Super-luminescent laser diodes (SLD) in 800 to 1300 nm wavelength windows have been widely used in optical coherence tomography (OCT) systems. The imaging resolution of OCT systems is proportional to the bandwidth of the SLD light source. Here we present a new design to achieve broad bandwidth (>100nm at 1310nm) in one chip by using two types of quantum wells. The bandwidth of an SLD with a single active region is determined by the material bandwidth, confinement factor, and the length of the active region. Neglecting spatial hole burning (SHB), the spectral density of amplified spontaneous emission (ASE) can be the function of cavity length and spectral density of spontaneous emission and net gain. The main factor that limits the ASE bandwidth is the net gain. The bandwidth of net gain has to be larger than 200 nm to obtain a 100 nm wide ASE spectrum if the ASE power is larger than several mW. SLDs usually work at very high pump current (>400mA) to achieve high output power. From simulations, we found the level of electron injection mainly determines the material gain. At the high injection level, large bandgap quantum wells can get high gain and dominate the spectrum if the improper design is used. So in our design, we put the small bandgap quantum wells at the N side to make the electron distribution in favor of long-wavelength material. Thus, and will be balanced at high current injection level (>550mA). Figure 7 shows the measured spectrum of such structure. The achieved spectral width is larger than 100nm and out put power is larger than 5 mW.

Date Published: 3 May 2007
PDF: 7 pages
Proc. SPIE 6534, Fifth International Conference on Photonics and Imaging in Biology and Medicine, 653404 (3 May 2007); doi: 10.1117/12.741096

Published in SPIE Proceedings Vol. 6534:
Fifth International Conference on Photonics and Imaging in Biology and Medicine
Qingming Luo; Lihong V. Wang; Valery V. Tuchin; Min Gu, Editor(s)