Published in: 18th International Conference on Transparent Optical Networks (ICTON), 10-14 July 2016 Trento,
Italy (IEEE, DOI: 10.1109/ICTON.2016.7550712)
The use of ion beam techniques for the fabrication of integrated optical elements
I. Bányász1*, S. Berneschi 2, M. Fried3, V. Havranek4, N. Q. Khanh3, G.U.L. Nagy5, A. Németh1, G. Nunzi-
Conti2, S. Pelli2,6, Rajta5,. C. Righini2 E. Szilágyi1, M. Veres7, Z. Zolnai3
1Department of Nuclear Materials Science, Wigner Research Centre for Physics, Hungarian Academy of
Sciences, P.O.B. 49, H-1525, Budapest, Hungary
2MDF-Lab, “Nello Carrara” Institute of Applied Physics, IFAC-CNR, Via Madonna del Piano 10, 50019 Sesto
Fiorentino (FI), Italy
3Research Institute for Technical Physics and Materials Science, Centre for Energy Research, Hungarian
Academy of Sciences, Budapest, P.O.B. 49, H-1525 Hungary
4Nuclear Physics Institute AV CR, Řež near Prague, 250 68, Czech Republic
5MTA Atomki, Institute for Nuclear Research, Hungarian Academy of Sciences, H-4001 Debrecen, P.O. Box 51,
6“Enrico Fermi” Center for Study and Research, Piazza del Viminale 2, 00184 Roma, Italy
7Department of Applied and Nonlinear Optics, Wigner Research Centre for Physics, Hungarian Academy of
Sciences, P.O.B. 49, H-1525, Budapest, Hungary
* Tel: +3613922222Ext2506, Fax: +3613955515, e-mail:firstname.lastname@example.org
Active and passive optical waveguides are fundamental elements in modern telecommunications systems. A
great number of optical crystals and glasses were identified and are used as good optoelectronic materials.
However, fabrication of waveguides in some of those materials remains still a challenging task due to their
susceptibility to mechanical or chemical damages during processing. Ion beam implantation has been used for
such purposes, along with other emerging techniques, like direct pulsed laser writing.
Passive and active planar and channel optical waveguides, and optical Bragg gratings were fabricated in various
glasses (like Er: TeO2-WO3 glass) and undoped and doped crystals (CaF2, Er: LiNbO3, Bi4Ge3O12, Bi12GeO20)
using masked or unmasked macrobeams or microbeams of light and medium-sized ions (H, He, C, N, O) and
gold in the 500 keV – 15 MeV energy range. Functionality of the optical elements was tested by diffraction
efficiency measurements, m-line spectroscopy and end fire coupling technique. Structural changes in the
implanted samples were studied by various optical microscopic techniques, spectroscopic ellipsometry, atomic
force microscopy, Rutherford backscattering and microscopic Raman spectroscopy. The results show that it is
possible to produce integrated optical elements of unique properties using ion beam techniques.
Keywords: integrated optics, planar waveguide, channel waveguide, optical Bragg grating, ion implantation,
focussed ion beam
Active and passive optical waveguides and optical gratings are fundamental elements in modern
telecommunications systems. A large number of optical crystals and glasses were identified and are used as
suitable optoelectronic materials. However, fabrication of waveguides in some of these materials remains still a
challenging task due to their susceptibility to mechanical or chemical damages during processing. Ion beam
implantation is able to modify the optical properties of optical materials, such as some polymers, glasses and
crystalline materials. Numerous practical applications exist, e.g. waveguides, special coatings, optical
confinement of semiconductor lasers, impurity additions for lasing regions, fabrication of nonlinear optical
elements, and production of photochromic layers (in optical disks) [1-4]. The first ion implanted waveguides
were produced by Schineller et al. by proton implantation into fused silica glass in 1968 .
