Fig. 1. Schematic illustration of the energy level diagram of rotational transitions between two vibrational states (v and v’). The rotational transitions in the P-branch correspond to transitions accompanied by an excess of one unit of angular momentum, i.e. ΔJ = -1 , and in R-branch to transitions with ΔJ = +1 With this system a combination of control-probe lasers resonant with P(J+1)-R(J-1) forms a Λ interaction and P(J+1)-R(J+1) forms a V interaction producing a comb of transparencies over the spectrum covered by the R-branch.

Fig. 2. Schematic representation of the experimental set-up. PD: photodetector, IF: interference filters, S: splice between the HC-PCF and a solid SMF, FPC: fiber polarization controller, EDFA: erbium-doped fiber amplifier, ECDL: external cavity diode laser. The inset on the left-hand side is a SEM of the HC-PCF used as the acetylene cell.

Fig. 3. (a) The transmission spectrum of a ~1m long acetylene-filled HC-PCF at a pressure of ~0.1-1 mbar. Inset: schematics of Λ and V interactions. (b) Measured (black line) and theoretical (grey line) transmission spectra for coupled power in the range of 400-500 mW, gas pressure in the range of 0.1-1 mbar and a fiber length of ~2 m. The asymmetry in some of the transparency traces are due to the probe-frequency detuning from the absorption transition.

Fig. 4. Evolution with the control-laser Rabi frequency of the transparency height (A) and full-width-at-half-maximum (B). The operating pressure range is 0.1-1 mbar and the fiber length is ~2 m.

Fig. 5. (49 kB) Animation of the evolution of the electromagnetically induced transparency with control-laser power launched into the HC-PCF for P(15)-R(13) combination.

Fig. 6. Measured and theoretical transmission trace of R(11) line in the absence of control beam (A) and in the presence of ~800 mW control power (B). The operating pressure range is 0.001-0.01 mbar and length of fiber ~2m.