Intensity modulation of light by light in a periodically
poled MgO-doped lithium niobate crystal
Ping Hu (胡 萍)
1,2
, Guangzhen Li (李广珍)
1
, Juan Huo (霍 娟)
3
, Yuanlin Zheng (郑远林)
1,2
,
and Xianfeng Chen (陈险峰)
1,2,
*
1
State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics
and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
2
Key Laboratory for Laser Plasma (Ministry of Education), IFSA Collaborative Innovation Center,
Shanghai Jiao Tong University, Shanghai 200240, China
3
Quantum Engineering Research Center, Beijing Institute of Aerospace Control Devices, CASC,
Beijing 100094, China
*Corresponding author: xfchen@sjtu.edu.cn
Received September 1, 2015; accepted October 27, 2015; posted online December 7, 2015
In this Letter, we investigate a method for controlling the intensity of a light by another light in a periodically
poled MgO-doped lithium niobate (PPMgLN) crystal with a transverse applied external electric field. The power
of the emergent light can be modulated by the power ratio of the incident ordinary and extraordinary beams. The
light intensity control is experimentally demonstrated by the Mach–Zehnder interference configuration, and the
results are in good agreement with the theoretical predictions.
OCIS codes: 190.4223, 230.6120.
doi: 10.3788/COL201513.121902.
With the development of high-speed optical communica-
tion technology, optical modulators, as important parts of
an optical communication system, have begun to face the
new challenges in recent years
[1]
. These challenges include
how to meet the increasing requirements of communica-
tion technology, and how to expand the field of optical
modulation, and have attracted advanced research atten-
tion. Many types of optical modulation techniques have
been tried to realize the control of light via various
structures, materials, and effects, such as double-layer
graphene
[2]
, photoresponsive-liquid crystals
[3]
, silicon
photonics
[4,5]
, electro-optic polymers
[6]
, metal-oxide semi-
conductors
[7]
, Ti:LiNbO
3
crystals
[8]
, GaAs/GaAlAs quan-
tum wells
[9–11]
, dye-sensitized nanocrystalline TiO
2
solar
cells
[12]
, Mach–Zehnder interference
[13,14]
, and electro-optic
effects
[15–17]
. Generally speaking, optical modulation
focuses on the manipulation of light ’s phase, intensity, am-
plitude, and group velocity, among which the intensity
modulation is the most mature field. Optical intensity
modulation is mainly based on optical effects, such as
the electro-optic effect, the magneto-optical effect, and
the acousto-optic effect. Recently, two widely used meth-
ods of optical intensity-modulation technology are the
electro-absorption modulator
[18]
, and electro-optic modu-
lation based on nonlinear optical crystals.
In our previous study, we demonstrated that the inten-
sity modulation could be realized by rotating the linear
polarization state through changing the external electric
field
[19]
. In this Letter, we introduced a new method of op-
tical intensity modulation by applying another control
light based on the polarization-coupling (PC) cascading
effect in an Mg O-doped, periodically poled lithium niobate
crystal (PPMgLN)
[20–22]
. In PC cascading, on the condition
of the wavelengths disagreeing with the quasi-phase
matching, energy oscillates between the two orthogonally
polarized coupling beams. If we introduce a beam at one
polarization, it is expected that it will the affect original
energy oscillation and further realize the modulation of
the light of the other polarization. We found that this
energy transfer depends on the intensity of two input
beams, which means the light intensity with a fixed linear
polarization can be modulated by another light. It is
interesting because this kind of light modulation can work
in the weak-light region.
In the PPMgLN, the optical axis of each domain is al-
ternately aligned at the angles of þθ and −θ with respect
to the plane of polarization by the transverse external dc
electric field. The angle θ is called the azimuth angle and is
proportional to the electric field intensity. During the PC
cascading, an ordinary wave (OW) and an extraordinary
wave (EW) are two orthogonally polarized lights. The rel-
ative azimuth angle between the dielectric axes of two ad-
jacent domains is given by θ ≈ γ
51
E
y
∕½ð1∕n
e
Þ
2
− ð1∕n
o
Þ
2
,
where n
o
and n
e
are the refractive indices of the OW and
EW, E
y
is the transverse dc electric field intensity, and γ
51
is the electro-optic coefficient. It is estimated that θ is very
small, so that the periodic alternation of the azimuth
can be considered as a periodic perturbation. So, the
coupled-wave equations of OW and EW are given by the
following
[23]
:
dA
1
∕dz ¼ −iκA
2
expðiΔβzÞ; (1)
dA
2
∕dz ¼ −iκ
A
1
expðiΔβzÞ; (2)
with Δβ ¼ β
1
− β
2
− G
m
, G
m
¼ 2πm∕Λ, and
COL 13(12), 121902(2015) CHINESE OPTICS LETTERS December 10, 2015
1671-7694/2015/121902(5) 121902-1 © 2015 Chinese Optics Letters