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ntals and Applications 6 (2008) 3–11
Photonics and Nanostructures – FundameReview
Chalcogenide glass photonic crystals
Darren Freeman a, Christian Grillet b, Michael W. Lee b, Cameron L.C. Smith b,Yinlan Ruan c, Andrei Rode a, Maryla Krolikowska a, Snjezana Tomljenovic-Hanic b,C.Martijn de Sterke b, Michael J. Steel b,e, Barry Luther-Davies a, Steve Madden a,
David J. Moss b, Yong-Hee Lee d, Benjamin J. Eggleton b,*a Centre for Ultrahigh-bandwidth Devices for Optical Systems (CUDOS), Laser Physics Centre, Australian National University,
Canberra, ACT 0200, Australiab Centre for Ultrahigh-bandwidth Devices for Optical Systems (CUDOS), School of Physics,
University of Sydney, Sydney, NSW 2006, Australiac Centre of Expertise in Photonics, School of Chemistry and Physics, University of Adelaide, Adelaide, SA 5005, Australia
d Nanolaser Laboratory, Department of Physics, Korea Advanced Institute of Science and Technology (KAIST),
Daejeon 305-701, Republic of Koreae RSoft Design Group, Inc., 65 O’Connor Street, Chippendale, NSW 2008, Australia
Received 30 July 2007; received in revised form 2 November 2007; accepted 13 November 2007
Available online 19 November 2007
Abstract
All-optical switching devices are based on a material possessing a nonlinear optical response, enabling light to control light, and
are enjoying renewed interest. Photonic crystals are a promising platform for realizing compact all-optical switches operating at
very low power and integrated on an optical integrated circuit. In this review, we show that by making photonic crystals from a
highly nonlinear chalcogenide glass, we have the potential to integrate a variety of active devices into a photonic chip. We describe
the fabrication and testing of two-dimensional Ge33As12 Se55 chalcogenide glass photonic crystal membrane devices (waveguides
and microcavities). We then demonstrate the ability to post-tune the devices using the material photosensitivity. In one proposal we
hope to introduce a double-heterostructure microcavity using the photosensitivity alone.
# 2007 Elsevier B.V. All rights reserved.
PACS : 42.70.Qs; 42.82.Cr; 42.65.Pc; 42.70.Gi
Keywords: Integrated optics; Photonic crystal; Chalcogenide glass; Nonlinear optics; Microcavity; Resonator
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Chalcogenide glass photonic crystal platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Exploiting the nonlinearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Exploiting the photosensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
* Corresponding author.
E-mail addresses: [email protected] (D. Freeman), [email protected] (C. Grillet), [email protected] (B.J. Eggleton).
1569-4410/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.photonics.2007.11.001
D. Freeman et al. / Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 3–114
3. Fabrication of planar photonic crystals in a chalcogenide glass using a focused ion beam . . . . . . . . . . . . . . . . . . . 5
4. Tapered fiber coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Chalcogenide L3 nanocavities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Photosensitive post-tuning of W1 waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Photonics is evolving towards miniaturized optical
functionality, aiming to integrate multiple components
onto the same chip. Nanophotonic devices typically
make use of a high refractive index contrast to achieve
tight optical confinement, allowing wavelength-scale
resonators and waveguide bends. Two-dimensional
(2D) photonic crystals (PhCs) consist of a thin, high
refractive index dielectric slab, perforated with a
periodic lattice of air holes. PhCs, with engineered
defects, are now recognized as a promising platform for
the control of light in a photonic integrated circuit at the
wavelength scale. This has led to the demonstration of
compact photonic devices for integrated optical circuits
[1]. Research is advancing towards more complex and
‘‘active’’ devices, such as modulators and switches. It is
hoped that 2D PhCs will find utility in compact all-
optical processors, incorporating optical logic gates,
switching, pulse regeneration, wavelength conversion,
dispersion management and a variety of other applica-
tions at low power levels [2,3].
