Proposal and simulated characteristics of high-extinction-ratio electroabsorption modulator based on multimode interference waveguide

Abstract

We proposed an electroabsorption modulator (EAM) based on a 1 × 1 multimode interference waveguide (MMI-EAM). A partial electroabsorption (EA) region is asymmetrically placed in a MMI. In a multiple quantum well core layer of the region, the electrorefractive index change is also exhibited in addition to the EA effect, which leads to change in the position of a self-image at the output port of the MMI waveguide. Owing to the combination of the EA effect and change in electrorefractive index, the extinction ratio is significantly improved compared with a conventional EAM with almost the same area of the EA region. We discuss the optimization of the MMI-EAM structure and investigate its modulation characteristics theoretically using the beam propagation method. The results show that the extinction ratio can be increased by 25 dB in the MMI-EAM with the length of 152 μm and the width of 6 μm.

Proposal of compact multimode interference optical modulator with high extinction ratio

“…A triply coupled QW (TCQW) structure is newly designed for the enhancement of the QCSE, and the MMI waveguide is symmetrically divided into three regions with isolation trenches. The length of the MMI waveguide is decreased by 30% compared with that of the previously proposed MMI-EAM 31) with the high extinction ratio maintained.…”

“…In addition, in the vicinity of the output port, interference occurs between the propagated lights that are out of phase by approximately π rad, leading to a high extinction ratio caused by the interference effect, as also observed in a Mach-Zehnder interferometer. 31) The synergy of the EA effect and the electric-field-induced index change effect greatly enhances the extinction of the output light compared with a conventional EAM.…”

“…32) In this paper, we propose a 1 × 1 MMI optical intensity modulator 33) with a smaller footprint than the previously proposed MMI-EAM. 31) Although it has already been reported in Ref. 33, we discuss the design of a quantum well (QW) structure for a larger QCSE and its modulation characteristics in more detail.…”

“…28) Novel MMI-based intensity modulators have also been proposed. 29,30) We have also proposed an MMI-EAM 31) for ultrahigh extinction ratios based on both electrorefractive index change and the EA effect based on the quantumconfined Stark effect (QCSE). 32) In this paper, we propose a 1 × 1 MMI optical intensity modulator 33) with a smaller footprint than the previously proposed MMI-EAM.…”

“…The length was reduced by 30% compared with that in the MMI modulator previously proposed. 31) The core layer is 182 nm thick consisting of multiple TCQWs sandwiched by 50 nm thick undoped InGaAlAs layers for a separate confinement heterostructure. The lower and upper cladding layers are n-and p-doped InP layers, respectively.…”