Direct observation of the spatial hole burning and the saturation of the spontaneous emission in InGaAsP/InP lasers

The saturation behavior of the spontaneous emission intensity from a diffused-stripe InGaAsP/InP laser is studied. In InGaAsP/ InP DH lasers, a spontaneous emission can be observed through the InP substrate without any optical loss. The spatial distribution and the spectrum of the emission were directly observed from the substrate surface. The spatial hole burning was observed in the wider stripe lasers but in the case of narrow stripe lasers, the spontaneous emission almost uniformly saturates. The spectrum of the emission from the center of the narrow stripe lasers was analyzed and it was confirmed that, above the threshold current, the spectra in the lasing region saturated over the entire spectral region.