Julie Eng, the CTO of Coherent, has received the Lisa Su Woman of Innovation Award, honouring women driving innovation in semiconductors.
She spoke to Gazettabyte about her career, women in engineering, and her perspectives on optical technologies and their developments.
It was the end of the first day at the ECOC conference, held in Copenhagen late last month, when Julie Eng arrived at the conference centre full of energy. All the more remarkable given that she had just stepped off a flight from the US and, after the interview, was going to a dinner engagement.
Eng spent two days at ECOC before returning to the US to receive the Dr Lisa Su Woman of Innovation Award, established by the Global Semiconductor Alliance (GSA) to honour women driving innovation in semiconductors. The award is named after the CEO of AMD, Lisa Su, the inaugural recipient, while Eng is the fourth woman to receive the award.
Eng has also been elected this year to the US National Academy of Engineering. Here, an existing member nominates a candidate who is evaluated on their life’s body of work. Academy members must then recommend the candidate for successful admission.
Early path to engineering
Eng’s career in photonics began with an aptitude for maths and an early example of pragmatic decision-making.
Growing up in the middle of the US, she had never met a scientist or an engineer. Her father was a businessman and her mother, an English teacher. Her school required students to take maths exams set by the local mechanical engineering society, and Eng excelled at it.
“Even when it wasn’t required anymore, I kept taking them because you could win money,” says Eng, laughing. “It was easier than babysitting.”
Eng remained unsure about engineering, so she took a 5-year university programme, three years studying liberal arts and two years at an engineering school. This led to a summer research programme at AT&T, at a time when fibre was being laid in the US Northeast corridor. “It was very exciting, I learned about semiconductor lasers and everything,” she says.
She joined AT&T Bell Labs but then lived through the telecom bubble and its aftermath. She then joined Finisar in 2003, where she eventually became responsible for its optical transceiver design, which generated over $1 billion in revenues. During her tenure, the unit released 270 products. Eng then headed Finisar’s 3D sensing unit, stepping away from communications for five years.
II-VI acquired Finisar in 2019 and had its own 3D sensing business, so Eng ran the two units combined. II-VI then bought Coherent, changed its name, and it was the CEO, Chuck Mattera, who asked Eng to become Coherent’s CTO.
The CTO role
Eng realised there was no clear job definition once starting her role, so she contacted other companies’ CTOs to hear of their experiences and advice. “One of the things I heard and liked was making sure that the CTO office is useful to the company’s business units,” she says. “So, I have tried to make the link tighter.”
Much of the advice she received made immediate sense: staying up to date with the latest technologies, introducing them to the company to ensure the right people are aware of them, and focussing on work of value.
“One thing I do is bring together people inside the company with an idea of innovation,” says Eng.
This year, Coherent held its first Innovation Summit. “To attend, you had to submit a paper, like at a regular conference,” says Eng. There was also a second track for R&D pitches. “A bit like [the TV shows] Shark Tank or Dragons’ Den,” says Eng. There was a pool of money, with the CTO’s Office selecting the finalists that then pitch their ideas to a panel of judges.
Eng says the CTO role is unlike her previous jobs. Before, she was responsible for delivering products which had its own frenetic pace. “I don’t have that anymore,” she says. “Instead, it’s unclear what you should do, so I had to coalesce around what I think the role really is, and what I think are my team’s deliverables.”
Her team’s work spans a vast breadth of topics and applications. For example, Eng has a team working on lasers for fusion energy generation. “It stretches very wide, but it doesn’t mean we have the same pounding pace that manufacturing and production jobs have,” she says.
Eng has now work for two CEOs during her time as Coherent’s CTO. The current CEO, Jim Anderson, joined Coherent in June 2024. Eng says one of Anderson’s strengths is ensuring R&D spending is directed to the highest growth and most profitable areas. “It sounds like motherhood and apple pie, but he has got a methodology for it,” says Eng, pointing to his semiconductor industry background. Semiconductors are a more mature industry than optical components, and Anderson has been at IC companies with their own fabs, so he understands manufacturing, she says. ”Now Michael Hurlston is CEO at Lumentum, so more semiconductor people are coming into our industry,” says Eng.
Technology Trends
Being seated with the CTO is a good opportunity to ask quick-fire questions about technology.
Do VCSELs have a future beyond 200 gigabit-per-second (Gbps) and what role will co-packaged optics play?
“I don’t have anything specific to announce yet, but I’m not willing to say that 200 gigabits is when VCSELs max out,” says Eng, who is also a big fan of VCSELS for co-packaged optics.
