UM 2p6

2.6 Structure Files

The structure file details the structure: position, size and refractive index of inclusions, cladding and jacket. The order of truncature of the Bessel expansions are also given in this file, but can be redefined in the parameter file. The structure file is a text file which can be edited with your usual text editor. Table 1 gives an example of the structure of the file (each line of the table should be a line of the file). The file has a header defining global parameters and the cladding structure:

1. Symmetry: symmetry class, 0 if no symmetries are used, 1 for C_1v , 2 for C_2v , 4 for C_4v, 6 for C_6v , 8 for C_8v , 10 for C_10v . Other symmetries are not yet implemented.
2. Number of cylinders in the irreductible sector (integer)(ie the smallest angular sector given for that symmetry in Ref. [4]) The irreductible sector is (0,π/10) for C_10v , (0, π/6) for C_6v , (0, π/2) for C_2v , (0, π) for C_1v , the entire plane if no symmetries are used.
3. Order of truncature for Fourier Bessel expansions around cylinders (integer): The Fourier-Bessel expansion around each cylinder will be truncated from -order to order
4. Order of truncature for Fourier-Bessel expansion in the cladding and jacket (also called gorder, integer): The Fourier-Bessel expansion on the cladding and the jacket will be truncated from -gorder to gorder
5. Matrix epsilon (complex) : permittivity of the matrix (or background)
6. Jacket epsilon (complex) : permittivity of the jacket.
7. Cladding inner (real) and outer radius (real) (the latter is also called the jacket radius). If no cladding is used, set the cladding and jacket permittivities to a same value, set the inner radius to be the jacket radius and give an arbitrary outer radius (say, for example, inner radius+1.0).
8. Cladding epsilon (real) : permittivity of the cladding. If no cladding is used, give the same permittivity as for the jacket. If the structure should have no jacket and no cladding, set the matrix, cladding and jacket permittivities to a same value.
9. After the header follows the list of cylinders, with following specifications:

(a) r, theta (real): cylindrical coordinates of the center of the cylinder, theta is in rad

(b) radius (real): radius of the cylinder

(c) epsilon (complex): permittivity of the cylinder

(d) symm_cat (integer):

• -1 if no symmetries are used:

• 0 if the cylinder is located at the origin

• 1 if the cylinder is on the border of the irreductible sector.

• 3 if the cylinder is not on the border of the irreductible sector.

(e) axis (integer):

• 0 : if the cylinder is at the center or not on the border

• 1 if the cylinder is on the θ = 0 axis

• 2 if the cylinder is on the other border of the irreductible sector (for example θ = π/6 for a C_6v structure)

Parameters on a same line are separated by blanks, tabulations and/or commas. Comments can be added at the end of each line. Additional blank lines between parameters are not permitted. Splitting the lines in the cylinder list is possible if no comments are added. When the permittivities of the cladding and the matrix are equal, fibre replaces the reflection and transmission matrices by the null matrix and the identity matrix respectively. The same applies to the cladding/jacket interface. However, setting the cladding inner and outer radii to be equal is not a valid way of “suppressing” the cladding, and may lead to division by zero operations. If the Sellmeier equation of Silica should be used to compute a permittivity according to the wavelength, one has to set the concerned permittivity(ies) to (-1.0d0,-1.0d0). Note that in this case all dimension become absolute: the dimensions given in the structure file and in the parameter file (for the wavelength) are then in μm.

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