A split-step birefringence simulation method is proposed to investigate the gating efficiency and intensity distribution of the Kerr signal field considering the evolution of the switch beam and probe beam in their path. Using this simulation method, we investigated the switch-beam power-dependent gating efficiency and conducted an experiment to prove its reliability. Furthermore, we analyzed the optical intensity distribution of the Kerr signal exiting the Kerr medium under different switch-beam powers. This study provides an effective theoretical tool for the design and optimization of optical Kerr gates.
We used Maxwell’s partial differential equations of electrodynamics to quantify radiation and scattering on rough surfaces. The electrical field and the magnetic field are the results from the near-field. To find the bidirectional reflectance distribution function (BRDF) of the far-field, we present an algorithm for BRDF based on near-to-far-field projection and Poynting vector analysis. This algorithm accounts for characteristics of the BRDF function, focuses on the Poynting vector of the outgoing radiation, and creates a virtual projection surface to serve for the BRDF. The near-field data are recorded on a rectangular shape, and the far-field data are recorded on a virtual hemispherical surface. The BRDF can be calculated using Green’s theorem for the selected area on the virtual hemispherical surface. The results show that, for RMS 0.1 to 0.5 μm, the incident wavelengths are 400 to 700 nm, the surface roughness ranges from smooth to slightly rough, the simulation agrees with the scattering theory, and the accuracy of the algorithm is significantly higher than that of the Cook–Torrance BRDF model.
A highly linearized microwave photonic link (MPL) based on a dual-drive Mach–Zehnder modulator (DDMZM) is proposed. Eliminating or suppressing these nonlinear distortions is achieved by adjusting the polarization of the light and the frequency of the radio frequency (rf) signal as well as controlling the dc bias voltage of DDMZMs. The proposed technique is verified by the simulation test of two-tone and three-tone. Theoretical analysis and simulation experiments show that under the two-tone condition, when the modulation depth is <0.8, intermodulation distortion (IMD) and even-order harmonic distortion (HD) can be completely eliminated, and third-order HD can be suppressed under the background noise level. Compared with traditional MPL, the spurious free dynamic range of MPL is improved by 11 dB. In addition, in the three-tone test, when the modulation depth is <1, the second-order distortion is completely eliminated and the IMD3 third-order HD are suppressed. The scheme can be used in single octave or multiple octave systems.
The value range of AoP (angle of polarization) is physically limited to [0, π]. However, for most programing languages such as Matlab and C/C++, the range of inverse tangent function is commonly limited to [-π/2, -π/2]. Therefore, this paper derives a practical formula for AoP calculation based on the inverse tangent function of common programming languages. Because AoP is a periodical function, the conventional gray image cannot effectively display the AoP levels. The hue component of HSV (hue, saturation and value) color space is also periodical. Therefore, this paper maps the AoP to hue component and then transforms HSV space to RGB space. Different AoP reference orientations will produce different false color displays. In our experiment, polarization images of a fishbowl scene are captured by a DoFP (division of focal plane) polarization camera, and a sequence of false RGB images with different reference orientations are produced.
In underwater direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) system, high peak-to-average power ratio (PAPR) brings in-band distortion and out-of-band power. It also decreases the signal-to-quantization noise ratio of the analog-to-digital converter and the digital-to-analog converter. A time–frequency-domain interleaved subbanding scheme is proposed to reduce the PAPR of underwater DCO-OFDM system with low computation complexity and bit error rate (BER). The system BER is evaluated by the distances of the underwater optical wireless communication (UOWC), as well as by the signal attenuation of the UOWC channel. A least-square channel estimation method is adopted for adaptive power amplification at the receiver side, to further decrease the system BER.
A midinfrared high birefringence Ge20Sb15Se65-based hexagonal lattice photonic crystal fiber (PCF) with central defect core and dual-rhombic air holes cladding is proposed. The finite difference time-domain method with perfectly matched layer absorption boundary conditions are used to numerically analyze the guided modes of the designed PCF. The properties of this PCF including the birefringence, beat length, dispersion, and nonlinearity are investigated in the 3 to 5 μm midinfrared range. The results show that for the optimized structure parameters of Λ = 2 μm, D = 1.7 μm, H = 1.76, and d = 0.4 μm, the highest birefringence of 0.1513 and beat length of 33.04 μm are obtained. The maximum nonlinearity coefficients of 3726 and 2585 w − 1 km − 1 for x- and y-polarization modes are achieved. The distinctive dispersion is acquired, which is all-normal for x-polarization mode while has single zero dispersion points at 3.96 μm for y-polarization mode. The designed PCF will have broad application in midinfrared optical fiber sensing, nonlinear optics, and precision optical instruments.
A rate-adaptive multilevel coded modulation (RA-MLC) scheme based on fixed code length and a corresponding decoding scheme is proposed. RA-MLC scheme combines the multilevel coded and modulation technology with the binary linear block code at the transmitter. Bits division, coding, optional interleaving, and modulation are carried out by the preset rule, then transmitted through standard single mode fiber span equal to 100 km. The receiver improves the accuracy of decoding by means of soft information passing through different layers, which enhances the performance. Simulations are carried out in an intensity modulation-direct detection optical communication system using MATLAB®. Results show that the RA-MLC scheme can achieve bit error rate of 1E-5 when optical signal-to-noise ratio is 20.7 dB. It also reduced the number of decoders by 72% and realized 22 rate adaptation without significantly increasing the computing time. The coding gain is increased by 7.3 dB at BER=1E-3.
We propose an efficient scheme to prepare multipartite entanglement of atomic ensembles trapped in separate cavities.
Our scheme has high fidelity even with realistic noise based on the repeat-until-success strategy. By employing the
quantum memory of the atomic internal state, the scaling efficiency decreases only with the number of atomic ensembles
by a slow polynomial law. Moreover, the atomic ensembles also can function as quantum repeaters, which enable our
system to compatible with the current experimental technique for quantum communication using atomic ensembles.
The quantum bit error rate (QBER) based on the weak coherent pulse's quantum key distribution is analyzed. It is
indicate that the coefficient of QBER is not a constant but is increased exponentially with the transmission distance.
Based on the three groups' experimental data, the function fitting for the coefficient of QBER has been done respectively.
We discovered that these fitting functions have the same function form. Subsequently we use fitting function to optimize
the mean photon number for the BB84 quantum key distribution with decoy states. The result shown that the optimized
mean photon number depend on the transmission distance. Using these results and the GYS's experimental parameters
we compared the key generation rates proposed by Lo et al with the modified one. We find that the latter is superior to
the former within a certain distance.
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