fabricated by us. Figures 5 and 6 show the results for the two kinds of fibers, respectively. The FSR is about 8.06 nm for the PANDA-PMF of length 761 mm in Figure 5. Meanwhile, the FSR is about 1.05 nm for the PCF of length 564 mm as shown in Figure 6.2 /⌬L values for the PANDA-PMF and the PCF are about 3.8 ϫ 10 Ϫ4 and 3.9 ϫ 10 Ϫ3 at 1545 nm wavelength, respectively. It is clear that, compared with 2 /⌬L, d(n x Ϫ n y )/d is small, and can be ignored in our PCF case. Thus, from Eqs. (1) and (3), the birefringences are ϳ3.8 ϫ 10 Ϫ4 and ϳ3.9 ϫ 10 Ϫ3 at the 1545-nm wavelength for the PANDA-PMF and the PCF, respectively, and the beat lengths L B are about 3.6 mm and 0.33 mm, respectively.Our asymmetric core design for highly birefringent PCF is similar to the one proposed in [4]. The difference is only the intentional stress-induced birefringence added in the fabrication process. In [4], the expected value of birefringence for hole size d/⌳ of 0.431 and normalized frequency ⌳/ of ϳ3.76 was below 1.0 ϫ 10
Ϫ4. It is clear that our experimental value is one order of magnitude higher than the theoretical value in [4]
CONCLUSIONIn conclusion, we have designed and fabricated a photonic-crystal fiber with a high birefringence by utilizing the asymmetric core design and intentional stress-induced anisotropy. A short beat length of 0.33 mm at 1545 nm was observed for the PCF. Birefringence of the PCF was improved to one order of magnitude higher than the value reported by T.P. Hansen et al. [4].
INTRODUCTIONMicrowave engineering has been rendering important contributions to both diagnostic and therapeutic medicine. Clinical investigation plays a vital role in the diagnosis of disease for medical practioners to reach conclusive decisions after procedures such as inspection, palpation, and percussion. A number of medical devices, which uses microwaves, were developed for biomedical applications [1]. Exhaustive studies of dielectric parameters of various human tissues at different RF frequencies were reported by Gabriel et al. [2, 3]. Dielectric parameters of human blood at microwave frequencies using coaxial line and the waveguide method were reported by Cook [4]. Also, human tissue samples were studied at microwave frequencies by Cook [5] and Land et al. [6]. Sample cell-terminated transmission-line methods have obtained good response at lower microwave frequency, but the accuracy is very much comprised at higher microwave frequencies [5,7,8]. The open-ended coaxial-line method allows measure- ments in a wide range of frequencies [9,10]. Standard waveguide dielectric samples allow measurements in the entire microwave region with a good degree of accuracy, except at lower frequencies where the sample size is very large [11]. Microwave medical tomography is emerging as a novel nonhazardous method of imaging for the detection of fracture, swelling, and diagnosis of tumors. For active and passive microwave imaging for disease detection and treatment, monitoring requires proper knowledge of the dielectric properties of body ...
