Side-polished-fiber based optical coupler assisted with a fused nano silica film

We have proposed and demonstrated a novel method for fabricating a fiber coupler by sandwiching a fused nanosilica film with a pair of side-polished fibers (SPFs). The silica nanoparticles (SNPs) deposited on the polished regions of the SPFs fuse under hydroxide flame and form an adhesive silica film, which bonds the SPF pairs tightly and matches the refractive index of the fiber cladding. Couplers with various coupling ratios can be available with the SPF–SNP–SPF sandwiching method. The fabricated optical fiber couplers have an excess loss lower than 0.5 dB, a wavelength dependence loss less than 0.35 dB in the wavelength range of 1520–1620 nm, and a polarization dependent loss better than 0.12 dB and also show immunity to variation of temperature and humidity. Such SPF–SNP–SPF sandwiched optical fiber couplers are large in core diameter, robust in structure, easy to fabricate, and compatible with fiber-optic systems and possess high potentiality in photonics applications such as all-optical fiber communication.