Light ions like H and He of relatively low energies were used for the implantation of the optical waveguides
from the beginning until recently [6, 7]. Medium- and higher mass ions were also used to modify optical
properties of materials, like Li+, B+, Na+, Ar+, Bi+ by Webb and Townsend .
Planar waveguide formation in case of implantation by low-energy ions was attributed to formation of a low
refractive index barrier layer around the stopping range of the ions due to nuclear interaction with the target. To
achieve a sufficiently high refractive index contrast, high ion fluences, in the order of 1015 -1017 ions/cm2, were
to be applied 
Waveguide formation in case of implantation with high-energy medium-to high mass ions, “swift heavy ions”
is mainly due to the dominant electronic interaction with the target material [10-12]. That method enables
waveguide formation with ultralow fluences, down to around 1012 ions/cm2.
1. DESIGN AND TEST OF ION IMPLANTED INTEGRATED OPTICAL ELEMENTS
Main physical parameters of the optical elements to be fabricated via ion implantation can be determined by
simulations using the SRIM (Stopping and Range of Ions in Matter) code . Ion species and energy have to be
chosen according to the desired thickness of the optical element.
Depth distributions of the implanted ions in the sample give good approximations for the structure of the
waveguides if nuclear interaction is the dominant one. In case of swift heavy ions, it is the ionisation vs. depth
distribution which can be used for the prediction of the waveguide structure.
An example of planar waveguide design (with SRIM) and test (using spectroscopic ellipsometry, SE) is shown
in Fig. 1. Note that double energy implantation and higher implanted fluence result in thicker barrier layer .
Figure 1 Depth distributions’ of N ions, calculated with SRIM (dotted curves), and boundaries of the barrier
layers (vertical bars) for single- (left) and double energy (right) N+ -implanted planar waveguides
A Rutherford backscattering (RBS) study of a
three-layer Bragg grating can be seen in Fig. 2.
Sample was prepared by repeating Chemical
Vapour Deposition (CVD) of SiO2 thin layers (first
300 nm and then twice 200 nm) and low-energy ion
implantation of each layer by 130 keV Zn+ ions on
a silicon substrate. The aim of that experiment was
to fabricate Bragg gratings of sinusoidal profile
using the combination of CVD and low-energy ion
implantation. Both the raw RBS spectrum and the
calculated depth distribution (inset) of Zn in the
sample show regular quasi sinusoidal distributions.
The high implanted fluences (2·1016 ions/cm2 each)
resulted in about 3 % peak Zn concentration (see
inset). That concentration implies high modulation
of the refractive index, so that even a low number
of implanted grating layers could result in high
Three methods were applied to the fabrication of
channel waveguides in Er: TeO2-WO3 glass, Er: LiNbO3 and eulytine and sillenite type BGO crystals. The first
one was implantation through a special silicon membrane mask that contained 24 μm wide slits. The second
method was patterning an 8 μm thick AZ4562 photoresist layer on the surface of the sample. The photoresist was
processed to obtain trapezoidal line profiles to facilitate waveguide side wall formation when the samples were
implanted through it. The thickness of the channel waveguides was between 5 μm and 15 μm. Finally, slightly
defocussed microbeams of nitrogen, oxygen and carbon ions were also used to direct writing of channel
waveguides of 8 and 15 μm widths in the same materials.
The simplest method to asses channel the implanted waveguide waveguides was optical microscopy. An
example o is presented in Fig. 3.
2 RBS measurement of an ion implanted Bragg
Phase contrast microscopic image of three channel waveguides fabricated using a 15 µm wide
microbeam of 5.0 MeV N3+ ions in Er: TeO2-WO3 glass. The N3+ ion fluences were 0.5∙1016 ions
cm2 (B) and 2∙1016 ions
cm2 (C). Higher contrast indicates higher refractive index modulation.
A more sophisticated method for the visualisation of
channel waveguides is micro Raman spectroscopy. One
can see a series of micro Raman spectra taken across an
ion implanted channel waveguide in Er: TeO2-WO3 glass
in Fig. 4. It can clearly be seen that ion implantation
induced structural changes in the sample that manifest
themselves in new Raman peaks, not present in the
pristine sample. A semiconductor laser of wavelength of
785 nm was used in the experiment.
