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7/22/2019 Practicum Lab Report-Updated
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Practicum Lab ReportOptoelectronics I
Submitted By
Shahid Abbas
Matriculation Number : 32246751
Imtisal Qadeer
Matriculation Number : 32107641
Submitted To
Imran Memon
Date of Performance
December 11, 2012
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1 Table of Contents1. Theoretical Background ...................................................................................................... 4
1.1 Distributed Bragg Reflector (DBR) ............................................................................... 4
1.1.1 Optical Thickness ................................................................................................. 4
1.2 FABRY PEROT FILTER .............................................................................................. 4
1.3 Stopband ..................................................................................................................... 5
1.4 Snell's Law ................................................................................................................... 6
1.5 Refractive Index ........................................................................................................... 6
2 Simulation ........................................................................................................................... 7
2.1 Task 1 .......................................................................................................................... 7
2.1.1 Simulation of TOP DBR (3 Step Filter III) .............................................................. 7
2.1.2 Simulation of Filters .............................................................................................. 8
2.1.3 Mathematical Analysis .........................................................................................10
2.1.4 Conclusion ...........................................................................................................10
2.2 Task 2 .........................................................................................................................10
2.2.1 Filter with Stack Formula (HL)^12 C (LH)^12 .......................................................11
2.2.2 Filter with Stack Formula (LH)^12 C (HL)^12 .......................................................11
2.2.3 Filter with Stack Formula L(HL)^12 C L(HL)^12 ...................................................12
2.2.4 Filter with Stack Formula H(LH)^12 C H(LH)^12 ..................................................12
2.2.5 Conclusion ...........................................................................................................13
2.3 Task 3 .........................................................................................................................13
2.3.1 DBR Material SiO2/ZrO2.......................................................................................13
2.3.2 DBR Material SiO2/Si3N4......................................................................................14
2.3.3 DBR Material SiO2/TiO2.......................................................................................14
2.3.4 Mathematical Analysis .........................................................................................15
2.3.5 Conclusion ...........................................................................................................15
2.4 Task 4 .........................................................................................................................15
2.4.1 For m = 3 Periods ................................................................................................152.4.2 For m = 3 Periods ................................................................................................16
3 Measurements ...................................................................................................................16
3.1 Reflection ....................................................................................................................16
3.1.1 Sample DBR ........................................................................................................17
3.1.2 Sample filter 1 ......................................................................................................17
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3.1.3 Sample filter 2 ......................................................................................................18
3.1.4 Sample filter 3 ......................................................................................................18
3.1.5 Sample filter with 3-Periods .................................................................................19
3.1.6 Sample filter with 9-Periods .................................................................................19
3.2 Transmission ..............................................................................................................20
3.2.1 Sample filter with 3-Periods .................................................................................20
3.2.2 Sample filter with 9-Period ...................................................................................20
4 References ........................................................................................................................21
5 Appendix ............................................................................................................................21
5.1 Matlab Code for Simlation ...........................................................................................21
5.2 Matlab Code for Measurement ....................................................................................21
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1. Theoretical Background
1.1 Distributed Bragg Reflector (DBR)
It is a structure which consists of an alternating sequence of layers of two optical
materials having different refractive indices. When light strikes at the junction of two
materials, a specific wavelength of light reflects back. The most frequently used design
is that of a quarter-wave mirror, where each optical Layer thickness corresponding to
one quarter of the Wavelength for which the mirror is designed. The latter condition
holds for normal incidence; if the mirror is designed for larger angles of incidence,
accordingly thicker layers are needed [1]. This structure is shown in fig. 1.
Figure 1. Structure of Bragg Mirror [2]
Reflection of a light component will occur whenever following condition satisfies;
Optical thickness = /4 = x d ---------------------------------------
(i)
Where d is geometrical thickness of layer.
1.1.1 Optical Thickness
Optical thickness is the product of refractive index with geometrical thickness ofmaterial.
1.2 FABRY PEROT FILTER
It is a filter which transmits a narrow band of wavelengths and rejects wavelengths
outside of the band. An interesting feature of this filter is, its ability to select a different
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peak wavelength as the filter is tilted [3]. They are made by placing two Distributed
Bragg Reflectors side-by-side, spaced by vicinity called cavity. It is shown in Fig. 2.
Figure 2. Structure of Fabry Perot Filter [2]
Different light components may be obtained by adjusting the cavity thickness. This isshown in following diagrams.
1.3 Stopband
The range of Wavelength which are highly reflected or not to be allowed pass through is
known as stopband.
Stopband is drawn in the percentage of reflection taken on Y-Axis while wavelength on
X-Axis. A typical Stopband is shown in Fig. 4.
