ACT Science Coffee

1. Photonic Neurons: Spiking
Information Processing with
Lasers
Ruaridh Smith
TUN.com

2. Talk Outline
• My background
• Motivation
• Introduction
• Project aims
• Laser principles
• Experimental setup
• Methodology
• Results
• Applications
• Summary www.verywell.com

3. My Background
Flying Physics Photonics
www.eyeem.com
skiptonaircadets.co.uk

4. Motivation
• Moore’s law is an observation that the transistor count in electronic
devices doubles every two years.
• Slowing due to fundamental restrictions to bandgap constraints and
thermal control.
• Combining optical methods with electronic components is now being
looked at as a way to overcome these restrictions.
• Neuromorphic computing presents an alternative to traditional
computation with bio-inspired processing.
sage.buckinstitute.org

5. Introduction – What is a Photonic
Neuron?
• Emulation of the brain’s computing power in an optical device.
• Biological neurons use electrical potentials to send information.
• Optical circuits are capable of creating an ultrafast response up
to 7 orders of magnitude faster than biological neurons.
russia-now.com

6. Project Aims
• Create a photonic neuron in a VCSEL through optical
injection.
• Observe neuron-like behavior in a two VCSEL network.
• Annalise temporal response of the network in a dynamic
system.

7. Laser Principles
Light Amplification by Stimulated Emission of Radiation
en.wikipedia.org/wiki/Stimulated_emission
en.wikipedia.org/wiki/Laser_construction

8. Laser Principles – VCSEL
Vertical Cavity Surface Emitting Laser
• Semiconductor laser
• Low threshold currents
• Easily coupled into
optical circuits
• Very reliable
www.olson-technology.com

9. Experimental Set up – 1 VCSEL
50/50 Coupler
50/50 Beam Splitter
Pm
VCSEL
Temp.
Controller
Current
Driver
OSA
PBS
Pd
Oscilloscope
Tunable
Laser
Pd
Isolator Variable
Attenuator
Polarisation
Controller
Isolator
Circulator
Circulator
Polarisation
Controller
Tunable
Laser
Polarisation
Controller

10. Methodology – Polarised Optical
Injection
Orthogonal
mode ⏊
Parallel mode //
Wavelength
Power
Tunable laser
1
Parallel mode
//
Orthogonal mode ⏊Tunable laser 2
Orthogonal
mode ⏊
Parallel mode //

11. Results - Static Injection 1 VCSEL
Double injection into ONE VCSEL (~0 GHz)
Current: 0.999mA, Temperature corresponding to 291 K,
Initial switching power 20.48 µW
Wavelength
Power
⏊
// ⏊
//
Wavelength
Power
Wavelength
Power
⏊
//
0
2
4
6
8
10
12
0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00
Outputpower(µW)
Input Power (µW)
Parallel peak
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30 35
Outputpower(µW)
Input Power (µW)
Orthogonal peak

12. Experimental Setup – 2 VCSEL
VCSEL
Temp.
Controller
Current
Driver
50/50 Coupler
50/50 Beam Splitter
Pm
VCSEL
Temp.
Controller
Current
Driver
OSA
PBS
Pd
Oscilloscope
Tunable
Laser
Pd
Isolator Variable
Attenuator
Polarisation
Controller
Isolator
Circulator
Circulator
Polarisation
Controller
Tunable
Laser
Polarisation
Controller

13. Results - Static injection 2 VCSELs
Double injection into a TWO VCSEL network (~0 GHz)
VCSEL 1: Current: 0.999mA, Temperature corresponding to 291 K
VCSEL 2: Current: 0.810 mA, Temperature corresponding to 298 K
Initial switching power 21.31 µW
Wavelength
Power
⏊
// //
⏊
Wavelength
Power
VCSEL 1 VCSEL 2
0
1
2
3
4
5
6
0 20 40 60 80 100 120 140
Outputpower(µW)
Input power (µW)
Parallel Peak
0
1
1
2
2
3
3
4
4
5
5
0 20 40 60 80 100 120 140
Outputpower(µW)
Input power (µW)
Orthogonal peak

14. Experimental Setup – Dynamic 2 VCSEL
System
VCSEL
Temp.
Controller
Current
Driver
50/50 Coupler
50/50 Beam Splitter
Pm
VCSEL
Temp.
Controller
Current
Driver
OSA
PBS
Pd
Oscilloscope
Tunable
Laser
Pd
Isolator Variable
Attenuator
Polarisation
Controller
Isolator
Circulator
Circulator
Polarisation
Controller
Tunable
Laser
Polarisation
Controller
SG
MOD
PS

15. Results – Dynamic 2 VCSEL System
(a)
FIG. 4. (a) Shows the externally injected negative signal with a perturbation duration of 9 ns and a 7.44 GHz detuning
respective to the 1st VCSEL. (b-c) Show the time series of the parallel and orthogonal output at the 1st VCSEL respectively, (d-
e) show the time series of the parallel and orthogonal output at the 2nd VCSEL respectively and (f-g) show temporal maps of
the parallel and orthogonal output measured at the 2nd VCSEL respectively. The temporal maps (f-g) show the consistency of
the perturbations over 65 consecutive responses. Bias currents applied to the 1st and 2nd VCSEL are 1.5 mA and 1.6 mA
respectively with corresponding temperatures 291 K and 298 K. The initial power required to produce the first polarisation
switch from the first tuneable laser is 61.2 µW and the max power recorded for the second injection is 0.435 mW

16. Results – Dynamic 2 VCSEL System
(b)
FIG. 5. (a) Shows the externally injected positive signal with a perturbation duration of 7 ns and a 4.61 GHz detuning
respective to the 1st VCSEL. (b-c) Show the time series of the parallel and orthogonal output of the 1st VCSEL respectively, (d-e)
show the time series of the parallel and orthogonal output of the 2nd VCSEL respectively and (f-g) show temporal maps
measured at the parallel and orthogonal output of the 2nd VCSEL respectively. The temporal maps (f-g) show the consistency of
the perturbations over 65 consecutive responses. Bias currents applied to the 1st and 2nd VCSEL are 1.25 mA and 1.28 mA
respectively with corresponding temperatures 291 K and 299 K. The initial power required to produce the first polarisation switch
from the first tuneable laser is 200 µW and the max power recorded for the second injection is 261 µW.

17. Applications
• Demonstrates initial step towards a photonic neural network.
• Such a system has the potential to be scaled into a network
with many connections to further mimic neural activity.
• ACT applications:
• Development of a compact, low power computing solution to solve
simple tasks.
• Neuro-inspired ultrafast communication links in space.
• VCSEL principles can be applied to other nano-photonic devices for
detection and measurement.
istockphoto.com

18. Summary
• Experimentally investigated photonic neuron creation in a
VCSEL through polarised optical injection.
• Showed neuron-like pulse can be transferred into a second
VCSEL to build towards a network.
• Obtained results for a dynamic 2 VCSEL system at ultrafast
switching speeds.
physicsworld.com