E. Brockmüller
F. Wellmann
O. Kimmelma
T. L. Lowder
S. Novotny
J. Neumann
D. Kracht

Fiber components based on large-mode chirally coupled core specialty fibers for all-fiber laser systems

Proc. SPIE 12573, Specialty Optical Fibres
Type: Zeitschriftenaufsatz (non-reviewed)
Fiber-based laser systems enable high output power in combination with diffraction limited beam quality. Their output power is generally limited by the onset of nonlinear effects. The chirally coupled core (CCC) fiber provides a large mode field diameter while also suppressing higher-order-modes. This is needed to further increase a laser’s output power and maintaining single-mode operation. However, the integration of specialty fibers in an all-fiber laser setup is in most cases not possible because suitable fiber components are not available. We report on the development of a cladding light stripper and a signal-pump combiner with integrated 34/250-µm CCC fibers which allow for the development of spliceless all-fiber amplifier systems. The cladding light stripper is manufactured by structuring the CCC-fiber’s cladding using a CO2-laser to interrupt pump light guiding within the cladding. The cladding light stripper enables a stripping efficiency of 19 dB and was tested up to a stripped optical power of 100W, which is sufficient to enable kW-class amplifier systems. The signal-pump combiner relies on a side-pumped design with four pump input fibers. Its characterization reveals a pump-to-signal fiber coupling efficiency of 90\% and a signal-to-pump isolation of 30 dB. Component stability was tested at a pump input power of 500W. An S2 -measurement confirmed that the spatial mode content of the signal light propagating through the CCC-fiber-based signal-pump combiner remains unaffected. Furthermore, a signal-pump combiner was subjected to temperature cycles between -5 and 85 °C over a time period of <1000 h and showed no degradation.