1) Clad coating 2) Dispensing core monomer
with needle scan
3) UV cure
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In the Mosquito method, single-mode waveguides are made by injecting a higher-index
liquid monomer into a lower-index liquid monomer while moving the injection needle; the
process can be repeated to make parallel waveguides, and the assembly is then cured
under UV light.
withstand even the heat from solder
To create single-mode rather than the
original multimode waveguides using
the Mosquito method, the researchers decreased the dispensing pressure for
the core monomer, increased the needle-scan velocity, and used a thinner needle.
Data showed that the core diameter
was inversely proportional to the square
root of the needle-scan velocity. With
a high-enough needle-scan speed, core
diameters as small as 5 µm could be
created. The researchers settled on a
40 mm/s scan speed, producing a core
diameter of 7. 9 µm—the 12 waveguides
were spaced 254 µm apart.
Near-field intensity profiles of the
waveguides closely fit a Gaussian profile
with mode-field diameters (MFDs) of
8. 27 and 9. 47 µm at 1310 and 1550 nm
wavelengths, respectively. For comparison, the MFDs for a standard single-mode fiber were also measured, and were
6. 41 and 7. 36 µm for 1310 and 1550 nm
Propagation losses for the fabricated
waveguides were also measured using
the cut-back method, in which ever-shorter lengths of the same waveguide
are characterized and the loss then calculated. The propagation losses were determined to be 0.29 and 0.45 dB/cm at
1310 and 1550 nm wavelengths, which
are very low and show that the core-cladding boundary is smooth, minimizing scatter.
Insertion and coupling losses were
measured using a standard single-mode
fiber coupled into the waveguide without
using any index-matching fluid. The
insertion loss (which takes into account
the coupling losses and the loss within
the waveguide itself) was 2. 52 and 4.03
dB at 1310 nm and 1550 nm, respectively, while the coupling loss was estimated to be 0.5 dB at 1310 nm per
end, including the Fresnel reflection loss.