Enhancing FSO Link Performance in Adverse Conditions using a Fiber-
Bundle Based Receiver Design.
Nathan HutchinsDr. Peter LoPresti
Outline
• Introduction• Background
• Basic Optics• The Problem With Turbulence• Kolmogorov, Rytov, and Cn
2
• Bundle-Based Design
• Experimentation• Data Analysis• Conclusions• Future Work
Introduction
• Goal• Design a receiver that reduces the
effect of turbulence on an FSO signal while maintaining a small SWaP requirement.
• FSO• Free-Space Optics
• SWaP• Size, Weight, and Power
BackgroundStandard Receiver
• Field of View (FOV)• FOV <0.1⁰ without Alignment device.• FOV ±0.5-1⁰with Alignment device.
• Alignment/Beam Steering Device• Mechanical Device
• Vibrations, Power, Cost, Weight, Reliability, Durability
BackgroundMisalignment
If the angle of incidence of the incoming beam is too steep the beam can miss the detector.
BackgroundTurbulenceWhat is Turbulence?• change of refractive index
• heat • movement• particulate dispersion in the air
The Problem
Turbulence
Turbulence can cause the incoming beam to be erratic and miss the detector as well as causing ‘hot spots’.
The ProblemKolmogorov, Rytov, and Cn
2
• Kolmogorov Power Spectrum• 𝛷𝛷𝑛𝑛 𝜅𝜅 = 0.033𝐶𝐶𝑛𝑛2𝜅𝜅 ⁄−11 3
• Power Law for Propagation Distance
• 𝛷𝛷𝑛𝑛 𝜅𝜅, 𝑧𝑧 = 0.033𝐶𝐶𝑛𝑛2(𝑧𝑧)𝜅𝜅 ⁄−11 3
• Wave Equation• 𝛻𝛻2𝐸𝐸 + 𝑘𝑘2𝑛𝑛2 𝑅𝑅 𝐸𝐸 + 2𝛻𝛻 𝐸𝐸 � 𝛻𝛻 log𝑛𝑛 𝑅𝑅 = 0
• Rytov Variance • 𝜎𝜎𝑅𝑅2 = 1.23𝐶𝐶𝑛𝑛2𝑘𝑘 ⁄7 6𝐿𝐿 ⁄11
6
• Assumptions• Wave backscattering can be neglected• Depolarization effects can be
neglected• The refractive index is delta
correlated in the direction of propagation
• The paraxial approximation will hold• Limit the data analyses to weak
turbulence cases
The DesignTransmitter
Bundle-Based DesignReceiver
Graded-IndexLenses
Parabolic Lens(Aspheric)
Focal Length: 3mm
400 μm Fiber
Bundle-Based ReceiverRay Diagram
Bundle-Based ReceiverCapturing LensesFocal Length: 3mmTarget Width: 400µm
What Improvements Come with our Design?
• Larger FOV• Mobile Enabled
• Greater chance of receiving light sent through increased turbulence areas.
• Less sensitive to changes in wavelength.
• Multi-User is Possible.• Off-Axis Signal Collection
Performance in Turbulent Media
• The Goal• To Quantify/Model this
performance and verify results
• How?
ExperimentsThe Setup
ExperimentsData Collection
ExperimentsData Collection
Standard Receiver
Bundle Receiver
ExperimentsData Collection
• Rearranged Rytov Variance• 𝐶𝐶𝑛𝑛2 = 𝜎𝜎2
1.23∗𝑘𝑘 �7 6∗𝑙𝑙 �116
• Procedure• Using MATLAB
• Analyze Data input for 1’s/0’s• Take The Variance of the 1’s/0’s
• Plug Variance (σ) in to the Rearranged Rytov Variance Equation.
