Optical Tilt Research Articles

A Novel Tilt Correction Technique for Irradiance Sensors and Spectrometers On-Board Unmanned Aerial Vehicles

In unstable atmospheric conditions, using on-board irradiance sensors is one of the only robust methods to convert unmanned aerial vehicle (UAV)-based optical remote sensing data to reflectance factors. Normally, such sensors experience significant errors due to tilting of the UAV, if not installed on a stabilizing gimbal. Unfortunately, such gimbals of sufficient accuracy are heavy, cumbersome, and cannot be installed on all UAV platforms. In this paper, we present the FGI Aerial Image Reference System (FGI AIRS) developed at the Finnish Geospatial Research Institute (FGI) and a novel method for optical and mathematical tilt correction of the irradiance measurements. The FGI AIRS is a sensor unit for UAVs that provides the irradiance spectrum, Real Time Kinematic (RTK)/Post Processed Kinematic (PPK) GNSS position, and orientation for the attached cameras. The FGI AIRS processes the reference data in real time for each acquired image and can send it to an on-board or on-cloud processing unit. The novel correction method is based on three RGB photodiodes that are tilted 10° in opposite directions. These photodiodes sample the irradiance readings at different sensor tilts, from which reading of a virtual horizontal irradiance sensor is calculated. The FGI AIRS was tested, and the method was shown to allow on-board measurement of irradiance at an accuracy better than ±0.8% at UAV tilts up to 10° and ±1.2% at tilts up to 15°. In addition, the accuracy of FGI AIRS to produce reflectance-factor-calibrated aerial images was compared against the traditional methods. In the unstable weather conditions of the experiment, both the FGI AIRS and the on-ground spectrometer were able to produce radiometrically accurate and visually pleasing orthomosaics, while the reflectance reference panels and the on-board irradiance sensor without stabilization or tilt correction both failed to do so. The authors recommend the implementation of the proposed tilt correction method in all future UAV irradiance sensors if they are not to be installed on a gimbal.

A modified Langevin-Debye model for investigating the electro-optic behaviour of de Vries smectic liquid crystals

ABSTRACTAn external electric field applied across a planar-aligned cell in Smectic A* phase of de Vries smectic liquid crystal induces director redistribution over a cone, resulting in a substantial increase in the birefringence and the apparent optical tilt angle. Such an electro-optic response is modelled by Shen et al. [Y. Shen et al., Phys. Rev. E 88, 062504 (2013)], who modified their previous hollow cone with a diffuse cone model by introducing the molecular distribution function limited over a range of tilt angles, that lie in between θmin and θmax. The limits in these two tilt angles are assumed to be temperature independent though the tilt angle in between the two values can be temperature dependent. However, the high resolution measurements of birefringence and the layer thickness indicate the presence of temperature dependent diffuse cone angle in SmA* phase.. In the proposed model, we replace θmin by θT, a temperature dependent fitting parameter and the change shows that a better fit of the experimental data to the model is obtained. We determine the temperature dependence of θmin and show that this angle increases as SmA* to SmC* phase transition temperature is approached.

A liquid pendulum based optical tilt sensor

In this paper a simple, low-cost single axis optical tilt sensor is presented. The presented sensor body is a transparent, cube shaped container made of an acrylic sheet. Additionally, it is half filled with liquid (i.e. water) based on its inner volume. In order to sense the liquid column inclination during the tilting of the sensor body, two pairs of optical trans-receiver have been used and their unique orientation across the sensor body claims relatively high measuring range. The basic working principle of the sensor depends on Snell’s law of refraction and reflection. Experimentally, it is observed that the developed prototype is able to sense the tilt angle in the range of ±90°, but a significant linear range is found in ±20°. In this range, the sensor has a resolution of 0.02° and sensitivity of 225mV/°.

