This PDF file contains the front matter associated with SPIE Proceedings Volume 12894, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Co-packaging of optics and electronics is essential to alleviating scaling bottlenecks in short-reach high-bandwidth applications such as datacenter links and interconnections. One transmit-side solution includes a shared WDM or gray optics laser source and dense arrays of high-speed, low power consumption modulators. With this in mind, we have demonstrated high-speed NRZ and PAM-4 direct detection links based on surface normal electro-absorption modulators (SNEAMs). SNEAMs are particularly attractive for co-packaged optics and other short-reach applications due to their low power consumption, high-speed, polarization independence, wide operating wavelength band, and small footprint. Here we describe short-reach transmission studies of SNEAMs at baud rates up to 80 Gbaud (160 Gbps PAM-4) and over optical bands spanning up to 32 nm. We show the potential for dense modulator arrays with a proof-of-concept experiment that integrates a 4-channel array of SNEAMs with a 4-channel array of electronic drivers. We also report a demonstration of SNEAMs as remote modulators in a centrally-sourced WDM passive optical network.

Distance-adaptive modulation is effective at enhancing network capacity as it allows the maximum possible modulation order to be selected for each optical path. However, present single-carrier systems can only select just one modulation order for each optical path and hence the adaptability to transmission characteristics is strictly limited. In contrast, digital subcarrier multiplexing systems can select a combination of modulation orders for multiple subcarriers on each optical path and can flexibly adapt to various transmission characteristics. This paper numerically evaluates the transmission characteristics of digital subcarrier multiplexing systems. The interaction between laser phase noise and chromatic dispersion is well examined by extensive simulations, and two-phase estimation methods are compared. The results show that digital subcarrier multiplexing systems with the appropriate phase estimation method enable longer transmission distances.

We report a 2-CH EML array and its assembling technique for the next-generation IM-DD system. In this paper, we fabricate an arrayed EML consisting of BH DFB-LDs and high-mesa EA modulators in a single chip. We obtained a 3-dB bandwidth above 67 GHz (bandwidth is higher but could not be measured due to equipment limit), low inter-channel crosstalk below -20 dB, and an excellent eye quality at 112 GBaud PAM4/PAM6/PAM8.

The data center interconnect is moving toward 1.6 Tbit/s, which is posing challenges for reaching a solution that is cost effective and technically feasible. Intensity modulation and direct detection (IM/DD) transmission over O-Band using standard single-mode fiber is a potential low-cost solution. However, limitations imposed by chromatic dispersion and four-wave-mixing (FWM) needs to be understood, such as in the case when operating at 8 x 100 GBaud PAM4 in LWDM configuration. In this paper, a statistical approach has been adopted to evaluate the probability of outage by considering practical link parameter fluctuations such as wavelength variation and drift, polarization variation and the natural variation of the fibers zero dispersion wavelength. Numerical modeling shows that IM/DD can be used up to distances of 5 km if transmission power is maintained under 0 dBm. Coherent transmission can extend the distance beyond 5 km due to its signal processing capabilities. However, it is desirable to reduce its complexity for cost effective and power efficient data center applications. Using dual wavelength transmission and DP-16 QAM transceivers, which share similar components to the IM/DD counterpart, the feasibility of simplifying this architecture is studied. The analysis shows that the complexity of the coherent approach can be reduced without significant penalties for distances up to 10 km.

Due to the rapid increase in the amount of information required in the ICT market, major standardization bodies are currently actively discussing the 800G/1.6T specifications. On the client side, IEEE802.3 has started discussions on 800G/1.6T in 2021, and on the line side, OIF has started discussions on 800G, also in 2021. However, no further discussions on 3.2T have been made so far, and it is estimated that the discussions will start in 2025 or later. This paper discusses the scheme and configuration of 3.2T optical transceivers, based on the status of standardization discussions up to now, and provides an overview of t the perspectives.

Achieving the highest transmission speeds requires both a well designed device and a strategy on how to exploit the device in the system. Modern communications relies on ever more complex control and signal processing tools that can help us meet the potential of silicon photonics devices. We will provide two examples of the design strategies to expand the bandwidth of silicon modulators (traveling wave and microring). Our systems strategies have allowed us to set records for transmission rates and for shoreline density. Our examples come from coherent detection. Our use of low cost silicon photonics solutions will help push adoption of coherent detection to metro and short reach links, including data centers.

