Advances in the structures
and designs of thin optical films known as waveguides, essential components
of photonic devices such as lasers, modulators, couplers, and optical
sensors, are being made by researchers in Hong Kong.
At The Chinese University of Hong Kong, properties of sol-gel materials
used in waveguides have been enhanced for possible applications in a number
of fields, ranging from clinical medicine to wide bandwidth optical communications.
of high purity, organic and inorganic dopants into sol-gel material led
to the development of a fibre optic oxygen sensor capable of operating
in temperatures from -175OC to 200OC. The sensor takes advantage of the
behaviour of an organic dye which phosphoresces strongly in the absence
of oxygen, but with phosphorescence reducing in the progressive presence
It was also
found that by doping sol-gel film with a dye of nonlinear optical characteristics,
a substantial change in the refractive index occurred with the application
of low-power continuous-wave argon ion laser.
could be attractive for use in optical signal processing components. Another
enhancement was the preparation of high quality dye-doped titania-silica
thin film distributed feedback waveguide lasers of variable refractive
Investigator, Dr Dennis Lo, said: The distributed feedback waveguide
lasers appear ideal as transmitters for wideband communication, and communication
requiring a large number of connections as in local area networks.
dye-doped sol-gel slab glows when excited by a blue laser
Researchers at the City University of Hong Kong, meanwhile, have produced
a range of novel optical waveguide designs which solve a major problem
caused by the polarization of light.
transmission characteristics of optical waveguides depend, in general,
on the polarization state of light, the polarization state of output light
from an optical fibre is random.
that when a photonic integrated circuit (PIC) such as a modulator is connected
to an optical fibre, as in most practical applications, the output of
the PIC may become unstable. Principal Investigator Prof Kin-seng Chiang
and his team approached the problem by producing waveguide designs that
are polarization insensitive.
based on phase matching or optical interference, polarization independence
is achieved when polarization modes of the waveguide propagate with the
same phase velocity; with a so-called zero-birefringence waveguide. With
an anisotropic crystal like lithium niobate, the optic axis of the crystal
must be oriented precisely at a specific angle to the physical axis of
the device, which brings difficulties in fabrication.
believes he is the first scientist to point out that zero-birefringence
waveguides can be designed with isotropic materials like glass and semiconductor
material. Work is continuing with experimental waveguide designs and verifying
their polarization-insensitive properties.
Dr Dennis Lo: firstname.lastname@example.org
Prof Kin-seng Chiang: email@example.com