To date, most 2D PhCs have been made from Si or III–
V semiconductors, and their active functions have
typically exploited thermal or free-carrier nonlinear
effects, both of which are relatively slow [4–6]. Recently,
all-optical switching has been achieved in a Si PhC
cavity, with a free-carrier lifetime reduced to 70 ps using
recombination at the surfaces and internal dislocations
[7]. Chalcogenide glasses are infrared transmitting
materials containing the chalcogen elements S, Se or
Te, compounded with network forming elements such as
As, Si and Ge. In this paper we review our work on a PhC
platform using these glasses, aiming to exploit their high
third-order Kerr nonlinearity for all-optical ultra-fast
switching at low powers. The Kerr nonlinearity can be
regarded as instantaneous (< 100 fs) with no recovery
time. Chalcogenide glasses can be processed using
conventional lithographic techniques.
In Section 1, we show how the chalcogenide glass
PhC platform [8–11] appears to be a promising
architecture for confining and guiding light at the
wavelength scale, and where the Kerr nonlinearity and
photosensitivity of the material can be exploited to
achieve a new range of compact integrated devices [12–
14]. In Section 2, we will describe a fabrication method
using focused ion beam (FIB) milling [8–10]. Evanes-
cent coupling with tapered fibers is discussed in Section
3, while Section 4 investigates microcavities (0D or 1D
defects) in a 2D PhC membrane [9,12,15]. Finally, in
Section 5, we describe our post-process tuning
technique which utilizes the photosensitivity of
chalcogenide glass to modify the optical properties of
a planar photonic crystal device [13,14]. Our recent
demonstration of a ‘‘double heterostructure’’ micro-
cavity, made by microfluidic infiltration and with
Q� 4� 103, will be described elsewhere [16].
2. Chalcogenide glass photonic crystal platform
2.1. Exploiting the nonlinearity
When an optical cavity (resonator) contains a
nonlinear material, an increase in incident power leads
to an increase in circulating intensity, and via the
nonlinear light–matter interaction there is a small shift
in the resonant frequency which then alters the coupled
power into the resonator. This effect can be exploited to
make all-optical active devices. The transfer function of
such a system, operated at a fixed wavelength, can
display a steep transition between two states (low/high
transmission) or even optical bistability (memory of the
previous state) (Fig. 1). The required power can be
significantly lowered by using a highly nonlinear
material and a high-finesse (or high Q) microcavity
that enhances the intensity. It is well known that the
required incident power scales with V=Q2, where V is
the mode volume. Such devices, potentially using
multiple wavelengths, may serve as all-optical logic
gates (or ‘‘photonic transistors’’), and become the basis
of more complex all-optical circuits.
Ultra-small, high-Q cavities can be created by
introducing a carefully designed defect into a PhC
lattice [17–19], which can be used to create active
D. Freeman et al. / Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 3–11 5
Fig. 1. Schematic of an all-optical switch, a ‘‘photonic transistor’’. In
the off-state (A), the input signal does not penetrate the gate; in the on-
state (B), a control signal opens the gate through nonlinear interaction
and allows the input signal to be transmitted. One signal can serve both
roles.
devices with predicted power levels of only a few mW
[20,21]. Most experimental work has focused on PhCs
made from crystalline semiconductors [4–6], with much
less research into PhCs made from Kerr-type highly
nonlinear materials. For a purely third-order (xð3Þ)nonlinearity, the effective refractive index is a first-
order function of the instantaneous intensity, according
to nðIÞ ¼ n0 þ n2I, where n0 is the linear refractive
index and n2 is the nonlinear Kerr coefficient.
Chalcogenides have generated a great deal of interest
because of their attractive properties: glasses can be
formed over a wide range of compositions; the
refractive index is high, typically between 2.4 and 3
(allowing a 2D photonic band-gap); linear absorption
losses are low over a wide wavelength range (near- to
mid-infrared); they possess a large xð3Þ nonlinearity (n2
from 100 to 1000� that of silica, i.e. from 3� 10�14 to
3� 10�12 cm2/W, comparable to AlGaAs below half-
bandgap [22]); and low two-photon absorption (b). Just
as important as the large nonlinearity is the large figure
of merit, FOM¼ n2=bl, which should be > 1 to enable
all-optical processing, and is often > 5 (� 12 for
As2S3). In addition to reducing the switching power
requirement, the pure Kerr-like nonlinearities offer
instantaneous response times and the switching speed is
expected to be only limited by the resonator Q factor.
