Voices of CS: Charlie Carver and Hadleigh Schwartz

Hadleigh Schwartz, Charlie Carver, and Xia Zhou

PhD students Charlie Carver and Hadleigh Schwartz unveiled Lasertag, a framework that integrates laser steering with optical tracking to maintain laser connectivity, at the 29th Annual International Conference On Mobile Computing And Networking (MobiCom). Lasertag stole the spotlight with a live demonstration that earned a Best Demo Award. The team also received a second-place award in the Student Research Competition for their pioneering work.

The system establishes a constant laser-based connection with high-velocity targets, opening doors to transformative applications such as VR content streaming and wireless power delivery. Lasertag offers a unique framework for building and deploying practical laser-based mobile systems. It creates a constantly connected laser-based tether between the Lasertag core unit and a mobile, remote target, enabling fully wireless, gigabit-level communication and wireless power delivery. Its potential applications span communication, sensing, and efficient wireless power delivery.

Lasers have unique physical properties, which make them appealing for many applications. Laser-based streaming of virtual reality content could enable higher quality experiences for VR headset users, or wireless power delivery via lasers could allow robots to work longer without returning to a charging station. These applications require constantly tracking and steering a directional laser beam to a moving target at shorter ranges (i.e., a few meters). However, before Lasertag, there were no systems for achieving this, which was a barrier to realizing laser-based mobile applications.

The response from the research community has been positive, with Lasertag’s ability to navigate the complexities of lasers and optics earning accolades. The journey continues as Lasertag is set to take the stage at The 19th USENIX Symposium on Networked Systems Design and Implementation (NSDI) this April.

While currently a researcher’s tool, Lasertag lays the foundation for a future where laser-based applications seamlessly integrate into daily lives. From enhanced VR experiences to prolonged robot functionality through wireless power delivery, Lasertag is poised to revolutionize how we interact with technology. Carver and Schwartz worked with Associate Professor Xia Zhou and colleagues from the Mobile X Laboratory. The laboratory’s projects explore how to turn light into a powerful medium for data communication and object or behavioral sensing.

Best demo award presentation
Zhou, Schwartz, Carver receive the Best Demo Award at the 29th Annual International Conference On Mobile Computing And Networking (MobiCom).


We caught up with Carver and Schwartz to learn more about their research and effective collaboration methods.

Q: What sparked this project?
When I started my PhD last fall, Charlie and Xia described to me several of their past projects involving lasers for communication and sensing. At the time, they were trying to develop a system for laser-based streaming of virtual reality (VR) content, essentially to enable users to view high-resolution 3D/360° content without a wired connection between the VR headset and gaming console.
A big challenge they were facing was how to continuously track and steer the narrow laser beam to a receiver on the headset. This application and problem sounded so cool, I knew that it was what I wanted to work on. Charlie had an initial version of Lasertag in development, so he gave me some tasks to help with, and ultimately, I was able to get more involved in the project.

Xia and I started working on the idea back in 2019, where we were originally interested in diffuse, room-scale, laser communication for mobile VR. The project has evolved significantly since that point, and we ultimately swapped the diffuse laser light with an efficient steerable beam.


Q: What was your role in the project? What did you do?
I was very interested in the optical circuit (i.e., a series of lenses and optical components) that could allow Lasertag to work. I spent a lot of time using ray tracing and optics software to validate and improve our theoretical optical circuit designs. I also spent a good amount of time testing out different lasers, LEDs, and variations on the optical circuit to improve the system’s efficiency and usability.

I’ve been primarily responsible for leading the project, which has entailed designing/building the optical circuits, electronic circuits, software, experiments, and anything else involved. I absolutely could not have finished without help from all our collaborators, especially Hadleigh, who offered invaluable insights and support during the final stretch of the work.


Q: How long did you work on the project? What did you have to do, or read to prepare to make the system?
Charlie and Xia formed the initial idea for the project back to 2019, but the current version using dedicated tracking was started in March of 2022 at Dartmouth. I joined the project in Fall of 2022, and the NSDI paper was published in May 2023. In addition to the simulations and computer programming stages, there was a significant amount of engineering work, including physically realizing our optical circuit, developing electronic circuits to power and communicate with different components of the system, and optimizing both the software and hardware to support tracking/steering to objects moving very fast.


Q: What were the things you had to overcome for this research project?
Research can certainly be difficult. In addition to addressing all of the traditional research challenges, like quickly pivoting when something doesn’t work as expected or spending hours debugging code or experiments, we had to contend with some specific challenges that come with working with lasers and optics.
For instance, the optical circuit needed to be precisely designed to get Lasertag to work as best as possible. This sometimes meant spending a day making micro-adjustments to the lens positions to get the laser beam in focus or get the geometry of the beam’s propagation through the optical circuit correct.


