Polymer-Embedding Germanium Nanostrip Waveguide of High Polarization Extinction

Area of Science:

• Photonics
• Materials Science
• Optoelectronics

Background:

• Semiconductor-polymer heterogeneous waveguides are emerging components in integrated photonics.
• Accurate characterization of optical parameters for materials like germanium (Ge) is essential for device design.
• Spectroscopic ellipsometry faces challenges with highly absorbing materials, necessitating alternative measurement techniques.

Purpose of the Study:

• To investigate the optical properties of a germanium nanostrip embedded in a polymer waveguide.
• To assess the potential of this heterogeneous waveguide for optical applications.
• To develop a method for verifying optical parameters of nanostrip components.

Main Methods:

• Fabrication of a germanium nanostrip embedded in a polymer.
• Optical transmission measurements of the waveguide across a specific wavelength range.
• Analysis of propagation loss for transverse magnetic (TM) and transverse electric (TE) modes.
• Modeling of bandgap narrowing using Tauc fitting.

Main Results:

• The germanium/polymer waveguide exhibits strong TE mode absorption from 1500 nm to 2004 nm.
• TM mode propagation loss decreases from 20.56 dB/cm at 1500 nm to 4.89 dB/cm at 2004 nm.
• Observed TE mode absorption at 2004 nm exceeds the bulk crystalline Ge cut-off wavelength, attributed to bandgap narrowing in amorphous Ge.

Conclusions:

• The transmission characteristics of the waveguide accurately verify optical parameters (refractive index and extinction coefficient) of the germanium nanostrip.
• The redshift in absorption is linked to a narrowed Tauc-fitted bandgap due to grain ordering in the amorphous germanium layer.
• Precise characterization of light-absorbing nanostrips in waveguides is vital for the development of integrated photonic devices.