It combines two measurement curves in one graph: The L/I curve shows the dependence of the optical light intensity of the laser on the operating current and is used to determine the operating point and threshold current. The V/I curve shows the voltage applied to the laser as a function of the operating current. If the derivative functions are calculated from this, anomalies (kinks) of the laser diodes can be recognised even more clearly.

LIV test systems usually consist of a photodiode, integrating spheres and source-measure units (SMUs). In combination with a spectroradiometer, additional spectral properties of the laser diodes such as peak wavelength and half-width (FWHM) can be determined. These quantities often show a dependence on the operating current. For a VCSEL, this can mean a shift of the peak wavelength towards higher wavelengths with increasing operating current. Depending on the laser type and requirements, further measurement technology is necessary. The efficiency of laser diodes often decreases significantly with increasing temperature. Therefore, a temperature-dependent analysis is relevant for applications in the automotive sector, for example. Specwin Pro supports the connection of an external temperature unit for tests from 15 to 150 °C.