We have fabricated two types of InGaN superluminescent diodes applying two different concepts of cavity suppression: a tilted waveguide geometry and passive absorber solution. Both types of devices showed superluminescence behavior, but both eventually lased under the application of high enough current. The lasing threshold turned out to be higher for tilted waveguide devices. By using long (2 mm) waveguides, we managed to demonstrate the power in superluminescent mode exceeding 100 mW in blue/violet part of the spectrum.
The design process of superluminescent diode has been discussed on the basis of nitride diodes with bend-waveguide geometry. The devices were fabricated by MOVPE technique on bulk GaN substrates and emitted light at the wavelength of around 420 nm. The effectiveness of the cavity suppression design was confirmed by measurements of high-resolution emission spectra. Further optimization was carried out by appropriate selection of the angles of the waveguide bend and the chip length. Thus; we succeeded in fabrication of high optical power superluminescent diodes with slope efficiency fully comparable to that of laser diodes (greater than 0.9 W/A).Comparison of emission spectra of a superluminescent diode and a laser diode.
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