Analysis of Non-Idealities in the Generation of Reconfigurable Sinc-Shaped Optical Nyquist Pulses

Optical sinc-shaped Nyquist pulses are widely used in microwave photonics, optical signal processing, and optical telecommunications due to their numerous advantages, like rectangular shape in the frequency domain, the orthogonality and the consequential possibility to use these pulses to transmit data with the maximum possible symbol rate. Ideal sinc pulses with the rectangular spectrum are just a mathematical construct. However, high-quality sinc pulse sequences offer the same advantages and can be generated by a phase-locked rectangular frequency comb with mode-locked lasers, intensity modulators, and integrated devices. Nevertheless, any non-idealities in the pulse and comb generation might lead to a degradation of the system performance, especially for metrology. Here, we investigate and analyze the effect of three major non-idealities, namely, the roll-off factor, the side band suppression ratio (SSR), and the ripple of sinc-shaped reconfigurable optical Nyquist pulse sequences based on 3, 5, and 9-line optical phase-locked frequency combs. We compare these results with the existing literature for the three-line comb followed by the experimental verification of the simulation results. We illustrate that by increasing the number of comb lines, the pulse sequences have superior performance and contribute to lesser root-mean-square (r.m.s.) error. We also discuss the trade-off between the r.m.s. error and the optical power loss for increasing the SSR

High-resolution signal-in-space measurements of VHF omnidirectional ranges using UAS

In this paper, we describe measurement results of the signal-in-space of very high frequency (VHF) omnidirectional range (VOR) facilities. In aviation VOR are used to display the current course of the aircraft in the cockpit. To understand the influence of wind turbines (WT) on the signal integrity of terrestrial navigation and radar signals, the signal content and its changes, respectively, must be investigated. So far, only numerical simulations have been carried out on the frequency-modulation (FM) part of the Doppler-VOR (DVOR) signal to estimate the influence of WT on DVOR. Up to now, the amplitude-modulated (AM) part of the DVOR was not assessed at all. In 2016, we presented an unmanned aerial system (UAS) as a carrier for state-of-the-art radio-frequency (RF) measurement instrumentation (Schrader et al., 2016a, c; Bredemeyer et al., 2016), to measure and to record the true signal-in-space (both FM and AM signal) during the flight. The signal-in-space (which refers to time-resolved signal content and field strength, respectively) is measured and sampled without loss of information and, furthermore, synchronously stored with time stamp and with precise position in space, where the measurements were taken

Terahertz electromagnetic fields (0.106 THz) do not induce manifest genomic damage in vitro

Terahertz electromagnetic fields are non-ionizing electromagnetic fields in the frequency range from 0.1 to 10 THz. Potential applications of these electromagnetic fields include the whole body scanners, which currently apply millimeter waves just below the terahertz range, but future scanners will use higher frequencies in the terahertz range. These and other applications will bring along human exposure to these fields. Up to now, only a limited number of investigations on biological effects of terahertz electromagnetic fields have been performed. Therefore, research is strongly needed to enable reliable risk assessment. Cells were exposed for 2 h, 8 h, and 24 h with different power intensities ranging from 0.04 mW/cm2 to 2 mW/cm2, representing levels below, at, and above current safety limits. Genomic damage on the chromosomal level was measured as micronucleus formation. DNA strand breaks and alkali-labile sites were quantified with the comet assay. No DNA strand breaks or alkali-labile sites were observed as a consequence of exposure to terahertz electromagnetic fields in the comet assay. The fields did not cause chromosomal damage in the form of micronucleus induction

Precision Signal-in-space Measurements of Terrestrial Navigation Systems using Multicopter

The project WERAN aimed to determine the interaction of wind turbines (WT) with signals of terrestrial navigation systems such as VHF omnidirectional radio ranges (VOR) and RADAR. One of the main goals of the project was to quantify the additional VOR bearing error caused by wind turbines by means of measurement and numerical simulations. In this presentation we will discuss the results of on-site measurements and compare those with numerical simulations. A remote- controlled multicopter with precision localization has been used as measurement platform. It carries a compact but capable high frequency instrumentation and integrated antennas to measure simultaneously both the AM reference signal and the FM signal of a Doppler VOR as true signal-in- space. Actual position, time stamp and measurement data are simultaneously stored at the platform. These measurements give insight into the signal content and signal integrity of VOR with and without WT. Furthermore, varying operational conditions of WT such as rotation vs idle state or angular movement of the nacelle may have different influence on the additional bearing error. During the follow-up project WERAN plus we will use the measurement data and simulation results to derive a model-based assessment tool. This will allow for prediction of the degree of interference (additional bearing error) of additional WT in the area around VOR with given topology