arXiv subjects

Steve Blair

Publications and source records attributed to Steve Blair.

8 recordsLinked to original sources

arXiv2026

Design Considerations for Phase Modulation in Testable Photonic Systems and Co-packaged Optics

As silicon photonic integrated circuits (PICs) scale in complexity, testing and calibration increasingly depend on effective phase modulation mechanisms. This work compares thermally induced phase modulation and carrier-based electrical modulation in Mach-Zehnder and microring modulators. The devices are designed and evaluated for extinction ratio, tuning efficiency, power consumption, and modulation bandwidth. The study identifies key trade-offs among modulation speed, energy consumption, and tuning controllability that directly influence the suitability of these methods for test signal generation and calibration tasks. The results highlight the relative advantages and limitations of thermal and electrical approaches across different operating regimes. These findings provide practical design guidance for selecting phase modulation strategies in scalable silicon photonic systems with integrated test and calibration requirements.

cs.ET↗

arXiv2026

Silicon Photonics Testing: Design for Testability, Fault Detection, and Manufacturing Variation Analysis in Photonic Integrated Circuits

This paper proposes a design-for-test (DFT) methodology and architecture for testing and validation of silicon photonic integrated circuits. We describe the design of silicon photonic circuits and components that comprise the proposed DFT architecture. The designs are extensively simulated and validated as test-access and fault-detection circuitry. We demonstrate how the DFT approach can be deployed on photonic integrated circuits and how they can be tested for correct operation, in terms of signal power and phase. The application is demonstrated on two distinct types of designs -- an optical neural network comprising optical devices in a feed-forward topology, and on an optical logic circuit with feedback loops.

cs.ET↗

arXiv2026

Reconfigurable Curved Beams at Terahertz Frequencies Using Inverse-Designed Bilayer Diffractive Structures

Curved electromagnetic beams at terahertz (THz) frequencies have recently emerged as a powerful example of wavefront engineering, with applications in imaging and high-capacity wireless communications. Unlike canonical self-accelerating solutions such as Airy beams, general curved-beam propagation enables arbitrary, application-specific trajectories that are not constrained by analytic beam families. Here, we demonstrate a passive and reconfigurable approach for generating trajectory-engineered THz curved beams using inverse-designed bilayer diffractive optical elements (DOEs). Two phase-only diffractive layers are optimized using gradient-based inverse design to produce predetermined curved propagation paths. Reconfiguration is achieved by a 180° rotation of the second layer, which modifies the effective phase profile of the cascaded structure without altering the incident wave or individual layer designs. The proposed system can produce distinct curved trajectories with controlled transverse displacement and beam confinement, as confirmed by scalar diffraction simulations and experimental measurements. Overall, this work establishes inverse-designed cascaded DOEs as a compact and scalable platform for reconfigurable trajectory control of THz beams, providing a flexible alternative to analytic self-accelerating beams for radiative near-field THz communications.

physics.optics↗

arXiv2026

Holographic Mapping of Orbital Angular Momentum Using a Terahertz Diffractive Optical Neural Network

Using orbital angular momentum (OAM) in the terahertz (THz) range provides a new degree of freedom for communication and imaging systems. This study presents a compact diffractive optical neural network designed to recognize discrete and superposed OAM states at THz frequencies. The network consists of six diffractive layers trained to spatially separate nine OAM modes with topological charges from 1 to 9. Each mode is projected to a distinct position on the output plane, enabling direct recognition of its state. The structure was fabricated through low-cost 3D printing techniques with high-impact polystyrene (HIPS), allowing for scalable and practical implementations. Experimental validation at 0.3 THz demonstrates good fidelity of mode discrimination and mapping. The proposed approach offers a robust and economical pathway for OAM decoding, offering new opportunities for beam manipulation through THz systems based on diffractive optical neural networks.

physics.optics↗

arXiv2026

Control of Extraordinary Optical Transmission in Resonant Terahertz Gratings via Lateral Depletion in an AlGaN-GaN Heterostructure

