Mid-infrared photonics in silicon needs low-loss integrated waveguides. While monocrystalline germanium waveguides on silicon have been proposed, experimental realization has not been reported. Here we demonstrate a germanium strip waveguide on a silicon substrate. It is designed for single mode transmission of light in transverse magnetic (TM) polarization generated from quantum cascade lasers at a wavelength of 5.8 μm. The propagation losses were measured with the Fabry-Perot resonance method. The lowest achieved propagation loss is 2.5 dB=cm, while the bending loss is measured to be 0.12 dB for a 90°bend with a radius of 115 μm.

At the end of the 1970s, it was confirmed that dielectric multilayers can sustain Bloch surface waves (BSWs). However, BSWs were not widely studied until more recently. Taking advantage of their high-quality factor, sensing applications have focused on BSWs. Thus far, no work has been performed to manipulate and control the natural surface propagations in terms of defined functions with two-dimensional (2D) components, targeting the realization of a 2D system. In this study, we demonstrate that 2D photonic components can be implemented by coating an in-plane shaped ultrathin ( l/15) polymer layer on the dielectric multilayer. The presence of the polymer modifies the local effective refractive index, enabling direct manipulation of the BSW. By locally shaping the geometries of the 2D components, the BSW can be deflected, diffracted, focused and coupled with 2D freedom. Enabling BSW manipulation in 2D, the dielectric multilayer can play a new role as a robust platform for 2D optics, which can pave the way for integration in photonic chips. Multiheterodyne near-field measurements are used to study light propagation through micro-and nano-optical components. We demonstrate that a lens-shaped polymer layer can be considered as a 2D component based on the agreement between near-field measurements and theoretical calculations. Both the focal shift and the resolution of a 2D BSW lens are measured for the first time. The proposed platform enables the design of 2D all-optical integrated systems, which have numerous potential applications, including molecular sensing and photonic circuits. Keywords: Bloch surface wave; 2D optics; manipulation; micro-and nano-optics; nanophotonics; platform INTRODUCTION One or several elements are considered to comprise a two-dimensional (2D) optical system if they fulfill two conditions. First, the in-plane light propagation must have two spatial non-imaginary propagation constants. Second, the corresponding optical elements should have a 2D degree of freedom in shape. The previous statements may appear to imply that the reduction from three-dimensional (3D) to 2D is primarily a reduction in the degree of freedom. However, one of the main advantages is that 2D elements can have arbitrary shapes, which is difficult to achieve in 3D.There are various methods for addressing a 2D optical environment. One approach is represented by the use of wave-guiding media wherein the light is confined and propagated in a sandwiched structure. However, in the case of slab waveguides, the light is almost completely buried in the inner layers of the waveguide; thus, direct spatial mapping remains difficult or impossible. As an alternative to waveguides, a second route for 2D optics is represented by surface plasmons (SPPs) on smooth planar or structured metallic films. SPPs are electronic-electromagnetic modes sustained at an appropriate metallic/dielectric interface wherein the field reaches its maximum intensity at the surface of the metal.

A germanium (Ge) strip waveguide on a silicon (Si) substrate is integrated with a microfluidic chip to detect cocaine in tetrachloroethylene (PCE) solutions. In the evanescent field of the waveguide, cocaine absorbs the light near 5.8 mm, which is emitted from a quantum cascade laser. This device is ideal for (bio-)chemical sensing applications.

We present a portable microsystem to quantitatively detect cocaine in human saliva. In this system, we combine a microfluidic-based multiphase liquid-liquid extraction method to transfer cocaine continuously from IR-light-absorbing saliva to an IR-transparent solvent (tetrachloroethylene) with waveguide IR spectroscopy (QC-laser, waveguide, detector) to detect the cocaine on-chip. For the fabrication of the low-cost polymer microfluidic chips a simple rapid prototyping technique based on Scotch-tape masters was further developed and applied. To perform the droplet-based liquid-liquid extraction, we designed and integrated a simple and robust droplet generation method based on the capillary focusing effect within the device. Compared to well-characterized and commonly used microfluidic H-filters, our system showed at least two times higher extraction efficiencies with potential for further improvements. The current liquid-liquid extraction method alone can efficiently extract cocaine and pre-concentrate the analytes in a new solvent. Our fully integrated optofluidic system successfully detected cocaine in real saliva samples spiked with the drug (500 μg/mL) and allowed real time measurements, which makes this approach suitable for point-of-care applications.

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We present a room temperature operated 5.35μm quantum cascade detector which was tested at high frequencies using an optical heterodyne experiment. Two slightly detuned continuous wave distributed feedback single mode quantum cascade lasers were used to generate a beating signal. The maximum frequency at which the resulting microwave signal could be detected was 23GHz. The cutoff behavior of our device was modeled with a simple RLC circuit and showed excellent agreement with the experimental data.

A measurement of the linewidth enhancement factor α of a distributed feedback quantum cascade laser is presented. The measurement is based on a heterodyning experiment, in which one of the lasers is modulated at radio frequency. A value of α=0.02±0.20 is obtained for a modulation frequency of 500MHz. As the frequency is decreased, α increases and is consistent with a thermal chirp effect.

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