Surface photovoltage spectroscopy equations for cathode materials with an AlxGa1 xAs buffer layer are determined in order to effectively measure the body parameters for transmission-mode (t-mode) photocathode materials before Cs-O activation. Body parameters of cathode materials are well fitted through experiments and fitting calculations for the designed AlxGa1 xAs/GaAs structure material. This investigation examines photo-excited performance and measurements of body parameters for t-mode cathode materials of different doping structures. It also helps study various doping structures and optimize structure designs in the future.

A novel long wavelength photodetector with dual-wavelength spectral response is designed and fabricated using a step-shaped Fabry-P′erot (F-P) filter structure. The step-shaped GaAs/AlGaAs distributed Bragg reflectors and the InP PIN photodetector are grown on a GaAs substrate using low pressure metal organic chemical vapor deposition. High quality GaAs/InP heteroepitaxy is realized by employing a thin low temperature buffer layer. The photodetector structure is optimized by theoretical simulation. This device has a dual-peak distance of 19 nm (1 558 and 1 577 nm). The 3-dB bandwidth of 16 GHz is simultaneously obtained with peak quantum efficiencies of 8.5% and 8.6% around 1 558 and 1 577 nm, respectively.

The use of Bell Laboratories layered space-time (BLAST) architecture as a digital signal processing algorithm is proposed in this letter. It is aimed at improving the nonlinearity tolerance of a polarization division multiplexing (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. The application of this channel estimation algorithm simulates system performance under different dispersion compensation (DC) maps. Simulation results show that, compared with intra-symbol frequency-domain averaging (ISFA) algorithm, at least 5-dB Q-factor improvement is achieved for the PDM CO-OFDM system at 112-Gb/s data rate over an 800-km standard single-mode fiber (SSMF) without DC.

Fiber nonlinearity limits the use of coherent optical orthogonal frequency division multiplexing (CO-OFDM) to upgrade wavelength-division multiplexing (WDM) systems using legacy non-return-to-zero-on-off-keying (NRZ-OOK) channels. This letter proposes to compensate for the fiber nonlinearity of CO-OFDM with NRZ-OOK neighbors by combining digital signal processing (DSP)-based self-phase modulation (SPM) post-compensation with pilot-tone-based cross-phase modulation (XPM) compensation. The simulation results demonstrate that the optimum low-pass filter bandwidth for pilot-tone-based XPM compensation depends on the pilot-to-signal ratio value and launch optical power. Our method allows a 4-dB increase in the launch power for a 40-Gb/s single polarization CO-OFDM channel placed in the middle of six 10.7-Gb/s NRZ channels in a 50-GHz space and 1 200-km WDM system.

A photon-counting-based iterative parallel interference cancellation (PIC) scheme for free-space opticalcommunications in the presence of multiple-access interference, shot noise, background radiation, and turbulence fading is designed. An efficient chip-level iterative equivalent noise estimation algorithm is also derived. Simulation results show that the proposed scheme can achieve a single-user performance,bound with the fast convergence property. More importantly, it can eliminate the bit-error rate floor of the conventional optical code-division multiple-access system with the aid of a relatively short spreading code length.

We investigate the temperature dependence of radiation-induced attenuation (RIA) at 1 310 nm for a Ge/P co-doped fiber after a steady-state \gamma -ray irradiation. A irradiation facility 60Co source is used to irradiate the fiber at a dose rate of 0.5 Gy/min, satisfying a total dose of 100 Gy. The test temperature ranges from –40 to 60 oC by 20 oC, and the RIA of the fiber is obtained using a power measuring device. The experimental result demonstrates that RIA exhibits a steady, monotonic, and remarkable temperature dependence after approximately 48 h of accelerated annealing at 70 oC. The optical fiber irradiated with a high dose and annealed sufficiently can be used as a temperature sensor.

A fundamental 1 \times 2 beam splitter based on the self-imaging phenomena in multi-mode one-dimensional (1D) photonic crystal (PC) waveguides is presented, and its transmission characteristics are investigated using the finite-difference time-domain method. Calculated results indicate that a high transmittance (>95%) can be observed within a wide frequency band for the 1 \times 2 beam splitter without complicated structural optimizations. In this letter, a simple and compact 1 \times 4 beam splitter is constructed by combining the fundamental 1 \times 2 beam splitter with the flexible bends of 1D PC waveguides. Such beam splitters can be applied to highly dense photonic integrated circuits.

