Fiber-based quantum secure direct communication without active polarization compensation

Quantum secure direct communication(QSDC)that allows people to directly transmit confidential information through insecure channels is an important branch of quantum communication.The widespread adoption of the QSDC demands the development of simple and stable systems.However,most of the existent QSDC systems involve a complex self-alignment process at the initial stage and additional hardware to compensate environmental disturbance.In this study,we present a fiber-based QSDC system without active polarization compensation.Our system comprises a stable transmitter and a novel Sagnac-Mach-Zehnder interferometer for security detection.This robust system simplifies the self-alignment and is immune to environmental disturbance.The robustness of the system was theoretically and experimentally verified,and low bit error rates in a 12 min continuous operation with an active polarization scrambler were attained.In addition,we performed a proof-of-principle QSDC demonstration,and a secrecy capacity of 3.43 kbps over a 5 km fiber with a detection bit error rate of 0.85%±0.07%and a quantum bit error rate of 0.42%±0.05%were achieved.Experimental results confirm the viability of the proposed QSDC system for practical applications.

Magnetostrictive Polarization Compensation on SOI Rib Waveguide

We proposed a novel application of magnetostriction for tuning differential -group- delay (DGD) and polarization- dependent-loss (PDL) of silicon- on -insulator waveguide. A magnetic-field induced change in PDL of over 4dB and a change in DGD by Ips was

High-speed polarization mode dispersion compensation in a 43-Gb/s RZ-DQPSK transmission system over 1200 km of standard single-mode fibre

This paper reports that the designed optical polarization mode dispersion compensator shows a good performance under the real-time variation of differential group delay, state of polarization and principal state of polarization in a （40×43）-Gb/s dense-wavelength-multiplexing, 1200-km enhanced return-to-zero differential-quadrature-phase-shift- keying （RZ-DQPSK） system. The polarization mode dispersion tolerance of the system is improved by 26 ps using the optical polarization mode dispersion compensator. The short and long time stabilities are tested with the bit error ratio recorded.

Polarization mode dispersion compensation in a novel dual polarization differential quadrature phase shift keying system

A novel dual polarization differential quadrature phase shift keying （DP-DQPSK） system is proposed, whose receiver is the same as the single polarization DQPSK system, while it does not need polarization de-multiplexing like the conventional polarization division multiplexing QPSK （PDM-QPSK）. Polarization mode dispersion （PMD） is mainly considered and PMD compensation for the DP-DQPSK system is studied. As the feedback signal for PMD compensation, the degree of polarization of the signals is discussed in detail. The results show that PMD tolerance can be improved by 89 ps within 1 dB optical signal noise ratio penalty after PMD compensation for the DP-DQPSK system.

A Novel Compact-Structure Arrayed-Waveguide Grating Device

Arrayed waveguide grating (AWG) device,a novel compact structure,is presented based on silicon on insulator (SOI) material.A total internal reflection (TIR) waveguide mirror is fabricated at the middle of each arrayed waveguide.An approach of compensating TE TM mode polarization is presented by using the phase difference,which is caused by TIR at the waveguide mirror.This AWG device has advantage for its small size and simple technigue of fabrication.The experimental results are given and the feasibility of fabrication is tested.

Rotating polarizer, compensator, and analyzer ellipsometry

In this paper we propose theoretically a set of ellipsometric configurations using a rotating polarizer, compensator, and analyzer at a speed ratio of N1ω：N2ω：N3ω. Different ellipsometric configurations can be obtained by giving different integral values to N1, N2, and N3. All configurations are applied to bulk c-Si and GaAs to calculate the real and imaginary parts of the refractive index of the samples. The accuracies of all ellipsometric configurations are investigated in the presence of a hypothetical noise and with small misalignments of the optical elements. Moreover, the uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients are studied. The comparison among different configurations reveals that the rotating compensator–analyzer configuration corresponds to the minimum error in the calculated optical parameters.

