1. UEF // University of Eastern Finland
Characterization of a ring resonator
Advanced Laboratory Practices, 26th May 2016
Atri Halder
Optical fibers and Integrated optics
2. Resonance
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Guiding in optical fibers / Atri Halder, 26.05.2016
If the frequency of the applied force matches with the
natural frequency of any structure, then the
amplitude of the field increases after each oscillation.
This phenomena is known as resonance.
Y(λ) =
1
π
2𝑎
(λ−λ0)2+𝑎2
4. Ring Resonator
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Guiding in optical fibers / Atri Halder, 26.05.2016
Resonance condition: L × 𝑛 𝑒𝑓𝑓 = N. λ 𝑑
where, L = 2πR
R is the radius of the ring resonator.
λ 𝑑 is the wavelength of light coupled to the
input.
𝑛 𝑒𝑓𝑓 is the effective refractive index of the
waveguide.
5. Full width at half maxima (FWHM)
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Guiding in optical fibers / Atri Halder, 26.05.2016
where 𝑛 𝑔 is the group index of the medium, r is the self coupling
coefficient, a is the resonator round trip loss coefficient and λ 𝑟𝑒𝑠 is the
resonance wavelength.
FWHM =
(1−𝑟𝑎)λ 𝑟𝑒𝑠
2
π𝑛 𝑔 𝐿 𝑟𝑎
8. Quality Factor (Q-factor)
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Guiding in optical fibers / Atri Halder, 26.05.2016
It represents the number of oscillations required by the
confined optical field to get its energy reduced to 1/e of the
initial energy.
Q =
λ 𝑟𝑒𝑠
𝐹𝑊𝐻𝑀
20. Comparison
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Guiding in optical fibers / Atri Halder, 26.05.2016
Characteristics Gap of 300 nm Gap of 400 nm
FWHM 0.55 nm 0.475 nm
FSR 1.507 nm 1.526 nm
Finesse 2.74 3.21
Q-factor 3005.7 3291.25
Loss 18.40 dB/cm 15.84 dB/cm
21. Conclusion
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Guiding in optical fibers / Atri Halder, 26.05.2016
• There was a high loss in between the bus and the ring.
• The structure was so small that there was always a problem of
coupling.
• As the gap between the bus and the ring was increased, the resonance
varied a lot and we can conclude that for a gap of 400 nm the
resonance was best.
• The whole experimental work was quite challenging.
• Though we got a good result for different parameters of the ring
resonator, we failed to generate good data for the drop port. It was due
to imperfections of the structure and lot of dust particles on the
sample.
