Experimental study of guided-wave modes in 1.3 μm InGaAsP light-emitting diodes

We report the results of an experimental study of the far-field characteristics of InGaAsP edge-emitting light-emitting diodes. Our results show that the asymmetric structure in the transverse far-field distribution of the device is caused by modes which are supported by the asymmetric dielectric waveguide. These modes propagate in the InP cladding layer with the higher refractive index at an angle to the fundamental mode. Their relative intensities, compared to the fundamental mode intensity, increase as the active layer thickness decreases below 0.1 μm, accounting for the observed concomitant decrease in the fiber-coupling efficiency of these devices.