SnO₂ nanosheet films about 200 nm in thickness are successfully fabricated on fluorine-doped tin oxide (FTO) glass by a facile solution-grown approach. The prepared SnO₂ nanosheet film is applied as an interfacial layer between the nanocrystalline TiO₂ film and the FTO substrate in dye-sensitized solar cells (DSCs). Experimental results show that the introduction of a SnO₂ nanosheet film not only suppresses the electron back-transport reaction at the electrolyte/FTO interface but also provides an efficient electron transition channel along the SnO₂ nanosheets, and as a result, increasing the open circuit voltage and short current density, and finally improving the conversion efficiency for the DSCs from 3.89% to 4.62%.

The GaAs based InGaAs metamorphic structures and their growth by molecular beam epitaxy (MBE) are investigated. The controlling of the source temperature is improved to realize the linearly graded InGaAs metamorphic structure precisely. The threading dislocations are reduced. We also optimize the growth and annealing parameters of the InGaAs quantum well (QW). The 1.3-μm GaAs based metamorphic InGaAs QW is completed. A 1.3-μm GaAs based metamorphic laser is reported.

An air-stable photovoltaic device based on znic oxide nanoparticles (ZNP) in an inverted structure of indium tin oxide (ITO)/ZnO/poly (3-hexylthiophene) (P3HT): [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM)/MoO₃/Ag is studied. We find that the optimum thickness of the MoO₃ layer is 2 nm. When the MoO₃ blocking layer is introduced, the fill factor of the devices is increased from 29% to 40%, the power conversion efficiency is directly promoted from 0.35% to 1.27%. The stability under ambient conditions of this inverted structure device much is better due to the improved stability at the polymer/Ag interface. The enhancement is attributed to the high carriers mobility and suitable band gap of MoO₃ layer.

Optical models directly effect the irradiance distribution of observed surface. Traditionally, approximate Lambertian models are widely used in designing the light-emitting diodes (LED) arrays in spite of their errors compared with the experimental data. But now a novel LED optical model for uniform illumination system has been proposed, in which the curve-fitting technique is used to reduce the inherited errors and modify those previous models. The points from the curve of the LED light intensity are adopted, and a spline curve is designed for fitting, which obtains the revised mode. To verify its feasibility, we apply the new model in a 4 × 4 array design. The results show that compared with the approximate Lambertian, the light intensity distribution produced by the fitting model is more uniform and intense, as is expected.

A new type of solid-conversion gas detector is investigated for high energy X-ray industrial computed tomography (HECT). The conversion efficiency is calculated by using the EGSnrc Monte Carlo code on the Linux platform to simulate the transport process of photons and electrons in the detector. The simulation results show that the conversion efficiency could be more than 65%, if the X-ray beam width is less than about 0.2 mm, and a tungsten slab with 0.2 mm thickness and 30 mm length is employed as a radiation conversion medium. Meanwhile the results indicate that this new detector has higher conversion efficiency as well as less volume. Theoretically this new kind of detector could take place of the traditional scintillation detector for HECT.

Frequency synthesizer is an important part of optical and wireless communication system. Low power comsumption prescaler is one of the most critical unit of frequency synthesizer. For the frequency divider, it must be programmable for channel selection in multi-channel communication systems. A dual-modulus prescaler (DMP) is needed to provide variable division ratios. DMP is considered as a critical power dissipative block since it always operates at full speed. This paper introduces a high speed and low power complementary metal oxide semiconductor (CMOS) 15/16 DMP based on true single-phase-clock (TSPC) and transmission gates (TGs) cell. A conventional TSPC is optimized in terms of devices size, and it is resimulated. The TSPC is used in the synchronous and asynchronous counter. TGs are used in the control logic. The DMP circuit is implemented in 0.18 μm CMOS process. The simulation results are provided. The results show wide operating frequency range from 7.143 MHz to 4.76 GHz and it comsumes 3.625 mW under 1.8 V power supply voltage at 4.76 GHz.