2.2. Exploiting the photosensitivity
Chalcogenide glasses are also known to exhibit a
wide range of photostructural effects. Photosensitivity
is known to arise from structural rearrangements
induced by the absorption of light at photon energies
near the electronic band-edge of the material, leading to
changes in the refractive index and the density (volume)
[23]. Photosensitivity has been used for the creation of
directly written waveguides [24–27], strong Bragg
gratings [28] and for post-tuning of optical components
such as distributed feedback lasers [29] and quantum
cascade lasers [30]. The possibility of post-trimming the
properties of individual components is highly attractive,
relaxing the fabrication tolerances and allowing novel
devices to be more easily created. For example, devices
which use strong coupling between a cavity and a two-
level system (atom or quantum dot), such as ‘‘single
photon’’ sources, require precise tuning of the cavity to
the emission peak. The ability to tune the cavity
resonance via a photosensitive chalcogenide film
applied to the PhC device appears to be promising.
We have proposed the following device to directly
exploit the chalcogenide photosensitivity. ‘‘Double
heterostructure’’ cavities suggested by Ref. [17] rely
on modification of the lattice constants along a line
defect. Light is confined to the central region (larger
lattice constant) due to differences in the mode-gap
frequencies along this line defect. In the same way, we
recently proposed a novel scheme for creating high-Q
cavities in PhCs of photosensitive material. Spatially
selective post-exposure to light in a photosensitive PhC
membrane alters the refractive index (Fig. 2a), which in
simulations [13] was predicted to yield nanocavities
with Q� 106 for a refractive index change of Dn ¼ 0:04
(Fig. 2b), consistent with photosentitivities seen in
chalcogenide glasses. In Section 5 we present the first
experimental demonstration of post-tuning the disper-
sion of a 2D PhC waveguide made from a chalcogenide
glass using the material photosensitivity.
3. Fabrication of planar photonic crystals in achalcogenide glass using a focused ion beam
In high index contrast structures, especially PhCs,
the optical fields are strong at the interfaces and the
etched surfaces must be extremely smooth to avoid
scattering losses. Compared to Si, fabrication processes
using alternative high-index materials, such as chalco-
genide glasses, have had less time to mature and suffer
from increased roughness, poorer sidewall profiles, and
higher optical losses. At CUDOS we have elected to
fabricate our first prototype devices using a focused ion
beam (FIB), because directly milling out the structures
is a single-step, maskless process, resulting in smooth
sidewalls. A scanning electron microscope (SEM) is
incorporated into the dual-beam instrument to provide
immediate feedback after fabrication. (A parallel effort,
involving KAIST, has subsequently demonstrated that
electron-beam lithography followed by chemically
assisted ion beam etching (CAIBE) is another promis-
ing process.)
D. Freeman et al. / Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 3–116
Fig. 2. (a) Refractive index distribution in the plane of the chalcogenide-based PhC waveguide and (b) calculated Q of the defect mode as a function
of the refractive index perturbation for a step profile (squares) and for a Gaussian profile (triangles).
To summarise, free-standing PhC membranes were
created in the following manner: thin free-standing
membranes of Si3N4 (silicon nitride) were fabricated on
a Si substrate; the chalcogenide glass Ge33As12Se55
(AMTIR-1) was coated onto the underside, through
window openings in the substrate; a thin conductive
layer of C was applied to the top; the lattice of holes was
milled through the membrane using a beam of Ga+ ions
scanned by the FIB; and finally the C was removed
before optical testing. Each of these steps will now be
discussed.
To create the support membranes, low-pressure
chemical vapor deposition (LPCVD) was used to coat
the Si wafers on both sides with 100 nm of Si3N4.
