We report on the progress of our efforts to apply silicon nitride photonic integrated circuits (PIC) to the miniaturization of optical coherence tomography (OCT) with the goal of facilitating its widespread use in ophthalmology at the point of care. In particular, we highlight the design and optical characterization of photonic building blocks allowing the realization of a silicon nitride PIC-based multi-channel swept-source OCT system in the 1060 nm wavelength region. Apart from waveguide structures, these building blocks include 3D-printed microlenses on the PIC end facets for efficient light coupling to and from the PIC.
We present a miniaturized optical coherence tomography (OCT) setup based on photonic integrated circuits (PIC) for the 850 nm range. We designed a 512-channel arrayed waveguide grating (AWG) on a PIC for spectral domain OCT (SD-OCT) that is co-integrated with PIN-photodiodes and analog-to-digital-converters on one single chip. This image sensor is combined with all the necessary electronics to act as a camera. It is integrated into a fiber-based OCT system, achieving a sensitivity of >80dB and various samples are imaged. This optoelectronic system will allow building small and cost-effective OCT systems to monitor retinal diseases.
The miniaturization of optical coherence tomography (OCT) systems could open up potential new markets, such as point-of-care application, home OCT to regularly monitor disease and treatment progress, and in low-resource settings. Photonic integrated circuits (PIC) are considered an attractive approach to miniaturize OCT. We present our recent achievements in in vivo retinal imaging with a PIC-based Mach-Zehnder interferometer integrated in a state-of-the-art ophthalmic OCT system. The system achieves 94 dB at 750 µW on the sample, running at 50 kHz. Preliminary results of a fully packaged 4-channel opto-electronic OCT engine further demonstrate the potential of PIC-based OCT.
We report on a swept-source OCT system based on a photonic-electronic integrated circuit. It enables a parallelization of data acquisition resulting in an effective A-scan rate of 4x100 kHz at a central wavelength of 840 nm.
The monolithic co-integration of photonic elements forming the multiplexed interferometers and the system electronics on one chip allows a very compact OCT engine in a photonic package. Integrated in an ophthalmic system, the maximum sensitivity was estimated to be 91 dB with an optical power of 4x520 µW at the model eye. An eye phantom was imaged at 400 kHz showing its layered structure.
Silicon nitride waveguide based photonic integrated circuits (PICs) are intensively investigated for a wide range of sensing applications in the visible to sub 1-µm near-infrared spectral region. The monolithic co-integration of silicon photodiodes and read-out electronics offers additional benefits in terms of performance and miniaturization. We discuss challenging aspects related to the efficient coupling and routing of light to, from, and within PICs and present interfacing photonic building blocks offering potential solutions. We demonstrate the suitability of these interfacing building blocks by using them for the realization of a PIC-based multi-channel optical coherence tomography concept at 840 nm.
In this paper, we report our recent advances in the development of CMOS compatible PECVD silicon nitride waveguide based photonic key building blocks for optical coherence tomography (OCT) in the 850 nm wavelength region and for biosensing applications in the visible domain around 650 nm wavelength. We discuss the design and experimental verification of compact low-loss waveguide bends, broadband couplers with varying power splitting ratios required for PIC based OCT systems, arrayed waveguide gratings for spectral domain OCT, and a monolithically integrated optically pumped organic solid-state laser for low-cost biosensing applications.
A swept source optical coherence tomography (SS-OCT) system with the interferometer engine being a photonic integrated circuit (PIC) has been developed. Furthermore, an Arrayed Waveguide Grating (AWG), representing a grating on a PIC, for spectral domain OCT (SD-OCT) has been integrated in a fiber-based OCT system. With measured sensitivities of ~87 dB (SS-OCT) and ~80 dB (SD-OCT), scattering tissue imaging becomes feasible for OCT-on-chip systems. In this study, we present two OCT-on-chip systems and first results of biological tissue imaging in-vivo and exvivo.
We report several PECVD silicon nitride photonic building blocks required for the implementation of a CMOS-compatible photonic integrated circuit technology platform operating in the 850 nm and 600 nm wavelength domain. In particular, for the 850 nm wavelength region we discuss a low-loss broadband 1x2 power splitter and a loop mirror. In the 600 nm wavelength region, we present new results on an optically pumped integrated dye-doped polymer laser that couples its light directly into a silicon nitride waveguide. Moreover, we discuss design considerations for a waveguide based gas sensing concept detecting target gas specific absorption changes in a thin dye-doped polymer cladding layer.
We report the simulation, design and experimental validation of various PECVD silicon nitride photonic building blocks required for the implementation of a CMOS-compatible photonic integrated circuit technology platform operating in the 850 nm and 600 nm wavelength domain. In particular, we discuss an inverted taper structure for efficient coupling of light to and from the chip, propagation and bend losses as well as broadband power and polarization beam splitters in the 850 nm region. In the 600 nm wavelength region, we demonstrate the realization of an optically pumped integrated dye-doped polymer laser that couples its laser light directly into a silicon nitride waveguide.
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