We report a numerical method to analyze the fractal characteristics of far-field diffraction patterns for two-dimensional Thue-Morse (2-D TM) structures. The far-field diffraction patterns of the 2-D TM structures can be obtained by the numerical method, and they have a good agreement with the experimental ones. The analysis shows that the fractal characteristics of far-field diffraction patterns for the 2-D TM structures are determined by the inflation rule, which have potential applications in the design of optical diffraction devices.

A simultaneous blue-light and red-light emitting glass of SrO-B₂O₃-P₂O₅ doped with Eu₂O₃ is prepared in air, and then heat-treated without any reductive reagent. A transition combination is found to consist of a band emission peaked around 430 nm and a series of line emission from 593 nm to 611 nm, corresponding to the typical 4f⁶→5d 4f⁷ transition of Eu²⁺ and ⁵D₀→⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺, respectively. Some unidentified crystals such as Sr (PO₃)₂ and SrB₂O₄ as hosts for Eu2+ with more stronger crystal field lead to this enhancement of photoluminescence (PL) intensity superior to the asprepared parent glass.

According to the perturbation theory, the coupled-mode equations for guided optical waves in the magneto-optical fiber Bragg gratings (MFBGs) under non-uniform magnetic field are derived. The equivalent relation between the magnetically-induced non-uniform fiber Bragg grating (MnFBG) and the corresponding non-magnetic chirped grating is expressed and verified by the piecewise-uniform MFBG model under linear magnetic field. On the basis of the equivalent relation, the MnFBGs can be effectively investigated by means of simulations. The characteristics of the MnFBGs under three typical magnetic field distributions with application to optical pulse compression are simulated, and the minimal pulse width can be achieved for the same magneto-optical coupling parameter of 2.2 × 10³ m⁻¹.

In this work, the theoretical model of FBG when it is affected by double external variables (temperature and transverse pressure) and triple external variables (temperature, axial strain and transverse pressure) is deduced, respectively. The simulated results show that the properties of cross sensitivity would change in a certain regulation with the external effects and fiber parameters. At the same time, some valuable suggestions about how to improve the measurement accuracy are put forward as well.

The high peak-to-average power ration (PAPR) values of optical orthogond frequency division multiplexing (OFDM) signal limit the system nonlinear tolerance (NLT). In this paper, a novel method based on Hadamard precoding is proposed to reduce the peak-to-average power ratio in optical direct detection OFDM system. The proposed scheme is successfully applied to an experimental system of optical direct-detection OFDM signal transmission through fiber. In this experiment, the 2.5 Gbit/s binary phase shift keying (BPSK) optical OFDM signals with Hadamard precoding are generated and transmitted though a single mode fiber. The experimental results show that the proposed scheme can reduce PAPR by almost 1.5 dB. Meantime the received sensitivity is improved by 2 dB with 100 km fiber transmission compared with that of an ordinary optical direct detection OFDM system.

In this paper we design a new kind of sinc-sampled fiber Bragg grating which is fabricated in high birefringence fiber (HBF). The sampled grating has two sets of reflection spectra along two perpendicular polarization directions. The grating’s channel number can be doubled approximately by designing the refractive index difference between the fast and slow axes of the fiber, which enhances the utilization ratio and reduces the claim for photosensitivity of the fiber. The group delay characteristics are theoretically studied and side-lobes are depressed by apodization as well to get the optimized spectra. The results show that the comb-like spectra of the grating have promising applications in both multi-wavelength polarized fiber lasers and fiber sensing networks.

An electronic digital equalizer for polarization multiplex coherent fiber optic communication systems is designed to compensate polarization mode dispersion (PMD) and residual chromatic dispersion (CD) of transmission channel. The proposed equalizer is realized with fraction spaced infinite impulse response (IIR) butterfly structure with 21 feedforward taps and 2 feedback taps. Compared with finite impulse response (FIR) structure, this structure can reduce implementation complexity of hardware under the same condition. To keep track of the random variation of channel characteristics, the filter weights are updated by least mean square (LMS) algorithm. The simulation results show that the proposed equalizer can compensate residual chromatic dispersion (CD) of 1600 ps/nm and differential group delay (DGD) of 90 ps simultaneously, and also can increase the PMD and residual CD tolerance of the whole communication system.

