tailieunhanh - Advances in Measurement Systems Part 12

Tham khảo tài liệu 'advances in measurement systems part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Waveength nm Fig. 21. Ratio response of the system at different polarization states Fig. 22. Experimental arragement to study the impact of PDL on wavelength measurements Estimation of the maximum variation in the measured wavelength is important as we can determine the system s worst case performance. The maximum and minimum values of the fluctuation of PDL of the filter arm due to the 3 dB coupler and the fiber filter can be calculated using Equation 14 . A comparison of the estimated maximum and minimum of the PDL of the filter arm with the measured PDL of the filter arm is shown in Fig. 23. Measured PDL of the fllte arm Estimated minimum Estimated maximum Wavelength nm Fig. 23. Maximum and minimum PDL of the fiber filter arm and its comparison with the measured PDL. Passive All-Fiber Wavelength Measurement Systems Performance Determination Factors 437 For a ratiometric system both of the arms contribute to the total ratio variation. The PDL of the reference arm and filter arm obtained from the experiment provides the maximum and minimum power levels of each arm. Based on that a numerical simulation can be carried out to find the maximum ratio variation and can be estimated using Equation 15 . The estimated variation in ratio and wavelength of the system and its comparison with the measured versions are shown in Fig. 24 a and Fig. 24 b respectively. To estimate the wavelength error the local slope of the ratio spectrum is used. The wavelength error which is a consequence of ratio variation in practice depends on the slope of the system which is low at shorter wavelengths and high at longer wavelengths which results in a larger error at shorter wavelengths than at longer wavelengths. In the example shown in Fig. 24 for a fiber filter of mm radius and 15 turns it is estimated that the maximum wavelength error at 1500 nm is nm from the original value. Any measured error in wavelength should be within this estimated wavelength error range. From the figure .