This PDF file contains the front matter associated with SPIE Proceedings Volume 11712, including the Title Page, Copyright Information, and Table of Contents.

The substantial increase in communication throughput driven by the ever-growing machine-to-machine communication within a data center and between data centers is straining the short-reach communication links. To satisfy such demand - while still complying with the strict requirements in terms of energy consumption and latency - several directions are being investigated with a strong focus on equalization techniques for intensity- modulation/direct-detection (IM/DD) transmission. In particular, the key challenge equalizers need to address is the inter-symbol interference introduced by the fiber dispersion when making use of the low-loss transmission window at 1550 nm. Standard digital equalizers such as feed-forward equalizers (FFEs) and decision-feedback equalizers (DFEs) can provide only limited compensation. Therefore more complex approaches either relying on maximum likelihood sequence estimation (MLSE) or using machine-learning tools, such as neural network (NN) based equalizers, are being investigated. Among the different NN architectures, the most promising approaches are based on NNs with memory such as time-delay feedforward NN (TD-FNN), recurrent NN (RNN), and reservoir computing (RC). In this work, we review our recent numerical results on comparing TD-FNN and RC equalizers, and benchmark their performance for 32-GBd on-off keying (OOK) transmission. A special focus will be dedicated to analyzing the memory properties of the reservoir and its impact on the full system performance. Experimental validation of the numerical findings is also provided together with reviewing our recent proposal for a new receiver architecture relying on hybrid optoelectronic processing. By spectrally slicing the received signal, independently detecting the slices and jointly processing them with an NN-based equalizer (wither TD-FNN or RC), significant extension reach is shown both numerically and experimentally.

We present a silicon-based Chaotic-Cavity Optical Physically Unclonable Function(CCO-PUF) embedded inside smart-sensor based devices utilizing nonlinear-optical properties of bi-axial crystals present inside a chaotic cavity. The photonic circuit produces statistically diverse yet reproducible multimodal photonic outputs that provides a large statistical degree of freedom for generating randomness in the device responses upon electrical as well as photonic triggering that can be employed for producing authentication keys for users seeking on-demand access to IoT devices . Such PUFs can be very robust against side-channel attacks and machine-learning attacks for their wide operability range, complex nano-photonic operation and strong degree of pseudo-randomness.

We describe recent progress in quantum secured optical networks in the UK. The Cambridge Quantum Network has been operating for several years with 3 nodes separated by between 5-10 km of installed fibre. All links are secured by QKD systems operating with secure key rates in excess of 1 Mb/s, the highest recorded long term key rates in a deployed network. The network operates in the presence of 100Gb/s classical traffic with no significant reduction of secure key generation rate. In addition, the Bristol Quantum Network has four nodes 1-3km apart connected in a mesh protected by two pairs of QKD systems. The network is designed to be very dynamic, switching both QKD and WDM classical traffic to enable rapid reconfiguration and is used as a testbed for QKD protected dynamic applications. The two metropolitan networks are being connected by a 410 km QKD link, with 4 spans, the longest of which operates over 129km of fibre with an attenuation of 28dB achieving secure key rates of 2.7kb/s, the longest and highest loss QKD field trial to date. A 120km extension of the UK quantum network from Cambridge to BT Labs, Adastral Park operates with fully commercially available components and is an important testbed comprising 3 intermediate nodes and operates with 5 x 100Gb/s classical channels. This helps determine how to proceed with a large-scale commercial deployment of QKD.

The high capacity demand, to support broadband services and everything-to-internet connectivity is pushing the limits of both access and metro networks, requiring the adoption of novel strategies for the optical transceiver modules. This represents an opportunity for the adoption in these network scenarios of novel photonic technologies based on single-mode vertical cavity surface emitting lasers (VCSELs) at long wavelengths. On one hand, the access network evolution requires a line rate increase beyond 10 Gb/s, targeting 50 Gb/s propagation in passive optical networks (PONs) over a few tens of kms in standard single mode fiber (SSMF) with simple, cost effective and energy efficient transceivers. On the other hand, the future metropolitan area network (MAN) will need to handle multi-Tb/s traffic in a very dynamic scenario, over variable distances up to hundreds of kms while promoting sustainability, reducing the CapEx and OpEx costs and power consumption. Both needs can be fulfilled by adopting VCSEL direct modulation with multicarrier modulation formats such as discrete multitone (DMT), in combination with distinct transmitter architectures and receiver solutions to support different aggregate capacity requirements and transmission reaches. In any case DMT with bit/power loading enables flexible rate and adaptive distance for metro network applications and link adaptation and PON resource usage optimization for future access networks. In this work, we report our recent results on the adoption of VCSEL technology in both scenarios, with special focus on the receiver and transmitter adopted architectures.

