Toward optical coherence tomography on a chip: in vivo three-dimensional human retinal imaging using photonic integrated circuit-based arrayed waveguide gratings.

In this work, we present a significant step toward in vivo ophthalmic optical coherence tomography and angiography on a photonic integrated chip. The diffraction gratings used in spectral-domain optical coherence tomography can be replaced by photonic integrated circuits comprising an arrayed waveguide grating. Two arrayed waveguide grating designs with 256 channels were tested, which enabled the first chip-based optical coherence tomography and angiography in vivo three-dimensional human retinal measurements. Design 1 supports a bandwidth of 22 nm, with which a sensitivity of up to 91 dB (830 µW) and an axial resolution of 10.7 µm was measured. Design 2 supports a bandwidth of 48 nm, with which a sensitivity of 90 dB (480 µW) and an axial resolution of 6.5 µm was measured. The silicon nitride-based integrated optical waveguides were fabricated with a fully CMOS-compatible process, which allows their monolithic co-integration on top of an optoelectronic silicon chip. As a benchmark for chip-based optical coherence tomography, tomograms generated by a commercially available clinical spectral-domain optical coherence tomography system were compared to those acquired with on-chip gratings. The similarities in the tomograms demonstrate the significant clinical potential for further integration of optical coherence tomography on a chip system. The goal of an optical coherence tomography (OCT) imaging system that is integrated on a photonic chip has taken a step closer to reality. Elisabet Rank and coworkers from Austria have shown that arrayed waveguide gratings (AWGs), integrated-optical devices commonly used to separate different wavelength channels in an optical communications system, can be used to replace diffraction gratings in an OCT system. Several designs of silicon nitride AWGs with 256 channels in the near-infrared were fabricated and then tested in an OCT system which was able to capture in-vivo tomograms and angiography of the human eye’s retina, with comparable quality to a conventional system. The next stage of the OCT-on-a-chip research will focus on exploring the use of multimode interference structures, integrated photodiodes, and compact light sources.