Square openings were lithographically defined in the
backside Si3N4 layer with inductively coupled plasma
(ICP) etching. The backside layer then acted as a mask
for anisotropic wet etching with an aqueous KOH
solution. The resulting wafer had truncated pyramid
holes, with Si3N4 membranes under tension on the top
Fig. 3. Chalcogenide glass PhC W1 waveguide, carbon still present, viewed f
cold-cathode field-emission SEM.
side. ICP etching was then used to thin the top side, in
order to reduce the milling time and the optical
perturbation due to the Si3N4 (having a refractive index
of around 2).
The Si3N4 membranes, 30 nm thick, were vacuum
coated with 300 nm of AMTIR-1 glass, supplied by
Amorphous Materials Inc. (Garland, TX), using ultra-
fast pulsed laser deposition [31]. Energy-dispersive X-
ray analysis indicated that the films had the same
stoichiometry as the bulk glass, but measurements using
an SCI Filmtek 4000 metrology tool indicated a higher
refractive index than the bulk, 2.69 versus 2.54 at
1:55mm. This is most likely due to differences in the
bond structure, and annealing the films would have
lowered the index [32]. For our application, the higher
index and higher photosensitivity of unannealed films
was considered advantageous. The top side was
vacuum-coated with around 50 nm of amorphous C
using a thermal gun, to eliminate charging when FIB
milling and SEM imaging.
rom the Si3N4 side at normal incidence and 30�, using a Hitachi S-4500
D. Freeman et al. / Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 3–11 7
An Orsay Physics Canion FIB column was used to
mill the structure of Fig. 3, using Ga+ ions at an energy
of 30 keV and probe current of 95 pA, with the beam
scanned by an in-house custom-developed pattern
generator. We employed vector scanning rather than
the more commonly available raster scanning, in an
attempt to minimize the surface roughness inside the
holes. By milling through the Si3N4 before the AMTIR-
1, rounding of the entry surface of the PhC was
significantly reduced. AMTIR-1 is much softer than
Si3N4, which served to mask out the beam pedestal and
improve the sidewall profile. The holes were milled
over multiple passes, by first scanning the beam in a
small circle at every lattice site, then in a slightly larger
circle, progressively widening the holes with each pass
over the lattice. Since the structure is a membrane, there
is no scattering and redeposition from the bottom of the
hole, as would otherwise be the case. Each circle was
traced at a constant linear speed of 1 mm/s for 170
repetitions, with a radius increment of 20 nm for the
next circle. This amounts to 0.57 s per hole (compared
to just 0.20 s with Au substituting for C). The lattice
constant was 550 nm and the outer circle had a diameter
of 270 nm, producing an actual diameter of � 330 nm
(measured from the SEM images relative to the lattice
constant).
The C film was difficult to observe in SEM images of
the final milled structures, because it is electron
transparent for energies 0 2 keV. Before optical
testing, the C layer was easily removed by exposure
to an Ar/O2 microwave-excited plasma, unlike earlier
work with Au which required wet etching to remove.
Fig. 4 presents SEM images aquired after carbon
removal (using frame integration to reduce charging).
The visible roughness on the top surface was present
before FIB milling, and was probably created when the
Fig. 4. PhC W1 waveguide of Fig. 3, after the removal of carbon, viewed fr
integrated at TV-S scan speed to mitigate the specimen charging, followed
nitride was ICP thinned. It serves to demonstrate the
polishing effect of the FIB, near the edges of the holes.
To assess the quality of the PhCs produced using this
method, one may measure the transmission spectrum of
a large and uniform lattice, as a function of angle,
position and polarization, for comparison with numer-
ical simulations [10]. It was found that the wavelengths
of the ‘‘Fano’’ resonances would shift slightly as the
collection fiber was scanned across the structure,
revealing an unwanted distortion in the lattice [33],
due to an unavoidable slow drift in the FIB system
during milling. This has subsequently been corrected,
using active feedback of the beam position [33,34], to
create the devices presented here. Based on the high
quality seen in SEM images (low roughness, near-
vertical side-walls), and the high level of unifomity
across large regions, we expect to achieve low-loss in-
plane waveguiding, and loss measurements are in
progress. The optical loss due to FIB damage
(amorphization and Ga contamination) has so far not
been determined for these structures, but fortunately the
chalcogenide is already amorphous.
