Abstract
1. Introduction
Optical fiber communication has the advantages of large capacity, high quality, stable performance, anti-electromagnetic interference, and strong confidentiality[
Figure 1.(Color online) A typical fiber-optic communication network for the core, metro and access network scenarios, where the IM/DD links are addressed in the metroedge and intra-/inter-data center networks. CO: center office; RN: remote node; DCI: datacenter interconnects. © [2020] IEEE. Reprinted, with permission, from Ref. [
In addition to this continuous development of traditional telecommunications networks, content providers have recently promoted higher requirements for optical interfaces with higher data rates, usually in the form of data centers with their own network infrastructure as shown in Fig. 1. Nowadays, due to the storage, transmission and processing of large amounts of data, the traffic in the data center will greatly increase[
Moreover, with the continuous development and maturity of 5G technology, the mobile fronthaul network based on the optical access network has also received extensive attention from academia and industry[
Figure 2.(Color online) A schematic diagram of the IM/DD system based on DML. DSP: digital signal processing; DAC: digital-to-analog convertor; LDD: laser diode driver; DML: directly modulated laser; SMF: single mode fiber; MMF: multi-mode fiber; ADC: analog-to-digital convertor.
The semiconductor laser is one of the most important components in the IM/DD system. It determines the achievable data rate of the system from the bottom. Thus, long-term efforts have been made in semiconductor laser research in order to obtain broad bandwidth, low noise, and high power efficiency, so that it meets the increasing demand of the transmission data rate[
The most commonly used three types of DMLs are the Fabry–Perot (FP) laser, the vertical cavity surface emitting laser (VCSEL), and the distributed feedback (DFB) laser. For the low-cost VCSEL, due to its multi-transverse-mode operation, the transmission distance is limited by the modal dispersion, and is usually tens of meters. On the other hand, due to its short cavity length, the modulation bandwidth of the VCSEL can achieve up to 30 GHz[
Based on the previous discussion, it is very attractive to apply DML-based IM/DD system in data centers and 5G fronthaul network due to its advantages of low cost, low system complexity, and high energy efficiency, which perfectly match the application scenarios of data centers and 5G fronthaul network, in which a large number of high-speed optical interconnections are needed. However, the future demand of high data rate in data centers and 5G fronthaul network is challenging the existing DML-based IM/DD system, and the main bottleneck is the modulation bandwidth of the DML. Therefore, it is necessary to explore the prospects, challenges, and future development of DMLs in the applications of future data centers and 5G fronthaul network. In this paper, this topic is comprehensively discussed. We narrow our focus on the DFB DMLs and DFB-based advanced DMLs, because their transmission distance is guaranteed by the single-mode operation and they have huge potential to achieve broader modulation bandwidth. In Section 2, the data rate demands and technical standards of data centers and 5G fronthaul networks are reviewed in detail. And the modulation bandwidth requirements of the DML are included. In Section 3, the technical routes and achievements of recent DMLs are reviewed and discussed based on the rate equation theory model. In Section 4, the prospect of applying DMLs in the future data centers and 5G fronthaul networks is discussed in terms of feasibility, technical complexity and future improvement direction.
2. Industry requirements and standards for data centers and 5G networks
For a long time, components used for photoelectric conversion and electro-optical conversion (especially DMLs) have been the bottleneck of the end-to-end channel bandwidth in high-speed IM/DD systems. This is mainly due to the following facts: fundamentally speaking, the design, manufacturing and packaging process of such optoelectronic components and devices that support a wide bandwidth while maintaining low noise levels are challenging. Technological advancements in different fields, including material technology, design, manufacturing and packaging are strictly required. Recently, a significant progress has been made in the design and manufacture of such broadband components to greatly enhance the channel capacity of the IM/DD system[
2.1. Data center
As the core platform for the cloud computing, the need to develop data centers is becoming more and more urgent. The current data centers are far from being able to meet the needs of today's society in terms of quantity and performance. Most big data processing and calculations are carried out in data centers. According to the Cisco Global Cloud Computing Index White Paper, 99% of global communication traffic is related to data centers. Among them, most data communications are still concentrated inside the data center. Due to the explosion of data volume and the rapid growth of network traffic, data centers are upgrading from 10G/40G to 25G/100G/400G architectures. Traditional electrical interconnection is difficult to meet the increasing transmission bandwidth and transmission rate requirements of data centers, which brings huge opportunities for optical interconnection. Optical transmission has the advantages of large bandwidth and long-distance transmission. Its main application scenario is to provide a large-bandwidth information transmission channel between the two points. The use of optical interconnection between data centers and within data centers will greatly enhance the data processing and computing capabilities of the data centers. In today's data center network, almost every connection uses optical interconnection technology, including the connection between servers and switches within a few meters of the data center. And simply the growth of the data traffic in the data center does not really benefit the internet of things. Only when numerous data centers are interconnected can it be possible to benefit data transmission under the internet of things. Scalable data center architecture meets the growth of east–west traffic in modern ultra-large-scale data center architecture, making data center interconnection possible. A large amount of data traffic will use optical transmission to enter the data center, and information cloud data is shared between data centers, so that optical transmission will be used not only for data transmission within the data center, but also for interconnection between data centers. Therefore, the scale of optical transmission in the data center optical interconnection market will far exceed that of telecom operators.
