中国激光, 2021, 48 (16): 1606001, 网络出版: 2021-07-30   

基于光栅局域温度控制的高精度多相移的产生和滤波器的制备 下载: 736次

High-Precision Multiphase Shifts Generation and Filter Fabrication Based on Grating Local Temperature Control
作者单位
1 中国科学院上海光学精密机械研究所空间激光信息传输与探测技术重点实验室, 上海 201800
2 中国科学院大学材料与光电研究中心, 北京 100049
3 中国空间技术研究院西安分院空间微波技术国家级重点实验室, 陕西 西安 710100
摘要
提出了一种利用局域温度控制的高精度相移控制技术制备多相移光纤光栅滤波器的方法。首先,分析了多相移光纤光栅中相移量和相移位置的误差对多相移光纤光栅滤波器的插入损耗、带宽和形状因子的影响,得到了高性能多相移光纤光栅制备所需的相移量精度(0.0029π)和相移位置精度(368 μm)。然后,实验证实了利用局域温度控制引入高精度相移(相移量精度为0.0007π,相移位置精度为30 μm)的可行性。最后,利用所提方法制备了多相移光纤光栅,并对其光谱进行了测试和理论仿真。结果表明,基于所提方法制备的多相移光纤光栅滤波器的频率响应接近理论仿真下的理想滤波器特性,插入损耗约为0.5 dB,3 dB带宽约为366 MHz,20 dB带宽约为972 MHz,形状因子约为0.38。所提制备多相移光纤光栅滤波器的方法精确、简单、经济,没有对光纤光栅的结构造成永久性的改变,具有相移量可擦除的优势,可进一步应用于制备新型可调谐光纤滤波器。
Abstract

Objective Ultranarrow bandpass optical filters are key components for signal processing in the fields of microwave photonics, dense wavelength-division multiplexing, coherent communication, and optical fiber sensing. The ideal ultranarrow bandpass optical filter has a rectangular frequency response composed of an ultraflat passband and a very steep edge. The flat passband has high signal fidelity and can prevent the signal from being distorted, whereas the steep edge can suppress the crosstalk between the adjacent bands. Fiber Bragg gratings (FBG) that achieve various frequency responses are commonly used in bandpass optical filters towing to their small size, anti-electromagnetic interference, low insertion loss, and compatibility with other optical fiber devices and systems. However, the ordinary uniform FBG bandwidth is relatively large, in a dozen GHz or hundred GHz. Although the phase-shifted fiber Bragg grating can achieve a bandwidth below 100 MHz, its Lorentz or quasi-Lorentz line frequency response limits its application in high-resolution signal processing. Recently, the multiphase-shifted FBG (MPSFBG) containing multiple phase shifts have been used to design the ultranarrow bandpass optical filters. The MPSFBG can obtain the narrow band flat-top filter response with small insertion loss and good rectangularity by optimizing the position of each π phase shift. In actual preparation, there are errors in the control of the phase-shift amount and phase-shift position, which result in the difference between the actual optical spectra and theoretically calculated optical spectra under ideal conditions. Therefore, the introduction of a high-precision phase shift is the key to the fabrication of the MPSFBG.

Methods This study presents a method for fabricating the MPSFBG by introducing a high-precision phase shift into the FBG using local temperature control. First, the influence of the phase-shift amount and position errors on the insertion loss, bandwidth, and shape factor of the MPSFBG filter is analyzed in the theoretical part of this study, and the phase-shift amount and position precision required by the MPSFBG to obtain the narrow band flat-top filter response with small insertion loss and good rectangularity are obtained. In the experimental part, the principle of introducing a phase shift into the FBG using the local temperature control scheme is analyzed, and the structure for local temperature control is designed. The phase-shift amount and position precision achieved using the designed local temperature control structure in uniform FBG are experimentally measured. Finally, a dual-phase-shifted FBG is fabricated using this method. In addition, its frequency response is measured.

Results and Discussions The method proposed in this study uses local temperature control to introduce high-precision phase shifts into the FBG to assist the MPSFBG in achieving a phase-shift amount and position precision of 0.0007π and 30 μm, respectively (Fig. 9 and Fig. 10). This precision meets the phase-shift precision required by the MPSFBG in the theoretical analysis to obtain the narrow band flat-top filter response with small insertion loss and good rectangularity. In addition, this phase-shift erasing is possible because the phase shifts introduced by it do not permanently change the structure of the FBG, providing an efficient and economical method for fabricating the MPSFBG. The frequency response of the dual-phase-shifted FBG filter fabricated using this method is consistent with the theoretical fitting result under ideal conditions, and the insertion loss of about 0.5 dB, 3 dB bandwidth of about 366 MHz, 20 dB bandwidth of about 972 MHz, and shape factor of about 0.38 are realized (Fig. 11).

Conclusions In this study, a method for fabricating an MPSFBG filter using high-precision phase-shift control technology based on local temperature control is presented. First, in the theoretical part of this study, the effect of the amount and position errors of the phase shifts on the insertion loss, bandwidth, and shape factor of the MPSFBG filter is analyzed. The amount precision (0.0029π) and position precision (368 μm) requirements of the phase shifts are obtained for the MPSFBG achieving the narrow band flat-top filter response with low insertion loss and good rectangularity. The experimental part confirmed the feasibility of using local temperature control to introduce the high-precision phase shifts (phase-shift amount precision is 0.0007π, phase-shift position precision is 30 μm). Finally, the MPSFBG is fabricated using this method, and its optical spectrum is tested and theoretically simulated. The results show that the frequency response of the MPSFBG filter fabricated using this method is close to the ideal filter characteristics from the theoretical simulation, and insertion loss of about 0.5 dB, 3 dB bandwidth of about 366 MHz, 20 dB bandwidth of about 972 MHz, and the shape factor of about 0.38 are realized. The method proposed in this study for fabricating the MPSFBG is accurate, simple, and economical. Moreover, the phase shifts generated using this method do not result in permanent changes to the structure of the FBG; thus, it is erasable, which can be used to fabricate the new tunable fiber filters.

梁虹, 应康, 王迪, 魏金金, 李璇, 皮浩洋, 魏芳, 蔡海文. 基于光栅局域温度控制的高精度多相移的产生和滤波器的制备[J]. 中国激光, 2021, 48(16): 1606001. Hong Liang, Kang Ying, Di Wang, Jinjin Wei, Xuan Li, Haoyang Pi, Fang Wei, Haiwen Cai. High-Precision Multiphase Shifts Generation and Filter Fabrication Based on Grating Local Temperature Control[J]. Chinese Journal of Lasers, 2021, 48(16): 1606001.

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