Researchers turn a small photonic chip into a functional temperature sensor

Similar to electronics, photonic circuits can be miniaturized on a chip, resulting in a so-called photonic integrated circuit (PIC). Although these developments are more recent than for electronics, this field is developing rapidly. However, one of the main issues is to convert such a PIC into a functional device. This requires optical packaging and coupling strategies to bring light in and get light out of the PIC.

For example, for optical communication, a connection must be made to optical fibers, which then transport the light pulses over long distances. Alternatively, the PIC may house an optical sensor that requires external light for its readout.

Since light on a PIC propagates in very small channels with sub-micrometer dimensions, called waveguides, this optical coupling is very challenging and requires careful alignment between the PIC and external components. The optical components are also very fragile, so proper packaging of the PIC is essential to result in a reliable device.

The research team of prof. Van Steenberge and prof. Jeroen Missinne at Ghent University and imec are developing solutions to overcome the packaging and integration challenges associated with PICs for next-generation telecommunications systems, sensors and biomedical devices.

One of their activities is focused on using very small lenses (microlenses) to more easily connect the optical channels on PICs to external optical fibers or other elements. They demonstrated microlenses that can be integrated into the PIC itself during the manufacturing process or external microlenses that are added during the packaging process.

The latter is the subject of a recent paper in the Journal of Optical Microsystems.

A small ball lens with a 300 um diameter was used to create an efficient connection between a sensor on a PIC and a optical fiber which can be connected to standard readout equipment.

In addition, the paper describes the input steps required to transform the PIC into a functional and fully packaged miniature sensor probe (less than 2 mm in diameter). The type of optical sensor developed in this demonstration was a Bragg grating Temperature sensor which can measure up to 180°C.

The sensor is realized in the framework of the European SEER project together with Argotech (Czech Republic) and the Photonics Communication Research Laboratory at the National Technical University of Athens (Greece). In this project, several European partners focus on the integration of optics sensors in the manufacturing routines for making composite parts such as those used in aircraft, which will ultimately allow process optimization, energy savings and cost savings.