Investigations of the spectral characteristics of 980-nm fiber pump lasers

Al,,58Gao,42 waveguide whose total thickness is 500 nm. The NSOM system, described schematically in Fig. 2,13 uses cantilevered optical elements3 with a resolution of -100 nm. The principles of scanning and control have been described in Refs. 3 and 4. The output from the cantilevered optical fibers passed through a monochromator and was detected by use of a sensitive silicon APD. Figure 3a14 describes a spatially resolved L-I curve measured with the high-resolution fiber placed at the wire center. We note a clear threshold at 100 mA and a linear response up to about one and a half times threshold. In Fig. 3b we show the optical spectrum, measured with a 2-nm resolution, of the light collected from the wire region at a drive current of 140 mA. We observe essentially a single-moded emission at 806 nm that did not change for drive currents of 100 mA to 150 mA. Figure 3c shows a detailed image of the fundamental heart-shaped lasing mode, measured at several drive currents below and above threshold with the monochromator set to 806 nm. The measured pattern at 150 mA, which is highlighted in Fig. 3d, confirms the predicted shape’ with a remarkable accuracy. In addition to the high resolution scans of the wire region, we have also scanned the complete laser cross section and recorded the spatially resolved spectra at several drive currents. These measurements revealed emission from the sloped areas as well as the top corners ofthe structure yielding important information on current and injected carrier leakage paths in these complex devices. In conclusion, we have performed high spatial resolution measurements of light-current characteristics, emission spectra, and nearfield intensity distributions of QWR diode lasers using NSOM techniques. Our results provide important information relevant to the design of these devices. Nanonics Ltd., Jerusalem, Israel is acknowledged for providing the cantilevered optical fibers used in these experiments. *Electrical Engineering Department, Technion, Haqa, Israel **Physics Department, Swiss Federal Institute of Technology, Lausanne, Switzerland 1. E. Kapon et al., Optoelectron. Dev. and Technol. 8,429 (1993). 2. E. Kapon et al., Superlattices and Microstructures 12,491 (1992). 3. S. Shalom, K. Lieberman, A. Lewis, S. R. Cohen, Rev. Sci. Instrum. 63,4061 (1992). 4. U. Ben-Ami, N. Ben-Ami, G. Fish, N. Tessler, R. Nagar, G. Eisenstein, A. Lewis, J. M. Nielsen, A. Moller-Larson, Appl. Phys. Lett. 65,648 (1994).