We present a systematic study of how thermal annealing (450–1000 °C) affects optical propagation loss in low-pressure chemical vapor deposited (LPCVD) stoichiometric silicon nitride (Si3N4) thin films and waveguides at visible wavelengths. Slab-mode characterization using prism coupling shows that the loss remains within measurement uncertainty up to anneal temperatures of ~900 °C, above which it increases sharply at all measured wavelengths. After accounting for modeled scattering, the residual loss is consistent with an absorption-like increase of 11.1 ± 1.48 dB/cm at 447 nm following 975 °C annealing. This behavior is corroborated by measurements on high-confinement waveguides. For the Si3N4 stack investigated here, annealing above 900 °C substantially increases visible-wavelength propagation loss, highlighting a trade-off between infrared-optimized annealing and visible performance.

Integrated waveguides enable efficient nonlinear frequency conversion for both classical and quantum photonics applications by creating intense light-matter interactions in compact, high-confinement waveguide geometries. Traditional design approaches using analytical mode treatments or full-field finite-difference time-domain (FDTD) simulations are limited either in generality or in computational cost, and they do not readily support broad exploration of nonuniform structures for nonlinear processes. We introduce the nonlinear eigenmode expansion method (nonlinear-EME), which integrates linear eigenmode propagation and second-order nonlinear coupling into a single resource-efficient framework. Nonlinear-EME supports full-vector modal fields, complete mode lists, propagation losses, pump depletion, and nonuniform waveguide structures with a reduced computational cost compared to FDTD. We demonstrate initial simulations of continuous-wave second-harmonic generation in uniform and tapered waveguides.

Far-UVC light (200-230 nm) is emerging as a uniquely powerful spectral window: it inactivates airborne pathogens while remaining safe for human exposure, enables background-free molecular spectroscopy and offers untapped bandwidth for free-space optical links. However, its promise has been limited by the absence of compact and scalable light sources. We present an integrated photonic platform for compact and scalable far-UVC generation via nonlinear frequency conversion of visible laser diodes. Leveraging advances in visible light photonic integrated circuits (PICs), our architecture achieves high local visible-light intensities in low-loss waveguides. The heterogeneous integration of nonlinear crystals enables robust frequency conversion across hundreds of nanometers. This wide tunability is achieved through a geometric phase-matching mechanism at the waveguide-crystal interface, called Cherenkov phase-matching, and enables demonstration of UV emission spanning 203 to 319 nm. This approach supports both second-harmonic and sum-frequency generation along the propagation length, drastically reducing pump-source requirements through cross-mode interaction in multi-mode lasers, enabling continuous-wave operation using low-cost diode lasers. We present theoretical modeling, device design, and experimental validation of Cherenkov-style frequency conversion. To optimize performance, we investigate visible-wavelength loss mechanisms in low-loss PIC platforms and explore on-chip integration of visible laser diodes. This work establishes a pathway to compact, chip-scale far-UVC sources, extending integrated photonics deep into the ultraviolet, offering a p ractical a lternative t o e xcimer l amps a nd far-UVC LEDs. With continued refinement, Cherenkov phase matching c ould e nable a new c lass o f ultraviolet photonic systems, opening applications previously inaccessible to integrated platforms across healthcare, life sciences, and spectroscopy.

We present a systematic study of how thermal annealing (450–1000°C) affects optical propagation loss in low-pressure chemical vapor deposited (LPCVD) stoichiometric silicon nitride (Si 3 N 4 ) thin films and waveguides at visible wavelengths. Slab-mode characterization using prism coupling shows that the loss remains within measurement uncertainty up to annealing temperatures of ∼900°C, above which it increases sharply at all measured wavelengths. After accounting for modeled scattering, the residual loss is consistent with an absorption-like increase of 11.1 ± 1.48 dB/cm at 447 nm following 975°C annealing. This behavior is corroborated by measurements on high-confinement waveguides. For the Si 3 N 4 stack investigated here, annealing above 900°C substantially increases visible-wavelength propagation loss, highlighting a trade-off between infrared-optimized annealing and visible performance.

