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Title:Loss in Vertical-Cavity Source-Emitting Lasers as a Result of Impurities
Author(s):Tai, Charlene
Contributor(s):Choquette, Kent D.
Subject(s):vertical cavity surface emitting laser
semiconductor laser
optical loss
oxide-confined micro-cavity
Abstract:Vertical-­cavity source emitting lasers (VCSELs) are useful for optical communication light sources because of their low cost and operating power. An understanding of the cavity optical loss is necessary in order to best optimize the design and performance of the devices. Using a method which measures the sub-threshold emission spectra, the loss can be quantitatively calculated. With this, optical loss of VCSELs with varying doping levels can be evaluated. With a semiconductor parameter analyzer, light output power as a function of injection current is measured for each different set of VCSELs to find the threshold current. The resulting current density can be found for each laser mesa size and the point where loss becomes independent of the aperture size can be identified. Using and optical spectrum analyzer, the spectral separation between the cold-cavity fundamental mode and the first higher-order mode can then be found without thermal effects by measuring the spectral splitting for each VCSEL biased at an injection current of approximately 0.9 times the threshold. The spectral splitting of small diameter lasers can be used to calculate the optical loss using the Helmholtz wave equation with an imaginary refractive index. The field amplitude loss can be extracted from the imaginary part of the resulting wavenumber. Two VCSEL samples with different doping are measured in this study. The calculated size-dependent loss is found to be the same for the two samples and thus it seems that that effects of the different doping are not sufficient to affect the cavity loss. It is, however, clearly shown that the introduction of impurities to create a doped pn junction does indeed create optical loss.
Issue Date:2014-12
Date Available in IDEALS:2015-11-05

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