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Integrated photonics research publications

On this page you can explore peer-reviewed papers published by our Group of Integrated Photonics.

Feel free to check out as well our students' theses, read more about opportunities for students, or learn about our research activities.

2025 | 2024 | 2023 | 2022 | 2021 | 2020 | ACCESS

2025

"Platform-Dependent Feasibility of All-Optical Switching in Photonic Integrated Circuits"

by Pedro Godoy et al.

"Second-order nonlinear frequency conversion in InGaP-on-insulator waveguides"

by Lucas Ahler et al.

  • How can we generate new wavelengths of light on a chip? This work demonstrates sum- and difference-frequency generation in InGaP-on-insulator waveguides, achieving efficient conversion between 930 nm, 1550 nm, and 2325 nm. By leveraging the strong nonlinear properties of InGaP in a silicon-compatible platform, this research advances integrated photonics for applications in quantum frequency conversion and broadband infrared light generation. These results highlight how nanofabrication, optical engineering, and nonlinear optics come together to develop next-generation photonic technologies, opening new opportunities for research in chip-scale light sources and quantum photonics.
    Published in Optics Letters. Also available in Optica Open.
    [PDF]

"Broadly tunable and robust UV laser generation on a chip"

by Asger Brimnes Gardner et al.

  • A cutting-edge photonic platform has been developed for compact ultraviolet (UV) light generation, spanning an impressive wavelength range of 222–319 nm. By integrating silicon nitride waveguides with barium borate cladding, this approach addresses challenges in tunability, fabrication tolerance, and scalability. Using Čerenkov nonlinear frequency conversion, the platform opens doors to impactful applications such as quantum technologies, pathogen disinfection, and advanced optical communication. This work represents a significant advance in integrated photonics, showcasing the exciting possibilities of UV light in modern technology.
    Published in Optics Express.
    [PDF]

"High-efficiency InGaP-on-silicon frequency downconversion for quantum communication applications at 1550 nm"

by Lucas Ahler et al.

"Polarization-controlled dual-cavity optical feedback for ultra-narrow linewidth and wide C-band tunability in an SG-DBR laser"

by Jeppe Surrow et al.

  • Presented at the SPIE Optics + Optoelectronics Conference in Prague, this talk highlights a semiconductor laser design achieving both sub-100 Hz linewidth and 42 nm tunability across the C-band. By carefully controlling the polarization of the optical feedback, the laser remains stable even in regimes where coherence collapse would typically occur. This approach offers a scalable solution for compact, low-noise lasers suited for quantum applications, LiDAR, and coherent optical communication.
    [PDF]

"Ultra-narrow linewidth laser across the C-band using polarization-controlled dual-cavity feedback"

by Jeppe Surrow, Simon Thomsen et al.

  • This research presents a semiconductor laser with an ultra-narrow linewidth and broad tunability across the C-band. By utilizing polarization-controlled external optical feedback, the laser achieves a significant reduction in linewidth—from MHz to sub-kHz—while avoiding coherence collapse. This breakthrough opens up new possibilities for applications in fields like coherent optical communications and precision spectroscopy, offering a powerful solution for systems requiring both high tunability and ultra-narrow linewidths. By overcoming previous limitations in laser stability, this approach enables the development of more reliable and scalable photonic technologies.
    Published in Optics Express.
    [PDF]

2024

"Widely tunable integrated GaAs and AlGaAs platforms for efficient second-order frequency conversion"

by Emil Zanchetta Ulsig, Magnus Madsen et al.

  • This paper discussed integrated coherent sources in the mid-infrared (mid-IR) which 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.
    Published in Optics Express.
    [PDF]

"Open-source toolbox for photographic characterization of optical propagation"

by Simon Ragner Sørensen et al.

  • Photonic integrated circuits (PICs) are vital for advancing compact and scalable optical systems, but accurately characterizing optical losses before commercialization is essential. Traditional methods like optical backscatter reflectometry (OBR) are effective but require specialized telecom equipment. This paper published in Optics Letters introduces the top-down method as a versatile alternative, utilizing standard CMOS cameras to detect light scattering and measure optical propagation losses in various waveguides. Demonstrated on AlGaAs and alumina platforms, this method covers a spectral range of 450–980 nm and integrates easily into existing setups. The open-source analysis tool and straightforward implementation make it a cost-effective solution, providing comparable accuracy to established techniques like the cut-back method and Fabry-Perot interferometers while also enabling nonlinear effect detection such as sum-frequency generation.
    [PDF] also in Optica Open

"Nonlinear Schrödinger equation for integrated photonics"

by Kevin Bach Gravesen et al.

