Abstract
We demonstrated a kind of birefringence-controllable hybrid photonic crystal fibers (HPCFs) by selectively infiltrating air holes of PCFs with index-tunable liquids processing higher index than silica background. Detailed theoretical investigations on mode couplings from fundamental core mode to high-index-liquid-rod modes and birefringence properties of several HPCFs were presented. Strong wavelength dependence of phase and group birefringence was found, and HPCFs with different arrangements of high index liquid rods possess distinct birefringence characteristics. Then, the Sagnac interferometers (SIs) based on two typical HPCFs with different liquid-rod arrangements were theoretically and experimentally studied. The results indicated the SIs exhibit different transmission spectra and temperature responses due to the distinct birefringence features of HPCFs. A temperature sensitivity of -45.8 nm/°C at 56.5 °C was achieved using one HPCF, and a sensitivity of -11.6 nm/°C from 65 °C to 85 °C was achieved using the other HPCF. The thermal tunable HPCFs with birefringence-controllable properties will provide great potential for a variety of tunable optical devices and sensors.
Highlights
Photonic crystal fibers (PCFs) [1,2] are a class of optical fibers constituting wavelength-scale microstructure running along fiber length
By detailed theoretical simulation of mode couplings between core fundamental mode and high index rod mode and birefringence properties of several hybrid photonic crystal fibers (HPCFs), we found that coupled high-index-rod modes have impacts on the birefringence properties
Distinct birefringence properties were achieved for HPCFs under different arrangements of high index rods
Summary
Photonic crystal fibers (PCFs) [1,2] are a class of optical fibers constituting wavelength-scale microstructure running along fiber length. The modal group birefringence has a zero value at a certain wavelength and an ultra-high sensitivities of 26.0 nm/°C (63,882 nm/RIU) at 50.0 °C was experimentally achieved For this kind of PCFs having several air holes filled with high index liquids [21,22,23], the fundamental core mode can couple with high-index-liquid-rod modes. Taken all the HPCFs above studied together, we conclude that the existence of high index rods makes this type of HPCFs have specific birefringence characteristics different from index-guiding Hi-Bi PCF [3,4], the elliptical hollow core birefringent PBGF [5] and all-solid PBGF with elliptical cladding rods (the B has smaller values in the middle and higher values at both edges) [6]. The birefringence features can be concluded by the characteristics of the SIs
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