arXiv subjects

Alexander Kotz

Publications and source records attributed to Alexander Kotz.

8 recordsLinked to original sources

arXiv2026

LadderTeam: Dual-Agent Laddering Elicitation Framework

Eliciting detailed and actionable software requirements from end-users is a critical phase in the iterative development of a software product or application. To ensure the feedback collected is detailed and actionable, software teams can leverage the laddering interview technique. While effective for ensuring granular and actionable items from the software feedback, these interviews are subject to several limitations. They are traditionally a manual process associated with a time and financial burden, limiting scalability; interviewers must balance probing for depth while managing interviewee behavioral and cultural constraints. To address these limitations, we present \textbf{LadderTeam}, an open, reproducible framework that automates UX wireframe interviews using a dual-agent Large Language Model (LLM) architecture. An active interviewer agent executes one of three probing strategies (ACV, 5-Whys, and JTBD) to elicit actionable software requirements from usability feedback comments, while a concurrent background Judge agent evaluates probe-response pairs and triggers real-time guardrails to prevent topic drift. To rigorously evaluate LLM laddering without participant variance confounds, we introduce a controlled simulation methodology utilizing scripted ground-truth transcripts to isolate probe quality as the sole experimental variable. Across 216 interviews, \textbf{LadderTeam} achieved 99.1\% chain convergence and an 81.0\% ground-truth actionable response match (86.1\% reluctant personality, 75.9\% terse personality) with zero drift across all runs. All evaluation code, all transcripts, inputs, and a live demonstration platform will be open-sourced upon acceptance.

cs.SE↗

arXiv2026

Broadband suspended lithium tantalate Mach-Zehnder modulator achieving a 460 Gbit/s net data rate

Thin-film lithium tantalate photonic integrated circuits have recently been demonstrated as a promising next-generation electro-optic platform, offering favorable properties including reduced DC drift, higher optical power handling, and lower birefringence compared to lithium niobate. However, high-speed LiTaO3 modulators reported to date have predominantly relied on silicon substrates, whose large dielectric constant compromises microwave velocity matching and imposes RF conductor losses that limit the achievable electro-optic bandwidth. Here, we implement a silicon substrate undercut technique to suspend the electrode region of lithium-tantalate-on-insulator (LTOI) Mach-Zehnder modulators (MZMs), effectively decoupling the traveling-wave electrodes from the high-permittivity silicon handle wafer, thereby reducing microwave losses. In addition, the undercut removes any susceptibility to parasitic surface conductance (PSC) induced losses of the oxide-silicon interface. The fabricated MZM achieves a 3 dB electro-optic bandwidth of 110 GHz, with a half-wave voltage of 5.1 V for an 8 mm-long device. Exploiting the extended bandwidth, we demonstrate a high single-lane intensity-modulation and direct-detection (IMDD) net data rate of 460 Gbit/s using PAM8 signaling. These results establish silicon substrate undercut as an effective and process-compatible pathway to unlock the full electro-optic potential of lithium tantalate on its native silicon-based wafer platform.

physics.optics↗

arXiv2026

Low voltage and high-bandwidth thin-film lithium tantalate modulator on a silicon dioxide substrate

Modern communication networks demand ever-increasing transmission bandwidth, placing stringent requirements on low-cost, high-performance electro-optic modulators. Substantial advances have been made in integrated photonics employing lithium niobate on insulator. In contrast, photonic integrated circuits based on lithium tantalate -- a material already commercially adopted for wireless filters -- have been developed, offering reduced DC drift, higher optical power handling, and lower birefringence. These advantages enable more complex and dense photonic integrated circuits, and make lithium tantalate a promising material platform for next-generation integrated electro-optic modulators. However, in contrast to the extensively studied thin-film lithium niobate platform, thin-film lithium tantalate modulators have only been explored on silicon substrates. Here, we report the first fabrication and characterization of thin-film lithium tantalate electro-optic modulators manufactured on a 4-inch (100 mm) fused-silica substrate for adapting a low-loss slow-wave microwave electrode to improve the electro-optic bandwidth. By employing a slow-wave electrode design to achieve velocity matching between microwave and optical signals, the demonstrated modulator achieves a 3-dB electro-optic bandwidth of 64 GHz with a low half-wave voltage of 1.53 V, with potential to operate at the measured 100 GHz electrical bandwidth, if the employed spectral biasing is removed. The modulator moreover exhibits low bias drift, with a constant switching voltage down to 10 mHz. This performance enables high-speed data transmission comparable to state-of-the-art lithium niobate modulators fabricated on quartz substrates. Using the fabricated devices, a net single lane data rate of 440.6 Gbps is achieved using PAM8 signaling.