  • The nonlinear Schrödinger (NLS) equation has been pivotal in photonics, offering profound insights into light behavior in nonlinear optical media. This paper published in the Journal of the Optical Society of America B presents a novel derivation of the NLS equation from Maxwell’s equations, focusing on degenerate four-wave mixing without assuming plane-wave approximations or neglecting field polarization. This comprehensive model is applicable to various waveguides, especially heterogeneous structures, and leads to a precise expression for the optical Kerr effect based on optical power rather than intensity, which is crucial for integrated photonics. By rigorously deriving the Kerr coefficient and group index, this study provides a robust tool for designing advanced photonic devices, enhancing the accuracy of nonlinear phase shift predictions and facilitating innovations in optical communications and frequency synthesis.
    [PDF]

"Low-kappa DBR grating filters on an InP generic photonic integration foundry platform"

by Rakesh Ranjan Kumar et al.

  • Integrated distributed Bragg reflector (DBR) gratings are crucial for enhancing photonic technologies, which include optical communications, sensing, and single-mode lasers. Improving DBR performance, specifically by narrowing the grating filter bandwidth, is essential to achieve better laser linewidths and higher single-mode power. While fiber-based grating filters benefit from attributes like long length and low loss, integrated DBR filters face challenges due to fabrication non-uniformities. This study published in the Journal of the Optical Society of America B proposes using indium phosphide (InP)-based DBR gratings to achieve narrow bandwidths by adjusting the corrugation widths within a rib-waveguide. Experimental results demonstrated achieving bandwidths as narrow as 0.68 nm, offering significant advancements in photonic integrated circuits by providing a scalable solution with low propagation loss. This method holds promise for creating narrow-linewidth lasers, vital for emerging photonic technologies.
    [PDF]

"Continuous-wave second-harmonic generation in the far-UVC pumped by a blue laser diode"

by Eric J. Stanton, Peter Tønning, Emil Z. Ulsig et al.

  • This paper published in Scientific Reports presents the development of a compact, solid-state far-UVC laser source leveraging a chip-scale pump laser and advanced nonlinear materials. By optimizing Cherenkov phase-matching in a silicon nitride (SiN) waveguide bonded to a beta barium borate (BBO) crystal, the device efficiently converts blue laser light to far-UVC wavelengths. The robust design allows for high-yield production and broad wavelength tunability, with potential applications in disinfection, non-line-of-sight communication, and Raman spectroscopy. This innovative approach not only reduces the size and cost of far-UVC lasers but also opens up new possibilities for their widespread use in various scientific and industrial fields.
    [PDF]

2023

"Frequency noise measurements using coherent self-heterodyne detection"

by Simon Thorndahl Thomsen et al.

  • Published in Optics Letters, this paper demonstrates a refined way to extract the frequency noise (FN) spectrum of lasers by tailoring the delay in a conventional delayed self-heterodyne setup to sub-coherence lengths. The method achieves direct proportionality between electrical spectrum analyzer traces and the FN spectrum, which provide the intrinsic linewidth of the lasers. This proposed method is validated by comparing the FN spectrum with that obtained from a commercial frequency noise analyzer. The method provides a cost-effective alternative for FN measurements, which also requires minimal post-processing as compared to the state-of-the-art.
    [PDF]

"Efficient and robust second-harmonic generation in thin-film lithium niobate using modal phase matching"

by Mikkel T. Hansen et al.

  • Published in Frontiers in Photonics, this paper reports on a design of a double-ridge waveguide for efficient and robust second-harmonic generation (SHG) using the thin-film lithium-niobate-on-insulator (LNOI) platform. Perfect phase matching (PhM) is achieved between the fundamental waveguide mode at 1,550 nm and a higher-order mode at the second harmonic. The fabrication tolerances of the PhM condition are simulated using a finite-difference method mode solver, and conversion efficiencies as high as 3.92 W−1 are obtained for a 1-cm long waveguide. This design allows access to the largest element of the second-order nonlinear susceptibility tensor, and represents a scalable alternative to waveguides based on periodically-poled lithium niobate (PPLN). The design has the potential for generating pairs of entangled photons in the infrared C-band by spontaneous parametric down-conversion (SPDC).
    [PDF]

"Single-photon downconversion in GaAs, AlGaAs and InGaP-on-insulator"

by Emil Zanchetta Ulsig et al.

  • Published in the IEEE Photonics Conference, this paper proposes a design for second-order sum, difference, and spontaneous parametric conversion from InGaP-on-insulator waveguides. Experimental results of these nonlinear effects are measured from similar integrated waveguides in AlGaAs- and GaAs-on-insulator, highlighting the strengths of each platform and the prospects of implementing with InGaP-on-insulator.
    [PDF]

"Deterministic photon source interfaced with a programmable silicon-nitride integrated circuit"

by Ying Wang et al.

  • Published in npj Quantum Information, this paper presents a breakthrough in quantum information technology by demonstrating the integration of a deterministic photon source with a programmable silicon-nitride photonic circuit. This integration is pivotal for scalable quantum networks and quantum computing. Single-photon generation is successfully combined with an advanced photonic chip, enhancing the control and manipulation of quantum states at the photon level. This development opens new avenues for high-fidelity quantum information processing and secure communication systems, marking a significant step towards practical quantum technologies.
    [PDF]

"Mid-infrared difference-frequency generation in AlGaAs-on-insulator waveguides"

by Magnus Linnet Madsen et al.

