A megapixel camera, based on time-gated, single-photon avalanche diode (SPAD) image sensors, has been developed at École polytechnique fédérale de Lausanne (EPFL). The camera can detect single photons and convert them into electrical signals at a rate of about 150 million times per second. It has a 24,000-frame-per-second (FPS) frame rate and features 3.8-ns time gating. Because of its time-gating speed, the camera can be used to capture extremely fast motion or to increase the dynamic range of an acquired image. The camera’s developers began by creating tiny SPAD pixels and reducing the power consumption of each pixel to less than 1 µW. To reduce pixel size and power requirements, the researchers used a feedback mechanism that could quench the electron avalanche triggered by photon detection almost immediately. This improved the overall performance and reliability of the pixels. Researchers have developed the first megapixel photon-counting camera based on single-photon avalanche diode (SPAD) image sensors. The new camera can capture images in faint light at unprecedented speeds. Courtesy of Arianna M. Charbon, Kazuhiro Morimoto, Edoardo Charbon. The researchers used enhanced layout techniques to pack the SPAD sensors tightly, improving the detection area density and enabling the camera to hold a million pixels. The array size of the sensor is almost 4 times higher than that of other sensors, while the pixel pitch is one of the smallest. The researchers then applied integrated circuit design techniques to create a uniform distribution of fast electrical signals over the large-scale pixel array. The team used the sensor to capture 2D and 3D scenes over 2 miles with resolution of 5.4 mm and precision greater than 7.8 mm. The camera’s extended dynamic range in dual exposure operation mode was demonstrated, and spatially overlapped multi-object detection was demonstrated in single-photon, time-gated, time-of-flight experiments. Shutter speeds varied by only 3% over the million pixels, demonstrating that the sensor could feasibly be made using available mass-production techniques. By combining time-of-flight information with the ability to capture a million pixels simultaneously, the camera enables 3D images to be reconstructed at extremely high speeds. The researchers said that the camera was able to capture complex scenes that are difficult for other imaging techniques to measure, such as an object viewed through a partially transparent window, and that it was able to take conventional images at unprecedented dynamic ranges. The researchers plan to further improve the performance and timing resolution of the camera and to further miniaturize the components to make the camera more practical for a variety of applications, such as augmented reality and lidar systems for autonomous vehicles. “Thanks to its high resolution and ability to measure depth, this new camera could make virtual reality more realistic and let you interact with augmented reality information in a more seamless manner,” professor Edoardo Charbon said. Charbon developed the idea for the new camera and is the founder and head of the Advanced Quantum Architecture Laboratory (AQUALab), where the image sensor was designed. “For transportation applications, this new camera could help achieve unprecedented levels of autonomy and safety by enabling multiple low-power lidar devices to be used on a vehicle, providing fast, high-resolution 3D views of the surroundings,” researcher Kazuhiro Morimoto said. “In a somewhat more distant future, quantum communication, sensing, and computing could all benefit from photon-counting cameras with multi-megapixel resolution.” The research was published in Optica (www.doi.org/10.1364/OPTICA.386574).