Low-loss high-index-contrast planar waveguides with graded-index cladding layers

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Waveguide Technology

Background:

• High-index-contrast (HIC) waveguides are crucial for miniaturized photonic integrated circuits.
• Scattering loss due to sidewall roughness is a major limitation in HIC waveguides.
• Existing methods for loss reduction often compromise the high-index-contrast condition.

Purpose of the Study:

• To experimentally demonstrate propagation loss reduction in HIC glass waveguides.
• To investigate the effectiveness of graded-index (GRIN) cladding layers for loss mitigation.
• To achieve low propagation loss without sacrificing the HIC property.

Main Methods:

• Fabrication of arsenic-based sulfide strip waveguides with integrated thin GRIN cladding layers.
• Experimental measurement of propagation loss in the fabricated waveguides.
• Analysis of scattering loss reduction attributed to the GRIN cladding structure.

Main Results:

• Achieved a record low propagation loss of 1.5 dB/cm in small-core (1.6 μm x 0.35 μm) waveguides.
• Demonstrated significant reduction in scattering loss originating from sidewall roughness.
• Maintained the high-index-contrast (Δn = 1.37) condition with the GRIN cladding.
• Showcased the general applicability of the GRIN cladding design to other HIC systems like Si/SiO2.

Conclusions:

• Graded-index (GRIN) cladding layers effectively reduce propagation loss in HIC glass waveguides.
• This technique offers a viable solution for minimizing scattering loss in optical devices.
• The GRIN cladding approach is a versatile design applicable to various HIC waveguide platforms.