臺大光電所所訊

Investigating the opacity of corneal and scleral scattering medium via numerical solutions of Maxwell’s equations

Professor Snow H. Tseng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所曾雪峰教授

Similar in structure, the cornea and sclera both consist of collagen fibrils, yet, the opacity differs significantly. Here we employ numerical solutions of Maxwell’s equations to model light propagation through cornea-like and sclera-like scattering medium, respectively. By varying the specific structure of the scattering medium, we investigate geometrical factors that can account for the opacity, including wavelength, size and the position of the dielectric cylinders. The reported numerical analysis may shed light to understanding the opacity of scattering medium.

Fig. 1. Schematics of the geometrical structure of cornea and sclera of a human eye. The scleral collagen fibrils are irregular in shape and position, whereas the corneal collagen fibrils are smaller and regular in position.

[http://www.nikon-lenswear.com.tw/zh/eyes-and-vision/how-your-eyes-work]

[http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v4/v4c023.html]

Fig. 2. Light transmission through scattering medium diminishes with increased constituent dielectric cylinder diameter d: (a) 120 nm, (b) 200 nm, (c) 280 nm, and (d) 360 nm. The amplitude and direction propagation of light is randomized for each wavelength.

Broadband Silicon Photonics Polarization Beam Splitters Designed Using Genetic Algorithm

Professor Ding-Wei Huang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所黃定洧教授

In this work, we present a design method for a directional coupler-type polarization beam splitter (PBS) for ultrabroadband operation based on a genetic algorithm (GA). The PBS is discretized into short sections, with the geometric parameters of each section optimized using a GA. For PBSs with an operating wavelength range λ = 1400–1650 nm, the insertion losses are less than 0.14 dB and 0.58 dB, and the maximum crosstalk is −20.6 and −16.2 dB for the TE and TM modes, respectively. Under the fabrication error of +/-10nm for the waveguide widths, the device shows negligible performance variation.

Fig. 1. Schematic of the Broadband silicon photonics polarization beam splitter.

Fig. 2. Output power at the Bar and Cross ports for the TE and TM modes calculated by 3D-FDTD simulation.