Influence of Refractive Index Distribution on Brillouin Gain Spectrum in GeO_(2)-Doped Optical Fibers

GeO_(2) is commonly used as dopant to adjust the refractive index profile(RIP)and the acoustic velocity profile(AVP)in the fiber,thereby forming different Brillouin gain spectrum(BGS)characteristics such as Brillouin gain,acoustic mode number and peak intensity difference.When an optical fiber is used in optical fiber sensing or communication system,its BGS characteristics may play an important role in determining the performance of the system.In this paper,finite element analysis(FEA)method is used to study the influence of refractive index distribution and its corresponding AVP on the BGS in step-index,graded-index,and complex-index optical fibers.A new method has also been proposed to efficiently discriminate acoustic mode solution and obtain the new and full images of total Brillouin gain and acoustic modes number of the fiber as a function of the refractive index distribution,considering the influence of changing the refractive index difference and the geometric size simultaneously.For each type of optical fiber,the recommended parameter range is provided for optical fiber sensing and optical fiber communication.Moreover,the suitable optical fiber with close peak intensity in its multi-peak BGS is explored and achieved,which can be used in Brillouin beat spectrum detection systems to improve sensing accuracy.

Erahertz spectral analysis of Xiling Zhimu with different geological conditions and plant age

Objective: In order to identify the quality of different geological conditions and plant ages of Xiling Zhimu. Methods: This article uses the terahertz spectroscopy to detect and analyze different geological conditions and ages of Zhimu (Anemarrhenae Rhizoma) from the same origin. Results: The terahertz time-domain spectroscopy of different geological conditions and ages has a decrease relative to the reference amplitude and has a delay. The refractive index has obvious differences, and the refractive index can be used as a way to identify the tablets. The absorption coefficients of different ages Zhimu samples has significant differences in the range of 1.0-2.0 THz. The absorption coefficients of different geological conditions Zhimu samples has significant differences in the range of 1.1-2.0 THz. Conclusions: The differences caused by different production methods should be considered in the identification of genuine regional drug. When the Zhimu is grown due to different geological conditions and plant ages, its efficacy will also change. we can detect this change by terahertz spectroscopy.

Terahertz spectral analysis of Yunpian Lurong

Objective: Provide a rapid and simple method to identify Yunpian Lurong. Method: Terahertz spectroscopy was used to detect Yunpian Lurong. Result: Compared with the reference wave, the spectral amplitude of Yunpian Lurong decreases significantly. The frequency - domain spectra of Yunpian Lurong are different from conventional Lurong. Compared with the spectrum of free space, both of them have obvious absorption to THz wave, but the intensity and location of absorption are different, which provides a basis for the identification of Yunpian Lurong. The refractive index of the two samples is obviously different, which may be related to the different internal structure and composition content of the samples. The absorption coefficient of the two samples are different as well, when the frequency ranges from 0 to 2.4 THz, the absorption coefficients of the two kinds of Lurong samples have obvious difference, which makes it easy to distinguish the Yunpian Lurong. Conclusion: This study proves that terahertz spectroscopy can be used as an efficient and convenient method to identify Yunpian Lurong.

Absorption Spectra and Refractive Index Changes of an Exciton in a Core/Shell Quantum Dot

The absorption spectra and the refractive index changes are calculated theoretically for an exeiton in a core/shell quantum dot. The advantage of our methodology is that one can investigate the influence of the repulsive core by varying two parameters in the confinement potential. The dimensionality effect of exciton quantum dots on the optical absorptions has been studied. It has been found that in the same regime, the optical absorption intensities of excitons axe much smaller for the core/shell quantum dots than for the two-dimensional quantum rings. The linear and the nonlinear optical absorption coefficients and refractive index changes have been examined with the change of the confinement potential. The results show that the optical absorptions and the refractive index changes are strongly affected by the repulsive core of core/shell quantum dots. Moreover, the calculated results also reveal that as the inner radius increases, the peak values of the absorption coefficients and the refractive index changes of an exciton will show the optical Aharonov-Bohm oscillation in core/shell quantum dots.