A novel (to the best of our knowledge) liquid level sensor based on multimode interference (MMI) effects is proposed and demonstrated. By using a multimode fiber (MMF) without cladding, known as no-core fiber, liquids around the MMF modify the self-imaging properties of the MMI device and the liquid level can be detected. We show that the sensor exhibits a highly linear response with the sensing range and multiplexed operations easily controlled by just modifying the length of the no-core fiber. At the same time, we can measure the refractive index of the liquid based on the maximum peak wavelength shift. We can also use the sensor for continuous and discrete liquid level sensing applications, thus providing a liquid level sensor that is inexpensive with a very simple fabrication process.

/pdf/fiber-optic-sensor-for-liquid-level-measurement-1us2xcchd4.pdf

Fiber-optic sensor for liquid level measurement.

Impact of public lighting on pedestrians' perception of safety and well-being

Aim: To evaluate the changes in correlations of 
higher order aberrations of the first corneal surface 
with halo phenomena, a form of image degradation, under 
night vision conditions measured objectively after 
successful LASIK surgery.
 Methods: This is a prospective, observational, 
analytical study of 110 eyes that undergone successful 
LASIK surgery for myopia and astigmatism. Pre-operative 
sphere was -3.48±1.70 D [0 to -8.00 D] and pre-
operative cylinder was -0.86±0.87 D [0 to -4.00 D]. 
Visual disturbance caused by halo phenomena with the 
Starlights v1.0 and pupil size with Colvard pupilometry 
were measured after adaptation to a dark environment 
(0.17 lux). Corneal aberrations were computed for a 
corneal diameter representative of the eye9s entrance 
pupil under night vision conditions. Results: The halo disturbance index increased in 
this study by a factor of 2.15 after successful LASIK 
surgery. Total RMS for monochromatic higher order 
aberration displayed a significant correlation with halo 
disturbance index (r=0.42; p<0.01). However, only 
secondary astigmatism (r=0.36; p<0.01) coma (r=0.25; 
p=0.02) and spherical aberration (r=0.40; p<0.01) were 
responsible for such behavior, with the remaining 
corneal aberrations until the 6th order not displaying 
any significant correlation when considered individually.
 Conclusion: Patients undergoing LASIK procedures 
display an increase of halo phenomena around lights in 
night vision conditions, even when the results of the 
surgery are considered entirely satisfactory according 
to current international standards of predictability, 
efficacy and safety. Secondary astigmatism, coma and 
spherical aberration are the higher order aberrations 
until the 6th order that significantly correlated with 
halo disturbance index.

https://bjo.bmj.com/content/bjophthalmol/91/8/1031.full.pdf

Night vision disturbances after successful LASIK surgery.

A water level measurement using an interdigital capacitive sensor with low-cost, low-energy, good repeatability, high linearity, and ease of installation is proposed with a support of experimental results. This sensor comprises a printed circuit board (PCB) with configuration of two interpenetrating comb electrodes. The comb electrode is 70–80 mm width, 300 mm height with 1–2 mm spacing between each comb. This configuration of electrode causes the capacitance between comb electrodes to vary by the water level. Microcontroller is used to calculate the capacitance between comb electrodes in terms of a discharge time correlated to the water level. A practical water level measurement technique using two comb electrodes designated as level and reference sensors is presented. This technique can directly be applied to water with different conditions without recalibration. This sensor is able to measure absolute levels of water with 0.2 cm resolution over 30 cm range. In addition, it is also sensitive enough to trace the variability of water level. A flood monitoring simulation is carried out in wave flume where this sensor is used to detect the rising wave.

A self-calibration water level measurement using an interdigital capacitive sensor

Background: We objectively assessed the optical quality and intraocular scattering by means of parameters provided by a clinical double-pass system in healthy young subjects and thereby we obtained new reference data for clinical diagnosis. We calculated normal values of neural contrast sensitivity function (nCSF) from the measured modulation transfer function (MTF) and the contrast sensitivity function (CSF).



