Practicum Lab Report-Updated

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


3.2 Transmission ..............................................................................................................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 = 171.48 nm



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c. For 3'26" of SiO2 (Quarter)


Physical Thickness of Cavity = 200.71nm


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


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


2.3.3 DBR Material SiO2/TiO2

Refractive Index of TiO2= 2.7



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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


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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3.1.5 Sample filter with 3-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.


3.2.2 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
http://www.timbercon.com/Bragg-Mirrors.htmlhttp://www.timbercon.com/Bragg-Mirrors.htmlhttp://www.timbercon.com/Bragg-Mirrors.html


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Practicum Lab Report-Updated

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