Abstract
Near-infrared (NIR) light sources are widely utilized in biological and medical imaging systems owing to their long penetration depth in living tissues. In a recently developed biomedical non-invasive cross-sectional imaging system, called optical coherence tomography (OCT), a broadband spectrum is also required, because OCT is based on low coherence interferometry. To meet these operational requirements, we have developed a NIR broadband light source by integrating self-assembled InAs quantum dots (QDs) grown on a GaAs substrate (InAs/GaAs QDs) with different emission wavelengths. In this review, we introduce the developed light sources and QD growth techniques that are used to control the emission wavelength for broadband emission 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 a wavelength of around 1.2 μm, the central emission wavelength can be controlled to be between 0.9–1.4 μm by the use of an In-flush technique, the insertion of a strain-reducing layer (SRL) and bi-layer QD growth techniques. These techniques are useful for applying InAs/GaAs QDs as NIR broadband light sources and are especially suitable for our proposed spectral-shape-controllable broadband NIR light source. The potential of this light source for improving the performance of OCT systems is discussed.
Highlights
1.1 Broadband light source required in optical coherence tomography (OCT) systemNear-infrared (NIR) light is commonly utilized in biomedical imaging systems owing to its long penetration depth in biological samples
These results demonstrate that the emission intensity and bandwidth of the In-flushed quantum dots (QDs) can be controlled by optimizing ΔT in the In-flush process, and the peak wavelength can be maintained at 1.05 μm
We outlined our proposed spectral-shape-controllable light source based on monolithically grown multiple QDs, and the growth techniques that have been developed for controlling the growth area and emission wavelength of the self-assembled InAs QDs on GaAs substrate
Summary
Near-infrared (NIR) light is commonly utilized in biomedical imaging systems owing to its long penetration depth in biological samples. 1.3 Proposal for spectral-shape-controllable broadband light source based on monolithically grown multi-color InAs QDs. An NIR broadband light source based on multiplestacked self-assembled InAs QD layers with different emission wavelengths has been realized. The techniques for controlling the central emission wavelength of the InAs QDs grown on GaAs are described in sections 3 and 4 These are based on previously reported bi-layer QD growth and Inflush techniques, which can be applied to broadband light sources centered at 1.3 and 1.05 μm, respectively. We introduce EL data obtained from stacked QD layers with controlled emission wavelengths These results are applicable for the monolithic growth technique, and enable the integration of multiple QD ensembles, providing the possibility to span the 0.9–1.4 μm range. We discuss the potential of these approaches for realizing novel NIR broadband light sources that meet the three requirements for ideal OCT light sources
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