Ultra low loss splice between high and low numerical aperture polarization maintaining fibers

The dataset shows measured powers and resulting losses at different stages of splicing PM2000D (high numerical aperture (NA)) fiber to different low NA polarization mainitaining PANDA-type fibers from Nufern (PM1550B-XP, PM1300B-XP, PM980B-XP, PM1950) and Thorlabs (PM2000). The fibers were spliced with Fujikura LZM100 splicer after automatic angular positioning based on camera end view. The splicing method is based on thermal expansion of the cores (TEC) through heating of the spliced section until their dopand distribution becomes gradual and uniform at the fiber connection. The steps include: butt coupling - before the splicing when the fibers are centered and positioned angularly, short splice - standard splice for duration of 650 µs with power obtained from Power Calibration function of the splicer for a given machine setting (here 660 bits in machine power units, corresponding to approximately 20 W), long splice - heating of the already spliced section for approximately 6 seconds to preheat the fiber before the TEC, TEC splice - long heating for 10 to 60 seconds while monitoring the losses until minimal losses are obtained. The results show much lower losses from the high NA fiber to lower NA with achievable < 0.1 dB loss values. In the opposite direction the losses increase to approximately 0.4 dB due to much larger core diameters of the lower NA fibers resulting in part of the mode overlapping with the cladding of the high NA PM2000D fiber. The losses were measured with and without polarization control at different wavelengths and no dependence of the losses upon excited polarization mode was found.