Twin-Field Quantum Key Distribution Protocol Based on Wavelength-Division-Multiplexing Technology

Quantum key distribution(QKD) generates information-theoretical secret keys between two parties based on the physical laws of quantum mechanics. Following the advancement in quantum communication networks, it becomes feasible and economical to combine QKD with classical optical communication through the same fiber using dense wavelength division multiplexing(DWDM) technology. This study proposes a detailed scheme of TF-QKD protocol with DWDM technology and analyzes its performance, considering the influence of quantum channel number and adjacent quantum crosstalk on the secret key rates. The simulation results show that the scheme further increases the secret key rate of TF-QKD and its variants. Therefore, this scheme provides a method for improving the secret key rate for practical quantum networks.

High-performance and fabrication friendly polarization demultiplexer

A compact and fabrication friendly polarization demultiplexer(P-DEMUX) is proposed and characterized to enable wavelength-division-multiplexing and polarization-division-multiplexing simultaneously. The proposed structure is composed of a polarization-selective microring resonator in ultrathin waveguide and two bus channels in the silicon nitridesilica-silicon horizontal slot waveguides. In the slot waveguide, the transverse electric(TE) mode propagates through the silicon layer, while the transverse magnetic(TM) mode is confined in the slot region. In the designed ultra-thin waveguide, the TM mode is cut-off. The effective indexes of the TE modes for ultrathin and slot waveguides have comparable values. Thanks for these distinguishing features, the input TE mode can be efficiently filtered through the ultra-thin microring at the resonant wavelength, while the TM mode can directly output from the through port. Simulation results show that the extinction ratio of the proposed P-DEMUX for TE and TM modes are 33.21 dB and 24.97 dB, and the insertion losses are 0.346 dB and 0.324 dB, respectively, at the wavelength of 1551.64 nm. Furthermore, the device shows a broad bandwidth(> 100 nm) for an extinction ratio(ER) of > 20 dB. In addition, the proposed P-DEMUX also has a good fabrication tolerance for the waveguide width variation of-20 nm≤ △w_(g)≤ 20 nm and the microring width variation of -20 nm≤ △w_(r) ≤20 nm for a low insertion loss of < 0.75 dB and low ER of <-18 dB.

10-Gb/s Transmission in WDM PON Employing Reflective Semiconductor Optical Amplifier and Fibre Bragg Grating Equaliser

We propose a 10-Gb/s Wavelength- Division-Multiplexed Passive Optical Network （WDM-PON） scheme with upstream transmi- ssion employing Reflective Semiconductor Op- tical Amplifier （RSOA） and Fibre Bragg Gra- ting （FBG） optical equaliser. Transmissions of 10-Gb/s non return-to-zero signals using a 1.2- GHz RSOA and FBG optical equaliser with different setups are demonstrated. Significant performance improvement and 40-kin standard single mode fibre transmission are achieved using FBG optical equaliser and Remotely Pum- ped Erbium-Doped Fibre Amplifier （RP-EDFA）, where they are used to equalise the output of the band-limited RSOA and amplify the seed light and upstream signal, respectively.