The demand for portable gas sensors is increasing in both environmental and health sciences industries. Resonant optical sensors, such as planar micro-resonators, offer a combination of high sensitivity and a compact design, making them suitable for these applications.
The sensing principle of guided-wave sensors is based on the variation in their spectral response when exposed to target molecules. The laser used to probe these spectral shifts should emit a single-mode and polarization-stable beam, with the ability to be spectrally tuned.
A team of researchers from the University of Toulouse in France set out to create a compact optical microsystem for ammonia gas detection using a near infra-red single-mode laser diode source called a vertical cavity surface emitting laser (VCSEL).
VCSELs are compact semiconductor laser diodes that can be tuned over a few nanometers by adjusting the operating current. The specific VCSEL chip used in this study includes a grating relief etched at its surface, ensuring a stable polarization of the emitted beam. However, the beam divergence of this VCSEL chip is too large for most optical microsystems, requiring a method to integrate a collimation microlens directly onto the small-sized VCSEL chip.
Published in the Journal of Optical Microsystems, the researchers demonstrated that 2-photon-polymerization 3D printing could be used to fabricate a microlens for the VCSEL chip in just 5 minutes. They optimized the lens design and fabrication conditions to achieve a suitable surface quality and focal length. This reduced the beam divergence from 14.4° to 3° and improved the beam spot size to 55µm at a distance of 2 mm. The researchers also studied the effects of the lens on the device’s spectral properties and proposed a new design to maintain the tuning range.
This work showcases the potential of 2-photon-polymerization 3D printing as a rapid and accurate method for collimating VCSELs, opening the path for the development of optimized laser chips integrated into portable optical sensing systems.
More information:
Qingyue Li et al, Direct 3D-printing of microlens on single mode polarization-stable VCSEL chip for miniaturized optical spectroscopy, Journal of Optical Microsystems (2023). DOI: 10.1117/1.JOM.3.3.033501
Citation: Rapid fabrication of a polymer lens on a laser chip for miniaturized spectroscopy (2023, July 14) retrieved 14 July 2023 from https://phys.org/news/2023-07-rapid-fabrication-polymer-lens-laser.html
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