Q: What are your research interests? How did you decide to pursue this type of research? When did you decide to focus on it?
Light-based sensing and communication. I first learned about this field and decided to focus on it when I started by PhD in Fall 2022.

Throughout my PhD, I have been studying the use of light to build next-generation wireless communication and sensing systems. Compared to radio frequencies, light boasts wavelengths that are orders of magnitude smaller and a bandwidth that is ten thousand times larger, enabling ultra-precise sensing and fast, competition-free communication. My research has focused on laser light to fully leverage these benefits. Unlike traditional luminaries, e.g., light-emitting diodes, laser diodes provide superior communication and sensing performance thanks to their GHz modulation speeds, narrow spectral wavelengths, strong linear polarization, high-power densities, and high electro-optical conversion ratios.


Q: What sort of research questions or issues do you hope to answer?
I hope to continue building practical light-based sensing and communication systems. Right now I’m still figuring out what specific issues in this area I want to address in my PhD.

I’m broadly interested in questions pertaining to mobile systems and networking. More specifically, I’m interested in supporting next-generation wireless applications by exploring novel uses of light.


Q: What do you think is the most interesting thing about doing research?
The ability to find a problem or challenge that interests you and then fully dive into tackling it. You get to test out ideas that seem crazy or unlikely, spend time learning new things, and really use every tool in your skillset.

I’ve encountered many applications that pervasive wireless technologies are ill-equipped to handle (usually due to underlying physics-based limitations). Oftentimes, approaching these challenges from a different perspective leads to unexpected breakthroughs that shift the status quo. I love discovering these opportunities — and so far throughout my research career — consider how light can solve them.


Q: Could you share some advice on ensuring the success of collaborative efforts?
I think in addition to the obvious importance of clear communication, it’s valuable to keep an open mind about all ideas that may be pitched throughout the course of the collaboration and involve people from different fields or areas of expertise.

It’s very important to respect other people’s ideas, especially if they have outside perspectives, and to be an active listener and learner. Positive encouragement and appreciation also go a long way, as I believe everyone should feel that their contributions are valued.


Q: What is your advice to students on how to navigate their time at Columbia? If they want to do research, what should they know or do to prepare?
If you think you would enjoy research, don’t hesitate to get started. I spent a significant portion of my undergrad hesitating to reach out to professors or get involved in research because I was nervous that I was under-qualified or would fail. In my opinion, as long as you like to solve problems and are motivated to pick up new skills, you can succeed. Taking classes in an area that interests you, reading existing research papers, and working on personal projects in which you quickly learn and apply new skills are all valuable ways to prepare for research. And if you start research and find that it is not for you, that is totally reasonable, and now you know!

I think Columbia has many opportunities for undergraduate research, and students shouldn’t hesitate to take advantage of these opportunities. However, too many opportunities may feel daunting, as so many options exist. In my opinion, successful research is only possible if you’re truly interested in the topic and want to see it progress, so I would encourage students to be judicious when considering new projects and aim for the ones you see yourself happy to work on. At the end of the day, that’s what matters most.


CS Welcomes New Faculty

Xia Zhou, Brian Borowski, and Kostis Kaffes join the department. They will facilitate research and learning in mobile computing, software systems, and networks.

Xia Zhou
Associate Professor
PhD Computer Science, University of California Santa Barbara 
MS Computer Science, Peking University 
BS Computer Science and Technology, Wuhan University 

Xia Zhou is an expert in mobile computing and networks whose research is focused on wireless systems and mobile health. Zhou joins Columbia after nine years at Dartmouth where she was the co-director of the Dartmouth Networking and Ubiquitous Systems and the Dartmouth Reality and Robotics Lab. At Columbia, she will direct the Mobile X Laboratory.


Brian Borowski
Lecturer in Discipline
PhD Computer Science, Stevens Institute of Technology 
MS Computer Science, Stevens Institute of Technology 
BS Computer Science, Seton Hall University 

Brian Borowski is an expert in software systems who aims to present a blend of theoretical and practical instruction so his students can be successful after graduation, regardless of the path they choose. He studied underwater acoustic communication and won several awards for his teaching at Stevens Institute of Technology.


Kostis Kaffes
Assistant Professor
PhD Electrical Engineering, Stanford University
MS Electrical Engineering, Stanford University
BS Electrical and Computer Engineering, National Technical University of Athens 

Kostis Kaffes is interested in computer systems, cloud computing, and scheduling across the stack. He arrives in Fall 2023 and will spend the next year doing research at Google Cloud with the Systems Research Group.