Xiujuan Jiang

为解决激光脉冲信噪比单次测量中难以同时兼顾高时间分辨率、大时间窗口与高动态范围的问题，本文提出一种基于深度学习的光谱超分辨方法。建立了具有时间拓展递归的自参考光谱干涉系统的正向物理模型，利用其生成的数据训练专用的深度神经网络，从低分辨率光谱干涉图中重建出高分辨率光谱，进而提取精确的脉冲信噪比。在本文的数值仿真实例中，采用分辨率为0.01 nm的高质光谱图像与分辨率为0.05 nm的低质光谱图像进行模型训练，在保持20 fs高时间分辨率的基础上，脉冲信噪比测量的动态范围可从1.3×10⁸提升到2.2×10⁸~4.9×10⁸之间，时间窗口可从13 ps扩大到24~52 ps的区间，而且重建脉冲保真度高，在一定程度上打破了传统测量中技术指标的相互制约。本研究表明，计算重建方法可为高性能激光脉冲信噪比单次测量提供一种有参考价值的思路，且本文的算法框架具备推广至其他超快光学诊断过程的潜力。

Third harmonic generation (THG) via intermodal phase matching in fibers provides a convenient way to generate ultraviolet (UV) wavelengths. In this study, we systematically compare three THG configurations based on 1089 nm pumping to demonstrate UV output characteristics and dependencies on pump parameters and microfiber layout: (i) narrow-band conversion using a single long microfiber, (ii) narrow-band conversion using cascaded short microfibers, and (iii) broad-band conversion with a Raman-broadening pump. In the narrow-band case using a relatively long silica microfiber (waist diameter 520 nm, waist length 6 mm), third harmonic at 363 nm is generated at 1.14 $\mu$W average power, making a notable record in similar works. With multiple short silica microfibers (waist diameter 520 nm, waist length 3 mm), the idea of cascading the interaction media to improve THG performance is experimentally tested; the results show that the crucial phase relation required for coherent overlap of third harmonic components is satisfactorily achieved, while signal enhancement is counteracted by serious losses in the system, indicating that efficient signal delivering is a key issue in fiber-based optical frequency conversions. With the broad-band pump including the specific 1089 nm wavelength, the intermodal phase matching model for THG is verified, and a non-destructive approach is suggested to check the waist diameter of a fabricated microfiber.

Ultraviolet fiber lasers are highly desired in different fields such as lithography, laser processing, optical communications, optical storage, and biomedicine. On the other hand, all-fiber frequency conversion technology is of great significance in scientific research and practical applications, as it provides an alternative to the current solutions based on nonlinear crystals. Developing special optical fibers with both suitable mechanical performance and conversion efficiency and reducing the difficulty in their preparing are the key challenges in bringing this novel technology into practical application. In this work, three step-index optical fibers with simple structure are designed, they being a conventional single-cladding fiber (CSCF) with high numerical aperture, a microfiber (MF), and a W-type double-cladding fiber (WDCF), and the third-harmonic generation in ultraviolet band is studied by using them, respectively. The fundamental (pump) wavelength used in this work is 1064 nm and the third-harmonic wavelength is 355 nm.In order to achieve good transmission in the ultraviolet band, the cores of all three optical fibers are designed to be made of pure silica glass, and the core diameters are determined according to the phase matching condition for the fundamental wave and the third harmonic, by solving the eigenvalue equations. The cladding of CSCF is fluorine-doped silica glass, and the cladding of MF is air; for WDCF, the inner cladding and outer cladding are fluorine-doped silica glass and fluoroplastics, respectively. Both the CSCF and the WDCF have solid cladding, and their core diameters can be greater than 2 μm, so they have adequate mechanical properties. In comparison, due to the air cladding and thin core (the core diameter has to be less than 1 μm for phase matching), the MF is fragile in structure and thus its mechanical performance is rather poor.The conversion efficiencies of these three fibers are investigated in detail, by solving numerically the coupled mode equations for the pump and the third harmonic with the Runge-Kutta method. The effect of random fiber roughness (i.e. core diameter fluctuation) and enhancement in conversion efficiency by cascading the fibers are also analyzed. The results show that the conversion efficiency in MF is the highest, with an efficiency of 2% for a 5-mm-long single MF segment and over 20% for cascaded MFs; however, MF requires strict fabrication accuracy, and the tolerance of core diameter is only ± 0.3 nm. The CSCF has the lowest conversion efficiency, which is 0.1% for a 50-mm-long single segment and at the level of about 1% after cascading, and the tolerance of core diameter is ± 1 nm. The conversion efficiency of WDCF is between those of CSCF and MF, nearly 2% with a 50-mm-long segment and about 16% when four such segments are cascaded; WDCF bears core diameter tolerance of ± 3 nm, which is three times that of CSCF and 10 times that of MF. Therefore, the W-type double-cladding fiber WDCF actually integrates the advantages of conventional single-cladding fiber CSCF and microfiber MF, showing both satisfactory mechanical performance and conversion efficiency, as well as reduced fabrication difficulty, which provides a promising solution for all-fiber third-harmonic generation in the ultraviolet band.

