arXiv subjects

Leslie A. Rusch

Publications and source records attributed to Leslie A. Rusch.

7 recordsLinked to original sources

arXiv2026

Machine Learning Models to Identify Promising Nested Antiresonance Nodeless Fiber Designs

Hollow-core fibers offer superior loss and latency characteristics compared to solid-core alternatives, yet the geometric complexity of nested antiresonance nodeless fibers (NANFs) makes traditional optimization computationally prohibitive. We propose a high-efficiency, two-stage machine learning framework designed to identify high-performance NANF designs using minimal training data. The model employs a neural network (NN) classifier to filter for single-mode designs (suppression ratio $\ge$ 50 dB), followed by a regressor that predicts confinement loss (CL). By training on the common logarithm of the loss, the regressor overcomes the challenges of high dynamic range. Using a sparse data set of only 1,819 designs, all with CL greater or equal to 1 dB/km, the model successfully identified optimized designs with a confirmed CL of 0.25 dB/km. {This demonstrates the NN has captured underlying physical behavior and is able to extrapolate to regions of lower CL. We show that small data sets are sufficient for stable, high-accuracy performance prediction, enabling the exploration of design spaces as large as $14e6$ cases at a negligible computational cost compared to finite element methods.

cs.LG↗

arXiv2025

Comb-Driven Coherent Optical Transmitter for Scalable DWDM Interconnects

Driven by the growing demand for large-scale artificial intelligence applications, disaggregated compute nodes and high-radix switches in next-generation computing clusters are set to surpass the capacity of current optical interconnect technologies. Such a surge turns several aspects of transmitters into critical bottlenecks: shoreline bandwidth density and energy efficiency are effectively limiting the scalability. We present a comb-driven coherent optical transmitter architecture on a Si/SiN platform that provides the bandwidth density, energy efficiency, and compact footprint required for such co-packaged-enabled optical interconnects. We evaluate scalability through critical building blocks, including ultra-compact microring-assisted Mach--Zehnder modulators (MRA-MZMs) and dense wavelength-division multiplexing (DWDM) interleavers. Single-tone experiments demonstrate a net line rate of 400 Gbps per polarization (16-QAM, 120 GBd) in silicon within the O-band, achieving a record shoreline density of 4 Tbps/mm while consuming only 10 fJ/bit for modulation. We also demonstrate transmission rates of up to 160 GBd QPSK in back-to-back and 100 GBd over 7 km of fiber without dispersion compensation. Using a quantum-dot frequency comb, six 100 GHz-spaced WDM channels transmit 1.08 Tbps over 5 km. System-level analyses show that by leveraging advanced modulation formats through the integration of wavelength and polarization multiplexing, our proposed architecture can realistically support combined transmission rates exceeding 10 Tbps per fiber within practical limits of power consumption and packaging, outlining a clear path toward future petabit-scale interconnects.

physics.optics↗

arXiv2025

Enhanced Over-the-Air Federated Learning Using AI-based Fluid Antenna System

This paper investigates an over-the-air federated learning (OTA-FL) system that employs fluid antennas (FAs) at an access point. The system enhances learning performance by leveraging the additional degrees of freedom provided by antenna mobility. We analyze the convergence of the OTA-FL system and derive the optimality gap to illustrate the influence of FAs on learning performance. With these results, we formulate a nonconvex optimization problem to minimize the optimality gap by jointly optimizing the positions of the FAs, the beamforming vector, and the transmit power allocation at each user. To address the dynamic environment, we cast this optimization problem as a Markov decision process and propose the recurrent deterministic policy gradient (RDPG) algorithm. Finally, extensive simulations show that the FA-assisted OTA-FL system outperforms systems with fixed-position antennas and that the RDPG algorithm surpasses the existing methods.

eess.SP↗

arXiv2024

Ultrafast Coherent Dynamics of Microring Modulators

Next-generation computing clusters require ultra-high-bandwidth optical interconnects to support large-scale artificial-intelligence applications. In this context, microring modulators (MRMs) emerge as a promising solution. Nevertheless, their potential is curtailed by inherent challenges, such as pronounced frequency chirp and dynamic non-linearity. Moreover, a comprehensive understanding of their coherent dynamics is still lacking, which further constrains their applicability and efficiency. Consequently, these constraints have confined their use to spectrally inefficient intensity-modulation direct-detection links. In this work, we present a thorough study of MRM coherent dynamics, unlocking phase as a new dimension for MRM-based high-speed data transmission in advanced modulation formats. We demonstrate that the phase and intensity modulations of MRMs exhibit distinct yet coupled dynamics, limiting their direct application in higher-order modulation formats. This challenge can be addressed by embedding a pair of MRMs within a Mach-Zehnder interferometer in a push-pull configuration, enabling a bistable phase response and unchirped amplitude modulation. Furthermore, we show that its amplitude frequency response exhibits a distinct dependency on frequency detuning compared to phase and intensity modulations of MRMs, without strong peaking near resonance. Harnessing the ultra-fast coherent dynamics, we designed and experimentally demonstrated an ultra-compact, ultra-wide-bandwidth in-phase/quadrature (I/Q) modulator on a silicon chip fabricated using a CMOS-compatible photonic process. Achieving a record on-chip shoreline bandwidth density exceeding 5Tb/s/mm, our device enabled coherent transmission for symbol rates up to 180Gbaud and a net bit rate surpassing 1Tb/s over an 80km span, with modulation energy consumption as low as 10.4fJ/bit.

physics.optics↗

arXiv2024

Auto-Encoder Optimized PAM IM/DD Transceivers for Amplified Fiber Links

We examine pulse amplitude modulation (PAM) for intensity modulation and direct detection systems. Using a straight-forward, mixed noise model, we optimize the constellations with an autoencoder-based neural network (NN), an improve required signal-to-noise ratio of 4 dB for amplified spontaneous emission (ASE)-limited PAM4 and PAM8, without increasing system complexity. Performance can also be improved in O-band wavelength division multiplexing system with semiconductor optical amplifier amplification and chromatic dispersion. We show via simulation that for such a system operating at 53 Gbaud, we can extend the reach of PAM4 by 10-25 km with an optimized constellation and a NN decoder. We present an experimental validation of 4 dB improvement of an ASE-limited PAM4 at 60 Gbaud using an optimized constellation and a NN decoder.

eess.SP↗

arXiv2021

Silicon Photonics in Optical Access Networks for 5G Communications

Only radio access networks can provide connectivity across multiple antenna sites to achieve the great leap forward in capacity targeted by 5G. Optical fronthaul remains a sticking point in that connectivity, and we make the case for analog radio over fiber signals and an optical access network smartedge to achieve the potential of radio access networks. The edge of the network would house the intelligence that coordinates wireless transmissions to minimize interference and maximize throughput. As silicon photonics provides a hardware platform well adapted to support optical fronthaul, it is poised to drive smart edge adoption. We draw out the issues in adopting oursolution, propose a strategy for network densification, and cite recent demonstrations to support our approach.

cs.NI↗

arXiv2021

IRS-Empowered Wireless Communications: State-of-the-Art, Key Techniques, and Open Issues

In this article, we overview intelligent reflecting surface (IRS)-empowered wireless communication systems. We first present the fundamentals of IRS-assisted wireless transmission. On this basis, we explore the integration of IRS with various advanced transmission technologies, such as millimeter wave, non-orthogonal multiple access, and physical layer security. Following this, we discuss the effects of hardware impairments and imperfect channel-state-information on the IRS system performance. Finally, we highlight several open issues to be addressed.

cs.IT↗