The maximum output power offiber lasers limited by the thermal degradation of double-clad fiber coatings is theoretically simulated. We investigated the thermal effects on high-power continuous wave (CW) fiber lasers with a focus on heating at the splice joints as well as on the doped fiber caused by quantum defects. Whether thermal interface materials are used or not, the thermal contact resistances between the fiber and its heat sink are measured separately while using different cooling equipments. Though the thermal management of splices is more difficult than that of active fibers, a temperature increase of 0.019 K/W is obtained for a splice joint into which the pump light launches. The splice joint sustains 3 kW of total passing power.

The dependencies of stimulated Brillouin scattering (SBS) threshold in pulsed fiber amplifiers on spectral linewidth, pulse duration, and repetition rate are measured and discussed. Experimental results show that the SBS threshold is highly related to spectral linewidth and pulse duration. Therefore, the power handling limitation in a pulsed fiber amplifier may be the average power in some cases and the peak power in others.

This letter reports the application of the scanning heating laser source technique to detect microcracks that may be undetected by conventional methods. In the proposed approach, we monitor changes in the transmitted surface acoustic waves (SAWs) as a heating source is scanned over the crack. The experimental system for microcrack detection by a scanning heating laser source is obtained by exploiting the strong dependence of the transmission efficiency of acoustic pulses on the state of the contacts, whether open or closed, between the crack faces. Microcracks can be detected successfully by confirming the heating position at the point of maximal improvement of the transmission efficiency of the SAWs.

A wavelength-tunable, efficient, and high-average power single diode-pumped continuons wave (CW) Yb:SSO laser is reported. A maximum output power of 8.8 W at 1 062.6 nm is obtained using the absorbed pump power of 11.7 W, which corresponds to a slope efficiency of 85.5% and an optical-to-optical conversion efficiency of 48.9%. The wavelength tuning of the Yb:SSO laser pumped by the 976-nm LD is also investigated. The results show the tuning range from 1 002.30 to 1 068.47 nm, which corresponds to a tunability range of 66.17 nm.

In this linear-cavity passively mode-locked laser based on semiconductor saturable absorber mirror, an Ybdoped fiber is shared by two branch cavities as gain medium. These two cavities can respectively output single-wavelength pulse with the wavelength tuning range of 1 009.7–1 057.6 nm and 1 011.6–1 052.6 nm by adjusting volume Bragg grating. When two cavities output pulses together, the dual-wavelength pulses with the maximum and minimum wavelength separation of 34.8 and 2.4 nm, respectively, are achieved by net gain equalization method to suppress mode competition at room temperature. The maximum pulse energies of dual-wavelength pulses are 0.47 and 0.33 nJ separately; their repetition rates are 11.39 and 11.41 MHz.

The third-order optical nonlinearities of dimethyl sulfoxide (DMSO) are investigated using the optical Kerr effect (OKE) and Z-scan techniques with femtosecond pulses. We are able to fit the OKE signal theoretically by convolving the autocorrelation of the incident pulse intensity profile with the impulse responses of the samples, illustrating the instantaneous nonlinear response of DMSO. We verify that the purely electronic cloud distortion causes the observed signal for DMSO. The Z-scan technique is used to estimate the third-order susceptibility of DMSO, which is about a quarter of that for CS2 and mainly comes from the nonlinear refraction with an intensity of less than 140 GW/cm2.

The effects of bismuth doping content and temperature on the absorption property and near-infrared (NIR) luminescence of Bi-doped La2O3-Al2O3-SiO2 (LAS) glasses are presented. The emission intensity reaches the maximum when the Bi2O3 content in 3.0Bi-LAS is 1.83%. The emission spectra reach their peaks at 1 190 and 1 117 nm, with full-width at half-maximum (FWHM) values of 330 and 228 nm under 500 and 700-nm excitations, respectively. As the Bi2O3 content increases, the peak wavelengths and FWHMs of emission bands increase, but their lifetimes decrease. The lifetime of 2.0Bi-LAS is 460 μs at 9 K, and is almost temperature independent until 350 K. The NIR emission of Bi in the system has strong resistance to thermal quenching from 9 to 350 K.

