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Double-fused vertical-cavity surface-emitting lasers ͑VCSELs͒ have demonstrated the highest temperature performance of any 1.5 m VCSEL, but further optimization is needed to reduce their temperature sensitivity. We present and analyze threshold current measurements of these devices between Ϫ90°C and 30°C stage temperature. Despite a zero gain peak offset from the emission wavelength at room temperature, the pulsed threshold current has its minimum near Ϫ50°C corresponding to about Ϫ30 nm gain offset. This is in contrast to a common VCSEL design rule. Temperature effects on the optical gain of the strain-compensated InGaAsP/InP active region are found to be the main cause for the disagreement. A design rule modification is proposed. Numerical simulation of an optimized 1.55 m VCSEL shows that gain offset improvements are counteracted by loss mechanisms.

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