The goals for the Real Time Optical Receiver project are to Infuse Consultative Committee for Space Data Systems High Photon Efficiency standard into missions, such as Artemis and to provide a real time ground receiver solution (fiber device, detector, real time FPGA-based receiver) that is: (1) Scalable: data rate, atmosphere conditions, telescope aperture, etc., and (2) Uses COTS components when available and work with companies to move custom parts to COTS

Downey, Jennifer N.

Katz, Evan J.

Tedder, Sarah A.

English

NASA Technical Reports Server

National Aeronautics and Space Administration
www.nasa.gov
Presenter: Dr. Evan Katz*
PI: Jennifer Downey*  
(jennifer.n.downey@nasa.gov)
PM: Dr. Sarah Tedder* 
(sarah.a.tedder@nasa.gov)
*NASA Glenn Research Center
February 2020
https://ntrs.nasa.gov/search.jsp?R=20200001447 2020-03-28T19:19:02+00:00Z
2Project Introduction
Motivation
Photon-counting Optical ground stations are: 
• Custom made  Expensive
• Not standardized
• Limited in number  reduces availability
Goals 
1. Infuse Consultative Committee for Space Data Systems High Photon Efficiency standard 
into missions, such as Artemis.
2. Provide a real time ground receiver solution (fiber device, detector, real time FPGA-
based receiver) that is:
• Scalable: data rate, atmosphere conditions, telescope aperture, etc.
• Uses COTS components when available and work with companies to move custom 
parts to COTS.
• Lower recurring costs (>$1M  $400k)
Real Time Optical Receiver
Polarization
Controller
Photonic Lantern
COTS
SNSPD 
Detectors
FPGA-based 
receiver
Channel 
Combining 
Electronics
&
ADC
3Test Bed Block Diagram
Optical Transmitter Link Emulation Real Time Optical Receiver
Polarized
Laser
FPGA-based 
Transmitter
EO Modulator
Bias Controller
Driver 
Amplifier
Polarization
Controller
Photonic Lantern
COTS
SNSPD 
Detectors
FPGA-based 
receiver
Channel 
Combining 
Electronics
&
ADC
Spatial Light 
Modulator
Acoust-
Optic 
Modulator
4CCSDS Optical Communications High Photon Efficiency 
Telemetry Signaling Transmit Waveform VHDL/Verilog
> Released internationally 
CCSDS High Photon 
Efficiency Telemetry 
Signaling Transmit 
Waveform January 2020 
including:
 VHDL/Verilog source code
 Bitfiles and Vivado project 
for Xilinx VC707 commercial 
off the shelf development 
board
> https://software.nasa.gov/s
oftware/LEW-20090-1
Code release enables user to have an 
HPE signal transmitted out the VC707 
FPGA with no development.
5Link emulation
Optical Transmitter Link Emulation Real Time Optical Receiver
Polarized
Laser
FPGA-based 
Transmitter
EO Modulator
Bias Controller
Driver 
Amplifier
Polarization
Controller
Photonic Lantern
COTS
SNSPD 
Detectors
FPGA-based 
receiver
Channel 
Combining 
Electronics
&
ADC
Spatial Light 
Modulator
Acoust-
Optic 
Modulator
6Creation of wavefront emulated atmospheric conditions
Telescope
Incoming wavefront
Simulation Emulation
• Complex amplitude phase hologram created 
from simulated wavefront.
• Hologram applied to beam with spatial light 
modulator generates emulated wavefront.
• Emulation accuracy not fully verified
• Results preliminary
• Optical turbulence is modeled with phase 
screens distributed based on the Hufnagel-
Valley turbulence strength profile.
• Simulation model verified.
• Details in: Chahine et al, “Beam propagation through atmospheric 
turbulence using an altitude-dependent structure profile with non-uniformly 
distributed phase screens”, Tuesday poster session.
Simulated Intensity Phase Hologram Emulated intensity
7Fade Emulation
Purpose\Impact: 
• Enable laboratory tests of ground receiver and components with 
emulated atmosphere effect of fade.
Simulated beam profile at receiver.  Fade simulated using 
Hufnagel Valley 𝑪𝑪𝒏𝒏𝟐𝟐 model with 20 cm diameter aperture.
Acousto-Optic Modulator (AOM): 45 dB max extinction 
ratio, max frequency 55 MHz
Simulated beam profile at transmitter; 1m beam radius
8Fade Generation with Acoustic Optical Modulator
Fade profile generated by AOM matches the input fade profile within 0.5 dB.
