A team of researchers from the University of Toulouse in France is using two-photon polymerization 3D printing to reduce the divergence of a vertical laser diode to be integrated into a compact optical gas sensor.
The demand for wearable gas sensors is steadily increasing in environmental and health sciences as well as in industry. Optical resonance sensors, especially planar microresonators, offer high sensitivity and compact size, ideal for these applications. Researchers at the University of Toulouse developed a compact optical microsystem for ammonia gas detection. The light source is an infrared-emitting VCSEL (vertical cavity surface emitting laser), a semiconductor laser that is easy to spectrally tune and has high polarization stability.
However, the beam divergence of the VCSEL chip is too large for common applications in optical microsystems. Reducing the spot size to below 100µm is necessary for optimal results. Since commercially available VCSEL chips with lower divergence are not yet available, the challenge was to integrate a collimating microlens directly on the chip.
The scientists presented their solution in the Journal of Optical Microsystems: they used 2-photon polymerization 3D printing to create a microlens in just one step. The beam divergence could thus be reduced from 14.4° to 3°, which corresponds to a spot size of only 55 µm. They also analyzed the effects of lens addition on the spectral properties of the device and came up with an improved design. Their research demonstrates the potential of 2-photon polymerization 3D printing for post-assembly collimation of VCSELs and paves the way for optimized laser chips in portable optical measurement systems.
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