Integrated(de)multiplexer for orbital angular momentum fiber communication

The quickly increasing data transfer load requires an urgent revolution in current optical communication. Orbital angular momentum(OAM) multiplexing is a potential candidate with its ability to considerably enhance the capacity of communication. However, the lack of a compact, efficient, and integrated OAM(de)multiplexer prevents it from being widely applied. By attaching vortex gratings onto the facets of a few-mode fiber, we demonstrate an integrated fiber-based OAM(de)multiplexer. A vortex grating fabricated on the fiber facet enables the direct multiplexing of OAM states at one port and the demultiplexing of OAM states at the other port. The measured bit error rate of the carrier signal after propagating through a 5-km few-mode fiber confirms the validity and effectiveness of the proposed approach. The scheme offers advantages in future high-capacity OAM communication based on optical fiber.

Sensitivity-enhanced surface plasmon resonance sensor utilizing a tungsten disulfide (WS_2) nanosheets overlayer

Tungsten disulfide （WS2）, as a representative layered transition metal dichalcogenide （TMDC） material, possesses important potential for applications in highly sensitive sensors. Here, a sensitivity-enhanced surface plasmon resonance （SPR） sensor with a metal film modified by an overlayer of WS2 nanosheets is proposed and demo onstrated. The SPR sensitivity is related to the thickness of the WS2 overlayer, which can be tailored by coating a WS2 ethanol suspension with different concentrations or by the number of times of repeated post-coating. Benefitting from its large surface area, high refractive index, and unique optoelectronic properties, the WS2 nanosheet overlayer coated on the gold film significantly improves the sensing sensitivity. The highest sensitivity （up to 2459.3 nm/RIU） in the experiment is achieved by coating the WS2 suspension once. Compared to the case without a WS2 overlayer, this result shows a sensitivity enhancement of 26.6%. The influence of the WS2 nano- sheet overlayer on the sensing performance improvement is analyzed and discussed. Moreover, the proposed WS2 SPR sensor has a linear correlation coefficient of 99.76% in refractive index range of 1.333 to 1.360. Besides sensitivity enhancement, the WS2 nanosheet overlayer is able to show additional advantages, such as protection of metal film from oxidation, tunability of the resonance wavelength region, biocompatibility, capability of vapor, and gas sensing.

Secure orthogonal time-frequency multiplexing with two-dimensional encryption for optical-wireless communications

This paper firstly,to the best of our knowledge,proposed two-dimensional(2D)encryption based on the Arnold transformation for implementing a secure DC-biased optical orthogonal time-frequency multiplexing(DCO-OTFM)in optical-wireless communications(OWCs).The encrypted data is transformed to the particular 2D matrix and decrypted by the only key to get the correct information.Meanwhile,the number of keys in 2D encryption is enormous,which prevents eavesdroppers from exhaustively searching secret keys rapidly to find the right decryption.Numerical results demonstrate that the secure DCO-OTFM based on 2D encryption can effectively prevent signal decryption from the eavesdropper,which has good secure performance for applying in OWC.