The amount of information required in the ICT market is increasing at a faster rate than expected, and the practical application of ultrahigh-speed optical transceivers and optical components with transmission speeds up to 400 Gb/s or higher is rapidly progressing. These optical transceivers and optical components need to be developed with higher transmission speed, smaller size and lower power consumption, necessitating the adoption of optical integrated technologies and fine CMOS processes. Under these circumstances, international standardization bodies such as IEEE 802.3/OIF/IEC and other MSA groups are actively creating standards, and this paper reports mainly on these latest topics.

Metro area network (MAN) connectivity is rapidly evolving towards a much more dense, complex and diverse scenario to be dynamically addressed with flexible cost-efficient and high-capacity technology and architecture solutions, dealing with an even more open and disaggregated paradigm. In this work, sliceable bandwidth/bitrate variable transceiver (S-BVT) architectures adopting modular approach and suitable photonic technologies (such as VCSEL), enabling to efficiently and dynamically exploit both spectral and spatial dimensions, are discussed, considering design, implementation, cost and flexibility aspects. Recent numerical and experimental results are reported, showing how to enable scalability towards supporting multi-Tb/s connectivity in flexible and dynamic large MAN.

Hyperscale datacenters are driving the growth of datacom laser diode market. Small wavelength drift over temperature, small footprint and low power consumption makes directly modulated distributed feedback (DFB) lasers ideal for uncooled operation in intra-datacenter interconnects. DFB lasers require significantly less process steps than electroabsorption modulated lasers (EMLs), used typically for higher speeds and longer distances. AlGaInAs-based lasers are exceptionally desirable for uncooled operation compared to InGaAsP because of the material’s better electron confinement, resulting in better power conversion in high temperature operation, higher possible operation frequency and more stable operation in AlGaInAs based lasers. Directly modulated DFB lasers must be operated with relatively high bias current to achieve the desired bandwidth. This together with the absence of active cooling raises a reliability concern. Modulight has already demonstrated a very stable 10 Gb/s device operating in O-band with predicted median lifetime of 180 years at 85°C². Using similar epitaxial design, 25 Gb/s operation is already possible. DFBs can be further optimized by limiting the device resistance and capacitance by optimizing the doping profile as well as the contact pad. Miniaturization of the laser chip is limited by the dicing process, but the effective device size can be reduced by limiting the active area in the chip.

Digital coherent reception is an attractive candidate for increasing the channel capacity without expanding the bandwidth needed. The receiver DSP circuit must be able to compensate for the IQ-phase/power mismatch with low computation power requirements. In this paper, we propose a novel DSP circuit suitable for short-reach transmission systems including intra-datacenter networks. The proposed DSP circuit offers polarization-mode demultiplexing, compensation for IQ-phase/power mismatch, and estimation of carrier phase and frequency offset. The proposed DSP circuit consists of three-stage one-tap FIR filters; therefore, complicated calculations are not required. Its good demodulation performance is confirmed by simulations.

We present a scalable and novel modular optical metro core node architecture employing photonic WDM integrated switches. Multi-degree switching ROADM nodes are used at the metro-core level, while access network is constituted by low-cost ROADM nodes. Photonic integrated switches have been designed as the building blocks to realize this modular metro node architectures, namely photonic WDM space switches with express and add/drop ports, photonic integrated WSS aggregation/disaggregation functions for merging/dropping the network traffic, and photonic integrated multi-cast switch (MCS), to achieve, together with bandwidth variable transceivers aggregators, multi-Terabits/second operation per link. In particular, photonic WDM space switches and photonic integrated WSS are designed as building blocks to realize this novel modular metro node architectures. Moreover, dynamic re-configurable metro-access nodes based on low-cost photonic integrated mini-ROADMs will be presented. The lossless photonic WDM switches are based on InP technology and employ semiconductor optical amplifiers as on-chip gain element and for fast switching. The photonic WDM circuits allow to switch multiple format data signals in wavelength, space and time for full flexibility, scalability of the interconnected network elements, as well as capacity. Applications will be discussed and experimental results will be reported. Finally advances in compact photonic integrated InP switch design using the InP generic technology will be discussed.

