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Photonics100 honouree Garrett Cole named Optica Fellow

Garrett Cole

Garrett Cole, Manager, Thorlabs Crystalline Solutions, and a recent honouree in the Photonics100 2024, has been named an Optica Fellow "for advancements in precision optical metrology, namely the pioneering development and successful commercialisation of novel substrate-transferred crystalline optical interference coatings".

Optica's board of directors recently elected 129 members from 26 countries to its 2024 Fellow Class, drawn from 216 nominations submitted by current Fellows. 

Electro Optics caught up with Cole ahead of the launch of the Photonics100 2024.

EO: What are you currently working on? What will the impact be?

Garrett Cole: I continue spearheading basic research as well as commercial development of "semiconductor supermirrors", based on substrate-transferred single-crystal GaAs/AlGaAs optical interference coatings. I initiated these efforts in 2007 as a postdoctoral researcher at Lawrence Livermore National Laboratory and originally pursued it to overcome thermal noise limitations in ion-beam sputtered mirrors. I continued down this path of research when I moved to Vienna, Austria, in 2008 as a Marie Curie Fellow at the Austrian Academy Sciences, working with Markus Aspelmeyer at the Institute for Quantum Optics and Quantum Information (IQOQI), which was headed by 2022 Nobel Laureate in Physics, Anton Zeilinger. 

These efforts culminated in the founding of Crystalline Mirror Solutions (CMS) in 2012. After seven years of successful commercialisation of our mirror technology, CMS was acquired by Thorlabs in December 2019. 

Improving the sensitivity of optical precision measurement systems has a far-reaching impact, from fundamental scientific research efforts to advanced technologies including trace chemical analysis, inertial navigation, and broadband communications. Crystalline coatings have now redefined the performance metrics of ultrastable resonators for cavity-stabilised laser systems, enabling the world's lowest-noise lasers for precision spectroscopy, optical atomic clocks, and neutral atom quantum computing systems. Our mirrors and cavities are deployed worldwide in nearly all major metrology institutes, prominent academic clock and spectroscopy groups, as well as industrial and defence labs. 

Exciting paths forward, to be expanded upon below, are extending the operating wavelength range of these coatings, while simultaneously pursuing efforts to scale the maximum diameter of our mirrors. The latter efforts are being pursued with the aim of making crystalline coatings applicable in future gravitational wave detectors.

What was the most surprising thing you found in the course of your latest research?

Garrett Cole: It has been a very fun ride thus far... When I moved to Vienna in 2008, my focus was on fundamental quantum optomechanics research. I did not leave California intending to found a high-technology start-up in Austria! The biggest surprise was that these efforts were a truly unexpected spin-off of basic science. The commercialisation of crystalline coatings via CMS, further matured under Thorlabs Crystalline Solutions, stands as yet another example of how the exploration of foundational questions can generate unique high-tech products. It has been a very rewarding (yet at times tumultuous) experience in bringing this mirror technology “out of the laboratory and into the light”, but if given a second chance, I would nonetheless pursue it all over again!

What’s your biggest research priority in the coming year?

Garrett Cole: There are two parallel paths that my group is pursuing for the coming year(s): 1) The development of extremely high reflectivity mid-infrared mirrors for trace gas detection and laser-based manufacturing, and 2) Scaling up the maximum achievable diameter of our coatings (aiming for >300mm), making these mirrors amenable to laser-interferometer-based gravitational-wave detectors.

In the mid-IR domain, in early 2023 we demonstrated the highest finesse ever achieved in this spectral range, constructing a linear cavity with a finesse >400,000 (corresponding to a mirror reflectance >99.999%) at a centre wavelength of 4,500nm. This was enabled by an improved manufacturing process that allowed us to achieve the lowest optical scatter plus absorption ever measured at these wavelengths (by nearly an order of magnitude compared with competing PVD processes). This marks an important milestone in optical coating development, whereby mid-infrared mirrors can now reach comparable levels of optical losses, as was realised in visible and near-infrared coatings in the mid-1970s. Prototype mid-IR crystalline mirrors have been sent to beta customers for applications in radiocarbon detection, for biomedical marker investigations, and for combustion experiments relevant to climate modelling efforts. Pushing these mirrors to longer wavelengths, we aim to extend this technology to 10.6µm mirrors for CO2 laser systems. This is particularly enticing given the large commercial market for laser machining and integrated circuit lithography. 

