Accurate determination of waveguide-fed p-i-n photodiode absorption

Experimental and theoretical determinations of the absorption of a waveguide fed GaInAs photodiode are presented. The absorption is determined as a function of the propagation length using μ-p-i-n diodes regularly spaced along the GaInAs absorbing layer. The detector absorption is as high as 2060 dB/cm. However, for propagation lengths longer than ~200 μm it falls to about 120 dB/cm. The results are analyzed using two different approaches. The first consists in determining the eigenmodes of both the passive waveguide and the detector/waveguide structure. The second is the beam propagation method (BPM). Both methods demonstrate that the absorption curve can be fully explained by the existence of two modes, of which the one with the lowest absorption is induced by the presence of an undoped InP buffer layer. Both eigenmode decomposition and BPM are in quantitative agreement with the experimental data