title: Transformation between directional couplers and multi-mode interferometers based on ridge waveguides.
abstract: We present a unique comparison of ridge-type directional couplers (DC) and multi-mode interferometers (MMI) in terms of their transformational relationship. The two devices are intimately related as the MMI is derived from the DC. We show for the first time the continuous evolution from the two-mode coupling characteristic of DC to the multimode mixing and interference characteristic of MMI, as the DC is structurally transformed into the MMI. We also show that DC can be designed to have the MMI features of compactness and polarization-insensitivity, two traits that reflect their shared lineage. However, the design of DC requires careful control of a large set of design parameters, while the MMI design is more robust and involves fewer design variables.
authors.forename: Shuh Ying
authors.initials: SY
authors.lastname: Lee
authors.forename: Stevanus
authors.initials: S
authors.lastname: Darmawan
authors.forename: Chee-Wei
authors.initials: CW
authors.lastname: Lee
authors.forename: Mee-Koy
authors.initials: MK
authors.lastname: Chin