Figure 4. Optical non-reciprocity versus dropped pump power in the single-fibre-coupling case.

(a) Reciprocal transmission is expected with pump off. (b) With pump on, typical non-reciprocal transmission spectra are recorded as the forward signal experiences phase-matched parametric amplification but the backward does not. (c) The optical isolation is characterized only as a function of the dropped pump power. The error bars represent the standard deviations of measured isolation uncertainties under the same conditions, and their fluctuations are mainly affected by the uncertainties of backward signal transmission. Parameters: the simultaneously injected forward and backward signal powers are equal to 1.46 μW and κ₁=2π × 0.4 MHz.