A method used to enhance mode selectivity of VCSELs with large oxide apertures

Vertical-cavity surface-emitting diode lasers (VCSELs) exhibit excellent performance characteristic: they are principally single-longitudinal-mode devices and their circular optical beam is low divergent and without astigmatism. These virtues, however, are limited in standard VCSELs to relatively low outputs because of an excitation of higher-order transverse (HOT) modes with an increase in a VCSEL active-region diameter. Therefore the above attractive VCSEL performance requires then additional suppression of HOT modes. In the present paper, the advanced optical-electrical-thermal-gain fully self-consistent VCSEL model has been applied to compare efficacy of two such suppression methods. As expected, in the standard VCSEL without any modification and with the relatively large active-region (12 μm diameter), the HOT LP
₅₁
and LP
₆₁
modes have been found at room temperature (RT) to be the lowest-threshold ones. In the first modified VCSEL with additional 3 DBR periods of radius 3.5 μm located centrally on the original DBR mirror, no essential improvement has been obtained. But the VCSEL with an additional layer of a thickness equal to a ¼ of the lasing wavelength beyond the same central active region (the inverted-relief structure) has been found to be extraordinarily selective and the fundamental LP
₀₁
mode exhibits at RT much lower threshold than any other transverse modes.