为了实现对钞券表面涂层高速在线检测，研制了一种基于高速钞券质量检查机的实时近红外弱信号检测系统。首先，根据涂层材料的特性，采用近红外波段的发光二极管和光电二极管，研制了驱动和弱信号采集电路；然后，利用现场可编程门阵列和图形化虚拟仪器平台实现了数据的实时传输和处理；最后，提出了计算信号峰值强度的峰值标准差法并分析了该算法的实时性，进行了钞券表面涂层检测和算法实时模拟实验。实验结果表明，在钞券22 m/s的运行速度下，无论衬底是简单或复杂，未涂布钞券的信号均明显高于已涂布钞券的信号，分别差约为7 000，4 000，1 400，衬底图文越复杂，信号差越小。算法开始至结束的时间约为2~3 ms，远小于22 ms的钞券时间间隔，算法速度满足实时要求。本文研制的系统具有高速、实时、稳定的特点，可高效检测纸张表面的涂层有无，有望为涂层在线质量检测提供一种全新的方法。

纸币是国家发行并强制使用的货币符号，2019年中国人民银行发行的2019年版第五套人民币纸币，两面采用了抗脏污保护涂层，使纸币的整洁度明显改善。作为“国家名片”，在纸币生产过程中，对每一道工艺都有严格的质量控制，涂层是通过涂布机将涂布液转移、固化至纸币两面，由此称为涂布工艺。为了更加合理地控制涂布质量，生产中需要检测纸币涂层的厚度。针对该需求，文中建立了纸币图纹作为复杂衬底的涂层厚度光学漫反射模型，采用傅里叶近红外光谱仪和激光共聚焦显微系统对已涂布和未涂布的纸币进行识别并定量检测。文中首先根据涂层物质在近红外光谱可被有效识别的特点，对涂层的近红外吸收光谱数据提出了基于多元散射校正（MSC）与二阶导组合的分析方法，确定4 346.764 cm⁻¹为特征波数。再根据反射率、粗糙度对涂层厚度的模型解耦，最后通过激光共聚焦显微系统检测了已涂布纸币的涂层变化，并将其与模型的厚度解耦结果关联，得出测量涂层厚度最小为3.807 μm，最大为12.738 μm。最终结果表明该检测方法对纸币生产中涂层质量控制具有重要的实践指导意义。

微电子机械系统（Micro-Electro-Mechanical System，MEMS）具有小型化、高集成度的特点，随着MEMS结构深宽比的不断增大，对MEMS结构尺寸的测量提出更高的要求。过焦扫描光学显微技术（Through-focus Scanning Optical Microscopy，TSOM）是一种高精度无损的光学测量方法，通过采集一组离焦图并沿扫描方向截取TSOM图像，利用库匹配的方法从中提取待测结构的尺寸信息。该方法对于纳米级结构测量有着极高的灵敏度，然而对于微米级特征尺寸存在建库困难且易受环境干扰的问题。本文针对微米级MEMS沟槽结构，在传统的光学显微镜基础上进行改造，建立了TSOM光学系统采集离焦图像，利用图像特征提取方法生成TSOM特征向量集，结合机器学习的方法建立不同槽宽尺寸的回归预测模型，对微米级MEMS槽宽尺寸实现纳米级测量精度，单点重复性测量2 μm槽宽的相对标准差（Relative Standard Deviation，RSD）在1%左右，10 μm和30 μm槽宽RSD分别低于0.2%和0.35%，结果表明该方法对于微米级MEMS沟槽测量具有极高的应用前景。

In this Letter, we report on a novel architecture for a self-starting mode-locked figure-eight erbium-doped fiber laser using a loss-imbalanced nonlinear optical loop mirror (NOLM) with a bidirectional output coupler. An all-polarization-maintaining structure is adopted. A 2 × 2 optical coupler with a splitting ratio of 50:50 is used at the junction to form an NOLM. Another coupler with a splitting ratio of 10:90 is introduced at one end of the fiber loop. The 10:90 coupler plays two roles: power attenuator and bidirectional output coupler. This architecture can achieve both large modulation depth and good self-starting ability simultaneously. With this architecture, the self-starting mode-locking operation is achieved easily with pump power above the threshold. The clockwise and counter-clockwise mode-locked output powers are 10.1 and 10.3 mW, respectively, with the repetition rate of 3.63 MHz. The spectral bandwidths of the clockwise and counter-clockwise mode-locked output pulses are 7.4 and 2.9 nm, and the corresponding pulse widths of the direct outputs are 530.6 fs and 1.55 ps, respectively.

A self-starting simple structured dual-wavelength passively mode-locked (ML) erbium-doped fiber (EDF) laser is proposed in this Letter. An all-fiber ring cavity is adopted and a transmission-type semiconductor saturable absorber is used as modelocker. In this laser, there are two gain humps located at the 1530 nm region and the 1550 nm region, respectively. Along with the length of EDF increasing, the intensity of the hump at 1530 nm region is gradually suppressed because of the re-absorption of emission by the ground state. With the proper length of EDF, the gain intensities of two regions are very close. When the pump power is above the ML threshold, the self-starting dual-wavelength ML operation is achieved easily without manual adjustment. The two spectral peaks with close intensities are located at 1532 and 1552 nm, respectively. The effect of intracavity dispersion on the output spectrum is also experimentally demonstrated.