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Photonic Crystal Fibre
Published in Shyamal Bhadra, Ajoy Ghatak, Guided Wave Optics and Photonic Devices, 2017
Samudra Roy, Debashri Ghosh, Shyamal Bhadra
This dispersion slope is an important parameter that gives an idea about the sensitivity of the dispersion for a small wavelength variation. In an air–silica system, air is effectively dispersionless at optical frequencies. Due to the dominance of the electronic resonances in a silica molecule, the refractive index of silica decreases across the wavelength range concerned with a sharp slope at shorter wavelengths. The material dispersion curve of silica strictly increases with the wavelength and has a zero dispersion point (ZDP) at 1.27 μm. The ZDW is very important as it determines the boundary between the normal (β2 > 0) and the anomalous dispersion (β2 < 0) regions. The ZDP also affects the efficiency of other nonlinear phenomena that are responsible for supercontinuum (SC) generation. The amazing flexibility of tailoring the dispersion leads to MOFs with two (sometimes even more!) ZDPs, which open up new and interesting features of pulse propagation. The large extent to which the dispersion of MOFs can be tailored simply by changing the MOF design parameters is graphically shown in Figures 15.20 and 15.21. The ZDW shifting can be clearly seen in all four graphs.
Optical Fiber
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Reference Guide, 2002
David R. Goff, Kimberly Hansen, Michelle K. Stull
FWM:FWM is a phenomenon that arises from the nonlinearity of the refractive index of the optical fiber.FWM is a third-order distortion mechanism. It is very similar to CTB (composite triple beat) distortion in the CATV realm.FWM becomes worse as the fiber dispersion drops. It is worst at the zero-dispersion point. Higher chromatic dispersion results in less FWM.FWM is worst in WDM channel designs where the spacing is equal. (Equal channel spacing is, unfortunately, the case in standardized DWDM designs.)FWM becomes worse as wavelengths are spaced closer together.Fiber designs with larger effective areas exhibit less FWM nonlinearity.
Design of Single-Mode Optical Fiber Waveguides
Published in Le Nguyen Binh, Guided Wave Photonics, 2016
Figures 5.8 through 5.11 show the variations of core/cladding radii with respect to the total dispersion factor. We observe the following effects of the variation of the core/cladding radii on the dispersion factor over the entire 1300–1600 nm spectral region As the core radius, a0, is increased the total dispersion curve is shifted upwards, at the same time the second zero dispersion point is shifted to a higher wavelength region. Meanwhile, the first zero dispersion point remains unchanged and the third zero dispersion point gradually shifts to a lower wavelength region. By analyzing the behavior of the dispersion curves of several simulated results, we obtain the maximum sensitivity of changes in a0 to total dispersion is about 88.88 ps/(nm-km-μm). As the first cladding radius, a1, is decreased the total dispersion curve shifts upwards. The maximum sensitivity due to incremental change in a1 to total dispersion is about 64.68 ps/(nm-km-μm).As the second cladding radius a2 is decreased, the total dispersion curve shifts upwards, but the first zero dispersion point shifts to a lower wavelength region, a maximum sensitivity due to incremental changes of a2 to total dispersion in the fiber windows region of 0.99 ps/(nm-km-μm) is obtained.
The characteristics of petroleum seepage in coal seams: a case study of Ordos Basin
Published in Petroleum Science and Technology, 2022
Jie Zhang, Jianjun Wu, Sen Yang, Wenyong Bai, Qingsong Zhuo
The fitting curve of the dispersion point of the petroleum seepage distance within 30 months was obtained according to the cloud diagram of the petroleum seepage range in the coal seam, as shown in Figure 14. The petroleum seepage range can be roughly divided into three stages. From the 0 to the 5th month, the radial seepage distance is about 10 m, which indicates that the seepage movement is slow. Here, the petroleum seepage velocity is almost zero, so the petroleum seepage range is small. The petroleum seepage range linearly grows from the 5th to the 20th month, and the maximum radial seepage distance is about 215 m. According to the change in petroleum seepage pressure, the petroleum seepage pressure increases continuously during this period. The petroleum seepage velocity increases continuously. Therefore, the petroleum seepage range presents a linear increase trend. From the 25th to the 30th months, the petroleum seepage velocity tends toward zero, so the petroleum seepage range is small at this stage. The final radial seepage distance is about 221 m. In the early stage, the radial seepage distance is small, During the second stage, the radial seepage distance increases linearly. Finally, the seepage distance stabilizes during final stage.
Highly nonlinear dispersion-flattened high-index-core Bragg fibres for supercontinuum generation
Published in Journal of Modern Optics, 2019
Jiajin Zheng, Wenjie Lei, Yao Qin, Hui Zou, Kehan Yu, Wei Wei
Figure 3(c) shows the chromatic dispersion changed with an increase in dn from 0.01–0.04, while Λ was fixed at 1.2 µm, d/Λ=0.15 and R = 5 µm. The chromatic dispersion of the HICBFs at wavelengths from 0.8 µm to 1.5 µm was almost the same as that of the HICBF, as shown in Figure 3(a). That waveguide dispersion curve declines with the decrease of RI difference and the total dispersion value decreases. The trend of red shift of the zero dispersion point was more obvious compared with Figure 3(a) and the total dispersion also gradually shifts to the normal dispersion region. The optimization of larger and more refined range of zero dispersion point can be realized by adjusting the dn difference slightly. It is very important to realize the phase matching of nonlinear process (such as four wave mixing and dispersive wave amplification) when generated supercontinuum by adjusting the zero dispersion point. There are two ZDW shifts to long wavelength with the increases of dn and the dispersion remains between −5 and 12 ps/(km·nm).
Novel large negative dispersion and tunable zero dispersion wavelength of photonic crystal fiber
Published in Waves in Random and Complex Media, 2018
Dechang Huang, Zhaodi Huang, Dongming Zhan
Photonic crystal fibers (PCFs), as a novel optical fiber, are usually formed by a solid pure silica core region surrounded by multiple air holes with the same diameter arrayed in a regular triangular lattice, become one of the most versatile platforms for the design of various dispersion fibers since first fabricated in 1998. Several types of large negative dispersion fibers design using PCF have been reported previously [6–11]. For example, Chen et al. investigated a double-core structure. The inner core has a circle germanium-doped region. The outer core is formed by removing the 3rd ring air-holes around the core, and the simulation results show the dispersion coefficient D is −1320 ps(nm km) at 1.55 μm [12]. Recently, Yuan et al. designed a dual concentric-core photonic crystal fiber (DCCPCF). Although the large negative dispersion value of −39500 ps (nm km) is achieved around 1.55 μm, the bandwidth is only 7.4 nm [13]. Habib et al. propose a PCF based on a modified octagonal structure for broadband dispersion compensation covering the S, C, and L communication bands i.e. wavelength ranging from 1460 nm to 1625 nm in 2012. The results shown that the proposed PCF can obtain negative dispersion coefficient of about −400 to −725 ps/(nm km) over S and L-bands and a relative dispersion slope (RDS) close to that of single mode fiber (SMF) of about 0.0036 nm−1. However, the design PCF has no zero dispersion point in the communication band, which is a disadvantage of this design [14].