FG Theoretische Elektrotechnik
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Integrated and fiber-packaged magnetic field sensors with a sensitivity sufficient to sense electric pulses propagating along nerves and a spatial resolution fine enough to resolve their propagation directions will trigger tremendous steps ahead in medical diagnostics and research. Nitrogen-vacancy centers in diamond are best suitable for such sensing tasks under ambient conditions. Current research on uniting a good sensitivity and high spatial resolution is facilitated by scanning or imaging techniques. However, these techniques employ moving parts or bulky microscopes. Both approaches cannot be miniaturized to build robust, adjustment-free, hand-held devices. In this work, we introduce concepts for spatially resolved magnetic field sensing and two-dimensional gradiometry with an integrated magnetic field camera. The camera utilizes infrared absorption optically detected magnetic resonance (IRA ODMR) mediated by perpendicularly intersecting infrared and pump laser beams forming a pixel matrix. We demonstrate our scalable 3 ×3 pixel sensor’s capability to reconstruct the position of an electromagnet. In a reference measurement, we show an IRA ODMR sensitivity of 44 nT Hz−1/2.
The design and optimization of optical components, such as Bragg gratings, are critical for applications in telecommunications, sensing, and photonic circuits. To overcome the limitations of traditional design methods that rely heavily on computationally intensive simulations and large data sets, we propose an integrated methodology that significantly reduces these burdens while maintaining high accuracy in predicting optical response. First, we employ a Bayesian optimization technique to strategically select a limited yet informative number of simulation points from the design space, ensuring that each contributes maximally to the model’s performance. Second, we utilize singular value decomposition to effectively parametrize the entire reflectance spectrum into a reduced set of coefficients, allowing us to capture all significant spectral features without losing crucial information. Finally, we apply XGBoost, a robust machine learning algorithm, to predict the entire reflectance spectra from the reduced data set. The combination of Bayesian optimization for data selection, singular value decomposition (SVD) for full-spectrum fitting, and XGBoost for predictive modeling provides a powerful and generalizable framework for the design of optical components.
This article reports on an interlaboratory measurement comparison involving on-wafer S-parameter measurements from 10 GHz to 1.1 THz. Seven laboratories are involved, and each participant has measured an individual reference substrate fabricated from a high-resistivity silicon wafer in the same batch. One- and two-port co-planar waveguide (CPW) structures are designed, simulated, and fabricated. The measurements from 10 GHz to 1.1 THz, extending across six frequency bands, are conducted using different equipment in terms of vendors and specifications (e.g., probe pitch size). Despite such differences, this interlaboratory study has shown a generally good agreement between results from different participants when uncertainties are considered. The comparison with simulated reference values demonstrates agreement within 0.08 for |S11| and 2 dB for |S21| measurements of matched devices up to 1.1 THz. The measurement comparison demonstrates the need for a standardized measurement approach and, with that, a potential to achieve accurate on-wafer CPW measurements up to THz frequencies, underpinning the development of integrated circuits for such high frequencies.
Radio frequency (RF) AlGaN/GaN high‐electron‐mobility transistors (HEMTs) on semi‐insulating GaN substrates showed an unexpectedly low output power of ≤1.7 W mm⁻¹ and a power added efficiency (PAE) of ≤15% for Vds = 20 V at 20 GHz, despite their good DC current densities (>1 A mm⁻¹) and minor trapping effects in pulsed characterization, comparable to GaN‐on‐SiC HEMTs. With theoretical calculations of Pout and PAE, and the detailed analysis of transistors and structures, a 1500 Ω/□ parasitic conductive interface (PCI) between the GaN substrate and the epitaxial layers was identified as a root cause. GaN substrates suffer from environmental Si contamination forming such a PCI. It was first detected by eddy current measurements showing that the insulating GaN:Fe buffer and GaN:Mn substrate did not effectively suppress the PCI. Nevertheless, it was effectively isolated by the GaN:Fe buffer to maintain a good DC performance for GaN‐on‐GaN HEMTs and allowing for a record gm‐max of 535 mS mm⁻¹. The S‐parameters confirmed this and indicated that the PCI causes a feed‐back effect, reducing the k‐point and fmax. Furthermore, loading effects were revealed on the ports of the HEMTs due to the PCI's resistive nature, and coplanar waveguide measurements showed 5 dB mm⁻¹ of propagation loss and severe changes in the characteristic impedance.
Space-fed large antenna arrays offer superior efficiency, simplicity, and reductions in size, weight, power, and cost (SWaP-C) compared to constrained-feed systems. Historically, horn antennas have been used for space feeding, but they suffer from limitations such as bulky designs, low aperture efficiency (≈ 50%), and restricted degrees of freedom at the continuous aperture. In contrast, planar patch arrays achieve significantly higher aperture efficiency (> 90%) due to their more uniform aperture distribution, reduced weight, and increased degrees of freedom from the discretized aperture. Building on these advantages, we proposed an array-fed Reflective Intelligent Surface (RIS) system, where an active multi-antenna feeder (AMAF) optimizes power transfer by aligning with the principal eigenmode of the AMAF-RIS propagation matrix T. While our previous studies relied on the Friis transmission formula for system modeling, we now validate this approach
through full-wave simulations in CST Microwave Studio®. By comparing the Friis-based matrix, TFriis, with the full-wave solution, Tfull.wave, we validate the relevance of the Friis-based
modeling for top-level system design. Our findings confirm the feasibility of the proposed AMAF-RIS architecture for next generation communication systems.
Waveguide filters ideally require resonance chambers, whose shape is defined by sharp corners. As this is difficult to obtain by classical means of production, a cost-effective rectangular band-pass filter (BPF) based on multilayer waveguide (MLW) technology for V-band is proposed in this paper. The conveniently compact design of the filter is then supplied into a streamlined and automated procedure to transfer the design into production data. This in turn eliminates man made errors in production and leaves room for scalability.
At the Ferdinand-Braun-Institut (FBH), we have been using our proven hybrid micro-integration technology for more than a decade to realise ultra-compact photonic modules for quantum applications [1]. Our latest innovations: Next-generation laser modules covering an extended wavelength range [2], and newly developed light control units for use in optical atomic clocks [3].
In this paper, InP HBTs featuring maximum oscillation frequencies fmax in the sub-THz range are characterized by conducting on-wafer 16 -term calibration. A direct comparison between 8 -term calibration and 16 -term calibration demonstrates that the 16 -term calibration improves the way transistor Mason's gain is derived. The on-wafer measurements of transistors with emitter widths of 0.5μm and 0.85μm yield extracted fmax values of 0.44 THz and 0.33 THz, respectively. The study shows that choosing proper on-wafer calibration techniques is highly important for reliable transistor characterization.