Spontaneous emission factor of oxidized vertical-cavity surface-emitting lasers from the measured below-threshold cavity loss

A method to estimate the spontaneous emission factor $\beta$ is proposed and applied to the 780 nm oxidized vertical-cavity surface-emitting lasers. The proportionality of the measured cavity loss multiplied by optical power to injected current is used. Our results agree better with theoretical calculations than those of conventional light-current curve fitting. The spontaneous emission factor of 0.0021 is obtained for a 2-$\mu$ m-square device at room temperature. Since only the below-threshold information of cavity loss and output power are used in our method, the obtained $\beta$ values are independent of any complex and unexpected above-threshold effects such as thermally induced mode-size contraction, as they should be.