Measuring Linewidth Enhancement Factor by Relaxation Oscillation Frequency in a Laser with Optical Feedback

Area of Science:

• Optics and Photonics
• Laser Physics
• Semiconductor Devices

Background:

• The linewidth enhancement factor (alpha factor) is a critical parameter in semiconductor lasers, influencing their modulation characteristics and spectral properties.
• Existing methods for measuring the alpha factor often require complex experimental setups, precise control of external targets, or knowledge of numerous laser parameters.

Purpose of the Study:

• To develop a simplified and more accessible method for measuring the linewidth enhancement factor (alpha factor) in lasers with external optical feedback (EOF).
• To derive a measurement formula for the alpha factor that relies solely on relaxation oscillation (RO) frequencies.

Main Methods:

• Derivation of a new measurement formula for the alpha factor based on relaxation oscillation (RO) frequencies under external optical feedback (EOF).
• The proposed method requires only the measurement of RO frequencies at a few different positions of a target along the light beam, eliminating the need for symmetric reciprocal movement.
• Validation of the method through both numerical simulations and experimental verification.

Main Results:

• A novel formula for determining the alpha factor using only RO frequencies was successfully derived.
• The proposed method simplifies the measurement process by not requiring knowledge of internal or external laser parameters.
• The technique was demonstrated to be effective even for lasers with an alpha factor less than 1.
• Experimental results confirmed the accuracy and feasibility of the proposed measurement method.

Conclusions:

• The developed method offers a significant advancement in measuring the alpha factor, making it more practical and widely applicable.
• This technique reduces experimental complexity and broadens the scope of alpha factor measurement to include cases with low alpha values.
• The findings contribute to a better understanding and characterization of semiconductor laser dynamics.