Changes in the electroholographic properties of a paraelectric
potassium lithium tantalate niobate crystal by electrostriction
Qingxin Meng
n
, Xiangda Meng, Huishun Chen, Zhongxiang Zhou
Department of Physics, Harbin Institute of Technology, Harbin 150001, China
article info
Article history:
Received 6 January 2014
Received in revised form
30 April 2014
Accepted 3 June 2014
Available online 17 June 2014
Keywords:
Electroholography
Kerr effect
Electrostriction effect
Paraelectric phase KLTN
abstract
We theoretically studied the diffraction properties of an electroholographic (EH) optical switch made
from a K
0.95
Li
0.05
Ta
0.61
Nb
0.39
O
3
crystal, assessing the influence of the Kerr effect and electrostriction
effect (ES). Specifically, we studied how the diffraction properties changed with temperature, writing-
beam angle and polarization angle, when the ES effect is ignoring or accounting for it. We then analyzed
the origin of the influence of ES on the diffraction properties. Our results revealed that ES increased the
maximum diffraction efficiency and the specific field. We concluded that ES influenced the diffraction
properties by decreasing the Bragg mismatch angle and increasing the effective Kerr coefficient.
& 2014 Elsevier B.V. All rights reserved.
1. Introduction
Electroholography (EH) is a beam-steering method based on
the reconstruction of volume holograms by using an externally
applied electric field [1]. It has gained much interest for several
applications such as volume holographic storage, optical filters,
and electric-field-controlled optical switches [2–4]. EH is particu-
larly suitable for optical switches because of its rapid response
time and tunable properties [5–7].
In recent decades, most EH resear ch on high-speed optical
switches has focused on the paraelectric phase of K
1y
Li
y
Ta
1x
Na
x
(KL TN), advantageous because of its high Kerr coefficient (quadratic
electro-optic coefficient) and high diffraction efficiency near its phase-
transition temper ature (Curie temperatur e, T
C
) [8–10]. It has been
observed that applying an external electric field to paraelectric KLTN
induces electrostriction (ES). Recently, Tian et al. found that KL TN
exhibited a high ES coefficien t of 8.8 10
16
m
2
V
2
near its Curie
temperature [11]. Similar to how the piezoelectric effect influences the
behavior of optical switches made from in crystalline LiNbO
3
based on
the line electro-optic effect [12] , the deformation induced by ES would
affect the diffraction efficiency of linear gratings, impacting the
diffraction properties of EH optical switches made from paraelectric
crystalline KL TN. However , previous studies have not often discussed
how ES affects the diffraction properties of EH devices [4–6].
T o investigate the diffraction properties of EH devices, in this paper
we chose a K
0.95
Li
0.05
Ta
0.61
Nb
0.39
O
3
crystal, which is in its paraelectric
phase near room temperatur e. We studied its diffraction properties in
two contexts, ignoring ES or accounting for it, to assess how ES
influenced the specific field E
s
and the diffraction efficiency η.Wethen
analyzed the origin of the influenceofESonthediffractionproperties.
2. Influence of the Kerr effect on the diffraction properties of
EH optical switches
2.1. Principle of EH optical switching in crystalline paraelectric KLTN
Fig. 1(a–c) shows diagrams that describe the principle of the EH
optical switch, operating based on Kerr effect, fabricated from a
paraelectric KLTN crystal. Fig. 1(a) shows the recording process for
a sinusoidal—space– charge grating, accomplished by the interfer-
ence of two writing beams with the wavelength λ
1
; writing-beam
angle between the two beams is defined as θ, with one beam
incident along the x axis. The space–charge field over real space
can be defined as
E
sc
ðxÞ¼E
sc
cos
2π
Λ
x
¼ E
sc
cos ðk
G
,
x
,
Þ; ð1Þ
where Λ is the grating period, E
sc
is the amplitude of the field, k
G
,
is
the grating vector, and ϕ is the angle between the grating vector
and the z axis.
Fig. 1(b) shows the process of reading a switch without an
applied field. In this process, a plane wave with a wavelength λ
1
or
λ
2
(λ
2
is a random wavelength, different from λ
1
) impinges on the
crystal. Because of the quadratic electro-optic effect (Kerr effect) in
the paraelectric KLTN crystal, there is only quadratic index phase
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journal homepage: www.elsevier.com/locate/optcom
Optics Communications
http://dx.doi.org/10.1016/j.optcom.2014.06.004
0030-4018/& 2014 Elsevier B.V. All rights reserved.
n
Corresponding author. Tel./fax: þ86 451 86414130.
E-mail address: mengqx@hit.edu.cn (Q. Meng).
Optics Communications 331 (2014) 175–180