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.

Mapping the electromagnetic field confinement in the gap of germanium nanoantennas with plasma wavelength of 4.5 micrometers

“…The dielectric function of the 250 nm thick germanium film is determined, and bow-tie antennas are designed, fabricated, and embedded in a polymer. By using a near-field photoexpansion mapping technique at k ¼ 5.8 lm, we demonstrate the existence in the antenna gap of an electromagnetic energy density hotspot of diameter below 100 nm and confinement volume 10 5 times smaller than k Plasmonic nanoantenna designs are quickly evolving in the direction of practical molecular sensing applications 1 as their wavelength range is being extended from the visible towards the mid-infrared 2,3 (IR), where molecules indeed display unique spectral fingerprints (IR wavelengths k between 2.5 lm and 25 lm). The two main features of plasmonic nanoantennas are electromagnetic field enhancement and confinement in subwavelength regions.…”

Monolithically integrated mid-infrared sensor using narrow mode operation and temperature feedback

“…Dielectric-loaded surface plasmon polariton waveguides (SPPW) enable high efficiency radiation coupling between the laser and the detector and, at the same time, they serve as an interaction region. 14 The gap between the laser and the detector can be increased to 100 lm, which is sufficient to detect the absorption in liquid solutions. The introduction of the dielectric loaded SPP waveguide in the Quantum Cascade Laser/Detector (QCLD) system makes a big step towards advanced solutions in on-chip mid-infrared absorption spectroscopy.…”

“…The detailed description of the material is given elsewhere. 14 Device fabrication started with the definition of the first order DFB grating via electron beam lithography and reactive ion etching (RIE). The grating period was chosen to be 0.96 lm (corresponds to the emission at 1586 cm À1 ) with a nominal grating duty-cycle of 50% and nominal grating depth of 500 nm.…”

Diagonal-transition quantum cascade detector

“…12 A quantum cascade device that, under bias voltage, emits and, at zero bias, detects at the same wavelength was reported. 13,14 In this letter, we present the diagonal transition QCD, a design, where the active transition occurs between two energy levels, each localized in different, but adjacent wells. The same concept has been demonstrated for quantum cascade lasers, 15 by using a diagonal active transition, the upper laser lifetime could be increased, which eventually improved the slope efficiency and decreased the threshold current density.…”