Abstract:ZnO:Cu/ZnO core/shell nanocrystals are synthesized by a two-step solution-phase process. The morphology, structure and optical properties of the samples are detected by scanning electron microscopy, Raman, absorption and luminescence spectroscopy. The increase of particle size confirms the growth of ZnO shell. The segregation of CuO phase observed in ZnO: Cu core is not detected in ZnO:Cu/ZnO core/shell nanocrystals from Raman spectra. It is suggested that some Cu ions can be segregated from ZnO nanocrystals, and the separated Cu ions can be incorporated inside ZnO shell after the growth of ZnO shell. The visible emission mechanism is discussed in detail, and the photoluminescence analysis indicates that the core/shell structure helps to eliminate the surface-related emission.

Abstract:A photonic crystal fiber based surface plasmon resonance (PCF-SPR) sensor is simulated by finite element method and experimentally realized. The calculations show that there is an obvious loss peak in the vicinity of 1.2 m while the PCF of LMA-8 is used as a sensor. The suspension of silver nanoparticle mixed with hexadecyl trimethyl ammonium bromide (CTAB) is inhaled into the PCF to form a metal film which can be stimulated to generate plasmon in the experiment. A spectrometer is utilized to detect the continuous broadband transmission spectrum from the PCF. The experimental results verify the loss peak. Compared with the theoretical calculations, the offset of loss peak about 40 nm can be acceptable, because the uniformity of the metal coating is difficult to guarantee and the film thickness is difficult to control.

Abstract:A novel superimposed photodetector (PD) is put forward. The photodetector can obtain a couple of differential photocurrent signals from one input optical signal. The light injection efficiency and the vertical work distance of this new photodetector are much higher than those of the others. The superimposed photodetctor is designed based on the standard 0.18 m CMOS process. The responsivity, bandwidth and transient response of the photodetector are simulated by a commercial simulation software of ATLAS. The responsivities of two obtained photocurrent signals are 0.035 A/W and 0.034 A/W, while the bandwidths are 3.8 GHz and 5.2 GHz, respectively. A full differential optical receiver which uses the superimposed photodetector as input is simulated. The frequency response and 4 Gbit/s eye diagram of the optical receiver are also obtained. The results show that the two output signals can be used as the differential signal.

Abstract:The transfer function of the microring resonator is deduced, and the effects of the normalized loss, coupling coefficient and surrounding media on the resonance performance are investigated thoroughly. Utilizing the improved fused tapering technique and ingenious self-coiling coupling method, a high-quality microring resonator (radius of about 500 m) with larger extinction ratio (>10 dB) and sharper resonance is designed and fabricated by a segment of continuous sub-micrometer fiber. The microring resonator constructed in this way demonstrates extremely small connection loss with communication fiber in contrast to the planar waveguide technology.

Abstract:Molybdenum trioxide (MoO₃) as a cathode buffer layer is inserted between LiF and Al to improve the efficiency of white organic light-emitting diodes (OLEDs) in this paper. By changing the MoO₃ thickness, a higher current efficiency of 5.79 cd/A is obtained at a current density of 160 mA/cm² for the device with a 0.8 nm-thick MoO3 layer as the cathode buffer layer, which is approximately two times greater than that of the device without MoO₃. The mechanism for improving the device efficiency is discussed. Moreover, at a voltage of 13 V, the device with a 0.8 nm-thick MoO₃ layer achieves a higher luminance of 22370 cd/m², and the Commission Internationale de I’Eclairage (CIE) color coordinate of the device with 1 nm-thick MoO₃ layer is (0.33, 0.34), which shows the best color purity. Simple electron-only devices are tested to confirm the impact of the MoO₃ layer on the carrier injection.

Abstract:The metal-conducting single-walled carbon nanotubes (m-SWNTs) with small diameters (0.7 nm 1.1 nm) are selectively removed from the single-walled carbon nanotubes (SWNTs) by using HNO₃/H₂SO₄ mixed solution. Semiconducting single-walled carbon nanotubes (s-SWNTs) can be separated efficiently from the SWNTs with high controllability and purity based on this novel method, and the outcome is characterized by Raman spectrum. Moreover, the organic field effect transistors (OFETs) are fabricated based on the poly (3-hexylthiophene-2, 5-diyl) (P3HT), and untreated SWNTs and separated SWNTs (s-SWNTs) are mixed with P3HT, respectively. It could be found that the P3HT/s-SWNT device exhibits a better field effect characteristic compared with the P3HT device. The current on/off ratio is increased by 4 times, the threshold voltage is also increased from ?28 V to ?22 V, and the mobility is increased from 3×10^?3 cm²/Vs to 5×10^?3cm²/Vs.

