Researchers Turn Tiny Photonic Chips Into Functional Temperature Sensors

Similar to electronics, photonic circuits can be miniaturized onto chips, resulting in photonic integrated circuits (PICs). Although these developments are later than those in electronics, the field is witnessing rapid development in recent years.
However, a major challenge is how to convert such a PIC into a functional device - this requires optical packaging and coupling strategies to bring light into the PIC and take light out of the PIC.
For example, for optical communications, optical fibers are needed to make connections and then transmit light pulses over long distances. Alternatively, the PIC could house an optical sensor that requires external light to read.
Because the light on the PIC travels in very small channels (called "waveguides") of sub-micron dimensions, this optical coupling is very challenging and requires careful alignment between the PIC and the external components. The optics are also very fragile, so proper packaging of the PIC is critical to producing a reliable device.
The research groups 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 telecom systems, sensors and biomedical devices.
One of their efforts is to use very small microlenses to more easily connect optical channels on PICs to external optical fibers or other components. Finally, they succeeded in demonstrating microlenses that can be integrated into the PIC itself during fabrication or external microlenses that can be added during packaging.
The latter was the subject of a paper recently published in the Journal of Optical Microsystems.
During the course of the study, a small ball lens, 300 microns in diameter, was used to create an effective connection between the sensors on the PIC and an optical fiber that could be connected to a standard readout device.
In addition, the paper describes the import steps required to convert the PIC into a functional and fully encapsulated miniature sensor probe (less than 2 mm in diameter). The type of optical sensor developed in this demonstration is a Bragg grating temperature sensor that can measure up to 180°C.
The sensor was realized within the framework of the European SEER project with Argotech (Czech Republic) and the Photonics Communication Research Laboratory of the National Technical University of Athens (Greece).
In this project, several European partners focus on the integration of optical sensors into manufacturing processes for the fabrication of composite components such as aircraft, ultimately leading to process optimization, energy and cost savings.