Waist diameter dependent temperature and strain sensitivities of tapered high birefringence fiber in Sagnac interferometer

•Strain-insensitive Sagnac interferometer with tapered high birefringence fiber.•Merged Sagnac and modal interferences in Sagnac interferometer.•Discrimination of temperature and strain.•Taper waist diameter dependent temperature and strain sensitivities. The relation of the temperature and strain sensitivities to the waist diameter of the tapered high birefringence fiber (THBF) in Sagnac interferometer is theoretically analyzed and experimentally demonstrated. With a large waist diameter, the occurred Sagnac interference shows sensitive to both temperature and strain. The temperature and strain sensitivities decline as the waist diameter decreases. By contrast, when the waist diameter of the THBF is sufficiently small, both Sagnac and modal interferences are simultaneously generated. The former is only sensitive to temperature, whereas the latter is sensitive to both temperature and strain. As the waist diameter of the THBF decreases, the temperature sensitivities of both the Sagnac and modal interferences diminish, but the strain sensitivity of the modal interference improves. Therefore, the proposed THBF Sagnac interferometer enables simultaneous measurement of temperature and strain variations. Importantly, the strain-insensitive characteristic of Sagnac interference facilitates the discrimination between temperature and strain variations.