More Like this

1. Lithium niobate photonics: Unlocking the electromagnetic spectrum

   https://doi.org/10.1126/science.abj4396  

   Boes, Andreas ; Chang, Lin ; Langrock, Carsten ; Yu, Mengjie ; Zhang, Mian ; Lin, Qiang ; Lončar, Marko ; Fejer, Martin ; Bowers, John ; Mitchell, Arnan ( January 2023 , Science)

   BACKGROUND Electromagnetic (EM) waves underpin modern society in profound ways. They are used to carry information, enabling broadcast radio and television, mobile telecommunications, and ubiquitous access to data networks through Wi-Fi and form the backbone of our modern broadband internet through optical fibers. In fundamental physics, EM waves serve as an invaluable tool to probe objects from cosmic to atomic scales. For example, the Laser Interferometer Gravitational-Wave Observatory and atomic clocks, which are some of the most precise human-made instruments in the world, rely on EM waves to reach unprecedented accuracies. This has motivated decades of research to develop coherent EM sources over broad spectral ranges with impressive results: Frequencies in the range of tens of gigahertz (radio and microwave regimes) can readily be generated by electronic oscillators. Resonant tunneling diodes enable the generation of millimeter (mm) and terahertz (THz) waves, which span from tens of gigahertz to a few terahertz. At even higher frequencies, up to the petahertz level, which are usually defined as optical frequencies, coherent waves can be generated by solid-state and gas lasers. However, these approaches often suffer from narrow spectral bandwidths, because they usually rely on well-defined energy states of specific materials, which results inmore »a rather limited spectral coverage. To overcome this limitation, nonlinear frequency-mixing strategies have been developed. These approaches shift the complexity from the EM source to nonresonant-based material effects. Particularly in the optical regime, a wealth of materials exist that support effects that are suitable for frequency mixing. Over the past two decades, the idea of manipulating these materials to form guiding structures (waveguides) has provided improvements in efficiency, miniaturization, and production scale and cost and has been widely implemented for diverse applications. ADVANCES Lithium niobate, a crystal that was first grown in 1949, is a particularly attractive photonic material for frequency mixing because of its favorable material properties. Bulk lithium niobate crystals and weakly confining waveguides have been used for decades for accessing different parts of the EM spectrum, from gigahertz to petahertz frequencies. Now, this material is experiencing renewed interest owing to the commercial availability of thin-film lithium niobate (TFLN). This integrated photonic material platform enables tight mode confinement, which results in frequency-mixing efficiency improvements by orders of magnitude while at the same time offering additional degrees of freedom for engineering the optical properties by using approaches such as dispersion engineering. Importantly, the large refractive index contrast of TFLN enables, for the first time, the realization of lithium niobate–based photonic integrated circuits on a wafer scale. OUTLOOK The broad spectral coverage, ultralow power requirements, and flexibilities of lithium niobate photonics in EM wave generation provides a large toolset to explore new device functionalities. Furthermore, the adoption of lithium niobate–integrated photonics in foundries is a promising approach to miniaturize essential bench-top optical systems using wafer scale production. Heterogeneous integration of active materials with lithium niobate has the potential to create integrated photonic circuits with rich functionalities. Applications such as high-speed communications, scalable quantum computing, artificial intelligence and neuromorphic computing, and compact optical clocks for satellites and precision sensing are expected to particularly benefit from these advances and provide a wealth of opportunities for commercial exploration. Also, bulk crystals and weakly confining waveguides in lithium niobate are expected to keep playing a crucial role in the near future because of their advantages in high-power and loss-sensitive quantum optics applications. As such, lithium niobate photonics holds great promise for unlocking the EM spectrum and reshaping information technologies for our society in the future. Lithium niobate spectral coverage. The EM spectral range and processes for generating EM frequencies when using lithium niobate (LN) for frequency mixing. AO, acousto-optic; AOM, acousto-optic modulation; χ (2) , second-order nonlinearity; χ (3) , third-order nonlinearity; EO, electro-optic; EOM, electro-optic modulation; HHG, high-harmonic generation; IR, infrared; OFC, optical frequency comb; OPO, optical paramedic oscillator; OR, optical rectification; SCG, supercontinuum generation; SHG, second-harmonic generation; UV, ultraviolet.« less
2. Degenerate optical parametric amplification in CMOS silicon

   https://doi.org/10.1364/OPTICA.478702  

   Heydari, David ; Cătuneanu, Mircea ; Ng, Edwin ; Gray, Dodd J. ; Hamerly, Ryan ; Mishra, Jatadhari ; Jankowski, Marc ; Fejer, M. M. ; Jamshidi, Kambiz ; Mabuchi, Hideo ( March 2023 , Optica)

