Spontaneous emission distribution in planar VCSELs (original) (raw)

Spie Proceedings Series, 1997

Abstract

Recently a high level of in-plane emission in VCSELs has been reported [1]. Existence of the problem for vertical cavities has been previously demonstrated in connection with electron beam pumped lasers [2] and LED [3]. The effect results in increasing threshold and a reduction of efficiency of the devices [2]. Prilimenary estimation shows importance of the problem for large diameter VCSEL as well [4]. Thus, suppression of the in-plane emission gives a way of improvement of VCSEL operational characteristics. Features of the spontaneous emission (SE) pattern is a basis for simulation and modelling of the effect. In this paper the SE is considered for both λ- and λ/2- cavities in the framework of a planar multilayer structure model taking into account the QW optical spectrum. The model is suitable for large diameter VCSELs with weak radial boundaries and allows the consideration of both in-plane and vertical propagating modes. Besults of calculation show that, for a λ/2-cavity, all in-plane propagating modes have weak coupling to a dipole of the active region (QW), unlike the λ-cavity case where there is a mode having a field maximum in the position of QW and thus strong dipole coupling. This leads to a 2 - 4 times reduction of spontaneous emission in the in-plane direction for the λ/2-cavity. However, this is still comparable with the SE in vertical modes and therefore can not be neglected, as is usually assumed. The vertical modes in general propagate at different angles to the pure vertical direction and hence have an in-plane component of the propagation constant. Analysis shows the pure vertical part of the SE to be extremely small compared to the total. Thus, the in-plane component of the SE should be taken into account to improve VCSEL design.

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