Internally Sensed Optical Phased Arrays

166 Pages·2016·15.97 MB·English

Internally Sensed Optical Phased Arrays
Lyle Edward Roberts
A thesis submitted for the degree of
Doctor of Philosophy
at the Australian National University
Submitted
5th July, 2016
c Copyright by Lyle Edward Roberts 2016
�

To my family,
and friends.

Declaration
This thesis is an account of research undertaken between February 2012 and March 2016
at the Centre for Gravitational Physics, Department of Quantum Science, in the Research
School of Physics and Engineering at the Australian National University, Canberra, Aus-
tralia.
Exceptwhereacknowledgedinthecustomarymanner,thematerialpresentedinthisthesis
is, to the best of my knowledge, original and has not be submitted in whole or part for a
degree in any university.
Lyle Edward Roberts
July 2016
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Acknowledgements
It is di�cult to express my immense gratitude for my supervisors, Professor Daniel Shad-
dock, Dr Robert Ward, and Professor David McClelland. Without you, none of the work
presented in this thesis would have been possible.
Daniel, it has been an incredible privilege to be your student. For five years you have been
my supervisor, my mentor, but more importantly my friend. I have learnt so much from
you, and I can’t thank you enough for it.
Rob, you are an extraordinary scientist. You have always encouraged me to challenge
myself, be creative, and to persevere no matter how challenging the situation. I owe you
somuch. Iwillforeverbeinaweofyourencyclopaedicknowledgeandprodigiousintuition
of optics, control systems, gravitational waves, and pretty much everything else, really. I
have thoroughly enjoyed my time working with you, and I look forward to continuing to
work with you into the future.
David,thesuccessoftheCentreforGravitationalPhysicsisatestamenttoyourexuberant
personality and remarkable academic prowess. I am sincerely grateful for your continued
support and guidance over the years.
One of the best parts of working at the Centre for Gravitational Physics is being exposed
to exceptional researchers such as Bram #Swagmolen, Jong Chow, Roland Fleddermann,
and Terry McRae. Thank you for always being willing to help when I need it.
My time as a PhD student has been thoroughly enjoyable thanks to the incredible support
and endless supply of entertainment provided by the graviteers. I thank Sam, Silvie,
Jarrod, Georgia, Shasi, Paul, Thanh, Roland, Tarquin, Cathy, Chatters, Andrew Wade,
DavidMcManus, Perry, andBenCourtney-Barrerfortheirfriendshipandencouragement.
I am also grateful for the guidance that veteran graviteers Danielle Wuchenich, Andrew
Sutton, Dave Bowman, and Timothy Lam have provided me over the years. I couldn’t
ask for a better team of people to work with.
In 2012, I was fortunate enough to participate in the NASA Ames Academy for Space
Exploration. During my time there I forged friendships with some of the most incredible
space cadets I will ever meet. Ryan, Michael, Anthony, Tyler, Steph, Alec, George, Alana,
Doug and Christie, Mark, Arlen, Chris, Trish, Swarna, Laura, Takako, Ty, and Eleni; I
am so grateful for your love and motivation over the years. Thank you for inspiring me to
achieve greatness, and for introducing me to In-N-Out burger.
I also extend my sincerest gratitude to Kyle Hardman, Dr Carlos Kuhn, and Dr Nicholas
Robins for their help setting up the new high-power optical phased array lab. Thank you
for helping me construct the “clean tent” and letting me borrow1 an optical bench.
I would like to thank my family for all their love and encouragement. I could not have
done this without you. I thank my parents, my grandparents, and my brothers for always
believing in me, and for raising me with such an enthusiasm for science and engineering.
Most of all, I thank my loving and patient wife, Nadine. You are the light in my life.
1You’re not getting it back.
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Abstract
The performance of existing ground based space debris laser ranging systems can be im-
proved by directing more light onto space debris by coherently combining multiple lasers
using an optical phased array (OPA). If the power delivered to target is su�ciently high
then these systems may also provide the capability to remotely manoeuvre space debris
via photon radiation pressure and/or ablation. By stabilising the relative output phase of
multiple lasers, OPAs form a coherent optical wave-front in the far field. Since the phase
of each laser can be controlled independently, they also have the ability to dynamically
manipulate the distribution of optical power in the far field, potentially enabling them to
compensate for atmospheric turbulence. This beam-forming functionality, combined with
their inherent scalability and high power handling capabilities make OPAs a promising
technology for future space debris laser ranging and manoeuvring systems.
In this thesis we describe the iterative development of a high-power compatible internally
sensed OPA, which—in contrast to externally sensed OPAs that sense the output phase
of each laser externally using free-space optics—relies on the small fraction of light that is
reflectedbackintothefibreattheoutputoftheOPAtostabiliseitsrelativeoutputphase.
This allows internally sensed OPAs to be implemented entirely within fibre without any
dependenceonfree-spaceopticsattheoutput,o↵eringpotentialadvantagesoverexternally
sensed techniques when operating in the presence of shock and vibration.
A proof-of-concept experiment demonstrated the viability of internal sensing, but also
highlighted a number of weaknesses that would a↵ect its utility, specifically in supporting
high optical powers greater than 100s of mW. An improved high-power compatible intern-
ally sensed OPA was designed to overcome these restrictions by isolating sensitive optical
components from high optical powers using asymmetric fibre couplers. This concept was
initially demonstrated experimentally using slave lasers o↵set phase-locked to a single
master laser, and then again using fibre amplifiers in a master oscillator power amplifier
configuration. TheexperimentaldemonstrationofthefibreamplifiercompatibleOPAsta-
bilised the relative output phase of three commercial 15 W fibre amplifiers, demonstrating
a root-mean-squared output phase stability of �/194, and the ability to steer the beam at
up to 10 kHz.
The internally sensed OPA presented here requires the simultaneous measurement, and
control of the phase of each emitter in the OPA. This is accomplished using digitally en-
hanced heterodyne interferometry and digitally implemented phasemeters, both of which
relyheavilyonhigh-speeddigitalsignalprocessingresourcesprovidedbyfield-programmable
gate-arrays.
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