1：Experimental Design and Method Selection:

The design involves cascaded planar and non-planar tapered directional couplers (DCs) to multiplex and demultiplex modes in a five-mode waveguide. Tapering is used to enhance bandwidth and reduce polarization dependence.

2：Sample Selection and Data Sources:

A five-mode (de)multiplexer is fabricated using polymer materials (EpoCore and EpoClad) on an oxidized Si substrate.

3：List of Experimental Equipment and Materials:

Equipment includes a prism coupler (Metricon 2010) for refractive index measurement, a mode solver (COMSOL) for simulations, 3D finite-difference beam propagation method (3DFD-BPM, BeamPROP by RSoft) for transmission simulations, photolithography and oxygen reactive ion etching (RIE) for fabrication, an ASE source (B&A AS4600), a tunable laser (Santur TL-2020-C-107), an optical power meter, an infrared camera (MicronViewer 7290A), and an optical spectrum analyzer (OSA, Anritsu MS9740A). Materials include EpoCore and EpoClad polymers.

4：Experimental Procedures and Operational Workflow:

Fabrication involves spin-coating, photolithography, etching, and curing processes. Characterization includes launching light into waveguides, measuring output powers and spectra, and capturing near-field patterns.

5：Data Analysis Methods:

Data is analyzed using simulation tools and measured outputs to calculate coupling efficiencies, insertion losses, and crosstalks.