H-plane cross-shaped waveguide circulator in
magneto-photonic crystals with five ferrite posts
Yong Wang (王 勇)
1
, Dengguo Zhang (张登国)
2,
*, Shixiang Xu (徐世祥)
2
,
Biaogang Xu (许彪刚)
2
, and Zheng Dong (董 政)
2
1
College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
2
College of Electronic Science and Technology, Shenzhen University, Shenzhen 518060, China
*Corresponding author: dgzhang@szu.edu.cn
Received July 7, 2017; accepted September 15, 2017; posted online October 19, 2017
A novel H-plane cross-shaped circulator based on magneto-photonic crystals is experimentally investigated. The
band gap of the TE mode for the photonic crystals is calculated by the plane wave expansion method. The
transmission characteristics of the circulator are simulated by the finite element method. We perform the experi-
ments in the microwave regime to validate the numerical results. At the central frequency of 10.15 GHz, the
measured isolation and insertion loss of the circulator reaches −30.2 and −3.93 dB, respectively. The bandwidth
of the circulator is about 550 MHz. The optimal experimental value of isolation is higher than the numerical
value.
OCIS codes: 160.5293, 230.5298, 130.5296, 160.3820.
doi: 10.3788/COL201715.111601.
Photonic crystals (PCs)
[1,2]
, also known as photonic band
gap (PBG) structures and have gained worldwide interest
during the past decades, are periodic structures belonging
to a new type of artifi cial materials that allow people to
manipulate the flow of light. Due to the unique character-
istics of PCs, such as PBG, photonic localization, and sur-
face states, many devices have been fabricated based on
the PCs’ structures
[3–12]
.
Circulators suppress multiple reflections between
components and thereby improve tolerance with respect
to fabrication imperfections and environmental fluctua-
tions. In recent years, several kinds of two-dimensional
(2D) magneto-PC (MPC) circulators are numerically
studied
[13–15]
. However, to the best of our knowledge, the
fabrication of an MPC circulator is barely reported. Con-
sequently, it is worth paying attention to experimentally
validating the MPC circulator.
In our previous work, a compact PC defect structure
is provided to realize cross-shaped waveguide with an
ultra-wide bandwidth
[16]
. Based on the waveguide junction
of Ref. [
16], a new H-plane cross-shaped MPC circulator
is envisaged and is first experimentally developed in the
microwave regime in this Letter.
The MPC circulator is composed by putting a nonrecip-
rocal sample at the central point of the cross-shaped wave-
guide’s junction, as shown in Fig.
1(a). The MPCs are
formed by introducing five gyrotropic Ni-Zn ferrite cylin-
ders in the center of the Al
2
O
3
square lattice PCs
(SLPCs). The ferrite cylinder with the bigger radius r
2
is labeled in blue. Under the external direct current
(DC) magnetic field, not only does the ferrite cylinder play
the role of a resonator, but it also provides a 90° Faraday
rotation angle. In order to improve the isolation of the cir-
culator, four auxiliary rotation ferrite rods (blue) with
smaller radius r
1
¼ 2 mm are inserted in the SLPCs
(red) around the central ferrite cylinder. The lattice con-
stant of the PCs is a ¼ 12 mm. The Al
2
O
3
rods’ radius is
r
0
¼ 2 mm with relative permittivity ε
a
¼ 9.2. In the par-
tially transparent rectangular waveguide, the rods of the
MPCs are fixed on the upper and bottom plates, as shown
in Fig.
1(b). At the end of the waveguide, four Flange in-
terfaces (22.86 mm × 10.16 mm) are designed to connect
the test equipment.
By using commercially available photonic band cal-
culation software (BandSOLVE, Rsoft Design Group),
the band structure of the 2D Al
2
O
3
PCs is simulated with
the plane wave expansion method. The numerical analysis
is carried out here for only TE polarization. As shown
in Fig.
2, there is an ultra-wide PBG in the SLPCs
with the normalized frequency range of 0.3525ð2πc∕aÞ–
0.4687ð2πc∕aÞ. The numerical central frequency of the
PBG is 0.4016ð2πc∕aÞ. By calculating with the light
speed c ¼ 3×10
8
m∕s, the frequency range of the PBG is
8.81–11.72 GHz, and the central frequency is 10.04 GHz. In
principle, PCs forbid the propagation of electromagnetic
waves within the PBG frequency range and reflects imping-
ing electromagnetic waves back.
The authors have performed experiments to validate
the PBG of the SLPCs. The experimental results perfectly
Fig. 1. (Color online) (a) Structure of 2D MPC circulator with
ferrite posts; (b) schematic diagram of the H-plane circulator.
COL 15(11), 111601(2017) CHINESE OPTICS LETTERS November 10, 2017
1671-7694/2017/111601(4) 111601-1 © 2017 Chinese Optics Letters
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