Ileana-Cristina Benea-Chelmus

Silicon photonics has emerged as a key platform for next-generation communication and sensing technologies, enabling compact, scalable, and energy-efficient optical systems compatible with large-volume semiconductor manufacturing. When combined with highly nonlinear organic electro-optic materials, silicon photonics gains functionalities unavailable in silicon alone, opening new opportunities for ultrafast modulation and for direct transduction between high-frequency wireless electromagnetic fields and guided optical signals. In this work, we investigate hybrid silicon–organic devices based on patch-array antennas integrated with silicon waveguides for the detection of free-space terahertz waves. A telecom probe beam is routed through the silicon circuitry and converted into a plasmonic slot mode that interacts with the terahertz field accumulated in the nanoscale gap of the antenna. The latter is filled with a poled organic material providing the Pockels nonlinearity required for electro-optic terahertz modulation. We design various patch-antenna geometries and compare them to more conventional bowtie antennas. We show that patch-array antennas provide enhanced sensitivity at selected frequencies through a stronger resonant field concentration, in contrast to bowtie layouts that instead exhibit broadband responses owing to their tapered dipolar design. We further analyze how the detected signal depends on the relative position of the terahertz beam spot with respect to these two types of antenna on the chip, thus reconstructing the spatial coupling behavior of the two configurations. These results clarify the trade-offs between bandwidth, sensitivity, and spatial tolerance in planar antenna-coupled plasmonic terahertz detectors and provide practical design guidelines for integrated optical sampling of terahertz signals.

Tunable lasers are essential for optical communication, spectroscopy, and precision sensing, where fast and stable wavelength control is required. Conventional tuning approaches rely on either current or temperature tuning, mechanical actuation, or bulky external modulators, limiting speed, stability, or integration. Here, we introduce an external cavity semiconductor laser incorporating a resonant electro-optic metasurface as the external mirror, enabling ultrafast frequency and amplitude control within a compact, motion-free platform. The metasurface provides narrowband feedback that ensures single-mode operation and voltage-controlled tuning across a wide current range. We demonstrate mode-hop-free linear frequency tuning with rates up to 180 terahertz per second and frequency excursions reaching 110 megahertz under a 10-volt peak radio-frequency drive. By biasing the laser near threshold, we further achieve intensity modulation efficiencies exceeding 100% at 4 volts. These results establish electro-optic metasurfaces as a powerful route toward compact, high-speed, mode-hop-free tunable lasers for free-space communication, ranging, and high-resolution spectroscopy.

Photonic molecules can mimic interactions of atomic energy levels, offering new ways to manipulate cavity eigenstates. Current methods using evanescent coupling of multiple cavities face challenges in scalability, flexibility, and coupling control, especially for complex systems. Here we introduce a new method that uses a single multimode optical ring resonator to create photonic molecules. Our design uses multiple waveguide transverse modes in one resonator, providing flexibility to engineer complex interactions without typical coupling constraints. We demonstrate arbitrary intermode coupling through transmissive mode converters, allowing precise tuning of resonance splitting and intrinsic losses. This approach enables selective bright-dark mode pair generation and the exploration of novel photonic phenomena such as exceptional points. This multimode photonic molecule overcomes traditional limitations and offers new possibilities for integrated photonic circuits, optical processing, and studies in non-Hermitian and nonlinear photonics.

Deployment of terahertz communication and spectroscopy systems relies on the availability of low-noise and fast detectors, with plug-and-play capabilities. However, most current technologies are stand-alone, discrete components. They are often slow or susceptible to temperature drifts and require tight beam focusing to maximize the signal-to-noise of the detector. Here, we demonstrate an integrated photonic architecture in thin-film lithium niobate that addresses these challenges by exploiting the electro-optic modulation induced by a terahertz signal onto an optical beam at telecom frequencies. Leveraging on the low optical losses provided by this platform, we integrate a double array of up to 18 terahertz antennas within a Mach–Zehnder interferometer, considerably extending the device collection area and boosting the interaction efficiency between the terahertz signal and the optical beam. We show that the double array coherently builds up the probe modulation through a mechanism of quasi-phase-matching, driven by a periodic terahertz near-field pattern, circumventing physical inversion of the crystallographic domains. This provides means to fully custom-tailor the frequency response of the device, limit it to a desired frequency band and effectively suppress out-of-band signals. The large detection area ensures correct operation with diverse terahertz beam settings. Furthermore, we show that the antennas act as pixels that allow reconstruction of the terahertz beam profile impinging on the detector area. Our on-chip design in thin-film lithium niobate overcomes the detrimental effects of two-photon absorption and fixed phase-matching conditions, which have plagued previously explored electro-optic detection systems, especially in the telecom band, paving the way for more advanced on-chip terahertz systems.

