An method for characterizing a modulator for fabricating a silicon photonics circuit and an apparatus (e.g., a silicon photonics wafer) made via the method are described. The method includes determining an absorption spectrum of a modulator and determining, based at least on the determined absorption spectrum, an operational bandwidth of the modulator. The method further includes selecting a laser for coupling with the modulator using the operational bandwidth of the modulator. In this way, the laser is selected such that it has an emission bandwidth that corresponds to the operational bandwidth of the modulator.