Parameter Value
Atmosphere model Hufnagel Valley
Beam wavefront Gaussian
Wavelength 1550 nm
Diameter of source aperture infinite
Beam radius 1 m
Beam curvature Infinite (collimated beam)
Cn2 at ground 1.7*10-14
RMS wind speed 21 mps
Source altitude 24 km
Receiver altitude 122 m
Visibility Infinite (at 550 nm)
measured
simulated
9Receiver Subsystems Under Development
Free-space to Fiber Coupling: 
• Photonic lantern (one multimode fiber input to 7 FMF outputs)
• Input fiber core size, number of outputs, and output fiber core size scalable to application
• In house prototyping capability; development partnership with University of Sydney; 
commercialization through Chiral Photonics.
Single Photon Detector: 
• COTS Quantum Opus detectors, portable, rack-mounted
• Array of single-pixel detectors sharing one cryostat; couple to SMF or FMF
• Continuous operation, includes amplifier electronics, 60-80% efficient
Detector Channel Combining:
• 1 ADC per detector channel; digital combining
FPGA-based Receiver: 
• Real Time processing; COTS Vadatech platform
• Transmit and receive compatible with CCSDS downlink optical waveform (high photon efficiency)
• FPGA VHDL/Verilog code will be released
10
Photonic lantern
Optical Transmitter Link Emulation Real Time Optical Receiver
Polarized
Laser
FPGA-based 
Transmitter
EO Modulator
Bias Controller
Driver 
Amplifier
Polarization
Controller
Photonic Lantern
COTS
SNSPD 
Detectors
FPGA-based 
receiver
Channel 
Combining 
Electronics
&
ADC
Spatial Light 
Modulator
Acoust-
Optic 
Modulator
11
7:1 Few-Mode Fiber Photonic Lantern
55 µm,
.126 NA
Light from 
Back-end 
Telescope 
Optics
Multimode input of lantern
55 µm
Cladding
• Purpose: efficiently deliver atmospheric 
distorted light to 7 single pixel fiber-
coupled COTS detectors
• Made at NASA GRC 
• Developed in collaboration with Univ. of 
Sydney
70 mm
12SPIE Photonics West 2019www.nasa.gov
Coupling loss at emulated atmosphere conditions
Current FMF lanterns offer similar performance in atmospheric conditions to 
MMF previously used in optical ground stations. (~0.9 dB loss on average)
Increasing Turbulence
D/r0 Loss Relative 
to the GI-MMF 
(dB)
8.6 0.86
4.0 1.83
2.0 0.66
1.2 0.69
0 0.53
Unperturbed
beam (flat top)
13
Superconducting Nanowire 
Single-Photon Detector System
Optical Transmitter Link Emulation Real Time Optical Receiver
Polarized
Laser
FPGA-based 
Transmitter
EO Modulator
Bias Controller
Driver 
Amplifier
Polarization
Controller
Photonic Lantern
COTS
SNSPD 
Detectors
FPGA-based 
receiver
Channel 
Combining 
Electronics
&
ADC
Spatial Light 
Modulator
Acoust-
Optic 
Modulator
14
Quantum Opus SNSPD Detector System Description
System Parameters Previous 
Specs
Current Specs
Wavelength 1550 nm 1550 nm
Fiber coupling SMF FMF
Dark counts < 100 cps < 10 kcps
Reset time 50 ns 20 – 30 ns
Jitter (SNSPD + Amp) < 100 ps ≈ 50 ps (min)
Electronics Room temp 
amplifiers, 500 
MHz, AC-
coupled 
Room temp 
amplifiers, 500 
MHz, DC-coupled 
56
6 
m
V
20 ns
850 ps 
rising edge
Quantum Opus SNSPD 
and electronics 
Typical output pulse
Parameter Measured
Reset time (90/10) 20 – 30 ns
Pulse height ≈ 600   mV
Rising edge 850 ps
Opus OneTM from Quantum Opus, LLC
Helium compressor
All detectors are few mode fiber (FMF)-
coupled with blackbody dark count 
reduction coatings, and DC-coupled, i.e. 
RL filter to ground and increased 
feedback resistance to obtain higher 
count rates.
15
FPGA-based receiver
Optical Transmitter Link Emulation Real Time Optical Receiver
Polarized
Laser
FPGA-based 
Transmitter
EO Modulator
Bias Controller
Driver 
Amplifier
Polarization
Controller
Photonic Lantern
COTS
SNSPD 
Detectors
FPGA-based 
receiver
Channel 
Combining 
Electronics
&
ADC
Spatial Light 
Modulator
Acoust-
Optic 
Modulator
16
Receiver
Current Capability:
• Receiver demonstrated in laboratory with post 
processing software receiver:
• Supports up to 130 Mbps with 4 detectors
Future Capability:
• To be demonstrated with the real-time receiver:
• 260 Mbps with 7 detectors
