Electro-Optical Liquid Crystal Waveguide Switch [ PDF 0.22 MB ]

FRAUNHOFER INSTITUTE FOR PHOTONIC MICROSYSTEMS IPMS
2
1
1 Fiber-optic coupled 1 × 2 liquid
crystal switch.
2 Wafer with processed top parts
ELECTRO-OPTICAL LIQUID
CRYSTAL WAVEGUIDE SWITCH
of the liquid crystal switch chips.
In optical telecommunication networks and
trodes. Hence, a refractive index change
fiber-optic sensor networks, the dynamic
is produced in this region, which acts as
optical path control is realized through
a waveguide core. Light coupled in this
Fraunhofer Institute for
various control functions including optical
region is guided and can be collected at the
Photonic Microsystems IPMS
switching. The ever-growing demands on
waveguide output. The Fraunhofer IPMS
switching performance as well as scalability
uses nematic liquid crystals in their isotropic
Maria-Reiche-Str. 2
and integration with other network devices
phase as core materials for its EOIW based
01109 Dresden
pose continuously technological challenges
devices. The particularity of these liquid
on existing technologies. The Fraunhofer
crystals is that they exhibit, when heated
Contact
IPMS developed innovative optical switches
just above their nematic-isotropic phase
Dr. Michael Scholles
based on electro-optically induced wave-
transition, a remarkably large EO Kerr
Phone +49 351 8823-201
guides (EOIW) in liquid crystals, which excel
effect (with EO Kerr constants of about
[email protected]
both in performance as well as capabilities
10-10 m / V²). Accordingly, an electric field
offered by the underlying technology.
of a few V / µm applied on liquid crystals in
Dr. Florența Costache
Phone +49 351 8823-259
[email protected]
this particular phase can give rise to local
Electro-optically induced waveguides
anisotropies in the order of ∆n < 10-3. This
in liquid crystals
∆n is large enough to permit the formation
www.ipms.fraunhofer.de
of a waveguide in the EOIW based device.
An optical waveguide, i.e. EOIW, can be
In addition, these liquid crystals in isotropic
induced in a layer made from a material
phase show excellent transparency over a
of large electro-optical (EO) constant by
broad spectral range as well as response
applying an electrical field across it, within
times shorter than a microsecond.
regions delimited by stripe-shaped eleclc-multiplexer-e
4
Out1
In
Out2
3
5
These are properties of utmost importance
part made of glass coated with ITO, which
or multi-mode operation. The Fraunhofer
for the device performance.
acts as the counter electrode. When visible
IPMS can further extend the functionality
light is coupled into the chip, the activated
of the chip to optical interconnection and
Design – Fabrication – Operation
waveguide can be directly visualized.
attenuation as well as power splitting
Switches based on the EOIW concept are
Advantages
and modulation in a straightforward way
with appropriate design and technology
manufactured at the Fraunhofer IPMS by
adjustments.
means of planar silicon technology. The
Optical switches with no moving parts,
Fraunhofer IPMS’ optical switch chip (fig. 1)
such as the Fraunhofer IPMS’ liquid crystal
is made from two processed silicon wa-
based devices, warrant high operation
fers – forming the base and the top parts
stability and reliability. The switch makes
„„ No moving parts
of the chip – each including structured
use of isotropic liquid crystals, which
„„ Stability of switching
electrode stripes and low refractive index
provide the device short switching times
„„ Reliability
claddings. Fig. 2 shows an image of the
and excellent transparency over a broad
„„ Continuously voltage-adjustable output
wafer with structured chips (i.e. the top
spectral range. These devices are fabricated
wafer). The wafers are bonded together
by means of high precision, planar silicon
„„ Precision silicon micro-technology
enclosing in between a layer made of liquid
technology and therefore are suitable for
„„ Wafer level scale manufacturing
crystal. For device operation, an electrical
high volume, cost-effective manufacturing.
„„ Scalability and integrability with other
field is applied between selected electrodes
An additional benefit is that these switches
from both parts of the chip and across the
can be easily integrated with other devices.
liquid crystal layer. Light waves are guided
Their design can be adjusted according to
on the paths, in this way “activated”, at an
the desired application.
optical loss of about 0.5 dB / cm.
Key features
characteristics
devices
Applications
„„ Fast fiber-optic sensor networks
A 1 × 2 fiber-optic switch chip is available to
Technology options
„„ Optical telecommunication networks
date. Figs. 3 and 4 show the most impor-
„„ Laser technology
tant measured characteristics of the chip:
The technology based on such “active” op-
„„ Signal monitoring
insertion loss at the chip’s two output chan-
tical waveguides permits, just by structuring
„„ Fiber-to-fiber interconnection
nels and switching time. For the purpose of
of suitable electrode paths on the chip, the
„„ Signal attenuation
the demonstration of the EOIW underlying
fabrication of optical switches with multiple
concept, fig. 5 presents a chip with the top
inputs and outputs for either single-mode
3 Measured insertion loss vs.
applied voltage for the two output
channels.
Technical specifications
For more
4 Switching time vs. the applied
Parameter
information
electrical field on the waveguide.
scan here
The blue marked area designates
Unit
Value
Insertion loss* (at 1550 nm)
dB
<3
Attenuation range
dB
0 - 30
Wavelength range
nm
400 - 1600
Optimized for wavelength
nm
1550
5 Input to output 1 switching by
Switching time
ns
< 100
means of induced waveguides in
the parameter space for currently
available devices.
the liquid crystal chip.
* for TM polarization