The fiber Bragg grating has been widely used in sensors. We have studied the spectral properties of uniform Bragg gratings in photonic crystal fibers under transverse pressure. By the finite element method, the relation between the birefringence and the pressure was simulated in bare photonic crystal fibers. The results show that the birefringence is changed even under weak pressure. A new method based on polarization-dependent loss is presented for measuring pressure. The maximal amplitude of the polarization-dependent loss varies linearly in the pressure range of 0 to 4 MPa with a slope of 0.75 MPa−1.
Two-mode highly birefringent optical fibers support two spatial modes. The two spatial modes can be used to set up two
detectors. The birefringence would change with the variety of environment. Therefore, two-mode highly birefringent
optical fibers can sense two parameters synchronously. A finite element method (FEM) was used to numerically
calculate the distribution of pressure, distribution of temperature and the birefringence variety versus pressure and
temperature in two-mode highly birefringent photonic crystal fibers. Based on the single parameter sensor, the
muti-parameter sensor was analyzed. The results show that the muti-parameter sensor can measure pressure and