   Silicon is a common material for photonics due to its favorable optical properties in the telecom and mid-wave IR bands, as well as compatibility with a wide range of complementary metal–oxide semiconductor (CMOS) foundry processes. Crystalline inversion symmetry precludes silicon from natively exhibiting second-order nonlinear optical processes. In this work, we build on recent works in silicon photonics that break this material symmetry using large bias fields, thereby enablingχ⁽²⁾interactions. Using this approach, we demonstrate both second-harmonic generation (with a normalized efficiency of 0.20%W⁻¹cm⁻²) and, to our knowledge, the first degenerateχ⁽²⁾optical parametric amplifier (with an estimated normalized gain of 0.6dBW^−1/2cm⁻¹) using silicon-on-insulator waveguides fabricated in a CMOS-compatible commercial foundry. We expect this technology to enable the integration of novel nonlinear optical devices such as optical parametric amplifiers, oscillators, and frequency converters into large-scale, hybrid photonic–electronic systems by leveraging the extensive ecosystem of CMOS fabrication.
3. InGaP quantum nanophotonic integrated circuits with 1.5% nonlinearity-to-loss ratio

   https://doi.org/10.1364/OPTICA.440383  

   Zhao, Mengdi ; Fang, Kejie ( February 2022 , Optica)

   Optical nonlinearity plays a pivotal role in quantum information processing using photons, from heralded single-photon sources and coherent wavelength conversion to long-sought quantum repeaters. Despite the availability of strong dipole coupling to quantum emitters, achieving strong bulk optical nonlinearity is highly desirable. Here, we realize quantum nanophotonic integrated circuits in thin-film InGaP with, to our knowledge, a record-high ratio of$1.5\mathrm{\%<\#comment/>}$between the single-photon nonlinear coupling rate ($g/2\mathrm{\pi <\#comment/>}=11.2\mathrm{M}\mathrm{H}\mathrm{z}$) and cavity-photon loss rate. We demonstrate second-harmonic generation with an efficiency of$71200\pm <\#comment/>10300\mathrm{\%<\#comment/>}/\mathrm{W}$in the InGaP photonic circuit and photon-pair generation via degenerate spontaneous parametric downconversion with an ultrahigh rate exceeding 27.5 MHz/µW—an order of magnitude improvement of the state of the art—and a large coincidence-to-accidental ratio up to$1.4\times <\#comment/>{10}^4$. Our work shows InGaP as a potentially transcending platform for quantum nonlinear optics and quantum information applications.
4. Athermal lithium niobate microresonator

   https://doi.org/10.1364/OE.398363  

   Ling, Jingwei ; He, Yang ; Luo, Rui ; Li, Mingxiao ; Liang, Hanxiao ; Lin, Qiang ( July 2020 , Optics Express)

   Lithium niobate (LN), possessing wide transparent window, strong electro-optic effect, and large optical nonlinearity, is an ideal material platform for integrated photonics application. Microring resonators are particularly suitable as integrated photonic components, given their flexibility of device engineering and their potential for large-scale integration. However, the susceptibility to temperature fluctuation has become a major challenge for their implementation in a practical environment. Here, we demonstrate an athermal LN microring resonator. By cladding an x-cut LN microring resonator with a thin layer of titanium oxide, we are able to completely eliminate the first-order thermo-optic coefficient (TOC) of cavity resonance right at room temperature (20^°C), leaving only a small residual quadratic temperature dependence with a second-order TOC of only 0.37 pm/K². It corresponds to a temperature-induced resonance wavelength shift within 0.33 nm over a large operating temperature range of (−10 – 50)^°C that is one order of magnitude smaller than a bare LN microring resonator. Moreover, the TiO₂-cladded LN microring resonator is able to preserve high optical quality, with an intrinsic optical Q of 5.8 × 10⁵that is only about 11% smaller than that of a bare LN resonator. The flexibility of thermo-optic engineering, high optical quality, and device fabrication compatibility show great promisemore »of athermal LN/TiO₂hybrid devices for practical applications, elevating the potential importance of LN photonic integrated circuits for future communication, sensing, nonlinear and quantum photonics.

   « less
5. Optical parametric oscillation in silicon carbide nanophotonics

   https://doi.org/10.1364/OPTICA.394138  

   Guidry, Melissa A. ; Yang, Ki Youl ; Lukin, Daniil M. ; Markosyan, Ashot ; Yang, Joshua ; Fejer, Martin M. ; Vučković, Jelena ( September 2020 , Optica)

   Silicon carbide (SiC) is rapidly emerging as a leading platform for the implementation of nonlinear and quantum photonics. Here, we find that commercial SiC, which hosts a variety of spin qubits, possesses low optical absorption that can enable SiC integrated photonics with quality factors exceeding${10}^7$. We fabricate multimode microring resonators with quality factors as high as 1.1 million, and observe low-threshold ($8.5\pm <\#comment/>0.5\mathrm{m}\mathrm{W}$) optical parametric oscillation using the fundamental mode as well as optical microcombs spanning 200 nm using a higher-order mode. Our demonstration is an essential milestone in the development of photonic devices that harness the unique optical properties of SiC, paving the way toward the monolithic integration of nonlinear photonics with spin-based quantum technologies.