Figure 3. Transmission of Different Light Components through Fabry Perot Filter [2]
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Figure 4. Stopband between 1400 nm and 1700 nm [2]
1.4 Snell's LawSnell's law states that the ratio of the sine of the angles of incidence and refraction is equivalent to the
reciprocal of the ratio of the indices of refraction. Mathematically it is given by;
-----------------------------------------------------------------(ii)
Diagrammatically it is show in Fig. 5.
Figure 5. Refraction of Light Ray [2]
1.5 Refractive Index
The refractive index of a medium is the ratio of speed of light in vacuum to the speed of
light in that medium.
Where c is speed of light in vacuum and is speed of light in a medium.
The next two part of this report will be about the lab performance.
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2 Simulation
In this part of practical, we were given different materials and their thickness. We were
also given their reference wavelength, periodicity of material layers and refractive
indices. We used this data to observe graphs of Reflection and Transmission by
simulation in Openfilters Software. We export data for each observation of combination
and later plotted this data in Matlab Software.
2.1 Task 1
Given Data
a. Deposition Rate of SiO2= 58.46 nm/min
b. Refractive Index of SiO2= 1.47
c. Deposition Rate of Si3N4= 24.11 nm/min
d. Refractive Index of Si3N4= 1.82
2.1.1 Simulation of TOP DBR (3 Step Filter III)Physical Thickness = Deposition Time x Deposition Rate
a. For 1'36" of SiO2
Physical Thickness = 58.46 (1+36/60)
Physical Thickness = 93.53 nm
b. For 3'08" of Si3N4
Physical Thickness = 24.11 (3+8/60)
Physical Thickness = 75.54 nm
In Open Filter software using stack formula = (HL) ^ m HWhere
H: material having high refractive index Si3N4 (1.82)
L: material having lower refractive index SiO2(1.47)
m : Number of Periods
Number of periods m = 12.5
Stack Formula = (HL)^12H
After configuration of DBR, reflection analysis of the generated results was exported in
numerical data format in a file. Later on this file was used to draw following graph using
Matlab Software.
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Figure 6. Simulation of TOP DBR
2.1.2 Simulation of Filters
The thickness of upper and lower DBR is same as that of created in 2.1.1. In this part,
three filters were simulated by varying the cavity thickness. Each time filter wassimulated with stack formula;
Stack Formula = H(LH)^12 2C H(LH)^12
Where
C is material of cavity. In this case SiO2.
The reflection and transmission plots were generated in Openfilter software and the
data was exported to produce graphs in Matlab, which are show in diagrams for each
filter.
Following is the measurement of cavity thickness.
a. For 2'26" of SiO2(Quarter)
Physical Thickness of Cavity = 58.46 (2+26/60)
Physical Thickness of Cavity = 142.25 nm
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Figure 7. Simulation of Filter with Physical Thickness of Cavity = 142.25 nm
b. For 2'56" of SiO2 (Quarter)
Physical Thickness of Cavity = 58.46 (2+56/60)
Physical Thickness of Cavity = 171.48 nm
Figure 8. Simulation of Filter with Physical Thickness of Cavity = 171.48 nm
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c. For 3'26" of SiO2 (Quarter)
Physical Thickness of Cavity = 58.46 (3+26/60)
Physical Thickness of Cavity = 200.71nm
Figure 9. Simulation of Filter with Physical Thickness of Cavity = 200.71 nm
2.1.3 Mathematical Analysis
Thickness of Layer = Reference Wavelength / 4*(Effective Refractive Index)
d = / 4*eff ---------------------------------------------------(iii)
= 4*d*eff ----------------------------------------------------(iv)So, for SiO2
= 4*93.536*1.47 = 549.99 nm
For Si3N4
= 4*75.5446*1.82 = 549.965 nm
2.1.4 Conclusion
It is concluded that as we increase our Deposition time the thickness of cavity
increases, and as much as thickness of cavity increases, the transmission is moved
towards the right side.
2.2 Task 2
To design filters with different configurations of Stack Formulae.
Find out the best design amongst them.
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Given Data
Reference wavelength = 550 nm
Cavity material = Ormocomp
Refractive index of Ormocomp = 1.55
Number of periods (m) = 12 DBR materials = (SiO2and Si3N4)
Optical thickness = 1/2
2.2.1 Filter with Stack Formula (HL)^12 C (LH)^12
2.2.2 Filter with Stack Formula (LH)^12 C (HL)^12
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2.2.3 Filter with Stack Formula L(HL)^12 C L(HL)^12
2.2.4 Filter with Stack Formula H(LH)^12 C H(LH)^12
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2.2.5 Conclusion
For the best filter design, the filter should have many layer with the upper most layer
should be of high refractive index that provide the maximum reflection. After comparing,
we realized that the design of filter in 2.2.4 was the best.
