COL 12(10), 102301(2014) CHINESE OPTICS LETTERS October 10, 2014
1671-7694/2014/102301(4) 102301-1 © 2014 Chinese Optics Letters
As is known to all, electrical diode plays a crucial role
in electronic circuits owing to the ability of unidirec-
tional ow of the current ux. An all-optical diode is a
one-way device that can control unidirectional ows of
optical signals, which will greatly benet the develop-
ment of the all-optical signal processing. In order to
realize the on-chip integration of the optical devices,
photonic crystals (PCs) have been put forward to pave
the way, where the propagation of light resembles the
movement of electron in semiconductors
[1–20]
. The unidi-
rectional non-reciprocal PCs waveguides have attract-
ed much interest of many researchers
[3,4]
. By means of
breaking the reciprocity or time-reversal symmetry, the
unidirectional light propagation can be achieved based
on magneto-optic eect, optical nonlinearity, opto-
acoustic eect, indirect inter-band photonic transitions,
and so on
[5–12]
. Although the functions of these devices
realize the complete optical isolation, the on-chip inte-
grated characteristics cannot be eectively satised due
to the fabrication problems or operation bandwidths.
Recently, a unidirectional on-chip optical diode has
been presented by Wang et al.
[13–15]
. The device consists
of two dierent silicon two-dimensional (2D) square-
lattice PCs with a hetero-structure and its operation
mechanism results from the directional band-gap dier-
ence with spatial inversion symmetry breaking. Howev-
er, the wavelength operation bandwidth has only scores
of nanometers. A kind of unidirectional wavelength lter
was proposed by Feng et al.
[16]
based on the rectangular
defects in a 2D square-lattice PCs and its operation
principles are the match and mismatch of mode’s sym-
metry between the defect and the adjacent waveguides.
However, it is clear that the rectangular defects lead
Ultra-wideband optical diode based on photonic
crystal 90° bend and directional coupler
Jin Lu (卢 瑾)
1
, Hongliang Ren (任宏亮)
1,2*
, Shuqin Guo (郭淑琴)
1
,
Dongyuan Gu (顾东袁)
1
, Hao Wen (温 浩)
1
, Yali Qin (覃亚丽)
1
,
Shouli Zhou (周守利)
1
, Weisheng Hu (胡卫生)
2
, and Chun Jiang (姜 淳)
2
1
College of Information Engineering, Zhejiang University of Technology, Hangzhou 310023, China
2
State Key Laboratories of Advanced Optical Communication Systems and Networks,
Shanghai Jiao Tong University, Shanghai 200240, China
*
Corresponding author: hlren@zjut.edu.cn
Received March 20, 2014; accepted July 16, 2014; posted online September 26, 2014
We propose an ultra-wideband optical diode device based on two-dimensional square-lattice photonic crystals.
For the device, the odd mode is completely transmitted in one direction and converted to the fundamental
even mode, but completely reected in the other direction. The operation bandwidth of the device is pre-
served within a rather wide range of frequencies, which is over 6.5% of the central frequency. A directional
coupler and 90° bend are utilized as the composite function device with mode lter and mode converter. It
is possible that the photonic crystal device can help to construct on-chip optical logical devices and benet
greatly to the optical systems with multiple spatial modes.
OCIS codes: 130.3120, 230.1150, 230.5298.
doi: 10.3788/COL201412.102301.
to the rather narrow operation bandwidth and fabrica-
tion diiculties. Liu et al.
[17]
presented an ultra-compact
mode converter by using an aperiodic design methodol-
ogy. In both phases of optimization, the straightforward
approach requires a lot of numerical simulations. More-
over, these radii of optimized rods in coupler region have
low order of magnitude, which will result in great chal-
lenge to the fabrication of these devices. Khavasi et al.
[18]
proposed unidirectional transmission within a relatively
wide range of frequencies. In the structure, an eicient
mode converter and mode lter are engineered along a
line defect PC waveguide, respectively, where the mode
converter with multiple path is rather complex, and
the high conversion eiciency also requires the irregular
location shift of the rods.
Here an optical diode device with the ultra-wideband is
proposed. In this case, the mode converter and mode l-
ter functions are jointly realized by a directional coupler
and 90° bend. The mode lter consists of a PC direc-
tional coupler and it prevents the even mode and allows
the odd mode to pass. The mode converter block can
combine the high-order odd mode to form an even mode
by one directional coupler and two 90° bends. Hence, the
output wave is an even mode, whereas the input wave is
an odd mode and thus the presented device can also be
optical diode with unidirectional propagation.
The functionality of an optical diode is shown in
Fig. 1. The input and output waveguides only sup-
port a fundamental even mode and a higher order odd
mode. For the structure, the higher order odd mode
A from the left is converted into the even mode C on
the right, whereas the fundamental even mode A from
the left entrance is completely reected back to the
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