• Timing recovery and decoder implementation in FPGA 
VHDL/Verilog code in progress 
17
For further details see following publications: 
• Downey, J., Vyhnalek, B., Tedder, S., and Lantz, C. “Detector channel combining results from a high photon efficiency optical 
communications link test bed”, Proceedings of SPIE, Free-Space Laser Communications XXXII (2020).
• Nappier, J., Vyhnalek, B., Tedder, S., and Lantz, C. “Characterization of a Photon Counting Test Bed for Space to Ground Optical Pulse 
Position Modulation Communications Links”, Proceedings of SPIE, Free-Space Laser Communications XXXI (2019).
• Vyhnalek, B., Downey, J., and Tedder, S. “Single-Photon Counting Detector Scalability for High Photon Efficiency Optical 
Communications Links” , Proceedings of SPIE, Free-Space Laser Communications XXXII (2020).
• Vyhnalek, B. E., Tedder, S. A., and Nappier, J. M. “Performance and Characterization of a Modular Superconducting Nanowire Single 
Photon Detector System for Space-to-Earth Optical Communications Links”, Proceedings of SPIE, Free-Space Laser Communications 
XXX (2018).
• Vyhnalek, B., Tedder, S., Katz, E., and Nappier, J. “Few-Mode Fiber Coupled Superconducting Nanowire Single-Photon Detectors for 
Photon Efficient Optical Communications”, Proceedings of SPIE, Free-Space Laser Communications XXXI (2019).
• Tedder, S. A., Vyhnalek, B. E., Leon-Saval, S., Betters, C., Floyd, B., Staa, J., and Lafon, R. “Single-Mode Fiber and Few-Mode Fiber 
Photonic Lanterns performance evaluated for use in a Scalable Real-time Photon Counting Ground Receiver “, Proceedings of SPIE, 
Free-Space Laser Communications XXXI (2019).
• Tedder, S. A., Floyd, B., Chahine, Y. K., Croop, B., Vyhnalek, B. E., Betters, C.,   Leon-Saval, S. “Measurements of few-mode fiber 
photonic lanterns in emulated atmospheric conditions for a low earth orbit space to ground optical communication receiver 
application”, Proceedings of SPIE, Free-Space Laser Communications XXXII (2020).
18www.nasa.gov
For more information, please contact:
Jennifer Downey  (jennifer.n.downey@nasa.gov)
Dr. Sarah Tedder (sarah.a.tedder@nasa.gov)
19
Backup
20
The FPGA-based transmitter currently supports all O2O waveform 
modes
High Photon Efficiency Ground Station 
Transmitter Diagram
20
4 x 
Amplifiers
4 x 15cm
Telescopes
4 x
Modulators
FPGA-based
Transmitter
(GRC)
Ethernet 
packet source
4 x Lasers
21
Proposed Collaboration with ANU for High 
Photon Efficiency Transmitter
ANU to provide
> Transmitter telescope(s)
> Lasers, modulators 
> FPGA electronics
NASA GRC RealTOR to provide:
> Details of system design and assembly
> Support of assembly and testing (remotely and directly) 
> Specifications and sources to purchase FPGA electronics
> FPGA VHDL/Verilog code for CCSDS transmitter: 
> Available at https://software.nasa.gov/software/LEW-20090-1
22
High Photon Efficiency Ground Station Receiver Diagram
Current Capability:
Receiver demonstrated in laboratory with 
post processing receiver:
• Supports up to 130 Mbps with 4 
detectors
Future Capability:
To be demonstrated with the real-time 
receiver:
• 260 Mbps with 7 detectors
70 cm 
Telescope
Back-end 
Optics
Photonic 
lantern SNSPDs
Ethernet 
packet sink
Channel 
Combining 
& ADC
FPGA-
based 
Receiver
23
Proposed Collaboration with ANU for High 
Photon Efficiency Receiver
ANU to provide
> Pad and dome including electrical and plumbing needs, telescope
> Back end optics design to support photonic lantern or other fiber solution.
> Detector, FPGA electronics, channel combining electronics
NASA GRC RealTOR to provide:
> Details of system design and assembly
> Support of assembly and testing (remotely and directly)
> Specifications and sources to purchase COTS components: 
> Detectors
> Fibers/Fiber device
> Channel combining electronics
> FPGA electronics
> FPGA VHDL/Verilog for CCSDS receiver (future release)
> Design of photonic lantern for University of Sydney to fabricate


Real Time Optical Receiver Project

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