COL 9(4), 042501(2011) CHINESE OPTICS LETTERS April 10, 2011
Compact triplexer in two-dimensional hexagonal lattice
photonic crystals
Hongliang Ren (
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, Jianping Ma (
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, Hao Wen (
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, Yali Qin (
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Zhefu Wu (
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, Weisheng Hu (
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, Chun Jiang (
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, and Yaohui Jin (
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1
College of Information Engineering, Zhejiang University of Technology, Hangzhou 310023, China
2
College of Computer Science and Technology, Zhejiang University of Technology, Hangzhou 310023, China
3
State Key Laboratory of Advanced Optical Communication Systems and Networks,
Shanghai Jiao Tong University, Shanghai 200240, China
∗
Corresponding author: hlren@zjut.edu.cn
Received October 18, 2010; accepted December 7, 2010; posted online March 15, 2011
We design a compact triplexer based on two-dimensional ( 2D) hexagonal lattice photonic crystals (PCs).
A folded directional coupler (FDC) is introduced in the trip lexer beside the point-defect micro-cavities
and line-defect waveguides. Because of the reflection feedback of the FDC, high channel drop efficiency
can be realized and a compact size with the order of micrometers can be maintained. The proposed device
is analyzed using the plane wave expansion method, and its transmission characteristics are calculated
using the finite-difference time-domain method. The footprint of the triplexer is about 12× 9 µm, and
its ex t inct ion ratios are less than –20 dB for 1310 nm, approximately –20 dB for 1490 nm, and under
–40 dB for 1550 nm, making it a p otentially essential device in future fiber-to-the-home networks.
OCIS codes: 250.5300, 230.5750, 230.7370.
doi: 10.3788/COL201109.042501.
The fiber-to- the-home (FTTH) sys tem has been deemed
a promising so lution for broadband access networks,
in which an optical triplexer plays a highly important
role
[1,2]
. Three wavelength channels are desig ned in the
filter device, i.e., 1310 nm for the up-stream signal, as
well as 1490 and 1550 nm for the down-stream signals
according to ITU G.983 recommendations. Conventional
optical triplexers are currently mo stly fabricated using
a planar lightwave circuit and arrayed waveguide grat-
ing technology
[1−5]
. The former is the most promising
candidate for low-cost devices, and has been developed
commercially. The latter is the most c ommonly used
planar waveguide device in dense and coarse wavele ngth-
division-multiplexing (WDM) communication systems.
These traditional technologies present numerous co n-
siderable advantages, such as high performance, high
reliability, and easy integration.
However, these co nventional devices are disadvanta-
geous in terms of their large size, which is about the order
of millimeters to centimeters. Consequently, it is gradu-
ally becoming unsuitable for the demands of integrated
optoelectronic devices. Based on two-dimensional (2D)
photonic crystals (PCs) with ar tificia l periodic struc-
tures, even smaller devices can be fabricated
[6−8]
. Thus
far, many researchers have designed these devices in
PCs
[9−18]
, and the disadvantage presented by the large
device footprint can be overcome, indicating that high
density optical integration can be realized. Using a
point-defect micro-cavity in PCs with a square lattice,
the triplex e rs were engineered with compact sizes and
high efficiency by Shih et al.
[19]
Moreover, Park et al.
proposed a triplexer based on the squa re lattice PCs;
these have smaller sizes than that presented by Shih et
al.
[20,21]
Shi et al. also put forward a triplexer by cascad-
ing two stages of directional couplers base d on a PC with
a hexagonal lattice of dielectric rods in air
[22]
. Consider-
ing fabrication technology, however, it is easier to ma ke
triplexers base d on hexagonal lattice PCs with the air
holes perfora ted in a high dielectric refr active index slab
compared with the PCs with high dielectric refractive
index rods in air.
Recently, a three-port channel drop filter with a folded
directional co upler (FDC) has been proposed based on
2D PCs; compact sizes and high drop efficiency are
realized through the directional c oupler
[23]
. In this let-
ter, a FDC is used to design a new triplexer based on
hexagonal lattice PCs with the air holes perforated in
a high dielectric refractive index slab. In the struc-
ture, the FDC is elaborately engineered to filter a wave-
length signal of 1310 nm with high efficiency using the
Fig. 1. Structure of the proposed triplexer. The radius of the
PC air holes is r = 0.33a, where a is the lattice constant. In
the bus waveguide section b etween the two micro-cavities, the
waveguide propagation constant is changed to meet the p hase
term, and the radius of border air holes in the waveguide sec-
tion is R
3
= 0.295a.
1671-7694/2011/042501(4) 042501-1
c
2011 Chinese Optics Letters