Integration of Emission-Wavelength-Controlled InAs Quantum Dots for Ultra-Broadband Near-Infrared Light Source

Near-infrared (NIR) light sources are widelyutilized in biological and medical imaging systems owing totheir long penetration depth in living tissues. In a recentlydeveloped biomedical non-invasive cross-sectional imagingsystem, called optical coherence tomography (OCT), abroadband spectrum is also required, because OCT is basedon low coherence interferometry. To meet these operationalrequirements, we have developed a NIR broadband lightsource by integrating self-assembled InAs quantum dots(QDs) grown on a GaAs substrate (InAs/GaAs QDs) withdifferent emission wavelengths. In this review, we introducethe developed light sources and QD growth techniques thatare used to control the emission wavelength for broadbandemission spectra with center wavelengths of 1.05 and 1.3 μm.Although the strain-induced Stranski-Krastanov (S-K)mode-grown InAs/GaAs QDs normally emit light at awavelength of around 1.2 μm, the central emissionwavelength can be controlled to be between 0.9–1.4 μm bythe use of an In-flush technique, the insertion of a strainreducinglayer (SRL) and bi-layer QD growth techniques.These techniques are useful for applying InAs/GaAs QDs asNIR broadband light sources and are especially suitable forour proposed spectral-shape-controllable broadband NIRlight source. The potential of this light source forimproving the performance of OCT systems is discussed