Influence of ZnO nanoparticles on the polarization, dielectric and electro-optic behaviour in the smectic C* and hexatic I* phases

Here we report the results of the dielectric and polarization measurements in the smectic and the tilted hexatic phases of a liquid crystal-nano composite consisting of commercially available ferroelectric liquid crystal (FLC) doped with the ZnO nanoparticles (NPs). It has been observed that the inclusion of NPs not only decreases in the transition temperature but also dielectric strength of the Goldstone mode without altering the associated relaxation frequency. An additional relaxation observed for the FLC-ZnO nanocomposite, but not present in the pure material is attributed to the manifestation of the primary director mode. The observed results are analyzed using the generalized Landau model to understand the effect of the coupling between the polarization and optical tilt angle. While there is no change in either the magnitude of the tilt or the polarization across the orthogonal to tilted smectic phase transitions, clear changes are seen for both the parameter across the transition to the hexatic phase. The FLC-ZnO nanocomposite exhibits decreased rotational viscosity and a faster response time, a feature attractive from an application point of view.

Design of liquid crystals with ‘de Vries-like’ properties: the effect of an ethynyl spacer in the core structure

ABSTRACTWe investigate the origins of ‘de Vries-like’ liquid crystalline behaviour by introducing an ethynyl spacer in the core of the tricarbosilane-terminated 5-phenylpyrimidine mesogens QL16-6 and QL17-6. The rationale for this structural change is based on the assumption that an ethynyl spacer would create more free volume in the core sub-layer and therefore decrease the orientational order parameter S2 in the SmA phase. The tricarbosilane-terminated mesogens WL41-5 and WL42-6 with a 5-(phenylethynyl)pyrimidine core in either a normal or inverted orientation were synthesised, and their mesomorphic and ‘de Vries-like’ properties characterised using polarised optical microscopy, differential scanning calorimetry, birefringence measurements, small–angle (SAXS) and 2D X-ray scattering. Reduction factors R derived from SAXS and optical tilt angle measurements suggest that neither WL41-5 (R = 0.49) nor WL42-6 (R = 0.80) exhibit ‘de Vries-like’ properties. The S2(T) profiles show an increase in orientational order with decreasing temperature and a sharp discontinuity at the SmA-SmC transition, which is consistent with ‘de Vries-like’ behaviour. However, the Leff(T) profiles suggest an increase in interdigitation that reduces the positive effect of increasing S2 in compensating for the molecular tilt.

A study of Sub-micron Fan-out Wafer Level Packaging solutions

Abstract In Fan-out Wafer Level Packaging (FOWLP) processes, redistribution layer (RDL) line width reduction is a key challenge to expand the FOWLP market to multi-chip interconnections, including interconnections between SoC and DRAM, split-die connection of FPGA, and interconnections between image sensors and SoC. Next generation FOWLP requires 1.0 μm RDL and future FOWLP is targeting 0.8 μm RDL. To meet these requirements, Canon has developed new projection optics with a high NA and wide-field that is best suited for sub-micron FOWLP. These projection optics are a new option for FPA-5520iV steppers, offering NA 0.24 imaging and a 52 × 34 mm exposure field. FPA-5520iV steppers with NA 0.24 provide excellent 0.8 μm resolution performance throughout all imaging fields thanks to Canon's wave-front aberration based projection optics manufacturing methods and on-axis optical tilt focus sensor.

Multi-channel and multi-polarization radar measurements around the NEEM site

Abstract. Ice properties inferred from multi-polarization measurements, such as birefringence and crystal orientation fabric (COF), can provide insight into ice strain, viscosity, and ice flow. In 2008, the Center for Remote Sensing of Ice Sheets (CReSIS) used a ground-based VHF (very high frequency) radar to take multi-channel and multi-polarization measurements around the NEEM (North Greenland Eemian Ice Drilling) site. The system operated with 30 MHz bandwidth at a center frequency of 150 MHz. This paper describes the radar system, antenna configurations, data collection, and processing and analysis of this data set. Within the framework derived from uniaxial ice crystal model, we found that ice birefringence dominates the power variation patterns of co-polarization and cross-polarization measurements in the area of 100 km2 around the ice core site. The phase shift between ordinary and extraordinary waves increases nonlinearly with depth. The ice optic axis lies in planes that are close to the vertical plane and perpendicular or parallel to the ice divide depending on depth. The ice optic axis has an average tilt angle of about 11.6° vertically, and its plane may rotate either clockwise or counterclockwise by about 10° across the 100 km2 area, and at a specific location the plane may rotate slightly counterclockwise as depth increases. Comparisons between the radar observations, simulations, and ice core fabric data are in very good agreement. We calculated the effective colatitude at different depths by using azimuth and colatitude measurements of the c axis of ice crystals. We obtained an average effective c axis tilt angle of 9.6° from the vertical axis, very comparable to the average optic axis tilt angle estimated from radar polarization measurements. The comparisons give us confidence in applying this polarimetric radio echo sounding technique to infer profiles of ice fabric in locations where there are no ice core measurements.