For the internal interconnection of the data center, the most ideal method is that each server is connected to all other servers, so that the application layer software does not need to communicate with the central computer responsible for computing task scheduling. However, such a network structure will be extremely complex and costly. In practice, the data center adopts a topological hierarchical structure, and the interconnection between clusters is converged through a packet switching network. Parallel optical transmission technology is an important method of the data center internal communication. This transmission method can not only greatly increase the communication rate, but also combines the parallel data channel structure in the large-scale network architecture, and the data processing speed is also greatly improved. The short-distance optical connection usually uses a DML with low cost, low power consumption, and enough modulation bandwidth. In order to achieve higher transmission rates and reduce the transmission cost per bit, the application of optical integrated circuits (PIC) and wavelength division multiplexing (WDM) technologies has gradually become the mainstream.
As a key factor in the data center, optical modules have broad development prospects. The interconnection of 40G to 100G is imminent. Generally speaking, a short-distance 100 Gb/s optical interconnection can use
To meet the ever-increasing bandwidth requirements of data centers, data rates, device power consumption, and space density need to be increased on a large scale. In the next few years, the speed of optical transceivers in data centers will increase by 4 times, while power consumption and space occupation will remain unchanged. The traditional binary on–off keying (OOK) modulation method can reach a rate of 20 Gb/s or more in an IM/DD system. In order to achieve a higher rate of transmission, it is necessary to put forward higher requirements on the bandwidth and dispersion performance of optoelectronic devices, and at the same time new technologies are required to be applied to short-distance optical connections. These new technologies include dispersion compensation, low-power integrated silicon optical circuits, and the evolution of new DML array to build parallel multi-channel. Parallel channel technology includes multi-fiber technology and multi-wavelength technology. At the transmitting end, the electrical signal passes through the drive circuit to modulate the laser array to generate parallel multi-path optical signals, and then these optical signals are coupled into the optical fiber for transmission. At the receiving end, the optical signal is converted into an electrical signal by the photodetector array, and then the electrical signal is recovered by the receiver circuit.
2.2. 5G fronthaul
The 5G radio access network (RAN) mainly adopts the small-scale centralized mode of the gNB macro station, the centralized unit (CU), and the distributed unit (DU) in the early stage. In the future mature period, the CU and the DU separation mode can be adopted and CU cloudification and CRAN centralized construction mode can be implemeted. For the small-scale centralized scenario of CRAN, the DU is mainly deployed in the access computer room, and the centralized scales of base stations are usually from 3 to 5, which are connected to the nearest secondary optical switch or directly connected to the ODF of the base station computer room, no need to cross the backbone optical ring. For the large-scale centralized scenario of CRAN, the DU is deployed in a common convergent computer room or integrated service access site. The centralized scale is usually 10–20 base stations and it crosses the backbone optical ring.
As an industrial cooperation organization, the Common Public Radio Interface (CPRI) Alliance defines publicly available specifications for the internal interface of the 5G fronthaul network between Radio Equipment (RE) and Radio Equipment Control (REC)[
The 5G fronthaul mainly realizes signal transmission between active antenna unit (AAU) and DU. The technical solutions mainly include optical fiber direct connection and WDM solutions. WDM solutions can be divided into passive, active, and semi-active. The main technical characteristics are as follows:
(1) Optical fiber direct connection scheme: the AAU and DU are directly connected by optical fiber. AAU and building baseband unit (BBU) are equipped with 25 Gb/s white light modules. Generally, a single 5G S111 base station requires 6-core fiber resources when using dual-fiber bidirectional interconnection. Considering that the large-scale construction of 5G base stations will consume huge access layer fiber resources, the industry proposes a 25 Gb/s BiDi (bidirectional) solution. The data signals in both directions of AAU and DU are transmitted in one fiber using different wavelengths. It can save half of the fiber resources by reducing from six cores to three cores.