We report on multi-wavelength generation through simultaneous second-order and third-order nonlinear parametric processes following cascaded stimulated Raman scattering (SRS) in silica fibers. The fiber system consists of a short standard step-index silica fiber and a microfiber tapered from it. When this system is pumped with a 130 ps laser at 1040 nm, multiple new wavelengths in the UV (340–370 nm) and green (507–547 nm) bands arise through four-wave mixing (FWM)/sum-frequency generation (SFG) from the pump and its Raman signals. The evolution of these wavelengths with pump power is demonstrated in detail. Matching of frequencies and propagation constants in the involved processes is verified. This work provides a compact and simple method of multi-wavelength generation with fibers.

将TiNi基记忆合金薄膜与光纤相结合可制成智能化、集成化且成本经济的微机电系统和微传感器件. 本文采用磁控溅射法在二氧化硅光纤基底上制备TiNi记忆合金薄膜, 系统讨论了溅射工艺参数以及后续退火处理对薄膜质量的影响. 采用自研制光纤镀膜掩膜装置在直径为125 μm的光纤圆周表面上形成均匀薄膜. 实验表明: 在靶基距、背底真空度、Ar气流量和溅射时间一定的条件下, 溅射功率存在最佳值; 溅射压强较大时, 薄膜沉积速率较低, 但薄膜表面粗糙度较小. 进行退火处理后, 薄膜形成较良好的晶体结构, Ti_49.09Ni_50.91薄膜中马氏体B19'相和奥氏体B2相共存, 但以B19'为主. 根据本文研究结果, 在玻璃光纤基底上制备高质量的TiNi基记忆合金薄膜是可实现的, 本工作为下一步研制微机电系统和微型传感器做了基础准备.

A scheme using cascaded silica microfibers is proposed for efficient third-harmonic (TH) generation. By tuning the phase difference via input pump power, the TH from the microfibers could overlap coherently, yielding great output enhancement. Conversion efficiency ∼ 20 % is demonstrated analytically and numerically. Moreover, as the TH output features are dominated by behavior analogous to optical interference, the influence of random diameter deviation of each microfiber is reduced, and the conversion process could be well controlled.

Noninvasive prenatal detection of monogenic diseases based on cell‐free DNA is hampered by challenges in obtaining a sufficient fraction and adequate quality of fetal DNA. Analyzing rare trophoblastic cells from Papanicolaou smears carrying the entire fetal genome provides an alternative method for noninvasive detection of monogenic diseases. However, intracellular labeling for identification of target cells can affect the quality of DNA in varying degrees. Here, a new approach is developed for nondestructive identification of rare fetal cells from abundant maternal cells based on endoplasmic reticulum staining and linear discriminant analysis (ER‐LDA). Compared with traditional methods, ER‐LDA has little effect on cell quality, allowing trophoblastic cells to be analyzed on the single‐cell level. Using ER‐LDA, high‐purity of trophoblastic cells can be identified and isolated at single cell resolution from 60 pregnancies between 4 and 38 weeks of gestation. Pathogenic variants, including –^SEA/ deletion mutation and point mutations, in 11 fetuses at risk for α‐ or β‐thalassemia can be accurately detected by this test. The detection platform can also be extended to analyze the mutational profiles of other monogenic diseases. This simple, low‐cost, and noninvasive test can provide valuable fetal cells for fetal genotyping and holds promise for prenatal detection of monogenic diseases.

The influence of nonlinear phase modulations on third-harmonic (TH) conversion in silica microfibers is experimentally demonstrated. By utilizing such influence, enhanced narrow-bandwidth ultraviolet TH is generated at a high signal-to-noise ratio (33 dB) and an average power of several hundred nanowatts. Detailed trends of TH power against input pump power were characterized with peak pump power up to 2.5 kW, and the results agree with predicted features, confirming that harmonic output could be optimized with adaptive control of the phase mismatch.

An effective approach is presented to improve intermodal third-harmonic generation in microfibers. It is demonstrated that structure-independent incident pump power could be utilized, via its effect on nonlinear phase modulations, to compensate for the phase mismatch caused by diameter deviation. The output harmonic of a fabricated microfiber can be optimized adaptively; thus, efficient third-harmonic generation with efficiency reaching several percent could realistically be achieved.

A scheme to enhance the fundamental-mode third harmonic generation efficiency in microfibers is presented. By introducing an appropriate counter-propagating pulse train, large propagation constant mismatch is partly overcome and nonlinear phase shifts could be corrected for, thus quasi-phase matching between the fundamental pump mode and the fundamental third harmonic mode is achieved, enabling the harmonic power to grow along the direction of propagation. Depending on the microfiber and pulse parameters, phase matching can enhance the conversion efficiency by several orders of magnitude with respect to the non-phase matched case. This scheme offers an alternative approach for harmonic generation and could potentially be applied to other small core waveguides.