Improved wide-field emmetropic human eye model based on ocular wavefront measurements and geometry-independent gradient index lens.

There is a need to better understand the peripheral optics of the human eye and their correction. Current eye models have some limitations to accurately predict the wavefront errors for the emmetropic eye over a wide field. The aim here was to develop an anatomically correct optical model of the human eye that closely reproduces the wavefront of an average Caucasian-only emmetropic eye across a wide visual field. Using an optical design program, a schematic eye was constructed based on ocular wavefront measurements of the right eyes of thirty healthy young emmetropic individuals over a wide visual field (from 40° nasal to 40° temporal and up to 20° inferior field). Anatomical parameters, asymmetries, and dispersion properties of the eye's different optical components were taken into account. A geometry-independent gradient index model was employed to better represent the crystalline lens. The RMS wavefront error, wavefront shapes, dominant Zernike coefficients, nasal-temporal asymmetries, and dispersion properties of the developed schematic eye closely matched the corresponding measured values across the visual field. The developed model can help in the design of wide-field ophthalmic instruments and is useful in the study and simulations of the peripheral optics of the human eye.

Influence of base-region thickness on the performance of Pnp transistor-VCSEL.

We have recently reported a 980nm GaAs-based three terminal Pnp transistor-vertical-cavity surface-emitting laser (TVCSEL) operating at room temperature with optical power up to 1.8mW. However, the current gain ß = ΔIc/ΔIb was near zero just before lasing and became negative after the lasing threshold. The main cause of the negative current gain was found to be a gradual and position-dependent forward-biasing (saturation) of the base-collector junction with increasing bias even before lasing threshold. In this article, detailed multi-physics device simulations are performed to better understand the device physics, and find ways to avoid the premature saturation of the base-collector junction. We have optimized the thickness of the base region as well as its doping concentration and the location of the quantum wells to ensure that the T-VCSEL is in the active mode throughout its range of operation. That is, the emitter-base junction is forward biased and base-collector junction is reversed biased for sweeping the excess charges out of the base region.