A NARROW BEAM 1.3-MU-M-SUPER LUMINESCENT DIODE INTEGRATED WITH A SPOT-SIZE CONVERTER AND A NEW-TYPE REAR ABSORBING REGION

The device structure and performance of 1.3-mu m narrow beam superlumi nescent diodes (NB-SLD's), which consist of a spot-size converter and a new type rear absorbing region, are reported. A butt-jointed selecti vely grown spot-size converter (SSC) is employed to realize the narrow beam characteristics. The rear absorbing region is designed as a tape r structure with a part of the region is inclined from the active-stri pe axes. In order to investigate the effects of both SSC length and ac tive-region length on device performance, two types of NB-SLD's, whose SSC and active-region lengths differ, are fabricated. An electrode to sweep out photoexcited carriers in the absorption region is formed on one device. By comparing the characteristics of these devices, we cla rify that a 500-mu m-active-region device is suitable for high-output power operation, and a 400-mu m-active-region device is suitable for r ealizing short coherent length. The light-output power is 13.9 mW at 2 00-mA-injection current for the former device, and the full-width at h alf-maximum (FWHM) of the spectrum is 62.6 mm (calculated coherence le ngth is 26.5 mu m) for the latter device. Very small spectral modulati on index (0.015 at 5 mW-output power) is attained by grounding the abs orption-region electrode. For the SSC length, a 300-mu m SSC device sh ows very narrow far-field patterns (FFP's) and very good fiber-couplin g characteristics. The FWHM of horizontal and vertical FFP's are 8.9 a nd 10.6 degrees, respectively. Because of this narrow beam divergence, the coupling efficiency of -1.9 dB to a flat-end 4-mu m spot-size fib er is obtained without lenses. The alignment tolerance of this device to the fiber for both horizontal and vertical direction is more than 3 mu m at a loss of when -1 dB from the optimum coupling.