Structure files
Structure files (.mof or .txt files, also called position files) contain a full description of the fibre's structure to be simulated, including position, shape and refractive indices of each inclusion, of the cladding and jacket, the definition of material properties and symmetry properties, as well as truncation order of Fourier-Bessel series.
Structure files can be generated using Winfield's structure editor (recommended), within the parameter file (this is largely obsolete), or manually for advanced users.
Contents
General structure
Structure files are text files that can be edited with any text editor (eg emacs, vi, notepad), but because of their complicated data structure it is recommended to use Winfield's graphical interface to edit structure files. Information below is for manual editing of structure files.
Each structure has a header containing version information, symmetry information, number of inclusions, and definition of the cladding and jacket. This header is followed by a lost of all inclusions. If user defined materials are use, each material is defined after the list of inclusions.
The structure of the structure file has evolved with the software and depends on the version of the software. Fibre and Winfield both can parse structure files of any previous versions, but will only write files to the latest structure format.
The structure described below corresponds to the latest versions.
Header
The header will look something like this:
new_version
2010002
6
4
3
1
(1.91268900000000,0.000000000000000E+000)
(1.91268900000000,0.000000000000000E+000)
18.1800000000000 18.3618000000000 (1.91268900000000,0.000000000000000E+000)
Line 1 should always be:
new_version
Line 2 indicates the version of fibre the file is written for:
2010002
Line 3 indicates the symmetry of the structure, through an integer number sym. If N=1,2,4 6,8,10,12 the symmetry is Csymv[1]. If sym is 0 no symmetries are used. If sym is -1, C_C6 symmetry is used, as described by J.M. Fini[2]. If sym=10000 C\infinity v is used. In the latter case only one inclusion at the centre of the structure can be present. In the example above
6
indicates that C6v symmetry is to be used.
Line 4 is the number Ninc of inclusions in the irreducible sector. In the example
4
means there are 4 inclusions in the irreducible sector. This also means 4 inclusions will be listed after the header.
Line 5 indicates the default order for truncation of Fourier Bessel series. This number is mostly ignored, but to avoid all bugs should be equal to the largest order of truncation of Fourier Bessel series used for a cylinder. In the example
3
indicates that no inclusion will use truncation orders in excess of 3: Bessel Series will go from -3 to 3 at most.
Line 6 indicates the order of truncation of Fourier Bessel series in the cladding and jacket regions. If no jacket or cladding are used, and the simulation is not a scattering simulation, this number should be 1 (never 0). In the example
1
indicates Fourier Bessel series in the background, matrix and jacket will go from -1 to 1.
Line 7 is a complex number giving the permittivity (or alias if material dispersion is used) of the background (or matrix). In the example
(1.91268900000000,0.000000000000000E+000)
indicates that the background has permittivity 1.912689+i.0.
Line 8 is a complex number giving the permittivity (or alias if material dispersion is used) of the external medimum (jacket). In the example
(1.91268900000000,0.000000000000000E+000)
indicates that the background has permittivity 1.912689+i.0.
Line 9 contains the inner and outer radius of the cladding (Real numbers) and the complex permittivity (or alias if material dispersion is used) of the cladding. In the example
18.1800000000000 18.3618000000000 (1.91268900000000,0.000000000000000E+000)
indicates the inner radius of the cladding is 18.18, the outer radius is 18.3618 and the cladding's permittivity is 1.912689+i.0. Note that the line can be split (eg the permittivity can be on the next line).
List of inclusions
The list of inclusions contains Ninc entries describing each inclusion. Each entry containts several real, complex and integer values, in the following order:
r, theta, radius, epsilon, symcat, axis, material, shape, radius_b, ellipse_theta, order, representation, radius_coating, epsilon_coating, material_coating
The numbers can be on one or several lines, an example would be:
0.000000000000000E+000 0.000000000000000E+000 2.00000000000000
(1.82520100000000,0.000000000000000E+000) 0 0 0
2 2.00000000000000 0.000000000000000E+000 3
0 1.92000000000000 (2.25000000000000,0.000000000000000E+000)
0
- r
- The radial polar coordinate of the inclusion's centre (distance to origin). In the above example r=0 (inclusion is at the origin).
- theta
- The angular polar coordinate of the inclusion's centre (distance to origin). In the above example theta=0.
