Hidden far-field beam profile artifacts in wide-angle radiometric goniometry

Area of Science:

• Photonics and Waveguide Optics
• Optical Engineering
• Laser Diagnostics

Background:

• Far-field intensity patterns are key for characterizing photonic devices and wave propagation modes.
• Analyzing subtle waveguiding effects using wide-angle far-field profilometry presents experimental challenges.

Purpose of the Study:

• To develop a compact and practical scanning radiometer for complete 2π sr far-field intensity measurements.
• To address the challenge of accurately characterizing far-field profiles, especially concerning subtle waveguiding effects.
• To propose a calibration method to prevent misinterpretation of laser modes caused by experimental misalignment.

Main Methods:

• Investigated a compact scanning radiometer geometry for comprehensive far-field intensity distribution measurement.
• Studied the impact of axial misalignment and tilt on far-field measurements.
• Developed and applied a variance-based instrument calibration procedure.

Main Results:

• Demonstrated a scanning radiometer capable of complete 2π sr far-field measurements.
• Identified that minor axial misalignment or tilt can lead to misclassification of fundamental mode lasers as higher-order mode devices.
• Successfully obtained accurate high-resolution far-field profiles of a ridge-waveguide semiconductor laser using the proposed calibration.

Conclusions:

• The proposed scanning radiometer geometry is practical for complete far-field analysis.
• A variance-based calibration is essential to avoid erroneous mode identification in the presence of misalignment.
• Accurate far-field profilometry is achievable for photonic devices, enabling reliable characterization of waveguiding properties.