An OOK-NRZ visible light communication (VLC) system is designed by using a single white LED and a 550 nm visible photodetector. The emitting model of the single LED is established, and the general expression of the detector’s output signals under OOK modulation is deduced. With the selected LED, detector and other related parameters, the designed communication system is optimized and its performance is analyzed. The optimized communication distance between the LED and the detector is 0.54 m at the communication bit rate of 1 Mbit/s. With the best communication distance, when the signal-to-noise ratio (SNR) is larger than 6.5 dB, the bit error rate (BER) can drop to 10⁻⁴. The analytical model and theory presented in this paper can be of certain practical meanings in the design of similar communication systems.

A new displacement measurement system is described in this paper according to the basic principles of traditional laser triangulation method. The range of the traditional measuring method is enlarged by measuring in sections. Three independent CCDs, which are distributed uniformly along the optical axis, are used to achieve subsection measurement. The plane mirror is regarded as a virtual detector. When imaging beam is reflected by the plane mirror, the beam is imaged on the CCD. The designed system is equivalent to add a CCD. The feasibility of the displacement measurement system is verified by the experiment.

An open path atmospheric composition monitor is designed based on ultraviolet differential absorption technology. Dark current correction and diode response correction are used to improve the detection limit and Savitzky-Golay filter is used to improve the measurement accuracy. The experimental results show that the designed system has the ability to measure NO and NO₂ in real time with reasonable accuracy. The detection limit of the system is about 0.25 ppm for NO and 0.28 ppm for NO₂. When the concentration level of the target gases is below 100 ppm, the system has good linearity and high measurement accuracy, i.e., the measurement accuracy is about 2% for NO and about 4% for NO₂. The detection limit of dark current can be improved by about 5 to 10 ppb, and the correction of diode response can improve the detection limit by around 30 ppb. Moving window average can improve the detection limit at low concentration levels but will generate more errors at higher concentration levels. Generally, the designed system meets the requirement of measuring multi-species air pollutants in real time and accurately.

A three-state protocol for the SARG04 decoy-state quantum key distribution (QKD) based on an unstable source is presented. The lower bound to the secure key generation rate is derived without using the basic hypothesis of the original decoy-state idea. The three-state SARG04 decoy-state protocol with an unstable parametric down-conversion source is considered in the simulation. The simulation results show that the protocol in this paper with an unstable source gives a key generation rate that is close to that with a stable source, and only slight advantage appears by using a stable source when the transmission distance is long. So the SARG04 decoy-state protocol with an unstable source still can obtain the unconditional security with a slightly shortened final key.

An experimental study of the optical phonons is presented for InAlN epilayers lattice-matched with GaN by means of Raman scattering, and theoretical simulations are done to investigate the zone-center optical phonons of InAlN alloy by using the modified random element isodisplacement (MREI) model. The calculated findings show that the LO and TO branches of InAlN crystal both exhibit nonlinear properties. A comparison is made between the theoretical results and the experimental data, and it shows that they are both consistent for the A1(LO) phonons of InAlN epilayers.

By using the Collins diffraction formula and expanding the aperture function into a finite sum of complex Gaussian functions, an analytical formula of the time light intensity distribution for oblique Gaussian beams passing through a moving cat-eye optical lens and going back along the entrance way is deduced. By numerical computation, the variation laws of the time intensity distributions of the cat-eye reflected light with the viewing angle, imaging distance, aperture and instantaneous field of view are given. The results show that the relationship between the light intensity at the return place and the detection time is linear, and it is of inverse proportion only when the viewing angle is very large. For the staring imaging optical lens, the nonlinear extent of the time distribution curve becomes larger with the decrease of the viewing angle. For the instantaneous imaging optical lens, there is still some cat-eye reflected light when the detection system is out of the viewing field of the target lens.