Supermode analysis and characterization of the coherent vertical cavity surface emitting laser array
Jahan, Nusrat
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Permalink
https://hdl.handle.net/2142/121320
Description
Title
Supermode analysis and characterization of the coherent vertical cavity surface emitting laser array
Author(s)
Jahan, Nusrat
Issue Date
2023-06-27
Director of Research (if dissertation) or Advisor (if thesis)
Choquette, Kent D.
Doctoral Committee Chair(s)
Choquette, Kent D.
Committee Member(s)
Gary Eden, James
Lyding, Joseph W.
Dragic, Peter D.
Department of Study
Electrical & Computer Eng
Discipline
Electrical & Computer Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
supermode, VCSEL, VCSEL array
Abstract
The coherent coupling of optical fields in ion-implanted photonic crystal vertical cavity surface emitting laser (VCSEL) arrays results in the formation of supermodes. These arrays consist of elements defined by defects in the photonic crystal etched into the top distributed Bragg reflector. Isolated gain apertures, created through ion-implantation, establish an antiguided profile with a low index in the cavity and a high index in the interelement region. We simulate the supermodes using a 2-dimensional complex waveguide model that considers the photonic crystal, free carrier and mirror loss, laser threshold gain, and carrier-induced index suppression for the antiguided index profile. We find the N-element antiguided nearest-neighbor coupled array exhibits N fundamental nondegenerate supermodes that oscillate within a narrow frequency range for N=2, 3, and 6. Complex waveguide modal simulations allow us to analyze the evolution of the dominant supermode examining the impact of index suppression. Experimental observations support our simulation results and validate the identification of the dominant supermode based on Fourier-transformed far-field patterns. Adjusting the injection conditions, we can couple the array elements into a desired supermode, particularly an in-phase supermode where all elements have the same phase. This in-phase supermode exhibits a narrow central lobe beam width, improving the beam divergence compared to a single-element VCSEL. As we increase the number of elements in the antiguided coherent array, we observe higher gain discrimination between fundamental supermodes and higher-order modes, accompanied by a narrower beam divergence, compared to a single VCSEL. Additionally, the fraction of optical power confined within the narrow spot of the in-phase coupled beam exceeds that of a single VCSEL, thus demonstrating potential for high-brightness single mode applications.
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