Soft contact lens materials are fabricated from polymers that have a relatively lower material rigidity. The flexible soft contact lens materials could reshape itself and deform to a different lens shape after placing on a rigid surface. Besides its flexibility, typically, lens material (such as hydrogel) contains water. The deformed lens shape along with posterior lens liquid films and lens liquid evaporation could further modify its in air optical performances. Thus, it is important to quantitatively study the soft material wavefront aberration correction properties directly in air. In this study, contact lenses were covered on a hard plastic phantom which has a similar surface curvature as the lens posterior surface. Appropriate lens hydration was maintained to minimize evaporation introduced surface deformation. A Shack-Hartmann wavefront measurement system was installed to measure lens-phantom system wavefront aberration in air. Transmission wavefront aberrations with and without covering spherical lenses (on phantom) were measured and the wavefront aberration difference were compared with labeled lens power. For a 0.5D negative lens, measured lens power is -0.53±0.07D and within 4-mm pupil size, higher order aberration RMS is 0.08 µm. Other lens power was also measured with an averaged power error less than 7%. The results indicate the measurement introduces minimized lens surface deformations (due to liquid evaporation) and has precise measurement repeatability. The technology offers a metrology to be potentially used to study lens deformations on different surface curvatures, which potentially provides a guidance for lens on-eye fitting performance investigation.
A visual just noticeable difference (VJND) is the amount of change in either an image (e.g. a photographic print) or in vision (e.g. due to a change in refractive power of a vision correction device or visually coupled optical system) that is just noticeable when compared with the prior state. Numerous theoretical and clinical studies have been performed to determine the amount of change in various visual inputs (power, spherical aberration, astigmatism, etc.) that result in a just noticeable visual change. Each of these approaches, in defining a VJND, relies on the comparison of two visual stimuli. The first stimulus is the nominal or baseline state and the second is the perturbed state that results in a VJND. Using this commonality, we converted each result to the change in the area of the modulation transfer function (AMTF) to provide a more fundamental understanding of what results in a VJND. We performed an analysis of the wavefront criteria from basic optics, the image quality metrics, and clinical studies testing various visual inputs, showing that fractional changes in AMTF resulting in one VJND range from 0.025 to 0.075. In addition, cycloplegia appears to desensitize the human visual system so that a much larger change in the retinal image is required to give a VJND. This finding may be of great import for clinical vision tests. Finally, we present applications of the VJND model for the determination of threshold ocular aberrations and manufacturing tolerances of visually coupled optical systems.
Germania doping is commonly used in the core of optical fiber due to its advantages compared to other materials
such as superior transparency in near-infrared telecommunication wavelength region. During fiber preform
manufacturing using the outside vapor deposition (OVD) process, Ge is doped into a silica soot preform by chemical
vapor deposition. Since the Ge doping concentration profile is directly correlated with the fiber refractive index profile,
its characterization is critical for the fiber industry. Electron probe micro-analyzer (EPMA) is a conventional analysis
method for characterizing the Ge concentration profile. However, it requires extensive sample preparation and lengthy
In this paper, a multiphoton microscopy technique is utilized to measure the Ge doping profile based on the
multiphoton fluorescence intensity of the soot layers. Two samples, one with ramped and another with stepped Ge
doping profiles were prepared for measurements. Measured results show that the technique is capable of distinguishing
ramped and stepped Ge doping profiles with good accuracy. In the ramped soot sample, a sharp increment of doping
level was observed in about 2 mm range from soot edge followed by a relative slow gradient doping accretion. As for the
stepped doping sample, step sizes ranging from around 1 mm (at soot edge) to 3 mm (at soot center) were observed. All
the measured profiles are in close agreement with that of the EPMA measurements. In addition, both multiphoton
fluorescence (around 420 nm) and sharp second harmonic generations (at 532 nm) were observed, which indicates the
co-existence of crystal and amorphous GeO<sub>2</sub>.
The concept of Anderson localization has been applied to electromagnetic waves for decades and strong photon localization effect has been observed in many two-dimensional systems including optical lattice and optical fibers. Among different types of optical fibers, both fibers with and without air hole were investigated. Air hole based fiber has significant higher refractive index contrast than other fibers which allow much lower filling fraction in order to observe Anderson localization. In a previous research, Anderson localization was observed near the fiber edge with an air fillfraction of 5.5%. At the fiber center region with only 2.2% air fill-fraction, Anderson localization disappeared. However, we observed Anderson localization in fibers with much lower air fill-fraction. In our experiments, random air line fibers with 150, 250 and 350 μm diameters were fabricated and characterized by scanning electronic microscopy (SEM). Averaged air line diameters were 177, 247 and 387 nm for the 150, 250 and 350 μm diameter fibers, respectively. Air fill-fraction was also measured at fiber center, middle and edge regions. Beam profiles were imaged into a charge couple device (CCD) and Anderson localization was observed. Unlike the previous research in which Anderson localization was only observed at the fiber edge due to non-uniform air line distribution, we observed Anderson localization within the fiber area with air fill-fraction significantly lower than the previous investigation. This is because with smaller air line diameter our fiber has higher air lines density than the previous report.