内窥镜物镜是双光子成像应用于医疗内窥成像的关键部件，物镜的成像质量和信号光收集效率对最终图像的质量至关重要。为光纤扫描式双光子成像系统设计了一款高收集效率、大视场、结构紧凑的物镜。在该系统中，920 nm飞秒激光从双包层光纤纤芯部分出射，经过物镜后激发样本，激发出的460 nm二次谐波和510 nm荧光再次经过物镜后被收集到光纤包层中。在此过程中，为了提高荧光的收集效率，对物镜组进行轴向色差设计，以使更多的荧光进入光纤包层部分。利用Zemax光学设计软件进行系统优化设计，设计结果表明：物镜组在920 nm波长下全视场范围内的调制传递函数在700 lp/mm处大于0.25，满足激发光的使用要求；在Zemax软件非序列模式下,将设计的物镜和传统梯度折射率物镜的信号光收集效率进行比较，仿真结果显示，所设计的物镜的信号光收集效率高达54%，比传统梯度折射率物镜提高了2倍以上。

Endoscopic objectives are key components of two-photon imaging used in medical endoscopy imaging. The imaging quality and signal light collection efficiency are crucial to the final image quality. An objective lens with high collection efficiency, 400 μm field of view, and compact structure is designed for the optical fiber scanning two-photon imaging system. In this system, a 920 nm femtosecond laser emerges from a double cladding fiber and excites the sample after the objective lens. The excited 460 nm second harmonic signal and 510 nm fluorescence are collected into the fiber cladding through the objective lens. In order to improve the collection efficiency during this process, we design the axial chromatic aberration of the objective so that more signal light enters the cladding. The design of the system is optimized by Zemax software. The results show that the modulation transfer function in the whole field of the objective at 920 nm is larger than 0.25 at 700 lp/mm, which meet the requirements of the system. Meanwhile, the signal light collection efficiency of the objective lens designed in the non-sequential mode and the traditional gradient index lens is compared. The simulation results show that the signal light collection efficiency of this objective lens is 54%, which is two times higher than that of the traditional gradient index lens.