Optic Disc Features in Highly Myopic Eyes: The ZOC-BHVI High Myopia Cohort Study.

Some studies reported that optic disc tilt and rotation might be risk factors for the susceptibility of high myopic eyes to develop glaucoma. However, data regarding optic disc manifestations in high myopia participants are few. It is crucial to characterize the features of optic disc manifestations among high myopes. To describe optic disc characteristics of Chinese highly myopic eyes and to investigate associated factors. This cross-sectional, observational study included 890 Chinese with bilateral high myopia (defined as ≤-6.00 diopters spherical power) in 2012. All subjects underwent cycloplegic autorefraction, ocular biometry, and fundus photography. The optic disc tilt ratio, degree of rotation, and β-zone peripapillary atrophy area were measured from the 45°optic disc-centered fundus photographs. Optic disc tilt was defined as optic disc tilt ratio, the ratio of maximum to minimum diameter of optic disc, exceeding 1.3. The definition of optic disc rotation was using optic disc rotation degree, the angle from long diameter and the vertical meridian, of >15°. Among 890 participants, 2 were excluded by ungradable optic disc-centered fundus photographs. In the 888 studied right eyes, the mean spherical power was -9.36 ± 3.46 diopters with a mean axial length of 27.51 ± 1.63 mm. The proportion of optic disc tilting, rotation, and β-zone peripapillary atrophy were 81.2%, 48.3%, and 92.8%, respectively. The mean ratio of optic disc tilting and rotation degree was 1.78 ± 0.53 and 21.08 ± 19.91°; the mean area of β-zone peripapillary atrophy/optic disc head was 1.11 ± 1.22. A multiple linear regression showed that older age (P < .001), female (P = .02), and more myopic spherical equivalent (P = .005) were related to the greater optic disc tilting ratio. Beta-zone peripapillary atrophy, optic disc tilting, and rotation are very common in highly myopic eyes in Chinese population. Older age, female, and more myopic spherical equivalent are risk factors of higher degree of optic disc tilting.

Design and Testing of a Micro-thermal Sensor Probe for Nondestructive Detection of Defects on a Flat Surface

This paper presents a design and testing of a micro-thermal sensor probe for realizing the proposed concept of non-contact surface defect detection, in which a change in heat flow across the gap between the tip of the micro-thermal sensor probe and a target surface is utilized to recognize the existences of surface defects. In the proposed concept of surface defect detection, the probe tip, where the micro-thermal sensor is embedded, is required to be placed as close as possible to the target surface for highly sensitive surface defect detection. For the purpose, an optical tilt detection assembly based on the laser autocollimation is designed to detect relative tilt of the micro-thermal sensor with respect to a target surface. A sensor probe assembly, in which the fabricated micro-thermal sensor is embedded to the tip of a hollow-shaped piezoelectric actuator by using a homemade sensor mount, is also designed in such a way that the sensor element will face to a target surface. A prototype micro-thermal sensor probe is constructed by integrating the optical tilt detection assembly and the sensor probe assembly, and some experiments have been carried out to verify the basic performances of the prototype micro-thermal sensor probe.

Association Between Optic Nerve Head Deformation and Retinal Microvasculature in High Myopia

