1. Free Space Laser Communication Cubesat Payload Development
MIDN 1/C Colston Polly
Primary Advisor: Assoc. Prof. Tae Lim
Off-site Advisors: Drs. Rita Mahon and Chris Moore at the U.S. Naval Research Laboratory

2. Background Significant benefits in optical communication Security
Data rates
Error minimization
Previous success
LADEE
OPALS
Change examples (maybe), and put full names

3. Challenges with Optical Communication
Beam divergence
Availability of ground stations
Earth’s atmosphere
Weather

4. What was accomplished in Spring/Summer 2015
MIDN 1/C Dods, Blanchard, and A. Kelly
Proof-of-concept demo for optically communicating 6U cubesat
Laboratory tabletop test (~ 6 ft)
Desired data rate
Data rates prediction
Experimental determination and comparison
Link Margin
Established working link margin
Solidworks Model
Lay foundation for future years’ work
Collaboration with NRL advisors at the Chesapeake Bay Detachment (CBD)
Summer internship of MIDN 1/C Polly at NRL-CBD

5. Physical setup

7. Transmit Computer Connected through Ethernet to MiniMc
MiniMc (Media Converter)
Signal modulator
Single mode fibers
Laser diode
Collimator
Transmits signal across free space

8. Receive Copies transmit, but in reverse.
Collimator acts as light bucket
MiniMc demodulates signal
Multimode fibers

9. Inefficiency losses mW dBmW Produced 0.55 -2.60 Loss_Tx 0.01 0.08 Tx
0.54
-2.68
Loss_Space
0.03
0.25 Rx
0.51
-2.92
Loss_Rx
0.33
4.52
Computed
0.18
-7.45

10. Link margin
Difference potentially due to short distance (quantum saturation)

11. Future work This academic year and next (AY2015-2016)
Longer range tests
50 meter - Kilometer scale (Rickover Hallway to Across the Severn)
Signal acquisition
Auto alignment system: position sensing detector and fast steering mirror
Tracking system
Keeping the free-space comm link between moving objects: two axis gimbals
Future academic years (AY )
Optical comm payload (3U) design for 6U cubesat
Component design, integration, testing
Pointing, acquisition, and tracking system design
Developing concept of mission operations

12. Who are we looking for? Two (2) midshipmen who are interested in:
Optical design for laser communication
Link budget analysis
Alignment system design and testing
Tracking system design and testing
Mission concept of operations and systems engineering for cubesat payload development

13. Back-Up Slides

14. Link Budget test goals Component Inefficiencies Determined
Actual beamwidth
Needs further test distance to be determined.
Detector Sensitivity
Needs further test distance/greater attenuation (likely around 10 dBmW more).
Adequate predictive capability
Predicted dBmW at media converter
Got dBmW at media converter

15. SNR-to-Data Rate Relationship
Our system uses On-Off Keying (OOK)
To find data rate
Large ping between two computers
Use WireShark, a network-analyzing program, to determine time delay
Attenuate signal over several trials
On-Off Keying – explain.

16. SNR-to-Data Rate Relationship
Computed Power [mW]
Computed Power [dBmW]
Data Rate [MBps]
Ethernet
n/a
45.02
Trial 1
0.180 
-7.45
1.45
Trial 2
0.110 
-9.59
1.44
Trial 3
0.053
-12.76
Trial 4
0.011
-19.59
Trial 5
0.001
-30.00

17. SNR-to-data rate relationship
“Waterfall” ~ approx. -40 dBmW
Max Data Rate (1.45 MBps)
Data Rate [MBps]
Sensitivity Limit (-42 dBmW)
SNR [dBmW]

18. Solidworks

19. Sponsors/help NRL optical communications team
Chris Moore and Rita Mahon
Working on optical communication aboard naval platforms