Strategy of optical negative feedback for narrow linewidth semiconductor lasers.

Area of Science:

• Optics and Photonics
• Semiconductor Physics
• Laser Engineering

Background:

• Semiconductor lasers are susceptible to frequency modulation (FM) noise.
• Optical feedback mechanisms can be used to control laser properties.
• Fabry-Perot optical filters offer frequency-selective feedback.

Purpose of the Study:

• To systematically investigate a coherent optical negative feedback scheme.
• To analyze FM noise reduction in a semiconductor laser coupled to a Fabry-Perot filter.
• To determine optimal conditions for minimizing laser linewidth and noise.

Main Methods:

• Calculation of rate equations modeling a noise-added semiconductor laser.
• Coupling the laser model with a Fabry-Perot optical filter.
• Analysis of feedback phase and its effect on reflectivity and discrimination efficiency.

Main Results:

• FM noise is minimized when the free-running laser frequency matches the filter's valley frequency.
• Linewidth is also minimized at this optimal lasing frequency.
• Laser frequency exhibits reduced sensitivity to injection current fluctuations under optical negative feedback.

Conclusions:

• Coherent optical negative feedback effectively reduces FM noise and linewidth in semiconductor lasers.
• Optimal performance is achieved when the laser frequency aligns with the Fabry-Perot filter's valley frequency.
• The scheme enhances laser frequency stability against injection current variations.