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Smart functional fiber devices are indispensable for optical fiber based communication and sensing systems, in which the integration of fiber structure with smart semiconductor materials is essential. Among various choices, the colloidal quantum dot (CQD) is of great interests and its advantages includes: (a) the concentration of the photo-excited electrons can be relatively high due to the quantum confinement in the CQD, which means the refractive index of CQD could be altered with less power consumption; (b) CQD is a nanoscale dispersion solution thus the functional material can be deposited conformally on fiber, silicon chips or other complex structure surface; (c) CQD is a highly tunable material, and the chemical composition and operation wavelength can be specially designed for any wavelength window.
In this work, we developed a platform to deposit the CQD with fiber structures for smart sensing and communication applications. First, we construct optical fiber antennas for gas sensing, in which the CQD conformally coated on the fiber surface behave like olfactory receptors. The gas molecules adsorbed on the quantum dots change the local carrier concentration in quantum dot solids, which leads to a change in their refractive index. This interaction of gas molecules with quantum dots could be transformed into optical signals through the optical fiber antennae. Owing to the large surface area, highly tunable physical and chemical properties of colloidal quantum dots, combined with the versatile fiber microstructure, the optical fiber antennae with quantum dots offer a new degree of freedom to precise, real-time and large-scale gas monitoring. Second, by using the light-excited carriers in CQD, a light controlled fiber device has been achieved as a delayed interferometric comb filter. The transmission spectrum can be easily tailored by mW-scale optical power. This device was applied in a 50 km standard single mode fiber (SSMF) based communication system with 12.5 Gbs On-Off-Keying (OOK) direct modulation for chirp management and dispersion compensation to achieve the error-free transmission.
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