underwater optical communications
TRANSCRIPT
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UNDERWATER OPTICAL COMMUNICATIONSBy Jasmine HintonPHY 241Spring 2021
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Overview• Optics is a branch of physics focused
on the study of lights’ nature and its’ use.
• Geometric optics • Formation of images due to
reflection and refraction• Light treated as a ray
• Physical optics• Light treated as electromagnetic
wave • Quantum Optics • Optical Engineering (mix between
optics and electrical engineering)
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Break Down
• Concepts learned this semester that apply here, with formulas • Overview of UWOC (Underwater
Wireless Optical Communications) • Photodetectors (Receiver) • SPADs vs SNSPDs
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Reflection, Refraction and Polarization• Law of Reflection: 𝜃!= 𝜃"
• Index of refraction: 𝑁 = #$
• Speed of light in medium
• Snell’s Law: 𝑛%𝑠𝑖𝑛𝜃% = 𝑛&𝑠𝑖𝑛𝜃&
• Polarization• By Reflection & By Scattering• Helps clarify transmitted videos, images • Brewers’ Law: 𝑡𝑎𝑛𝜃! =
"!""
(by reflection)• Optical Bandpass Filter
• US Navel Academy – Laser Polarization
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Interference
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Dispersion = Spreading of white light into full spectrum of wavelengths.
Rainbow
*Not just visible light
Diffraction – Bending of a light wave around the edges of an opening/obstacle.
Diffusion – Spreading of light from a light source
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Lenses
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Propagation, Light Intensity
• PowerLossduetoPropagation(BeerLambertLaw)
• 𝑃 𝑑, 𝜆 = 𝑃!𝑒"# $ %
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Dissertation –King Abdullah University of Science and Technology
Recent Achievements on UWOC –Chinese Optics Letters
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Attenuation 𝑘(𝜆) • Absorption Coefficient 𝑎 𝜆
• Scattering Coefficient 𝑏 𝜆
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UNDERWATER OPTICAL
COMMUNICATIONS
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TRANSMITTER
RECEIVER
PhotodetectorsPure Sea Water
Clear ocean water
Coastal ocean water
Turbid harbor water
The Underwater Wireless Optical System
Medium
LDsLEDs
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Photodetectors: Convert light energy into electrical energy
SNSPDs
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SPADs
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A Comparison: Advantages
• SPADs:• Less power to operate • Transmission distance
extended • One experiment
shown up to 112 m • Compared to APD
which has 73 m
• SNSPDs: • High detection efficiency • Low dark count rate • Low timing jitter (<100
ps) • Fast recovery time (<10
ns) • Increases image
scalability
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A Comparison: Disadvantages
• SPAD: • Max counting rate: 100 MHz
(not ideal for GHz links) • Efficiency, timing jitter and
recovery time may not be as good as the SNSPD • Smaller range of
wavelengths can be used
• SNSPDs:• Very cold temperatures
required (more expensive)• Has mainly been tested in the
infrared range • More experimenting needed in
and visible spectrum
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Which is better?
•As of now, the SPAD looks to be a better option for specifically UWOC
Deep Space Optical Communications has the cold temperatures needed for SNSPDs. Underwater, this is more difficult to achieve
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Remaining Questions:
• Using different types of materials with SNSPDs, SPADs • There are different versions of each
• Other ways to change the devices slightly to see how performance will change? – Array combinations • More research needed using SNSPDs underwater = SPADs,
APDs have been around longer, so more about them is known.
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THANK YOU!
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Thank you!
Questions?