Dan M. Marom

True time delay (TTD) beamforming is critical for wideband phased-array antennas to prevent beam squint and waveform distortion. We present a free-space optical true time delay (OTTD) spectral processor enabling independent, continuously tunable, large-stroke delay control across multiple wavelength channels. A double-pass, self-imaging configuration with a diffraction grating and micro-electro-mechanical system (MEMS) tilting micro-mirrors introduces adjustable optical paths via angular beam steering, providing continuous group delay tuning without additional propagation loss or distortion. The system supports 40 C-band channels spaced at 100 GHz, each independently tuned over a ±0.55 ns range (1.1 ns total) with insertion loss varying between 6 and 8 dB. Optical and electrical characterizations confirm accurate group-delay control, a flat radio frequency (RF) response up to 40 GHz, and a fine delay resolution of ∼0.1 ps. Signal integrity was verified via intensity-modulation direct-detection transmission, achieving error-free performance [bit error rate (BER) <10−9] at 32 Gb/s across the full delay range. Using a time-of-flight technique that, to our knowledge, resolves for the first time the OTTD dynamic transition in the time domain, the measurement identified smooth, millisecond-scale MEMS response times. Combining wide channel bandwidth, large stroke, and fast, low-loss continuous tuning, this scalable OTTD processor is highly promising for broadband microwave photonic beamforming and multibeam next-generation wireless and radar systems.

We investigate energy-efficient, traffic-adaptive resource provisioning for 6G x-haul networks by integrating a reconfigurable low-loss switching sub-system (referred to as an interlacer) into the TEFNET24 reference network topology from Telefónica. The interlacer combined with the digital subcarrier multiplexing (DSCM) transceivers forms a WDM-PON approach, enabling subcarrier-level switching at the network access, providing lower distribution loss than conventional power splitter (PS)-based TDMA-PON approaches. Moreover, under the practically low crosstalk levels reported for our interlacer implementations, the reduced distribution loss can be traded for increased modulation cardinality (e.g., 16QAM to 64QAM), allowing for reducing the number of allocated transceivers. We further examine a machine learning (ML)-driven framework for dynamic capacity provisioning and validate it using a real-world operator trace mapped onto the national-scale TEFNET24 topology, capturing 4G/5G load patterns with projections toward 6G. We compare static, semi-static, and fully dynamic strategies and show that ML-aided dynamic provisioning reduces transceiver overallocation by up to 63.7% relative to static methods, with the strongest gains during off-peak hours when traffic variability is highest. Finally, we quantify two complementary energy-saving mechanisms enabled by dynamic operation—subcarrier deactivation and transceiver sleep mode—with the latter yielding up to 21% total network energy savings while maintaining quality of service under time-varying demand.

As bandwidth demands continue to rise, wavelength-level granularity in wavelength division multiplexing (WDM)-based optical networks becomes a limiting factor, as scaling such networks places increasing load on the WDM nodes. This motivates a shift toward coarser switching granularities. Node architectures will thus evolve from wavelength switching to waveband-selective switching and eventually to fiber cross-connects as capacity requirements grow. Multi-granular optical node (MG-ON) architectures support this transition by integrating wavelength, waveband, and spatial switching. However, during dynamic routing and resource assignment, MG-ON architectures may suffer from inefficient utilization of wavelength, waveband, and spatial resources. This can lead to increased connection request blocking. To address this, we propose a dynamic routing and resource assignment algorithm combined with an augmented optical grooming strategy for MG-ON networks. We evaluate the proposed approach in terms of connection accommodation, switch count, and per-switch port requirements across multiple network configurations. Its performance is compared with baseline WDM networks and existing MG-ON grooming strategies.

Incoherent beam combining is widely used in high-power laser systems due to its simplicity, stability, and scalability, as it avoids frequency, phase, and polarization locking. However, efficiently coupling light from large multimode VCSEL arrays into multimode fibers with matched modal capacity, while preserving brightness, remains challenging. This work presents a 3D-printed microscale photonic lantern (PL) for efficient incoherent combining of multimode sources, enabling direct multiplexing of many few-mode VCSELs into MMFs with matched modal capacity. Unlike conventional PLs designed for single-mode inputs, the proposed PL supports few-mode sources. We demonstrate PLs multiplexing 7, 19, and 37 six-mode VCSELs, fabricated directly on the laser apertures, achieving coupling losses as low as −0.6 dB(19–MM PL) and −0.8 dB (37-MM PL) into a 50 μm, NA = 0.22 step-index MMF. Comprehensive experiments demonstrate efficient power delivery, preserved brightness, and relaxed alignment, highlighting 3D-printed PLs as compact and scalable solutions for high-power laser systems and optical communications.