Integrated photon-pair sources are a core component of chip-based quantum computing, communication, and metrology. Although such sources have been demonstrated at conventional telecom wavelengths, the 2 μm band remains comparatively less explored, despite offering advantages for free-space quantum communication, low-loss transmission in emerging fiber networks, and integration with silicon photonic platforms. In this paper, we demonstrate spontaneous parametric down-conversion (SPDC) in straight GaAs- and AlGaAs-on-insulator waveguides. This platform offers strong second-order nonlinearity and geometry-tunable dispersion, which are advantageous for efficient on-chip pair generation. Measurements of the joint spectral intensity and heralded second-order correlation function show broadband emission around 2 μm with strong spectral anti-correlations. To our knowledge, this is the first direct joint-spectral characterization of an integrated SPDC source in this wavelength regime.

InGaP integrated on a silicon substrate has emerged as a promising platform for nonlinear and quantum photonics, offering high nonlinear conversion efficiency and scalability with silicon-based fabrication infrastructure. This work presents an experimental demonstration of sum- and difference-frequency generation in InGaP waveguides. We generate light at 930 nm, 1550 nm and 2325 nm, achieving conversion efficiencies of 4.5 ± 0.5 /W, 1.4 ± 0.2 /W and 0.43 ± 0.04 /W, respectively. These results highlight the potential of InGaP-on-insulator for advanced photonic applications, including broadband infrared light generation and quantum frequency conversion. We discuss a roadmap for this technology to achieve even broader wavelength coverage, higher efficiencies and quantum-frequency conversion of single-photons.

We present a detailed characterization of a hybrid photonic platform for robust and broadly tunable ultraviolet (UV) laser generation using Čerenkov nonlinear frequency conversion (CNFC). By integrating silicon nitride waveguides with barium borate (BBO) cladding, the platform achieves UV emission across an unprecedented wavelength range of 204–319 nm. Compared to state-of-the-art UV photonic devices, our approach addresses longstanding challenges in spectral range, tunability, and integration. Theoretical modeling and experimental validation demonstrate remarkable fabrication tolerance, maintaining phase matching over a 1500 nm waveguide width variation. Angle-resolved far-field mapping reveals key trade-offs in waveguide design and emission profile. These findings offer a compact, scalable solution addressing critical needs in disinfection, quantum technologies, and free-space optical communication.

Atomic and trapped-ion systems are the backbone of an emerging generation of quantum-based positioning, navigation, and timing (PNT) technologies. The miniaturization of such quantum systems offers tremendous technological advantages, especially the reduction of system size, weight, and power consumption. Yet this has been limited by the absence of compact, standalone photonic integrated circuits (PIGs) at the wavelengths suitable for these instruments. Mobilizing such photonic systems requires the development of fully integrated, on-chip, active components at sub-micrometer wavelengths. We demonstrate heterogeneous photonic integrated circuits operating at 980 nm based on wafer-scale bonding of InGaAs quantum well active regions to tantalum pentoxide passive components. This high-yield process provides >95% surface area yield and enables integration of >1300 active components on a 76.2 mm (3 inch) silicon wafer. We present a diverse set of functions, including semiconductor optical amplifiers, Fabry-P & eacute;rot lasers, and distributed feedback lasers with a 43 dB side-mode suppression ratio and a >250 GHz single-mode tuning range. We test the precise wavelength control and system-level functionality of the on-chip lasers by pumping optical parametric oscillation processes in microring resonators fabricated on the same platform, generating short-wavelength signals at 778 nm and 752 nm. These results provide a pathway to realize fully functional integrated photonic engines for the operation of compact quantum sensors based on atomic and trapped-ion systems. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Efficient down-conversion in InGaP-on-silicon waveguides enables single-photon conversion from 930 nm to 1550 nm (C-band), advancing scalable, CMOS-compatible quantum communication and sensing from quantum dots. This integration showcases a promising approach for high-performance, monolithically integrated quantum frequency converters in photonic platforms.

Integrated coherent mid-infrared (mid-IR) sources are crucial for spectroscopy and quantum frequency conversion (QFC) to facilitate scalable fiber-based application of single photons. Direct mid-IR emission with broad tunability poses fundamental challenges from the gain media and mirror components. This paper presents a characterization of a second-order nonlinear platform. It showcases a mid-IR parametric coherent source with a continuous tuning range exceeding 230 nm centered around 2425 nm, achieved through difference-frequency generation (DFG). The nonlinear coefficient d 14 of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) on insulator is experimentally determined via second-harmonic generation (SHG) in waveguides of various lengths, and the tolerance of the process is investigated. These materials are explored for their high conversion efficiency, utilizing monolithic epitaxial quantum dots and integrated waveguides for QFC. The results demonstrate efficient and tunable mid-IR emission suitable for compact, scalable quantum emitters, with applications in environmental and health monitoring. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

We present distributed feedback (DFB) diode lasers heterogeneously integrated with tantalum pentoxide (Ta2O5/tantala) waveguides. DFB gratings etched in tantala waveguides provide the necessary feedback for single mode lasing with 43 dB side mode suppression ratio.

