Fig. 1. Schematic of the dynamic change of the fiber structure during the HC-NANF drawing.

Fig. 2. (a) Sensitivity of the fiber nested outer tube size to the preform nested tube size for the different tube thicknesses. (b) Sensitivity of the fiber nested outer tube size to the gas pressure difference for the different tube thicknesses.

Fig. 3. Simulation results of the fiber loss with different nested outer tube thicknesses.

Fig. 4. (a) SEM image of the fabricated HC-NANF. (b) Measured spectral attenuation using the cut-back method. Inset: the near-field camera image of the fabricated fiber output beam. (c) Measurement results of the fabricated fiber length using φ-OTDR.

Fig. 5. Schematic diagram of the FLOM-PD principle.

Fig. 6. Effect of the temperature change on the frequency stability.

Fig. 7. TCD simulation results of the fabricated HC-NANF.

Fig. 8. Experimental setup for the TCD measurement of the HC-NANF.

Fig. 9. Change of the phase difference between the two paths with time.

Fig. 10. Experimental setup of the optical frequency comb transfer system based on the HC-NANF.

Fig. 11. (a) Measured repetition frequency jitter of the optical frequency comb. (b) Frequency stability of the 250 MHz frequency transfer system based on the NANF and the SMF.

Fig. 12. Simulation results of the changes in the frequency stability of the frequency transfer system based on the NANF and the SMF due to periodic temperature changes.