Experiment and Simulation of a Selective Subwavelength Filter with a Low Index Contrast

• Main Authors: Tao Li, Mohamed Asbahii, Jian-Yee Lim, Hong Xie, Chan-Wai Koh, Min-Hao Goh, Kian-Soo Ong, Hang Zhang, Ding Ding
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: Nanomaterials
• Subjects: contrast; nanophotonics; grating; selective
• Online Access: https://www.mdpi.com/2079-4991/9/10/1497

Subwavelength gratings have been of great interest recently due to their ability to eliminate multiple orders. However, high index contrast (<inline-formula> <math display="inline"> <semantics> <mrow> <mo>&#916;</mo> <mi>n</mi> <mo>&#8764;</mo> <mn>3</mn> </mrow> </semantics> </math> </inline-formula>) is typically achieved using metals or high-index dielectrics surrounded by vacuum in order to maintain good optical selectivity. Here, we theoretically propose and experimentally realize a selective subwavelength grating using an index contrast of <inline-formula> <math display="inline"> <semantics> <mrow> <mo>&#916;</mo> <mi>n</mi> <mo>&#8764;</mo> <mn>1.2</mn> </mrow> </semantics> </math> </inline-formula> without vacuum. Despite its low index contrast, our simulation and experiments show that good optical selectivity is achieved using the same physics as subwavelength gratings made of high-index contrast. Such polymer-based encapsulated gratings are easier to scale up for use in large-area applications such as photovoltaics and lighting.