Transverse propagation of ultraviolet and infrared femtosecond laser pulses in photonic crystal fibers

Abstract

-We studied the influence of angular orientation of a photonic crystal fiber (PCF) on optical power that reaches the fiber core during femtosecond grating inscription at 267nm and 800nm. In our numerical study we considered two types of PCFs: three PCF designs with a standard hexagonal lattice and one highly birefringent PCF with three rows of air holes. A dedicated figure of merit, the Transverse Coupling Efficiency (TCE), is used throughout the paper to estimate the influence of the PCF cladding on laser power that reaches the core region. We found that at an inscription laser wavelength of 800nm and for a high filling factor hexagonal lattice PCF, the TCE can reach 1.4. This means that the microstructure can actually help deliver higher power to the core region of the PCF than what can be achieved with a conventional step-index fiber of similar diameter. For a highly birefringent PCF even higher TCE values (up to 2.8) can be achieved for a wide range of orientations.

Photonic Crystal Mikaelian Lenses and Their Potential Use as Transverse Focusing Elements in Microstructured Fibers

“…We have also already tackled this issue in previous publications in which we have estimated the influence of the air hole lattice on the optical power that reaches the core of hexagonal lattice and highly birefringent MOFs [36], [37]. By doing so we were also able to show that it is possible to optimize the hexagonal lattice parameters in order to provide for enhanced transverse coupling [35].…”

“…1. Although strictly speaking, transverse pulse propagation through a MOF has a 3-dimensional nature, most of the numerical descriptions of this problem so far relied on a 2-dimensional geometry [29]- [37]. Carrying out full three-dimensional simulations of the propagation of laser pulses through a MOF requires considerable computing power, which is essentially due to the large fiber dimensions (usually diameters of 80 m or 125 m) compared to the wavelength of light ($1 m for infrared sources).…”

Challenges in the fabrication of fibre Bragg gratings in silica and polymer microstructured optical fibres

“…In a single material MOF, the refractive index change can be induced in the entire fibre cross‐section and therefore a larger core region should be considered. Figure explains how the TCE is eventually calculated . When applied to the same fibre as that frequently encountered in literature, i.e.…”

“…In another attempt to quantify the effect of the microstructure on the transverse coupling of the inscription laser intensity to the MOF core region, Baghdasaryan et al introduced a figure of merit named ‘Transverse Coupling Efficiency’ (TCE). This TCE is defined as the ratio of the core field intensity in the presence of a microstructured cladding, to the core field intensity in absence of that same microstructured cladding.…”

Opportunities for designing microstructured optical fibers for efficient femtosecond laser grating inscription

“…Here we present two approaches to exploit the design flexibility of MOFs to identify possible air holed cladding designs that can facilitate FBG writing [15], [21]- [24]. First we study MOFs in standard hexagonal lattice to identify a range of lattice parameters that minimally impedes light delivery to the core region.…”