(2) Passive WDM solution: It means that both the AAU and DU are equipped with color light modules, and a passive multiplexer/demultiplexer is deployed at both ends to realize color light channel signal multiplexing without any active transmission equipment. This solution only needs one core optical fiber cable when it is based on single-fiber bidirectional mode in unprotected scenarios. Currently, the main commercial products of passive WDM solutions are based on fixed wavelength coarse wavelength division multiplexing (CWDM) solutions.
(3) Semi-active WDM solution: Deploy active WDM equipment on the DU or BBU side, and only deploy the passive multiplexer and demultiplexer on the AAU side, and realize network operation and maintenance such as optical module status monitoring and wavelength tuning through optical signal top adjustment. This solution is the focus of recent operator research and future deployment, and is actively promoting product development, standardization, and testing verification.
(4) Active WDM solution: Active devices are deployed on both the AAU side and the DU side for service access and transmission. The feature of this solution is that the transmission and wireless professional equipment management interface is clear, and the transmission equipment supports complete network operation and maintenance management and control capabilities. At the AAU side, taking into account the working environment, power supply situation, comprehensive network cost, as well as factors such as low latency of the order of 100
The WDM technology for 5G fronthaul can be further divided into four schemes: CWDM, LAN-WDM based on local area network channel, medium wavelength division multiplexing (MWDM) and dense wavelength division multiplexing (DWDM) based on the used frequency band and channel spacing difference. On the whole, CWDM technical standards are relatively mature. At present, passive and semi-active CWDM have commercial products, which are the main deployment solutions for the short-term C-RAN scenario to solve the shortage of optical fiber resources. Semi-active MWDM, LAN-WDM and DWDM are in the process of product development and standardization, to support richer control functions and improve maturity and stability.
Currently, China Communication Standardization Association (CCSA) and ITU-T are mainly responsible for the standardization of 5G fronthaul. CCSA TC6 has formally established a project and started the standardization work of the WDM system and color light module based on 25 Gb/s data rate, including four typical programs of CWDM, LWDM, MWDM and DWDM. ITU-T SG15 is also focusing on G.698.x serial standards. The formulation of 25 Gb/s DWDM standards, including fixed wavelength and tunable wavelength, has made significant progress in related parameters and assignment research. In addition, ITU-T has also started to discuss the standardization of 25 Gb/s CWDM system for fronthaul. In fronthaul application scenarios, 25, 50, and 100 Gb/s rates introduce one or more key technologies such as single-fiber bidirectional and WDM. Optical module types show a diversified and dispersed development trend, see Table 2 for details.
3. State-of-the-art works of DMLs
3.1. Rate equations of semiconductor lasers
Firstly, we discuss the coupled rate equations for charge carriers and photons, which are helpful to describe the dynamic characteristics of semiconductor lasers. From this basic analysis framework, the directions of improving DML modulation bandwidth are outlined. Accompanied with a review of the resent research achievements of DMLs, the prospect of applying DML-based IM/DD system in future data centers and 5G fronthaul is explored.
