Blue LED Thin Film Narrow Band-Pass Filter

Ilya FedarovichOE570 THIN FILMS02/15/2016

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Executive summary

System/Component details Design Band-pass filter that transmits light emitted from blue LED. Center Wavelength 470nm, Bandwidth 30nm, Incidence angle 0+/-

5 deg. Materials used: BK7 glass, TiO2 Titanium Dioxide, Si02 Silicon

Dioxide Design must use no more than 3 materials, and materials can only

be Oxides and Fluorides.

Design objectives – use complex-matrix form of Fresnel equations to verify that design meets specifications.

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Preliminary design calculation

TiO2 [Titanium Dioxide] was chosen as material with high reflectance [H]. SiO2 [Silicon Dioxide] was chosen as material with low reflectance [L]. TiO2 refractive index was found in refractiveindex.com database to be 2.77 at 470nm wavelength SiO2 was found to be 1.46 at 470nm. Quarter Wave Optical Thickness was calculated to be 80nm for [L] and 42nm for [H]. Formula used is shown below.

We then set-up Maple code that was based on complex-matrix Fresnel equations:

Single Matrix Formula:

Phase difference between layers Formula:

Reflectance Formula:

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Preliminary design drawings – 2D layout

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Issues Encountered

First issue encountered was theperformance of Square-Band Passfilter vs Fabry Perot filter.

In our design approach, it was bestsuited to use Fabry Perot, as it waseasier to achieve the narrow band specification, and also easier tocompensate for phase shift at designangle requirement.

However Square-Band Pass filter has anadvantage of sharp cutoff frequency transition, which we overcame by using multiple cavity approach that can be seen in System1 design.

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Issues Encountered

Second Issue was to eliminatethe outside wavelengths to allowfor only narrow band to pass.

There are two solutions thatwe implemented in our design:

1. Using Anti-Reflection coating on both top and bottom of the

system.

2. Comparing the LED spectra to the solution, and deciding whether the restrictions reasonably met in this

application

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Final design – System1

Graph of reflectance for wavelengths on design specific bandwidth

Graph of reflectance for wavelengths 400nm-600nm

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Final design – System2

Graph of reflectance for wavelengths on design specific bandwidth

Graph of reflectance for wavelengths 400nm-600nm

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Final design – System3

Graph of reflectance for wavelengths on design specific bandwidth

Graph of reflectance for wavelengths 400nm-600nm

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Final design – Graphical illustrations and diagrams

System response centered around Wavelength of 470nm

System response within the Bandwidth of 30nm at FWHM

Angle of Incidence Response within the design limits

Cost minimization requirement met – no more than 3 types of materials used

Materials used are only Oxides or Fluorides

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Final design – Graphical illustrations and diagrams

System response centered around Wavelength of 470nm

System response within the Bandwidth of 30nm at FWHM

Angle of Incidence Response within the design limits

Cost minimization requirement met – no more than 3 types of materials usd

Materials used are only Oxides or Fluorides

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Final design – Graphical illustrations and diagrams

System response centered around Wavelength of 470nm

System response within the Bandwidth of 30nm at FWHM

Angle of Incidence Response within the design limits

Cost minimization requirement met – no more than 3 types of materials used

Materials used are only Oxides or Fluorides

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Conclusion

Best design achieved by our simulation is System2 design. It most closely met most the criteria.

If cost was not a factor, it could be feasible to improve the design by adding more cavities to the stacks, which will improve the quality of the band pass filter.

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Resources

1. http://ecee.colorado.edu/~mcleod/pdfs/AOL/labs/10030.pdf2. http://edge.rit.edu/content/P11543/public/NormClusterSpectrum.png3. http://www.gen-opt.com/lamda_admin/Lamda_Edit/UploadFile/2011222112937198.pdf4. http://www.google.com/patents/US60116525. https://books.google.com/books?

id=7zTtQJl8F2wC&pg=PA299&lpg=PA299&dq=band+pass+filter+equation+thin+film&source=bl&ots=oqInrXtKyw&sig=gqUl3S1G4RZ1GZpu8rEnBgRbqNE&hl=en&sa=X&ved=0ahUKEwju7665vfHKAhUGMz4KHfyeBZMQ6AEIVjAJ#v=onepage&q=band%20pass%20filter%20equation%20thin%20film&f=false

6. http://www3.ntu.edu.sg/eee/urop/congress2003/Proceedings/abstract/NUS_FoS/Material%20Science/Gerard%20Paul%20M%20Leyson.pdf

7. http://www.filmetrics.com/reflectance-calculator8. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.439.7906&rep=rep1&type=pdf