Rapid progress in nonlinear plasmonic metasurfaces enabled many novel optical characteristics for metasurfaces, with potential applications in frequency metrology [Zimmermann et al. Opt. Lett. 29:310 (2004)], timing characterization [Singh et al. Laser Photonics Rev. 14:1 (2020)] and quantum information [Kues et al. Nature. 546:622 (2017)]. However, the spectrum of nonlinear optical response was typically determined from the linear optical resonance. In this work, a wavelength-multiplexed nonlinear plasmon-MoS2 hybrid metasurface with suppression phenomenon was proposed, where multiple nonlinear signals could to be simultaneously processed and optionally tuned. A clear physical picture to depict the nonlinear plasmonic bound states in the continuum (BICs) was presented, from the perspective of both classical and quantum approaches. Particularly, beyond the ordinary plasmon-polariton effect, we numerically demonstrated a giant BIC-inspired second-order nonlinear susceptibility 10⁻⁵ m/V of MoS2 in the infrared band. The novelty in our study lies in the presence of a quantum oscillator that can be adopted to both suppress and enhance the nonlinear quasi BICs. This selectable nonlinear BIC-based suppression and enhancement effect can optionally block undesired modes, resulting in narrower linewidth as well as smaller quantum decay rates, which is also promising in slow-light-associated technologies.

A new timing detection method based on acousto-optic modulation is demonstrated. The timing detector is immune to dispersion effects and the environmental and laser amplitude noise can be well suppressed by a balanced configuration. With 1 mW power per pulse train, the measured timing noise floor is about 1×10⁻¹⁰ fs²/Hz, which is close to the shot noise limit. The integrated timing jitter is 26 as at [1 Hz, 1 MHz]. With 170 fs pulse width and typical detector parameters, the calculated detector’s timing noise floor is more than 5 and 12 orders of magnitude lower than that of a BOC, at 1 mW and 1 µW input power, respectively. This timing detector has a variety of potential applications in ultra-long fiber link stabilization, quantum metrology, weak signal timing control, etc.

We experimentally demonstrate a novel and practical timing detector based on a double-pass acousto-optic frequency shifter. With time and frequency multiplexing, for the first time to our knowledge, a balanced detection is realized using only a single photodiode, which greatly decreases the excess electronic noise during photodetection. With a total input optical power of 1.4 mW (0.35 mW per pulse train), an almost shot-noise-limited detection floor of 28.3 zs/√Hz is achieved, and the timing jitter integrated from 1 kHz to 1 MHz is reduced from 99.0 as (without eliminating the photodetector electronic noise) to only 30.4 as. Even with an input power of 50 µW per pulse train, 221.4 zs/√Hz detection floor and 268.0 as integrated timing jitter at [1 kHz and 1 MHz] are still maintained. This timing detector provides a powerful tool for high-precision metrology, ultra-long-distance ranging, and large-scale timing synchronization.

Arm locking is one of the key technologies to suppress the laser phase noise in spaced-based gravitational waves observatories. Since arm locking was proposed, the phase margin criterion was always used as the fundamental design strategy for the controller development. In this paper, we find that this empirical method from engineering actually cannot guarantee the arm locking stability. Therefore, most of the advanced arm locking controllers reported so far may have stability problems. After comprehensive analysis of the single arm locking’s transient responses, strict analytical stability criterions are summarized for the first time. These criterions are then generalized to dual arm locking, modified-dual arm locking, and common arm locking, and special considerations for the design of arm locking controllers in different architectures are also discussed. It is found that proportional integral controllers can easily meet our stability criterions in most of the arm locking systems. Using a simple high gain proportional integral controller, it is possible to suppress the laser phase noise by 5 orders of magnitude within the science band. Our stability criterions can also be used in other feedback systems, where several modules with different delays are connected in parallel.

We developed the Global–Local Integrated Topology inverse design algorithm (denoted as the GLINT algorithm), which employs a trajectory-based optimization strategy with waveguide–substrate material-flipping structural modifications, enabling the direct optimization of discrete waveguide–substrate binary structures. Compared to the conventional Direct Binary Search (DBS), the GLINT algorithm not only significantly enhances computational efficiency through its global search–local refinement framework but also achieves a superior 20 nm × 20 nm optimization resolution while maintaining its optimization speed—substantially advancing the design capability. Utilizing this algorithm, we designed and experimentally demonstrated a 3.5 µm × 3.5 µm dual-port wavelength division multiplexer (WDM), achieving a minimum crosstalk of −11.3 dB and a 2 µm × 2 µm 90-degree bending waveguide exhibiting a 0.31–0.52 dB insertion loss over the 1528–1600 nm wavelength range, both fabricated on silicon-on-insulator (SOI) wafers. Additionally, a 4.5 µm × 4.5 µm three-port WDM structure was also designed and simulated, demonstrating crosstalk as low as −36.5 dB.