Microfluidics and integrated optics combined to study the interaction of particles or solution with light flowing through a microfluidic channel. Involves dye excitation through evanescent wave coupling.

1. Fabrication of optical waveguides for
integrated optic and optofluidic device
applications
By
Prathul Nath P P
15PH62R06
Under the supervision of
Dr. Shivakiran Bhaktha B N
Department of Physics,
Indian Institute of Technology Kharagpur
Master of Technology
Thesis Viva

2. Outline
 Aim.
 Introduction .
 Fabrication Techniques.
 Characterization Techniques.
 Co-doped Waveguide system.
 On Chip Microfluidics.
 Conclusion and Scope of Future work.
 References.

3. AIM
The aim of this project is to fabricate a device based on
co-doped
waveguide system which can give out light of different
wavelengths
and to use it as a multiple light source to study the
interaction of light
with particles which is flowing through a micro fluidic
channel
integrated on the waveguide system.

4. Introduction
 It combines microfluidics
and optical technology.
 Able to control flow
parameters and to
manipulate particles in a
solution by making use of
light.
 Enables real time tunability
of optical properties that
are difficult to reconfigure
in conventional solid state
Lab on a chip biosensing device
Courtesy : http://onlinelibrary.wiley.com

5. 1.Sol Gel Synthesis
 Wet-chemical synthesis technique for preparation of oxide
gels, glasses, and ceramics at low temperature.
 Involves mixing of different precursors in a specific order and
stirring under a specific temperature for a certain amount of
time.
 Then the prepared sol is filtered out using 0.2 μm Whatman
puradisc syringe filter and then taken for dip coating.
 Following samples have been made:
1) SiO2(70%)-Hf02(30%).
2) SiO2(70%)-Hf02(23%)-ZnO(7%) with Tb(1 mol%).
3) SiO2(70%)-Hf02(23%)-ZnO(7%) with Eu(1mol%) & Tb(1 mol%).
4) SiO2(70%)-Hf02(23%)-ZnO(7%) with Eu(0.5mol%) & Tb(1 mol%).
Fabrication Techniques

6. 2. Dip Coating
 The dip-coating method consists of soaking the
substrate (Silicon wafer) in the solution and withdrawing
it at a constant speed.
 Compared to spin coating, the film is more uniform and
smooth.
 Around 20-25 layers are coated for a standard sample
making it time consuming.
 After each coating sample is kept inside a furnace at
Dip coating stages.
Courtesy:
http://www.solgel.com

7. 3.UV Photolithography
 We have made Rib waveguides using this technique on
SiO2(70%)-Hf02(30%)-waveguide.
 We have made multiple microchannels on the
waveguide structure fabricated.
Steps in Photolithography.

8. Rib waveguide (SiO2 (70%)-HfO2
(30%)) channels without light
coupling
Rib waveguide (microchannels)
with light coupling
The channels are of width around35 µm. The light is
coupled through
the waveguide channels by Butt coupling.

9. 4. Micro Fluidic Channel Fabrication
• PDMS has become virtually
the default material for forming
micro- fluidic devices. It comes
with a master and cross linker
with 10:1.
•We made use of simple
technique to make micro
channel design which is by
using an optical fiber.
• Multiple optical fiber pieces
are put on the PDMS solution
and pushed to bottom and
then is heated on a hot plate
Microscopic image of micro fluidic
channel.
Microscopic image of fiber used.

10. Characterization Techniques
1. M Line Spectroscopy
Prism coupling on Si-Hf waveguide
(refractive index =1.565, thickness=
1µm and propagation loss = 0.5
dB/cm)
• Prism coupling couples a substantial fraction of the
power contained in a beam of light like laser into a thin
film based on evanescent wave formation.
• Used to find the refractive
index, thickness and
propagation loss of
waveguides.
• From the equation below we
find refractive index and
thickness.

11. 2. XPS Spectroscopy
 XPS analysis on Si(70%) –Hf(23%) – 7%ZnO
ternary waveguides doped with Europium and
terbium (at three different concentrations) showing
Eu and Tb oxidation states.
XPS peaks for both Eu and Tb.

12. 3. Photoluminescence
We have conducted Room temperature PL studies on
SiO2 (70%)
–HfO2 (23%) – 7%ZnO ternary waveguides doped
with
Europium .
and terbium.
PL and PLE setup being used.

