Huakang Yu

Alexandrite lasers exhibit exceptional power-scaling potential at room temperature, yet this capability remains underexplored. We have demonstrated a continuous-wave (CW) alexandrite laser achieving a record output power of 20.4 W in single transverse-mode operation, surpassing all prior reports for laser diode pumped systems. The demonstrated fundamental-mode laser exhibits a high optical-to-optical efficiency of 34%, near-diffraction-limited beam quality M ² < 1.05, and exceptional stability (RMS < 0.2% over 2 hours), stemming from elaborate dynamically stable resonator optimization and excellent heat dissipation. This advance provides compelling evidence for the superior room-temperature power-scaling capability of alexandrite with excellent efficiency and exceptional beam quality .

Narrow-linewidth lasers at short/visible wavelengths are crucial for quantum and atomic applications. However, such lasers are often accessible in bulky tabletop systems and remain scarce in on-chip photonic platforms. Here, we report an on-chip visible Brillouin-quadratic microlaser in a 117-μm-diameter thin-film lithium niobate (TFLN) microdisk via dispersion engineering. Enabled by the ultra-high optical Q factor of 4.0×10⁶, high optical mode density, small mode volume, strong photon-phonon interaction and high second-order nonlinearity of the TFLN microdisk, simultaneous generation of Stokes Brillouin lasing (SBL) with 10.17 GHz Brillouin shift and its second harmonic generation (SHG) are demonstrated, exhibiting a low threshold of only 1.81 mW. Further measurement confirms the intrinsic narrow-linewidths of both the SBL ( ~ 254 Hz) and the SHG ( ~ 864 Hz) along with a normalized frequency-double efficiency of 3.61%/mW. This demonstration of an on-chip ultra-narrow linewidth bi-chromatic Brillouin laser paves the way for on-chip quantum information processing and precise metrology.

The generation of supercontinuum spectra on integrated nonlinear optical platforms opens up new possibilities for applications in spectroscopy, metrology, signal processing, optical communications, and more. As an extremely promising low-loss nonlinear integrated photonics platform, there is an urgent need to achieve efficient and broadband supercontinuum generation (SCG) on thin-film lithium niobate (TFLN). However, most advancements in this field have not fully exploited the potential of χ(2) nonlinearity, leading to constraints in both spectral width and flatness. In this work, we introduce broadband quasi-phase matching into TFLN, effectively leveraging the synergistic effects of χ(2) and χ(3) nonlinearities. By combining cascaded χ(2) frequency upconversion, self-phase modulation (SPM), and dispersive wave (DW) generation, we have achieved, for the first time, a broadband, flat, three-octave-spanning SCG covering the ultraviolet–visible–NIR region (320–2500 nm, −30 dB) with microjoule-level energy in z-cut quasi-phase matching TFLN. The ultraviolet–visible spectral region consists of second–fourth harmonics, while the NIR region is composed of the spectrally broadened pump wave by SPM and DW generated by soliton fission, with a conversion efficiency of up to 31% from the pump to the ultraviolet–visible region. We conducted a comprehensive study on the critical roles of χ(2) and χ(3) nonlinearities in SCG and provided a systematic, in-depth analysis of the spectral evolution process. The experimental results show excellent agreement with numerical simulations. Our work paves the way for SCG across the full transparency window of LN.

Narrow-linewidth lasers at short/visible wavelengths are crucial for quantum and atomic applications, such as atomic clocks, quantum computing, atomic and molecular spectroscopy, and quantum sensing. However, such lasers are often only accessible in bulky tabletop systems and remain scarce in integrated photonic platform. Here, we report an on-chip visible Brillouin-quadratic microlaser in a 117-um-diameter thin-film lithium niobate (TFLN) microdisk via dispersion engineering. Enabled by the ultra-high Q factor of 4.0X10(6) and small mode volume, strong photon-phonon interaction and high second-order nonlinearity of the TFLN microdisk, narrow-linewidth Stokes Brillouin lasing (SBL) is demonstrated with 10.17 GHz Brillouin shift under a 1560-nm pump, exhibiting a short-term narrow linewidth of 254 Hz and a low threshold of only 1.81 mW. Meanwhile, efficient second harmonic generation (SHG) of the SBL signal is also observed at 780 nm, with a normalized conversion efficiency of 3.61%/mW, made possible by simultaneous phase matching fulfillments for both narrow-linewidth SBL and its SHG. This demonstration of an integrated ultra-narrow linewidth visible wavelength Brillouin-quadratic lasers opens new avenues toward chip-scale quantum information processing and precise metrology.

Herein, the lasing action of fabricated bulged CH₃NH₃PbBr₃ microwires is demonstrated with features of a low threshold, narrow linewidth, single‐mode operation, and high intensity. Benefiting from the bulged end facets, the CH₃NH₃PbBr₃ microwires are feasible for constructing a high‐brightness, whispering‐gallery‐mode(WGM)‐type, and single‐mode laser while suppressing Fabry–Pérot‐type multi‐mode lasing. Numerical simulation unveils that the bulged end facets result in the significantly reduced reflectivity of fundamental waveguided modes. The obtained microlasers require neither complex structures (such as distributed Bragg reflector) nor careful pumping adjustment, suggesting the practical feasibility of a higher single‐mode lasing intensity than conventional WGM perovskite microlasers. The results provide new routes to realize high‐performance perovskite microlasers and their potential application in sensing refractive index.

With the development of laser technology, nonlinear optics plays a crucial role in frequency conversion. However, the generation of second harmonics in nonlinear optical crystals is generally subject to rigorous phase-matching conditions that hinder the performance of broadband tunability. It is believed that introducing disorders in nonlinear optical materials is helpful to overcome this obstacle. In this work, we have prepared a nonlinear microcrystal-doped glass (NMG) composite material, allowing for tunable and polarization-independent nonlinear conversion from visible to near-infrared. The linear dependence of SHG intensity versus sample thickness indicated the facilitation of random quasi-phase matching by using the NMG. Our results provide a more stable and promising platform for disordered nonlinear photonic materials and suggest the possibility of more efficient nonlinear conversions using the NMG composite glass fibers in future.

本文报道了一种基于微纳光纤中双模式干涉的亚波长聚焦方法。利用微纳光纤中两种特定导模在微纳光纤端面处的干涉效应，我们在微纳光纤端面处获得了单焦点或多焦点的聚焦光场，并可通过调节两个模式之间的相位差、功率比分别实现聚焦光场的焦深调谐、焦斑相对强度调谐，从而达到对纳米颗粒可调谐、选择性的捕获。根据干涉聚焦光场中不同焦点处所对应的捕获刚度和势阱深度的不同，可以对不同大小的纳米颗粒进行分类。这种微型化全光纤的亚波长聚焦方法,将可应用于操纵纳米颗粒、超分辨率光学成像和纳米光刻等领域。