All-optical Analog-to-digital Conversion Research Articles

Phase-frequency jointly quantizing method for cost-effective all-optical analog-to-digital conversion

We propose for the first time a two-dimensional phase-frequency jointly quantizing method for cost-effective all-optical analog-to-digital conversion (ADC), both on power consumption and structure complexity. By fully harnessing the power-dependent phase and frequency shift of the probe and pump light, respectively, that simultaneously occurs during the cross-phase modulation process, the method is studied with an on-chip interferometer structure based on nonlinear silicon-organic hybrid slot waveguide. Simulation results show the 4-bit quantization resolution is achieved by using only one interferometer, where N interferometers should be used in the conventional methods with resolution of N-bit. The proposed method provides an efficient optical quantization technique for all-optical ADC, also opens a new mind for exploring advanced all-optical ADC techniques using multi-dimensional degrees of freedom of light.

All-optical analog comparator.

An analog comparator is one of the core units in all-optical analog-to-digital conversion (AO-ADC) systems, which digitizes different amplitude levels into two levels of logical ‘1’ or ‘0’ by comparing with a defined decision threshold. Although various outstanding photonic ADC approaches have been reported, almost all of them necessitate an electrical comparator to carry out this binarization. The use of an electrical comparator is in contradiction to the aim of developing all-optical devices. In this work, we propose a new concept of an all-optical analog comparator and numerically demonstrate an implementation based on a quarter-wavelength-shifted distributed feedback laser diode (QWS DFB-LD) with multiple quantum well (MQW) structures. Our results show that the all-optical comparator is very well suited for true AO-ADCs, enabling the whole digital conversion from an analog optical signal (continuous-time signal or discrete pulse signal) to a binary representation totally in the optical domain. In particular, this all-optical analog comparator possesses a low threshold power (several mW), high extinction ratio (up to 40 dB), fast operation rate (of the order of tens of Gb/s) and a step-like transfer function.

Equiangular spiral photonic crystal fiber for code synchronization in all-optical analog-to-digital conversion based on lumped time delay compensation scheme

In this paper, we propose a lumped time delay compensation scheme for the all-optical analog-to-digital conversion (ADC) based on soliton self-frequency shift (SSFS) and optical interconnection techniques. By inserting a length of equiangular spiral photonic crystal fiber (PCF) between quantization and coding modules, the time delay of quantized pulses can be compensated. Simulation results show that the pulses can be synchronized utilizing a span of equiangular spiral PCF with flat negative dispersion of −258.92 ps/nm km in the wavelength range 1350nm to 1675nm. In addition, the amount of time delay and time error are analyzed, a maximum supportable sampling rate of 40GSa/s is obtained.

All-optical quantization scheme by slicing the supercontinuum in a chalcogenide horizontal slot waveguide

In this paper, we propose an integratable spectral quantization scheme for all-optical analog-to-digital conversion (AOADC) by slicing the supercontinuum, which is generated in a chalcogenide (As2S3) horizontal slot waveguide. The numerical simulation results show that a 4-bit quantization resolution is successfully achieved along with a signal-to-noise ratio of 23.96 dB and an effective number of bit (ENOB) of 3.98 bit. The required As2S3 waveguide length and input peak power are only 1.5 cm and 900 mW, respectively, owing to the high nonlinear coefficient of 115.8 W−1/m. It is believed that this proposed scheme can find important applications in the photonic integratable AOADC with low power consumption.

Time-stretch analog-to-digital conversion with a photonic crystal fiber

All-optical analog-to-digital conversion (ADC) has been extensively researched to break through the inherently limited operating speed of electronic devices. In this paper, we use the photonic crystal fiber (PCF) for time-stretch (TS) analog-todigital (A/D) conversion system through generating low noise, linear chirp distribution and flat super-continuum (SC). Based on the radio frequency (RF) analog signal modulated to the linearly chirped super-continuum, the large-dispersion photonic crystal fiber is used for time-domain stretching.

Resolution Improvement of All-Optical Analog-to-Digital Conversion Employing Self-frequency Shift and Self-Phase-Modulation-Induced Spectral Compression

We demonstrate and investigate resolution improvement of optical quantization using soliton self-frequency shift (SSFS) and optical coding using optical interconnection for an all-optical analog-to-digital conversion (ADC). Incorporating spectral compression into the optical quantization allows us to improve the resolution bit according to the spectral compression ratio with keeping its throughput. The proposed scheme consists of optical quantization using SSFS and self-phase modulation (SPM) induced spectral compression and optical coding using optical interconnection based on a binary conversion table. In optical quantization, the powers of input signals are discriminated by referring to the center wavelengths after the SSFS. The compression of the spectral width allows us to emphasize the differences of their center wavelengths, and improve the number of resolution bits. Optical interconnection generates a bit-parallel binary code by appropriate allocation of a level identification signal, which is provided as a result of optical quantization. Experimental results show the eight periods transfer function, that means, the four read-out bit operation of the proposed scheme in binary code. Simulation results indicate that the proposed optical quantization has the potential of 100 GS/s and 4-b resolution, which could surpass the electrical bandwidth limitations.

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

We propose and demonstrate the all-optical analog-to-digital conversion (ADC) using optical delay line encoders. Experimental results show that input analog signals are successfully converted into 3-bit digital signals at a bit rate of 40 Gb/s.

2-Bit All-Optical Analog-to-Digital Conversion by Slicing Supercontinuum Spectrum and Switching with Nonlinear Optical Loop Mirror and Its Application to Quaternary ASK-to-OOK Modulation Format Converter

Recently, the research on all-optical analog-to-digital conversion (ADC) has been extensively attempted to break through inherently limited operating speed of electronic devices. In this paper, we describe a novel quantization scheme by slicing supercontinuum (SC) spectrum for all-optical ADC and then propose a 2-bit all-optical ADC scheme consisting of the quantization by slicing SC spectrum and the coding by switching pulses with a nonlinear optical loop mirror (NOLM). The feasibility of the proposed quantization scheme was confirmed by numerical simulation:.We conducted proof-of-principle experiments of optical quantization by slicing SC spectrum with an arrayed waveguide grating and optical coding by switching pulses with NOLM. We successfully demonstrated optical quantization and coding, which allows us to confirm the feasibility of the proposed 2-bit ADC scheme.