By Twan Korthorst, Director of Photonic Solutions, Synopsys
While the study of photonics began in the 1960s with the invention of the laser (and later provided the internet’s infrastructure), the field of photonics has moved into mainstream electronic designs today. This shift is driven by the exponential growth in data and the need for high performance with low power.
The unique properties of light make it possible to create innovative low-power data transfer, processing and sensing chips, and chiplets. However, these need to be connected to traditional electronic systems to realize their true potential. The complexity of photonic design problems requires engineers to have a thorough understanding of the physics of photonics and often geometrical optics.
Read on to learn more about the history of photonics, why it is important for the semiconductor industry, the opportunity to power key market applications, and the future of photonic integrated circuits (PICs).
Put simply, photonics is the physical science of light waves and encompasses the generation, detection, and manipulation of how light propagates. As you might remember from your high school physics class, the behavior of light can sometimes be best described as a wave and sometimes as a particle (photon), depending on the scenario.
Take the example of a ray of light bending through a glass lens. In this case, the path of the light can be understood by a classical particle characteristic, a ray of ‘light particles’ travelling through a medium and bouncing off surfaces. In addition, light being created or absorbed by a solid-state device such as a laser diode or charge-coupled device (CCD) detector displays light’s modern particle nature. In this scenario, light behaves like a stream of particles, each one of which carries a certain, fixed amount of energy (photon energy). An example that demonstrates the wave-like behavior of light, similar to acoustical waves, is the Doppler effect. An ambulance siren sounds different when the ambulance drives towards you or in the opposite direction. The same is observed when studying the universe; the color of a star shifts depending on the speed and direction from the observer’s position. And light can also interfere, like waves in a pond. This is used in integrated photonic devices like a Mach-Zehnder modulator, where light is manipulated to constructively or destructively combine using phase differences between two light ‘waves.’
As previously mentioned, the term photonics came on the scene over 60 years ago with the invention of the laser (and later the laser diode). It originally described a field where the goal was to use light to perform functions traditionally accomplished using electronics.
Photonics became more popular in the 1980s with the introduction of fiber optic communications. Integrated photonics started to supply devices for long-haul telecom where copper links were replaced with optical fiber links. To fit more wavelengths of light into fiber, devices were being developed that could act as a prism on a chip and could miniaturize and transfer more data through an optical fiber.
When this technology was being developed, researchers learned that there were a lot more devices that could mimic electrical devices (e.g., amplifiers, switches, and filters) by manipulating the face of the light the way electronics engineers do. A whole toolbox has been developed since then, mainly used today in optical transceivers for data communication.
It’s clear that there are increasing opportunities for the application of photonics in the design and manufacturing process for devices, systems, and ICs that are used in high-speed data communications, advanced sensing, and imaging. By using photonic technology, designers can expect orders-of-magnitude speed improvements along with reduced power consumption for data transmission and ultrasensitive sensing capabilities in multiple domains.
Photonic ICs use photons rather than electrons to process and distribute information. In a more traditional electronic chip, electrons pass through electrical components such as resistors, inductors, transistors, and capacitors; in a photonic chip, photons pass through optical components such as waveguides, lasers, polarizers, and phase shifters.
By harnessing light instead of electricity, integrated photonic technology provides a solution to the limitations of electronics like integration and heat generation, taking devices to the next level, with the so-called “more than Moore” concept to increase capacity and speed of data transmission. PICs offer advantages such as miniaturization, higher speed, low thermal effects, large integration capacity, and compatibility with existing processing flows that allow for high yield, volume manufacturing, and lower cost.
Because of the above advantages, photonics technology is employed in a wide range of applications that are used by the everyday consumer both directly and indirectly. It should be no surprise that the tele- and data communications field is still heavily dependent on photonic devices for fiber optic networks that greatly increase the capacity and speed of our wired and wireless communications.
The world of light itself has been transformed by the introduction of affordable, powerful LEDs that cut power consumption while providing high-quality, flexible lighting solutions. Solid-state lasers now appear in applications from medical to industrial. Lightweight, compact light sensors are designed in consumer devices as diverse as cellphone cameras, bar code scanners, printers, DVD players, and automotive sensors.
Finally, the emerging field of photonic computing aims to supplement or replace traditional electronic-based printed circuit boards (PCBs) and ICs with optoelectronic circuits.
Looking specifically at PICs, the key application field is data communications, followed by sensing (e.g., for agriculture and autonomous driving), and biomedical applications such as lab-on-a-chip and wearable devices, as well as use in the defense and aerospace industries. We expect to see improvements and additional applications for PICs as designers take on more technical challenges for which integrated photonics may be proven useful by feasibility studies.
While there is much promise in the field, there are also challenges that come along with photonic technology that designers need to be aware of. One of those challenges is the issue of scaling. Photonics simply doesn’t scale like electronics; when photons propagate in a circuit, they like bends instead of sharp corners. This means that the square area that a photonic circuit consumes tends to be larger than an electrical IC.
We know how to fabricate very large digital ICs with many transistors, building in redundancies and tolerances for the fabrication. In photonics, the sensitivity to fabrication variations is much larger than what we are used to in digital electronics. There is much research being done to learn more about how we can fabricate photonics in a way that accounts for these sensitivities.
There is also extensive research being done around building 2.5/3D setups combining electronics and photonics. As mentioned before, the physics of how light propagates more or less determines the physical dimensions. If you look at optical transceivers or at an array of optical IO chiplets surrounding an ASIC switch, the digital switch ASIC is smaller than the photonic IC. There is a trend towards designers using the photonic IC as an interposer platform that control and digital electronics can be stacked upon.
The field of photonics has become an exciting new frontier, and we are seeing only the beginning of its revolution. The work being done by photonic engineers is both creative and demanding, requiring the latest research, tools, and techniques as well as maintaining a good familiarity with the limits of manufacturability and a working knowledge of quantum and physical optics.
Going forward, we’ll see more applications for photonics as engineers continue to use specialized software tools to model the behavior of light and learn more about how to best optimize designs to achieve the desired performance in a buildable package. To learn more about Synopsys’ photonic solutions portfolio and additional applications of photonics, visit our photonics webpage.
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