Manipulation of light is in strong demand in information technologies. Among the wide range of linear and nonlinear optical devices that have been used, growing attention has been paid to photonic crystals that possess a periodic modulation of dielectric function. Among many photonic bandgap (PBG) structures, liquid crystals with periodic structures are very attractive as self-assembled photonic crystals, leading to optical devices such as dye lasers. Here we report a new hetero-PBG structure consisting of an anisotropic nematic layer sandwiched between two cholesteric liquid-crystal layers with different helical pitches. We optically visualized the dispersion relation of this structure, displaying the optical diode performance: that is, the non-reciprocal transmission of circular polarized light at the photonic-bandgap regions. Transmittance spectra with circularly polarized light also reveal the diode performance, which is well simulated in calculations that include an electro-tunable diode effect. Lasing action was also confirmed to show the diode effect with a particular directionality.

Under SO tamponade, macular microstructural changes were identified by spectral-domain optical coherence tomography and were associated with duration of SO tamponade. Most of the microstructural changes were recovered after SO removal, if needed, combined with macular surgery. Anatomic resolution was accompanied by postoperative visual improvement.

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PurposeTo evaluate the effects of wearing rigid gas permeable (RGP) contact lenses on the topographic changes in keratoconus.MethodsSeventy-seven keratoconic eyes that wore multicurve RGP contact lenses and 30 keratoconic eyes that wore no contact lenses were retrospectively analyzed. The mean follow-ups were 22.6 and 20.5 months in the lens-wearing and control groups, respectively. Visual acuity, comfort, daily wearing time, and corneal staining were evaluated for both groups. The changes in topographic indices were compared between the lens-wearing and control groups.ResultsMulticurve RGP lens corrected logarithm of the minimum angle of resolution visual acuity of the lens-wearing group significantly improved from -0.016±0.065 to -0.032±0.10 at follow-up (p=0.05). In the lens-wearing group with advanced keratoconus, the Sim Kmax, Sim Kmin, apical power, astigmatic index, and anterior elevation significantly decreased from 57.68±4.26 diopter (D), 50.50±2.32 D, 62.79±5.11 D, 7.20±0.55 D and 67.36±16.30 µm to 55.51±4.28 D, 49.62±3.26 D, 60.31±5.41 D, 5.90±0.51 D and 60.61±16.09 µm, respectively (paired t-test, p<0.05). The irregularity index of 3 mm did not significantly change. Meanwhile, in the control group, the apical power and irregularity index increased from 55.56±7.25 D and 3.06±1.68 D to 57.11±7.75 D and 3.25±1.71 D, respectively (paired t-test, p=0.008, p=0.01).ConclusionsProperly fitted multicurve RGP contact lenses are not likely to contribute to the progression of keratoconus.

Sex ratio at birth remains highly skewed in many Asian countries because of son preference. The ratio in South Korea, however, declined beginning in 1990 and reached the natural range in 2007. We study changes in child gender effects on fertility and parental investment during this period of decreasing sex ratio at birth. We find that gender discrimination on the extensive margin (fertility), such as sex-selective abortions and son-biased stopping rules, have nearly disappeared among recent cohorts. On the intensive margin (parental inputs), boys receive higher expenditures on private academic education, have mothers with fewer hours of labor supply, and spend less time on household chores relative to girls. These gender gaps have also narrowed substantially, however, over the past two decades. We consider alternative explanations, but altogether, evidence suggests the weakening of son preference in South Korea.

Central serous chorioretinopathy (CSC) is a common condition characterized by serous detachment of the neurosensory retina at the posterior pole. We built a deep learning system model to diagnose CSC, and distinguish chronic from acute CSC using spectral domain optical coherence tomography (SD-OCT) images. Data from SD-OCT images of patients with CSC and a control group were analyzed with a convolutional neural network. Sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve (AUROC) were used to evaluate the model. For CSC diagnosis, our model showed an accuracy, sensitivity, and specificity of 93.8%, 90.0%, and 99.1%, respectively; AUROC was 98.9% (95% CI, 0.983–0.995); and its diagnostic performance was comparable with VGG-16, Resnet-50, and the diagnoses of five different ophthalmologists. For distinguishing chronic from acute cases, the accuracy, sensitivity, and specificity were 97.6%, 100.0%, and 92.6%, respectively; AUROC was 99.4% (95% CI, 0.985–1.000); performance was better than VGG-16 and Resnet-50, and was as good as the ophthalmologists. Our model performed well when diagnosing CSC and yielded highly accurate results when distinguishing between acute and chronic cases. Thus, automated deep learning system algorithms could play a role independent of human experts in the diagnosis of CSC.

Sex ratio at birth remains highly skewed in Asian countries due to son preference. In South Korea, however, it has declined to the natural ratio. In this paper, we investigate whether son preference has disappeared in Korea by analyzing parents' time and monetary inputs by the sex of their child. We exploit randomness of the first child's sex to overcome potential bias from endogenous fertility decisions. Our findings show that mothers are more likely to work after having a girl, girls spend twice as much time as boys in housework activities, and parents spend more on private education for boys.

The third-order Kerr nonlinear optical effect of a one-dimensional photonic bandgap structure of a cholesteric liquid crystal is investigated. In a femtosecond nonlinear transmission measurement, nonlinear optical changes in the bandgap edges are observed. From analysis of the dispersion relation, Kerr nonlinear coefficients of nematics, forming the cholesteric liquid crystal, are found to be enhanced by 1-2 orders of magnitude through the photonic bandgap structure.