1 / 2016-04-18 14:59:27

Birefringence and nonlinearity analysis of a photonic band-gap fiber used in fiber ring resonators

9851,9850,9849,9364,9848,9847

The resonant fiber optic gyro (RFOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect in the fiber ring resonator (FRR). However, the RFOG still suffer from various noises, including polarization fluctuation, Kerr effect, Rayleigh backscattering, and so on. Among these noises, the temperature polarization fluctuation has been regarded the main reason to the long-term instability of the RFOG. As one of the main optical noise sources in the RFOG, the optical Kerr-effect noise comes mainly from the input-intensity mismatch between the clockwise (CW) and counter clockwise (CCW) light waves input to the resonator. To avoid the deleterious effects associated with polarization instability, RFOGs typically use a polarization maintaining fiber (PMFs). However, in the traditional PMFs such as panda and bow-tie fibers, high birefringence are achieved by introducing anisotropy in the geometry or stress in the fiber profile, and they are highly temperature dependent.
The PBFs guide light mainly in the air-filled region, surrounded by a micro-structured cladding of air holes and silica.The air-guiding mechanism and the exceptionally high air-filling factor means only a small fraction of light propagating in silica and hence lower nonlinearity and high thermal stability. Moreover, the birefringence in PBFs is induced by form rather than stress, therefore the temperature dependence would be lowered naturally, and they have the features of low sensitivity to magnetic and radiation compared with the conventional ones as well. The use of a PBF therefore offers a new means of solving the old nonreciprocal noises of temperature induced polarization instability and Kerr-effect noise by confining the most energy of the propagated light by the air-guide mechanism but does not increase the size and complexity of the sensors. However, most of PBFs used in RFOGs are not polarization-maintaining (PM) designed, the polarization crosstalk is inevitable. The performance of PBF-based RFOG can be improved further by designing PM-PBF with lower nonlinearity.
In this paper, an air-core PBF with very high birefringence, ultra nonlinearity and simple structure. The effects of structure parameters on the birefringent and nonlinear properties are analyzed numerically. Finally, an optimized design with phase birefringence of 6.25×10-3 is obtained, and the group birefringence can be as high as 7×10-2 at the wavelength of 1.55μm, the nonlinear coefficient at the wavelength of 1.55μm is as low as 4.9×10-3 (W. Km)-1, which is 220 times lower than a traditional SMF-28 fiber. As an outstanding PM fiber, the PBF can be applied to reduce the polarization fluctuation and Kerr effect-induced drift in resonant fiber optic gyroscope (RFOGs), and so on.