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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 0.58 μ m 3 . 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 −1 with 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. Lithium niobate (LN) devices are promising for future photonic integrated circuits. Here, the authors demonstrate an electro-optic LN modulator with a very small modal volume based on photonic crystal resonator architecture.

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 × 10 18 Hz/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. On-Chip integration of laser systems led to impressive development in many field of application like LIDAR or AR/VR to cite a few. Here the authors harness Pockels effect in an integrated semiconductor platform achieving fast on-chip configurability of a narrow linewidth laser.

Soliton microcombs are a promising new approach for photonic-based microwave signal synthesis. To date, however, the tuning rate has been limited in microcombs. Here, we demonstrate the first microwave-rate soliton microcomb whose repetition rate can be tuned at a high speed. By integrating an electro-optic modulation element into a lithium niobate comb microresonator, a modulation bandwidth up to 75 MHz and a continuous frequency modulation rate up to 5.0 × 10 14 Hz/s are achieved, several orders-of-magnitude faster than existing microcomb technology. The device offers a significant bandwidth of up to tens of gigahertz for locking the repetition rate to an external microwave reference, enabling both direct injection locking and feedback locking to the comb resonator itself without involving external modulation. These features are especially useful for disciplining an optical voltage-controlled oscillator to a long-term reference and the demonstrated fast repetition rate control is expected to have a profound impact on all applications of frequency combs. A microwave-rate soliton microcomb whose repetition rate can be modulated at 75 MHz. Moreover, the repetition rate can be locked to an external microwave reference by direct injection locking or feedback locking without external modulation.

Optical microcomb underpins a wide range of applications from communication, metrology, to sensing. Although extensively explored in recent years, challenges remain in key aspects of microcomb such as complex soliton initialization, low power efficiency, and limited comb reconfigurability. Here we present an on-chip microcomb laser to address these key challenges. Realized with integration between III and V gain chip and a thin-film lithium niobate (TFLN) photonic integrated circuit (PIC), the laser directly emits mode-locked microcomb on demand with robust turnkey operation inherently built in, with individual comb linewidth down to 600 Hz, whole-comb frequency tuning rate exceeding 2.4 × 10 17  Hz/s, and 100% utilization of optical power fully contributing to comb generation. The demonstrated approach unifies architecture and operation simplicity, electro-optic reconfigurability, high-speed tunability, and multifunctional capability enabled by TFLN PIC, opening up a great avenue towards on-demand generation of mode-locked microcomb that is of great potential for broad applications. Here the authors demonstrate a laser system that can directly output soliton microcombs, with high power efficiency and reconfigurability, paving the way for communication, computing, and metrology based on integrated photonics.

The invention of the laser unleashed the potential of optical metrology, leading to numerous advancements in modern science and technology. This reliance on lasers, however, also introduces a bottleneck for precision optical metrology, as it requires sophisticated photonic infrastructure for precise laser-wave control, leading to limited metrology performance and significant system complexity. Here, we take a key step toward overcoming this challenge by demonstrating a Pockels laser with multifunctional capabilities that elevate optical metrology to a new level. The chip-scale laser achieves a narrow intrinsic linewidth down to 167 Hz and a broad mode-hop-free tuning range up to 24 GHz. In particular, it delivers an unprecedented frequency chirping rate of up to 20 EHz/s and an exceptional modulation bandwidth exceeding 10 GHz, both of which are orders of magnitude greater than those of existing lasers. Leveraging this laser, we successfully achieve velocimetry at 40 m/s over a short distance of 0.4 m, and measurable velocities up to the first cosmic velocity at 1 m away—a feat unattainable with conventional ranging approaches. At the same time, we achieve distance metrology with a ranging resolution of <2 cm. Furthermore, for the first time to our knowledge, we implement a dramatically simplified architecture for laser frequency stabilization by directly locking the laser to an external reference gas cell without requiring additional external light control. This approach enables long-term laser stability with a frequency fluctuation of only ±6.5 MHz over 60 min. The demonstrated Pockels laser combines elegantly high laser coherence with ultrafast frequency reconfigurability and superior multifunctional capability. We envision its profound impact across diverse fields including communication, sensing, autonomous driving, quantum information processing, and beyond.

As unique building blocks for advancing optoelectronics, 2D semiconducting transition metal dichalcogenides have garnered significant attention. However, most previously reported MoS2 photodetectors respond only to visible light with limited absorption, resulting in a narrow spectral response and low sensitivity. Here, a surrounding homojunction MoS2 photodetector featuring localized p‐type nitrogen plasma doping on the surface of n‐type MoS2 while preserving a high‐mobility underlying channel for rapid carrier transport is engineered. The establishment of p‐n homojunction facilitates the efficient separation of photogenerated carriers, thereby boosting the device's intrinsic detection performance. The resulting photoresponsivity is 6.94 × 104 A W−1 and specific detectivity is 1.21 × 1014 Jones @ 638 nm, with an optimal light on/off ratio of ≈107 at VGS = −27 V. Notably, the introduction of additional bands within MoS2 bandgap through nitrogen doping leads to an extrinsic broadband response to short‐wave infrared. The device exhibits a photoresponsivity of 34 A W−1 and a specific detectivity of up to 5.92 × 1010 Jones @ 1550 nm. Furthermore, the high‐performance broadband response is further demonstrated through imaging and integration with waveguides, paving the way for next generation of multifunctional imaging systems and high‐performance photonic chips. A surrounding homojunction MoS2 photodetector featuring a localized p‐type nitrogen plasma doping region and an underlying high‐mobility channel is engineered. This design boosts the efficient separation and collection of photogenerated carriers. Moreover, doing‐induced bands within the bandgap of MoS2 enables an extrinsic broadband response to short‐wave infrared, paving the way for next‐generation multifunctional imaging systems and high‐performance photonic chips.

