Abstract
The development of highly efficient light-controlled functional fiber elements has become indispensable to optical fiber communication systems. Traditional nonlinearity-based optical fiber devices suffer from the demerits of complex/expensive components, high peak power requirements, and poor efficiency. In this study, we utilize colloidal quantum dots (CQDs) to develop a light-controlled optical fiber interferometer (FI) for the all-optical control of the transmission spectrum. A specially designed exposed-core microstructure fiber (ECMF) is utilized to form the functional structure. Two types of PbS CQDs with absorption wavelengths around 1180 nm and 1580 nm, respectively, are deposited on the ECMF to enable the functional FI. The wavelength and power of control light are key factors for tailoring the FI transmission spectrum. A satisfactory recovery property and linear relationship between the spectrum shift and the power of control light at certain wavelength are achieved. The highest wavelength shift sensitivity of our light-controlled FI is 4.6 pm/mW, corresponding to an effective refractive index (RI) change of 5 × 10-6 /mW. We established a theoretical model to reveal that the RI of the CQD layer is governed by photoexcitation dynamics in CQD with the light absorption at certain wavelength. The concentration of charge carriers in the CQD layer can be relatively high under light illumination owing to their small size-related quantum confinement, which implies that low light power (mW-level in this work) can change the refractive index of the CQDs. Meanwhile, the absorption wavelength of quantum dots can be easily tuned via CQD size control to match specific operating wavelength windows. We further apply the CQD-based FI as a light-controllable fiber filter (LCFF) in a 50-km standard single-mode fiber-based communication system with 12.5-Gbps on-off keying direct modulation. Chirp management and dispersion compensation are successfully achieved by using the developed LCFF to obtain error-free transmission. CQDs possess excellent solution processability, and they can be deposited uniformly and conformally on various substrates such as fibers, silicon chips, and other complex structure surfaces, offering a powerful new degree of freedom to develop light control devices for optical communication.
Highlights
Optical fibers are media that offer the lowest attenuation of light transmission, and they are widely applied in high-speed, large-capacity, and low-latency communication systems
We revealed that the colloidal quantum dots (CQDs) refractive index (RI) change exhibits a linear relationship with the photoexcited electron concentration
The incident light power shows a linear relationship with the RI change in the fiber devices, in consistency with the theoretical model
Summary
Optical fibers are media that offer the lowest attenuation of light transmission, and they are widely applied in high-speed, large-capacity, and low-latency communication systems. Solution-processed CQDs afford nanoscale dispersion, and the functional material can and conformally be deposited on fiber or silicon chips to fabricate robust devices. In this regard, many schemes have been proposed to develop fiber sensors based on the surface plasmonic effect and fluorescence wavelength [19,20,21]. Three factors are considered as the main reason for the low energy photoexcitation dynamics of CQD in our experiments: (a) the quantum confinement and the small size of the CQD enable high carrier (charge) density, typically 1018 ~1019 cm−3, at mW light injection; (b) the exposed core enable the near core deposition in the fiber by which the CQD could receive sufficient light energy illumination at the evanescent field [25]; and (c) the evanescent field along the core surface enhances the photoexcitation in CQD. The device is applied in a 12.5-Gbps directly modulated on-off keying (OOK) communication system for 50-km SMF transmission for chirp management and dispersion compensation
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