4. Tapered fiber coupling
Coupling light into and out of waveguides and
cavities that have very small mode field dimensions, for
example in 2D PhCs, has proven to be challenging. One
effective approach is evanescent coupling via silica
nanowires [9,19,35,36]. When the propagation constant
of the mode in the taper and the PhC are matched, power
can couple from the fiber to modes of the PhC structure.
This is observed as a dip in the transmission spectrum
through the tapered fiber. The silica fiber diameter must
be reduced to the mm-scale in order to obtain an
evanescently extended mode field [9] that can
om the Si3N4 side at 45�. One thousand and twenty-four frames were
by deconvolution with a model of the detector’s impulse response.
D. Freeman et al. / Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 3–118
Fig. 5. Scheme used to couple light from a curved tapered fiber to a
PhC nanocavity
Fig. 6. (a) Experimental measurement setup for evanescent coupling
from a silica nanowire to a PhC structure; (b) schematic showing the
backward-coupling from a tapered fiber to a PhC waveguide; (c)
transmission spectra through the tapered fiber as a function of fiber to
PhC waveguide separation.
efficiently interact with the PhC structure. The fiber
taper is manufactured using a flame brushing and
tapering process, that heats and stretches conventional
single-mode fiber. Taper waist lengths are typically a
few mm, with outer diameters demonstrated down to
800 nm. To restrict the interaction to the PhC cavity and
avoid coupling to the surrounding lattice, either a bow
or a loop was introduced into the taper waist (Fig. 5).
The tapered fiber ends were moved closer together by
3 mm and one end was twisted to create the loop, which
normally forms at the taper waist where the fiber
diameter is the smallest. Once the loop is formed, the
ends are then separated, tightening the loop to achieve a
circumference of approximately 0.4 mm. This also
reinforces the mechanical stability of the taper.
The taper is then brought into close proximity with
the PhC structure. Light from a broadband Er source, at
1550 nm, is launched into the single-mode fiber via a
polarizer, see Fig. 6a. We selected TE-like polarization
for the chalcogenide glass devices (with the electric
field mainly lying in the plane of the membrane). In the
taper region, light is adiabatically converted into the
fundamental evanescent taper mode. Transmission to
the output of the fiber is measured using an optical
spectrum analyzer (OSA).
We have optically probed various chalcogenide
PhC structures with the evanescent coupling techni-
que. These include: W1 waveguides formed by
leaving out a row of holes from the lattice; and L3
nanocavities formed by removing three adjacent holes
from the lattice and shifting the positions of the
remaining holes at each end of the nanocavity to
optimize the Q [37].
In the W1 waveguides, Fig. 6b, strong coupling
could be obtained when the fiber was in contact with the
PhC, leading to a transmission dip of down to �18 dB,
which corresponds to � 98% coupling efficiency.
Fig. 6c presents the transmission spectra and the
variation in coupling strength with the fiber to PhC
separation. We also found that the coupling to the W1
waveguide modes is highly dependent on precise lateral
positioning of the taper [9].
5. Chalcogenide L3 nanocavities
Coupling to L3 nanocavities was achieved using the
looped nanowires of Fig. 5. Numerical simulations
predicted Q> 104 for the optimal geometry. Unlike the
previous structures, these cavities were fabricated using
e-beam lithography followed by CAIBE [38]. Fig. 7
presents experimental measurements of a cavity with
both a side-hole shift and side-hole diameter reduction.
D. Freeman et al. / Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 3–11 9
Fig. 7. Transmission spectra through the tapered fiber for coupling to
a modified L3-type nanocavity, as a function of fiber to PhC separa-
tion.
Q values as high as 104 were measured for a fiber
separation of 800 nm. As this separation decreased and
the loading of the cavity increased, the measured Q
decreased to 2� 103, and the depth of the transmission
increased to 1.5 dB.
These data indicate that, although the transmission
depth is in this case was restricted to a few dB, limiting
the contrast ratio of a switching device, simple
chalcogenide PhC resonators might exhibit sufficiently
high Q to make all-optical switching feasible.
