Proposal of mosaic-based 2 × 2 3-dB couplers for prospective on-chip communication in mid-infrared wavelengths around 2.1 µm

Abstract

We propose two types of mosaic-based 2 × 2 3-dB couplers for wavelengths around 2.1 µm. For type I, the proposed device provides excess loss of < 0.22 dB and imbalance of < ± 0 . 07 d B over the wavelength range from 2.06 to 2.14 µm. Compared with the standard multimode-interference-based 2 × 2 3-dB coupler, the imbalance is improved by ∼ 0.4 d B . For type II, coupling length in the multimode-interference region is about three times shorter than the one based on multimode-interference theory. It provides excess loss of < 0.49 d B and imbalance of < ± 0 . 23 d B over the wavelength range from 2.06 to 2.14 µm. Both proposed devices show high fabrication tolerance to hole diameter variation. Especially for type II, the fabrication-tolerant direct binary search was effective to obtain such a structure. These mosaic-based 2 × 2 3-dB couplers will play an important role in highly integrated photonic circuits.