Coherence Length Characteristics from Broadband Semiconductor Emitters: Superluminescent Diodes versus Broadband Laser Diodes

This paper reports on the measurement and analysis of the coherence function for broadband emitters such as superluminescent diodes (SLDs) and novel broadband laser diodes (BLDs) from self-assembled InGaAs/GaAs quantum-dot (QD) and InAs/InP quantum-dash (Qdash) structures that emit at center wavelengths of 1150nm and 1650nm, respectively. Using the fiber-based spectral interferometry system, coherence lengths in fiber of 23 mu m and 48 mu m have been measured from the QD and Qdash BLDs. Larger spectral bandwidth of 137 nm and 78 nm have been measured from the QD and Qdash SLDs that yield coherence lengths in fiber of 3 mu m and 10 mu m, respectively. The coherence function of both BLDs and SLD reveals negligible secondary coherence subpeaks and sidelobes indicating the possibility of using these broadband sources to produce low artifacts optical coherence tomography (OCT) images.