Computer Science
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........21b&link_type=abstract
Thesis (PH.D.)--AIR FORCE INSTITUTE OF TECHNOLOGY, 1995.Source: Dissertation Abstracts International, Volume: 56-12, Section: B,
Computer Science
Scientific paper
The optical switching capabilities of Distributed Bragg Reflector (DBR) structures, including Vertical Cavity Surface Emitting Lasers (VCSELs) are examined. Reflectivity switching in the DBR/VCSELs is demonstrated using both thermal and carrier-generated effects to alter the mirror layers' refractive indices. Optical bistability in the DBR and VCSELs is demonstrated at room temperature, under CW photo-pumped excitation. The optical bistability is exhibited when the DBR/VCSEL is photo-pumped at the short wavelength edge of the high reflectivity band (stop band) of each device. In the DBR, reflectivity bistability is evidenced as the pump intensity is increased/decreased. The optical bistability hysteresis is controllable by spectral location of the pump on the stop band edge. In the VCSEL, which consists of a bulk GaAs gain region sandwiched by DBR mirrors, reflective bistability is also evidenced; additionally, this bistability is accompanied by a bistability in the VCSEL lasing output intensity, its laser spot size, and in its wavelength. Modeling of the DBR/VCSEL thermally -induced bistability was accomplished using an iterative, three dimensional Green's function solution to the laser -induced heat equation. The model reliably predicts thermally generated bistability, indicating a wavelength dependence, reflectivity jump, self-focusing induced spot size change, and wavelength jump commensurate with the experimental data. Reflectivity switching due to carrier effects is also demonstrated, the DBR and VCSELs exhibiting sub-picosecond switching speeds and contrast ratios of 3:1. Carrier heating, two-photon absorption, and thermal components of the reflectivity switching capabilities are examined and found to be consistent with measured nonlinear response characteristics for the refractive index in AlGaAs.
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