Photonic Digitization With Differential Encoding Based on Orthogonal Vector Superposition

Shuna Yang,Jun Ou,Yanrong Zhai,Qiliang Li,Hao Chi,Ran Zeng,Bo Yang

doi:10.1109/jphot.2019.2945780

Abstract

In this paper a novel photonic digitization scheme with differential encoding based on orthogonal vector superposition (OVS) is proposed and demonstrated. A phase modulator (PM) and two delay-line interferometers (DLIs) with π/2 difference in bias phase are employed to generate two orthogonal modulated signals. By adjusting and combining the intensity of two orthogonal signals with an OVS module, the desired phase shifts among different transfer functions can be obtained. The proposed scheme can differentially encode the input signal with enhanced bit resolution. Compared with the existing photonic digitization schemes based on modulators, this scheme features its simple configuration, because only a single PM, two DLIs and an OVS module are required; moreover, since the desired phase shifts of transfer functions are realized by attenuating the signal intensities, the proposed scheme can effectively alleviate the problem of phase bias drift induced by modulators. Proof-of-concept experiments of 3- and 4-bit photonic digitization systems based on OVS are successfully carried out, which demonstrate the feasibility of the approach.

Highlights

Digitization of wideband signals is essential for a wide range of applications, such as advanced radar systems, electronic monitor, real-time signal processing and spread spectrum communications [1]–[3]
Compared with the existing photonic digitization schemes based on modulators, this scheme features its simple configuration, because only a single phase modulator (PM), two delay-line interferometers (DLIs) and an orthogonal vector superposition (OVS) module are required; since the desired phase shifts of transfer functions are realized by attenuating the signal intensities, the proposed scheme can effectively alleviate the problem of phase bias drift induced by modulators
Since the integrated DLIs with suitable delay are not available at the time of experiment, we use an Mach-Zehnder modulators (MZMs) biased at 0 and π/2 respectively to obtain two orthogonal modulated signals, which are sufficient to demonstrate the concept of photonic digitization scheme based on OVS

Summary

Introduction

Digitization of wideband signals is essential for a wide range of applications, such as advanced radar systems, electronic monitor, real-time signal processing and spread spectrum communications [1]–[3]. By placing photodetectors (PDs) at different positions in interference pattern, the desired phase shifts among different modulation transfer functions can be obtained and the conversion of an input analog signal into digital data with linear binary coding is realized [16] This approach firstly introduced the concept of phase shift photonic digitization (PSPD), which avoids the problem relating to Vπ scaling in Taylor’s scheme. Since the peak-to-peak amplitude of a differential signal is usually much smaller than that of the original signal, the realized bit resolution can be effectively improved [19] Another scheme of PSPD is to use parallel intensity modulators with optical attenuation [20], which achieves the desired phase shifts by controlling the modulated signal intensity. Results show that a 4 GHz sinusoidal radio frequency signal can be efficiently digitalized with the digital signal-to-noise ratio (dSNR) of 19.14 dB and 24.44 dB

Quantization Principle

Results and Discussions

Conclusions