Silicon band-rejection and band-pass filter based on asymmetric Bragg sidewall gratings in a multimode waveguide

• Published in: Optics letters 2016-06, Vol.41 (11), p.2450-2453
• Main Authors: Qiu, Huiye, Jiang, Jianfei, Yu, Ping, Dai, Tingge, Yang, Jianyi, Yu, Hui, Jiang, Xiaoqing
• Format: Article
• Language: English
• Subjects: Asymmetry; Bandpass filters; Electric filters; Insertion loss; Ports; Reflection; Wave filters; Waveguides
• ISSN: 0146-9592; 1539-4794
• DOI: 10.1364/OL.41.002450

A silicon photonic wire filter based on an asymmetric sidewall Bragg grating in a multimode silicon-on-insulator strip waveguide is demonstrated. The operating principle is based on the contra-directional coupling between the transverse electric fundamental (TE0) and first-order (TE1) modes, which is enabled by the asymmetric spatially periodic refractive-index perturbations. An asymmetric Y-junction is cascaded at the input port of the filter so as to drop the Bragg reflection. Compared with conventional Bragg grating-based filters, this device eliminates the back reflection at the input port and the 6 dB inherent insertion loss at the drop port; moreover, a narrow 3 dB bandwidth can be obtained with a large critical dimension as a result of the weak coupling strength between the TE0 and TE1 modes inside the multimode waveguide. Experimental results show that a bandwidth of ∼2.8  nm is achieved by a large corrugation width of 150 nm. The insertion loss at the drop port is -2.1  dB, and the extinction ratio is -33  dB at the through port.