To evaluate the retinal microvasculature of peripapillary and macular regions in highly myopic eyes and investigate the association between the vascular parameters and optic nerve head (ONH) deformation. Cross-sectional study. Seventy-one subjects with highly myopic eyes and 26 subjects with emmetropic eyes were included. Horizontal B-scan images of the ONH were obtained using optical coherence tomography (OCT) and horizontal tilt angles were measured. Integrated automated algorithms in the Avanti OCT angiography were used to quantify the peripapillary vessel density and area of the foveal avascular zone (FAZ) at the level of superficial and deep vascular networks. Association between horizontal disc tilt and the vascular parameters was evaluated. The mean axial length and horizontal tilt angle were 26.73 ± 0.63mm and 9.77 ± 3.00 degrees in the highly myopic group and 23.46 ± 0.55mm and 5.95 ± 3.48 degrees in the emmetropic group, respectively. Highly myopic eyes exhibited significantly lower average peripapillary vessel density (P= .010) and larger superficial and deep FAZs (P= .001 and P < .001, respectively) compared with emmetropic eyes. Linear regression analyses showed that horizontal tilt angle significantly correlated the average peripapillary vessel density (P= .037) and the areas of superficial (P<.001) and deep (P < .001) FAZs. The retinal microvasculature was significantly different in highly myopic eyes according to the degree of horizontal optic disc tilt. In addition to peripapillary vessel density, FAZ can be affected by the degree of optic disc tilt.

Retinal Nerve Fiber Layer Protrusion Associated with Tilted Optic Discs.

This study resulted in the identification of an optic nerve head (ONH) feature associated with tilted optic discs, which might potentially contribute to ONH pathologies. Knowledge of such findings will enhance clinical insights and drive future opportunities to understand disease processes related to tilted optic discs. The aim of this study was to identify novel retinal nerve fiber layer (RNFL) anomalies by evaluating tilted optic discs using optical coherence tomography. An observed retinal nerve fiber protrusion was further investigated for association with other morphological or functional parameters. A retrospective review of 400 randomly selected adult patients with ONH examinations was conducted in a referral-only, diagnostic imaging center. After excluding other ONH pathologies, 215 patients were enrolled and evaluated for optic disc tilt and/or torsion. Gross anatomical ONH features, including size and rim or parapapillary region elevation, were assessed with stereoscopic fundus photography. Optical coherence tomography provided detailed morphological information of individual retinal layers. Statistical analysis was applied to identify significant changes between individual patient cohorts. A dome-shaped hyperreflective RNFL bulge, protruding into the neurosensory retina at the optic disc margins, was identified in 17 eyes with tilted optic discs. Available follow-up data were inconclusive regarding natural changes with this ONH feature. This RNFL herniation was significantly correlated with smaller than average optic disc size (P = .005), congenital disc tilt (P < .0001), and areas of rim or parapapillary elevation (P < .0001). This study reports an RNFL protrusion associated with tilted optic discs, which has not previously been assessed as an independent ONH structure. The feature is predominantly related to congenital crowded, small optic discs and variable between patients. This study is an important first step to elucidate diagnostic capabilities of tilted disc morphological changes and understanding associated functional deficits.

Study of variation in thermal width of nematic and induced smectic ordering phase of citric acid (CA) and 4-heptyloxybenzoic acid (7OBA) hydrogen bonded liquid crystal complexes

Hydrogen-bonded liquid crystals (HBLCs) have been derived from nonmesogenic citric acid (CA) and mesogenic 4-heptyloxybenzoic acid (7OBA) yielding a highly ordered smectic C (Sm C) phase along with the new smectic X (Sm X) phase which has been identified as fingerprint-type texture. Optical (polarizing optical microscopy), thermal (differential scanning calorimetry) and structural (Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy) properties are studied. A noteworthy observation is that the intermolecular H-bond (between CA and 7OBA) influences on its melting point and clearing temperature of the HBLCs which exhibits lower value than those of the individual compounds. A typical extended mesophase region has been observed in the present complex while varying the mixture ratio (1:1 to 1:3) than those of individual compounds. The change in the ratio of the mesogenic compound in the mixture alters thermal properties such as enthalpy value and thermal span width in nematic (N) region of HBLC complex. Optical tilt angle measurement of CA+7OBA in Sm C phase has been discussed to identify the molecular position in the mesophase.

