UofT’s Dr. Joyce Poon reveals how using light to relay information is revolutionizing telecommunication and neuroscience.
On January 13th, the University of Toronto (UofT) hosted the “Trip the Light Fantastic” webinar as part of their monthly Skule Lunch & Learn series. The webinar was spearheaded by Dr. Joyce Poon, director of the Max Planck Institute (MPI) of Microstructure Physics in Germany. She also serves as a part-time professor of electrical and computer engineering at UofT.
Dr. Poon specializes in silicon-based integrated photonics—no doubt a daunting set of words for the expert and layman alike—so parsing them may be necessary.
Photonics (derived from photon, the building block of light) is the science of creating, transmitting and detecting light. Integrated here pertains to integrated circuits, more commonly known as microchips.
Thus, silicon-based integrated photonics is the science of using silicon-based materials to create microchips that use light to transmit information instead of electricity.
Photonics in Data Communication
Light is theoretically the fastest form of energy in the universe and as such possesses an extremely high bandwidth. Today, we can easily video conference with friends across the globe and run a business from home because of photonic devices like fiber optics that use light to transfer enormous amounts of data across vast distances.
Efforts are in place to use photonic devices for short distance communication as well, such as data centers, supercomputers and even microchips themselves. The challenge has been that many photonic components were created from a miscellany of materials, many of which were costly and not readily available. The assembly methods were also extremely crude and antiquated. In the past fifteen years, however, a new technology has addressed many of these challenges: foundry silicon photonics.
The principle behind foundry silicon photonics is to utilize the manufacturing methodologies and capital already in place for producing electronic microchips, and funnel them into producing photonic microchips instead.
“Silicon-based integrated photonics can now be made into very large wafers and dense integration is possible as well,” explained Dr. Poon. “So, this has greatly changed the field and has rapidly evolved into a billion-dollar industry with major commercial players, including Intel for example.”
As the industry burgeons, research and development into its applications has also boomed. In her time with UofT, Dr. Poon has conducted research on extremely high-speed electro-optic transmitters as well as Quantum Key Distribution (QKD) transmitters—a form of data encryption that operates by transmitting polarized photons through a fiber optic cable between two devices.
Dr. Poon’s speciality, however, is integration circuits that utilize multi-level waveguides. A waveguide is any medium used to emit or channel a wave, whether it’s sound waves or electromagnetic waves like light. Traditionally, silicon photonics involve distributing light through only silicon. However, Dr. Poon has been collaborating closely with Singapore-based Agency for Science, Technology and Research (A*STAR) Institute of Microtronics, and has since created small and large-scale photonic wafers comprising multiple layers of silicon and silicon-nitride. Today, multi-layered photonic waveguides are being implemented in foundries across Europe and the United States.
Medical Application of Photonics
In the last fifteen years, a parallel evolution has also occurred in the field of neuroscience and neurobiology. Years of research and experimentation in the Deisseroth Lab at Stanford have given birth to optogenetics—a new field of study where neurons are genetically modified to not only respond to light but to even emit light when firing.
“Neurobiologists are now able to map brain circuits and brain activity with light,” Dr. Poon illustrated. “Because the neurons can be genetically modified to emit light when they’re firing, neurobiologists can now watch videos and observe neural activity in 2D and 3D.”
In fact, optogenetics grants neurobiologists an opportunity to not just map neural activity but to influence behavior itself. Since 2007, Deisseroth Lab has been involved in a plethora of experiments on animal behavior using optogenetics. In one of the experiments, sections of a mouse’s brain were modified to fire rapidly upon exposure to blue light, thereby resulting in altered behavior. A fiber optic probe designed to emit blue light was then inserted into the mouse’s brain. As the control portion of the experiment, the blue light was left switched off and the mouse traversed its chamber randomly. With the blue light switched on though, the mouse only ran in counter-clockwise circles!
Dr. Poon aims to deeply interface with the brain via neurophotonic probes—technology that marries optogenetics and integrated photonics. What distinguishes neurophotonic probes from electrical probes is that the latter, while cheaply available, pick up signals from all sectors of the brain. Effort must be made in trying to sift through this “noise”, and guesswork is often necessary. With neurophotonic probes, however, there is high specificity: precise sectors of the brain are genetically modified to emit light so there is no guesswork involved as to origin of the signals. In fact, neurobiologists can even specify which neuron types are being fired depending on the scope of the experiment. More importantly, the light sheet produced has enough optical power to light up the tissue while also limiting background fluorescence. The result is a vivid, high-contrast imaging of the brain tissue when compared to epifluorescence microscopes that are used today.