At OFC 2023, Coherent demoed, along with IBM, the use of compact VCSELs co-packaged optic modules for a government project. At the time, it was seen as a curiosity. Now, there is more momentum due to VCSELs having lower cost and lower power. Eng gave a talk at ECOC reporting 1pJ/bit using VCSELs. “There are some trade-offs, of course, because for any directly modulated laser in a fixed, high-heat environment,” she says. “The thermal solution has to work to ensure that you can hit the FIT (failures in time) rates.” Accordingly, VCSELs’ most promising role will be for scale-up network applications, where cost and power are key, and where a reach of 30m is sufficient.
Eng expects to see silicon photonics-based co-packaged optics to be also deployed due to its longer reach using single-mode fibre that also makes it compatible with optical circuit switches. In this architecture, the heat issue is avoided by moving the laser externally.
As for 200Gbps per lane linear pluggable optics (LPO) modules, Eng believes they will find a role in applications over short, controlled links. “Linear retimed optics (LRO) will definitely work, but I think people will try really hard to make linear pluggable optics work too.”
Coherent has set up a 400Gbps/lane lab to assess its own components and work with other firms that provide parts. That way, Coherent can measure performance and form an objective view.
Coherent also has optical circuit switches that use its liquid crystal technology, which does not move up and down like MEMS.
“Optical circuit switches solve problems for our customers and that’s my favourite kind of technology,” says Eng.
Using optical circuit switches allows systems to be reconfigured, in the event of a rack failure or, more generally, as large jobs are completed. Using such switches, AI accelerator clusters can be reassigned to new jobs within the data centre.
“For optical circuit switches, we estimated a $2 billion market by 2030, but we think we might have under-called it,” says Eng. “I also think there’s not going to be as many competitors as there are for transceivers.”
Coherent also has thermal materials such as silicon carbide, diamond, and diamond-loaded silicon carbide ceramics that are becoming increasing of interest for thermal management in the data centre.
Beyond datacom and telecom
Eng is also in charge of technologies used for non-telecom and datacom applications. One such application is semiconductor wafer inspection. Here, lasers are increasingly used to scan wafers to identify defects as the industry moves to 3nm and 2nm CMOS process nodes, with Coherent providing the lasers to semiconductor capital equipment makers.
Another laser application is for OLED displays. Here, a large laser creates a line beam for annealing, by sending heat into the semiconductor process used in the display.
Biomedical is another area albeit volumes are still low. One application is for brain imaging. By optically activating the brain, researchers can study degenerative diseases using Coherent’s lasers.
There is also activity in fusion energy start-ups. One type, known as magnetic fusion, uses superconducting tape inside the magnet. The superconducting material is deposited using pulsed laser deposition. The other approach, laser inertial fusion, uses giant lasers, optics, and crystals which Coherent makes.
“And anything quantum: quantum computing, quantum networking, and quantum sensing,” says Eng.
Women in Engineering
Eng gives talks to students promoting engineering, as well as to women in the field. Her own experience in engineering and the optical industry is positive; it is meritocratic, she says.
“I’m a very driven person and have not felt treated differently,” she says. “But you always notice when you are the only person who is different to everyone else in the room.”
Eng is keen to have diverse opinions in meetings, as it broadens the perspective and delivers better outcomes. To this aim, having people with different backgrounds helps. “It could be they grew up in a different country, or it could be that they think a different way, or they may be a different gender,” she says.
Optical industry challenges
For Eng, this is a notable period in photonics, and with it comes challenges.
One is a supply challenge due to the growth in demand. A second issue is the technical challenges posed by growing data rates. Data rates have been constantly increasing, but their rate of growth – the period of time between speed hikes – is getting shorter.
Eng has investigated how long it takes the entire industry to ship its first 10,000 units, and the time it takes to ship 10 million units in one year. In the past, it was a 10-year period; now it is two to three years.
“So, data rates are growing faster, the new technology is getting absorbed faster, but also you’ve got to ramp up the curve a lot faster,” she says.
Another issue she notes is the advantages and disadvantages of a standardised world.
With standardised transceivers, it is known what to make next. “I know without anybody asking me that the next thing I should do is work on 400-gig modulators, and I can make that decision and understand that completely independently of anyone else,” says Eng. But with co-packaged optics and near-packaged optics, it is becoming a non-standard world. That can also have advantages. It can’t be easily swapped in and out and does not have as many competitors.
However, the disadvantage is that multiple approaches may be needed. “Maybe you do some stuff, and then the customer realises it doesn’t work, and then you have to start over,” says Eng. Moving from that standardised to this non-standardised world has its pros and cons.
The AI opportunity
AI and the hyperscalers are now driving the photonics industry, but there are those concerned that this period may be another bubble.
“We only have the visibility we have, but all we can say is our visibility looks robust,” says Eng, noting that it is still the early innings when it comes to AI.
“There might be some ups and downs, for sure, but so far, what we see matches what the hyperscalers have said publicly about their capex spend.”