- radius
- The outer radius of the inclusion. In the above example radius=2.0 (ie inclusion's diameter is 4.0).
- epsilon
- The complex permittivity (or alias if material dispersion is used) of the inclusion. This must always be a complex number even if the imaginary part is zero. epsilon=1.825201+0.i.
- symcat
- symcat integer describing whether the inclusion is completely within or at an edge of the irreducible sector. Values of symcat:
| 0 | Inclusion is at the origin |
| 1 | Inclusion is on an axis of symmetry |
| 3 | Inclusion is entirely within the irreducible sector, not on any of the axes if symmetry. |
| -1 | No symmetries are used |
In the example symcat=0 as the inclusion is at the origin.
- axis
- This indicates which axis of symmetry the inclusion is on (if any):
| 0 | Inclusion is at the origin or not on an symmetry axis |
| 1 | Inclusion is on the theta=0 axis of symmetry |
| 2 | Inclusion is on the other axis of symmetry (theta=pi/sym for Csymv). |
In the example axis=0 as the inclusion is at the origin.
- material
- This integer number indicates which material the cylinder is made of:
| 0 | No material dispersion; use the permittivity defined in epsilon |
| -1 | use fused silica Sellmeier expansion |
| positive integer | Use material properties of material material in the material list (see below). |
In the example, material=0 indicating the permittivity is not wavelength dependent and is defined by epsilon.
- shape
- Integer number describing the shape of inclusion. Value can be
| 0 | inclusion has circular cross section with homogeneous refractive index |
| 1 | Inclusion has elliptic cross section |
| 2 | inclusion is circular with a refractive index coating (uses formulation from [3] |
| 3 | Inclusion is circular with concentric layers of refractive index, uses formulation as described in [4]. |
In the example shape=2 indicating the inclusion is circular with a coating.
- radius_b
- Real number: radius of second axis for elliptical inclusions (shape=1). Unused for shape=0,2,3. In the example, radius_b=2.0, but is in fact not used as shape=2.
- ellipse_theta
- real number giving the angle of the principal axis of the ellipse with respect to the y=0 axis. Only used if shape=1. In the example, ellipse_theta=0.
- order
- Integer number giving the order of truncation of Fourier Bessel series used to describe fields around this inclusion. Very important parameter, should never be 0! In the example order=3, Fourier Bessel series truncated from -3 to 3 are used to describe fields around this cylinder.
- representation
- Integer value defining whether matrices are expressed in terms of internal or external Fourier Bessel coefficients. Only for advanced users. This corresponds to the 'b or c' choice in winfield. representation=0 for 'b' (external) representation, 1 for 'c' (internal) representation. In the example representation=0, external field representations are used (default).
- radius_coating
- Real number: inner radius of coating if shape=2. Unused for shape=0,1,3. In the example radius_coating=1.92000000000000
- epsilon_coating
- The complex permittivity (or alias if material dispersion is used) of the inclusion. This must always be a complex number even if the imaginary part is zero. In the exampleepsilon_caoting=2.25+0.i. Only used if shape=2.
- material_coating
This integer number indicates which material the coating is made of, is shape=2.
| 0 | No material dispersion; use the permittivity defined in epsilon |
| -1 | use fused silica Sellmeier expansion |
| positive integer | Use material properties of material material in the material list (see below). |
In the example, material_coating=0, no material dispersion is used for the coating.
End of list of inclusion
The list of inclusion ends with a single integer number indicating how many materials are described in the materials list. If there are no user defiend materials, this number should be 0 and is the last entry in the file.
List of user defined materials
to be completed.
References
- ↑ P. R. McIsaac, ‘‘Symmetry-induced modal characteristics of uniform waveguides. I. Summary of results,’’ IEEE Trans. Microwave Theory Tech. MTT-23, 421–429 (1975).
- ↑ J.M. Fini, "Improved symmetry analysis of many-moded microstructure optical fibers", J. Opt. Soc. Am. B 21 (8) 1431-1436
- ↑ Kuhlmey, BT et al Multipole analysis of photonic crystal fibers with coated inclusions, Opt. Express 14 10851-10864 (2006)
- ↑ [1] T. Grujic, B.T. Kuhlmey, C.M. de Sterke, and C.G. Poulton, “Modelling of photonic crystal fiber based on layered inclusions,” Journal of the Optical Society of America B 26, pp. 1852-1861.
