An investigation of numerical aperture of air-core photonic bandgap fiber

Air-core photonic bandgap fiber (PBF) is the perfect choice of the next-generation fiber optical gyroscope (FOG), with excellent temperature, electromagnetism and radiation adaptability. Numerical aperture is an important optical parameter of PBF for application in FOG. The PBF's maximum theoretical numerical aperture (NA(max)) is calculated and compared with the far-field numerical aperture (NA(eff)) through experiments. The result indicates that the relationship between NA(max) and NA(eff) has much stronger dependence on wavelength than that of the conventional fiber, and they get close at wavelengths near the middle of the photonic bandgap with the error less than 5%. Furthermore, photonic bandgap fiber optical gyroscope (PBFOG) with no fusion splicing points is proposed, and the optimization method and results of the PBF's structure parameters for application in PBFOG are given from the aspect of numerical aperture.