Group Birefringence Regulation and Measurement With Twin Zeros in a Selectively Infiltrated Microstructured Optical Fiber Based on OFDR

We propose and demonstrate a selectively microfluidic-infiltrated method for the group birefringence regula-tion in a microstructured optical fiber. Meanwhile, an Optical Frequency Domain Reflectometry (OFDR) with an equivalent resolution of 0.6 Hz or 10 ⁻⁶ RIU is utilized to characterize its polarization separation and group birefringence change. By selectively infiltrating a fluid with a high thermal-optic coefficient into twin air holes nearby the silica fiber core, tunable group birefringence is observed and measured by polarization separation in beat frequency domain. Moreover, due to the co-effects of the filled and unfilled fiber segments, the twin critical zeros of the overall group birefringence are observed at 16.5° and 43.0°, respectively. The unique position exchange of LP ₀₁ ^x and LP ₀₁ ^y presents at the twin critical zeros, which is investigated via the OFDR technique as well. Therefore, by combining the unfilled fiber segment with negative group birefringence and filled fiber segment with positive group birefringence, dual zeros in group birefringence are achieved with position exchange of the LP ₀₁ ^x and LP ₀₁ ^y peaks in beat frequency domain. Our demonstration provides potentials in flexible regulation and real-time observation of the group birefringence in microstructured optical fiber.