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This page calculates the best theoretical collimating/focusing combinations of lenses enabling to inject the beam from a laser diode into a single mode fiber optics. Then, it displays a selection table with the caracteristics of several systems made of two lenses from the catalog and as close as possible from the best theoretical configurations. Each selected system can be uploaded in the "Advanced Calculations" software for analyzis and/or optimization using the "load" button. After the selection table, the "Handy Calculations" processed in the page are listed by order of executionw. It is possible to access to one of them by clickng on its categories + title.

The best theoretical combination is calculated from the laser diode divergence at FWHM (Full Width Half Maximum) in the 2 propagation planes (XZ parallel and YZ perpendicular to the gain medium plane), the wavelength and the fiber mode radius. The page calculates the waist widths and half divergences at 1/e² in the XZ and YZ planes, the optimal magnification of the collimating/focusing combination and the largest theoretical coupling efficiency obtained with. It is supposed that the system is afocal, meaning that the back focal plane of the first lens coincides with the front focal plane of the second lens.

The proposed combinations are using lenses from the catalogs. The first lens is selected with an effective focal length as small as possible and with an aperture avoiding beam obturation. The second lens is also selected with the effective focal length so that its ratio with the one of the first lens is as close as possible to the optimal magnification precedently calculated. It is also selected with an aperture avoiding beam obturation as well. The lenses search is processed to propose different types (aspherical/aspherical, aspherical/plano convex, plano convex/plano convex and ball lens/ball lens) of configurations. A maximum of 3 configurations by type are proposed.

For each configuration, the following caracteristics are displayed:

- type_{comp 1} : first lens type,
- ref._{comp 1} : first lens reference,
- mat._{comp 1} : first lens material,
- efl_{comp 1} : first lens effective focal lens,
- diam._{comp 1} : first lens diameter,
- type_{comp 2} : second lens type,
- ref._{comp 2} : second lens reference,
- mat._{comp 2} : second lens material,
- efl_{comp 2} : second lens effective focal lens,
- diam_{comp 2} : second lens diameter.

The theoretical coupling efficiency is calculated regardless of aberrations, and displayed in the C_th column.

The upload of a configuration in the "Advanced Calculations" software is made using the "load" button. The laser diodes and fiber optics parameters are also uploaded for further coupling efficiency calculations. The aperture of the system is specified for the maximum divergence of the beam at 1/e². The upload includes also a first optimization for positionning the waist of the laser diode in the focal plane of the first lens at the laser diode wavelength. A second optimization is then realized to position the fiber entrance very close to the back focal plane of the second lens at the considered wavelength.

Once loaded in the "Advanced Calculations" software, the calculation of the coupling efficiency can be done directly. If it is not satisfactory, an optimization can also directly be processed. The variable are by default the distance from the object to the first lens and the distance from the second lens to the observation surface (fiber entrance). Note that the distance between the two lenses is by default the sum of their focal lengths given in the catalogs. Therefore, the system is not rigorously afocal as this distance does not take into account the lenses thicknesses and the wavelength which has an effect on the focal length.

Note that in the case where the spot diagram is diffraction limited, the coupling efficiency is in general very close to the theoretical one. In the case where spherical aberration occures, an optimization on the spot size can be realized. However, it is not obviously increasing the coupling efficiency as it may unfavorably change the magnification and/or the waists position in the image space.