Attendees:
James Pond, Fellow at Ansys
Gilles Lamant, Distinguished Engineer at Cadence
Mitch Heins, Business Development Manager for Photonic Solutions at Synopsys
Pond began by discussing the prevalence of photonics in current devices like smartphones, which contain displays, cameras, VCSELs for facial recognition, and more photonic components. However, he noted less need for integrated photonics in mobile devices compared to data centers using optical interconnects between GPUs for high-bandwidth, low-power communication.
"With the Lumerical tools at Ansys, we deal with photonics more broadly. If I take out my cell phone today, it's completely full of photonic devices...The question is, 'Is it going to be integrated photonics or silicon photonics?' I see less need there, than in some of the compute-for-AI things in data centers, where connecting GPUs for high-bandwidth, low power communication is key."
Heins provided an example of how photonics is enabling new form factors, such as solid-state lidar systems integrated into cars instead of bulky roof-mounted units. He emphasized the importance of size, weight, power, and cost.
"One example of a change in form factor enabled by photonics is lidar. You used to see lidar-equipped cars drive around with what I call the 'Kentucky Fried Chicken bucket' on top. Now it's all solid-state, built into the frame of the car. They care about SWaP (size, weight, and power)."
Pond agreed, adding, "And cost."
Heins continued, foreseeing photonics being used for sensing and monitoring in manufacturing and industry, such as detecting gas leaks in pipelines.
Lamant expanded on other emerging applications of photonics beyond photonic integrated circuits, like aeronautics manufacturing, earthquake detection, surface measurements, and meta-lenses. He was encouraged by major fabs opening production lines for silicon photonics, driven by the datacom industry's demand.
"We're starting to see people doing a lot more photonic-based measurements on surfaces and meta-lenses...datacom actually has funding. Fabs are opening lines — not small lines, but big lines — with big wafers that are made with good yield, reliable production."
On the topic of curvilinear masks at advanced nodes, Lamant explained that curvilinear shapes are actually the natural result, with creating Manhattan-style corners being the difficult process. However, extracting parasitics and designing rules for curvilinear shapes poses a challenge for EDA tools.
"At 2nm or below, they are naturally manufactured with light in a curvilinear manner. It actually takes a lot of effort to force them to have corners...The challenge is maybe not on the foundry. It's on the DRC rules, and making sure you can design for it."
Heins added that semiconductor manufacturing has optimized processes for Manhattan shapes, so a shift to curvilinear patterning would require adjustments like different lithography illumination. Yet, the relatively large scales of photonic features could make this easier compared to advanced logic nodes.
Pond noted that photonics has always involved curvilinear shapes due to the nature of waveguides. So curvilinear masks may have less impact on photonic EDA versus other domains.
Regarding thermal effects, Lamant stated that heat and its fluctuations are crucial factors that photonic devices inherently rely on for tuning and functionality. Thermal crosstalk and extreme temperatures pose reliability challenges for surrounding electronics as well.
"Photonics uses thermal as one of the main ways to tune its own functionality. Thermal is a super-important parameter...Some of those devices go to 300ºC. Think about what that does to the electronics next to it, in terms of the device's aging, the conductors, the EMIR. Thermal is absolutely a big challenge for photonics."
Pond emphasized that even 1°C variations can severely detune resonant photonic components like ring modulators. Active tuning with heaters is commonly used to stabilize wavelengths, but power consumption is a concern.
"A 1° shift is enough to completely de-tune a ring modulator or something like that, so it's very small changes. Typically, we deal with this by actively tuning with heaters to keep everything aligned — all the wavelength channels, and so on."
For 3D hybrid chips, Heins warned that localized hotspots from heating photonic elements could impact surrounding electronics with many transistors in a concentrated area. Careful co-design and thermal analysis is critical.
"If you put a big heater on top of the photonic device to tune it, and it happens to be smack up against the electronics, you could have literally thousands of transistors that are being impacted by that one big heat source."
Pond reiterated that temperature differences between light paths in interferometric modulators are more detrimental than overall operating temperature.
Lamant concluded by stressing the importance of having EDA tools to analyze and understand both ambient and dynamic thermal effects at the photonic chiplet level as well as the system level with surrounding components.
"Designing for it means you need to have tools for analyzing it so you can understand what's happening within the device. There is an ambient one, which is kind of a static one, and then there is a crosstalk one. Those two become dynamic, they change with time."
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