Tunable lasers are essential for optical communication, spectroscopy, and precision sensing, where flexible and fast control of the laser wavelength is needed. However, conventional tunable laser systems often rely on mechanical actuation, which limits their tuning speed, stability, and repeatability. Alternative tuning methods, such as adjusting the temperature of the gain medium or the injection current, are either slow or suffer from unwanted coupling between frequency and intensity. Electro-optic modulators implemented after the laser offer fast frequency tunability but these components are bulky and prone to high insertion losses. Here, we introduce an external cavity semiconductor laser that achieves ultrafast frequency and amplitude tunability within a compact footprint without any moving parts. The laser employs a resonant electro-optic metasurface as the external mirror, providing narrowband feedback that enables simultaneous single-mode operation and voltage-controlled tuning across a wide range of currents. Leveraging a narrow linewidth design, we demonstrate mode-hop-free linear frequency tuning with rates of up to 70 THz/s, and frequency excursions reaching 110 MHz under a 10 V peak RF drive, clearly surpassing rates attainable through mechanical actuation. Moreover, by biasing the laser near its threshold, our platform enables intensity modulation with an efficiency above 100% at a peak voltage of 4 V. These results highlight the platform's potential for applications requiring high-speed and mode-hop-free tunable lasers, such as free-space optical communication, laser ranging, and high-resolution spectroscopy.

Modern communication and sensing technologies connect the optical domain with the microwave domain. Accessing the terahertz region from 100 GHz to 10 THz is critical for providing larger bandwidths capabilities. Despite progress in integrated electronics, they lack a direct link to the optical domain, and face challenges with increasing frequencies ( > 1 THz). Electro-optic effects offer promising capabilities but are currently limited to bulk nonlinear crystals, missing out miniaturization, or to sub-terahertz bandwidths. Here, we address these challenges by realizing photonic circuits that integrate terahertz transmission lines on thin-film lithium niobate (TFLN). By providing terahertz field confinement and phase-matched interaction with optical fields, our miniaturized devices support low-noise and broad bandwidth terahertz generation and detection spanning four octaves (200 GHz to > 3 THz). By leveraging photonics’ advantages in low-loss and high-speed control, our platform achieves control over the terahertz spectrum and its amplitude, paving the way for compact and power-efficient devices with applications in telecommunications, spectroscopy, quantum electrodynamics and computing.

Full characterization of electric-field waveforms in amplitude and phase is achieved across the terahertz to visible spectral range through interaction with an optical pulse shorter than a half-cycle period via the Pockels (linear electro-optic) effect. This technique of electro-optic sampling has become an indispensable tool in various areas, including ultrafast pump-probe, time-domain and frequency-comb spectroscopies, quantum optics, high-harmonic generation, and attosecond science, and holds great promise for further advances. Not only does it enable spectroscopic measurements with record dynamic range and temporal resolution, along with massively parallel real-time spectral data acquisition, but its remarkable sensitivity also allows the detection of vacuum fluctuations, i.e., “zero-point motion” of electric fields, profoundly impacting our understanding of the fundamental laws of nature.

Interferometers are essential tools for measuring and shaping optical fields, widely used in optical metrology, sensing, laser physics, and quantum mechanics. They superimpose waves with a mutual phase delay, modifying light intensity. A frequency-dependent phase delay enables spectral shaping for filtering, routing, wave shaping, or multiplexing. Conventional Mach-Zehnder interferometers generate sinusoidal output intensities, limiting spectral engineering capabilities. Here, we propose a framework that uses interference of multiple transverse modes within a single multimode waveguide to achieve arbitrary spectral shapes in a compact geometry. Designed corrugated gratings couple these modes, enabling energy exchange akin to a beam splitter for easy multimode handling. We theoretically and experimentally demonstrate spectra with independently tunable linewidth and free spectral range, along with distinct spectral shapes for various transverse modes. Our method applies to orthogonal modes of different orders, polarization, and angular momentum, offering potential for sensing, calibration, metrology, and computing.

Deployment of terahertz communication and spectroscopy systems relies on the availability of low-noise and fast detectors, with plug-and-play capabilities. However, most currently available technologies are stand-alone, discrete components, either slow or susceptible to temperature drifts. Moreover, phase-sensitive schemes are mainly based on bulk crystals and require tight beam focusing. Here, we demonstrate an integrated photonic architecture in thin-film lithium niobate that addresses these challenges by exploiting the electro-optic modulation induced by a terahertz signal onto an optical beam at telecom frequencies. Leveraging on the low optical losses provided by this platform, we integrate a double array of up to 18 terahertz antennas within a Mach-Zehnder interferometer, considerably extending the device collection area and boosting the interaction efficiency between the terahertz signal and the optical beam. We show that the double array coherently builds up the probe modulation through a mechanism of quasi-phase-matching, driven by a periodic terahertz near-field pattern, without physical inversion of the crystallographic domains. The array periodicity controls the detection bandwidth and its central frequency, while the large detection area ensures correct operation with diverse terahertz beam settings. Furthermore, we show that the antennas act as pixels that allow reconstruction of the terahertz beam profile impinging on the detector area. Our on-chip design in thin-film lithium niobate overcomes the detrimental effects of two-photon absorption and fixed phase-matching conditions, which have plagued previously explored electro-optic detection systems, especially in the telecom band, paving the way for more advanced on-chip terahertz systems.

Integrated photonic circuits from thin film lithium niobate are emerging as a promising platform to address the lack of miniaturized terahertz emitters and detectors within one single chip. In this talk, we will discover how terahertz transmission lines co-integrated with photonics fulfill the essential requirements for efficient terahertz-optical bidirectional conversion.