  • Mid-infrared (MIR) lasers are pivotal in environmental monitoring, industrial gas sensing, free-space telecommunication, and defense applications due to their unique absorption characteristics in the 1.4-10 µm range. This paper published in the Journal of the Optical Society of America B explores the design and simulation of a novel AlGaAs-on-silicon waveguide for efficient difference-frequency generation (DFG) at 2.3 µm. Using a tunable pump in the near-infrared and a tunable idler in the C-band, the waveguide achieves perfect phase matching through form birefringence, resulting in high nonlinear conversion efficiencies. The proposed waveguide, with optimized dimensions, promises a significant signal output power and a wide tunable range, advancing the potential for compact and versatile MIR light sources.
    [PDF]

2022

"Analysis and design of low-loss and fast all-optical switch elements on silicon nitride for integrated quantum photonics"

by Fabian Ruf et al.

  • This paper published in the Journal of Lightwave Technology presents groundbreaking advancements in the design of ultra-fast, low-loss all-optical switches on silicon nitride, essential for integrated single-photon applications. Using a novel traveling-wave model, it meticulously analyzes two ring resonator-based switches, highlighting their potential in achieving near-perfect signal transmission with minimal energy requirements. The study showcases innovative solutions like chirped Gaussian pulses to enhance performance, and offers a comprehensive framework for future development, promising significant strides in quantum computing and photonic networks with insertion losses as low as 0.1 dB.
    [PDF]

"Integration of GaAs waveguides on a silicon substrate for quantum photonic circuits"

by Atefeh Shadmani et al.

  • This paper published in Optics Express presents a breakthrough in quantum photonic integrated circuits (QPICs) by demonstrating GaAs waveguides with embedded quantum dots on a silicon substrate. Utilizing a novel adhesive bonding technique, high-quality fabrication is achieved, preserving excellent optical properties and single-photon emission capabilities. This integration not only maintains low-noise, high-efficiency photon generation but also opens the door to combining GaAs technology with various photonic platforms, marking a significant step towards scalable and hybrid QPICs for advanced quantum applications.
    [PDF]

"Efficient low threshold frequency conversion in AlGaAs-on-insulator waveguides"

by Emil Ulsig et al.

  • The paper published in Frontiers in Photonics explores the design and optimization of a novel single-photon source for quantum applications using difference frequency generation (DFG) in zinc-blende materials, specifically focusing on AlGaAs. Aimed at converting single-photons emitted by indium arsenide (InAs) quantum dots at 930 nm to the telecom C-band at 1550 nm, the study highlights the advantages of AlGaAs over conventional lithium niobate (LN) due to its higher second-order nonlinearity and better optical confinement. By integrating III-V materials on silica with a silicon substrate, the proposed design significantly enhances conversion efficiency, essential for large-scale quantum networks. Detailed simulations demonstrate efficient phase-matching and high conversion efficiency with relatively low optical power and short waveguide lengths, marking a substantial advancement in the development of practical, integrated quantum photonic devices.
    [PDF]

"Ultralow-linewidth ring laser using hybrid integration and generic foundry platforms"

by Mónica Far Brusatori, Daniel N. Duplat, Iterio Degli-Eredi, et al.

"A 10-kHz intrinsic linewidth coupled extended-cavity DBR laser monolithically integrated on an InP platform"

by Rakesh Ranjan Kumar, Andreas Hänsel, Mónica Far Brusatori, et al.

"Dynamics of semiconductor lasers under external optical feedback from both sides of the laser cavity"

by Mónica Far Brusatori, et al.

"Sikre UV-lamper har et væld af anvendelser"

by Emil Ulsig and Peter Tønning

  • The COVID-19 pandemic underscored the importance of sanitizing surfaces and wearing masks, but are these methods still the best? According to this Medicoteknik publication, an innovative approach using ultraviolet light offers ultraviolet light presents a promising alternative for disinfecting both surfaces and air. Traditional UV light at 254 nm effectively neutralizes pathogens but is harmful to humans. However, "Far-UVC" light, operating at 200-230 nm, offers a safe solution. This technology, using krypton chloride excimer lamps to emit light at 222 nm, can disinfect spaces while people are present. Developed by Aarhus-based UV Medico, Far-UVC lamps have been installed in hospitals, workplaces, and public spaces, proving effective in reducing the spread of infectious diseases without harming human health. This innovation could significantly mitigate the transmission of current and future pathogens, including common illnesses like flu and colds.
    [PDF]

2021

"TBC"

by TBC et al.

  • Published in TBC, this paper TBC
     

2020

"Efficient second harmonic generation in nanophotonic GaAs-on-insulator waveguides"

by Eric J. Stanton, Jeff Chiles, et al.

"Chip-based soliton microcomb module using a hybrid semiconductor laser"

by Arslan S. Raja, Junqiu Liu, et al.

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Revised 25.06.2025