Sensor reads single photons ultrafast

In imaging, every single photon counts. Now, thanks to an ultrasensitive sensor, individual photons can be read within a few picoseconds, yielding high-quality images even in extremely low-light situations.

Fraunhofer Institute for Microelectronic Circuits and Systems IMS has advanced the development of CMOS technology and introduced a diode based on single-photon avalanche photodiodes. Its pixel structure can count single photons 1000 times faster than other models.

It is now possible to process digital image signals directly on the microchip, according to new research out of Fraunhofer Institute for Microelectronic Circuits and Systems.

Fast, ultrasensitive optical systems are becoming increasingly important for medical imaging procedures, astronomy and automobile safety engineering. Often, the challenge lies in recording high-quality images under extremely low-light conditions. If photons are lacking, modern CMOS and CCD photodetectors cannot guarantee high-quality images that are simultaneously fast and ultrasensitive.

The new image sensor uses the internal avalanche breakdown effect, a result of photoelectric amplification. The number of avalanche breakdowns corresponds to the number of photons the pixels hit. To number these events, each of the sensor’s pixels comes with precise digital counters.

At the same time, the researchers have applied microlenses to each sensor chip, which focus the incoming beam in each pixel onto the photoactive surface. Processing the digital image signals takes place directly on the microchip, removing the need for analog signal processing.

“The image sensor is a major step toward digital image generation and image processing,” said Dr. Daniel Durini, group manager for optical components at Fraunhofer IMS. “It allows us to have the capability to use even very weak light sources for photography. The new technology installs the camera directly on the semiconductor and is capable of turning the information from the light into images at a significantly faster pace.”

The technology currently is being used for traffic testing in applications such as chip-based mini-cameras that protect vehicles, bicycles and pedestrians from collisions, or to help seatbelts and airbags function reliably.

Next, the team plans to develop more powerful, backlit sensors.

The image sensor, developed in cooperation with partners of the MiSPiA project (Microelectronic Single-Photon 3-D Imaging Arrays for low-light high-speed Safety and Security Applications), was displayed at Vision 2012 in Stuttgart.