In terms of scaling the maximum mirror size, the aims are more scientifically focused. Building upon more than a century of progress, state-of-the-art Fabry-Perot cavities have reached a point where their ultimate performance is limited by fundamental thermo-mechanical fluctuations, or Brownian motion, of the mirrors themselves. These unavoidable fluctuations now stand as a barrier to ever more precise measurements of time and space, such as those obtained using advanced optical atomic clocks and interferometric gravitational wave detectors. As a consequence of this limitation, researchers in the optical precision measurement community have been searching for two decades for a means to minimise the adverse effects of this so-called "thermal noise".

A breakthrough in this area requires the development of mirrors, or, more specifically, coating materials, that also exhibit high mechanical quality. The latter point may not be obvious at first glance, but based on statistical mechanics, most notably the fluctuation dissipation theorem, one finds that enhanced stability, realised through a reduction in the Brownian noise, is obtained by minimising the intrinsic elastic loss (think "internal friction") of the mirror coatings. This is a major impediment to improving laser-based gravitational-wave observatories. Our crystalline coatings offer significant advantages, however the largest mirrors that we can currently fabricate are ~20cm in diameter, while current gravitational-wave detector mirrors are ~35cm in diameter. We are actively pursuing collaborative projects in order to reliably produce such large mirrors, the good news is that this is an engineering challenge and there are no fundamental physical limitations. I thus see a bright future ahead for the implementation of our semiconductor supermirrors in these advanced astronomical instruments.

What is the most significant photonics technology to emerge in the past 12 months? 

Garrett Cole: What strikes me as impressive is the rapid advancement of quantum-focused optical technologies. Years ago, I had assumed that the most viable approach in the quantum computing space was semiconductor-based systems (for example superconducting circuits based on Josephson junctions or potentially spin systems based on Si or SiGe quantum dots). I was admittedly very sceptical that optical architectures requiring a wide variety of lasers and optical components, particularly atomic, molecular, and optical physics (AMO) platforms such as trapped ions or neutral atoms, would ever be a winning solution. Clearly, we are far from a fully functioning or commercially viable toolset, but I am blown away by the extremely rapid progress made on Rydberg atom and trapped ion quantum computing demonstrations over the last year. The emergence of visible photonic integrated circuits, leveraging heterogeneous integration of compound semiconductors with silicon nitride or potentially thin-film lithium niobate, look to further advance what is possible, significantly reducing the complexity of such advanced quantum optical systems. It will be very exciting to watch this space over the next few years...

What are the biggest challenges to the photonics industry in the next 12 months?

Garrett Cole: From my personal vantage point, supply chain issues continue to be the most daunting to deal with, even as we transition out of the pandemic. Specific to the work of my group, the long lead times we are experiencing in the supply of base materials negatively impacts both our commercial production and R&D efforts. Pre-pandemic, typical lead times for super-polished optical substrates was manageable at very roughly 4-6 weeks, or potentially 8-10 weeks for complex requests. In contrast, we are now facing waits at the 4-6 month level. This has led to lost sales and has severely slowed the pace of our research and development efforts. I see improvements on the horizon with a stabilising supply of high-quality synthetic fused silica and lightened loads at various vendors, but it is still quite frustrating to wait many months for items that had historically taken weeks to procure.

Which photonics sector has the greatest opportunity for growth?

Garrett Cole: I see significant growth opportunities via the rapid advances in photonic integrated circuits (PICs), particularly as these systems move to alternative wavelengths in the visible range and away from more common telecommunications-focused wavelength regions (e.g., around 1,550nm). Visible wavelength active and passive PICs have tremendous potential for revolutionising sensing and computing applications, especially given the potential for streamlining advanced quantum optics / quantum photonic systems with the ability to generate and manipulate light directly at the wavelengths of interest for typical atomic, molecular, and optical physics (AMO)-relevant solutions. At the other end of the spectrum, I see longer term (>12-month time frame) potential for PICs pushing into the mid-infrared spectral range for gas detection, environmental monitoring, and biomedical applications.

What are the challenges or opportunities faced by photonics researchers or companies in the US? 