Periodic metallic gratings on substrates can support a range of electromagnetic modes, such as leaky waveguide, guided-resonant, and Fabry-Perot (FP) cavity modes, which can strongly modulate optical transmission under resonant excitation. Here, we investigate how this coupling can be dynamically manipulated through charge-density control in a laterally patterned AlGaN/GaN heterostructure. The structure comprises metallic stripes separated by regions containing a two-dimensional electron gas (2DEG), forming a periodically modulated interface whose electromagnetic response is governed by the charge density between the stripes. In the unbiased state, the conductive 2DEG screens the incident terahertz field and suppresses excitation of guided modes. When the 2DEG is depleted, the change in boundary conditions allows efficient coupling into substrate resonances, producing a strong modulation at particular frequencies where extraordinary optical transmission (EOT) through the structure takes place. The results highlight the sensitive dependence of guided-mode-resonance (GMR) mediated EOT on inter-stripe charge distribution and demonstrate a direct interplay between carrier dynamics and resonant electromagnetic phenomena in the terahertz regime.

cond-mat.mtrl-sci↗

arXiv2020

The anisotropic quasi-static permittivity of single-crystal beta-Ga2O3

The quasi-static anisotropic permittivity parameters of electrically insulating gallium oxide (beta-Ga2O3) were determined by terahertz spectroscopy. Polarization-resolved frequency domain spectroscopy in the spectral range from 200 GHz to 1 THz was carried out on bulk crystals along different orientations. Principal directions for permittivity were determined along crystallographic axes c, and b, and reciprocal lattice direction a*. No significant frequency dispersion in the real part of dielectric permittivity was observed in the measured spectral range. Our results are in excellent agreement with recent radio-frequency capacitance measurements as well as with extrapolations from recent infrared measurements of phonon mode and high frequency contributions, and close the knowledge gap for these parameters in the terahertz spectral range. Our results are important for applications of beta-Ga2O3 in high-frequency electronic devices

cond-mat.mtrl-sci↗

arXiv2018

Manifestation of kinetic-inductance in spectrally-narrow terahertz plasmon resonances in thin-film Cd3As2

Three-dimensional (3D) semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with its linear energy dispersion. In analogy to two-dimensional (2D) Dirac semimetals, such as graphene, Cd3As2, a 3D semimetal, has shown ultra-high mobility, large Fermi velocity, and has been hypothesized to support plasmons at terahertz frequencies. In this work, we demonstrate synthesis of high-quality large-area Cd3As2 thin-films through thermal evaporation as well as the experimental realization of plasmonic structures consisting of periodic arrays of Cd3As2 stripes. These arrays exhibit sharp resonances at terahertz frequencies with associated quality-factors (Q) as high as ~ 3.7. Such spectrally-narrow resonances can be understood on the basis of a large kinetic-inductance, resulting from a long momentum scattering time, which in our films can approach ~1 ps at room-temperature. Moreover, we demonstrate an ultrafast tunable response through excitation of photo-induced carriers in optical pump / terahertz probe experiments. Our results evidence that the intrinsic 3D nature of Cd3As2 provides for a very robust platform for terahertz plasmonic applications. Overall, our observations pave a way for the development of myriad terahertz (opto) electronic devices based on Cd3As2 and other 3D Dirac semimetals, benefiting from strong coupling of terahertz radiation, ultrafast transient response, magneto-plasmon properties, etc. Moreover, the long momentum scattering time, thus large kinetic inductance in Cd3As2, also holds enormous potential for the re-design of passive elements such as inductors and hence can have a profound impact in the field of RF integrated circuits.

physics.optics↗

arXiv2014

Quantum Size Effect on Dielectric Properties of Ultrathin Metallic Film: A First-Principles Study of Al(111)

Quantum manifestations of various properties of metallic thin films by quantum size effect (QSE) have been studied intensively. Here, using first-principles calculations, we show quantum manifestation in dielectric properties of Al(111) ultrathin films. The QSE on the dielectric function is revealed, which arises from size dependent contributions from both intraband and interband electronic transitions. More importantly, the in-plane interband transitions in the films thinner than 15 monolayers are found to be smaller than the bulk counterpart in the energy range from 1.5~eV to 2.5~eV. This indicates less energy loss with plasmonic material of Al in the form of ultrathin film. Our findings may shed light on searching for low-loss plasmonic materials via quantum size effect.

cond-mat.mtrl-sci↗