Graphene oxide integrated polarization maintaining microfiber refractometer based on effective birefringence response

•It is the first time, to the best of our knowledge, that we observe the slow and fast axes may interchange in the tapered polarization maintaining fiber.•Based on this novel phenomenon, the effective birefringence of the tapered polarization maintaining fiber can respond to ambient refractive index.•The response sensitivity may be linearly and dramatically magnified because that the principal axes between the untapered and tapered sections are orthogonal in the tapered polarization maintaining fiber.•The tapered polarization maintaining fiber is relatively robust, which is conveniently post-processing to improve its sensitivity and expand its application scope.