COL 9(4), 041902(2011) CHINESE OPTICS LETTERS April 10, 2011
Bidirectionally tunable all-optical switch based on multiple
nano-structured resonators using backward
quasi-phase-matching
Jun Xie ( ddd), Yuping Chen (±±±)
∗
, Wenjie Lu (ºººªªª###), and Xianfeng Chen (xxx¸¸¸)
∗∗
Department of Physics, State Key Laboratory on Fib er-Optic Local Area Network and
Advanced Optical CommunicationSystems, Shanghai Jiaotong University, Shanghai 200240, China
∗
Corresp onding author: yp chen@sjtu.edu.cn;
∗∗
corresp onding author: xfchen@sjtu.edu.cn
Received September 20, 2010; accepted November 15, 2010; posted online March 15, 2011
Based on the second-order nonlinearity, we present a bidirectional tunable all-optical switch at C-band
by introducing backward quasi-phase-matching technique in Mg-doped periodically poled lithium niobate
(MgO:PPLN) waveguide with a nano-structure called multiple resonators. Two injecting forward lights
and one backward propagating light interact with difference frequency generations. The transmission of
forward signal and backward idler light can be modulated simultaneously with the variation of control
light power based on the basic “phase shift” structure of a single resonator. In this scheme, all the results
come from our simulation. The speed of this bidirectional optical switch can reach to femtosecond if a
femtosecond laser is used as the control light.
OCIS codes: 190.4390, 130.3120, 130.3130, 230.1150.
doi: 10.3788/COL201109.041902
Optical switch in lightwave communication has been
proposed for a long time. It aims to achieve controllable
optical signals using interruption in optical paths during
transmission to set optical devices on “ON” or “OFF”
states. Typically, optical switch has one or several trans-
mission windows. The function of optical switch can be
implemented in several ways, such as all-optical switching
in a warm laser pumped rubidium vapor or in the silicon
with a micrometer-sized planar ring resonator, or ultra-
fast low-power photonic-crystal all-optical switching with
high switching efficiency
[1−3]
. However, most of them
can perform the optical switching function in a single
direction rather than in two directions or in only a single
channel rather than multiple channels, allowing them
to be switchable simultaneously. In this letter, based
on the second-order nonlinearity in nano-structured res-
onators of optical crystal, we propose a type of optical
switching based on magnesium doped periodically poled
lithium niobate (MgO:PPLN)
[4−6]
, which can perform
double-way modulation in a single device and carry out
a simultaneous tunable bidirectional switching. Note
that an all-optical wavelength conversion can also be
achieved accompanied with an all-optical switching in
our presented scheme, enhancing the multifunctional
photonic integration in one optical device.
In this letter, we focus on the idea of back-propagation
frequency conversion in quasi-phase-matching (QPM),
which is used to study the slowing down of the
group velocity of light beams based on the second-
order nonlinearity
[7]
. This technique can make a large
difference transmission of signal at different wavelengths.
Thus, by designing the waveguide configuration, the all-
optical switching of both signal and idler lights can be
realized, continuously modulating the transmission of
multiple wavelengths by the control light. Thus, the va-
riety of control light can determine the adjustability of
the device. The switching state for forward signal light
can be transformed at a tunable signal wavelength range
due to the different parameter designs in the waveguide.
At the same time, the switching state can affect the
backward idler, i.e., the idler state of transmission is
opposite to the signal.
Figure 1 shows the schematic of the tunable optical
switch, which consists of MgO:PPLN waveguide as the
main body. The signal light of 1550 nm is located in the
C-band of optical communication, and the control light
is set to 1600 nm, which is used as a key button that
can change the state of the switch to “ON” or “OFF”.
In Fig. 1, the signal and control lights are injected into
the waveguide from the left side, and the incidence of
the idler light is from the right side. The wavelength of
the idler light is set to 730 nm for the backward QPM
(BQPM) condition. Moreover, the other lights propa-
gating in the waveguide should satisfy the QPM of the
difference frequency generation (DFG), i.e., ω
i
= ω
s
+ω
c
,
where ω
i
is the frequency of the idler light, ω
s
is the fre-
quency of the signal light, and ω
c
is the frequency of
the control light. Moreover, the phase shift between
the periodic positive and negative domains needs to be
considered as well (Fig. 2). The basic structure called
single resonator (SR) involves a phase shift in the sign of
χ
(2)
, whose length is 2L and the magnitude is microscale.
With two neighboring SR structures, light energy can be
transmitted and reflected due to the frequency conversion
and interactional energy exchange. The large number of
SRs makes the linear array modulate the propagating
beams in a waveguide
[7−9]
. Figure 2 shows the schematic
of the 3.64-cm-long multiple resonator (MR) waveguide,
with the waveguide length l=2NL, where N is the SR
population and 2L is the unit length of SR. In this kind
of waveguide, we consider two segments of equal length
L in a SR but with the reversed signs of χ
(2)
as the
“phase shift” of QPM. It is equivalent to a Fabry-Perot
cavity with nonlinear mirror, which introduces the phase
1671-7694/2011/041902(4) 041902-1
c
° 2011 Chinese Optics Letters
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