Abstract:This paper proposes an optical device which can continuously change the polarization state of terahertz (THz) waves. The device consists of metal gate, anti-reflection coatings, liquid crystal and mirror. By changing the refractive index of liquid crystal in the interface between the metal gate and the mirror, the phase difference between two beams with orthogonal polarization is varied and a continuous phase shift is achieved. The phase shift of the device is calculated by using the finite difference time domain (FDTD) method, and the transmittance and reflectance are calculated by using the rigorous coupled wave analysis (RCWA) method. The results reveal that the structure can realize continuously tunable phase shift for THz wave at 1 THz.

Abstract:A high-sensitivity metal-coated long-period fiber grating (LPFG) sensor based on material dispersion is designed. Based on the coupled mode theory, the influence of the material dispersion on the dual-peak characteristics of the metal-coated LPFG is studied. After considering the material dispersion, the jumping region of the dual-resonant-wavelength shifts toward the thinner film thickness, and the sensitivity of the dual-peak metal-coated LPFG sensor to liquid refractive index (RI) can be obtained to supply accurate parameter combinations. Experimentally, two kinds of silver-coated LPFGs with different film thicknesses and grating periods are fabricated to monitor the salt solution, and the sensitivities of these two sensors are compared. The experimental results are consistent with the theoretical analyses. This work has been supported by the National Natural Science Foundation of China (No.60777035), the Scientific Research Key Project Fund (No. 208040), the Innovation Program of Shanghai Municipal Education Commission (No.11ZZ131), and the Shanghai Leading Academic Discipline Project (No.S30502).

Abstract:Erbium-doped tellurite-based glasses (Er³⁺:TeO₂-ZnO-La₂O₃) are prepared by the conventional melt-quenching technique, and concentration-dependent luminescence properties of Er³⁺ are investigated. A significant spectral broadening of the 1.53 μm fluorescence corresponding to ⁴I_13/2 → ⁴I_15/2 transition is observed, and the fluorescence decaying becomes a nearly exponential way with the increasing Er³⁺concentration. Radiation trapping is evoked to explain the broadening of ⁴I_13/2 → ⁴I_15/2 emission line of Er₃₊ ions. The optimum doping content of Er₂O₃ for 1.53 μm fluorescence emission is about 1.5 mol%.

Abstract:The transmission spectra of one-dimensional (1D) photonic crystals (PCs) with parallel and twisted nematic liquid crystals (LCs) as defect layers are discussed by 4 × 4 matrix method, respectively. The results show that the photonic band gap (PBG) mainly depends on the periodic arrays of dielectric composites. The orientation of director and the symmetry of the director configuration have important influence on the location and amplitude of defect modes. The location and amplitude of defect modes can be controlled conveniently by changing the orientation of director. The symmetry of the director configuration can help us understand the defect modes spectra.

Abstract:A special optical fiber is investigated, which has a helical core in the cylindrical cladding. The beam propagation method (BPM) is used for analyzing the impacts of the geometric and physical parameters on the properties of mode losses of the helical-core fiber. The propagation loss is 0.32 dB/m for the fundamental mode and the propagation loss is 20.95 dB/m for the LP₁₁ mode in the wavelength range of 1050–1065 nm when the core diameter is 19 μm, the pitch of the core’s helix is 2.66 μmm, and the offset of the helix core from the center of the fiber axis is 31 μm. The core diameter of the single-mode helical-core fiber well exceeds that of the conventional large-mode-area fiber. The helical-core fiber can provide the effective large-mode-area single-mode operation without coiling fiber or selecting excitation mode.

Abstract:A novel Reed Solomon (RS) block turbo code (BTC) coding scheme of RS(63,58)×RS(63,58) for optical communications is proposed. The simulation results show that the net coding gain (NCG) of this scheme at the sixth iteration is more than that of other coding schemes at the third iteration for the bit error rate (BER) of 10⁻¹². Furthermore, the novel RS BTC has shorter component code and rapider encoding and decoding speed. Therefore, the novel RS BTC coding scheme can be better used in high-speed long-haul optical communication systems, and the novel RS BTC can be regarded as a candidate code of the super forward error correction (super-FEC) code. Moreover, the encoding/decoding design and implementation of the novel RS BTC are also presented

Abstract:We describe an all-optical wavelength conversion scheme for 1310 nm to 1550 nm based on nonlinear polarization rotation in a gain-transparent semiconductor optical amplifier (GT-SOA) which brings in the assistant light to improve the property of the converted light. From the SOA carrier density equations, the 1310 nm-to-1550 nm wavelength conversion scheme is analyzed by the Jones matrix. The phase shift between TE and TM modes and the converted light are simulated at bit rate of 30 Gbit/s. We also analyze the influence of the input signal power, the injected current and the assistant light power on the extinction ratio of the converted light.

