Few-Mode Fibers With Uniform Differential Mode Group Delay for Microwave Photonic Signal Processing

Jian Zhao,Tianhua Xu,Jinsheng Xu,Zhiqun Yang,Huan Zhang,Chao Wang

doi:10.1109/access.2020.3007169

Abstract

We present a novel design of few-mode fiber (FMF) with a uniform differential mode group delay (U-DMGD) among propagating modes and apply the FMF to a single-fiber delay line module for implementing microwave photonic finite impulse response (FIR) filters. By optimizing key parameters such as the core grading exponent and the dimension of the trench of FMF, a U-DMGD between adjacent modes among four modes (LP 01 , LP 11 , LP 02 and LP 31 ) over the entire C band is achieved. Wavelength dependence is entirely removed. An FIR microwave photonic filter (MPF) implemented using the designed 1-km FMF is investigated through numerical simulations. The free spectral range (FSR) of the MPF is 5.7 GHz, the 3-dB bandwidth is 1.26 GHz, and the main lobe-to-side lobe ratio (MSR) is 10.42 dB. Discussions on fabrication aspects have also been presented. The proposed single-fiber delay line structure based on FMF can significantly reduce the system complexity of microwave photonic signal processing.

Highlights

The microwave photonic filter (MPF), which is a pivotal module in microwave photonics, has been applied in various fields such as radar, phased array beamforming and radio over fiber networks etc [1]
PARAMETERS OPTIMIZATION OF few-mode fiber (FMF) WITH uniform differential mode group delay (U-DMGD) In order to investigate the optimum value of the core grading exponent α and the dimensions of the trench (RIC, RTR, and nTR) that allows U-DMGD among the modes, an optimization function J is introduced with an objective of minimizing ng at a specific wavelength: J (RIC, α, nTR, RTR) =2
Based on the explanation presented above, we studied the effect of four parameters (RIC, α, RTR, and nTR) on J at a selected wavelength of 1550 nm, in order to realize the design of the FMF with U-DMGD

Summary

INTRODUCTION

The microwave photonic filter (MPF), which is a pivotal module in microwave photonics, has been applied in various fields such as radar, phased array beamforming and radio over fiber networks etc [1]. PARAMETERS OPTIMIZATION OF FMF WITH U-DMGD In order to investigate the optimum value of the core grading exponent α and the dimensions of the trench (RIC , RTR, and nTR) that allows U-DMGD among the modes, an optimization function J is introduced with an objective of minimizing ng at a specific wavelength: J (RIC , α, nTR, RTR) = ( nLgP02−LP11 − nLgP11−LP01). Based on the explanation presented above, we studied the effect of four parameters (RIC , α, RTR, and nTR) on J at a selected wavelength of 1550 nm, in order to realize the design of the FMF with U-DMGD. The typical fabrication tolerances for nCO, nTR, RCO, RIC , RTR and α are listed in Table 3 according to [14] These discrepancies result in corresponding deviations in the DMGD relative to the targeted value.

SETUP OF MPF AND PERFORMANCE EVALUATION

CONCLUSIONS