ExperimentsCollected Data Example
sigma_0 sigma_1 Sigma^2_0 Sigma^2_1 Lambda L K Cn^2_0 Cn^2_1 Avg Avg1550 Box 1.48021E-03 1.87880E-03 2.19102E-06 3.5299E-06 1.55E-06 1.68 4.05E+06 1.34437E-14 2.16588E-14 1.46641E-14 2.05905E-141550 Box 2 1.51302E-03 1.76703E-03 2.28924E-06 3.12239E-06 1.55E-06 1.68 4.05E+06 1.40463E-14 1.91584E-141550 Box 3 1.56786E-03 1.64177E-03 2.45818E-06 2.69542E-06 1.55E-06 1.68 4.05E+06 1.50829E-14 1.65386E-141550 Box 4 1.57003E-03 1.76240E-03 2.465E-06 3.10604E-06 1.55E-06 1.68 4.05E+06 1.51247E-14 1.90581E-141550 Box 5 1.57394E-03 1.84693E-03 2.4773E-06 3.41113E-06 1.55E-06 1.68 4.05E+06 1.52002E-14 2.09301E-141550 Box 6 1.56806E-03 2.06636E-03 2.4588E-06 4.26986E-06 1.55E-06 1.68 4.05E+06 1.50867E-14 2.61991E-141550 Low 1.45155E-03 1.97636E-03 2.10701E-06 3.90601E-06 1.55E-06 1.68 4.05E+06 1.29282E-14 2.39665E-14 1.30963E-14 3.13108E-141550 Low 2 1.47475E-03 2.19843E-03 2.17488E-06 4.83312E-06 1.55E-06 1.68 4.05E+06 1.33446E-14 2.96551E-141550 Low 3 1.46706E-03 2.24288E-03 2.15225E-06 5.03053E-06 1.55E-06 1.68 4.05E+06 1.32058E-14 3.08664E-141550 Low 4 1.47316E-03 2.32184E-03 2.1702E-06 5.39093E-06 1.55E-06 1.68 4.05E+06 1.33159E-14 3.30777E-141550 Low 5 1.46010E-03 2.39198E-03 2.13189E-06 5.72156E-06 1.55E-06 1.68 4.05E+06 1.30808E-14 3.51064E-141550 Low 6 1.43883E-03 2.39492E-03 2.07022E-06 5.73564E-06 1.55E-06 1.68 4.05E+06 1.27025E-14 3.51928E-141550 med 1.39020E-03 2.30054E-03 1.93265E-06 5.2925E-06 1.55E-06 1.68 4.05E+06 1.18583E-14 3.24738E-14 1.1481E-14 3.23307E-141550 med 2 1.36573E-03 2.27473E-03 1.86522E-06 5.17438E-06 1.55E-06 1.68 4.05E+06 1.14446E-14 3.1749E-141550 med 3 1.35436E-03 2.34360E-03 1.83429E-06 5.49246E-06 1.55E-06 1.68 4.05E+06 1.12548E-14 3.37007E-141550 med 4 1.37463E-03 2.31476E-03 1.88961E-06 5.35813E-06 1.55E-06 1.68 4.05E+06 1.15943E-14 3.28764E-141550 med 5 1.37300E-03 2.30269E-03 1.88513E-06 5.30238E-06 1.55E-06 1.68 4.05E+06 1.15668E-14 3.25344E-141550 med 6 1.34907E-03 2.23500E-03 1.82E-06 4.99522E-06 1.55E-06 1.68 4.05E+06 1.11672E-14 3.06497E-141550 High 1.38441E-03 2.00649E-03 1.9166E-06 4.02599E-06 1.55E-06 1.68 4.05E+06 1.17599E-14 2.47027E-14 1.16966E-14 2.38777E-141550 high 2 1.40042E-03 1.97132E-03 1.96119E-06 3.8861E-06 1.55E-06 1.68 4.05E+06 1.20335E-14 2.38443E-141550 High 3 1.38221E-03 1.96113E-03 1.91051E-06 3.84601E-06 1.55E-06 1.68 4.05E+06 1.17225E-14 2.35984E-141550 high 4 1.35359E-03 1.93409E-03 1.83221E-06 3.74071E-06 1.55E-06 1.68 4.05E+06 1.12421E-14 2.29523E-141550 High 5 1.39842E-03 1.94269E-03 1.95559E-06 3.77405E-06 1.55E-06 1.68 4.05E+06 1.19991E-14 2.31568E-141550 high 6 1.36442E-03 2.01899E-03 1.86163E-06 4.07633E-06 1.55E-06 1.68 4.05E+06 1.14226E-14 2.50116E-14
