„Pump and signal power combiner with improved signal transmission efficiency”
(acronym: PREL_DS)

Project supported by the National Science Centre, Poland under the „PRELUDIUM 10” programme

Total cost: 150 000,00 PLN
Centre Contribution: 150 000,00 PLN
Duration: 15/06/2016 – 14/06/2019

Principal Investigator: dr inż. Dorota Stachowiak

The objective of proposed project is to carry out theoretical and experimental research concerning pump and signal power combiners used in all-fiber power amplifiers. Those combiners are designed in configuration (N+1)x1, which means that on the input they have one singlemode (SM) signal fiber and N number of multimode (MM) fibers for the pump radiation. At the output of the combiner passive double clad (DC) fiber is used, for example with diameters of core/inner cladding: 9/125 μm. In case of conventional power combiner in configuration (6+1)x1, input fiber bundle consist of 6 MM fibers (typical 105/125 μm) surrounding one SM fiber (9/125 μm). Such fiber bundle with total diameter of about 375 μm needs to be tapered down considerably in order to match to the 125 μm diameter of inner cladding of the output passive DC fiber. During this tapering process the core of input signal fiber will be also significantly tapered down, effecting with core diameter less than 3 μm in case of conventional telecomm 9/125 μm input fiber. Since the output DC fiber has a core diameter of 9 μm, splice between this fiber and fiber bundle with very small core diameter of signal fiber at the output causes high signal transmission losses. The proposed research will help to developed new power combiner construction, enabling to increase the singlemode signal coupling efficiency. The research will concern on configuration (5+1)x1, which means 5 MM fiber at the input, and not 6 as usual. Additionally as a signal input port will be used fiber with reduced cladding diameter (9/80 μm). At the output will be used singlemode passive DC fiber with core/clad diameter of 9/125 μm. Such configuration will allow to decrease the diameter of input fiber bundle before tapering, and thus decrease the tapering ratio. This specific configuration of combiner and using core diffusion technique will allow to significantly increase the efficiency of the combiner, and thereby the efficiency of fiber amplifier in which this combiner could be applied will be also increased. Moreover possible application of an inner mode field adapter (MFA) will be investigated. MFA is an equally important component as a power combiner in all-fiber construction technique and its task is to connect two fibers with different mode field diameter with minimal transmission losses. Creating an inner MFA for a signal radiation could allow for matching final mode field diameter of input signal port from the tapered fiber bundle and the mode field diameter of an output DC fiber. Thanks to this construction the coupling efficiency of a signal in the combiner will be considerably increased.