EFFECTIVE COUPLING FROM SEMICONDUCTOR-LASERS TO SINGLE-MODE FIBERS

The coupling efficiency can be improved when the output field from the laser is matched to the output held of the fiber, which can be usuall y achieved using a lens positioned between the laser and the fiber. A simple and popular method is to employ a hemispherical lens formed at the end of a tapered optical fiber. To obtain a tapered end with hemis pherical lens a simple process of pulling this fiber in the electrical are is used. In the experiments we measured coupling efficiency betwe en semiconductor lasers of different divergence angles of the laser be am and tapered fibers. The coupling efficiency up to 35% is usually po ssible to obtain, when for flat end fiber it is only 10%. Influences o f reflected light, such as threshold current change, power fluctuation , and noise generation, are much smaller for tapered than for flat-end fibers.