Abstract
Transverse mode control of a vertical-cavity surface-emitting laser
(VCSEL) is achieved by spatially filtered optical feedback. The spatial filter
consisted of a pinhole, either 42 $\mu$m or 81 $\mu$m,
in the 5.8$\,\times$ magnified
VCSEL image plane of a confocal lens arrangement. The pinhole was translated
to map out the voltage drop across the VCSEL from spatially-selective feedback.
For low injection currents, spatial filtered feedback enabled single fundamental
mode operation due to higher-order mode suppression by appropriately locating
the pinhole. For higher injection currents with five laser modes, spatial
selection of feedback enabled control of the relative mode intensities and
wavelengths. The maximum increase in mode intensity achieved was 1.8$\,\times$ for the 4 $\mu$m pinhole and 2.4$\,\times$ for the 81 $\mu$m pinhole. The maximum frequency shift achieved
was ${- 2.7}~$GHz and ${- 7.1}~$GHz with the 42 $\mu$ and the 81 $\mu$m pinholes. The spatially selective optical feedback
produced long-lived changes to the VCSEL even after the feedback was blocked—results
for two separate trials where the recovery time was 38 minutes are presented
(although results varied for different bias and feedback conditions).
© 2008 IEEE
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