A simple analytical model for confinement loss estimation in hollow-core Tube Lattice Fibers.

Luca Vincetti,Lorenzo Rosa

doi:10.1364/oe.27.005230

Abstract

In this work, we propose an analytical model for estimating confinement loss in Tube Lattice Fibers. It is based on the single-tube model and the inhibited coupling waveguiding mechanism. The comparison with numerical simulations of tube lattice fibers having different geometrical parameters and dielectric refractive indexes demonstrates the model validity and effectiveness. Being based only on analytical closed formulas, it constitutes a useful tool for rapid estimation of TLF CL. It also gives a more in-depth insight into the TLF guiding mechanisms, confirming the inhibited coupling is an appropriate and effective model for such kind of fibers.

Highlights

Since they were first proposed [1], and experimentally demonstrated [2], single-ring Tube Lattice Fibers (TLFs) have been showing extremely interesting optical properties, making them good candidates as hollow-core low-loss broadband fibers for applications from the terahertz band [3, 4] to visible and ultraviolet wavelengths [5, 6], including the mid-infrared [7, 8] spectral range. More recently they have proved to be a good platform for sensing [9,10,11]. Their waveguiding mechanism is known as Inhibited Coupling (IC): it is the same as Kagome Fibers and is based on the inhibition of the coupling between core modes and cladding ones [12,13]
A consequence of the guidance mechanism is the leaky nature of the core modes, so that Confinement Loss (CL) is one of the main loss mechanisms in TLFs
An empirical formula able to estimate the minimum value of CL in each of the fiber transmission bands has been proposed [15]

Summary

Introduction

Since they were first proposed [1], and experimentally demonstrated [2], single-ring Tube Lattice Fibers (TLFs) have been showing extremely interesting optical properties, making them good candidates as hollow-core low-loss broadband fibers for applications from the terahertz band [3, 4] to visible and ultraviolet wavelengths [5, 6], including the mid-infrared [7, 8] spectral range. In the same figure the CL spectrum of the FM is shown It highlights that the high-loss band is composed of several peaks with the maxima centered at the frequencies corresponding to the phase matching between FM and DMs. the strength of the anti-crossing and the peak amplitude is reduced as the DM spatial field oscillations become quicker and quicker. The advantage of the single-tube model relies on the fact that the modes of a ST fiber have been analytically analyzed in [17] Their cut-off can be effectively expressed in terms of two normalized quantities: the normalized frequency F and the tube aspect-ratio t/rext. We describe the single resonance loss curve with a Lorentzian function L(F), estimating the spectral location by means of the cut-off frequencies of the ST fiber modes FcHμ,Eν and FcEμ,Hν.

Model validation

Conclusion