Qingwei Wu

All-Optical Analog-to-Digital Conversion Based on Polarization-Differential Interference and Phase Modulation

A novel approach of an all-optical analog-to-digital converter is proposed and demonstrated. One single-phase modulator and a continuous-wave laser diode are used to quantize the sinusoidal tone analog signal. Software sampling measurements yielded an effective number of bits of 4.1. Benefits of the proposed setup are its simple design, high bandwidth, and stability. The scheme is primarily limited in the optical domain by the speed of the phase modulator and in electronic domain by electrical comparators and logic devices

All-Optical Analog-to-Digital Conversion Using Inherent Multiwavelength Phase Shift in LiNbO

All-optical analog-to-digital conversion utilizing inherent multiwavelength phase shift in lithium niobate phase modulator is proposed. In the experimental demonstration, a wavelength-tunable continuous-wave laser diode and a lithium niobate phase modulator are used to quantize the sinusoidal tone electrical analog signal. Using 16 different wavelengths, an effective number of bits of 4.3-bit has been obtained after software sampling measurement. Benefits of the presented approach in this letter are its simple realization of the phase shift and high stability.

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In this paper, an interferometric autocorrelator based on two-photon-absorption (TPA) detector is demonstrated. It can be used in the measurement of ultrashort pulse at 1.55 um wavelength region. From the second order autocorrelation trace of optical field, we can infer the pulse width. Accompanied with a linear detector, we can fully characterize the optical pulse, including intensity and phase profiles. A novel phase retrieval algorithm is proposed. It is a combination of an iterative loop and an evolution process. Simulation results show that our algorithm converges stably and can give a better approximation of the optical field than traditional algorithm.

Phase Modulator

An optical analog-to-digital conversion system is proposed and demonstrated. Using time- and wavelength- interleaved optical sampling pulse train; sampling rate of 40GS/s is realized. 2.5 GHz sinusoidal electrical analog signal is sampled and quantized using this system, achieving an effective number of bits of 3.45 bits. A novel technology that can dramatically improve the bandwidth of this system will also be presented in this paper, which manifests that our system can realized high bandwidth of more than 50 GHz using commercially available LiNbO(3) phase modulator.

Ultrashort pulse measurement using interferometric autocorrelator based on two-photon-absorption detector at 1.55-μm wavelength region

An adaptive thresholding scheme in photonic analog-to-digital conversion is proposed and experimentally demonstrated. Instead of a single-ended electronic comparator, differential detection technology is used to reduce the quantization noise induced by thresholding error. The main advantages of this scheme are the elimination of the dynamic setting of thresholding level and better tolerance to common-mode noise.

40GS/s Optical analog-to-digital conversion system and its improvement.

We present a novel scheme of a spectral encoded photonic analog-to-digital converter (ADC). Several cascaded unbalanced lithium niobate Mach-Zehnder modulators with doubling path length imbalances are used to convert the amplitude of the electrical analog signal to the shift of the transmission characteristic. Compared with former spectral encoded photonic ADCs, a particular benefit of our presented scheme is no requirement of any nonlinear effect to realize optical quantization.

Adaptive thresholding scheme in photonic analog-to-digital conversion

A novel balanced detection threshold scheme for all-optical analog-to-digital conversion is experimentally demonstrated. A 4-bit 10-GSamples/s all-optical analog-to-digital converter based on phase-shifted optical quantization and a balanced detection threshold scheme is realized to quantize a 9.9-GHz sinusoidal electrical signal, achieving a spur-free dynamic range of 24.2 dB. Compared with single-ended detection, the quantization result is improved with the balanced threshold scheme due to reducing the influence of the power fluctuation and improving the receiver sensitivity.

Spectral Encoded Photonic Analog-to-Digital Converter Based on Cascaded Unbalanced MZMs

An improvement of a photonic analog-to-digital converter based on phase-shifted optical quantization (PSOQ) is presented and verified. The resolution can be increased by employing an additional Mach-Zehnder modulator (MZM) to combine with the PSOQ scheme. The improved scheme with a quantization level of 32 (corresponding quantization bit number is 5 bits) is experimentally demonstrated by using two LiNbO3 modulators, and the experimental result with the effective number of bits 4.23 is obtained.

Experimental Demonstration of All-Optical Analog-to-Digital Conversion With Balanced Detection Threshold Scheme

A novel scheme of spectral encoded photonic analog-to-digital converter is proposed. Cascaded lithium niobate Mach-Zehnder modulators are used to convert the amplitude of the electrical analog signal to the shift of the transmission characteristic, and a set of interleaving spectral filters perform as the optical comparators. Compared with usual spectral encoded photonic analog-to-digital converter, particular benefit of our proposed scheme is no requirement of nonlinear effects to realize spectral quantization and encoding.

Improvement of Photonic ADC Based on Phase-Shifted Optical Quantization by Using Additional Modulators

A phase-shifted photonic analog-to-digital conversion system is experimentally demonstrated with 40 GS/S sampling rate. A 2.5 GHz sinusoid signal is quantized and the effective number of bits of 3.41 is obtained.