Guiding light with air core
SUDHANSHU KUMAR1 ,PAWAN KUMAR2, VIVEK
SRIVASTAV3 NIET, GR.NOIDA(UP)
coolsudhanshu.ranjan8@gmail.com
INTRODUCTION
Guiding light in dielectric fibers has several
applications in life. Fiber optics are used for
security and for increasing the bandwidth.
Conventional optical fiber has slight higher
refractive index of core as compared to
cladding. Two major limitations are:Absorption: - Absorption loss takes place
due to the atomic defects in the glass
composition .To overcome this loss fiber is
doped with ERBIUM which is used to
amplify the signal. They become significant
if the fiber core is exposed to ionizing.
Confinement Mechanism :-
It explains that
total internal reflection which confines light
only of a limited angle. Confinement
mechanism does not have angular
dependence.
Typical optical fiber cannot guide light
around sharp turn, which is significant in
optical integrated circuit. Light guided in a
hollow waveguide with an omnidirectional
reflecting film propagates primilarly through
air and will therefore have lower absorption
losses. The hollow waveguide fabricated
now a day, have internal metallic and
dielectric layer. It could be shown that
addition of dielectric layer to the metallic
waveguide could lower the losses. Such type
of structure can have lower losses as
compared to the combined metal and
dielectric structure. Here we have used a
large diameter multimode waveguide; you
can also fabricate a much tube that could in
principal be made to support a single mode.
PRINCIPLE OF OPERATION
The diagram and the refraction profile of a
hollow tube is shown in Fig.1.We cannot
distinguish between independent TE and
TM modes because in light guiding there are
several bends .We can also define a plane of
incident with respect to normal to the film
surface and the incident wave vector. Light
entering into such a tube will hit the wall
and explores the wide range of angle of
incident. As we know air region is bounded
by a structure that has a gap which
encompasses all angle and polarization the
wave will be reflected back into the tube and
will propagate along the hollow core as
long as Kz≠0.
SAMPLE PREPRATION PROCEDURE
Concentrated sulfuric acid is used to clean
Drummond 1.92mm o. d. silica glass
capillary tube. A LADD 30,000 evaporator
fitted with a sycon Instruments 100 film
thickness monitor is used for the evaporation
of first tellurium layer. The deep coating of
the capillary tube in a solution of 5.7g
polysterene DOW 615 APR in 90 g toluene
is used for depositing first polymer layer.
Tellurium is the next layer which is
deposited as above. Polyuretane diluted in
mineral spirits are used for making of
subsequent polymer layer. The device has a
length of 10 cm and consists of nine layer :
five Te and four polymer. The tellurium
layer has refractive index of 4.6(layer
thickness 0.8µm) while polystyrenes layer
has refractive index of 1.59(layer thickness
1.6 µm), According to the zeros of Bessel
Function as optimal design will vary the
layer thickness. IR spectroscopy is used to
monitor layer thickness and performance.
Fig. 1 Cross section of hollow waveguide
showing the hollow core and dielectric films
, also shown is the index of refraction profile
in the radial direction.
Reflectivity of deposited structure is
measured in radial direction. A Nicolet
FTIR microscope and a variable size
aperture is used to measure the reflectivity
of deposited structure. In a heat shrink tube
filled with silicon rubber the coated capillary
tube was inserted. At last, concentrated
hydro fluoride acid (48%) was used for
dissolving the glass tube. Flexible and
mechanically stable hollow tube assembly is
thus lined with mirror coating.
CONCLUSION
The reflectance measurement and simulation
for normal incidence, is shown in fig.2
(a).Here the predicted gap with is larger than
the measured gap width due to the defects in
Te layer. There are absorption (8µ ) peaks
due to the polyurethane. Fig 2(b ) , shows
the calculated value of reflectance at grazing
incidence for TM mode.
Fig .2 (a) Measured (dashed) and calculated
(dots) normal incidence reactance for hollow
waveguide in the radial direction. (b)
Calculated grazing incidence reflectance for
the TM mode.
Fig.3 Hollow tube transmission
measurement
REFERENCES
Fig.4. Transmission through the hollow
waveguide around a 900 bend as a function
of wavelength.
The omnidirectional frequency range is
defined from high frequency range(above)
by the normal incidence gap edge(arrow)
and from below by the grazing incidence
gap edge(arrow) the extent of the gap is
completely defined by these two data points.
The parameter used in this experiments has
the extent of omnidirectional range is
approx. 40%.
A Nicolet Magna 860 FTIR bench with an
MCT/A detector was used for measuring the
transmission through the tube. The
measurement of transmission was done
around a 900 bent at a radius of curvature of
1 cm, is comparable to the straight tube
transmission to correct for entrance and exit
effect .The diagram of the measurement
layout is given in Fig 3.
Above Fig Shows that a high transmission
around the 900 bent for a spectral band
thing at of concept indicating the low loss
characteristics and guiding abilities all
dielectric hollow waveguide is provided
the measurement.
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