Polycrystalline
silicon core optical fibers have been fabricated
by modified thermal annealing of amorphous silicon chemically deposited
at high pressure. The resulting fibers have small-diameter cores,
a geometry advantageous for optical guidance. Moreover, the combination
of chemical deposition and annealing avoids difficulties associated
with undesired transfer of oxygen impurities to the silicon core from
the molten cladding during the drawing process. The high aspect ratio
of the amorphous silicon core and the presence of the silica cladding
surrounding make the design rules for annealing to optimize their
polycrystalline structure different from those of conventional amorphous
silicon films. We find that optimization of the annealing allows for
an increase in the polycrystalline grain size and decrease in the
defects in the silicon core. A low optical loss of less than 1 dB/cm
at a wavelength of 2.2 μm is thus realized, much lower than
that reported for small core size (<10 μm) crystalline silicon
fibers and comparable to the loss in many planar semiconductor waveguides.
This loss is just below the threshold of 1 dB/cm often considered
necessary for many photonic and optoelectronic applications at near
to mid-infrared wavelengths in areas such as nonlinear photonics,
lasers, and in-fiber photodetectors. Further reduction in optical
losses as deposition and annealing techniques are improved can be
anticipated.