Smart pixels for real-time optical coherence tomography

Optical Coherence Tomography (OCT) is an optical imaging technique allowing the acquisition of three-dimensional images with micrometer resolution. It is very well suited to cross-sectional imaging of highly scattering materials, such as most biomedical tissues. A novel custom image sensor based on smart pixels dedicated to parallel OCT (pOCT) is presented. Massively parallel detection and signal processing enables a significant increase in the 3D frame rate and a reduction of the mechanical complexity of the complete setup compared to conventional point-scanning OCT. This renders the parallel OCT technique particularly advantageous for high-speed applications in industrial and biomedical domains while also reducing overall system costs. The sensor architecture presented in this article overcomes the main challenges for OCT Using parallel detection such as data rate, power consumption, circuit size, and optical sensitivity. Each pixel of the pOCT sensor contains a low-power signal demodulation circuit allowing the simultaneous detection of the envelope and the phase information of the optical interferometry signal. An automatic photocurrent off-set-compensation circuit, a synchronous sampling stage, programmable time averaging, and random pixel accessing are also incorporated at the pixel level. The low-power demodulation principle chosen as well as alternative implementations are discussed. The characterization results of the sensor exhibit a sensitivity of at least 74 dB, which is within 4dB of the theoretical limit, of a shot-noise limited OCT system. Real-time high-resolution three-dimensional tomographic imaging is demonstrated along with corresponding performance measurements.