Measurements of cavity-length-dependent internal differential quantum efficiency and internal optical loss in laser diodes

We measured the cavity length dependence of the internal differential quantum efficiency eta(int), and the internal optical loss alpha(int) in 1500-nm-wavelength laser diodes (LDs). By evaluating alpha(int) directly from gain/absorption spectra for various injection current densities and measuring the external differential quantum efficiency eta(ext) we obtained the eta(int) and eta(int), values of all the LDs with different cavity lengths. The obtained eta(int) and alpha(int) respectively showed strong and weak cavity length dependences, against the cavity length. and were both very different from those derived by the widely used method of plotting