Active Optical Signal Conditioning and Monitoring System

An optical signal conditioning technique for dynamic modulation of signals and real-time monitoring of events is pivotal for developing various optical systems at micro/nano dimensions. The utilities of such technique include controllable signal enhancement and distinctive response towards external stimuli, with reconfigurable operational range. Here, we propose and demonstrate an optical technique based on the parallel integration of fiber modal interferometers for optical response enhancement and multi-signal monitoring. Overlap of the interferometers’ characteristic spectra facilitates controllable signal filtering, attenuation, and amplification of interferometer’s response towards dynamic field over wide frequency range of 1 Hz – 1 kHz. Signal to noise ratio (SNR) enhancement of 9 dB is achieved by applying 1 volt about the reference interferometer. The system enables real-time modulation of optical signals and multipoint signal monitoring using machine learning for various applications such as mechanical vibrations, acoustic fields, biological samples, fluid movement, and other similar dynamic fields.

The Effects of Bilateral and Ipsilateral Auditory Stimuli on the Subcomponents of Visual Attention

Attention contains three functional network subcomponents of alerting, orienting, and executive control. The attention network test (ANT) is usually used to measure the efficiency of three attention subcomponents. Previous researches have focused on examining the unimodal attention with visual or auditory ANT paradigms. However, it is still unclear how an auditory stimulus influences the visual attention networks. This study investigated the effects of bilateral auditory stimuli (Experiment 1) and ipsilateral auditory stimulus (Experiment 2) on the visual attention subcomponents. We employed an ANT paradigm and manipulated the target modality types, including visual and audiovisual modalities. The participants were instructed to distinguish the direction of the central arrow surrounded by distractor arrows. In Experiment 1, we found that the simultaneous bilateral auditory stimuli reduced the efficiency of visual alerting and orienting, but had no significant effect on the efficiency of visual executive control. In Experiment 2, the ipsilateral auditory stimulus reduced the efficiency of visual executive control, but had no significant effect on the efficiency of visual alerting and orienting. We also observed a reduced relative multisensory response enhancement (rMRE) effect in cue condition relative to no cue condition (Experiment 1), and an increased rMRE effect in congruent condition compared with incongruent condition (Experiment 2). These results firstly provide evidence for the alerting, orienting and executive control effects in audiovisual condition. And the bilateral and ipsilateral auditory stimuli have different effects on the subcomponents of visual attention.

Response Enhancement of Pt–AlGaN/GaN HEMT Gas Sensors by Thin AlGaN Barrier with the Source-Connected Gate Configuration at High Temperature

AlGaN/GaN HEMT hydrogen gas sensors were optimized by AlGaN barrier thickness in the gate-source connected configuration demonstrated high response and robust stability up to 500 °C. First, we found that the hydrogen sensing performance of a conventional normally-on HEMT-based sensor was enhanced when zero voltage was applied on the gate in comparison with a floating-gate condition due to a reduced level of the base current. In the next step, to take advantage of the response increase by VGS = 0 V, a new type of sensor with a source-connected gate (SCG) was fabricated to utilize the normally-on operation of the GaN HEMT sensor as a two-terminal device. AlGaN barrier thickness was thinned by the dry-etching process to gain higher transconductance at a zero-gate bias with the reduction of the distance from the 2DEG channel to the AlGaN surface, thereby significantly improve the hydrogen response. The SCG GaN sensor with an ultra-thin AlGaN barrier (9 nm) exhibited responses of 85% and 20% at 200 and 500 °C, respectively, onto 4%-hydrogen gas, which demonstrates a promising ability for harsh environment applications.