实验技术与管理

针对“非线性光学—原理与应用”课程中材料非线性可饱和吸收效应及其在光纤激光器中应用的实验教学需求，设计一种基于氧化石墨烯-金纳米棒复合材料的高次谐波锁模光纤激光综合实验。通过异位法制备了氧化石墨烯-金纳米棒材料，并对其材料特性和可饱和吸收效应进行了表征和分析。将氧化石墨烯-金纳米棒材料制成集成光纤器件，应用到掺Er³⁺光纤激光器中，实现了重复频率为20.5557 MHz的基频脉冲与699.301 MHz的高次谐波脉冲输出，为复合低维材料制备及其在光纤激光器中的应用提供了一种思路和方法。将理论教学与科研实验相结合，激发了学生的科研兴趣，拓展了学生的创新思维，提高了学生独立解决问题的能力。

[Objective] Mode-locked fiber lasers are extensively employed in a variety of fields, such as ultrafast spectroscopy, optical communication, precision machining, precision metrology, and biomedical science, because of their compact design, narrow pulse duration, high peak power, and excellent beam quality. Saturable absorbers with desirable nonlinear optical properties are essential to achieve stable mode-locking operation. Graphene oxide(GO) has several advantages, including a low saturation intensity, substantial modulation depth, high damage threshold, and rapid recovery time. Additionally, gold nanorods(GNRs) have a high third-order nonlinear coefficient and an ultrafast response time. Hence, they are exceptionally promising for applications in both saturable absorption and reverse saturable absorption. The synergistic integration of GO and GNRs can amalgamate the strengths of these two materials, producing state-of-the-art saturable absorbers with enhanced performance. To meet the experimental teaching requirements of the course “Nonlinear Optics: Principles and Applications,” with a focus on the nonlinear saturable absorption effects of materials and their applications in fiber lasers, we propose a comprehensive experiment on high-order harmonic mode-locked fiber lasers based on a graphene oxide–gold nanorod(GO-GNRs) composite material. [Methods] In this study, the GO was synthesized from natural graphite powder by a modified Hummers method, while the GNRs were fabricated through a seed-mediated growth technique. Subsequently, the GO-GNRs composite was fabricated by an ex situ hybridization method, ensuring a uniform and stable combination of these two components. The GO-GNRs were characterized and analyzed to evaluate their material properties and saturable absorption behavior. To fabricate a fiber device, the GO-GNRs were deposited onto the cross-section of a D-shaped optical fiber to serve as a saturable absorber(SA). Thereafter, the fabricated GO-GNRs were integrated into an Er³⁺-doped fiber laser cavity, enabling ultrashort pulse generation via their SA property. [Results] By adjusting the pump power and polarization controller(PC), the fundamental mode-locked pulse was obtained with a central wavelength of 1 559.65 nm and a repetition rate of approximately 20.555 7 MHz. The mode-locking operation exhibited excellent long-term stability. When the pump power was increased to 600 mW, the 34^th-order harmonic mode-locked pulse was obtained by suitably adjusting the PC orientation, corresponding to a repetition frequency of 699.301 MHz and a signal-to-noise ratio(SNR) of 68.2 dB. The results demonstrated that GO-GNRs effectively enhanced nonlinear optical modulation, promoting the formation and stabilization of high-order harmonic mode-locking. [Conclusions] This comprehensive experiment effectively enhances students' abilities to apply theoretical knowledge to practical analysis and operations. Through the synthesis and characterization of low-dimensional materials, students can gain practical experience in nanomaterial fabrication and optical measurement techniques. In the mode-locked Er³⁺-doped fiber laser experiment, students can understand the working principles, structural design, and output characteristics of fiber lasers. By combining theoretical teaching with experiment, this work stimulates students' research interest, broadens their innovative thinking, and strengthens their ability to solve complex problems independently.