Conference Agenda

The advancement of hybrid integration technology for smaller electronics and photonics systems is exerting increased pressure on the development of new automated processes that enable reliable integration with high throughput. Simultaneously, the integration density and diversity of components in a package, including Micro-Electro-Mechanical Systems (MEMS), wafer-level optics, alongside photonics and III/V optoelectronics, are also on the rise.

To address these evolving needs, a novel integration approach based on laser-assisted bonding (LAB) is presented here. The developed LAB setup employs an original bottom illumination/irradiation architecture, coupled with simultaneous imaging through silicon, facilitating high-precision alignment for photonics waveguides. Moreover, the Automated Power Control of a LAB process enables overheat protection for the bonded surfaces, thereby enhancing the reliability and repeatability of the integration process.

In a practical demonstration, we showcase the effectiveness of the LAB process by applying it to integrate a multichannel 1x1mm III/V chip with a silicon photonic integrated circuit. The application of highly localized heat during the LAB process rapidly elevated the temperature of the photonic circuit above the pre-deposited solder layers' melting point. This, in turn, led to successful bond formation with impedance in the range of hundredths of an Ohm, accompanied by negligible thermal-induced stress to the bonded surfaces and minimal warpage.

These results not only validate the efficacy of the LAB process but also underscore its potential to push the boundaries of photonic integration. Particularly noteworthy is the rapid and energy-effective LAB process, featuring bottom illumination/irradiation and simultaneous through-silicon imaging. Thus, it facilitates bonding and active waveguide alignment—an essential aspect in achieving effective integration in the field of photonics. The obtained results contribute to advancing our photonic integration technology.

In the past couple of decades, optical coherence tomography (OCT) and photoacoustic imaging (PAI) have been developed and applied widely in biomedical and clinical research. Based on the interference of back-scattered light, OCT can reconstruct the sample in 3D with high resolution and high speed. Alternatively, PAI is a non-invasive modality that combines optical excitation and ultrasonic detection. It can be used to visualize absorption differences in tissues to construct the 3D images. In this work, we report on an assembly of a novel optical ultrasound detector for PAI. The sensor consists of an integrated optical micro-ring resonator (MRR) whose input and output waveguides are interfaced with optical fibers. These fibers are attached to specially developed miniature fiber holders which enable automated manipulation and firm attachment of the fibers to the waveguides. The sensor's application is related to the EU Horizon 2020 project REAP (www.projectreap.eu) as a part of development of versatile bioimaging platform focused on investigating drug-tolerant persister cancer cells. The compact dimensions and precision (fiber alignment with an accuracy of up to 0.1 um) of this device added a layer of intricacy to the undertaking.

The entire process of the device assembly is carried out at an automated station (from Ficontec) for micro-positioning, active/passive precision alignment, attachment via welding, soldering, bonding, and automated optical inspection. This station gives us several significant advantages, such as positioning accuracy, assembly time and reliability. The fiber folders comprise of U-grooved pieces of fused silica. Size of these chips can be selected from 1x1 mm2 to 3x2 mm2 with one or more grooves for fibers in the middle. Fibers can at first be attached and glued in the grooves of the holder. The holder can then be gripped and manipulated with an automated assembly station and aligned with the waveguides. Depending on the selected fiber the alignment tolerance is < 1 um. The progress of alignment is monitored by optical power through the waveguide. On the conference we shall report the achieved coupling loss, demonstrate the finished sensor device, and introduce our approach with a video of the precise alignment process.

COMPAS is an EU funded project (Grant ID 101135796) which main objective is to develop a compact, inexpensive and ultrasensitive photonic integrated circuit (PIC) sensing platform (PSP) for air and water monitoring, relying on the co-integration of light source, detectors and electronic IC for on-chip signal processing.

The sensing principle will rely on optical waveguide interferometers coated with optically active selective sensing layers. When a target molecule attaches to the sensing layer, the refractive index of that layer will change causing a slight phase shift in one of the modes of light. When the two modes rejoin, this change will be detected as an intensity change of the light passing through the waveguide.

A baseline PSP will rely on advanced assembly and packaging of individual components by PHIX, Europe's leading optical packaging supplier. The components, laser diode, waveguide chip and photodetectors will be assembled onto a submount. This will require high precision assembly in two directions (x and z) and require careful optical coupling.

An integrated variant of the PSP will also be developed. In this variant SINTEF will develop and process silicon wafers with integrated photodetectors, onto which they will also fabricate the optical waveguides. This allows for high accuracy alignment between these components. A laser diode light source, developed and produced by Lancaster University, will be flip chip mounted on the other end of the wave guide. Meta-surfaces on the top of the waveguides will increase the orthogonal light coupling needed.

The project will develop novel micro fluidic solutions to feed the sensing surfaces with liquid or gas in a controlled manner. The readout and analysis of the optical signal will be done by a novel analogue electronics concept developed by Oliveris.

This paper will go through the challenges and proposed solutions of the COMPAS PSP.