Birefringent fibers have attracted considerable attention in recent years for their potential applications in communication and sensing. In this thesis we selectively infiltrate high-index liquids or liquid crystals (LCs) into specified air holes of the photonic crystal fibers (PCFs) by using a selective blocking technique and the vacuum filling method to form half-filled birefringent PCFs and central-filled liquid crystal PCF (LCPCF). We first measure the bending loss of the half-filled PCF. Smaller bending loss was obtained as the PCF was bent in 0¢X due to the dominat index-guiding. Compared with the full-filled PCF, the half-filled PCF possesses a smaller bending loss for the reduction of liquid-filled air holes. The birefringent properties of the half-filled PCF and the LCPCF were then measured in cooperation with the Sagnac fiber loop. We can obtain the birefringence of the half-filled PCF of 2.39¡Ñ10^-4 at £f = 1411 nm, and the sensitivity to temperature, strain, and torsion can be obtained as -0.614 nm/¢XC, 0.466 pm/£g£`, and -0.316 nm/deg. These large sensitivities make the half-filled PCF useful in sensing applications. We also measured the birefringence of the central-filled LCPCF with variant laser irradiation and temperature. The optical and thermal birefringence variations from 2.8¡Ñ10^-3 to 4.12¡Ñ10^-3 and from 2.3¡Ñ10^-3 to 3.3¡Ñ10^-3 can be oberserved, respectively. The optically and thermally tunable birefringence of the central-filled LCPCF was experimentally demonstrated.