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  1. Abstract

    The development of integrated semiconductor lasers has miniaturized traditional bulky laser systems, enabling a wide range of photonic applications. A progression from pure III-V based lasers to III-V/external cavity structures has harnessed low-loss waveguides in different material systems, leading to significant improvements in laser coherence and stability. Despite these successes, however, key functions remain absent. In this work, we address a critical missing function by integrating the Pockels effect into a semiconductor laser. Using a hybrid integrated III-V/Lithium Niobate structure, we demonstrate several essential capabilities that have not existed in previous integrated lasers. These include a record-high frequency modulation speed of 2 exahertz/s (2.0 × 1018Hz/s) and fast switching at 50 MHz, both of which are made possible by integration of the electro-optic effect. Moreover, the device co-lases at infrared and visible frequencies via the second-harmonic frequency conversion process, the first such integrated multi-color laser. Combined with its narrow linewidth and wide tunability, this new type of integrated laser holds promise for many applications including LiDAR, microwave photonics, atomic physics, and AR/VR.

  2. Abstract

    Modern advanced photonic integrated circuits require dense integration of high-speed electro-optic functional elements on a compact chip that consumes only moderate power. Energy efficiency, operation speed, and device dimension are thus crucial metrics underlying almost all current developments of photonic signal processing units. Recently, thin-film lithium niobate (LN) emerges as a promising platform for photonic integrated circuits. Here, we make an important step towards miniaturizing functional components on this platform, reporting high-speed LN electro-optic modulators, based upon photonic crystal nanobeam resonators. The devices exhibit a significant tuning efficiency up to 1.98 GHz V−1, a broad modulation bandwidth of 17.5 GHz, while with a tiny electro-optic modal volume of only 0.58μm3. The modulators enable efficient electro-optic driving of high-Q photonic cavity modes in both adiabatic and non-adiabatic regimes, and allow us to achieve electro-optic switching at 11 Gb s−1with a bit-switching energy as low as 22 fJ. The demonstration of energy efficient and high-speed electro-optic modulation at the wavelength scale paves a crucial foundation for realizing large-scale LN photonic integrated circuits that are of immense importance for broad applications in data communication, microwave photonics, and quantum photonics.

  3. 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.

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  4. High-fidelity periodic poling over long lengths is required for robust, quasi-phase-matched second-harmonic generation using the fundamental, quasi-TE polarized waveguide modes in a thin-film lithium niobate (TFLN) waveguide. Here, a shallow-etched ridge waveguide is fabricated in x-cut magnesium oxide doped TFLN and is poled accurately over 5 mm. The high fidelity of the poling is demonstrated over long lengths using a non-destructive technique of confocal scanning second-harmonic microscopy. We report a second-harmonic conversion efficiency of up to 939 %.W−1(length-normalized conversion efficiency 3757 %.W−1.cm−2), measured at telecommunications wavelengths. The device demonstrates a narrow spectral linewidth (1 nm) and can be tuned precisely with a tuning characteristic of 0.1 nm/°C, over at least 40 °C without measurable loss of efficiency.

  5. Abstract

    Many technologies emerging from quantum information science heavily rely upon the generation and manipulation of entangled quantum states. Here, we propose and demonstrate a new class of quantum interference phenomena that arise when states are created in and coherently converted between the propagating modes of an optical microcavity. The modal coupling introduces several new creation pathways to a nonlinear optical process within the device, which quantum mechanically interfere to drive the system between states in the time domain. The coherent conversion entangles the generated biphotons between propagation pathways, leading to cyclically evolving path-entanglement and the manifestation of coherent oscillations in second-order temporal correlations. Furthermore, the rich device physics is harnessed to tune properties of the quantum states. In particular, we show that the strength of interference between pathways can be coherently controlled, allowing for manipulation of the degree of entanglement, which can even be entirely quenched. The states can likewise be made to flip-flop between exhibiting initially correlated or uncorrelated behavior. The phenomena presented here open a route to creating higher dimensional entanglement and exotic multi-photon states.

  6. We report cavity-enhanced second-harmonic generation and difference-frequency generation in a high-Q lithium niobate microring resonator with modal phase matching. The second-harmonic generation efficiency is measured to be 1,500% W􀀀1.