ExperimentsData Analysis 850nm
5.5E-16
5.7E-16
5.9E-16
6.1E-16
6.3E-16
6.5E-16
6.7E-16
6.9E-16
7.1E-16
7.3E-16
0 2E-14 4E-14 6E-14 8E-146.9E-16
6.95E-16
7E-16
7.05E-16
7.1E-16
7.15E-16
7.2E-16
7.25E-16
7.3E-16
7.35E-16
Cn^2
Sta
ndar
d Rx
Cn^2 Of The Lab
Cn^2
Bun
dle
Rx
850nm Cn^2 Ones
Cn^2_1 Cn^2_1_STD
5.6E-16
5.8E-16
6E-16
6.2E-16
6.4E-16
6.6E-16
6.8E-16
7E-16
6.6E-16
6.65E-16
6.7E-16
6.75E-16
6.8E-16
6.85E-16
6.9E-16
6.95E-16
7E-16
0 1E-14 2E-14 3E-14 4E-14 5E-14 6E-14 7E-14 8E-14
Cn^2
Sta
ndar
d Rx
Cn^2
Bun
dle
Rx
Cn^2 Of The Lab
850nm Cn^2 Zeros
Cn^2_0 Cn^2_0_STD
ExperimentsData Analysis 1310nm
1.5E-13
1.9E-13
2.3E-13
2.7E-13
3.1E-13
3.5E-13
3.9E-13
4.3E-13
02E-144E-146E-148E-141E-13
1.2E-131.4E-131.6E-131.8E-13
-1E-14 1E-14 3E-14 5E-14 7E-14 9E-14 1.1E-13 1.3E-13
Cn^2
Tra
ditio
nal R
x
Cn^2
Bun
dle
Rx
Cn^2 Of The Lab
1310nm Cn^2 Ones
Cn^2_1 Cn^2_1_STD
1.2E-131.3E-131.4E-131.5E-131.6E-131.7E-131.8E-131.9E-132E-132.1E-132.2E-132.3E-13
1.1E-131.12E-131.14E-131.16E-131.18E-13
1.2E-131.22E-131.24E-131.26E-131.28E-13
3E-15 2.3E-14 4.3E-14 6.3E-14 8.3E-14 1.03E-13 1.23E-13
Cn^2
Tra
ditio
nal R
x
Cn^2
Bun
dle
Rx
Cn^2 Of The Lab
1310nm Cn^2 Zeros
Cn^2_0 Cn^2_0_STD
ExperimentsData Analysis 1550nm
1.7E-13
1.72E-13
1.74E-13
1.76E-13
1.78E-13
1.8E-13
1.82E-13
1.84E-13
1.86E-13
1.88E-13
1.8E-14
2E-14
2.2E-14
2.4E-14
2.6E-14
2.8E-14
3E-14
3.2E-14
3.4E-14
0 5E-14 1E-13 1.5E-13 2E-13 2.5E-13 3E-13
Cn^2
Tra
ditio
nal R
x
Cn^2
Bun
dle
Rx
Cn^2 Of The Lab
1550nm Cn^2 Ones
Cn^2_1 Cn^2_1_STD
3.2E-14
3.3E-14
3.4E-14
3.5E-14
3.6E-14
3.7E-14
3.8E-14
3.9E-14
1.1E-14
1.15E-14
1.2E-14
1.25E-14
1.3E-14
1.35E-14
1.4E-14
1.45E-14
1.5E-14
0 5E-14 1E-13 1.5E-13 2E-13 2.5E-13 3E-13
Cn^2
Tra
ditio
nal R
x
Cn^2
Bun
dle
Rx
Cn^2 Of The Lab
1550nm Cn^2 Zeros
Cn^2_0 Cn^2_0_STD
ExperimentsData Analysis Cont.
Cn2 of Standard receiver
(Orange) is 10 times larger than Bundle Receiver (Blue)
0
2E-14
4E-14
6E-14
8E-14
1E-13
1.2E-13
1.4E-13
1.6E-13
1.8E-13
2E-13
2.2E-13
0 5E-14 1E-13 1.5E-13 2E-13 2.5E-13 3E-13
Cn^2
Bun
dle
Rx
Cn^2 Of The Lab
1550nm Cn^2 Ones
Cn^2_1 Cn^2_1_STD
Conclusion
Bundle-based receiver improves signal strength and reliability by counteracting the effects of turbulence, thereby making the effective Cn
2 as seen by the receiver to be smaller than the actual value of Cn
2
Future WorkTurbulence Simulations
• Model Turbulence in MATLAB• Model Bundle Receiver In MATLAB• Model How Well Bundle Receiver works
Future WorkIncreased Fiber Dimensions
Increase Fiber Dimensions from 400μm to 600μm
Future WorkOptical Tracking with Transmitter
Insert Switch Here
Thank You,Questions?
Bonus SlideThe Turbulence Box
Bonus SlideLiner Fiber Array Transmitter