Shape Control of Self-Written Waveguide

Shape Control of Self-Written Waveguide
Myung-Joon Kwack * , Masahiro Kanda * , Osamu Mikami * ,
Masatoshi Yonemura † , Akari Kawasaki † and Manabu Kagami †
*
Graduate School of Engineering
Tokai University, 1117, Kitakaname, Hiratsuka-shi, Kanagawa, Hiratsuka, Kanagawa 259-1292 Japan
Tel: +81-463-58-1211, Fax: +81-463-50-2016
E-mail: 8adgm003@mail.tokai-u.jp
†
Toyota Central R&D Labs., Inc., 41-1, Yokomichi, Nagakute, Aichi, 480-1192, Japan
Tel: +81- 561-71-7062
E-mail: yonemura@mosk.tytlabs.co.jp
Abstract— Recently, drastic increase of information flow has
become a serious problem in information and communication
technology, because of a data transmission rate limit in metallic
wiring. To solve this problem, we have paid a special interest to
optical interconnection by SWW (Self-Written Waveguide). We
studied about a mutual relationship between the SWW shape
and fabrication parameters, such as the laser irradiation power
and the optical mode. We examined the SWW by simulation
using the ray tracing method. Experimentally we fabricated
SWWs under several beam divergence angles. From these results
we confirmed that it seems possible to control the SWW shape
with specific parameters.
I. INTRODUCTION
Nowadays, we are living in a society based on information
society. In this society, a drastic increase in information flow
has become a serious problem. Because of this, the
development of information and communication technology
has become essential. Until recently, metallic wiring and
wireless technology were the most used means for
information and communication technology. However, these
have a data transmission rate limit, because of EMI (Electromagnetic
Interference), crosstalk between the adjacent
channels, high electricity consumption, and so on.
Furthermore, there is a limitation in the densification of the
implementation for the multi transmission channel.
To solve these problems, optical interconnection
technology developed in the latter half of the 20 th century.
This is now applied at the microscopic level (for example,
boards and chips) for developing Optical PCB (Printed Circuit
Board)[1].
Optical PCB is a hybrid circuit board with both optical
wiring and electronic wiring. There are many light signal
transmission mediums for optical wiring of Optical PCB. One
of them is the SWW (Self-Written Waveguide) which is
formed with curing of light curable resin by irradiation of
laser beams. However, it requires a technology which can
form SWWs according to design specifications, in order to
put optical interconnection technology to practical use.
We study about the SWW shape control technology
according to design with the experiment and the simulation
which are set some parameters. We have confirmed that a
mutual relationship between SWW with several fabrication
parameters. The final goal of this study is to make a theory
based upon our research, and to program software that
controls the forming of SWW.
In this paper, we will introduce the analysis of SWW
fabrication shape by ray tracing method, and important results
of the SWW forming experiment.
II. ANALYSIS OF SWW SHAPE CONTROL
We performed a shape analysis of SWWs using analysis
software based on the ray tracing method to confirm the
SWW shape change by changing parameters.
Fig.1 shows an image of the analysis model.
Beam divergence angle• •�
Light source
HPCF
core • •�200�m
clad • •�230�m
Plastic container
Light curable resin
2mm 2mm
Fig.1 Analysis model
To form SWWs, we will propagate the laser beam with a
divergence angle to HPCF (Hard Polymer Clad Fiber,
Core/Clad: 200/230�m). It is irradiated to a plastic container
(Full length: 2mm), which is filled with light curable resin.
Table1 shows the analysis condition.
Table 1 Analysis condition
Parameter Value
Number of rays 10,000
Curing threshold
More than 90% of
max. irradiation power
Refractive index of
light curable resin
Before curing 1.54
After curing 1.57
Beam divergence angle : θ 10°, 30°, 50°
978-1-4244-4522-6/09/$25.00 ©2009 IEEE 993
ISCIT 2009
1mm

