All-Optical Analog-to-Digital Conversion Using Optical Delay Line Encoders

Analog-to-digital conversion (ADC) has been widely studied as a key interface technology to connect continuous analog signals and manageable digital signals. Recent tremendous growth of high-speed digital signal processing and communication systems has encouraged the demand for a high-speed ADC. For the realization of a high-speed ADC, optical approaches have much attracted recently [1]. ADC consists of three processes: sampling, quantization, and coding. Whereas the feasible sampling techniques with a high-sampling rate have been proposed, there are few investigations of optical quantization and coding [2]–[6]. Previously, we have proposed the all-optical ADC composed of optical quantization using self-frequency shifting in a fiber and optical coding using a pulse shaping technique [3], [4]. Whereas optical coding using a pulse shaping technique is suitable for the generation of digital signals at a high bit rate of several hundreds Gb/s [4], the standard bit rate in current systems is up to several tens Gb/s. To match the bit rate of output digital signals to the standard one, another coding scheme that allowed us to output digital signals at lower bit rate is required. In this paper, we propose and demonstrate the all-optical ADC using optical delay line encoders that enables to set a bit rate of output digital signals in the range from several Gb/s to over a hundred Gb/s.