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Monolithically integrated mid-infrared lab-on-a-chip using plasmonics and quantum cascade structures.

ABSTRACT: The increasing demand of rapid sensing and diagnosis in remote areas requires the development of compact and cost-effective mid-infrared sensing devices. So far, all miniaturization concepts have been demonstrated with discrete optical components. Here we present a monolithically integrated sensor based on mid-infrared absorption spectroscopy. A bi-functional quantum cascade laser/detector is used, where, by changing the applied bias, the device switches between laser and detector operation. The interaction with chemicals in a liquid is resolved via a dielectric-loaded surface plasmon polariton waveguide. The thin dielectric layer enhances the confinement and enables efficient end-fire coupling from and to the laser and detector. The unamplified detector signal shows a slope of 1.8-7 μV per p.p.m., which demonstrates the capability to reach p.p.m. accuracy over a wide range of concentrations (0-60%). Without any hybrid integration or subwavelength patterning, our approach allows a straightforward and cost-saving fabrication.

SUBMITTER: Schwarz B

PROVIDER: S-EPMC4059934 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Polarization-independent dielectric meta-lens is proposed to monolithically integrate with a HgCdTe infrared photodetector to concentrate power flux into a reduced photosensitive area for performance enhancement. Although a reduction in photosensitive area could suppress the dark current, the more seriously reduced light absorptance would degrade the specific detectivity D*. The integration of the meta-lens could reverse the situation by improving the absorptance of the photosensitive region. The meta-lens composed of an array of nano-pillars with varying diameters is formed by carving the CdZnTe substrate of the HgCdTe detector so that the integration could be accomplished in situ. The meta-lens focuses the incident light through the CdZnTe medium and at the HgCdTe photosensitive region. The focal spot is about the wavelength size and the focusing efficiency is above 63%. Concerning a HgCdTe detector with a pitch size of 40 μm × 40 μm, when the photosensitive area is reduced to 5 μm × 5 μm, the meta-lens could still keep the light absorptance above 50%, which is 49 times higher than that of the device without the meta-lens. The dark current reduces with the decreasing photosensitive area in a linear manner. When the photosensitive area shrinks from 40 μm × 40 μm to 10 μm × 10 μm or 5 μm × 5 μm, the dark current reduces by 16 or even 64 times. Compared to the pristine device, the employment of the meta-lens together with the reduction in photosensitive area could enhance D* by 5.5 times for the photosensitive area as 5 μm × 5 μm. Further, the meta-lens exhibits a good dispersion tolerance over the wavelength range from 3.3 μm to 5 μm. The averaged detectivity enhancement over this spectrum range is around 3 times for the photosensitive area as 5 μm × 5 μm. The angular response of the meta-lens integrated detector depends on the focal length. For a focal length of 73 µm or 38 µm, the angle of view for a 5 μm × 5 μm photosensitive area is 4.0° or 7.7°. For the inter-pillar distance to be 2 µm in our design, the influence of the coupling effect between the nano-pillars on the performance of the meta-lens is little.

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Monolithically integrated mid-infrared lab-on-a-chip using plasmonics and quantum cascade structures.

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