Mid-IR Fused Fiber Couplers

We present results from our recent efforts on developing single-mode fused couplers in ZBLAN fiber. We have developed a custom fusion workstation for working with lower melting temperature fibers, such as ZBLAN and chalcogenide fibers. Our workstation uses a precisely controlled electrical heater designed to operate at temperatures between 100 – 250°C as our heat source. The heated region of the fibers was also placed in an inert atmosphere to avoid the formation of microcrystal inclusions during fusion.

We firstly developed a process for pulling adiabatic tapers in 6/125 µm ZBLAN fiber. The tapers were measured actively during manufacture using a 2000 nm source. The process was automated so that the heater temperature and motor speed automatically adjusted to pull the taper at constant tension. This process was then further developed so that we could fuse and draw two parallel 6/125 µm ZBLAN fibers, forming a single-mode coupler. Low ratio couplers (1-10%) that could be used as power monitors were manufactured that had an excess loss of 0.76 dB.