Fig. 1. (a) 3D sketch of a chiral PCF. (b) SEM image of the PCF used in the experiments. The hollow channels have a diameter d=1.7  μm and spacing Λ=3.8  μm(d/Λ=0.45), and the core diameter is ∼6  μm. The LP01-like core modes have (measured) losses 0.06 dB/m (LCP) and 0.05 dB/m (RCP), and effective indices 1.435599 (LCP) and 1.435601 (RCP) at 1550 nm, yielding circular birefringence BC=2.134  μRIU. (c) Measured and calculated circular birefringence BC versus wavelength. The inset is the calculated distribution of the Poynting vector.

Fig. 2. (a) Experimental setup to measure Brillouin frequencies in a chiral PCF. (b) Spontaneous Brillouin spectrum generated by pumping with 0.9 W of circularly polarized CW laser at 1550 nm. (c) Numerically calculated optoacoustic coupling coefficients (normalized) for different acoustic modes around 11 GHz. (d) Axial displacements (normalized to the square root of the power) of acoustic modes at 11.021 GHz and 11.039 GHz in (c).

Fig. 3. (a) Experimental setup to measure SBS threshold of different circularly polarized light in chiral PCF. EDFA, erbium-doped fiber amplifier; FPC, fiber-based polarization controller; and PBS, polarizing beamsplitter. (b) Stokes and transmitted pump power in a 38 m length of chiral PCF for LCP, RCP, and linearly polarized pump light (left to right).

Fig. 4. Stokes signal powers measured in a 25 m length of untwisted PCF, pumped by LCP, RCP, and linearly polarized light.

Fig. 5. (a) Measured Brillouin gain spectra (FWHM 41 MHz) when pumping with LCP (left) and RCP (right) light. The circles are measured data, and the full red line is a fit based on two Lorentzians (FWHM 31 and 65 MHz), indicated by the dashed red lines. (b) Left: Stokes gain spectra for LCP pump powers 0.54 W, 0.86 W, 1.36 W, and 2.09 W. Right: peak Stokes gain as a function of LCP pump power. The circles are the experimental data points and the line is a linear fit.

Fig. 6. (a) Experimental setup of circularly polarized Brillouin laser. (b) Laser power as a function of pump power for LCP (blue circles) and RCP (red crosses) pump light. (c) Theoretically fitted (blue) and measured (red) laser spectrum from sub-coherence delayed self-heterodyne system. Four sharp side peaks around the center peak is from the artifacts of the pump laser and unrelated to the experimental result. The inset is the spectrum of spontaneously scattered Stokes light from the identical chiral PCF and the linewidth-narrowed intracavity laser spectrum measured by delayed self-heterodyne system (the axis labels are same as those of the main figure).

Fig. 7. (a) Calculated normalized electric fields and effective indices for LCP and RCP modes. (b) Calculated axial displacements and frequencies for two acoustic modes that contribute to the backward Brillouin scattering in the chiral PCF.

Fig. 8. Experimental setup to measure Brillouin gain spectra of the chiral PCF. (Dashed line represents free space.)

Fig. 9. Power spectrum of the laser output before the narrowband filter, measured by the OSA. The lasing and back-reflected pump signals are clearly observed.

Fig. 10. (a) Experimental setup for delayed self-heterodyne measurement. (b) Experimentally measured self-heterodyne spectrum when the SMF delay is 26 km. (c) Experimentally measured self-heterodyne spectrum (red) and fitted curves (blue) with sub-coherent heterodyne formula [31] when the SMF delay is 2 km and 3 km.

Table 1. Signal Powers and Stokes Parameter |S3| in Chiral PCF Spooled to Different Diameters^a