ASE-FFT-based DBR reflection spectrum reconstruction and internal reflection analysis in monolithically integrated...

Area of Science:

• Photonics
• Integrated Optics
• Semiconductor Lasers

Background:

• Monolithically integrated tunable electro-modulated lasers (TEMLs) require precise characterization of internal optical properties.
• Non-destructive analysis methods are crucial for optimizing performance and yield in photonic integrated circuits (PICs).

Purpose of the Study:

• To develop and validate a non-destructive, on-chip method for analyzing internal reflection characteristics in TEMLs.
• To quantify distributed Bragg reflector (DBR) reflectivity, spectral shifts, and interface reflections within TEMLs.

Main Methods:

• Application of amplified spontaneous emission (ASE)-based fast Fourier transform (ASE-FFT) to below-threshold spectra.
• Selective inverse FFT of the DBR section to reconstruct its intrinsic Bragg spectrum.
• Harmonic amplitude ratio analysis for cavity loss estimation.

Main Results:

• Achieved 21% DBR reflectivity at 1542.2 nm and a ~3.2 nm redshift of the Bragg wavelength with 50 mA DBR current.
• Quantified ~11 dB reflection reduction from an antireflection coating and residual active-passive interface reflections.
• Observed absorption-induced spectral narrowing and baseline rise in distance-domain response due to electro-absorption modulator bias.

Conclusions:

• The ASE-FFT method provides a low-complexity, real-time, and spatially resolved tool for characterizing reflections in TEMLs.
• This technique is applicable for spectral characterization and reflection mapping of various photonic integrated circuits.
• The method eliminates the need for external light sources or interferometers, simplifying on-chip analysis.