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.
Managing the temperature of photonic chips within intricate electro-optic packages poses a notable challenge concerning the thermal crosstalk between the photonic chip, electronic chip, and the chip–fiber connection point. This is a multifaceted problem and requires packaging solutions that cannot only address high-performance thermal management but must also be scalable to high volumes. Glass has long been thought of as a suitable platform for next-generation photonic packaging due to its low thermal conductivity, which minimizes unwanted heat transfer between electronic and photonic components. Achieving proper thermal isolation between the chips and the chip–fiber interface necessitates a microscale thermal solution that guarantees accurate temperature regulation of the photonic circuitry without disrupting the optical coupling interface with the fiber array, due to the presence of epoxy used for fiber attachment. We propose a technique for the development of a substrate-integrated microthermoelectric cooler (SimTEC) for the effective temperature control of the electronic and photonic integrated devices. The proposed device uses glass substrate vias that are half-filled with p and n-type thermoelectric materials and the other half with copper. A COMSOL multiphysics model is developed to study the variations in the cooling performance of this SimTEC device based on changes in the via parameters. Interestingly, the maximum range of temperature gradient variation for SimTEC is 6 times greater compared to that of equivalent free-standing micro-TEC pillars. However, there are some challenges associated with implementing this method, as the temperature gradient (or cooling effect) achieved by SimTEC still falls short of that achieved by the free-standing micro-TEC pillars.
Micro-transfer printing (μTP) has been widely used to integrate photonic components, such as lasers, modulators, photodetectors, micro-LEDs, on Si photonic platforms. There is a push toward the μTP of optical components in photonics packaging as it enables wafer-scale integration with high alignment accuracy. We demonstrate for the first time the μTP of thick optical components, such as micro-lenses, in the range of 250 to 1000 μm thickness. We explore the reliability of bonding such components using an ultraviolet (UV) curable epoxy and compare them with the current state of the art. The results show that the average shear strength of lenses bonded with InterVia is 19 MPa which is higher than currently used optical epoxies. Also, μTP process has no effect on the surface roughness and microstructure of lenses. Using our approach, we demonstrate how thick silicon and fused silica lenses can be integrated into photonic integrated circuits (PICs) using a tether-free process that is highly scalable and robust.
The challenges associated with the photonic packaging of silicon devices is often underestimated and remains technically challenging. In this paper, we review some key enabling technologies that will allow us to overcome the current bottleneck in silicon photonic packaging; while also describing the recent developments in standardisation, including the establishment of PIXAPP as the worlds first open-access PIC packaging and assembly Pilot Line. These developments will allow the community to move from low volume prototype photonic packaged devices to large scale volume manufacturing, where the full commercialisation of PIC technology can be realised.
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