Garrett Cole: I would once again point to supply chain issues as I mentioned above. Clearly things are improving, but the delays associated with the procurement of critical materials and components could once again increase if political tensions continue to escalate. Stricter export control, or reduced global supply of key materials will lead to additional complications as tensions mount between global powers. On the other hand, I acknowledge very positive outcomes in terms of funding, particularly for semiconductor-focused efforts in the US, as well as both public and private funding for quantum-relevant activities. Things are net positive in terms of the photonics industry in the US from my perspective, but the situation is tenuous and care must be taken to continue to support this often overlooked market.

What is your proudest moment in photonics so far?

Garrett Cole: I am going to cheat here and list a few moments... Transitioning from basic research in order to build up a high-technology hardware start-up was an extremely challenging task, so it was fantastic to receive acknowledgement via various accolades. This includes start-up challenge prizes during the early days of CMS, while I count the receipt of select prizes as notably proud moments, such as the LIGHT2015 Young Photonics Entrepreneur Award that I received as part of the UNESCO-sponsored International Year of Light in 2015, a Berthold Leibinger Innovationspreis in 2016, and an SPIE / Photonics Media Prism Award for new Materials and Coatings in 2017. Most recently I was chosen as a "Trust Science Champion" as part of the UNESCO International Day of Light on May 16, 2021. I dedicated the latter to my father, an unwavering supporter, who had unfortunately passed away just 10 days before that was conferred.

Two more notable and very unique life experiences occurred in 2018 and 2019 when I was hosted by Jeff Bezos at the invitation-only MARS (machine learning, automation, robotics, and space) Conferences held in Palm Springs, CA, to discuss our work on the development of mirrors for future gravitational wave detectors (with Barry Barish and Dave Reitze of LIGO). During these multi-day events I was able to hobnob with technical luminaries such as Nathan Myhrvold (Microsoft's first CTO and a James Beard culinary award winner), Stephen Wolfram of Mathematica fame, plus titans of industry including then CEO of Intel, CTO of Ford and so on... There were also celebrity attendees such as Mark Hamill (Luke Skywalker!), Ron Howard (one of my favourite directors), and Adam Savage, formerly of Mythbusters. Those are life experiences that I will always cherish! Clearly the acquisition of CMS by Thorlabs was worthy of celebration and, on the technical front, it brings me joy to see our mirrors enabling the world's most stable lasers. Furthermore, I have been thrilled to assist in building space-qualified cavities to be deployed on satellite platforms for fundamental scientific endeavours, as well as for more practical uses (i.e., future space-based navigation networks).

What advice would you give to someone who wants to get to where you are/do the job you do?

Garrett Cole: I am not someone who plans or maps out my future, so my advice would be to follow your interests and see where the road takes you! Make sure to be open to new ideas and opportunities. Along your path do not hesitate to reach out to others that you may be interested in working with. As an example, the "seed" that ultimately led to the move to Vienna was an email I sent to an unknown contact at the Austrian Academy of Sciences. I thought that their work was interesting and had hoped to collaborate from LLNL. I did not know a single person there, nor have connections that could facilitate an introduction; I simply rolled the dice and wrote a friendly email inquiring about their work and made suggestions of how I could help. I never would have anticipated that less than two years later I would be living in Vienna because of that message! I have been privileged to work with outstanding folks over the years, and my network has grown immensely since I completed my doctorate nearly 20 years ago. I continue to make a concerted effort to help anyone who is interested in building up contacts or looking for advice on their technical efforts or in entrepreneurship. I recommend that everyone give back to the community however they can, for example by reviewing papers, serving on conference committees, speaking at university technical society functions, mentoring students, etc. Trying a variety of things, both technical and otherwise, will show you what you are proficient at and, even more importantly, what you enjoy doing!

Where can people see you in person over the next year?

Garrett Cole: I reliably attend Photonics West and CLEO (next year marks the first time that the event is hosted in Charlotte, North Carolina) and I will be returning to both in 2024. For CLEO I serve as the chair of the subcommittee focused on "Quantum Technology in Transition", covering the burgeoning commercialisation of quantum technologies. Of course I highly encourage folks to stop by and check out our office and lab space at Thorlabs Crystalline Solutions in sunny Santa Barbara, California. Following fun technical discussions it is less than 10 minutes to walk to the beach from our location!


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