Silicon-based decoder for polarization-encoding quantum key distribution

Silicon-based polarization-encoding quantum key distribution(QKD)has been extensively studied due to its advantageous characteris-tics of its low cost and robustness.However,given the difficulty of fabricating polarized independent components on the chip,previ-ous studies have only adopted off-chip devices to demodulate the quantum states or perform polarization compensation.In the cur-rent work,a fully chip-based decoder for polarization-encoding QKD was proposed.The chip realized a polarization state analyzer and compensated for the BB84 protocol without the requirement of additional hardware,which was based on a polarization-to-path conversion method utilizing a polarization splitter-rotator.The chip was fabricated adopting a standard silicon photonics foundry,which was of a compact design and suitable for mass production.In the experimental stability test,an average quantum bit error rate of 0.59%was achieved through continuous operation for 10 h with-out any polarization feedback.Furthermore,the chip enabled the automatic compensation of the fiber polarization drift when utiliz-ing the developed feedback algorithm,which was emulated by a ran-dom fiber polarization scrambler.Moreover,a finite-key secret rate of 240 bps over a fiber spool of 100 km was achieved in the case of the QKD demonstration.This study marks an important step to-ward the integrated,practical,and large-scale deployment of QKD systems.

A novel tunable polarization mode dispersion compensator with strain chirped fiber Bragg gratings

A tunable polarization mode dispersion (PMD) compensator based on strain-ckirped fiber Bragg gratings (FBGs) is proposed. It natures in flexible designing, large tuning range, without using linear or nonlinear chirped phase mask, fast tuning response time, continuously adjustable, all-fiber based, compact, and cheap.

Intense ke V IAP generation by orthogonally polarized multicycle midinfrared two-color laser fields

We theoretically investigate the attosecond pulse generation in an orthogonal multicycle midinfrared two-color laser field. It is demonstrated that multiple continuum-like humps, which consist of about twenty orders of harmonics and an intensity of about one order higher than the adjacent normal harmonics, are generated when longer wavelength driving fields are used. By filtering these humps, intense isolated attosecond pulses（IAPs） are directly generated without any phase compensation. Our proposal provides a simple technique to generate intense IAPs with various central photon energies covering the multi-ke V spectral regime by using multicycle midinfrared driving pulses with high pump energy in the experiment.

Electronic Properties of BaTiO3 （110） Polar Terminations

The band structures, electron, density differences, and surface energies of five different BaTiO3 （110） ter- minations were investigated by first-principles calculations. According to the calculated results of electron density differences, the bonding characteristics of these considered terminations were discussed. The computational results indicate that the BaTiO-terminated surface is metallic, while the 02-, O-, Ba- and TiO-terminated surfaces are all in- sulative. Furthermore, the computed surface energies suggest that for the considered terminations, the polarity com- pensation achieved through surface reconstruction or surface defect is more effective than by change in surface elec- tronic structure. The defected or reconstructed terminations predominate over cleavage and construction of BaTiO3 crystal along （110） direction.

TIME AND POLING HISTORY DEPENDENT ENERGY STORAGE AND DISCHARGE BEHAVIORS IN POLY(VINYLIDENE FLUORIDE-CO-HEXAFLUOROPROPYLENE) RANDOM COPOLYMERS

We studied cycle time （0.01-10 s with triangular input waves） and poling history （continuous versus fresh poling） dependent electric energy storage and discharge behaviors in poly（vinylidene fluoride-co-hexafluoropropylene） [P（VDF- HFP）] films using the electric displacement -- the electric field （D-E） hysteresis loop measurements. Since the permanent dipoles in PVDF are orientational in nature, it is generally considered that both charging and discharging processes should be time and poling history dependent. Intriguingly, our experimental results showed that the charging process depended heavily on the cycle time and the prior poling history, and thus the D-E hysteresis loops had different shapes accordingly. However, the discharged energy density did not change no matter how the D-E loop shape varied due to different measurements. This experimental result could be explained in terms of reversible and irreversible polarizations. The reversible polarization could be charged and discharged fairly quickly （〈 5 ms for each process）, while the irreversible polarization depended heavily on the poling time and the prior poling history. This study suggests that it is only meaningful to compare the discharged energy density for PVDF and its copolymer films when different cycle times and poling histories are used.