An efficient simulator for quantum systems is one of the original goals for the efforts to develop a quantum computer. In recent years, synthetic dimensions in photonics have emerged as a potentially powerful approach for simulation that is free from the constraint of geometric dimensionality. Here we demonstrate a quantum-correlated synthetic crystal that is based on a coherently controlled broadband quantum frequency comb produced in a chip-scale, dynamically modulated lithium niobate microresonator. The time–frequency entanglement inherent with the comb modes greatly extends the dimensionality of the synthetic space, creating a massive, nearly 400 × 400 synthetic lattice with electrically controlled tunability. With such a system, we are able to utilize the evolution of quantum correlations between entangled photons to perform a series of simulations, demonstrating quantum random walks, Bloch oscillations and multilevel Rabi oscillations in the time and frequency correlation space (demonstrated in a 5 × 5 mode subspace). The device combines the simplicity of monolithic nanophotonic architecture, high dimensionality of a quantum-correlated synthetic space and on-chip coherent control, which opens up an avenue towards chip-scale implementation of large-scale analogue quantum simulation and computation in the time–frequency domain.A special-purpose quantum simulator, based on a coherently controlled broadband quantum frequency comb produced in a chip-scale dynamically modulated monolithic lithium niobate microresonator, is demonstrated, opening paths for chip-scale implementation of large-scale analogue quantum simulation and computation in the time–frequency domain.

Since the invention of Lithium Niobate(LN) crystal, it has been one of the most commonly used optical material, serve commonly as a bridge between the electronics and optics. Due to the broad transmission window, large electro-optical coefficient, strong nonlinearity and significant piezo-electric response, this material has attracted attentions from various fields in the last few decades, including optical communication, RF photonics, optomechanics, nonlinear optics, quantum photonics and so on, which have given rise to a large variety of applications. However, the attempts to integrate such material on-chip turn out to be unsuccessful until recent years, when people find ways to direct etch the thin film lithium niobate. The ion plasma etching method defines LN waveguide with the high confinement of optical mode and low optical loss, greatly reduce the footprint of LN based products, as well as the energy consumption, optical loss and costs of single device. Meanwhile, the enhanced optical field density, enlarged surfaces effects, and also the engineerability unique for photonics devices also enables the discovery of new physics and the rise of new applications on the lithium niobate on insulator (LNOI) platform. In this thesis, some of the our recent progresses on LNOI will be introduced. Material property of TFLN (thin film Lithium Niobate) have be investigated, ranging from thermal property, electro-optics, photo-refraction to χ (2) and χ (3) nonlinearity; which give rise to new techniques and applications including thermal-invariant devices, on-chip broad-band photon source, followed by high efficient frequency converter, Pockels laser and comb laser. These new techniques, with high efficiency, low consumption of power, and full compatibility with other on-chip component including EO device, lasers, detectors, acoustic-optics components and other non-source devices, are ready for full integration of new generation of electrical/photonics hybrid system. Thanks to the nonlinearity of the LN, LNOI PIC (photonics integrated circuit) serves as a link between different optical band and between optics and electronics, paves a brand new way for photonics research and industry, and opens a door for applications which are previously inaccessible.

Deep-level transient spectroscopy (DLTS) is a widely used method to analyze the properties of deep defects in semiconductors. However, it has been rarely reported to measure the deep-levels of highly-doped silicon because the large leakage current badly affects the transient capacitance signal of DLTS technique, due to the trap occupancy dominated by thermal emission instead of capture of carriers. Herein, by employing an asymmetric structure to reduce leakage current, we observed two deep-level defect states of highly phosphorus-doped silicon (7 × 10 17  cm −3 ) in the DLTS spectrum, corresponding to the E -center (vacancy-P trap) and doubly negative charged states. Furthermore, the photocurrent spectrum of the sample under 4 K shows two mid-infrared response peaks, arising from the photoexcitation behavior of the above two defects. This finding provides a new route to measure the deep-level defect properties of highly-doped semiconductor materials using DLTS method. It also suggests potential applications of photoexcitation activity of defects in photoelectric detection.

As unique building blocks for advancing optoelectronics, 2D semiconducting transition metal dichalcogenides have garnered significant attention. However, most previously reported MoS 2 photodetectors respond only to visible light with limited absorption, resulting in a narrow spectral response and low sensitivity. Here, a surrounding homojunction MoS 2 photodetector featuring localized p‐type nitrogen plasma doping on the surface of n‐type MoS 2 while preserving a high‐mobility underlying channel for rapid carrier transport is engineered. The establishment of p‐n homojunction facilitates the efficient separation of photogenerated carriers, thereby boosting the device's intrinsic detection performance. The resulting photoresponsivity is 6.94 × 10 4  A W −1 and specific detectivity is 1.21 × 10 14 Jones @ 638 nm, with an optimal light on/off ratio of ≈10 7 at V GS = −27 V. Notably, the introduction of additional bands within MoS 2 bandgap through nitrogen doping leads to an extrinsic broadband response to short‐wave infrared. The device exhibits a photoresponsivity of 34 A W −1 and a specific detectivity of up to 5.92 × 10 10 Jones @ 1550 nm. Furthermore, the high‐performance broadband response is further demonstrated through imaging and integration with waveguides, paving the way for next generation of multifunctional imaging systems and high‐performance photonic chips.