13. Co-Doped waveguide system
 We have done PL Spectra to determine the peak
energy emissions and thereby we can actually
observe the effects of RE dopants over emissions.
 Prepared hybrid Nanocrystal embedded glass
ceramic waveguides (SiO2(70%) - HfO2(23%) -
ZnO(7%)) and co-doped it with Europium and
Terbium (1 mol%).
 ZnO is considered as a promising host for
optoelectronic device applications because of large
exciton binding energy and optical transparency in
the visible and near IR.

14. This plot shows emission spectrum of Eu -Tb co-doped system with both
same concentration. We can see emissions spanning from blue to red in the
system. So this system is a i

15. Possible Energy Transfer between Dopants
PLE at 612nm emission for highlighting
482nm energy level of terbium.
Energy levels of terbium and
europium

16. Fig a) shows two plots ; PLE at 612nm (black) for the same lattice
with only Eu (1mol%), which is the most intense peak of emission for
Eu and the next plot is PL at 355nm (red) for the same lattice with only
Tb (1 mol%). Fig b) shows the PLE spectra of the representative
glass sample doped with 1 mol% Eu and 1 mol% Tb. The curve in
green was measured by monitoring the most intense emission of Tb3+
in the green (542 nm) whereas the curve in red was obtained by
monitoring the Eu3+ (612 nm).

17. Emission due to Eu3+ at 591nm and 612nm is increasing with increase
in Eu concentration along with decrease of Tb3+ concentration. This is
a major proof as the Terbium emission at 542nm is being absorbed by
Eu (decrease in the Tb peak at 542nm) and results in Eu3+ emission at
591nm and 612nm.
PL for co-doped system at both 320nm and 380nm.

18. On- Chip Microfluidics
 Integrating Rib waveguide to PDMS microfluidic
channel.
 Inlet and outlet are made on the microfluidic
channel and is bonded on to the rib waveguide after
plasma treatment.
 Followed by putting inlet and outlet valves and
connecting it to syringe barrel for putting the
solution.
 PDMS has several attractive properties which
makes it the best material for micro fluidic devices.

19. Evanescent wave excitation of Dye
Setup for evanescent wave excitation of Rhodamine 6g.

20. Experimental setup showing evanescent wave excitation.
Shows emission spectra of rhodamine 6g.

21. Image taken through notch filter Showing dye left over outside PDMS on
waveguide channel (light coupled) getting excited by evanescent waves.
Microscopic images showing the intersection of fluidic channel and waveguide
channel without and with notch filter.
Waveguide channel
Waveguide channel
Microfluidic
channel
Microfluidic
channel

22. Conclusion and Scope of future work
 We have successfully integrated rib waveguide
system with microfluidics and analyzed the
interaction of solution flowing through fluidic channel
with light coupled to the rib waveguide channel.
 From our study on co-doped system, we have
observed that Eu-Tb co-doped system have
considerable emission at different wavelengths. The
idea is to integrate such a system with microfluidics
and to study the interaction at different wavelengths
in a single device or “Lab on a Chip” setup.

23. ACKNOWLEDGEMENT
I thank my project supervisor Dr. Shivakiran Bhaktha for
the
support and motivation through out the project. His
technical
expertise and guidance helped me a lot for the
completion of
this project.
I am also thankful to Departmental lab facility
;Lithography ,XPS and
UFS Thermoelectric lab for giving me access.
I thank all faculty members for their motivation and
valuable advices. I also thank all my Lab mates and

24. References
 An Introduction to Integrated Optics,Herwig Kogelnik.
 Scriven, L.E. (1988). "Physics and applications of dip coating and
spin coating". Better ceramics through chemistry III. pp. 717–729.
 Fabrication of microfluidic devices using PDMS, James Frienda
and Leslie Yeo.
 Theory of Prism-Film Coupler and Thin-Film Light Guides,P. K.
TIEN AND R. ULRICH.
 Optofluidic trapping and transport on solid core waveguides within
a microfluidic device, Bradley S. Schmidt1, Allen H. J. Yang2,
David Erickson3, and Michal Lipson1.
 UV photolithography by R.B Darling/ E-527.
 Eu-doped ZnO–HfO2 hybrid nanocrystal embedded low-loss glass-
ceramicwaveguides, Subhabrata Ghosh and Shivakiran Bhaktha B
N.
 Righini G C, Brenci M, Forastiere M A, Pelli S, Ricci G,Conti G N,
Peyghambarian N, Ferrari M and Montagna M.
 J. C. McDonald and G. M. Whitesides, “Poly(dimethylsiloxane) as
a material for fabricating microfluidic devices,” Acc. Chem. Res.,
35, 491–499, (2002)
 Peled A, Chiasera A, Nathan M, Ferrari M and Ruschin S 2008,