Room-Temperature Wide Measurement-Range Optical Fiber Fabry–Perot Tilt Sensor With Liquid Marble

We proposed a novel miniature liquid marble-based room-temperature optical fiber tilt sensor by using Fabry–Perot (F–P) interferometric detection, with the advantages of simple fabrication, wide range, good linearity, and low cost, aside from the immunity to electromagnetic interference. A mercury marble with a diameter of 1.3 mm and a length of 10 mm, acting as a light reflector, was dispensed into a capillary tube preprocessed by hydrophobic agent, therefore forming F–P interference with one end of a single-mode fiber. The developed sensor exhibited tilt-induced sensitivities of 6.62 $\mu \text{m}$ /ms−2 and 4.28 $\mu \text{m}$ /ms−2 with corresponding linearities of 3.44% and 4.28% within the ranges of 0°–90° and −90°–0°, respectively, due to asymmetric cavity lengths. The measured results were in agreement well with the governing model incorporating with contact angle hysteresis between mercury marble and capillary substrate.

Topographic Relationship Between Optic Disc Torsion and ß-Zone Peripapillary Atrophy in the Myopic Eyes of Young Patients With Glaucomatous-appearing Visual Field Defects.

The purpose of this study was to assess the topographic correlation between optic disc torsion (ODT) and beta-zone peripapillary atrophy (β-PPA) in young patients with myopia and glaucomatous-appearing visual field defects (VFDs). We consecutively recruited 110 eyes of 110 young patients with myopia and glaucomatous-appearing VFDs. Retinal nerve fiber layer (RNFL) and macular ganglion cell inner plexiform layer (mGCIPL) thicknesses were measured to compare between the groups with different ODT directions. For evaluating topographic correlation, the direction and degree of ODT and the direction and angles of β-PPA and point of maximum radial extent (PMRE) of β-PPA were measured on fundus photographs. Multivariate logistic regression analysis was performed to determine the clinical factors associated with inferior ODT direction. The relationships between torsional degree and clinical variables were evaluated using linear regression analyses. Among the 110 eyes, 19 had superior ODT and 91 had inferior ODT. Compared with myopic eyes with superior ODT, those with inferior ODT showed less severity of glaucoma as determined by RNFL or mGCIPL thickness and had a longer axial length, greater amount of optic disc tilt, larger β-PPA angle, and higher ratio of β-PPA area and disc area. ODT direction was significantly associated with the locations of β-PPA and PMRE. Torsional degree was significantly correlated with the β-PPA angle. ODT direction showed a significant association with the locations of β-PPA and PMRE of β-PPA. Torsional degree was correlated with the β-PPA angle in the myopic eyes of young patients with glaucomatous-appearing VFDs.

Effect of lateral fluorine substitution far from the chiral center on mesomorphic behaviour of highly titled antiferroelectric (S) and (R) enantiomers

Several new liquid crystalline chiral ester enantiomers in the (S) and (R) configuration were designed and characterised. In order to tune their mesomorphic properties, the molecular core was laterally substituted by fluorine atoms in different positions on the benzene ring placed in the molecular core far from the chiral centre. All the materials possess the self-assembling behaviour, specifically the paraelectric orthogonal smectic A*, the ferroelectric tilted smectic C* and antiferroelectric tilted smectic CA* phases over a broad temperature range down to room temperature. Properties of the materials were characterised by the polarising optical microscopy, differential scanning calorimetry, electro-optics and dielectric spectroscopy. Due to high chemical stability, reasonably broad temperature ranges of polar smectic mesophases (up to 110°C) and very high values of the optical tilt angle (40–45°) at saturation, these materials can be used as chiral dopants for the multicomponent orthoconic mixture design aimed for development of advanced electro-optic and photonic devices.

Ametropia, retinal anatomy, and OCT abnormality patterns in glaucoma. 2. Impacts of optic nerve head parameters

Clinicians use retinal nerve fiber layer thickness (RNFLT) measured by optical coherence tomography (OCT) as an adjunct to glaucoma diagnosis. Ametropia is accompanied by changes to the optic nerve head (ONH), which may affect how OCT machines mark RNFLT measurements as abnormal. These changes in abnormality patterns may bias glaucoma diagnosis. Here, we investigate the relationship between OCT abnormality patterns and the following ONH-related and ametropia-associated parameters on 421 eyes of glaucoma patients: optic disc tilt and torsion, central retinal vessel trunk location (CRVTL), and nasal and temporal retinal curvature adjacent to ONH, quantified as nasal/temporal slopes of the inner limiting membrane. We applied multivariate logistic regression with abnormality marks as regressands to 40,401 locations of the peripapillary region and generated spatial maps of locations of false positive/negative abnormality marks independent of glaucoma severity. Effects of torsion and temporal slope were negligible. The effect of tilt could be explained by covariation with ametropia. For CRVTL/nasal slope, abnormality pattern shifts at 7.2%/23.5% of the peripapillary region were detected, respectively, independent of glaucoma severity and ametropia. Therefore, CRVTL and nasal curvature should be included in OCT RNFLT norms. Our spatial location maps may aid clinicians to improve diagnostic accuracy.

