Time-stretched sampling of a fast microwave waveform based on the repetitive use of a linearly chirped fiber Bragg grating in a dispersive loop

Jiejun Zhang,Jianping Yao

doi:10.1364/optica.1.000064

Abstract

Conventional sampling techniques may not be able to meet the ever-increasing demand for increased bandwidth from modern communications and radar signals. Optical time-stretched sampling has been considered an effective solution for wideband microwave signal processing. Here, we demonstrate a significantly increased stretching factor in the photonic time-stretched sampling of a fast microwave waveform. The microwave waveform to be sampled is intensity modulated on a chirped optical pulse generated jointly by a mode-locked laser and a length of dispersion compensating fiber. The pulse is then injected into an optical dispersive loop that includes an erbium-doped fiber amplifier and is stretched by a linearly chirped fiber Bragg grating multiple times in the loop. A record stretching factor of 36 is achieved based on an equivalent group delay dispersion coefficient of 12,000 ps/nm. This result could help address the new challenges imposed on signal processors to operate at a very high sampling rate.

Highlights

The ever-increasing bandwidth of modern communications and radar signals has imposed new challenges on signal processors to operate at a very high sampling rate
A microwave waveform is modulated on a predispersed optical pulse, which is sent to a recirculating dispersive loop consisting of an linearly chirped fiber Bragg grating (LCFBG) and an erbium-doped fiber amplifier (EDFA)
A novel time-stretched sampling system with a large stretching factor has been demonstrated by the repetitive use of an LCFBG in a recirculating dispersive loop

Summary

INTRODUCTION

The ever-increasing bandwidth of modern communications and radar signals has imposed new challenges on signal processors to operate at a very high sampling rate. The use of a microwave waveguide with a large GDD coefficient has been explored in the past few years for spectrum analysis [18,19] It was demonstrated [20] that by forming a dispersive loop that incorporates a microwave dispersive element and a microwave amplifier, an equivalent microwave dispersive element with a GDD coefficient that is several times greater than that of the original dispersive element can be achieved by recirculating the microwave waveform in the loop. A microwave waveform is modulated on a predispersed optical pulse, which is sent to a recirculating dispersive loop consisting of an LCFBG and an erbium-doped fiber amplifier (EDFA). For a sampling system with a bandwidth of 32 GHz, the use of the proposed recirculating dispersive loop can extend the bandwidth by 36 times, or 1.15 THz (or a time resolution of 347 fs), with a frequency resolution of 4.93 GHz

PRINCIPLE

EXPERIMENT

Findings

DISCUSSION AND CONCLUSION