The principle of small-signal detection using a two-input non linear system and noise (stochastic detector) can be applied in the fields of electronics, optics, chemistry, biology, etc., provided that the detecting or sensing system can be triggered by two independent functions: one symmetrical and one antisymmetrical. In order to be able to detect signals with smaller amplitudes than in the case of usual single-input systems, one has to connect the signal to be detected and a first noise (it can be the noise in which the signal is hidden) to the antisymmetric input, while a correlated noise only must be connected to the symmetrical input. In the case of binary signals for instance (0 and 1), the system can then wash out completely the noise from one state (0 or 1) which is enough for recovering a good signal to noise ratio.
They applied this principle to two laboratory experiments:
1) in electronics, a two-input Schmitt trigger in which the switching threshold can be controlled independently in symmetrical and antisymmetrical ways. This is straightforward to realize and could be useful in electronics for building weak signal comparators.
2) in optics, a bistable vectorial laser, in which the symmetrical input is a magnetic input and the antisymmetrical input is an optical input. Such a setup, which should be miniaturized using VCSELs for instance, could be applied to all-optical sensors.
An application of the stochastic detector to the “last mile” problem is possible. Current solutions propose to use a laser beam propagating in free space. However, the atmospheric transmission channel adds noises due to meteorological perturbations and degrades the signal. The stochastic detector associated to a dual-wavelength transmitter (see figure below) could enhance the signal to noise ratio by a few dBs. This scheme is currently tested in the laboratory. An experiment using two wavelengths shows a signal to noise ratio improvement using a standard detector which plays the role of the nonlinear system.
The French laboratory has a well-established theoretical and experimental expertise on the physics of lasers, optical sensors and small-effect detection, on the physics of noise and non linear systems, and on optical communications. Its know-how includes the realization of optic and electronic set-ups, and also prototypes with the help of industries.
– noise as a useful means in a detection system
– the use of a two-wavelength transmitter in the “last mile” application, with one wavelength only carrying the information.
– Simple implementation
– Constant signal-to-noise ratio, whatever the signal and noise amplitudes
– Possible use of ambiant noise as the noise source (as in the last mile application for instance)
– Information securing: one can add some extra noise on the transmitter, it hides the signal for conventional detectors whereas it is useful to the stochastic detector.