Digital-Analog Hybrid Optical PLL System Based on Undersampling

Abstract

A digital-analog hybrid optical phase-locked loop system based on undersampling can be applied to a high-speed and high-sensitivity homodyne coherent demodulation laser communication system. After converting the signal light and local oscillator light into an analog electrical signal through a 90-degree optical bridge and a balanced detector, the analog-to-digital converter (ADC) under-samples the electrical signal, and the field programmable logic gate array (FPGA) The phase error signal is extracted for the controller, and the phase error signal is filtered by a digital loop to drive a direct digital frequency synthesizer (DDS) to generate an error signal with both frequency and phase controlled, thereby realizing optical phase locking. The present invention is characterized in that the extraction of the phase error signal is realized by means of under-sampling, which reduces the requirements on the electronic bandwidth and digital signal processing speed of the receiving end. At the same time, the local oscillator light is controlled by means of external modulation, which improves the loop control bandwidth and phase-locking performance. The invention can realize homodyne coherent demodulation with high speed and high sensitivity.

Description

technical field [0001] The invention relates to the field of coherent optical communication of high-speed homodyne coherent demodulation, in particular to a digital-analog hybrid optical phase-locked loop system based on subsampling, which can relax the requirements for the bandwidth of receiving electronic devices. Background technique [0002] Coherent laser communication has the advantages of high speed and high sensitivity, and is gradually replacing the traditional direct detection of intensity modulation. For the homodyne coherent reception of high-speed optical signals, an optical phase-locked loop is required at the receiving end to extract and lock the phase error signal of the local oscillator light and the received signal light. The realization of the optical phase-locked loop mainly has two technical difficulties: the first is the extraction of the phase-locked error signal under the high-speed modulation; the second is the control method of the local oscillator....

AI Technical Summary

Problems solved by technology

This method can increase the closed-loop bandwidth of the optical phase-locked loop to around 600KHz, but this type of local oscillator light control method is more complicated and the optical efficiency is lower

The prior art [2] (Xu Jian, Huang Liyan, He Guoliang, etc. A carrier phase estimation method in a coherent optical receiving device: CN105763265A.2016) proposes to use the carrier phase estimation method in the digital domain for signal demodulation, which This demodulation method does not require precise phase-locked control of the local oscillator, but requires a higher processing speed for DSP and ADC

It is not conducive to the miniaturization and weight reduction of the receiving device

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