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

Yuxi Ruan1, Bin Liu2, Yanguang Yu3

  • 1School of Electrical, Computer and Telecommunications Engineering, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia. yr776@uowmail.edu.au.

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Summary

This study introduces a novel method to measure the linewidth enhancement factor (alpha factor) using laser relaxation oscillation (RO) frequencies with external optical feedback (EOF). The technique simplifies alpha factor determination, requiring only RO frequencies and minimal target movement.

Keywords:
external optical feedbacklaser sensorslinewidth enhancement factorrelaxation oscillationself-mixing interferometry

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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.