AlGaN/GaN-based high electron mobility transistors (HEMTs), Schottky diodes and/or resistors have been presented as sensing devices for mechanical or chemical sensors operating in extreme conditions. Creation of appropriate diaphragms and/or cantilevers out of substrate materials is necessary for further improvement of sensing properties of such MEMS sensors. The sensitivity of the AlGaN/GaN based MEMS pressure sensor can be modified by membrane thickness. In case of SiC as substrate material of the epitaxial AlGaN/GaN heterostructure layers, we applied laser ablation technique for micromachining of the membranes. We were able to verify the feasibility of this process by fabrication of micromechanical membrane structures also in bulk 3C-SiC, borosilicate glass, sapphire and Al₂O₃ ceramic substrates by femtosecond laser (520 nm) ablation. On a 350 µm-thick 4H-SiC substrate we produced an array of 275 µm deep and 1000–3000 µm in diameter blind holes without damaging the 2 µm GaN layer at the back side. Our experiments indicate that pinhole defects in the ablated membranes are affected by ripple structures related to the polarization of the laser. We developed an ablation technique inhibiting the formation of pin holes caused by laser induced periodic surface structures (LIPSS).

Benefits and Limits of Modulation Formats for Optical Communications

Transmission Transparency and Potential Convergence of Optical Network Solutions at the Physical Layer for Bit Rates from 2.5 Gbps to 256 Gbps

In this paper we investigate optical properties of 1×16 splitters based on Y-branch and MMI approaches. These splitters were designed, simulated and the obtained results of both approaches were studies and compared with each other. Additionally, we will show that the used standard waveguide core size (usually 6 × 6 μm² to match the diameter of the single mode input/output fibers, i.e. to keep the coupling loses as low as possible) supports not only propagation of the single mode but of the first mode too, leading to an asymmetric splitting ratio (increasing non-uniformity of the split power over all the output waveguides). Decreasing waveguide core size it is possible to suppress presence of the first mode and this way to reduce non-uniformity.

This article presents extensive research and analysis of the location capability of Bluetooth low energy (BLE) in designing real-time location systems (RTLSs). The main assumptions for the proposed approach are to optimize precision of location to less than 2 m, its reach up to 20 m, and system response time not exceeding 5 s. In addition, the system should be characterized by low energy consumption, and low construction and operating costs. In order to meet the above assumptions, extensive studies of received signal strength indicator (RSSI) radio signal parameters and time interval (TI) parameters were carried out. The tests were performed at a distance of 1 to 20 m for different types of emitter (beacon)–scanner pairs (microprogrammable platform). Detailed studies of location accuracy were performed using several nonlinear regression methods. The selection and assessment of the reliability of the approximating models was based on the information criterion measures and cross-validation. The influence of the training set size and the test set size on the adopted model’s reliability was examined. Based on TI values, predicted response time was estimated for real-time localization, and the relationship between system dynamics and localization accuracy was investigated.

In this paper, we present a Fiber Bragg Grating interrogator combining wavelength and time division multiplexing to increase the number of interrogation up to 800 independent gratings. The unit consists of a super luminescent light emitting diode, a variable electro-optical attenuator and a spectrometer. The wavelength range is 85 nm spanning through the S, C and L optical communication bands. High variability is assured by independent settings of time delay and optional signal enhancement for each individual time window with simultaneous wavelength multiplexing. The variability of the setup is advantageous for such an application as in Civil and Mechanical engineering where large numbers of gratings or groups of gratings are used and allows to measure a wide range of setups of Fiber Bragg Gratings.