Blue LED Thin Film Narrow Band-Pass Filter Design Project
1. Blue LED Thin Film Narrow Band-Pass Filter
Ilya Fedarovich
OE570 THIN FILMS
02/15/2016
2. 2
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.
3. 3
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:
5. 5
Issues Encountered
First issue encountered was the
performance of Square-Band Pass
filter vs Fabry Perot filter.
In our design approach, it was best
suited to use Fabry Perot, as it was
easier to achieve the narrow band
specification, and also easier to
compensate for phase shift at design
angle requirement.
However Square-Band Pass filter has an
advantage of sharp cutoff frequency transition, which we overcame by
using multiple cavity approach that can be seen in System1 design.
6. 6
Issues Encountered
Second Issue was to eliminate
the outside wavelengths to allow
for only narrow band to pass.
There are two solutions that
we 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
7. 7
Final design – System1
Graph of reflectance for wavelengths on design specific bandwidth
Graph of reflectance for wavelengths 400nm-600nm
8. 8
Final design – System2
Graph of reflectance for wavelengths on design specific bandwidth
Graph of reflectance for wavelengths 400nm-600nm
9. 9
Final design – System3
Graph of reflectance for wavelengths on design specific bandwidth
Graph of reflectance for wavelengths 400nm-600nm
10. 10
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
11. 11
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
12. 12
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
13. 13
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.
