Abstract

The modification of the transverse mode structure owing to optical feedback (OF) has been studied in a vertical-cavity surface-emitting laser (VCSEL) supporting the two lowest order modes (LP₀₁ and LP₁₁) [1]. Preferential excitation of either mode can be effected by appropriate choice of optical feedback delay, τ [1]. On the other hand, solitary VCSEL supporting those modes has low mode partition noise (MPN) as is seen from its double peak RIN spectrum [2] (see Fig. 1a). In this work we study the RIN spectrum of a multi-mode cylindrical weak index guided VCSEL subject to weak optical feedback. The model incorporates the spatial dependence of carrier and optical field profiles, and Lang-Kobavashi rate equations [1]. We show that the RIN double peak structure and low MPN are maintained in the presence of OF. Variations in τ are shown to alter the RIN spectrum from a twin peak to a single peak structure due to transverse mode selection. It is also shown that multiple reflections in the external cavity can affect the mode selection depending on τ. The impact of thermal effects is also taken into account through the consideration of typical current dependent wavelength shifts. Narrower current ranges in which a particular transverse mode is selected are obtained when ohmic heating is considered. Finally, the effect of ohmic heating on RIN characteristics will be also addresed.

© 1998 IEEE