Figure 3. Threshold and power dependence of the symmetry breaking between clockwise and counterclockwise propagating light.

(a) Amount of light coupled into the resonator as a function of the laser frequency for increasing incident powers (by changing the EDFA output power, cf. Fig. 2). Higher powers (shown as darker colours) lead to an increased splitting between the clockwise (red) and counterclockwise (blue) modes. The incident power is 10% higher in the clockwise direction to avoid switching caused by fluctuations in the relative power. (b) Theoretical calculation of the power coupled into the resonator with the same parameters as in panel (a). (c) Maximum difference between clockwise and counterclockwise coupled powers as a function of the total input power. The black dots show the experimental measurements while the green curve is a theoretical fit for a pump power ratio of 0.9.