On the operational and manufacturing tolerances of GaAs-AlAs MQWmodulators
Goossen, K.W.; Cunningham, J.E.; Jan, W.Y.; Leibenguth, R.
Quantum Electronics, IEEE Journal of
Volume 34, Issue 3, Mar 1998 Page(s):431 - 438
Digital Object Identifier 10.1109/3.661450
Summary:We approach the question of optimization of surface-normal
p-i(multiquantum-well, MQW)-n modulators from the viewpoint of
investigating their tolerance to variations in wavelength and
temperature and errors in manufacture. The reflection characteristics of
two high-quality samples are carefully processed to eliminate
Fabry-Perot fringes, and then their spectra at any bias are
characterized with six phenomenological parameters which depend on
λ0, the zero-field exciton position. The two GaAs-AlAs
samples have λ0's of 833.8 and 842.3 nm, and so cover
a range useful for modulators designed to operate near 850 nm in the
normally reflecting condition, i.e., reflection decreases with field. A
linear interpolation of the parameters of these two samples is used to
predict the behavior of MQW diodes with λ0's around
this range, and so a fully comprehensive examination of normally
reflecting MQW modulators is performed. The performance aspect that is
examined is contrast ratio as a function of nonuniformities in the
devices or operating conditions given a voltage swing of 3 V. There are
two operational modes discussed. If the voltage offset of the bias is
allowed to vary via a feedback circuit, a contrast of 2:1 may be
maintained over an operating wavelength change (Δλ) of 17
nm with local variations of wavelength of ±1 nm, which
corresponds to a temperature variation of 60°C while allowing for
variations of laser driver wavelength of ±1 nm. If feedback Is
not permitted, we determine that, given tolerances to manufacturing
errors, a contrast of 1.5:1 may be maintained over a wavelength range of
~5 nm by either using stacked diode designs or extremely shallow quantum
wells
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