In high performance computer systems and large-scale data centers, data movement becomes a critical problem. To overcome this problem, co-packaged optics are attracted much attention for high performance LSIs like upcoming highcapacity switch ASICs. We proposed a new package substrate called active optical package (AOP) substrate. The AOP substrate is an organic package substrate where Si photonics dies are embedded. On the surface of the substrate, fan-out polymer waveguides, connecting high density Si-photonics I/O and low density single-mode fiber (SMF) array, are integrated. the AOP substrate will be used as same as conventional standard package substrates. Only a different point is to connect a pluggable optical fiber. Interlayer optical coupling between the Si and polymer waveguides was achieved with two micro mirrors. For example, light output from the Si waveguide end facet was reflected to upper side by the 1st micro mirror. The light was reflected again to the polymer waveguide end facet by the 2nd mirror fabricated above the 1st mirror. Compared to popular grating couplers, the mirror is suitable for low wavelength and polarization dependent optical coupling. Error free transmission of 28-GBaud NRZ optical signal through the Si waveguide, mirror coupling, and polymer waveguide was achieved without significant penalties. The optical coupling of the polymer waveguides to SMFs was also achieved by passive alignment using a low-cost MT-ferrule-compatible optical connector. The loss penalty of the passive alignment was about 3 dB.

The state of the art of fiber-optic communication technologies has advanced dramatically over the past 25 years. The highest capacity of commercial fiber-optic links available in the 1990s was only 2.5-10 Gb/s while today they can carry up to 800 Gb/s. The last decade of developments have enabled higher efficiency digital communication systems and solved problems with degraded signals. Optical transceivers are widely used in server network cards, switches, routers and wireless base station equipment in a variety of network architectures and applications. The new form factors are increasingly universal and designed to reduce their size and thus power consumption. Inside modules the optics and integrated circuits are getting closer together. Therefore, silicon photonics might represent a key enabling technology for further development of optical interconnect solutions needed to address growing traffic. This technology will play an important role in 500 m – 80 km distance applications. Industry is working on heterogeneous integration of InP lasers directly onto silicon chips. The advantage is scalable integration and elimination of the cost and complexity of the optical package for 400G and beyond. Revenue generated by optical transceivers is expected to more than double to around by 2025 at a compound annual growth rate for 2020-2025 of 15%.

Modern IoT and 5G applications are driving the growth of Internet traffic and impose stringent requirements to datacenter operators for keeping pace with the increasing bandwidth and low-latency demands. At the same time, datacenters suffer from increasing number of interconnections dictating the deployment of novel architectures and high-radix switches. The ratification of 400 GbE standard is driving the market of optical transceivers nevertheless, a technology upgrade will be soon necessary to meet the tremendous traffic growth. In this paper, we present the development of 800 Gb/s and 1Tb/s optical transceivers migrating to 100 Gbaud per lane and employing wafer-scale bonding of InP membranes and InP-DHBT electronics as well as advanced co-packaging schemes. The InP membrane platform is also exploited for the development of novel ultra-fast optical space switches based on a modular architecture design for scaling to large number of I/O ports.

This invited talk will introduce several useful means to boost federated learning carried out over passive optical networks for edge computing. One way is to introduce bandwidth slicing that is able to reserve network resource dedicated to the learning task and can well address the issues brought by stragglers during the training process. Another way is to devise aggregation function carried out at intermedium network nodes capable of significantly reducing the amount of traffic to be exchanged for global training while not impacting the learning performance. Simulation results show that the FL training efficiency can be significantly improved while achieving the same level of learning accuracy. For the specific FL task implemented in the context of edge computing, the training time can be saved up to 36 % to achieve the maximum learning accuracy.