Additionally, using foundry manufacturing allows for broad dissemination and complex designing capabilities for neurophotonic probes. Working with Singapore-based Advanced Micro Foundry (AMF), Dr. Poon and her team have created neurophotonic probes on eight-inch wafers using deep UV (DUV) lithography where each wafer can hold as many as 1800 shanks. The shanks can also be individually customized to emit light along their surface.
Furthermore, in collaboration with Caltech and the Krembil Brain Institute, Dr. Poon has been testing neurophotonic probes on mice neural tissue (in vitro) and even live mice (in vivo). By using optical phased array (OPA), each shank generates light at a different phase, resulting in light beams that can change direction as required (steering). These probes are then inserted into a mouse’s brain and used to generate light into specific regions of the brain.
Another type of probe that Dr. Poon has worked on is a light-sheet neurophotonic imaging probe, where the shanks have specialized gratings that emit a uniform plane of light (sheet). The sheet is also adjustable; that is, it can be emitted from uniform angles and intensity along the length of the shank. Once inserted into the brain, the light-sheet neurophotonic imaging probe enables researchers to inspect or excite multiple levels of the brain.
“Typically, in light-sheet microscopy with a standalone conventional microscope, the lenses used to form the light sheet are unable to image non-transparent organisms,” Dr. Poon reminded the audience. “So, you can only image some zebrafish larvae and a few other rudimentary organisms. But with light sheet neurophotonic imaging probes, we’ve conducted experiments in vitro and in vivo.”
Dr. Poon is currently also involved in integrating neurophotonic probes into miniature microscopes. Such a contraption could be placed directly onto a mouse and would lend itself to complex behavioral experimentation on live, unencumbered mice.
The Max Planck Society
Max Planck Gesellschaft (MPG), also known as the Max Planck Society, is an independent, non-profit research organization in Germany that boasts an annual budget of USD$2.2 billion (CAD$2.81 billion). There are a total of 91 Max Planck Institutes around the world, with 86 in Germany and the remaining institutes scattered across USA, Italy, Netherlands, Brazil and Luxemburg. Since its inception in 1948, MPG has produced twenty Nobel laureates and was behind 130 inventions in 2019 alone.
Dr. Poon leads her own department called Nanophotonics, Integration and Neural Technology (NINT) at the Max Planck Institute in Halle, Germany. With an annual budget of over USD$18 million (CAD$23 million), the department strives to create integrated photonics that allow interfacing with 3D displays, neurophotonic implants technology that activate/monitor neural activity, photonic hardware accelerators, and phase-change electronic and optoelectronic devices that are energy-efficient. NINT’s end goal is a new generation of computers that are not laptops or smartphones—but brain interfaces that use integrated photonic technology as their foundation.
Joining Forces
MPG and UofT are partnering to launch the Max Planck-University of Toronto Center For Neural Science and Technology in 2021. With a combined investment of USD$5 million (CAD$6.3 million) from both institutes, the center will dedicate itself to developing new tools to study the brain, conducting in vitro and in vivo experiments, and devising data analytic and data modelling methods. The main feature of the center will be a joint PhD program where students will be co-supervised by MPI scientists as well as UofT faculty. In the first year, students would primarily be involved in UofT coursework, after which the remaining three years will be spent conducting research at an MPI. Once they have completed their fourth year, graduates will be awarded a UofT degree in their respective field.
Future Applications of Integrated Photonics
During the Q&A section of the webinar, Dr. Poon further elucidated on the potential medical application of integrated photonics. For instance, a successful mapping of the brain’s neural network via neurophotonic imaging would allow neurobiologists to visualize and pinpoint mental diseases like dementia and Alzheimer’s, both of which are a result of damage or loss of nerve cells.
Additionally, Dr. Poon suggested a possibility of using neuroprosthetics to combat such diseases. These devices can be customized to interface with the brain in a way that can not only assist the afflicted section of the brain, but replace it altogether.
Other potential applications include non-invasive photonics that can be installed in the human mind to augment memory, enhance intelligence, or even allow people to learn different languages. As Dr. Poon concluded herself, “Who knows where we’ll be a hundred years from now?”
