Noise enhancement of telegraph signals in vertical cavity surface emitting lasers

Summary form only given. We present an experimental investigation of the response of a nonlinear, optical system to a random binary modulation (telegraph signal) changing the amount of applied external noise. The physical system which allows us to observe and characterize the phenomenon described is formed by a VCSEL followed by a polarized and a detection system. The signals from a variable intensity, white-noise generator and a pseudorandom binary sequence generator are summed and coupled into the laser input current. The polarized laser intensity, detected by the photodiode for different values of the input noise strength, is shown. For low noise the laser remains in its initial state. However, a small amplitude modulation is visible. Increasing the noise, some jumps occur. For an input noise around 400 mV/sub rms/, the output follows very well the input signal. For larger noise strengths, the laser dynamics are determined by the noise more than by the input string, with a strong decorrelation between input and output. The evaluation of the cross-correlation between input and output signal shows a peak for a well-defined, resonant value of noise. This is the first experimental evidence of SR for random, binary signals in a real system. To reconstruct the input signal, a suitable indicator can also be extracted from the bit-distribution and utilized to define the output response. The comparison of the input with the output signals is eventually reduced to a comparison of binary strings and can be treated by means of standard methods of information theory.