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