Measurement of the tuneable absorption in GaN-based multi-section laser diodes

We present an experimental technique to measure the absorption spectra of the absorber section of GaN-based multi-section laser diodes using optical gain spectroscopy. We find that the absorption of the examined laser diodes decreases with increasing negative bias, which results from a reduction of the internal field in the quantum wells by the external voltage. A maximum modal absorption as high as 250 cm(-1) at the laser wavelength of 413nm is measured at 1V absorber voltage.