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Highly efficient optical fiber coupler

A method and components to fibre-couple multiple light sources in a highly efficient way is proposed. The new technique simplifies the process with which a side coupling arrangement for a double-cladded target fibre can be realized. In addition it improves the coupling efficiency compared to the so far existing state of the art.

Challenge

In order to achieve a high power inside a target fibre, one usually uses multiple individual light sources and tries to couple their powers into said target fibre by either free-standing or fibre-based means. Fibre-based side coupling has been proven to be particulary favorable. But when attempting to further increase the coupling efficiency with this method one quickly reaches the manufacturing limits of what is technically feasible. The efforts of removing the cladding of the feeding fibre or the mechanical instability of extremely tapered fibres are just two examples to illustrate these drawbacks. However, a high coupling efficiency is essential in order to minimize thermal problems that originate from power losses during the coupling process.

Our Solution

The proposed technique for combining multiple light sources in a highly efficient way includes both new components and an improved manufacturing process. The use of jacketless intermediate feeding fibres within the coupling region renders the needs for a chemical or mechanical treatment of the original feeding fibre unnecessary. An octogonal shape of said intermediate fibres furthermore increases the coupling efficiency while mirrors on their end faces reflect uncoupled light back in the direction of the coupling region, resulting in a further increase of the efficiency.
While combining the target and (intermediate) feeding fibres, a special fixture significantly reduces the strain inside the target fibre. In addition, both kinds of fibres can be drawn with different forces which causes the feeding fibre to taper more than the target fibre. The fixture also arranges the fibres in a way that reduces the probability of coupling out light that has already been coupled in.
A second intermediate fibre (this time as part of the target fibre) can be used to taper the coupling region without reducing the target fibre core and therefore the target fibre mode field diameter.

Advantages

  • Coupling efficiencies up to 98%
  • Non-linear effects within the target fibre are suppressed
  • Reduction of thermal issues that are otherwise caused by the low coupling efficiency 
  • Monolithic setup, i.e. space saving and mechanically robust
  • Increased optical isolation of the pump diodes against reflected power
  • Applicable to both pulsed and continuous laser systems
  • Suitable for active, passive and polarization conserving applications
  • For single-mode, multi-mode and even coreless target fibres
  • High flexibility in the choice of fibre materials (Ytterbium, Erbium, Thulium)
  • Suitable for a large wavelength range

Applications

The use of the herein described procedures and components makes new fibre laser architectures like counter-propagating pumping possible. Further applications arise from the immense flexibility of the setup and its robustness.

Developmental Status

The expected performance gain of the new setup has been confirmed by measurements and simulations.

Patent Status

US patent application: US2013188911 (A1)
EP patent application: EP2618191 (A2)
Patent applicant: Laser Zentrum Hannover e.V.

References

Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers
Optics Express, Vol. 20, Issue 27, pp. 28125-28141 (2012) (doi: 10.1364/OE.20.028125)
Theeg T, Sayinc H, Neumann J, Overmeyer L, Kracht D
Laser Zentrum Hannover e.V., Hollerithallee 8, 30419 Hannover, Germany

Contact

Dipl.-Phys. Winfried Willemer
Patent Manager Physik
E-Mail: wwillemer(at)sciencebridge.de
Tel.: +49 551 30724 153
Reference: CPA-1528-LZH

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