August 10, 2010 / Vol. 8, No. 8 / CHINESE OPTICS LETTERS 749
A novel polarization channel drop filter based on
two-dimensional photonic crystals
Hongliang Ren (???÷÷÷)
1∗
, Yali Qin (ÚÚÚæææwww)
1
, Kai Liu (444 ººº)
1
, Zhefu Wu (ÇÇÇóóóÅÅÅ)
1
,
Weisheng Hu (¥¥¥))))
2
, Chun Jiang (ñññ WWW)
2
, and Yaohui Jin (777)
2
1
Institute of Fiber Optic Communication and Information Engineering, College of Information Engineering,
Zhejiang University of Technology, Hangzhou 310023, China
2
State Key Laboratory of Advanced Optical Communication Systems and Networks,
Shanghai Jiao Tong University, Shanghai 200240, China
∗
E-mail: hlren@zjut.edu.cn
Received February 25, 2010
A novel polarization channel drop filter (PCDF) based on two-dimensional (2D) photonic crystals (PCs) is
presented. It consists of two line defect waveguides and two point defect micro-cavities. In the line-defect
waveguides, the transverse-electric (TE) and transverse-magnetic (TM) polarization lights are guided using
photonic band-gap and total internal reflection effect, respectively. The light at the resonant frequency for
TE polarization can be transferred from one waveguide to the other using the proposed system. Compared
with the existing four-port PCDF based on PCs, the three-port structure can realize a multi-channel
wavelength system of PCDF more easily and can be an essential device in future polarization wavelength
division multiplexing (PWDM) systems.
OCIS co des: 250.5300, 230.5750, 230.7370.
doi: 10.3788/COL20100808.0749.
In the past two decades, photonic crystals (PCs) have
attracted great interest due to their p otential use in the
area of ultra-compact devices for photonic integrated
circuits (PICs)
[1−3]
. Many PC components, including
waveguides, polarization devices, channel drop filters
(CDFs), and so on, have been designed and fabricated
based on PCs
[4−11]
. Among these components, the po-
larization beam splitter (PBS) and CDF are considered
important for PICs and dense wavelength division mul-
tiplexing (DWDM) systems.
Recently, a PC polarization channel drop filter (PC-
PCDF) has been proposed
[9]
. The PC-PCDF can be
utilized as polarization channel dropping devices in fu-
ture integrated PWDM. In the structure, the transverse-
electric (TE) and transverse-magnetic (TM) polarization
lights are guided by photonic band-gap (PBG) and total
internal reflection (TIR) effect, respectively
[5,12,13]
. For
the TE polarized light, the PCDF is used as a narrow
bandwidth CDF via resonant systems, where two sym-
metrical micro-cavities with direct coupling are located
in the central region between two parallel line-defect
waveguides. The theoretical concepts of the four-port
filter based on two-dimensional (2D) PCs have been
studied thoroughly
[6−9]
. We likewise recently presented
a three-port CDF with a wavelength-selective reflection
micro-cavity
[14−16]
. In the three-port structure, two sep-
arate micro-cavities with different functions are used.
One micro-cavity is used to realize wavelength-selective
reflection feedback in the bus waveguide and consists
of a point defect micro-cavity side-coupled to the bus
waveguide. The other micro-cavity is used for a resonant
tunneling-based channel drop operation composed of a
point defect micro-cavity between the bus waveguide and
channel drop waveguide. By adding several channel drop
micro-cavities and wavelength-selective reflection feed-
back micro-cavities adjacent to the bus waveguide, the
three-port CDF can realize a multi-channel wavelength
system more easily than by using the four-port CDF
[16]
.
In this letter, we design a compact three-port PCDF
based on 2D PCs with hexangular lattice of air holes
perforated in high refractive index materials. Our de-
sign not only combines the functions of PBS and CDF
at the operating frequency but also avoids increasing
system complexity. PC-PCDF is realized based on the
three-port CDF. The TE polarization component of the
special wavelength range can be dropped from the bus
waveguide to the channel drop waveguide via the resonat-
ing system. In the two waveguides, the TE polarization
is guided by the PBG effect, and the TM polarization
is controlled by the TIR effect. For the CDF of the
TE polarization, the phase condition is studied in detail
at several operating frequencies to achieve high channel
drop efficiency. The device can realize the multi-channel
wavelength system of PCDF more easily than the pre-
vious four-port structure, and can be used in future
integrated PWDM systems.
The first requirement of PCDF is that both TE and
TM polarized lights must propagate with low loss in the
device
[9]
. The 2D PCs have a hexagonal lattice of air
holes in GaAs (ε = 11.0224). Generally, the PCs have
a PBG only for the TE modes, making it difficult to
obtain a complete PBG for both polarizations in PCs
with air holes perforated in a high index dielectric slab.
Although the complete PBG is realized in such PCs by
increasing the radius of air holes sufficiently, the method
leads to severe losses out of the plane.
Fortunately, the PBG effect is not the only mechanism
that can be used to guide the light in a PC waveguide
[12]
.
Previous studies demonstrated theoretically and exper-
imentally that the light can also be guided in a PC
1671-7694/2010/080749-04
c
° 2010 Chinese Optics Letters