The Effects of Optical Feedback on Polarization of Vertical Cavity Surface Emitting Lasers
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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Vertical Cavity Surface Emitting Lasers VCSELs are a type of semiconductor laser with a cavity oriented orthogonally to the planes of material growth. These lasers differ from conventional edge emitting lasers in several important ways. They have symmetric output beams and they are easily built into two dimensional arrays, making them very attractive as photonic components. The characteristic of interest in this thesis is polarization. While the asymmetric cavities of edge emitters exhibit a clear preference for light polarized in a particular direction, the cylindrically symmetric cavity of a VCSEL has no clear preference. Therefore, it should be relatively easy to change the polarization of a VCSEL. This thesis examines the polarization switching effects of optical feedback from an external reflector. By feeding back various amounts of cross-polarized light, the switching susceptibility of the VCSEL can be determined. Measurements confirmed that the polarization of a VCSEL can be switched through polarized optical feedback, with the degree of switching depending on the strength of feedback. This switching was a relatively rare behavior, indicating that most VCSELs had some type of preferential polarization. This preference could be due to the VCSEL structure itself or the manner in which it was excited.
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