Optical properties of photonic crystals - New Jersey Institute of ...

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Scientists at Sandia have devised the first 3D photonic crystal operating at a
wavelength of 1.5-micron (the all- important preferred wavelength for light traveling in
optical fibers). Repeatedly layering and etching films of different dielectric constants has
led to the fabrication of the vertical topology of the structure. For one layer of the
photonic crystal, first SiO2 is deposited, masked and then etched to achieve the desired
depth. The resulting "trenches" are filled with polycrystalline silicon. In the last process
step, the surface is polished. Then the entire process is repeated in order to obtain
multilayers. In the final step, the wafer is submerged in an HF/water solution to remove
the SiO2 .
The specifications of the structure are as follows:
distance between two parallel bars = 4.2 micrometers;
width of a bar = 1.2 micrometers;
thickness of layers = 1.6 micrometer.
The smoothness of the PGB crystal is controlled within 1% of the layer thickness
above the wafer. The crystal is cut down to 1 x 1 cm, which corresponds to 2400 rods per
layer. The band gap with a 12.5-micrometer wavelength extends over 1 micrometer. With
further optimization of the fabrication process, it should be possible to create a crystal
with a difference of 2 in the refractive indices. In this case, layers of Si3N4 can be used in
the photonic crystal. Photonic crystals will be components in future optical transistors---
by deflecting light, they will be able to act as optical switches; by trapping light, they will
be able to produce optical amplification within cavities. The crystals will also be part of
other optical integrated circuit components such as low-power nanolasers and
waveguides.