An analytic model of diode lasers applicable to both the lasing and the nonlasing states is described. For these homogeneously broadened devices, spectral envelope widths for TE00and TM00modes are related to power in each modal family and are shown to depend critically on spontaneous emission coupling into the transverse modes. Thus, lasers with real-refractive index waveguiding (and associated weak spontaneous emission coupling) operate single longitudinal mode above threshold, whereas gain-guided devices run multimode. After connecting gain and spontaneous emission, a charge conservation equation, containing optical power in the form of a stimulated emission term, pumping current, spontaneous emission, and spectral width, is derived. These equations are then demonstrated to suffice for determination of the completeLversusIcharacteristic. For lasers in which both charge and mode confinement exist, such as the buried heterostructure (BH) and channelled-substrate narrow stripe (CNS) types, it is shown that both TM00power and spectral envelope width approach limiting values at threshold, whereas TE00mode power grows in conjunction with TE00spectral envelope narrowing.