The analysis framework here is summarized from Coldren et al.[
Figure 3.Model used in the rate equation analysis of semiconductor lasers. Copyright © 2012 John Wiley & Sons, Inc. Reprinted, with permission, from Ref. [
where
3.2. Small-signal response
Small-signal response of the semiconductor laser can be analyzed by taking the differential of the rate equations Eq. (3) and Eq. (4). By considering
with rate coefficients:
where the differential carrier lifetime
And
where
Eq. (5) can be extended for multimode small-signal analysis:
The three rate coefficients
In the case of single mode, the small-signal responses
Thus, Eq. (5) becomes:
The small-signal solutions can be obtained:
where the modulation transfer function
3.3. Intensity modulation bandwidth
In practice, for the case of above threshold operating, the first term of Eq. (15) dominates over all other terms[
With the simplified
where
where
where
and the resonance frequency is
In order to increase the modulation bandwidth, both
Fig. 4 shows the sketch of the modulation transfer function for increasing values of relaxation resonance frequency
Figure 4.(Color online) The sketch of the modulation transfer function for increasing values of relaxation resonance frequency
3.4. A review of high-speed DMLs
Over the past few decades, numerous efforts have been made to develop high-speed DMLs, as summarized in Table 4. As discussed above, the most direct methods to increase the modulation bandwidth are to decrease the mode volume
To increase the differential gain, Ralston et al.[
To overcome the K-limited bandwidth (
Figure 5.(Color online) Schematics of different types of coupled-cavity lasers. (a) Two-section DBR laser. © [1998] IEEE. Reprinted, with permission, from Ref. [
Figure 6.(Color online) (a) Example of the detuned loading and PPR in a two-section DBR laser: round trip gain (blue curve) and phase (red dashed curve) function at the DBR threshold. The squared red marker represents the lasing mode; the blue markers indicate nonlasing cavity modes. The green asterisks on the reflectivity curve represent the modes locations in the maximum detuned loading condition. © [2013] IEEE. Reprinted, with permission, from Ref. [
As for the PPR effect, the passive feedback cavity reflects the light emitting from the rear facet of the active section and re-injects back to the active section. The passive cavity length is carefully designed so that the passive feedback cavity creates side PPR modes, which are located next to the lasing mode, as shown in Fig. 6(a) and Fig. 7(a). When the reflected light is in phase with the active section, the photons generated in the high frequency region is resonantly amplified by in the side modes, leading to another resonance in the frequency response, which can significantly enhance the modulation bandwidth, as shown in Fig. 7(b). With the passive feedback cavity, the PPR effect can always be obtained by carefully design. It is possible to combine the short cavity, the detuned loading effect, and the PPR effect to drastically enhance the modulation bandwidth to over 100 GHz[
Figure 7.(Color online) (a) Measured lasing spectrum at 27 mA with using PPR. (b) Measured small-signal responses of the laser at various bias currents, with using PPR. (c) Measured lasing spectrum at 27 mA without using PPR. (d) Measured small-signal responses of the laser at various bias currents, without using PPR. The laser has a 50-
4. Discussion
Since the first generation of optical communications, IM/DD technology has always been the core part of an optical fiber communication network. However, about ten years ago, the coherent optical communication technology has rapidly replaced IM/DD solutions in core/metropolitan area networks. Because the coherent detection scheme is applicable to all modulation formats, and can demodulate orthogonal polarization signals, which improves the spectral efficiency. Moreover, due to the use of the local oscillator signal, the receiver sensitivity of the coherent detection far exceeds that of the direct detection scheme, which enables long-distance communication. However, both the configuration and the DSP of the coherent communication system are complicated and expensive. Thus, the IM/DD solutions are superior for high-speed optical short-reach links because in this case low-cost is highly required. As the achievable data rate and the transmission distance of the IM/DD system increases, the division boundary becomes increasingly blurred in the application era of 200G and beyond. In order to meet the requirements of speed, cost, power consumption,and volume, research and development efforts are being carried out in three main aspects: modulation format, DSP, and modulation bandwidth. Powerful DSP and coding modulation techniques can be combined to optimize the spectrum efficiency and transmission performance. In Ref. [47], by utilizing discrete multitone (DMT) modulation and a nonlinearity-tolerant channel equalization algorithm for DSP, a 114-Gb/s high data rate is achieved based on a directly-modulated single-mode long-wavelength VCSEL whose modulation bandwidth is 22 GHz, which is not very broad. This approach reduces the requirement for the modulation bandwidth, which makes applying low-cost VCSELs in the beyond 100 Gbaud DML-based IM/DD system promising. To further improve the data rate, spatial division multiplexing (SDM) combined with DML-based IM/DD system is recognized as a promising technology[
Based on the discussion in section 3, a clear route of improving the modulation bandwidth of DMLs can be seen. In terms of materials, the main effort is to increase the differential gain and to reduce the gain nonlinearity. Hence, a InGaAlAs material system is preferred for high-speed DMLs. In terms of laser structure, two main approaches are taken: (1) short-cavity structure and (2) DFB-based (or DBR-based) coupled-cavity structure. With the short active section, the mode volume can be compressed effectively. Thus, the relaxation resonance frequency is increased. However, due to the
5. Conclusion
In this paper, the prospects, challenges, and future development of DMLs in the applications of future data centers and 5G fronthaul networks are comprehensively explored. The data rate demands and technical standards of the data centers and 5G fronthaul are reviewed in detail. Based on the modulation bandwidth requirements, the technical routes and achievements of recent DMLs are reviewed and discussed. It can be seen that applying DML-based IM/DD system in future data centers and 5G fronthaul networks to fulfill 100 Gbaud data rate is very promising.