To improve the performance of Si photonics-based wavelength locker, a new configuration for a compact wavelength locker with two grating couplers (GC) and a Mach-Zehnder interferometer (MZI) filter used in light source modules was proposed. Simulation results showed that the proposed two GC structure provides 1.4 times higher peak coupling power with over 10 μm mounting tolerance and the monitored values for the MZI filter system was enhanced over three times. This shows that there is feasibility on developing this topology for a compact wavelength locker in the short reach coherent communication.

Submarine cable systems have been playing a big role to cover the international traffic growth. The capacity of submarine cable systems needs to meet the traffic demands under the limitations of power feeding capability and space in cable and repeater housing. The space division multiplexing (SDM) technology has been paid attention as one of the candidates to increase the transmission capacity under these limitations. In this paper, we provide the latest SDM technologies that are deployed to submarine cable systems.

Space division multiplexing architecture based on multi-core fiber (MCF) is a promising solution for rapid traffic growth beyond 5G. We proposed and demonstrated a compact, high-performance, and economical 1×8 core selective switch with a 19-core MCF. A tilt-mirror-type 2D-MEMS array was deployed owing to its low optical loss, broad bandwidth, and scalability. The measured insertion loss of the fabricated device was from 0.8 to 4.0 dB. We also demonstrated a core selector and tap monitor for building a high-performance MCF-based ROADM configuration.

We present a frequency-domain method for measuring various types of optical fibers primarily using a vector network analyzer (VNA). Through proper E-O conversion to launch frequency sweeping signals into the fiber and O-E conversion at the receiving side, the VNA measures the complex transfer function (CTF) of the fiber transmission for a given launch condition. The group delay information can be calculated from the inverse Fourier transform of the CTF. Due to the long fiber length relative to the number of points used by VNA for frequency sampling, the measured CTF is under-sampled and aliased. With proper de-aliasing procedures, the aliased CTF can be transformed into a modified CTF in the local time frame. The output pulses can then be recovered with the full group delay information obtained. The group delay and dispersion of different modes or different cores can be obtained from the CTF over a range of wavelengths. For single mode fibers, we can obtain the group delay and chromatic dispersion from the wavelength dependence. For fibers with multiple modes, cores or polarization maintaining fibers with two distinct polarization modes, the group delay of each mode or core can be obtained simultaneously. For multimode fibers, we have developed a thorough procedure to conduct differential mode delay measurements and calculate modal bandwidth, equivalent to the time domain method defined by the standard. Overall, the VNA based frequency domain method can measure various types of optical fibers from short lengths of a few hundred meters to long lengths of many kilometers at different wavelengths. The technique is unique among fiber measurement techniques in that it can determine the group delay, dispersion, modal and bandwidth properties across different fiber types, not limited to just single mode fibers.

This paper investigates the detailed impact of all three graded-index-fiber (GIF) parameters on the balance between DMD and crosstalk. We report an optimized 4-LP-mode GIF offering LP₀₁, LP₁₁, LP₂₁, and LP₀₂, with a minimum |Δn_eff| = 0.6 × 10⁻³, maximum |DMD| = 5.4 ns/km, while minimum |A_eff| = 80 μm2 and bending loss (BL) of the highest order mode is 0.005 dB/turn (much lower than 10 dB/turn) at a 10 mm bend radius, for core-radius a = 7 to 9 μm, Δn = 0.014 to 0.016, and α = 2 to 4. In this study, we successfully addressed the challenge of degeneracy between LP₂₁ and LP₀₂ in FM-GIF, which has been difficult to overcome. To the best of the authors’ knowledge, this is the lowest reported DMD value (≈ 5.4 ns/km) achieved in such a weakly-coupled (|Δn_eff| = 0.6 × 10⁻³) 4-LP-GI-FMF.

We review our correlation based technique for fiber longitudinal power profile estimation which is a key for photonics tomography. Then, we discuss several applications based on this technique, anomaly loss monitoring, polarization dependent loss (PDL) monitoring, fiber-type identification, and nonlinear SNR estimation for optimizing quality of transmission. We show that these applications can detect the position of 3dB anomaly loss or PDL, and differences between deployed and designed fiber types in a multi-span transmission testbed. In addition, we discuss implementation of this technique in hardware and in software.

