Electrically actuated phase-change pixels for
transmissive and reflective spatial light
modulators in the near and mid infrared
JOSHUA HENDRICKSON,
1
HAIBO LIANG,
2
RICHARD SOREF,
3,
* AND JIANWEI MU
4
1
Air Force Research Laboratory, Sensors Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA
2
Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada
3
Physics Department and the Engineering Program, University of Massachusetts at Boston, Boston, Massachusetts 02125, USA
4
Microphotonics Center and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge,
Massachusetts 02139, USA
*Corresponding author: soref@rcn.com
Received 7 October 2015; revised 19 November 2015; accepted 21 November 2015; posted 23 November 2015 (Doc. ID 251566);
published 17 December 2015
Transmissive and reflective spatial light modulators have been designed and simulated for the 1.55 to 2.10 μm
spectral region. An electrically actuated layer of phase-change material (PCM) was employed as the electro-optical
medium for two-state self-holding “ light-to-dark” intensity modulation of free-space light beams. The PCM was
sandwiched between transparent conductive N-doped Si or indium tin oxide contact layers in a simple planar
structure. A 100 to 500 nm PCM layer of Ge
2
Sb
2
Te
5
(GST) was employed for optimum performance at 1.55 μm
where the transmissive-modulator insertion loss was around 4.5 dB. The GST light–dark contrast was found to be
32 dB. For the GST reflection device, an included metal film (Ag) improved the 1.55 μm performance metrics to
0.7 dB of insertion loss with a contrast around 26 dB. The calculated performance for both types of spatial light
modulators was robust to changes in the input incidence angle near normal incidence. Applications include infra-
red scene generation and signal processing.
© 2015 Optical Society of America
OCIS codes: (230.2090) Electro-optical devices; (230.6120) Spatial light modulators; (160.2100) Electro-optical materials;
(310.6845) Thin film devices and applications.
http://dx.doi.org/10.1364/AO.54.010698
1. INTRODUCTION
Optical control is one strategy for controlling the phase of a
phase-change material (PCM) over a large or small area of the
PCM film [1]. For such control, an optical pump beam focused
on the PCM-film region is used to change the phase from crys-
talline to amorphous or vice versa. This approach has been used
with great success in the visible region of the spectrum for re-
writable optical storage. However, an alternative electrical con-
trol technique has great value [2]. Electrical control means that
the PCM is sandwiched between two transparent conductors
with voltage applied across the conductors. An applied field
or current of suitable duration and strength then induces
the desired phase change [3]. Advantageously, the PCM film
is stable, or self-holding, in either phase. External electric power
is utilized only during the brief time of phase transition. The
optical properties of the two phases differ rather dramatically,
and this optical difference has a variety of important applica-
tions [4]. Therefore, the electrical PCM act uation discussed in
this paper affords an electro-optical (EO) effect for exploitation.
Although the near- and mid-inf rared regions present oppor-
tunities for new EO PCM applications, little has been done
there by way of experiment. At the moment, design and sim-
ulation are leading the way to experiments in this spectral
range. There are two categories of EO PCM modulation-and-
switching devices for the infrared: those that operate on light
beams traveling in free space [5–9] and those that handle wave-
guided light [10–14]. The present paper focuses on free-space
light and presents designs and predictions for a new class of
EO PCM spatial light modulators (SLMs) working in the 1.55
to 2.10 μm spectral region. We study transmissive and reflec-
tive devices, each comprised of multiple layers including a
rather thick mechanical support layer. The active EO region,
as mentioned, is a triple layer made of transparent conductive
layers that contact the front and back surfaces of the PCM layer.
An antireflection (AR) layer is useful in the transmissive SLM,
while in the reflective SLM a metallic mirror layer replaces one
of the transparent conducting layers. Both SLMs have a variable
two-state filter-passband characteristic.
10698
Vol. 54, No. 36 / December 20 2015 / Applie d Optics
Research Article
1559-128X/15/3610698-07$15/0$15.00 © 2015 Optical Society of America