arXiv subjects

Matthew Marshall

Publications and source records attributed to Matthew Marshall.

4 recordsLinked to original sources

arXiv2026

Bitcoin Smart Accounts: Trust-Minimized Native Bitcoin DeFi Infrastructure

Bitcoin's limited programmability and transaction throughput have historically prevented native Bitcoin from participating in decentralized finance (DeFi) applications. Existing solutions depend on honest-majority thresholds, or centralized custodial entities that introduce significant trust requirements. This paper introduces Bitcoin Smart Accounts (BSA), a novel protocol that enables native Bitcoin to access DeFi through trust-minimized infrastructure while maintaining self-custody of funds. BSA achieves this through a combination of emulated Bitcoin covenants using Partially Signed Bitcoin Transactions (PSBTs) and Taproot scripts, a Trusted Execution Environment (TEE)-based arbitration system, and destination chain smart contracts that enable DeFi platforms to accept self-custodial Bitcoin as collateral without necessitating protocol-level modifications. The setup leverages liquidity secured by the Lombard Security Consortium which provides a twofold advantage: for a DeFi protocol, liquidators rely on fungible assets with deep liquidity to quickly exit positions, while for a depositor, the general trust assumptions of honest majority (m-of-n) are reduced to existential honesty (1-of-k). We present the complete protocol design, including the Bitcoin architecture, the TEE-based arbitration mechanism, and the Smart Account Registry for protocol management. We provide a security analysis that demonstrates the correctness, safety, and availability properties under our trust model. Our design enables native Bitcoin to serve as collateral in lending markets and other DeFi protocols without requiring users to relinquish custody of funds.

cs.CR↗

arXiv2025

Simple Method for Stripping Polyimide-Coated Optical Fiber

We present a simple method for removing polyimide coatings from optical fibers using inexpensive and readily available solvents. Impacts of solvent mixing ratios, soak temperature, material expansion, wicking, and drying are described to provide empirical context for the method. We find that soaking fibers for six hours in a 2:1 mixture of methanol to acetone at room temperature enables easy stripping of a length slightly greater than the soak length.

physics.optics↗

arXiv2025

Characterization of Gradient Index Fibers

Gradient index (GRIN) fibers are used to improve the design of many fiber optic devices. However, the properties of the GRIN fiber must be determined to optimally engineer a device which incorporates GRIN fiber components. The index of refraction of most GRIN fibers varies quadratically in the radial direction, where the quadratic coefficient is characterized by the gradient index constant $g$. We measured $g$ for Thorlabs GIF50C GRIN fiber at both $780~\mathrm{nm}$ and $1550~\mathrm{nm}$ using equipment which is commonly available in an optics laboratory. This measurement was achieve by profiling the beam exiting various lengths of GRIN fiber. A custom-built beam profiler was used, which enabled the beam position to be referenced with respect to the facet of the GRIN fiber. We report a gradient index constant of $0.0057~\mathrm{\mu m}^{-1} \pm 0.0001~\mathrm{\mu m}^{-1}$ at $780~\mathrm{nm}$ and $0.0055~\mathrm{\mu m}^{-1} \pm 0.0001~\mathrm{\mu m}^{-1}$ at $1550~\mathrm{nm}$. These results are in close agreement with previously reported gradient index constant measurements made for different wavelengths.

physics.optics↗

arXiv2025

Iterative Refinement of Arbitrary Micro-Optical Surfaces

We introduce an adaptive optical refinement method enabling ultra-precise micro-milling of arbitrary surfaces. Through repeated iteration, our method reduces surface error without requiring significant specific surface engineering. This remediates the long sample preparation times and lack of refinement capability that previously reported methods suffer from. The iterative refinement milling method was used to produce spherical mirrors with small radii of curvature and low surface roughness for use in micro Fabry-Perot cavities. We demonstrate the use of this adaptive process to produce a variety of arbitrary surface geometries on both optical fiber tips as well as optical flats. We additionally discuss our capability to apply iterative refinement milling adaptively to various materials, including to construct GRIN lenses.

physics.optics↗