Acknowledgements
J. Huang and C. Li contributed equally to the paper. This work is supported by Open Fund of the State Key Laboratory of Optoelectronic Materials and Technologies; The International Cooperation Project of Sichuan Province; Sichuan Science and Technology Program (2020YFH0108); NWO Zwaartekracht program on Integrated Nanophotonics; ZJU-TU/e IDEAS project; and Key Research and Development Program of China (2018YFE0201000); Anhui Provincial Natural Science Foundation of China (1808085MF186).
References
[1]
[2] P J Winzer. Beyond 100G Ethernet. IEEE Commun Mag, 48, 26(2010).
[3] C Cole. Beyond 100G client optics. IEEE Commun Mag, 50, s58(2012).
[4] X D Pang, O Ozolins, R Lin et al. 200 Gbps/lane IM/DD technologies for short reach optical interconnects. J Lightwave Technol, 38, 492(2020).
[5] C Kachris, K Kanonakis, I Tomkos. Optical interconnection networks in data centers: Recent trends and future challenges. IEEE Commun Mag, 51, 39(2013).
[6] E Agrell, M Karlsson, A R Chraplyvy et al. Roadmap of optical communications. J Opt, 18, 063002(2016).
[7]
[8]
[9] A De La Oliva, X C Perez, A Azcorra et al. Xhaul: toward an integrated fronthaul/backhaul architecture in 5G networks. IEEE Wirel Commun, 22, 32(2015).
[10] R S Tucker. High-speed modulation of semiconductor lasers. IEEE Trans Electron Devices, 32, 2572(1985).
[11] N Zhu, Z Shi, Z Zhang et al. Directly modulated semiconductor lasers. IEEE J Sel Top Quantum Electron, 24, 1(2018).
[12]
[13] C Peucheret. Direct and external modulation of light. Experimental Course in Optical Communication(2009).
[14] T Tadokoro, W Kobayashi, T Fujisawa et al. 43 Gb/s 1.3
[15] C C Shen, T C Hsu, Y W Yeh et al. Design, modeling, and fabrication of high-speed VCSEL with data rate up to 50 Gb/S. Nanoscale Res Lett, 14, 1(2019).
[16] S Yamaoka, N P Diamantopoulos, H Nishi et al. Directly modulated membrane lasers with 108 GHz bandwidth on a high-thermal-conductivity silicon carbide substrate. Nat Photonics, 15, 28(2021).
[17] D Che, Y Matsui, X Chen et al. 400-Gb/s direct modulation using a DFB+R laser. Opt Lett, 45, 3337(2020).
[18] T Pfeiffer. Next generation mobile fronthaul and midhaul architectures. J Opt Commun Netw, 7, B38(2015).
[19]
[20]
[21] J D Ralston, S Weisser, I Esquivias et al. Control of differential gain, nonlinear gain and damping factor for high-speed application of GaAs-based MQW lasers. IEEE J Quantum Electron, 29, 1648(1993).
[22] J D Ralston, S Weisser, K Eisele et al. Low-bias-current direct modulation up to 33 GHz in InGaAs/GaAs/AlGaAs pseudomorphic MQW ridge-waveguide lasers. IEEE Photonics Technol Lett, 6, 1076(1994).
[23]
[24] S Weisser, E C Larkins, K Czotscher et al. Damping-limited modulation bandwidths up to 40 GHz in undoped short-cavity In0.35Ga0.65As-GaAs multiple-quantum-well lasers. IEEE Photonics Technol Lett, 8, 608(1996).
[25] Y Matsui, H Murai, S Arahira et al. 30-GHz bandwidth 1.55-
[26] I Vurgaftman, J R Meyer, L R Ram-Mohan. Band parameters for III–V compound semiconductors and their alloys. J Appl Phys, 89, 5815(2001).
[27] K Otsubo, M Matsuda, K Takada et al. 1.3-
[28] T Fukamachi, K Adachi, K Shinoda et al. Wide temperature range operation of 25-Gb/s 1.3-
[29] T Simoyama, M Matsuda, S Okumura et al. 40-Gbps transmission using direct modulation of 1.3-
[30] W Kobayashi, T Ito, T Yamanaka et al. 50-Gb/s direct modulation of a 1.3-
[31] M Matsuda, A Uetake, T Simoyama et al. 1.3-
[32]
[33]
[34] M Radziunas, A Glitzky, U Bandelow et al. Improving the modulation bandwidth in semiconductor lasers by passive feedback. IEEE J Sel Top Quantum Electron, 13, 136(2007).
