Design Considerations for Asymmetric Multiple Quantum Well Broad Spectral Width Superluminescent Diodes

We investigated the design of broad spectral width super luminescent diodes (SLDs) with asymmetric multiple-quantum-well (AMQW) active regions. The design is based on theoretical modeling, which starts with calculation of the gain. Two InGaAsP/InP AMQW SLD structures centered at 1.3 mum were grown and processed. Both gave a broad spectral width of >80 nm when operated at the transition carrier density (TCD). Structure 1 was designed based on gain simulations only and was found to be able to provide broad spectral width only at low injection currents. Thus, Structure 1 gives low output power. Based on this experience, structure 2 was designed to achieve a broad gain at a higher TCD than Structure 1. Experimental results show that structure 2 provided a reasonable power and broad spectral width at the TCD. Thus, we conclude that, compared with normal design criterion which depends on the gain spectrum only, the design of an AMQW SLD has to include a relatively high TCD to obtain reasonable output power. The SLDs were ridge waveguide structures with seven degree tilted-stripes. Use of double section waveguides could further broaden the SLD spectrum at the red side by >10 nm.