There are 4 steps in the analysis.
a) Draw an analysis model, and set the analysis parameters
(For example, the refractive index, number of rays from
the light source) of a waveguide and light curable resin.
b) Analyze the model using the ray tracing method, and
find the power distribution in the resin.
c) Find the resinous curing part with the threshold wherein
resin cured from maximum irradiation power and create
a curing SWW model with 3D CAD.
d) Place the curing model into the analysis model
After all these steps, repeat steps b) to d) 10 times.
Fig.2 shows the size increase of the SWW at each step of
the analysis. A comparison of each step confirms that the
SWW shape and size increasing speed are changed by
changing the beam divergence angle of the light source. Both
the maximum width and the shape on the fiber side of the
SWW increase as the beam divergence angle increases.
However, the smaller this angle, the faster the SWW travels
as far as the 2mm plastic cell. Note that the SWW increases
less in width at smaller angles. This is because the mode of
irradiation beam is changed by changing the beam divergence
angle of the light source. We infer that it may be possible to
change the shape of SWW by controlling these parameters.
Step
2nd
4th
6th
8th
10th
Distance from fiber axis[mm]
10
Beam divergence angle• •� [deg.]
30 50
Distance from fiber side [mm]
Fig.2 SWW shape dependence on the beam divergence angle
III. EXPERIMENT OF SWW FABRICATION
Three differing shapes of SWW can be created using
different methods. These are the straight shape, the taper
shape and the reverse taper shape. However, the taper shape is
the most advantageous shape for earning high tolerance width,
when making the connection to the VCSEL (Vertical Cavity
Surface Emitting Laser) side from the waveguide side[2].
This time, we did an experiment using parameters such as
994
beam divergence angle and SWW fabrication time to examine
the feasibility of SWW shape control.
The most influential parameter in forming SWW shapes is
the FFP (Far Field Pattern)[3]. We prepared the mode
scrambler with HPCF for driving all modes of optical fiber,
and stabilizing the FFP of irradiation beam. We used the
FWHM (Full Width Half Maximum) of the mode scrambler’s
FFP as the irradiation beam divergence angle. This is a
parameter of the SWW fabrication experiment.
Fig.3 shows the experimental setup. The first step is to
adjust the laser beam from the light source (�=456nm), using
an ND filter and a beam expander. In the second step, we
gather beams of light with an object lens, before propagating
to a mode scrambler. Finally, we propagate the beam to a
plastic cell (small container), which is filled with UV curable
resin. After completion, we observe the state of the SWWs
formed.
Plastic cell
(15mm)
Fig.3 Experiment setup
We fabricated SWWs with different divergence angles 7�,
28� and 36�(Measured at part ‘A’ on Fig.3) using three kinds
of mode scramblers. Fig.4 shows SWW fabrication results
with irradiation at time ‘6s.’ From these results, we confirm
that it is possible to fabricate the SWW with a straight shape
by decreasing the divergence angle. Likewise, it is possible to
fabricate SWW with a clear tapered shape by increasing the
divergence angle.
Divergence angle [deg.]
36
28
7
Object lens
Mode-scrambler
Beam expander
ND filter
A
0 5 10 15
Distance from the SWW growing end[mm]
Fig.4 SWWs fabricated with divergence angle of
7�, 28� and 36�. (Fabrication time: 6s)
Laser source
(456nm)
SWW
Fig.5 shows the dimension measurement results of SWW
fabricated with a divergence angle of 36�. We control the
irradiation power in order to adjust the time that it takes for
the SWW to increase to 15mm (which is the cell’s length).
From this result, we confirmed that it is possible to control the
SWW taper angle not only by changing the divergence angle,

ut also by changing the irradiation time. This is the case,
even when the fabrication times are increased by decreasing
the irradiation power. We notice that as the divergence angle
decreases, it becomes more difficult to change the SWW
shape, because it tends toward a straight shape at smaller
angles. However, we confirm that it is easier to control the
SWW shapes by varying the power at larger divergence
angles.
Fabrication time of SWW [sec.]
Diameter of SWW [mm]
6
7
8
9
10
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1mm
0 5 7 10 15
Distance from the SWW growing end [mm]
(a) Pictures of fabricated SWW
Fabrication time : 6s
0 2 4 6 8
Distance from the SWW growing end[mm]
(b) Evaluation of SWW shape
7s
8s
9s
10s
Fig.5 Evaluation of SWW shape (Divergence angle 36°)
IV. SUMMARY
We analyzed the SWW shape control by changing the
beam divergence angle of the light source with the ray tracing
method. From these results, we confirm the relationship
between the divergence angle of the irradiation beam and the
shape of the SWW. In the case of wider divergence angles,
the SWW increases in width. In lesser divergence angles, the
SWW increases in speed.
We examined an actual SWW fabrication by changing
parameters such as the irradiation beam divergence angle and
the fabrication time generated by changing irradiation power.
The results show a trend wherein larger divergence angles
fabricate tapered-shape SWWs. Also, we confirm that we can
control the taper angle of the SWW shape by changing the
irradiation power. These results were very similar to the
results of the previous simulation.
995
These results confirm the possibility of controlling SWW
shapes. Thus it is more feasible to practically use SWW in
optical interconnection. More studies are needed to
understand the relationships of these parameters and how they
effect the fabrication of SWW shapes. In the future, we plan
to pursue these studies to uncover a theory of these
parameters and their relationship to forming SWW.
REFERENCES
[1] H. Park, M. Joe and T. Lee , “Technical Guide of Optical
PCB(1)”, KPCA Handbook, 2007.
[2] Y. Mimura, T. Tokuhara, T. Shioda and O. Mikami, “Optical
Coupling using Tapered Self-Written Waveguide by Laser
Beam through 45-degree Mirror”, Proceedings of the School of
Information Science and Technology, Tokai University,
Vol.6(2), pp.33-36, 2006.
[3] M. Kagami, T. Yamashita and A. Kawasaki, “Three-
Dimensional Optical Waveguide Circuits Using a Light-Induced
Self-Written Technology”, R&D Review of Toyota CRDL,
Vol.37, No.1, pp.44-50, 2001