Continuously tunable photonic true-time-delay device for millimeter-wave beamforming.

We present a novel CMOS compatible plasma dispersion modulation scheme for slow wave photonic true-time-delay structure harnessing the frozen mode to enable applications in millimeter-wave (mmWave) beamforming. Leveraging the Soref-Bennett model for the electro-refractive effect in silicon plasma dispersion, continuous tunability of approximately 6.8 ps/V with a peak delay of approximately 11.4 ps is achieved for a low threshold voltage of 0.9 V. This plasma dispersion will enable fast and sophisticated modulation and beamforming in 5G mmWave and 6G terahertz communications.

Asthenopia and blink rate under visual and cognitive loads.

PURPOSE: Asthenopia has been associated with reading under visually stressful conditions. However, it is not known whether increased cognitive load contributes to asthenopic symptoms. The purpose of this study was to evaluate the contribution of increased cognitive load (with or without visual stress inducing conditions) to asthenopic symptoms associated with prolonged near work. METHODS: Thirty-three visually normal subjects, aged 18 to 30 years, participated in the study. Subjects read texts or watched videos under different visual stress and cognitive loads. Visual stress conditions were good visual quality, low contrast, and induced refractive error. The cognitive load levels were watching video, reading fairy tales, and reading technical articles. As an additional task, subjects also listened to technical articles. At the end of each condition, subjects rated the magnitude of any asthenopic symptoms, visual discomfort, and cognitive discomfort they experienced during the task. Electromyography potentials recorded from the lower orbicularis oculi muscle were used to obtain blink rate. RESULTS: Subjects reported greater internal symptoms for the refractive error condition coupled with higher cognitive load compared to good visual and low contrast conditions (p < 0.01). For the low contrast condition coupled with higher cognitive load, greater external symptoms were reported compared to good visual and refractive error conditions (p < 0.05). However, asthenopic symptoms were not reported for cognitively demanding tasks when the visual condition was good. Blink rates were not significantly different between the good visual and low contrast conditions within each cognitive load level. For the cognitively difficult reading conditions, blink rate was significantly decreased for the low contrast and good visual conditions compared to the refractive error condition. CONCLUSIONS: An interaction between cognitive and visual demands was observed. Greater cognitive loads accentuate the same differentiated symptoms normally caused by visual stressors.

Interactions of visual and cognitive stress.

BACKGROUND: The objective of this research is to assess the ocular and muscular response to long-duration reading under different visual and cognitive difficulty levels. METHODS: Thirty-five subjects, with 20/20 vision and without history of ocular pathology or cognitive deficits, participated in the study. Subjects read under different visual and cognitive difficulty levels for 6 (30-minute) conditions. Upper and lower orbicularis oculi, frontalis, and trapezius muscle activities were recorded using surface electromyography (EMG). Aperture size, pupil diameter, and pulse rate of the subjects were recorded with a video camera, pulse meter, and ISCAN eye tracker (ISCAN Inc.), respectively. RESULTS: The results show that the texts read with a refractive error caused increased orbicularis oculi EMG power and reduced aperture size (P < 0.001). There was no statistically significant difference between the conditions for pulse rate, pupil diameter, or EMG activity of the frontalis and trapezius muscles with either visual or cognitive stress presented in this experiment. CONCLUSION: Visual stress experienced due to reading under an induced refractive error is potentially mediated by a local mechanism, different from the mechanism underlying reading under low contrast or high cognitive demand.

Low-loss polynomial White cell optical true-time delay engine for wideband radio frequency array beam steering.

An optical true-time delay (OTTD) engine based on a polynomial White cell (quadratic) is designed and simulated with commercially available components with a time delay increment of at least 25 ps for wideband beam steering in the frequency range of 2-18 GHz. The simulated quantification of aberration losses show for the first time that aberration losses in the null cell are about 5.0 dB. However, for the longer delay arms, there is an additional loss of about 3.2 dB/delay each time a beam travels an arm with a lens train used as a delay element compared with the same delay generated without a lens train. We present a design and simulation of a low-loss delay arms quartic cell without a lens train by using a separate field lens for each delay arm for efficient wideband beam steering.

Objective measurements of lower-level visual stress.

PURPOSE: To determine the sensitivity of the electromyography (EMG) response of the orbicularis oculi muscle to selected lower-level visually stressful conditions to establish the extent to which it can be used as a measure of visual discomfort. METHODS: Thirty-one subjects (18 years or older) with 20/20 vision, without history of ocular pathology, oculomotor limitation, or cognitive deficits participated in the study. Subjects read on a computer display for 27 trials of 5 min duration under different low-level asthenopic conditions. The conditions were graded levels of font size, font type, contrast, refractive error, and glare. Orbicularis oculi activity was recorded using surface EMG. Blink-free epochs of EMG data were analyzed for power for all the conditions. Blink rate for all the trials was also measured. At the end of each trial, subjects rated the severity of visual discomfort experienced while reading. RESULTS: Conditions that benefit from squint (refractive error and glare) showed increased EMG power (p < 0.001) from the orbicularis and increased blink rate (p = 0.002), whereas those that do not benefit from squint (small font and low contrast) showed no significant EMG response and a significant decrease in blink rate (p = 0.003 and p = 0.01). All conditions resulted in significant visual discomfort; the p value for font type was 0.039 and p < 0.001 for the other conditions. CONCLUSIONS: The results suggest that the squint-beneficial conditions are operated by a local mechanism involving contraction of the orbicularis and increase in reflex blinking, whereas those that do not benefit from squint do not engage the orbicularis and decrease blink, possibly through central inhibition of spontaneous blinking. The EMG response is a sensitive objective measure for the squint-beneficial conditions. However, for the non-squint-beneficial conditions, blink rate may be a more sensitive objective measure, although EMG with longer trial durations should be tested.

Design and demonstration of a switching engine for a binary true-time-delay device that uses a white cell.

Optical true-time-delay devices based on the White cell can be divided into two general types: polynomial cells, in which the number of delays that can be obtained is related to the number of times m that a beam bounces in the cell raised to some power, and exponential cells, in which the number of delays is proportional to some number raised to the power of m. In exponential cells, the topic to be addressed, the spatial light modulator switches between a delay element and a null path on each bounce. We describe an improved design of this switching engine, which contains a liquid-crystal switch and a White cell. We examine astigmatism and corrections for it and present a specific design.