Photonics is becoming an increasingly important platform for the next generation of sensors in Lab-on-a-Chip (LOC) devices. Such devices should be self sufficient, cost effective, extremely portable, sensitive to low concentrations, and compatible with the environment for which they are designed, from hard environmental conditions to delicate living organisms. In this Optical Materials Express article, A. Lefebvre and co-workers propose the first building block for on-chip, cost-effective and efficient infrared thermal sources, which are an essential part of integrated non-dispersive infrared (NDIR) gas spectrometers, such as CO₂ sensors.

The authors describe a method, which uses CMOS compatible materials and processes, to fabricate such narrowband mid-infrared emitters. The basic platform is the well-known metal-insulator-metal (MIM) structure, which generates a high field enhancement in the few-nanometres-thin insulator layer and a narrow-tuneable resonance as a function of its geometrical dimensions. The authors present simulations and experiments showing that a periodic arrangement of MIM structures (period = 1.5 μm, widths from 800 to 653 nm) possesses narrow resonances varying between 2000 cm¯¹ and 3000 cm¯¹ as a function of the width of each MIM patch. It is also possible to combine structures of different dimensions in the same chip, yielding separate spectral lines, which are useful in a reference-probe experiment. Furthermore, the devices are polarization- and angle-insensitive, which enormously simplifies the design and the fabrication of this kind of emitters.

Finally, the authors demonstrate, as proof of principle, how these emitters perform when directly excited by a heat source. Although the emissivity data are still noisy, they clearly show promise for the use of this platform in future, highly sensitive, cost-effective and compact gas sensors.

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