We present on-chip distributed feedback (DFB) diode lasers monolithically integrated on tantalum pentoxide (tantala) integrated photonic circuits. The DFB grating etched in tantala waveguides provide the necessary feedback for single mode lasing around 980 nm with 43 dB side mode suppression ratio and 300 GHz continuous mode-hop free tuning.

Far-UVC light in the wavelength range of 200-230 nm has attracted renewed interest because of its safety for human exposure and effectiveness in inactivating pathogens. Here we present a compact solid-state far-UVC laser source based on second-harmonic generation (SHG) using a low-cost commercially-available blue laser diode pump. Leveraging the high intensity of light in a nanophotonic waveguide and heterogeneous integration, our approach achieves Cherenkov phase-matching across a bonded interface consisting of a silicon nitride (SiN) waveguide and a beta barium borate (BBO) nonlinear crystal. Through systematic investigations of waveguide dimensions and pump power, we analyze the dependencies of Cherenkov emission angle, conversion efficiency, and output power. Experimental results confirm the feasibility of generating far-UVC, paving the way for mass production in a compact form factor. This solid-state far-UVC laser source shows significant potential for applications in human-safe disinfection, non-line-of-sight free-space communication, and deep-UV Raman spectroscopy.

An alternative method for characterizing optical propagation in photonic integrated circuits based on imaging of scattered light is presented and demonstrated for the spectral range of 450-980 nm. The method is applied to waveguide structures of varying widths and is found to be independent of the input coupling. Propagation losses as low as 1.4 dB/cm are measured for spiral alumina waveguides. Using a tunable laser the optical losses are also determined for AlGaAs-on-insulator waveguides at 910-980 nm wavelengths and are compared to cut-back measurements. An open-source toolbox is introduced, allowing for reliable processing of data and estimation of optical propagation losses.

Integrated coherent sources in the mid-infrared (mid-IR) are essential for spectroscopy and quantum frequency conversion (QFC) of single photons to enable their use in fiber-based applications. Direct emission in the mid-IR is limited and requires complex fabrication and large power consumption. Here, a mid-IR laser is demonstrated with a continuous tuning range of >80 nm centered around 2360 nm, through difference-frequency generation (DFG). The nonlinear coefficient d₁₄ of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) on insulator is measured for the first time using second-harmonic generation (SHG) in waveguides with various lengths. These platforms are discussed to obtain a high conversion efficiency for tunable single photon emitters using monolithic epitaxial quantum dots and integrated waveguides for QFC.

The foundations of nonlinear optics are revisited, and the formalism is applied to waveguide modes. The effect of loss and dispersion are included rigorously along with the vectorial nature of the modes, and a new version of the nonlinear Schrödinger (NLS) equation is derived. This leads to more general expressions for the group index, for the group-index dispersion (GVD), and for the Kerr coefficient. These quantities are essential for the design of waveguides suitable for e.g. the generation of optical frequency combs and all-optical switches. Examples are given using the silicon nitride material platform. Specifically, values are extracted for the coefficients of the chi-3 tensor based on measurements of Kerr coefficients and mode simulations.

We present a Fabry-Perot diode laser heterogeneously integrated with tantalum pentoxide (Ta2O5/tantala) waveguides on a silicon substrate. Devices with etched facet and tantala loop mirrors, and of varying lengths and widths, are characterized.

Direct optical bonding of InGaP on silica is presented with a fabricated design allowing for efficient second-order nonlinear interactions. The design targets down-conversion to 1550 nm from InAs/GaAs quantum dots emitting single-photons near 930 nm. Measurements of propagation losses favorably compare with competing III-V materials.

We demonstrate spontaneous parametric downconversion in straight GaAs and AlGaAs-on-insulator waveguides, which yield a maximum pair generation rate of 1.2 × 10 10 s −1 mW −1 , normalized to the pump power. The joint spectral intensity is directly measured via time-of-flight spectroscopy.

We present the far-field angular distribution of a laser that emits near 222-nm wavelength. This laser is produced by second-harmonic generation of a blue laser diode and based on heterogeneous integration of barium borate on a silicon nitride waveguide.