| Summary: | A selective-filling high birefringent photonic crystal fiber (SF-HBPCF) based Sagnac interferometer (SI) was demonstrated. The SF-HBPCF was achieved by infiltrating a high index liquid into two symmetrical air holes of the innermost layer of an index-guiding un-birefringent PCF. The birefringence characteristics of the SF-HBPCF and the strain sensing characteristics of the SF-HBPCF based SI were theoretically analyzed in detail. The group birefringence presented unique characteristics, and particularly possessed a zero value at a certain wavelength. This directly resulted in the strain sensitivities having ultrahigh even infinite value at the certain wavelength. Besides, with the change of the loaded strain, the sensitivities of the interference dips presented disparate variation trend. In experiments, the results were well matched with theoretical simulation. And the strain sensitivities from 25 pm/με to 12 pm/με were achieved from 61 με to 789 με in the type of the SF-HBPCF.
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