Photonics

This study evaluates the performance of DVB-RCS2 (Digital Video Broadcasting—Return Channel via Satellite 2) satellite systems for the transmission of DICOM (Digital Imaging and Communications in Medicine) medical images in telemedicine applications, considering both conventional radio frequency (RF) and advanced optical wireless technologies, including optical wireless communication (OWC) and free-space optics (FSO). A comparative simulation framework is developed to assess transmission quality for both single images and complete datasets using key performance metrics such as bit error rate (BER) and quality factor (Q factor). The results demonstrate that optical wireless systems significantly outperform RF-based systems, with FSO achieving the best performance, followed by OWC, while RF systems exhibit noticeable performance degradation. These findings confirm the significant potential of optical wireless technologies to ensure high reliability and superior quality in satellite-based medical image transmission, particularly in remote and underserved areas.

Tunable diode laser absorption spectroscopy (TDLAS) is a well-established spectroscopic method used for remote gas concentration measurements in real-world environments. However, mechanical vibrations affecting optical components exposed to environmental conditions can limit the precision of these measurements. In this work, we experimentally demonstrate that precompensating the current modulation to enable rapid switching between two or three wavelengths reduces the integration time required to achieve a “frozen scene,” i.e., a state effectively free of mechanical vibration effects. This improvement was demonstrated by analyzing the overlapping Allan deviation of CO₂ measurements under atmospheric conditions (approximately 430 ppm) as a function of the instrument’s update rate, which ranged from 156 Hz to 30.86 kHz, achieving the fastest real-time remote TDLAS concentration measurements reported to date. The experimental setup included a drone-mounted retroreflector, and the Allan deviation was characterized both with the drone turned off and on while clamped to a stage. We observed that increasing the measurement frequency reduced the integration time required to freeze the scene, but the limited speed and resolution of the electronics used meant an optimal working point of 15.43 kHz for our configuration. Lastly, this characterization served to select the update rate to utilize during an outdoor measurement which confirmed the usefulness of the high update rates in the suppression of the effect of drone-induced mechanical noise on concentration measurements.

Optical frequency domain reflectometry (OFDR) generally employs a sliding-window analysis for distributed sensing, and the window parameters directly determine the spatial resolution and sensing performance of the system. In this work, the effects of zero-padding and window overlap on OFDR sensing performance were investigated. Experimental results demonstrate strain measurements from 0 μɛ to 2000 μɛ with a spatial resolution of 13.64 mm, achieving a sensitivity of 0.15 GHz/μɛ. The standard deviation of the measured strain in the nominally unstrained region was 1.20 με. Furthermore, temperature measurements from 25 °C to 75 °C achieved a sensitivity of 1.42 GHz/°C, and the standard deviation of the measured temperature in the unheated region was 0.15 °C. With the proposed method, sensing performance can be improved while maintaining the same spatial resolution. The proposed method provides a simple and hardware-independent approach for improving OFDR sensing performance.