6. Photosensitive post-tuning of W1 waveguides
We have recently demonstrated a novel post-
process tuning technique which utilizes the photo-
sensitivity of a chalcogenide glass to modify the
optical properties of a planar photonic crystal device.
Fig. 8. A schematic diagram showing the principle of in situ monitoring
A change in the dispersion of a W1 waveguide was
measured in situ, using evanescent coupling as
described in Section 3.
Fig. 8 shows the principle of the photosensitive post-
tuning experiment. The resonant coupling wavelength
was monitored by measuring the transmission spectrum
through the taper with an OSA. The dips in the
transmission spectrum are associated with coupling to
the modes of the PhC waveguide. The photoinduced
change in the PhC was observed by monitoring the shift
(in wavelength) of these dips, during the exposure of the
PhC sample to 633 nm light at an intensity of 1.3 W/
cm2.
The structure under test consists of a 70 mm W1
waveguide, i.e. a missing row of holes along the G–K
direction of a triangular lattice of air holes in a
chalcogenide membrane manufactured using e-beam
lithography followed by CAIBE [38].
The sample was exposed to light for a period of 5 h
and the transmission spectrum through the taper was
recorded at 1 min intervals during this time. Subse-
quently the sample was monitored for a period of 5 d to
verify the stability of the change. The experiment was
conducted at room temperature with the ambient room
light switched off. Fig. 9a shows the transmission
spectrum of the fiber taper due to coupling to the
fundamental PhC waveguide mode for different
exposure times. The resonance associated with the
TE0 mode was found to shift to longer wavelengths
with increasing exposure. Fig. 9b shows a plot of the
resonant wavelength versus exposure, which clearly
displays saturation at higher fluences. The circles in the
graph are experimental data points, whereas the curve
is a fit using an exponential model. The maximum
wavelength shift was 5:2� 0:4 nm, whilst the max-
imum increase in the resonance depth was 2 dB.
the photosensitive changes in a chalcogenide glass PhC waveguide.
D. Freeman et al. / Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 3–1110
Fig. 9. (a) Photosensitive tuning of the TE0mode during the exposure and (b) shift in coupling wavelength to the W1 waveguide, versus exposure
time at 633 nm.
Preliminary investigations into the photosensitivity
of unpatterened AMTIR-1 films [39] at 633 nm have
shown a decrease in the material refractive index and a
volume expansion, while Ref. [23] reported photo-
expansion in a range of As–Se–Ge glasses. For the PhC
waveguide, a refractive index decrease results in a shift
of the waveguide modes to shorter wavelengths. Our
calculations indicate that a wavelength shift of 5 nm is
obtained with an index change of Dn ¼ �0:01, and that
this change occurs linearly with index over the region of
interest. Conversely, expansion of the PhC causes a shift
towards longer wavelengths, and a 5 nm wavelength
shift of the TE0 mode is obtained for 0:31% material
expansion. Thus we attribute the observed wavelength
shift to a combination of these two competing effects.
However, the material expansion has the bigger effect in
this case leading to the observed resonance shift to
longer wavelengths.
7. Conclusion
We have given an overview of our proposed photonic
crystal platform, as a promising architecture for all-
optical switching on a chip. Using a focused ion beam,
or electron-beam lithography followed by chemically
assisted ion beam etching, we fabricated chalcogenide
glass photonic crystal waveguides and microcavities.
We then demonstrated post-tuning of these components
using photoinduced changes in the glass, a relatively
straightforward technique that is amenable to in situ
monitoring. According to our simulations, it should
even be possible to introduce microcavities using post-
fabrication light exposure.
Acknowledgements
The authors gratefully acknowledge the assistance of
the Australian Research Council under the ARC
Federation Fellowship and Centres of Excellence
programs. CUDOS (the Centre for Ultrahigh-bandwidth
Devices for Optical Systems) is an ARC Centre of
Excellence. In addition, the ANU group acknowledges
the assistance of the ANU Department of Engineering
for use of their LPCVD facility, as well as the ANU
Electron Microscopy Unit for use of their FIB. Y.
Ruan’s visit to KAIST was supported by a Young
Endeavour travel scholarship.
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