In collaboration with CNES, iXblue Photonics will present a technical paper at International Conference on Space Optics

 

iXblue photonics at ICSO 2021

 

Evaluation of the reliability of pump combiners

 

Session 31: Calibration & Laser techno

Authors: Dominique BISEL (iXblue Photonics), Benoît FAURE (CNES), Olivier GILARD (CNES), Arnaud LAURENT (iXblue Photonics)

Date & time: Thursday 1st April -

In this paper, we will describe the work carried out within the framework of the evaluation of the reliability of pump combiners under space environment.

Since a few years, several R&T have been led by CNES, to study or develop high-power amplifiers in the 1.5µm band for space applications. Whatever the pumping configuration, these systems integrate pump combiners to inject the high-power pump signal coming from fibered multimode diodes towards a passive double clad fiber which is spiced to the amplifying medium.

These combiners are made of one or more multimode fibers and a double-clad passive fiber with a core adapted to the active fiber and a multimode guide whose interface consists of the silica fiber and a so-called "low index" acrylate coating.

This coating doesn’t only act as a mechanical protection, but it also has an optical function. The index difference with the silica allows the light to be guided. A degradation of this coating can lead to a failure due to local over-heating. These components have usually a dissipative package, but in a space environment, this function can be altered, which must be associated with the risk of delamination of the double-clad fiber and the possible outgassing of the glue.

This study is focused on (2 + 1) * 1 type pump combiners, integrating 2 multimode channels on 105-125, 0.22NA fiber and a main channel on PM 12/125, 0.17-0.46NA fiber, adapted to the IXF-2CF-EY-PM-12-130-RAD, for an application in a 10-20W polarization maintaining amplifier. The double clad fiber used for all the combiners is the iXblue fiber: IXF-2CF-PAS-PM-12-130-RAD and most of these combiners also use the iXblue MM fiber: IXF-MMF-105-125-0.22-RAD.

To carry out this study, potential end-users were contacted to define environmental specifications, that were sent to several manufacturers of pump combiners to obtain technical and commercial offers as well as qualification results of their components. Following these 2 steps, the test plan was established as shown in the table hereafter, and 5 manufacturers were selected. After what, 4 pump combiners per reference were supplied.

The following combiners performances have been measured at reception and after each “environmental test”: Insertion losses up to 15W @ 1560nm, Pump efficiency up to 100W @ 915nm and Polarization extinction ratio

After each test, a component is declared non-compliant if it shows a significant degradation of pump or signal transmission or a bad extinction ratio.

This study highlighted the disparities existing between the different references. Indeed, only one reference went through all the environmental tests sequence without any degradation of performances, while the others showed a limited resistance to temperature variations or mechanical stress. It also shows which environmental conditions have the greatest impact on the combiner’s reliability.

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