Fig. 5
From: Statistical parity-time-symmetric lasing in an optical fibre network
Lasing characteristics of a statistical PT-symmetric cavity around the exceptional point. a, Measured values of the output power from the gain port I Gain (red circles) while varying the attenuation \({\cal L}\) at different gain values G (30, 25, 20 and 15 dB). The solid curves are best fits to guide the eye, with fittings obtained from Eqs 2–3 by a suitable choice of coupling κ and detuning Δ. As the loss is gradually increased at fixed gain, I Gain is non-monotonic. First I Gain decreases with \({\cal L}\) and goes through a minimum at the exceptional point (indicated by the vertical dashed line), and then increases with loss as the gain and loss sub-cavities decouple. b, Simulations for I Gain while varying the attenuation \({\cal L}\) at different values of G using Eqs 2–3, based on experimental parameters. The red circles correspond to the data in the top-most graph in a for G=30 dB. The area under the curves are shaded to highlight the gradual increase of the lasing power upon increasing gain. c, Same as a for the power from the loss port I Loss. Inset shows theoretical plots of I Gain and I Loss at G=30 dB for the statistical PT-symmetric configuration of our experiment (solid curves) and the ideal deterministic configuration (dashed curve, Δ=0) highlighting the bifurcation in output power as a consequence of PT-symmetry breaking upon passing through the exceptional point of the system. d, Same as b for I Loss instead of I Gain
