The reduction of the threshold current Ith to a practical value requires improving the rate of stimulated emission and also improving the efficiency of the optical cavity. First we can confine the injected electrons and holes to a narrow region around the junction. This narrowing of the active region means that less current is needed to establish the necessary concentration of carriers for population inversion. Secondly, we can build a dielectric waveguide around the optical gain region to increase the photon concentration and hence the probability of stimulated emission. This way we can reduce the loss of photons traveling off the cavity axis. We therefore need both carrier confinement and photon confinement. Both of these requirements are readily achieved in modern laser diodes by the use of heterostructured devices as in the case of high-intensity double heterostructure LEDs. However, in the case of laser diodes, there is an additional requirement for maintaining a good optical cavity that will increase stimulated emissions over spontaneous emissions.