off keying for different equalization configurations (adaptive linear filter with and without the help of short-memory sequence estimation) and forward error correction schemes (hard-decision codes with 7% and 20% overhead); drawing conclusions from the observed system-level limitations of the respective environments at this ultra-high baudrate, as well as from the operation margins and sensitivity metrics. From the demonstration, we highlight three results: successful operation with >6-dB sensitivity margin below the 7% error-correction at 140Gbaud over the entire 100m-80km range with only linear feed-forward equalization. Then the transmission of a 180Gbaud on-off-keying carrier over 80km considering 20% error-correction overhead. And finally, 10-km communication at 204Gbaud on-off keying with up to 6dB sensitivity margin, and regular 7%-overhead error-correction.
We report on the development of a submicron InP DHBT technology, optimized for the fabrication of ges50-GHz- clock mixed-signal ICs. In-depth study of device geometry and structure has allowed to get the needed performances and yield. Special attention has been paid to critical thermal behavior. Various size submicron devices have been modeled using UCSD- HBT equations. These large signal models have allowed the design of 50-GHz clocked 50 G Decision and 100 G Selector circuits. The high quality of the measured characteristics demonstrates the suitability of this technology for the various applications of interest, like 100 Gbit/s transmission.
An integrated selector-driver is designed for 100 Gbit/s operation and fabricated using 0.7 mum InP double-heterojunction bipolar transistor (DHBT) technology. The driver has a lumped architecture and operates in differential mode. Two complementary signals each with 2.7 V amplitude (3.2 V<sub>pp</sub>) have been measured at 100 Gbit/s.
Driven primarily by Cloud Service and data-center applications, short-reach optical communications has become a key market segment and growing research area in recent years. Short-reach systems are characterized by direct detection-based receiver configurations and other low-cost and small form factor components that induce transmission impairments unforeseen in their coherent counterparts. Innovative signaling and digital signal processing (DSP) plays a pivotal role in enabling these components to realize their ultimate potentials and meet data rate requirements in cost-effective manners. This paper presents an overview of recent DSP developments for short-reach communications systems and discusses future trends.
We report on a 116 Gbps on-off keying (OOK), 4 pulse amplitude modulation (PAM) and 105 Gbps 8PAM optical transmitter using an InP-based integrated and packaged externally modulated laser for high speed optical interconnects with up to 30 dB static extinction ratio and over 100 GHz 3 dB bandwidth with 2 dB ripple. In addition, we study the trade-off between power penalty and equalizer length to foresee transmission distances with standard single mode fiber.
A 120-GBd polarization multiplexed NRZ (PM-NRZ) signal is generated using a monolithic double side electro-absorption modulated distributed feedback (DFB) laser. Using a pre-amplified direct detection receiver and direct detection faster than Nyquist technique, the optical receiver sensitivities of-18.3 and-13.5 dBm are obtained for a 240-Gb/s (a net data rate of 200 Gb/s with 20% soft-decision forward error correction) PM-NRZ signal at back-to-back and after 2-km transmission, respectively. To the best of our knowledge, this is the highest baud rate transmission reported to date for single channel polarization multiplexed signal generated by a single device for short reach applications and the longest transmission distance (2 km) at baud-rate >100 GBd IM/DD system without CD compensation at 1.55 μm.
Designing error-correcting codes for optical communication is challenging mainly because of the high data rates (e.g., 100 Gbps) required and the expectation of low latency, low overhead (e.g., 7% redundancy), and large coding gain (e.g., >9dB). Although soft-decision decoding (SDD) of low-density parity-check (LDPC) codes is an active area of research, the mainstay of optical transport systems is still the iterative hard-decision decoding (HDD) of generalized product codes with algebraic syndrome decoding of the component codes. This is because iterative HDD allows many simplifications and SDD of LDPC codes results in much higher implementation complexity. In this paper, we use analysis and simulation to evaluate tightly-braided block codes with BCH component codes for high-speed optical communication. Simulation of the iterative HDD shows that these codes are competitive with the best schemes based on HDD. Finally, we suggest a specific design that is compatible with the G.709 framing structure and exhibits a coding gain of >9.35 dB at 7% redundancy under iterative HDD with a latency of approximately 1 million bits.
A monolithically integrated distributed feedback (DFB) laser and traveling-wave electro-absorption modulator (TWEAM) with ges 100 GHz -3 dBe bandwidth suitable for Non-return-to-zero (NRZ) operation with on-off keying (OOK) is presented. The steady-state, small-signal modulation response, microwave reflection, chirp characteristic, and both data operation and transmission were investigated. The DFB-TWEAM was found to be an attractive candidate for future short distance communication in high bitrates systems.
A modulator driver module for use in 100 Gbit/s optical data communication systems has been developed using an InP DHBT-based distributed amplifier chip and 50 Omega microstrip lines on quartz substrate. The module achieved a gain of 16 dB and a 3 dB bandwidth of 110 GHz. Clearly open 100 and 112 Gbit/s 2<sup>31</sup> - 1 non-return-to-zero pseudorandom bit sequence eye diagrams with an output voltage swing of 2.2 V<sub>pp</sub> have been measured.
Transmission of a 120-GBd PM-NRZ Signal Using a …
- K Zhong
K. Zhong et al., "Transmission of a 120-GBd PM-NRZ Signal Using a …," IEEE Photon. Technol. Lett., Vol. 28, no. 20, p. 2176 (2016).
First OpenFlow-based Software-Defined λ-Flow Architecture forFlex-Grid OFDMA Mobile Backhaul over Passive Optical Networks with Filterless Direct Detection ONUs
- V Hurm
V. Hurm, et al., "First OpenFlow-based Software-Defined λ-Flow Architecture forFlex-Grid OFDMA Mobile Backhaul over Passive Optical
Networks with Filterless Direct Detection ONUs," OFC 2013, PDP5B.2.
Fig. 3: Performances of (a) 204-GBaud, (b) 140-GBaud OOK for several number of equalizers