Photonics Related Works at International School of Photonics
&
Centre of excellence in Lasers and Optoelectronic Sciences
Cochin University of Science and Technology
V P N Nampoori
www.photonics.cusat.edu
Organization Chart of ISP and CELOS
Director : ISP Director: CELOS
Professor V P N Nampoori Dr C P Girjavallabhan
Nonlinear Optics, BioPhotonics Laser Technology
Neural Network Optoelectronics
Faculty Memebers Students Supporting Staff
Prof V M Nandakumaran
Theoretical Photonccs
Ph D Photonics, Nonlinear Dynamics, photonics
Materials, nanophotonics, biophotonicd,
theoretical Photonics
MTech : Optoelectronics and Laser Technology
Integrated five year MSc
(Photonics)
Prof P Radhakrishnan
Laser Technology ,Fibre Optics
Mr Kailasnatha
Fibre Optics
Dr Sheenu Thomas ( CELOS)
Photonics Materials
Guest Faculties
Research Associates
M Phil ( Photonics)
ISP
Manpower
development
R&D
activities
Extension
activities
Ph D MTech MSc
(5yrIntegrated)
Sponsored
Project
Consultancy
work
Conferences Photonics News
Optics to School
Photonium
PSI
R&D Activities
Fibre Optics Laser
Spectroscopy
Nonlinear
Optics
Nano
Photonics
Theoretical
Studies
Fabrication
Laser Spectroscopy
Photoacoustics
Thermal Lens
Fluorescence
Nonlinear Optics
Two Photon Absorption
Z-Scan
Wave Mixing
Fibre Optics
Sensors
Development of Polymer Optical Fibres
Dye doped fibres and planar waveguides
Nanophotonics
Laser Produced Plasma
Nonlinear dynamics as applied to lasers
Biophotonics and Biomedical Devices
ZnO – Material of 21st Century
- a unique combination of piezoelectric, thermal and optical properties
- a promising II-VI wide bangap semiconductor material
- a multifunctional semiconductor with manifold applications
solar cell,
transparent conductive thin film
gas sensor, thin film transistor……
- a material for short-wavelength opto-electronic devices
-UV light emitting devices and sensors, biosensors etc.
Hydrolysis
15 Minutes
Polyol Synthesis
ZincAcetate Dihydrate
+ Diethylene Glycol
Homogenised Zn(OH)2
precursor solution
ZnO colloids
Heating rate
4º/min
Aging
120ºC
0.01 to 0.166M80 ºC
ZnO nano crystals
Stirring
Synthesis of ZnO colloids
Size dependent absorption spectroscopy of nano colloids of ZnO
J. Appl. Phys. 102, 063524 2007
Optical
absorption
spectra for
colloidal
suspensions
showing the
red shift
associated
with
increased
particle size
Size dependent Optical band gap of nano ZnO colloids
J. Appl. Phys. 102, 063524 2007
The
optical
band gap
(Eg) is
found to
be size
dependen
t and
there is
an
increase
in the
band gap
with
decrease
in
particle
size
Excitation spectrum of ZnO colloid for an emission peak of 385 nm
J. Appl. Phys. 102, 063524 2007
Excitation wavelength dependence of fluorescence spectroscopy
J. Phys. D: Appl. Phys. 40 (2007) 5670–5674
Red shift in emission
peak with excitation
wavelength
The inefficient energy
transfer between the
upper and the lower
vibrational levels of the
excited state of these
particles owing to short
fluorescence lifetime is
primarily responsible
for the excitation
wavelength dependent
spectral shift of ZnO
colloids
J. Appl. Phys. 102, 063524 2007
Additional
emissions at
420 nm and
490 nm are
developed
with increase
in particle
size along
with the
known band
gap 380 nm
and impurity
530 nm
emissions.
Size dependent absorption spectroscopy of nano colloids of ZnO
Excitation wavelength of 255 nm
The dependence of mean particle size on
a) band gap enlargement
b) band to band emission
J. Appl. Phys. 102, 063524 2007
Band g
ap
Ban
d t
o b
and e
mis
sio
n
•The red shift in the UV
emission with particle
size closely follows the
red shift in the band
edge
•This allows us to
reconstruct the size
distribution curves in
the fluorescence
spectrum.
Fluorescence spectra of nano ZnO colloids of different particle size for
an excitation wavelength of 325 nm
J. Appl. Phys. 102, 063524 2007
With
decrease of
excitation
energy,
blue band
peaks get
suppressed
and UV and
green
fluorescence
peak
becomes
dominant at
larger
particle size.