physics.optics↗

arXiv2026

PLACID: Privacy-preserving Large language models for Acronym Clinical Inference and Disambiguation

Large Language Models (LLMs) offer transformative solutions across many domains, but healthcare integration is hindered by strict data privacy constraints. Clinical narratives are dense with ambiguous acronyms, misinterpretation these abbreviations can precipitate severe outcomes like life-threatening medication errors. While cloud-dependent LLMs excel at Acronym Disambiguation, transmitting Protected Health Information to external servers violates privacy frameworks. To bridge this gap, this study pioneers the evaluation of small-parameter models deployed entirely on-device to ensure privacy preservation. We introduce a privacy-preserving cascaded pipeline leveraging general-purpose local models to detect clinical acronyms, routing them to domain-specific biomedical models for context-relevant expansions. Results reveal that while general instruction-following models achieve high detection accuracy (~0.988), their expansion capabilities plummet (~0.655). Our cascaded approach utilizes domain-specific medical models to increase expansion accuracy to (~0.81). This novel work demonstrates that privacy-preserving, on-device (2B-10B) models deliver high-fidelity clinical acronym disambiguation support.

cs.CL↗

arXiv2025

Heterogeneously integrated lithium tantalate-on-silicon nitride modulators for high-speed communications

Driven by the prospects of higher bandwidths for optical interconnects, integrated modulators involving materials beyond those available in silicon manufacturing increasingly rely on the Pockels effect. For instance, wafer-scale bonding of lithium niobate films onto ultralow loss silicon nitride photonic integrated circuits provides heterogeneous integrated devices with low modulation voltages operating at higher speeds than silicon photonics. However, in spite of its excellent electro-optic modulation capabilities, lithium niobate suffers from drawbacks such as birefringence and long-term bias instability. Among other available electro-optic materials, lithium tantalate can overcome these shortcomings with its comparable electro-optic coefficient, significantly improved photostability, low birefringence, higher optical damage threshold, and enhanced DC bias stability. Here, we demonstrate wafer-scale heterogeneous integration of lithium tantalate films on low-loss silicon nitride photonic integrated circuits. With this hybrid platform, we implement modulators that combine the ultralow optical loss ($\sim$ 14.2 dB/m), mature processing and wide transparency of silicon nitride waveguides with the ultrafast electro-optic response of thin-film lithium tantalate. The resulting devices achieve a 6 V half-wave voltage, and support modulation bandwidths of up to 100 GHz. We use single intensity modulators and in-phase/quadrature (IQ) modulators to transmit PAM4 and 16-QAM signals reaching up to 333 and 581 Gbit/second net data rates, respectively. Our results demonstrate that lithium tantalate is a viable approach to broadband photonics sustaining extended optical propagation, which can uniquely contribute to technologies such as RF photonics, interconnects, and analog signal processors.

physics.optics↗

arXiv2025

Copper Damascene Process-Based High-Performance Thin Film Lithium Tantalate Modulators

