Remarks on stochastic resonance

A recent and interesting experimental paper B. McNamara, K. Wiesenfeld, and R. Roy, Phys. Rev. Lett. 60, 2626 (1988) has refocused attention on the problem of stochastic resonance by presenting measurements of the singal-to-noise ratio (SNR) of a noise driven, periodically modulated bistable ring laser. We point out that the theoretical SNR, as defined in this and a previous work, is always infinity, because additive modulation leads to a function in the power spectrum of the output. Quantitative information on stochastic resonance is contained in the strength of this function relative to the noise background. We qualitatively reproduce the SNR data with an analog simulator using a standard quartic bistable potential. In this, as in previous experiments and simulations, a peak in the observed power spectrum is a reflection of the function, but the amplitude of the peak is rendered finite (and hence measureable) only because of the finite resolution of the measurement system.