We investigate a quantization error improvement technique using a dual rail configuration for optical quantization. Our proposed optical quantization uses intensity-to-wavelength conversion based on soliton self-frequency shift and spectral compression based on self-phase modulation. However, some unfavorable input peak power regions exist due to stagnations of wavelength shift or distortions of spectral compression. These phenomena could induce a serious quantization error and degrade the effective number of bit (ENOB). In this work, we propose a quantization error improvement technique which can make up for the unfavorable input peak power regions. We experimentally verify the quantization error improvement effect by the proposed technique in 6 bit optical quantization. The estimated ENOB is improved from 5.35 bit to 5.66 bit. In addition, we examine the XPM influence between counter-propagating pulses at high sampling rate. Experimental results and numerical simulation show that the XPM influence is negligible under ∼40 GS/s conditions.

We investigate resolution improvement in optical quantization with keeping high sampling rate performance in optical sampling. Since our optical quantization approach uses power-to-wavelength conversion based on soliton self-frequency shift, a spectral compression can improve resolution in exchange for sampling rate degradation. In this work, we propose a different approach for resolution improvement by parallel use of dispersion devices so as to avoid sampling rate degradation. Additional use of different dispersion devices can assist the wavelength separation ability of an original dispersion device. We demonstrate the principle of resolution improvement in 3 bit optical quantization. Simulation results based on experimental evaluation of 3 bit optical quantization system shows 4 bit optical quantization is achieved by parallel use of dispersion devices in 3 bit optical quantization system. The maximum differential non-linearity (DNL) and integral non-linearity (INL) are 0.49 least significant bit (LSB) and 0.50 LSB, respectively. The effective number of bits (ENOB) estimated to 3.62 bit.

We report a trial of 100-GS/s optical quantization with 5-bit resolution using soliton self-frequency shift (SSFS) and spectral compression. We confirm that 100-GS/s 5-bit optical quantization is realized to quantize a 5.0-GHz sinusoid electrical signal in simulation. In order to experimentally verify the possibility of 100-GS/s 5-bit optical quantization, we execute 5-bit optical quantization by using two sampled signals with 10-ps intervals.