Polymer Spot Size Expander on Laser Diode Chip for Fiber Coupling

A miniaturized polymer spot size expander was successfully applied using UV-curable resin on the end face of a DFB laser diode chip emitting at 1.31
$\mu \mathrm{m}$
wavelength for the first time. The spot size could be expanded from the original 3.1
$\mu \mathrm{m}$
to 5.3
$\mu \mathrm{m}$
. The coupling efficiency with a single mode fiber was improved to be −1.2 dB from −3.3 dB, and 3-dB down positional tolerance along the optical axis was improved to be bigger than 60
$\mu \mathrm{m}$
from 20
$\mu \mathrm{m}$
without SSE.