Abstract: A multi-mode interference (MMI) device includes a substrate layer, a core layer deposited on the substrate layer for propagating an optical signal, and a cladding layer deposited on the core layer for guiding the optical signal. The core layer includes a core section suitable for propagating multiple optical signals having different wavelengths. The core section includes a shifting segment for uniquely shifting phases of the multiple optical signals. The shifting segment includes at least one or a combination of sections having different effective refractive index, a tilted segment, a curved section, and waveguides with variations in width, thickness or effective refractive index.