Figure 4. Non-degenerate optical modes.

(a) Transmittance of an optical split-mode (splitting ∼8.6 MHz) as a function of laser-cavity detuning, obtained by sweeping the laser frequency and measuring the resulting transmittance using an oscilloscope. The horizontal axis is calibrated using the EOM placed in the control arm (see Fig. 2a). The black solid line represents a fit of a double Lorentzian lineshape to the blue data points. The red shading is the area under the two fitted Lorentzian lineshapes. (b) Transmittance of the optical probe beam as a function of control-probe detuning with the control frequency fixed at the blue mechanical side band. When the probe beam co-propagates (|S₂₁|², dark green circles) with the control beam an optomechanically induced absorption window appears, while the oppositely propagating probe (|S₁₂|², light green squares) experiences increased transmission. (c) Asymmetric phase transmission for the same measurement as b. Light green squares correspond to arg(S₁₂), the dark green circles to arg(S₂₁). The solid lines in b are fitted simultaneously to |S₁₂|² (blue line) and |S₂₁|² (yellow line). The resulting parameters are inserted in S₁₂ (blue line) and S₂₁ (yellow line) to yield the lineshapes in c (Methods).