The requirement for increased data transmission rates in data centres (DC) and short-reach systems like passive optical networks (PON) continues relentlessly. Intensity modulation-direct detection (IM/DD) systems are preferred owing to their simple implementation compared to coherent optical systems. Due to increased DC clusters and network centralization, employing semiconductor optical amplifiers (SOA) in short-reach links is prudent owing to their ability for photonic integration, simultaneous multichannel amplification, and offering a small footprint. In this paper, we present the potential application of the SOA in future Terabit/s DC and optical access networks with SOA placed at distinct locations in an optical link and as a device enabling transmission of higher cardinality modulation.

Innovative multi band (MB) sliceable bandwidth/bitrate variable transceivers (S-BVTs) are proposed for future adoption in next-generation optical networks towards targeting the expected capacity scaling driven by the increasing traffic demand and emergence of new 6G services and applications with stringent requirements. To provide enhanced bandwidth/capacity and energy efficiency to support the envisioned growing demand, the use of MB technology is proposed and experimentally assessed up to 75 km of standard single mode fiber (SSMF) considering programmable MB S-BVTs. We demonstrate an aggregated capacity of 132.2 Gb/s exploiting S+C-bands and scalability towards enabling multi-Tb/s transmission within the metro/aggregation network segment. The sliceability of the MB S-BVT is demonstrated considering joint MB transmission (S+C) up to 2-hops network path of 75 km and an additional span of 50 km of SSMF for the C-band contribution. Different configurations based on single side band (SSB) and double side band (DSB) modulation and amplification technologies have been evaluated according to the particular scenario and band of operation. Finally, the programmability of the presented MB transceiver is also assessed as a key capability to promote network automation and flexibility. On this regard, a software-defined networking (SDN) agent based on open data model, such as OpenConfig, is implemented and validated to suitably reconfigure the transceiver according to the network requirements/demand. Key operational transceiver mode capabilities and configuration constraints, for the agent’s implementation, are identified towards supporting MB transmission within future optical networks.

We experimentally demonstrate the use of a feed-forward photonic neural network (PNN) for chromatic dispersion compensation in fiber transmission within IM-DD protocols. The PNN device is constituted by an 8-channel all-optical delayed complex perceptron integrated on a Silicon-On-Insulator platform. The PNN device is inserted after the transmitter and before the fiber, thus acting as a pre-compensator. The training is performed via a Particle Swarm Optimizer and aims to provide an open eye diagram at the end-of-line receiver. We observe a 5-order of magnitude Bit Error Rate reduction for -7 dBm of power at the receiver between bare and equalized transmission for 10 Gbps Non-Return-to-Zero signals in a 125 km fiber link (average excess loss of 15 dB). We also perform a study on the minimum number of channels in the PNN needed for full equalization. Overall, the experimental results validate our solution for channel equalization via a PNN with negligible latency and a power consumption of 250 mW on average.

Over the past few decades, the space industry has seen a profound transformation, leading to a redefinition of the business models of companies in the space sector. Among the various emerging technologies, photonics represents one of the largest fields of expansion, transforming sectors such as telecommunications, defense, navigation, remote sensing, and Earth and space observation. At the forefront of this technological transformation is integrated microwave photonics (MWP), a state-of-the-art solution that offers wide input bandwidth, management of high-frequency operations, and efficient distribution of radio frequency (RF) signals through Radio-over-Fiber (RoF) systems. These advantages, combined with inherent protection against electromagnetic interference (EMI) and low size weight and power consumption (SWaP), are a critical advantage in improving the performance of synthetic aperture radar (SAR) systems. This paper provides a brief introduction to microwave photonics for space applications, highlighting, through ongoing projects at our research laboratory, how it is gaining traction in the global market.

Perovskite is an emerging low-cost and high-quality material, that show significant potential to revolutionize photovoltaic and lighting sectors in Organic and Large Area Electronics (OLAE) devices. Their simple and inexpensive processing methods, such as solution-based synthesis and printing, make them attractive for flexible and lightweight electronic devices. In this work, perovskite suitability has been tested for telecommunication applications, particularly Li-Fi links. The perovskite devices were integrated into a telecom system, including an FPGA handling signal processing, LED array, analog transmitter circuitry, and driving electronics for the perovskite photodiode. 4-PPM modulation format has been adopted due to resilience in low SNR. The purpose is to thoroughly characterize the setup to assess the suitability of perovskite devices for Li-Fi scenarios or combined PV and Li-Fi usage. This research aims to advance the application of perovskites in telecommunication and expand their potential in various electronic devices.