2.3 Task 3To design filters with different materials of DBR. Use the best design configuration for
stack formula obtained in Task 2.
Given Data
Reference wavelength = 550 nm
Cavity material = Ormocomp
Refractive index of Ormocomp = 1.55
Number of periods (m) = 12
Optical thickness = 1/2 Stack formula = H(LH)^12 C H(LH)^12
2.3.1 DBR Material SiO2/ZrO2
Refractive Index of ZrO2= 2.07
Refractive Index of SiO2= 1.47
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2.3.2 DBR Material SiO2/Si3N4
Refractive Index of Si3N4= 1.82
Refractive Index of SiO2= 1.47
2.3.3 DBR Material SiO2/TiO2
Refractive Index of TiO2= 2.7
Refractive Index of SiO2= 1.47
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2.3.4 Mathematical Analysis
ZrO2/SiO2, (2.07 - 1.47) = 0.6
TiO2/SiO2 (2.7-1.47) = 1.23
The filter combination of SiO2/TiO2having refractive index contrast of 1.23 gives a wider
stopband. and the filter (ZrO2/SiO2) having refractive contrast of 0.6 gives a lower stop
band .Wider stop band gives more efficient result then the lower stop band.
2.3.5 Conclusion
By changing the materials of DBR, stopband ranges vary. In order to achieve wide
stopband, DBR should be used of materials which have high difference of refractive
indices.
2.4 Task 4
Analyse the characteristic of filters by changing the periods.
Given Data
Reference wavelength = 650 nm
Cavity material = mrUVCur06
Refractive index of mrUVCur06 = 1.45
DBR materials = (SiO2and Si3N4)
Optical thickness = 1/2
Stack formula = H(LH)^m C H(LH)^m
2.4.1 For m = 3 Periods
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2.4.2 For m = 3 Periods
2.4.3 Conclusion
By changing the periods of Bragg Reflector we can improve the reflectivity and take out
desirable of wavelength.
3 MeasurementsIn this part we observed practically, what we have already simulated and calculated
theoretically. This was basically a physical verification process that we conducted usinga Microscope, 2 Halogen lamps (HL100), Spectrometer & a Computer with vendorprovided software to show the light intensity on run-time. Our task is to measure thefollowing parameters on different samples
Transmission
Reflection
3.1 Reflection
For Reflection we use one of the two halogens which were placed above the microscope,contrary to the other one. We passed light from above and measured its reflection from the fiber
connected between spectrometer and upper part of microscope. Samples used are as follows,with their respective observed graphs.
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3.1.1 Sample DBR
3.1.2 Sample filter 1
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3.1.3 Sample filter 2
3.1.4 Sample filter 3
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3.1.5 Sample filter with 3-Periods
3.1.6 Sample filter with 9-Periods
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3.2 Transmission
For transmission we use the one of the two halogens which was placed below the microscope,
contrary to the other one. We passed light from below and measured it from the fiber connected
between spectrometer and upper part of microscope.
3.2.1 Sample filter with 3-Periods
3.2.2 Sample filter with 9-Period
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4 Conclusion
The experimental work gives us idea about how to investigate the characterization of
optical filters such as DBR and FP filters.
In order to achieve a desired Brag reflector or Fabry-Perot Filter we can simulate with
the help of computer software Openfilter, so that the optical problems of the design canbe analysed.
Secondly by using the software OOIBase 32, it was learnt how to measure the
spectrum received by applying Halogen light to the samples of DBR and filters.
5 References
1. http://www.timbercon.com/Bragg-Mirrors.html
2. S.O. Kasap; Optoelectronics and photonics, Principles and Practices
3. http://www.sspectra.com/fp
6 Appendix
6.1 Matlab Code for Simlation
r=data(:,1); %Seperating Row from the 2D data of Reflection
c=data(:,2); %Seperating Column from the 2D data
plot(r,c,'r') %Plotting them
xlabel('Wavelength \lambda (nm)')
ylabel('Transmission/Reflection(%)')grid on
r1=data1(:,1); %Seperating Row from the 2D data of Transmission
c1=data1(:,2); %Seperating Column from the 2D data
hold on
plot(r1,c1,'b')
legend('Transmission','Reflection')
6.2 Matlab Code for Measurement
r=data(:,1); %Seperating Row from the 2D data
c=data(:,2); %Seperating Column from the 2D dataplot(r,c,'b') %Plotting them
title('Task4-9periods')
xlabel('Wavelength \lambda (in nm)')
ylabel('Transmission')
grid on
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