Fishbone-like PbMoO4 nanostructures are successfully obtained via the surfactant-assisted hydrothermal method at 160 C. Polyethylene glycol (PEG2000) is used as the template agent. The nanostructures are characterized via X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible light (UV-Vis) spectroscopy, and photoluminescence (PL) measurements. The PbMoO4 morphology is highly associated with the molecular nature of PEG2000. PbMoO4 nanoparticles obtained from PEG2000 have a fishbone-shaped, scheelite-type tetragonal structure, in which numerous secondary branches vertically grow on both sides of the main stem. The structures exhibit broad PL emission bands with the maximum at 306 and 390 nm when excited at 250 nm. In addition, the UV-Vis absorption edge of the structures is in the 280 to 310 nm region, and the band gap is 4.07 eV. A plausible formation mechanism for the fishbone-like PbMoO4 nanostructures is also discussed.

An ultra broad band polarizer that operates in the telecommunication wavelength band is proposed. This device, which consists of a single suspended germanium resonant grating layer, is designed using the inverse mathematical method and the rigorous vector diffraction theory. Calculated results indicate that the ultra broad band polarizer exhibits extremely high reflection (R>99%) for TE polarization light and high transmission (T>99%) for TM polarization at the wavelength range greater than 300 nm, and it has an extinction ratio of approximately 1 000 at the 1 550-nm central wavelength. The results of the rigorous coupled wave analysis indicate that the extremely wide band property of the TE polarization is caused by the excitation of strong modulation guided modes in the design wavelength range.

Wave packet propagation techniques are used to find experimentally reliable laser parameters that yield optimal production. The photoionization and photodissociation dynamics of sodium iodine molecules are interpreted into several channels. Several frequencies are found to be suitable for NaI molecules during the photoionization and dissociation processes. Photon-dressed excited states and electron-dressed ionic continuum states facilitate the search for available laser parameters.

Iris recognition technology recognizes a human based on his/her iris pattern. However, the accuracy of the iris recognition technology depends on accurate iris localization. Localizing a pupil region in the presence of other low-intensity regions, such as hairs, eyebrows, and eyelashes, is a challenging task. This study proposes an iris localization technique that includes a localizing pupillary boundary in a sub-image by using an integral projection function and two-dimensional shape properties (e.g., area, geometry, and circularity). The limbic boundary is localized using gradients and an error distance transform, and the boundary is regularized with active contours. Experimental results obtained from public databases show the superiority of the proposed technique over contemporary methods.

A parametric optimization method is proposed in the design of a high-efficiency free-form illumination system. The proposed method is intended to provide rectangular uniform illumination with a light emitting diode (LED) source. An initial illumination system is first constructed and parameterized. The parameters of the initial system are optimized according to actual simulation results, and one design sample is presented. A liquid crystal on silicon (LCoS) micro-projector test module is fabricated and tested based on the design sample. Compared with the conventional micro-projectors using rotational symmetry devices, the micro-projector system designed with the parametric optimization method can send 1.65 times the source power to the LCoS active area with a 4:3 target ratio, and the uniformity reaches 98%.

Fabrication details of air-bridged Kerr nonlinear polymer photonic crystal slab structures are presented. Both the two-dimensional photonic crystal slab and the one-dimensional nanobeam structures are fabricated using direct focused ion beam etching and subsequent wet chemical etching. The scanning electron microscopy images show the uniformity and homogeneity of the cylindrical air holes. The optical measurement in the near-infrared region is implemented using the tapered fiber coupling method, and the results agree with the numerical calculations by using the three-dimensional finite-difference time-domain method.

An all-optical serial-to-parallel converter (SPC) utilizing two cascaded phase modulators and optical band-pass filters (OBPFs) is experimentally investigated and applied to demultiplex an 80-GBd optical time-division multiplexing (OTDM) return-to-zero (RZ) differential quadrature phase-shift keying (QPSK) signal. Two 40-GBd OTDM tributaries are error-free demultiplexed with a power penalty of approximately 4 dB in the worst case. With its advantages of compact structure, high speed, low power penalty, simultaneous two-tributary operation, and no assistance from a light source, the SPC has potential for use in future OTDM networks. However, the performance of the SPC still needs improvement.