Soliton self-frequency shift and spectral compression in highly nonlinear fibers for resolution improvement of all-optical ADC

Analog-to-digital conversion (ADC) has been investigated as a key interface technology to convert analog signals into digital ones. Recent tremendous advances in optical communications and digital signal processing have encouraged the research on all-optical ADC with high speed and high resolution [1]. The process of ADC consists of sampling, quantizing, and coding. Some techniques of optical sampling have come to reality. However, optical quantization has been a challenge. Several optical quantization techniques have been proposed, in which the use of nonlinear effects in fiber is one promising approach [2,3]. Soliton phenomena such as soliton self-frequency shift (SSFS) and higher order soliton formation have been employed for quantization process in all-optical ADC [2,4]. A 4-bit all-optical ADC scheme has been reported recently by employing SSFS in combination of spectral compression of chirped ultrashort pulses [5]. Here we demonstrate a soliton self-frequency shift of ∼150 nm and spectral compression in highly nonlinear fibers (HNLFs) with 580-fs pulses at 1550-nm wavelength. The wavelengths of the resulting solitons can be tuned effectively by adjusting the input power. The results indicate that a resolution of 5 bits for optical quantization can be achieved.