The open aperture z scan traces of ZnO colloids of different
particle sizes at a typical fluence of 866 MW/cm2
The closed aperture z scan traces of ZnO colloids of different particle
sizes at a fluence of 866 MW/cm2
Size dependent enhancement of nonlinear optical properties
of nano colloids of ZnO
The third-order
optical susceptibility,
increases with
increasing particle
size (R)
In the weak
confinement regime,
R2 dependence of
is obtained for ZnO
nano colloids.
(3)
(3)
The optical limiting response of ZnO colloids of different particle sizes
Increasing particle size reduces the limiting threshold and enhances
the optical limiting performance.
• Wide application in LAN/WAN/CATV
• Cost effective
• Short length of fiber is needed when compared to EDFA
• Wavelength tunable
• Good amplifiers in visible communication region
• Disdavantage: Bleaching of laser dye at higher pump power
Dye doped fiber amplifier
Fabrication of Polymer preforms• Photo-copolymerization
• Interfacial gel polymerization
• Centrifugal method
The most commonly used polymer for the fabrication of
polymer optical fiber is Polymethylmethacrylate (PMMA)
Interfacial gel polymerisation
Monomer
+ Dye+
RI agents
PMMA Tube
Cla
ddin
g
Cla
ddin
g
Preform
Cla
ddin
g
Co
re
Cla
ddin
g
Centrifugal method
Rotation
Cla
ddin
g
Cla
ddin
g
Co
re
1. Preform feeder
2. Polymer Preform
3. Furnace
4. Fiber puller
5. Pick-up spool
1
2
3
4
5
Electronic control
circuit
Light propagation through the drawn fiber
Stripe illumination pumping to measure the
line narrowing at different pump power
Nd:YAG
CCD
Monochromator
532n
m p
uls
ed
Cylindrical
Lens
Dye doped POF Collecting fiber
0 2 4 6 8 10 12
5
10
15
20
25
30
35
40
45
FW
HM
(nm
)
Power(mJ)
Line narrowing with increase in pump energy
Dye Doped POF as an optical amplifier
Nd:YAG
laser
MOPO Laser
(signal)
Optical
delay setup
1ns
Photodetector
(New focus)
Beam
dump
Beam
dump
355nm pump
for MOPO
532nm
Beam
splitter
Beam
splitter
Focusing
lens
Dye doped
polymer fiber
Collecting
fiber
CCD/Monochromator
(Acton Spectrapro)
Beam
Splitter
Digital Storage Oscilloscope
(Tektronix-500MHz-5Gs/S)
Microscopic
Objective
Signal W/O Pump
Amplified output when pump was given
0 20 40
4
6
8
10
12
14
Sig
nal gain
(dB
)
Fiber Length(cm)
Gain at different fiber lengths
0 2 4 6 8 10
0
2
4
6
8
10
12
14
slope=1.25853dB/KW
B Linear Fit of Data1_B
Gain
(dB
)
Power(KW)
Gain at different pump power
Nd:YAG
532nm
1064
nm
Beam dump
Dichroic mirror
NDF Wheel
Convex Lens
Dye doped POF
Six axis fiber aligner
CCD Monochromator-PC data
acquisition
Fluorescence collecting
fiber
fluorescence emission from dye doped
POF-Mode Structure
Multimode laser emission from dye doped polymer optical fiber.
590 591 592 593 594 595 596 597 598 599 600
0
5000
10000
15000
20000 D=335m
(a)
0.23nm
Em
issi
on In
tens
ity(A
U)
Wavelength(nm)
592 593 594 595 596 597 598 599 600 601
0
1000
2000
3000
4000
5000
(b)
0.18nm
D=405m
Em
issi
on In
tens
ity(A
U)
Wavelength(nm)
594 596 598 600 602
0
2000
4000
6000
8000
10000
12000
14000
(c)D=510m
nm
Em
issio
n Inte
nsity(
AU
)
Wavelength(nm)
Mode spacing decreases as diameter increases
D-Diameter, n- Refractive index,
Mode spacing is according to spherical Fabry -Perot etalon
nD
2
Fabrication and characterization
of Solid state energy transfer Dye Laser materials
Photograph of the polymer rods doped with C-540:RhB pair
Multiwavelength operation
Possibility of multi wavelength operation for a dye mixture doped polymer optical fiber
λ1
λ2
λ3
Many of the fabricated rods exhibit multiple emission peaks
M.Kailasnath, P.R.John, P.Radhakrishnan, VPN.Nampoori and CPG .Vallabhan. A comparative study of
energy transfer in monomer and polymer matrices under pulsed laser excitation. Journal of Photochemistry and
Photobiology A. Chemistry (Elsevier), Accepted, October 29,2007
Quantitative analysis of Energy transfer from fluorescence
Lifetime measurements
A decrease in the lifetime of the donor C 540 in the presence
of acceptor was observed
Conclusions
Dye mixture doped polymer can be used as energy transfer dye
laser materials and as polymer optical fibre preforms.
