Twist effect on spectral properties of two-mode fiber acousto-optic filters

Sun Do Lim,Byoung Yoon Kim,Hyun Chul Park

doi:10.1364/oe.16.013042

Abstract

The splitting and the shift of resonance peaks in the output spectrum of two-mode fiber acousto-optic devices caused by twist perturbation are described. An elliptical-core two-mode fiber and a two-mode photonic-crystal fiber are used for the analysis. The splitting of the resonance peaks are found to be almost linearly proportional to the twist angle of the fiber with the slopes of about 0.58 nm/(rad/m) for the elliptical-core fiber and about 0.29 nm/(rad/m) for the photonic crystal fiber. The experimental results compare well with the theoretical predictions.

Highlights

All-fiber acousto-optic tunable filters (AOTFs) are of interest for their applications to optical communications and sensing with their advantages of low insertion loss, wide tuning range, and fast switching speed [1,2,3]
A 180 degree-twist of an elliptic-core (e-core) two-mode fiber (TMF) in an AOTF resulted in the improvement of side mode suppression from -9.7 dB to -15.5 dB [5]
We describe in detail our observation of the splitting and the shift of resonance peaks in the output spectra of TMF AOTFs under fiber twist of up to multiple turns

Summary

Introduction

All-fiber acousto-optic tunable filters (AOTFs) are of interest for their applications to optical communications and sensing with their advantages of low insertion loss, wide tuning range, and fast switching speed [1,2,3]. A 180 degree-twist of an elliptic-core (e-core) two-mode fiber (TMF) in an AOTF resulted in the improvement of side mode suppression from -9.7 dB to -15.5 dB [5]. We describe in detail our observation of the splitting and the shift of resonance peaks in the output spectra of TMF AOTFs under fiber twist of up to multiple turns. The e-core TMF supports only one of the LP11 mode lobe orientations along the major axis of the core ellipse, whereas the PCF supports both the lobe orientations over the wavelength range of our interest. We show that the resonance peaks of the AOTF split as the fiber is twisted and the separation is almost linearly proportional to the twist angle. Theoretical calculations based on the coupled-mode theory provide an accurate explanation of the experimental observations

Theory

Δβa z sin

Elliptical-core TMF AOTF

Two-mode photonic crystal fiber AOTF

Conclusion