COL 10(6), 062301(2012) CHINESE OPTICS LETTERS June 10, 2012
Optical filter based on internal reflection and optical
rotatory dispersion of NaBrO
3
crystal
Bin Zhang (
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)
1
, Liang Zhang (
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)
2
, Xuefeng Pan (
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)
1
, Weidong Tao (
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)
1∗
,
Jianguo Pan (
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)
3
, Jianfeng Dong (
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)
2
, and Changqing Xu (
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)
4
1
Faculty of Science, Ningbo University, Ningbo 315211, China
2
Faculty of Information Science and Engineering, Ningbo University, Ningbo 315211, China
3
Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, China
4
Department of Engineering Physics, McMaster University, Hamilton, ON, L8S 4K1, Canada
∗
Corresponding author: taoweidong@nbu.edu.cn
Received October 12, 2011; accepted January 10, 2012; p osted online March 5, 2012
Based on the optical rotatory dispersion and zero reflection of the p-polarization light at the Brewster
angle, a novel optical filter that employs only one NaBrO
3
crystal and one polarizer are proposed and
demonstrated. Performance of the optical filter is studied both t heoretically and experimentally. Results
show that the green light is becomes nearly extinct when the angles of the polarizer are set at 80
◦
and
260
◦
, whereas the red light becomes nearly extinct when the angles of the polarizer are set at 116
◦
and
296
◦
. Isolation of more th an 8 dB can be achieved. The measured extinction ratios are 12.3 and 12.6 dB
for green and red lights, respectively.
OCIS codes: 230.7408, 160.1585, 260.5430.
doi: 10.3788/COL201210.062301.
As a wavelength selector, optical filters are used to se -
lect a certain narrow band or line(s) of spectrum from
a broad band of spectrum
[1]
. In optical communica-
tion and optical sensing, optical filters play important
roles in wavelength division multiplexing
[2,3]
. Optical
filters are also very useful in some other areas such as
solar physics
[4]
, laser, radar, and so on. Optical filters
are widely used as the Lyot filters, atomic r esonance
filters
[5]
, Faraday anomalous dispersion optical filters
[6]
,
Fabry-Perot filters, fiber Bragg grating filters
[7]
, Mach-
Zehnder interferometers, acousto-optic tunable filters
[8]
,
and compact optical filters, such as those based on pho-
tonic crystal
[9]
.
In 2003, Ye reported a wavelength-tunable optical
filter
[10]
based mainly on the optical rotatory dispersio n
effect of quartz crystal. However, quartz crysta ls are an-
tisotropic. As a result, the optical rotation only occurs
along the direction of the optical ax is of quartz crystal,
which limits the application of the optical filter. In con-
trast, the optical rotation resulting fro m chiral media of
electromagnetic waves, such as sodium bromate crystal
has attracted a lot of interest recently
[11−14]
. However,
few studies on sodium bromated based devices such as
optical filter have been reported. In this letter, we rep ort
a very large sodium bromate crystal successfully g rown
from a water solution. A new optical filter based on
the obtained isotropic crystal (i.e., sodium bromate) is
designed and fabricated. The optical filter is based on
the rotatory disper sion effect and the zero reflectivity
of the p-polarization at the Brewster angle. The optica l
properties of the optica l filter are studied.
Figure 1 shows a picture of a sodium bromate cr ystal
grown from a water solution. The length of the crystal
is approximately 3.86 cm. To the best of our knowledge,
this is the largest value reported to date on sodium bro-
mate crystal. Notably, a large sodium bromate crystal
is essential in fabricating optical devices such as optical
filter.
Figures 2 and 3 show the diagr ams of the design of the
optical filter based on sodium bromate cry stal.
As shown in Figs. 2 and 3, a beam incident passes
through Interface 1 at the angle i
1
. The illustration of
light vector decomposition on I nterfaces 1 and 2 is s hown
in Fig. 3. The polariza tion intensity after the polarizer is
set is
~
A = A
0
. The polarization is rotated by θ (counter-
clockwise) from the initial polarization direction of the
incident light, which is horizontal. The vector
~
A ca n be
decomposed into ~a = A
0
cos(−θ )
~
i along the X direction
Fig. 1. Photo of sodium bromate cry stal.
Fig. 2. Schematics of the optical filter.
1671-7694/2012/062301(4) 062301-1
c
2012 Chinese Optics Letters