Mode purity measurement is crucial for various applications utilizing few-mode fibers and related devices. In this paper, we propose a simple and accurate method for measuring the mode purity of the output optical field in few-mode ring-core fibers (RCFs). Mode purity can be calculated solely from the outgoing intensity distribution with high precision. This method is theoretically capable of measuring the mode purity of RCFs that support orbital angular momentum modes with an infinite number of azimuthal orders and has strong applicability to various RCF types and image qualities simultaneously. We demonstrate our approach numerically and verify it experimentally in a few-mode RCF supporting four (five) mode groups at 1550 (1310) nm. A polarization test method is proposed to verify its accuracy. We believe that this straightforward and cost-effective characterization method for RCFs and RCF-based devices can promote the development of mode-division multiplexing technology and its applications.
2023, 11(9): 1592
Multimode fiber has a richer spatial dimension than single-mode fiber, and is an ideal platform for studying many novel nonlinear effects. We established a strong linear coupling and short-range fiber model to understand the interactive effects of linear coupling and nonlinear effects. We find that strong linear coupling can compensate for the group delay between eigenmodes and cause energy fluctuation between modes which weakens the nonlinear effects. In high energy pulses, the interaction of linear coupling and nonlinear effects can help producing weak dispersion waves when the spectrum is broadened. Since linear coupling in a mode group is common and unavoidable, these results may provide a certain theoretical explanation for multi-mode nonlinear phenomena.
2020, 16(5): 379
A twist sensor with hybrid few-mode tilted fiber Bragg grating (FM-TFBG) and few-mode long period grating (FM-LPG) in fiber laser cavity is demonstrated. The FM-LPG is utilized to excite LP11 core mode. The FM-TFBG is used for sensing. The transverse modes at 1 553.9 nm and 1 550.5 nm are LP01 and LP21 core modes, respectively, which are coupled from forward-propagating LP11 core mode. These two excitation wavelengths have opposite variation tendencies, which participate in sensing. The twist sensitivity of 0.16 dB/° from -40° to 40° is achieved. The proposed sensor has potentially used for structure monitoring in many areas.
2019, 15(3): 161
对自行研制的主振荡功率放大结构短脉冲双包层光纤激光系统(2 W，30 ps)的偏振特性进行了研究.分别研究了种子源激光和经过包层泵浦放大后输出激光在连续工作和脉冲输出情况下的偏振特性，结果表明在不加偏振控制措施情况下，系统输出为椭圆偏振光，偏振度和偏振角都容易受到光纤扰动的影响；在激光腔内加入起偏器后，输出线偏振光，偏振态相对比较稳定，但是偏振角度仍然容易受到光纤扰动的影响.实验证明：经过高功率放大后，输出激光的偏振态稳定性有一定程度的下降，在进行激光相干合成前需进一步加以控制.主振荡功率放大 偏振特性 光纤激光器 脉冲 Master oscillator power amplifier Polarization Fiber laser system Pulse
光子晶体光纤(PCF)以其独特的光学特性和灵活设计的特点，而成为近年来研究的热点。随着各种新型PCF的问世以及研究的深入，使其应用领域不断扩大。文章对PCF在全光网中的各项应用进行了分析，重点对PCF在光纤光栅和光纤激光器、放大器、光开关、波长变换器方面的研究进展进行了介绍。光子晶体光纤 非线性光学 全光网络 光电器件 光纤光栅 Photonic Crystal Fiber (PCF) nonlinear optics all-optical network photoelectronic device fiber grating