Methods:  Eligible subjects were healthy adults aged from 18 to 30 years with a logMAR visual acuity (VA) of 0.0 or better and normal values of CSF. Optical quality measurements for a 4.0 mm pupil were performed using the Optical Quality Analysis System (OQAS) based on the double-pass technique. The following parameters were analysed: the modulation transfer function cutoff frequency (MTFcutoff), the Strehl2D ratio, the OQAS values (OV) at 100, 20 and nine per cent contrasts and the objective scatter index (OSI).



Results:  A total of 178 volunteers responded to the call, of whom 181 eyes were finally part of the study taking into account the criteria for inclusion. The values for the optical quality parameters were: 44.54 ± 7.14 cpd (MTFcutoff), 0.27 ± 0.06 (Strehl2D ratio), 1.48 ± 0.24 (OV100%), 1.58 ± 0.32 (OV20%), 1.64 ± 0.39 (OV9%), and 0.38 ± 0.19 (OSI). The nCSF calculated was 1.76 ± 0.21 (3 cpd), 2.13 ± 0.23 (6 cpd), 2.01 ± 0.28 (12 cpd) and 1.86 ± 0.33 (18 cpd).



Conclusion:  The normal values provided can be a useful tool for discriminating healthy eyes from early abnormal ones in which the optical quality or sensory function is impaired.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1444-0938.2010.00535.x

Optical quality and intraocular scattering in a healthy young population.

An intensity-based fiber-optic liquid-level gauge for continuous measurement is described. The sensing principle is based on the total internal reflection of light within the fiber optic, and for this, a measurement is made of the power attenuation which occurs in the fiber optic immersed in the liquid tank when the liquid level varies. The light from a LED is modulated before being directed into the fiber to minimize measurement errors. The device contains an alarm programmable to signal any liquid level in the tank (high or low), and data can be sent via Internet in real time to a distant point.

Fiber-optic liquid-level continuous gauge

New parameter relationships for public lighting design (i.e. average illuminance, luminaire spacing, and mounting height) were calculated from a large sample of data sets optimized with a multi-objective evolutionary algorithm. Optimization criteria included maximum energy efficiency and overall uniformity. The relations thus derived are a simple and elegant method for designing any type of public lighting installation without the need to use complex, expensive and/or unavailable software. It would therefore be desirable that manufacturers include such parameters in the product datasheet in order to make the calculation easier.

A simple method for designing efficient public lighting, based on new parameter relationships

We deduce a mathematical equation for corneal asphericity after refractive surgery when the Munnerlyn formula is used. For this, an analytical least-squares procedure is used. The equation explains the discrepancies found by different authors when the Munnerlyn formula or its paraxial approximation is used. Equations for corneal asphericity deduced here may be of clinical relevance, for example, in studying quantitatively the role of different factors (decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures) during corneal ablation.

Corneal asphericity after refractive surgery when the Munnerlyn formula is applied.

We provide a correction factor to be added in ablation algorithms when a Gaussian beam is used in photorefractive laser surgery. This factor, which quantifies the effect of pulse overlapping, depends on beam radius and spot size. We also deduce the expected post-surgical corneal radius and asphericity when considering this factor. Data on 141 eyes operated on LASIK (laser in situ keratomileusis) with a Gaussian profile show that the discrepancy between experimental and expected data on corneal power is significantly lower when using the correction factor. For an effective improvement of post-surgical visual quality, this factor should be applied in ablation algorithms that do not consider the effects of pulse overlapping with a Gaussian beam.

Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams.

Purpose:To evaluate the optical image quality, using 2 optical devices (an aberrometer and a double-pass device), and visual performance [contrast sensitivity function (CSF)] in patients with keratitis and after resolution of the disease.Methods:Twenty subjects with keratitis (18 patients with unila

Francisco Pérez-Ocón

Papers

Fiber-optic liquid-level continuous gauge

A simple method for designing efficient public lighting, based on new parameter relationships

Corneal asphericity after refractive surgery when the Munnerlyn formula is applied.

Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams.

Optical image quality and visual performance for patients with keratitis.