Results showed that radiative transfer mechanism plays the
major role in energy transfer.
Lifetime of the donor is only slightly affected in the presence
of acceptor.
Radiative transfer efficiency is enhanced in polymer phase
We have identified the concentration regions over which multi
wavelength operation is possible
Fabrication of dye doped Graded Index Polymer
Optical fiber preforms
M.Kailasnath, Rajeshkumar, P.Radhakrishnan, VPN.Nampoori and CPG .Vallabhan. Fabrication and fluorescence
characterization of dye doped graded index polymer optical fibre preform. Journal of Optics and Laser Technology (Elsevier),
Accepted, September 25, 2007
One starts with a hollow PMMA tube, which is filled
with the monomers mA and mB, which have lower and
higher n values respectively. Polymerization is carried
out by a UV lamp through the PMMA shell.
A and B co-monomers are further tailored so that
the two reactivity ratios are dissimilar, which leads to
increased incorporation of A near the tube walls
where the photo-initiation light is strongest
As monomer A gets used up near the outer edges of
the tube, monomer B (with the lower refractive
index) is incorporated in a higher proportion in the
middle of the tube, towards the end of the reaction.
A
AB A
A
A
AB
B
B
B
BB
B
Interfacial Gel Polymerization
Refractive Index
measurements
A photograph of the centre portion of the fringe pattern from a
mach-zender Interferometer
We used a large molecules
of DPP( di phenyl phthalate)
during the second
polymerization.
Index exponent
As the slope of the curve between ln g(r) and ln (r/a)
2
)0(
)(1
2
1)(
n
rnrg
2
1
0 21)(
a
rnrn
2
1
0 21 n
for r a
for b r a=
where a= core radius and
98.1exponent index The
For GI fibre,
Conclusions
Using Interfacial gel polymerisation,Graded index polymer
optical fibre preforms were fabricated with Rh.B dye doping.
Using the interferometric technique,the refractive index profile
was measured and the index exponent was calculated as 1.98.
These rods can be used to fabricate cladded polymer optical
fibre amplifiers in the visible region.
It was also seen that the dye concentration and the fluorescence
intensity are maximum along the axis of the preform
Fabrication of a compact polymer optical fiber
drawing machine
A compact cylindrical furnace for heating the polymer
optical fibre preform was developed and its temperature profile
was measured along the axis when maximum temperature is
around 200oC, the processing temperature of POF.
Heat conducting
ceramic
coil
Protective
covering
Aluminium lid
0 2 4 6 8 10 12
0
50
100
150
200
Te
mp
ara
ture
oC
Distance from the top of the furnace (cm)
Temperature profile inside the mini furnace
M.Kailasnath,VPN.Nampoori,P.Radhakrishanan, “Fabrication of a compact polymer optical fibre drawing machine”
DAE-BRNS National Laser Symposium, 2008, Baroda, India
The stepper motors used for the present device are DFM57SH51-1A.001,
which is of a 1.80/step. The driver is capable of reducing this step size up
to 0.2250/step thereby minimizing any possible vibration during the fibre
drawing process. At this step size, the motor takes 1600 steps for completing
a full rotation.
We can choose three more step sizes viz; 0.45, 0.9and 1.80/step.
In each one, the speed can be varied from Vmax /255 to Vmax independently
for the feeder and drawing motors there by effectively allowing the
fibre diameter tailorability.
The control electronics for the machine
The graphical interface developed for the device
A PIC 16F 873A chip is used for controlling the stepper motor
driver A3955B which is a 1/8 th stepper IC.
A visual basic software was developed to control the device.
The POF drawing machine
Conclusions
A wall mountable, compact and portable polymer optical fibre
drawing machine has been fabricated. The temperature profile
along the axis of the furnace was measured. This will help us
in predicting the neck down region, and inturn minimizing the
fibre preform waste. A soft ware for the diameter control of
the drawn polymer optical fibre was also developed .The drawn
polymer optical fibre is under characterisation.
• Biopolymers Chitosan and Agarose
• Chitosan based fiber optic humidity sensor
• Agarose based fiber optic humidity sensor
Biopolymers for Fibre optic sensors
Biopolymer- Chitosan
Chitosan is a fiber-like substance derived from
chitin.
