High-confinement waveguides for mid-IR devices

Abstract

We analyze the use of heavily doped semiconductor layers as a means to tightly confine light. The very low refractive index ( n≈1) that is present just above the plasma frequency renders large index steps possible. Slab waveguide structures with InP or GaAs cladding layers doped to n D ∼10 19 cm −3 are analyzed in the mid-IR wavelength range, λ=4– 15 μm . The performance of the waveguide in terms of achieved overlap with an active region of a given thickness versus the waveguide absorption, is compared to waveguides based on surface plasmons. The calculated results indicate that these plasma effect waveguides should be favourable in this respect for wavelengths λ≈6–10 μm using heavily doped InP as a cladding. In GaAs efficient use of the plasma effect is limited to wavelengths λ≳9 μm . Guidelines for required doping levels are given.