The evolution of passive optical networks (PONs) is rapidly progressing, with the next generation aiming to surpass 100Gb/s/ λ and target 200Gb/s/ λ —a typical fourfold increase over the current 50Gb/s/ λ power splitter (PS)-based PON standard. This paper outlines current research and development challenges in PONs and explores potential advancements using programmable photonic Nyquist-shaped Interleaver (NS-INT) filters paired with coherent point-to-multipoint (P2MP) digital subcarrier multiplexing (DSCM) transceivers. Specifically, we evaluated, based on analytical estimations and simulations, two NS-INT implementations for mobile transport: one based on ring resonators-assisted filters and a second utilizing an optical 18-tap cascaded asymmetric Mach–Zehnder Interferometer (aMZI). We compare their effectiveness in optimizing filtering and minimizing crosstalk (XT) across various coupling coefficient scenarios. Furthermore, we assess the feasibility of these designs by examining their performance under XT and signal impairment caused by filter narrowing effects, particularly in the presence of signal-to-filter center frequency misalignment. Bit error rate (BER) evaluations demonstrate a tolerance to frequency misalignments of up to 3 GHz across all architectures. Among them, our cascaded aMZI design exhibits superior performance, attributed to its inherent optical finite impulse response (FIR) filter characteristics as a minimum-phase filter.

Emerging services such as artificial intelligence (AI), 5G, the Internet of Things (IoT), cloud data services and teleworking are growing exponentially, pushing bandwidth needs to the limit. Space Division Multiplexing (SDM) in the spatial domain, along with Ultra-Wide Band (UWB) transmission in the spectrum domain, represent two degrees of freedom that will play a crucial role in the evolution of backbone optical networks. SDM and UWB technologies necessitate the replacement of conventional Wavelength-Selective-Switch (WSS)-based architectures with innovative optical switching elements capable of handling both higher port counts and flexible switching across various granularities. In this work, we introduce a novel Photonic Integrated Circuit (PIC)-based switching element called flex-Waveband Selective Switch (WBSS), designed to provide flexible band switching across the UWB spectrum (~21 THz). The proposed flex-WBSS supports a hierarchical three-layered Multi-Granular Optical Node (MG-ON) architecture incorporating optical switching across various granularities ranging from entire fibers and flexibly defined bands down to individual wavelengths. To evaluate its performance, we develop a custom network simulator, enabling a thorough performance analysis on the critical performance metrics of the node. Simulations are conducted over an existing network topology evaluating three traffic-oriented switching policies: Full Fiber Switching (FFS), Waveband Switching (WBS) and Wavelength Switching (WS). Simulation results reveal high Optical-to-Signal Ratio (OSNR) and low Bit Error Rate (BER) values, particularly under the FFS policy. In contrast, the integration of the WBS policy bridges the gap between existing WSS- and future FFS-based architectures and manages to mitigate capacity bottlenecks, enabling rapid scalable network upgrades in existing infrastructures. Additionally, we propose a probabilistic framework to evaluate the node’s bandwidth utilization and scaling behavior, exploring trade-offs among scalability, component numbers and complexity. The proposed framework can be easily adapted for the design of future transport optical networks. Finally, we perform a SWaP-C (Size, Weight, Power and Cost) analysis. Results show that our novel MG-ON achieves strong performance, reaching a throughput exceeding 10 Pb/s with high OSNR values ≈14–20 dB and BER ≈10⁻⁹ especially under the FFS policy. Moreover, it delivers up to 7.5× cost reduction compared to alternative architectures, significantly reducing deployment/upgrade costs while maintaining low power consumption.

Emerging services such as artificial intelligence (AI), 5G, the Internet of Things (IoT), cloud data services and teleworking are growing exponentially, pushing bandwidth needs to the limit. Space Division Multiplexing (SDM) in the spatial domain, along with Ultra-Wide Band (UWB) transmission in the spectrum domain, represent two degrees of freedom that will play a crucial role in the evolution of backbone optical networks. SDM and UWB technologies necessitate the replacement of conventional Wave-length-Selective-Switch (WSS)-based architectures with innovative optical switching elements capable of handling both higher port counts and flexible switching across various granularities. In this work, we introduce a novel Photonic Integrated Circuit (PIC)-based switching element called flex-Waveband Selective Switch (WBSS), designed to provide flexible band switching across the UWB spectrum (~21 THz). The proposed flex-WBSS supports a hierarchical three-layered Multi-Granular Optical Node (MG-ON) architecture incorporating optical switching across various granularities ranging from entire fibers, flexibly defined bands down to individual wavelengths. To evaluate its performance, we develop a custom network simulator, enabling a thorough performance analysis on all node’s critical performance metrics. Simulations are conducted over an existing network topology evaluating three traffic-oriented switching policies: Full Fiber Switching (FFS), Waveband Switching (WBS), and Wavelength Switching (WS). Simu-lation results reveal high Optical to Signal Ratio (OSNR) and low Bit Error Rate (BER) values, particularly under the FFS policy. In contrast, the integration of the WBS policy bridges the gap between existing WSS- and future FFS-based architectures, manages to relax bandwidth demands and mitigates capacity bottlenecks enabling rapid scalable network upgrades in existing infrastructures. Additionally, we propose a probabilistic framework to evaluate the node’s bandwidth utilization and scaling behavior, exploring tradeoffs among scalability, components’ number and complexity. The proposed framework can be easily adapted for the design of future transport optical networks. Finally, we perform a SWaP-C (Size, Weight, Power and Cost) analysis to underscore the advantages of the proposed architecture. Our results confirm that the proposed node incorporating PIC-based flex-WBSSs, prove to be a cost- and power-efficient solution compared to its counterparts, as reduce excessive initial network deployment/upgrade costs while at the same time minimizing power resource requirements.