2. RESULTS OF FUNCTIONALITY TESTS
The par excellence functionality test of planar optical waveguides is the so called m-line or dark line
We demonstrated functionality at 1.55 µm of
our planar waveguides fabricated in Er: TeO2-
WO3 glass via 3.5 MeV N+ ion implantation
using that technique . Functionality of ion
implanted planar waveguides up to near
infrared wavelength in other materials, like
CaF2, Bi4 (GeO4)3 and Bi12GeO20 was also
demonstrated . An example of m-line
spectra of an ion implanted planar waveguide
in Er: TeO2-WO3 can be seen in Fig. 5. Four
modes (dips in the reflected intensity) can be
seen in at 633 nm, while the waveguide is
monomode at 1550 nm.
Functionality of channel waveguides was tested using the end fire coupling method. Single mode optical fibres
were used to couple the light coming from semiconductor lasers into the channel waveguides. An example for
that test is presented in Fig. 6. Channel waveguides were fabricated in Er:TeO2-WO3 glass by implantation of 1.5
MeV N+ through a silicon mask containing long apertures of 24 µm width v. Depth and lateral confinements as
well as green upconversion can be seen. Another example is a channel waveguide implanted in a eulytine type
BGO crystal, using the same silicon mask, but using 3.5 MeV N+ ions, shown in Fig. 7.
Due to the large width of the waveguide, two modes appear laterally while the waveguide is monomode
4 Micro Raman spectra (A) taken across a channel waveguide (B) fabricated in an Er-
Te glass with 3.5
+ ion implantation
through a silicon mask). The parameter of the vertically shifted curves is the laser
microbeam position along the horizontal line in the microphotograph.
5 M-line spectra of waveguide. Fluence = 8∙10
, E =3.5 MeV. (a) at 635
nm and (b) at
Microphotograph of a 1530
nm laser beam
emerging from a channel waveguide.
fluence was 1
∙1016 ions/cm2 with 3.5 N+ ions.
Microphotograph of a 633 nm laser beam
emerging from a channel waveguide (A) and
photograph taken from above of the waveguide
end fire coupled 980 nm laser beam
fluence was 1∙10
Researches on the design and fabrication of planar and channel optical waveguides and Bragg gratings in optical
glasses and crystals, using implantation of various ions at relatively wide ranges of energy and fluence were
briefly presented. Guiding modes were detected in 3.5 MeV N+ ion implanted planar waveguides both in Er-Te
glass and sillenite type BGO crystals at λ = 1530 nm. Waveguides in sillenite type BGO worked only up to 1310
nm. Three methods were realized for channel waveguide fabrication in glasses and crystals: Implantation
through a special silicon mask or a photoresist mask using 1.5 MeV and 3.5 MeV N+ implantation, and direct
writing of the channel waveguides in the tellurite glass using focused beams of 6–11 MeV C3+ and C5+ and 5 and
10 MeV N3+ and N4+. Channel waveguides fabricated in Er-Te glass with 1.5 MeV implantation proved to work
up to the wavelength of 980 nm. Preliminary test showed that both 3.5 MeV N+ ion implantation through silicon
mask in eulytine and sillenite type BGO crystals and direct writing with high-energy focused C5+ ions in Er-Te
glass produced channel working that worked up to the wavelength of 1530 nm. The results so far confirmed
show that ion beam fabrication is an adequate method for fabrication of various types of optical elements. The
use of swift heavy ions is an especially promising method, since it requires very low fluences (down to 1012
ions/cm2), corresponding to short processing times.
This work was supported by the following funds: Hungarian National Research Fund (OTKA) project 101223
and TAMOP 4.2.2.A-11/1/KONV-2012-0036 Project, co-financed by the European Union and European Social
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