Elsevier

Optik

Volume 127, Issue 5, March 2016, Pages 2954-2958
Optik

Comparative analysis of fiber ring resonator based on different fibers

https://doi.org/10.1016/j.ijleo.2015.12.062Get rights and content

Abstract

A fiber ring resonator (FRR) is the core element in a resonant fiber optic gyro (RFOG) and its resonant depth, finesse and sensitivity determine the performance of RFOG. A configuration of FRR based on air-core photonic bandgap fiber (PBF), photonic crystal fiber (PCF) and panda polarization-maintaining fiber (PMF) is proposed, and the resonant depth, finesse and sensitivity of the FRR are comparative analyzed fully and in depth. It's found that: the FRR using PCF and PBF have better resonant depth than that of using PMF; the FRR using PCF has nearly the same performance as that using PMF, and may be a trade-off used in FRR before the existence of better PBF; the key factor that whether the FRR resonates in optimal resonant state is whether αc and kc of directional coupler satisfy the optimal resonant condition. These theoretical results are helpful to further study and optimize the RFOG based on different fibers.

Introduction

A resonant fiber optic gyro (RFOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect in the fiber ring resonator (FRR) [1]. Compared with the widely-used IFOG, the RFOG has the features of short fiber ring, high accuracy and wide dynamic range [2]. However, the accuracy of RFOG still suffer from various noises, including polarization fluctuation [3], [4], Kerr effect [5] and Rayleigh backscattering [6], and so on. Among these noises, the temperature polarization fluctuation has been regarded the main reason to the long-term instability of the RFOG [7]. Many efforts have been proposed to overcome this problem: using twin polarization-axis rotating splices [8], [9], a suppression of more than 20 dB to the temperature-related dependence can be achieved in the conventional polarization-maintaining FRR; ensuring the single ESOP excitation by integrating in-line polarizer [10] or using single-polarization-single mode fiber[11] in the FRR is another way to eliminate the effect of polarization. However, the birefringence of the conventional PMF is inevitably affected by the external temperature and stress fluctuation, owing to the light propagating in the silicon core. The appearance of photonic crystal fiber (PCF) [12] and air-core photonic bandgap fiber (PBF) [13], [14] provides a new method to overcome the problem. The birefringence of PCF and PBF are form induced rather than stress induced, therefore the temperature dependence would be lowered naturally, and they have the features of high birefringence, low sensitivity to magnetic and radiation compared with the panda polarization maintaining fiber (PMF). Especially, the PBF guides light in a hollow core, 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 higher stability [15].

As restricted by the present craft, the directional couplers for PBFs haven’t existed, the resonant loops of existed PBF-BFOG designs were closed by free-space coupling [16], conventional PM-coupler [17] or micro-optics structure [18]. While, the discrete loss and Fresnel reflection at the connection point are serious because of mode field mismatching between the PBF and other kind coupling elements. However, the appearance of directional couplers based on dual-core PCF [19] and dual-core PBF [7] can promote the applications of PCF and PBF in BFOG. In 2014, Ma et al. [7] proposed a single-polarization coupler based on dual-core PBF, and investigated the implications for RFOG, the FRR formed by connecting the PBF and dual-core PBF based coupler without any in-loop junctions has outer performance to suppress the temperature-related polarization fluctuation in RFOG compared with in-line polarizer integrated FRR. However, the significantly great round-trip loss occurring in the FRR is the first problem that the PBF based RFOG facing. For current commercial PBF, the propagation loss is at least two orders of magnitude greater than those in conventional PMF and PCF, and the backscattering is serious as well [7]. Thus, the PCF with low loss, low temperature sensitivity and high birefringence may be a trade-off used in FRR before the existence of better PBF.

In 2010, Ying et al. [20] presented an in depth analysis of sensitivity of PBF-based FRR compared with that of conventional fiber based FRR; in 2012, Feng et al. [21] investigated the effects of different structure parameters on the resonant depth, resonant finesse and limited sensitivity of an micro-optics structured PBF-FRR. However, an in depth fully analysis of an FRR based on PBF, PCF and PMF haven’t been done. In consideration of the importance of RFOG, it's necessary to make full and in depth analysis about the resonant characteristics of FRRs based on the conventional PBF, PCF and PMF.

In this paper, a configuration of FRR based on different types of fibers connected by dual-core fiber directional couplers is proposed and the effects of different structure parameters on the resonant depth, resonant finesse and limited sensitivity are comparative analyzed fully and in depth. Finally, the principle to obtain FRR with high resonant depth, resonant finesse and limited sensitivity simultaneously, is presented.

Section snippets

Structure of FRR and theory

Fig. 1 illustrates the configuration of the FRR based on different types of fibers. In FRR based on PBF, PCF and PMF, the directional couplers are assumed to be made of dual-core PBF, dual-core PCF and conventional directional coupler. Therefore, the large fusion-splice loss between PBF or PCF with conventional PMF can be ignored in this paper.

P1, P2, P3, P4 are the four ports of directional coupler, the initial light Ein is inputted into P1, can be written as follows:Ein=E0expi[ωt+ϕ(t)]where E0

Simulation and discussion

In order to study the effects of structure parameters on the performance of FRR based on different types of fibers, amount of simulation analysis are made comprehensively. The structure parameters include: r (the radius of FRR), L (the length of fiber), δω (the linewidth of laser), αc (the coupling loss of directional coupler), kc (the coupling coefficient of directional coupler). It's assumed that: I0 = 1 mW; η = 0.8; t0 = 1 s; λ = 1.55 μm; αL(PBF) = 20 dB/km (NKT HC-1550-PM-01), αL(PCF) = 2 dB/km (NKT

Conclusion

A configuration of fiber ring resonator (FRR) based on air-core photonic bandgap fiber (PBF), photonic crystal fiber(PCF) and panda polarization-maintaining fiber(PMF) connected by dual-core fiber directional couplers is proposed and the effects of different structure parameters on the resonant depth, resonant finesse and limited sensitivity are comparative analyzed fully and in depth. It's found that: the FRR using PCF and PBF have better resonant depth than that of using conventional fiber;

Acknowledgements

This research was supported by the National Major Scientific Instruments and Equipment Development Projects (NMSIEDP) (2012YQ2160185).

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