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 22nm,with which a sensitivity of up to 91 dB(830μW) and an axial resolution of 10.7 pm was measured.Design 2 supports a bandwidth of 48 nm,with which a sensitivity of 90 dB(480μW) and an axial resolution of 6.5μm 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.

CMOS optoelectronic spectrometer based on photonic integrated circuit for in vivo 3D optical coherence tomography

Photonic integrated circuits(PICs)represent a promising technology for the muchneeded medical devices of today.Their primary advantage lies in their ability to integrate multiple functions onto a single chip,thereby reducing the complexity,size,maintenance requirements,and costs.When applied to optical coherence tomography(OCT),the leading tool for state-of-the-art ophthalmic diagnosis,PICs have the potential to increase accessibility,especially in scenarios,where size,weight,or costs are limiting factors.In this paper,we present a PIC-based CMOS-compatible spectrometer for spectral domain OCT with an unprecedented level of integration.To achieve this,we co-integrated a 512-channel arrayed waveguide grating with electronics.We successfully addressed the challenge of establishing a connection from the optical waveguides to the photodiodes monolithically co-integrated on the chip with minimal losses achieving a coupling efficiency of 70%.With this fully integrated PIC-based spectrometer interfaced to a spectral domain OCT system,we reached a sensitivity of 92dB at an imaging speed of 55kHz,with a 6dB signal roll-off occurring at 2mm.We successfully applied this innovative technology to obtain 3D in vivo tomograms of zebrafish larvae and human skin.This ground-breaking fully integrated spectrometer represents a significant step towards a miniaturised,cost-effective,and maintenance-free OCT system.