Abstract:Millimeter-wave (mm-wave) radio over fiber (ROF) using dispersive single-mode fiber is susceptible to signal cancellation effect at the output of the uni-travelling carrier photodiode at the base station (BS). The fiber dispersion effect produces different phase shifts of the sidebands of the intensity-modulated lightwave which can produce a cancellation of the output signal when mixed with the optical carrier. In this paper, we propose and analyze a novel scheme of mm-wave ROF which uses microwave modulation at the central station (CS) and frequency upconversion before the BSs. This scheme can overcome fiber dispersion-induced signal cancellation effect.

Abstract:In order to increase the coupling efficiency and suppress the random angular jitter induced by atmosphere turbulent, the fine tracking system with fast steering mirror (FSM) is demonstrated. The field experiment results of free-space optical communication link across 16 km show that when there is no tracking, the range of the x-axis coordinates’ fluctuation achieves 46 pixels, corresponding to the incident angle of 73.6 μrad, and its mean square deviation is 6.5 pixels, corresponding to the incident angle of 10.4 μrad. When there is tracking, the range of fluctuation is suppressed to 10 pixels and 16 μrad, and the mean square deviation reduces to 1.5 pixels and 2.6 μrad for the spot’s centroid and the incident angle, respectively. Significantly, the coupling efficiency increases by 6 times, and the fluctuation of received light power decreases obviously.

Abstract:For the scheme of 80 GHz optical millimeter-wave (mm-wave) generation using two cascaded Mach-Zehnder modulators (MZMs), an exact analytical solution for the optical mm-wave affected by phase shift drift and splitting ratio is derived with the method of expanding Bessel series. The results show that for the carrier and the fourth-order sideband, the influence caused by phase shift drift is dominant, while the first-order, the second-order and the third-order sidebands are influenced by both phase shift drift and splitting ratio. It follows that the undesired sideband suppression ratio is at least 35.9 dB when the splitting ratio deviation is 0.001, and the phase shift drift is 1°. The performance of the system is perfect if the accuracy is achieved.

Abstract:A coded modulation scheme for deep-space optical communications is proposed, which is composed of an outer single-parity-check (SPC)-based product code, an interleaver, a bit-accumulator and a pulse-position modulation (PPM). It is referred as SPC-APPM code, which is decoded with an iterative demodulator-decoder using standard turbo-decoding techniques. Investigations show that the scheme has the advantages of low encoding and decoding complexities, good performance and flexible code rate for all rates above 1/2. Meanwhile, simulation results demonstrate that the SPC-APPM provides the performance similar to the low-density parity-check-APPM (LDPC-APPM), superior to the LDPC-PPM and product accumulate code-PPM (PA-PPM), although inferior to serially concatenated PPM (SCPPM). At the bit error rate (BER) of 10^?5, the performance of SPC-APPM is about 0.7 dB better than LDPC-PPM and 1.2 dB better than PA-PPM.

Abstract:Based on the Marshall-Palmer, Weibull raindrop size distribution and Mie electromagnetic scattering model, the relationships of attenuation coefficient of terahertz (THz) atmospheric window waves with precipitation rate and temperature are studied. Furthermore, combined with the loss of electromagnetic wave transmission in free space, the attenuation of THz communication and the transmission of current mobile communication signals through rain are compared and analyzed. The results show that the attenuation coefficient of THz transmission is increased with increasing precipitation rate, the difference of attenuation coefficient at different THz window waves is small, and the maximum difference is about 3 dB. The rain attenuation of THz wave is first decreased and then increased with increasing temperature, but the temperature has little effect on it. The attenuation of THz wave through rain is much larger than that of mobile communication signal.

Abstract:The single-layer porous silicon is prepared by electrochemistry etching method, which is used as an immunosensor for determining recombinant mouse zona pellucida 3 fusion protein (r-mZP3) by Raman spectroscopy analysis at room temperature. The molecule binding increases the effective optical thickness (EOT), and thus the Raman spectrum intensity decreases. The concentration and variation of Raman intensity show a good linear quantitative relation. The excellent sensing performance could open the way to a new family of optical sensors for biological standardization.

Abstract:A relatively simple plug-and-play control system of quantum key distribution (QKD) based on PCI7300 card is demonstrated, including mechanism design, key generation and key acquisition. The system works very well at the repetition frequency of 1 MHz, and the key generation rate is 100 k/s. A visibility of better than 95% over 50 km-long fiber at 1.31 m is obtained, which is stable under ordinary lab conditions for 24 h without any feedback control or adjustment. The presented system is a quite promising candidate to realize the QKD in the future.