Future 5G and beyond services rely on the network slicing concept, in which underlying network elements are split and/or aggregated to compose a synthetic network infrastructure (the slice) to satisfy the requirements of services that will be executed on top. Generally speaking, end-to-end network slices comprise multiple network segments, including optical and data centers networks. Therefore, the provisioning of end-to-end network slices is a challenging task that has to consider the characteristics of the different technologies to satisfactorily map the requirements coming/imposed from the services to be deployed. This requires that offers towards the fulfillment of the services to be supported are properly parametrized, enabling the possibility to translate them into specific slice and network services characteristics to be finally materialized in concrete infrastructure resources. On the other hand, there is a rising trend of quality assurance at all levels to satisfy the requirements of services deployed, requiring the runtime maintenance of quality of service/experience of the deployed slices. Due to the dynamic nature of services, it becomes essential to monitor the associated Key Performance Indicators (KPIs), derive from them current quality levels and implement the necessary mechanisms to steer the behavior of the slices towards the maintenance of optimal quality levels. Given such scenarios, in this paper we present a framework that enables the provisioning and orchestration of network slices in multi-domain/segment optical networks as well as an approach to proactively manage the maintenance of the required slices quality. The presented framework is validated through several experimental results.

In this paper, we review recent work on the development of a novel low-complexity equalizer that can enable single-lane <100 Gb/s short-reach optical links based on carrierless amplitude and phase modulation. This equalizer, named the CAP equalizer, can mitigate the transmission impairments in the link due to a non-ideal channel frequency response, providing significant performance advantage over conventional FFE and DFE equalizers and enabling higher data rates and longer reach. Its use is demonstrated in a VCSEL-based MMF link achieving data transmission of 112 and 124 Gb/s over 100 m OM4 MMF.

Free-space optical communication is a line-of-sight wireless communication scheme, which is preferred for its number of prime advantages over radio frequency wireless communication, such as no spectrum licensing, large bandwidth, inherent security, electromagnetic compatibility/electromagnetic interference immunity etc. Moreover, free-space optical communication also benefits from low-cost installation and maintenance. It has been studied for the next generation access networks, inter-building connections, ground-to-unmanned aerial vehicle links, underwater communication applications, inter-satellite links, deep space links etc. Among various detection approaches utilized in free-space optical communication, coherent detection can achieve the best sensitivity in a bandwidth-limited condition, effectively demodulate optical multilevel coded signals to attain high spectral efficiency, offer excellent background noise rejection. However, such an attractive free-space optical communication suffer from waveform distortion, scintillation, phase fluctuations etc. after transmission in atmospheric channels. Its link losses are almost dependent on atmospheric effects and climatic conditions. In this article, we present an up-to-date survey on coherent free-space optical communication, the atmospheric turbulent effects especially the impacts of turbulence in free-space optical links, and countermeasures against such impairments.

In this paper, we simulated the ADC/DAC resolution tolerance improvement by implementing probabilistic shaping (PS) distributions in PAM and QAM modulation schemes for 400G and 800G transmissions. We compared PS- and uniformdistributed PM-16QAM, PM-32QAM, and PM-64QAM performance in 800G coherent transmission in FR links. The PS distribution scheme is based on Maxwell-Boltzmann distribution, and 0.1378 FEC overhead is chosen. We demonstrate that for any of these modulation schemes the post-BER (post-FEC bit-error rate) performance is more sensitive to ADC resolution. Moreover, the application of PS distribution can offer us 0.5-dB improvement in received optical power (ROP) for LDPC-coded PM-16QAM and 0.7-dB improvement for PM-32QAM, while PM-64QAM can get 0.6-dB improvement in ROP. For PAM transmission, we simulated a 4-channel CWDM 400G transmission system with wavelengths 1271 nm, 1291 nm, 1311 nm, and 1331 nm for 4-PAM modulation scheme. The PS distribution scheme we used in PAM is exponential distribution, and the FEC overhead is also 0.1378. We demonstrated that the pre-SER (pre-FEC symbol-error rate) performance is also more sensitive to the ADC resolution compared to DAC resolution. Therefore, the PS LPDCcoded modulation represents a great candidate to improve the system performance and reduce the cost.