The sixth generation of communication networks necessitates a series of significant technological innovations to accommodate ultra-high rates, ultra-low latency, high energy efficiency, and software-defined programmability for supporting the emerging use cases and the exponential growth in traffic demands. Ultra-wideband (UWB) and spatial division multiplexing technologies have emerged as key enablers in meeting these challenges, offering both scalable network capacity and improved energy efficiency. In this paper, we propose an advanced optical transport architecture designed to fulfill the rigorous performance criteria of next-generation optical networks covering all critical network segments. At the core of this infrastructure—the backhaul segment—we introduce a three-layered UWB/SDM-based multi-granular optical node architecture that utilizes photonic integrated circuit (PIC)-based waveband selective switches, enabling scalable network performance and delivering over 10 Pb/s of flexible optical switching capacity while maintaining a high optical signal-to-noise and interference ratio. At the network edge—the fronthaul segment—we introduce a spatially diverse point-to-multipoint PIC-based optical subcarrier interconnectivity architecture that incorporates a low-loss module—referred to as the interlacer—which interconnects cascaded half-band Nyquist-shaped interleaver filters in order to flexibly perform routing at the subcarrier group level. Across all network segments, we consider innovative, energy-efficient optical digital-to-analog converter-based transceivers capable of achieving transmission rates in the order of terabits per second per channel, while ensuring a small footprint and low power consumption. These transceivers can be flexibly reconfigured to either direct detect or coherent operation, serving the specific needs of the different network segments. Extensive numerical simulations are conducted, with parameters mostly derived from experimental data, to assess the feasibility, scalability, and cascadability of the subsystems that are incorporated to optimize the overall performance of the proposed architecture. Finally, the overall design ensures full compatibility with a service management and orchestration framework, enabling software-defined programmability across all interconnected segments.

The value of colorless, directionless, and contentionless (CDC-)ROADM (reconfigurable optical add/drop multiplexer) nodes is strongly contested in the optical networking community. In this work, we compare known ROADM node designs incorporating different switching elements and account for their total nodal switching state support (in consideration of both channel routing and add/drop). This allows us to quantify the impact of directional/contentional accessibility constraints to add/drop transceivers. By considering the network node entity as a permutation network among its ingress/egress ports for all wavelength channels, which covers both through routing and add/drop assignments, we tabulate the node's switching capacity, or total allowable connection states, per different ROADM architecture, hardware constraints, and finite number of add/drop transceivers. We further introduce the impact of idle wavelength channels on fiber links, as well as bidirectional routing assignments. Our switching capacity enumerations demonstrate that CDC-ROADM outperforms other designs, but parallel contentional aggregation hardware (partially contentional) and directional transceivers (permanently assigned to port directions) offer competitive performance under certain scenarios (at lower and higher number of deployed transceivers, or a combination of both). These findings suggest that design alternatives to the “difficult to implement” CDC-ROADM exist, with nearly equivalent switching capacity, and additional system considerations must be taken into account for ROADM design selection such as hardware availability, cost, impact of traffic churn, and disaster recovery with over-provisioned add/drop transceivers.

In this paper, we analyze the spectral performance of space-division multiplexing (SDM) signals traversing cascaded wavelength-selective switches (WSSs), a key component of reconfigurable optical add/drop multiplexers (ROADMs). As SDM technologies such as few-mode fiber (FMF) and multi-core fiber (MCF) emerge to meet increasing data capacity demands, understanding the limitations imposed by repeated channel filtering becomes essential for system design. We investigate how the extent of spatial mixing — ranging from no mixing to weak or strong coupling — affects the MDL-limited passband and usable channel bandwidth. Our numerical analysis models full WSS transfer matrices, incorporates realistic random misalignment between switches, and evaluates the resulting MDL and effective channel bandwidth. We show that strong spatial mixing mitigates the accumulation of MDL, preserving broader passbands and improving network scalability. In the MCF case, we further demonstrate that fiber orientation plays a key role, as asymmetric supermode size result in angle-dependent filtering penalties. Our findings quantify the benefits of strong coupling and offer practical design guidelines for scalable SDM-ROADMs, maximizing bandwidth and minimizing system penalties in future optical networks.