Design and Testing of a 2D Optical Fiber Sensor for Building Tilt Monitoring Based on Fiber Bragg Gratings

In this paper, a new type of optical fiber tilt sensor based on fiber Bragg grating (FBG) is presented for 2D dual-axis tilt angle sensing. The tilt sensor is composed of two cylindrical floats suspended in water, connected with FBG. When the external environment causes the tilting of the sensor, the surface of the liquid within the container will form a new balanced liquid surface plane due to the gravity and change the height of the liquid at different locations in the container. So the buoyancy force of the cylindrical floats of the sensor will vary with the depth of liquid, thus the changed FBG strain will cause the FBG reflection central wavelength shift. According to the measured central wavelength shift by the optical spectral analyzer (OSA), we can obtain the two-axis tilt angle of the sensor. The proposed sensor can detect a tilt angle range of −5 degrees to +5 degrees and achieve a sensitivity of 0.1° with optical spectrum analyzer resolution of 0.01 nm. Due to its good sensing linearity, the proposed sensor can be applied in building tilt measurement.

Three-Dimensional Evaluation of Posterior Pole and Optic Nerve Head in Myopes with Glaucoma

The degree of myopia is represented by a global index, such as refractive error or axial length. However, the progression of myopia mainly develops in the posterior eyeball. Therefore, it is reasonable to assume that the evaluation of myopia should be confined to the posterior segment, where most of the growth and lengthening occurs. Swept source optical coherence tomography software can reconstruct the scans to the coronal view of the posterior pole, which provides additional anterior-posterior depth (z axis in the Cartesian coordinates) that is not provided with the common fundus photograph. We deduced that the parameter of deepest point of the eyeball (DPE) as a surrogate for posterior pole configuration. Between myopes with and without normal tension glaucoma (NTG) with similar axial length, myopes with NTG had deeper and more distant location of the DPE from the optic disc. The difference of the DPE position between the myopes with and without NTG may have implications for the larger optic disc tilt and torsion characteristic of myopes with NTG. Furthermore, these data suggest that myopes with NTG go through excessive posterior scleral remodeling, which may result in vulnerable optic nerve head.

Influence of Hydrogen Bond on Thermal and Phase Transitions of Binary Complex Liquid Crystals

A novel supramolecular liquid crystal (LC) is synthesized from the binary complex of 4-decyloxy benzoic acid and cholesteryl acetate. Fourier transform infrared (FTIR) spectroscopic study confirms the formation of intermolecular hydrogen bond between the mesogens. Various mesophases and corresponding textural changes in the complex are observed by comparing with its constituents through polarizing optical microscopic (POM) studies. The thermal stability factor of smectic phase for present complex is calculated. An interesting observation of present work is that investigation of extended thermal span of mesomorphic phases, decreased enthalpy, a nematic phase with a high clearing point and a low melting point. This is due to an arrangement of molecular reorientations and the development of new associations by hydrogen bonding. Optical tilt angle for smectic C phase is determined and the same is fitted to a power law.

Intraocular Lens Repositioning With Polypropylene Suture to Reduce Optic Tilt

Purpose: To describe a technique to reduce intraocular lens (IOL) tilt after sutureless intrascleral (SIS) fixation. Methods: Case report with review of surgical technique. Results: We report a technique that can be used to correct IOL tilt that may rarely accompany SIS IOL fixation. The procedure involves placing pupil-spanning polypropylene sutures on either side of the IOL optic to keep the optic parallel to the plane of the iris. Conclusion: Sutureless intrascleral IOL tilt correction can be achieved using polypropylene suture, thus obviating the need for more invasive surgical maneuvers, such as IOL exchange.