Superluminescent Diode With Circular Beam Shape

We report a new design for a superluminescent diode (SLD) that can provide a nearly circular output beam shape and a high output power in a tunable external cavity laser (T-ECL). The proposed SLD consists of an active region and a spot size converter (SSC) region. The active region is realized using a planar buried hetero structure for low electrical and optical leakages and the SSC region is realized using a buried deep ridge waveguide (BD-RWG) for narrow far-field patterns. In particular, we investigate the effects of the structural parameters in the SSC region on the output chip power and field patterns. In our structure, as the width of the passive waveguide core layer decreases, both the lateral and vertical far-field patterns tend to converge at ~ 13° under an etching depth of BD-RWG of ≥ 9 μm. The measured data agree well with the simulated results. Using this design, we can increase the output power of T-ECL from 3.7 to 7.9 mW at an injection current of 60 mA.