Metal-Clad Optical Waveguides: Analytical and Experimental Study

TLDR

Planar optical waveguides with metal‑clad dielectric films have been studied both theoretically and experimentally. A computational tool was developed to calculate phase and attenuation constants and mode wavefunctions for TE and TM modes in symmetric and asymmetric metal‑clad waveguides, and approximate slide‑rule expressions were derived and validated with numerical results for photoresist films clad with Al, Ag, and Au. Experimental measurements of attenuation and phase constants at 0.633 µm agree with theory, showing attenuations below 1 dB cm⁻¹, while abrupt unclad‑to‑metal‑clad transitions cause significant losses that can be mitigated with tapered transitions.

Abstract

Planar optical waveguides consisting of thin dielectric films with metal cladding have been investigated theoretically and experimentally. A computer program was devised to provide the phase and attenuation constants and wavefunctions for TE and TM modes in symmetric and asymmetric guides. Approximate expressions suitable for slide-rule calculation were also derived. Numerical results and illustrations are given for films of photoresist with Al, Ag, and Au cladding. Direct measurements of the attenuation and phase constants at 0.633 microm of numerous experimental waveguides are in reasonable agreement with theory. Attenuations <1 dB/cm, which is sufficiently small for application in devices, were measured. Calculated wavefunctions illustrate the mismatch of modes at transitions between unclad and metal-clad waveguides. Experimentally, we find substantial losses at such abrupt junctions. They can be overcome by simple tapered transitions.