基于光学奇异点的超宽带光纤模式转换特性

Mode Conversion Characteristics of Ultra-Wideband Fiber Based on Optical Exceptional Point

通过在光子晶体光纤(PCF)纤芯中沿着光传输方向引入对称增益-损耗折射率分布,构造宇称-时间(PT)对称性的非厄米系统,实现开放系统的光学奇异点(EP),以调控光纤耦合模式之间的相互作用。提出一种基于光学奇异点的新型光子晶体光纤模式转换方案,该方案能够在1.3μm至2.0μm波长范围内高效地实现LP_(01)和LP_(11)模式之间的非对称转换,效率可达99%,同时对各种结构参数表现出较好的容差。

Objective This study aims to explore the utilization of optical exceptional points(EPs) in non-Hermitian systems,particularly in the context of photonic crystal fibers(PCFs). EPs induce fascinating physical phenomena and applications,such as unidirectional zero-reflection light transmission and phase transitions in metamaterials. Here, we aim to investigate the implementation of EPs in PCFs to achieve mode conversion and modulate optical interactions between different modes.Methods To achieve this objective, we introduce a symmetric gain-loss refractive index distribution into the core of PCFs, creating a parity-time(PT) symmetric non-Hermitian system. This approach involves carefully designing and fabricating the PCF structure to ensure the desired refractive index profile. We then analyze the optical properties of the system, including the formation of EPs and their effects on mode coupling and conversion using a beam propagation method.Results and Discussions Our investigation effectively showcases the achievement of optical EPs within the tailored PCF architecture, facilitating the proficient manipulation of mode interactions. Specifically, we successfully realize asymmetric mode conversion between LP01 and LP11 modes spanning a wavelength range of 1.3 to 2.0 μm, boasting an efficiency rate of up to 99%. Furthermore, this structure facilitates the simultaneous conversion from the LP11 mode to the LP01 mode(Fig. 5). Leveraging counterclockwise transmission is instrumental in mitigating mode purity issues stemming from device reflections. Crucially, our proposed scheme demonstrates resilient performance across diverse structural parameters,underscoring its promise for practical applications.The observed mode conversion and modulation of optical interactions highlight the significance of EPs in nonHermitian systems, particularly in the context of PCFs. The symmetric gain-loss refractive index distribution plays a crucial role in creating the PT-symmetric system, forming EPs, and enabling effective control over mode coupling. The high efficiency and tolerance to structural variations further enhance the applicability of the proposed scheme in real-world scenarios.Conclusions In conclusion, our study presents an innovative approach for mode manipulation in PCFs based on optical exceptional points. By leveraging the unique properties of EPs in non-Hermitian systems, we demonstrate efficient and flexible mode conversion within a wide wavelength range. This research expands the application scope of EPs in photonics.It provides a promising solution for enhancing the functionality of photonic crystal fibers in various optical systems and devices.