Abstract：Based on fiber grating to achieve picosecond-level delay, a microsecond-level cascade structure combining fiber grating and single-mode fiber is proposed. This structure can achieve a narrow wavelength with a center wavelength of 1 550~1 553 nm and a spacing of 1 nm. The reflective delay line has four different delays: 1, 1.5, 2 and 2.5 μs. The single-wavelength-reflected chirped Bragg fiber grating is connected with a 103 m single-mode fiber to form a delay unit, and then an optical circulator cascades the four delay units and uses a fiber reel with an inner radius of 3 cm to integrate the transmission fibers of the four delay units. With the help of the mirror function of the fiber grating, the optical signals of different wavelengths are controlled to pass through different transmission distances to achieve the purpose of corresponding time delay. In this article, through the simulation analysis of the reflection spectrum of the chirped fiber Bragg grating, it can be found that the side lobes of the adjacent reflection spectrum will overlap. Therefore, six apodization functions are used to filter the side lobes. The results show that: the apodization function has different filtering effects on the side lobes of the reflection spectrum. The Cauchy apodization function can filter the side lobes and has the least impact on the reflection spectrum envelope. After Cauchy apodization, the reflectance of optical signals of different wavelengths can reach 1 in the range of the corresponding center wavelength of 1 nm, and the reflectance in other ranges is 0. Because the use of fiber reel to integrate the delay unit transmission fiber will produce a certain loss, the bending loss is simulated and analyzed. The results show that when the bending radius is the same, the loss is proportional to the working wavelength; when the working wavelength is the same, the bending loss is inversely proportional to the bending radius. When the bending radius is greater than 2.9 cm, the bending loss curve changes smoothly and tends to zero. Therefore, when the inner radius of the optical fiber winding reel is 3 cm, it is ensured that the volume is reduced without excessive loss. The waveforms of signals with a frequency of 2 000 Hz after different transmission distances are tested by a TDS784D oscilloscope. The results show that the signal parameters remain unchanged after 3 m and 5 km transmission lines. After long-distance transmission, the original signal characteristics can still be maintained. Therefore, the use of a 103 m transmission line can achieve the delay. The W-GGL optical power meter measured the output power at different frequencies. Compared with the output power of straight fiber, when the bending radius is 2~3 cm, the deviation is large, when the bending radius is equal to 3 cm, the deviation is 0.18 dBm, and when the bending radius is greater than 3 cm, it will approach infinitely. Therefore, the inner radius of the winding reel is set to 3 cm conforming to the loss range of the optical fiber delay line.
王 翀，杜 欢，王 静，王 菁，王景华. 采用光纤光栅级联结构实现光纤延迟线[J]. 光谱学与光谱分析, 2022, 42(07): 2241-2246.
WANG Chong, DU Huan, WANG Jing, WANG Jing, WANG Jing-hua. Using Fiber Grating Cascade Structure to Realize Fiber Delay Line. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(07): 2241-2246.
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