Principal source of Chitin is shellfish waste such
as shrimps, crabs, and crawfish.
Deacetylation of Chitin gives Chitosan
achieved by treatment with concentrated sodium
hydroxide solution (40- 50%) at 100ºC or higher for 30
minutes to remove some or all of the acetyl groups
from the polymer.
Applications….
– Used for the removal of metal ions from waste water
– The property of thin film formation, water binding
capacity and refractive index variation on water
adsorption of chitosan can be applied for constructing
a fibre optic humidity sensor
Biopolymer- Agarose
• Agarose is an unbranched polysaccharide
obtained from the cell walls of some
species of red algae or seaweed.
• Chemically, agarose is a polymer made up
of subunits of the sugar galactose.
• Structure of Agarose
(1 4)-3,6-anhydro-α-L-galactopyranosyl-(1 3)-β-D-galactopyranan
Chitosan based fiber
optic humidity sensor
Principle
The swelling nature of Chitosan in the
presence of water vapour causes variation of
refractive index.
This variation in refractive index is used to
modulate the intensity of light propagating
through a fiber with chitosan as cladding.
Theory
In the dry state the refractive index of the
cladding layer is larger than that of the
fiber cladding; it operates in the leaky
mode for higher modes.
In the humid air chitosan swells, its
refractive index decreases; more higher
modes are guided.
Mathematically
mc
cs
cs
out rPPP
)()(0
Where, c is the critical angle in the input-side PCS Fiber,
r() is the reflection coefficient,
m is the reflection number for the sensor head and
cs is the critical angle in the sensor head
Sensor Fabrication
Fiber Preparation
sensor element fabrication includes fibre preparation and deposition
of the chitosan film on the prepared fiber
Fiber : A plastic cladded silica(PCS) fiber of length 35cm with following
specification was taken.
1. Type F-MBC
2. Step Index
3. Multimode
4. Numerical Aperture= 0.37
5. Core Diameter = 400 m
6. Cladding Diameter = 430 m
Dip coating
The prepared fiber is fixed vertically on the dip coating unit.
The chitosan solution is kept under the fiber.
The speed of the motor is set to 0.875mm/sec in the vertical
direction.
The fiber is dipped into the solution with this speed and it is kept in
the solution for one minute to achieve a perfect adsorption with the
core of the fiber.
The fiber is taken out at the same speed.
The dip coated fiber is kept 24 hours at room temperature for drying.
Experimental Set-up consists of a source, detector and the humidity chamber
in which the chitosan coated fiber is fixed.
Source used for the experiment is a red LED emitting at
636nm.
A low power silicon photo detector (Newport 818-IR) was
used with a power meter (Newport make, Model 1815C).
The aerator is used to pump air into humidity chamber
via ethylene glycol (dry air) or water (humid air).
Humidity measuring unit used for calibration has a
measuring range 10% - 95% RH.
Dehumidifying agents: Air bubbled through ethylene
glycol bring down the chamber humidity to 20%RH,
Passing nitrogen gas into the chamber bring down the
chamber humidity to 17%RH.
Climate chamber
chamber is made of borosilicate glass.
Two fiber holders are fixed at the two side
walls of the climate chamber.
The sensor head of the digital humidity
measuring equipment is inserted into the
chamber.
10 20 30 40 50 60 70 80 90 100
-0.10
-0.09
-0.08
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0.00
0.01
Relative Humidity(%)
Norm
alis
ed P
ow
er(
dB
)
Sensitivity = 0.001dB/RH
Accuracy = +/-7%
Coating = Single layer
Core diameter = 400m
Length of sensor head = 5cm
Reverse day1 Forward day1 Reverse day2 Forward day2 Forward day3 Reverse day3
Calibration curve for quantitative determination of humidity with a
Chitosan-coated fiber probe
Agarose based fiber
optic humidity sensor
Swelling nature of hygroscopic material Agarosecauses refractive index changes in accordancewith the humidity. This phenomena have beenemployed in the design and development of fiberoptic humidity sensor.
Sensor Fabrication
The sensor element fabrication includes fibre preparation and deposition
of the agarose film on the prepared fiber.
method followed to prepare the solution for coating is boiling water bath
method.
– Agarose hydrogels with an optimum durability has a gelling temperature of
about 34–38 0C and a melting point of 94–97 0C.
– 1% of Agarose powder is mixed with pure water (the maximum solubility of
Agarose in water is 1.5%).
– the beaker is kept in a boiling water bath and at the same time the mixture of
Agarose and water inside the beaker is stirred until the agarose is
completely dissolved.