Interfacing electrical and optical systems is a ubiquitous requirement for modern networks. Competitive footprint, efficiency, and bandwidth figures have propelled interest in deploying integrated electro-optic modulators based on Pockels materials for such tasks. Due to its wide usage in legacy bulk electro-optic modulators, and triggered by the availability of 'on insulator' wafers, lithium niobate based devices have seen major advances. Recently, even more favorable properties have been demonstrated in lithium tantalate based devices, featuring similar Pockels effect, but exhibiting lower bias drift and lower birefringence, while equally benefiting from existing volume usage in wireless RF filters. Despite major progress in integrated modulators, these newly emerged ferro-electrical modulators cannot be integrated tightly with electronics yet using standardized processes, such as flip-chip bonding. Here, we overcome this bottleneck by incorporating the copper Damascene process in the fabrication of integrated lithium tantalate modulators. We demonstrate modulators featuring microwave losses that are ~10% lower than in designs relying on conventional gold electrodes. Our results allow us to reach data transmission figures on par with those of electro-optic modulators fabricated with other low-resistivity, yet less common, metals. Specifically, our fabricated modulators are able to achieve data transmission rates of 416 and 540 Gbit/s while preserving bit error ratios below the 25% SD-FEC threshold in a PAM4 and PAM8 transmission schemes, respectively. Together with the commercial availability of lithium tantalate as a Pockels material, our results open a path towards scalable and direct chip-on-wafer embedding of EO modulators with micro-electronic integrated circuits.

physics.optics↗

arXiv2024

Ultrabroadband thin-film lithium tantalate modulator for high-speed communications

The continuous growth of global data traffic over the past three decades, along with advances in disaggregated computing architectures, presents significant challenges for optical transceivers in communication networks and high-performance computing systems. Specifically, there is a growing need to significantly increase data rates while reducing energy consumption and cost. High-performance optical modulators based on materials such as InP, thin-film lithium niobate (LiNbO3), or plasmonics have been developed, with LiNbO3 excelling in high-speed and low-voltage modulation. Nonetheless, the widespread industrial adoption of thin film LiNbO3 remains compounded by the rather high cost of the underlying 'on insulator' substrates -- in sharp contrast to silicon photonics, which can benefit from strong synergies with high-volume applications in conventional microelectronics. Here, we demonstrate an integrated 110 GHz modulator using thin-film lithium tantalate (LiTaO3) -- a material platform that is already commercially used for millimeter-wave filters and that can hence build upon technological and economic synergies with existing high-volume applications to offer scalable low-cost manufacturing. We show that the LiTaO3 photonic integrated circuit based modulator can support 176 GBd PAM8 transmission at net data rates exceeding 400 Gbit/s. Moreover, we show that using silver electrodes can reduce microwave losses compared to previously employed gold electrodes. Our demonstration positions LiTaO3 modulator as a novel and highly promising integration platform for next-generation high-speed, energy-efficient, and cost-effective transceivers.

physics.optics↗

arXiv2024

Freeform terahertz structures fabricated by multi-photon lithography and metal coating

Direct-write multi-photon laser lithography (MPL) combines highest resolution on the nanoscale with essentially unlimited 3D design freedom. Over the previous years, the groundbreaking potential of this technique has been demonstrated in various application fields, including micromechanics, material sciences, microfluidics, life sciences as well as photonics, where in-situ printed optical coupling elements offer new perspectives for package-level system integration. However, millimeter-wave (mmW) and terahertz (THz) devices could not yet leverage the unique strengths of MPL, even though the underlying devices and structures could also greatly benefit from 3D freeform microfabrication. One of the key challenges in this context is the fact that functional mmW and THz structures require materials with high electrical conductivity and low dielectric losses, which are not amenable to structuring by multi-photon polymerization. In this work, we introduce and experimentally demonstrate a novel approach that allows to leverage MPL for fabricating high-performance mmW and THz structures with hitherto unachieved functionalities. Our concept exploits in-situ printed polymer templates that are selectively coated through highly directive metal deposition techniques in combination with precisely aligned 3D-printed shadowing structures. The resulting metal-coated freeform structures offer high surface quality in combination with low dielectric losses and conductivities comparable to bulk material values, while lending themselves to fabrication on planar mmW/THz circuits. We experimentally show the viability of our concept by demonstrating a series of functional THz structures such as THz interconnects, probe tips, and suspended antennas. We believe that our approach offers disruptive potential in the field of mmW and THz technology and may unlock an entirely new realm of laser-based 3D manufacturing.

physics.optics↗