Low Surface Reflectance Structure at Near Infrared Wavelength by Injection Molding

Abstract

Plastic lenses are utilized for optical communication devices such as AOC (Active Optical Cable), transceivers and connectors in order to improve coupling efficiency. In order to reduce the optical loss of the communication device one must also, reduce the Fresnel loss due to the refractive index of the transparent thermoplastic resin, the typical solution is, use of an Anti-reflection (AR) coating. Although it is possible to greatly lower the reflectance at the end face of the lens by this AR coating, the cost of the device is increased. To solve this problem we propose, reduction of reflectance in the near infrared wavelength band without AR coating by transferring the nanoscale concavo-convex structure through injection molding alone. Furthermore, to achieve low reflectance in various transparent thermoplastic resin, we propose a new method to drastically improve the transferability of the surface shape during injection molding. Utilizing this both methods, we successfully developed surface structure with a concavo-convex of 0.3 µm or more and a 2% or less reflectance at over 1 µm wavelength.