40 GSample/s All-Optical Analog to Digital Conversion With Resolution Degradation Prevention

In this letter, we report the experimental demonstration of a 40 GSample/s all-optical analog to digital converter (ADC). The proposed all-optical ADC consists of optical quantization and coding processes based on intensity-to-wavelength conversion by soliton self-frequency shift with an optical sampling process using an ultrastable optical pulse train. A 5-GHz sinusoidal analog input signal was successfully converted to a digitized output signal in real time with no degradation of resolution. (High sampling rate operation may lead to resolution degradation due to the reduction of pulse peak power and the narrowing of the interval between adjacent pulses.) To evaluate system performance, we estimated the effective number of bits from the experimental results as 3.79 b.