We experimentally demonstrate a two user non-orthogonal multiple access (NOMA) based indoor optical wireless communication link with gigabit-per-second data throughput. MATLAB based simulations are carried out to characterize the indoor power profile and bit-error rate (BER) performance. The experimental implementation consists of directly modulating a near infrared laser to transmit the superposition coded (SC) NOMA symbols with signals received using two separate receivers, which denote the two spatially separated users. The received signals captured using an oscilloscope are decoded using successive interference cancelation (SIC) technique implemented offline in MATLAB. The experimentally measured channel responses are used in simulations to compare the experimental and simulation results, showing good agreement between the two. Optical communication is demonstrated with overall data throughput of 1.02 Gbps with high fidelity interference cancellation. The data-rates achieved here are the highest reported for conventional NOMA implementation in optical wireless systems.

Physical Layer Security (PLS) exploits characteristics and properties of the physical layer for data encryption and supplements conventional cryptography for enhanced overall security. Most of the PLS methodologies rely on the (statistical) characteristics of the transmission channel to either generate secure encryption keys, or to exploit them together with other physical layer characteristics (i.e. advanced modulation schemes) for secure transmission. However, these approaches often lead to increased complexity and therefore become impractical for actual system implementation. Recent advancements in Quantum Key Distribution (QKD) systems allow for the utilization of ultra-secure and robust high-rate key exchange. In this work, we propose and describe practical techniques for exploiting and seamlessly integrating highrate QKD keys to encrypt modulation parameters and quantities of conventional modulation schemes like M-QAM, DMT and OFDM of communication links. Moreover, we present transmission scenarios, integrating QKD-PLS in free space optics links, together with their numerical evaluation. The main advantage of QKD exploitation to the proposed solutions comes from the seamless and transparent integration and application of high-rate keys which can either be used in their original form or feed a pseudo-random number generator, to modify the modulation properties/symbols in very high rates, such that eavesdropping and decoding of the encrypted information becomes almost impossible. Additionally, we present the architecture of a real time practical system utilizing and seamlessly integrating the QKD keys into transceiver links to form a robust and ultra-secure PLS ecosystem.

To face the challenges of open and disaggregated 6G networks and the prospect/threat of quantum computing, we propose to adopt continuous-variable QKD (CV-QKD), as a promising technology compatible and suitable to be integrated with conventional optical systems, in combination with software defined networking (SDN). In this work, we present our most recent advances on SDN-enabled flexible CV-QKD for future secure communications. We describe the proposed network architecture, identifying the relevant parameters and interfaces. We consider and analyze a Gaussian-modulated coherent state CV-QKD system, reporting recent experimental results at the varying of the QKD system wavelength, as relevant adaptable parameter, that can be configured by the SDN controller, for distributing highly secure keys in metropolitan networks. The capabilities and potentialities of our proposed approach for future secure communications in open and disaggregated 6G networks are also discussed.

The rising of applications with intense requirements in data volumes, storage space and CPU/GPU utilization, such as Machine Learning/Artificial Intelligence (ML/AI) applications, imposes different challenges on the Data Center Network design and operation. When compared to traditional data centers infrastructures, the recent explored disaggregated optical data center concept may bring multiple benefits in terms of optimized usage of the IT and network resources. Nevertheless, at the same time, it also brings some technical challenges. In such context, the paper discusses both data and control architectural solutions for optical disaggregated data centers for ML/AI applications, focusing on their benefits but also on the associated complexities.

High performance optical and electronics systems require efficient thermal management for safe and reliable operation. At commercial scale, conduction plates are employed as heat spreaders for removing heat from these systems. However, for high heat flux systems, higher performance heat spreaders must be used for operational reliability. In this manuscript, a two-phase heat spreader called the Pulsating Heat Pipe (PHP) heat spreader was developed as a superior alternative to conduction plates. The PHP was fabricated by additive manufacturing with aluminum. Propylene was investigated as the working PHP fluid with a fluid fill charge ratio of 75% by volume. Performance testing with a centralized heat source with edge heat rejection showed up to three times reduction in thermal resistance in comparison to baseline empty PHP. Peak thermal performance was achieved when the condenser section of the PHP was maintained at 0 °C and -10 °C. The PHP could transfer a heat flux more than 37 W/cm² without dry-out at these temperatures. Furthermore, a numerical model for performance prediction of the PHP based on semi-empirical heat transfer correlations was developed and validated against experimental data.