arXiv subjects

Aleksei Gaier

Publications and source records attributed to Aleksei Gaier.

4 recordsLinked to original sources

arXiv2026

Coherent transduction and dynamical back-action between light and millimeter waves

Electro-optic transduction can bypass the loss and noise of electronic frequency conversion at millimeter-wave frequencies by parametrically converting signals onto low-loss, low-noise optical carriers, with coupling rates that grow with frequency. Exploiting this growth, however, requires shrinking both the millimeter-wave and optical resonators while preserving their quality factors and spatial overlap, which has not yet been achieved. Here, we demonstrate a triply resonant transducer whose optical and millimeter-wave resonators have comparable dimensions and minimal mode volumes. Coupled lithium niobate Fabry-Pérot cavities, with free spectral ranges above 650 GHz and quality factors up to $10^6$, form a photonic molecule integrated with a quarter-wave gold resonator at 263 GHz. The device reaches a vacuum electro-optic coupling rate $g_0/2π\approx 60$ kHz, six times larger than previous millimeter-wave transducers and sixty times larger than at microwave frequencies. The device optically detects room-temperature thermal millimeter-wave photons at effective occupancies below one, which also serve as a calibration tone for transduction efficiency. Coherent transduction reaches cooperativities approaching 0.3, corresponding to internal efficiencies around 67%, accompanied by electro-optic dynamical back-action that broadens or narrows the optical resonances. These results demonstrate the advantage and feasibility of the frequency scaling of electro-optic coupling, establishing an architecture for weak-signal sensing and quantum and classical networking.

physics.optics↗

arXiv2026

All-photonic millimeter-wave and terahertz signal core at room and cryogenic temperatures

Millimeter-wave and terahertz technologies offer new opportunities for high-capacity communications, sensing, and quantum systems, but electronic signal chains above 100 GHz are limited by weak sources, noisy receivers, and lossy interconnects. Photonic approaches mitigate these constraints by enabling chip-scale high-frequency components, yet existing implementations generally retain lossy off-chip electrical or free-space links, hindering dense and compact integration for cryogenic or space-constrained settings. Here, we show a monolithic lithium tantalate photonic chip, termed a signal core, which generates, modulates, routes, and detects continuous-wave signals at discrete frequencies between 100 GHz and 2.5 THz. The architecture integrates high-frequency functional modules on chip and uses exclusively fiber-based optical interfaces. Bidirectional coherent electro-optic conversion enables signal generation, detection, and nanosecond-scale amplitude and phase modulation, while micro-coplanar striplines interconnect the modules into an end-to-end signal chain on a single chip. Our modules achieve single-photon electro-optic coupling rates of g_0/2π=10 kHz and peak drive-power-normalized photon-flux conversion efficiencies of 1.0%/mW for generation and 0.5%/mW for detection. It also operates at 4 K in a dilution refrigerator through the same fiber-only optical links. Together, these capabilities establish an all-photonic platform for millimeter-wave-to-terahertz systems and offer a broadly applicable architecture for applications constrained by electrical-interconnect loss, heat load, and footprint.

physics.optics↗

arXiv2026

Hz-resolution wide-span photonic integrated terahertz signal analyzer

Wide-span spectral and noise characterization at millimeter-wave and terahertz frequencies is increasingly important for emerging wireless, sensing, and spectroscopy systems, yet remains challenging for conventional electronic instrumentation because of the complexity and calibration burden of extender-, multiplier-, and mixer-chain architectures. Here we show that photonics can provide attractive alternatives to this highly challenging electronic instrumentation through an antenna-coupled thin-film lithium niobate electro-optic receiver. Our implementation performs fast spectral reconstruction across the widely separated WR 9.0 (80-125 GHz) and WR 2.8 (240-380 GHz) bands with a single component, with carrier-frequency errors below 3 MHz, scan speeds up to 25 THz/s, and a displayed average noise level below -104 dBm/Hz. We then extend to Hz-level resolution and demonstrate phase-noise characterisation capabilities across these ultra-wide bands by using a mode-locked femtosecond-laser frequency comb as a sampling clock, mapping high-frequency carriers to aliased intermediate-frequency tones. We validate the method by measuring the phase noise of 90.225 GHz and 270.675 GHz carriers using the same chip and system configuration. We further improve the sensitivity of the phase-noise measurement through cross-correlation between two optical probe-pulse channels. Finally, we show that the same technique can be applied synchronously to ten widely spaced frequencies distributed across more than 100 GHz, with the option to quantify their mutual coherence. These results establish TFLN integrated photonics as a scalable route toward compact millimeter-wave/terahertz instrumentation.

physics.optics↗

arXiv2026

Reconfigurable Single-Ring Photonic Molecule on Lithium Niobate

Resonant photonic structures enable optical enhancement and spectral filtering and are essential for lasers, quantum emitters, transducers, or modulators. Photonic molecules, formed by mode hybridisation in two coupled resonators, break the equidistant frequency spacing of zero-dispersion resonators and provide control over their spectrum. Reconfigurability over these devices is a key asset, allowing to align photonic resonances to target frequencies on-demand. While electro-optic materials such as thin-film lithium niobate (TFLN) have enabled frequency tuning beyond traditional thermo-optic effects, they require continuous bias, posing challenges to scalability. Here we demonstrate an optically programmable, erasable, and rewritable photonic molecule realized within a single TFLN racetrack resonator. A long-lasting photorefractive grating induced through interference of co-propagating dark and bright transverse modes promotes their hybridisation, forming a single-ring photonic molecule. We observe GHz-scale hybrid-mode splitting over a 700 GHz-wide optical bandwidth and hour-long lifetimes, and show that their coupling strength can be programmed by the optical pump used to write the grating. By selectively pumping orthogonal hybridised modes, we further demonstrate multiple reversible all-optical write-erase-rewrite cycles of these gratings. Finally, we use this technique to realize single-sideband mmWave transduction around 107 GHz with a 5 GHz tuning bandwidth. These results establish photorefraction as a reliable mechanism for reconfigurable resonances in TFLN, and suggest a route towards tunable microwave-optical functionalities within a reduced footprint.

physics.optics↗