– Agarose mixture is deposited on the optical fiber when the temperature of
the solution is above the gelling point.
– As the hot liquid cools down the hydrogel is deposited around the stripped
fiber.
– the hydrogel is kept for one day until it is partially dehydrated or reaches the
equilibrium with the environment.
Comparison of the Chitosan and Agarose coated sensor head.
Chitosan coated sensor head Agarose coated sensor head
Sensitivity 0.001 dB/RH 0.001 dB/RH
Response time 2 seconds 3 seconds
Linear response 17- 95 %RH (accuracy +/-7%) 40-95 %RH (accuracy +/-1%)
Raman spectra of PMMA O F
3
2
4
5
67
10
8 9
1
Figure 1 Experimental setup for measuring Raman spectrum. (1)DPSS at 532nm
(50mW); (2, 7) Dichroic mirror at 532nm; (3) ND filter; (4, 6, 8) lenses; (5) PMMA
POF of 310micron dia and 50cm length; (9) Monochromator with CCD (Acton
Pro); (10) Beam dump for reflected 532nm
500 1000 1500 2000 2500 3000 3500 4000
-5000
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
Figure 2. Raman spectrum of the PMMA POF pumpedby 532nm DPSS Laser (50mW). Inset shows the enhanced
spectral region 500-2000 cm-1.
500 1000 1500 2000
900
1200
1500
1800
2100
2400
2700
3000
3300
3600
3900
16
48
17
36
14
60
12
64
10
81
99
9
85
3 92
5
60
2
Ra
ma
n I
nte
ns
ity
(a.u
.)S h ift(cm
-1)
3454
2957
3001
2848
1736
1648
1460
1264
1081
999
925602
Ram
an
In
ten
sit
y (
a.u
.)
Frequency shift (cm-1)
Table 1. Observed Raman Bands in PMMA POF and their assignments.
Raman band (cm-1) Assignments
602 (C-COO), s(C-C-O)
853 (CH2)
925 (CH2)
999 O-CH3 rock
1081 (C-C) skeletal mode
1264 (C-O), (C-COO)
1460 a(C-H) of -CH3 , a(C-H) of O-CH3
1648 Combination band involving (C=C) and (C-COO)
1736 (C=O) of (C-COO)
2848 Combination band involving O-CH3
2957 s(C-H) of O-CH3 with s(C-H) of -CH3 and a(CH2)
3001 a(C-H) of O-CH3, a(C-H) of -CH3
3454 (22) Overtone of 1730cm-1
Variation of relative Raman intensity with fiber length
0 50 100 150 200
1.4
1.6
1.8
2.0
2.2
2.4
Figure.3. Variation of relative intensity ratio of Raman
bands at 2957 and 3001 cm-1 with fiber length.
Ls
Ram
an r
elat
ive
inte
nsity
Fiber length (cm)
25mW 40mW 50mW
Critical length Ls for the better detection of Raman signals from PMMA POF
The intensity (IR) of Raman signals is proportional to the transmitted pump intensity (IPt) and the length (L) of the fibre. The transmitted pump intensity is given by,
(1)
where IPi is the input pump intensity and a is the fibre attenuation coefficient. Hence the Raman intensity is given by,
(2)
For constant input pump power, (3)
exp( ) (1 )Pt Pi PiI I L I L
(1 )R PiI LI L
2( )RI L L
Nonlinear Dynamics and Theoretical Photonics
1 Study of control of Chaos in Nd YAG and directly modulated
semiconductor lasers
2 Synchronisation of chaotic semiconductor lasers under various types of
coupling schemes
a) Open loop coupling
b) Closed loop coupling
c) Global coupling
3 Directly modulated semiconductor lasers with delayed optoelectronic
feed back
Suppression of hysteresis with feed back
4 Synchronisation – antisynchronisation transition in coupled Nd YAG
lasers
5 Observation of chaotic behaviour in damped linear oscillator with
intermittent driving ( a result first of its kind)
Future plan of work
1. Nonlinear Optical studies using femto / pico second lasers
2. Chemical kinetics of fast reactions
3.Laser –tissue interactions in femto / pico second regimes
4.Optical Solitons in optical fibre
5. Plasma generation using fast laser pulses
6. Fibre –Bragg Gratings
7. Waveguide structures in substrates by laser writing.
8. Laser beam propagation in random media.
Coworkers
C P Girijavallabhan
V M Nandakumaran
P Radhakrishnan
Kailasnath
Bindu Krishnan
Litty
Sheeba
Rajesh M
Thomas K J
Santhi
Rajesh S
Parvathy