[35] U Troppenz, J Kreissl, M Möhrle et al. 40 Gbit/s directly modulated lasers: Physics and application. Proc SPIE, 7953, 79530F(2011).
[36] J Kreissl, V Vercesi, U Troppenz et al. Up to 40 Gb/s directly modulated laser operating at low driving current: Buried-heterostructure passive feedback laser (BH-PFL). IEEE Photonics Technol Lett, 24, 362(2012).
[37] S Mieda, N Yokota, W Kobayashi et al. Ultra-wide-bandwidth optically controlled DFB laser with external cavity. IEEE J Quantum Electron, 52, 1(2016).
[38] Y Matsui, R Schatz, T Pham et al. 55 GHz bandwidth distributed reflector laser. J Lightwave Technol, 35, 397(2017).
[39] G H Liu, G Y Zhao, J Q Sun et al. Experimental demonstration of DFB lasers with active distributed reflector. Opt Express, 26, 29784(2018).
[40]
[41] U Feiste. Optimization of modulation bandwidth in DBR lasers with detuned Bragg reflectors. IEEE J Quantum Electron, 34, 2371(1998).
[42] P Bardella, I Montrosset. A new design procedure for DBR lasers exploiting the photon–photon resonance to achieve extended modulation bandwidth. IEEE J Sel Top Quantum Electron, 19, 1502408(2013).
[43] G Morthier, R Schatz, O Kjebon. Extended modulation bandwidth of DBR and external cavity lasers by utilizing a cavity resonance for equalization. IEEE J Quantum Electron, 36, 1468(2000).
[44] K Vahala, A Yariv. Detuned loading in coupled cavity semiconductor lasers — effect on quantum noise and dynamics. Appl Phys Lett, 45, 501(1984).
[45] K Vahala, J Paslaski, A Yariv. Observation of modulation speed enhancement, frequency modulation suppression, and phase noise reduction by detuned loading in a coupled-cavity semiconductor laser. Appl Phys Lett, 46, 1025(1985).
[46] M Chaciński, R Schatz. Impact of losses in the Bragg section on the dynamics of detuned loaded DBR lasers. IEEE J Quantum Electron, 46, 1360(2010).
[47] L Zhang, J van Kerrebrouck, R Lin et al. Nonlinearity tolerant high-speed DMT transmission with 1.5-
[48] L Zhang, J J Chen, E Agrell et al. Enabling technologies for optical data center networks: Spatial division multiplexing. J Lightwave Technol, 38, 18(2020).
[49]
[50]
[51] S Kanazawa, H Yamazaki, Y Nakanishi et al. 214-gb/s 4-PAM operation of flip-chip interconnection EADFB laser module. J Lightwave Technol, 35, 418(2017).
[52]
[53] H Yamazaki, M Nagatani, F Hamaoka et al. Discrete multitone transmission at net data rate of 250 Gb/s using digital-preprocessed analog-multiplexed DAC with halved clock frequency and suppressed image. J Lightwave Technol, 35, 1300(2017).
[54] H Mardoyan, M A Mestre, J M Estarán et al. 84-, 100-, and 107-GBd PAM-4 intensity-modulation direct-detection transceiver for datacenter interconnects. J Lightwave Technol, 35, 1253(2017).
[55]
[56]
[57] S Lange, S Wolf, J Lutz et al. 100 GBd intensity modulation and direct detection with an InP-based monolithic DFB laser Mach–Zehnder modulator. J Lightwave Technol, 36, 97(2018).
[58]
[59]
[60]
[61] L Zhang, X Z Hong, X D Pang et al. Nonlinearity-aware 200 Gbit/s DMT transmission for C-band short-reach optical interconnects with a single packaged electro-absorption modulated laser. Opt Lett, 43, 182(2018).
[62]
[63] J M Estaran, H Mardoyan, F Jorge et al. 140/180/204-Gbaud OOK transceiver for inter-and intra-data center connectivity. J Lightwave Technol, 37, 178(2019).
[64]
[65]
[66]
[67] C Prodaniuc, N Stojanovic, C S Xie et al. 3-Dimensional PAM-8 modulation for 200 Gbps/lambda optical systems. Opt Commun, 435, 1(2019).
[68]
[69]
[70]
[71]
[72] M Chaciński, U Westergren, B Stoltz et al. Monolithically integrated 100 GHz DFB-TWEAM. J Lightwave Technol, 27, 3410(2009).
[73]
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