Abstract:Stable porphyrin-oxygenated carbon nanomaterial dispersions were prepared by blending porphyrin solutions with hydroxyl groups modified multi-walled carbon nanotubes (MWNTs-OH) and graphene oxide (GO) dispersions, respectively. Optical nonlinearity and optical limiting (OL) property of these blends are investigated in nanosecond regime. Results show that the OL performance of the blends can be tuned by changing the concentrations ratio of porphyrin and oxygenated carbon nanomaterials. The high concentration of oxygenated carbon nanomaterial leads to the poor OL performance. However, with the moderate concentration, the blends exhibit the low threshold value of OL and the enhanced OL performance at high fluence region. The superior OL performance can be attributed to complementary mechanisms and possible photoinduced electron or energy transfer between porphyrin moiety and oxygenated carbon nanomaterials.

Abstract:Integral imaging is a three dimensional (3D) display technology without any additional equipment. A new system is proposed in this paper which consists of the elemental images of real images in real mode (RIRM) and the ones of virtual images in real mode (VIRM). The real images in real mode are the same as the conventional integral images. The virtual images in real mode are obtained by changing the coordinates of the corresponding points in elemental images which can be reconstructed by the lens array in virtual space. In order to reduce the spot size of the reconstructed images, the diffuser in conventional integral imaging is given up in the proposed method. Then the spot size is nearly 1/20 of that in the conventional system. And an optical integral imaging system is constructed to confirm that our proposed method opens a new way for the application of the passive 3D display technology.

Abstract:A dual-core photonic crystal fiber (PCF) polarization splitter based on lead silicate glass is proposed. The characteristics of the polarization splitter are analyzed using full-vector finite element method. Compared with the silica glass PCF polarization splitter with the same structure, it is shown that the new material polarizer can realize splitting with less coupling loss and higher extinction ratio. When the wavelength is 1 550 nm and the PCF length in the beam splitter is 688 μm, the coupling loss is only 0.001 9 dB, and the extinction ratio for the input core is −64.1 dB.

Abstract:We design a channel-drop filter (CDF) with a linear gradient microcavity in a two-dimensional (2D) photonic crystal (PC). The model of three-port CDF with reflector is used to achieve high quality factor (Q-factor) and 100% channel-drop efficiency. The research indicates that adjusting the distance between reference plane and reflector can simultaneously influence the Q-factor due to coupling to a bus waveguide and the phase retardation occurring in the round trip between a microcavity and a reflector. The calculation results of 2D finite-difference time-domain (FDTD) method show that the designed filter can achieve the drop efficiency of 96.7% and ultra-high Q-factor with an ultra-small modal volume.

Abstract:Structure and design are proposed for a kind of novel polymer Mach-Zehnder electro-optic (EO) switch usingside-coupled M series-cascadedEO microrings. Formulations are proposed to analyze its switching characteristics. The dependences of the device’s performances on M are thoroughly analyzed and concluded. As the increase of M from 2 to 10, the switching voltages for the 9 devices are as low as 0.84 V, 0.82 V, 0.52 V, 0.5 V, 0.37 V, 0.36 V, 0.29 V, 0.28 V and 0.24 V, respectively; whereas the crosstalks under bar state are within -20.79--6.53 dB and those under cross state are within -20.36--5.29 dB. The analysis results indicate that a smaller M is preferred for dropping the insertion loss and crosstalk, and a larger M should be selected to increase the optical bandwidth and minimize the switching energy. Generally, due to low switching voltage, the proposed device shows potential applications in optical networks-on-chip.

Abstract:A tunable dual-wavelength fiber Bragg grating (FBG) laser based on a distributed feedback (DFB) laser injection is proposed and experimentally demonstrated. The wavelength spacing can be tuned by adjusting the operation temperature of the DFB laser. When the DFB works at 25 ℃, a dual-wavelength simultaneous oscillation at 1 549.67 nm and 1 553.44 nm with wavelength spacing of 3.77 nm is achieved. Our experimental results demonstrate the new concept of dual-wavelength lasing with a DFB laser injection and the technical feasibility.

Abstract:An organic light-emitting diode (OLED) device with high efficiency and brightness is fabricated by inserting CuOx/Cu dual inorganic buffer layers between indium-tin-oxide (ITO) and hole-transport layer (HTL). The CuOx/Cu buffer layer limits the operating current density obviously, while the brightness and efficiency are both enhanced greatly. The highest brightness of the optimized device is achieved to be 14 000 cd/m2 at current efficiency of 3 cd/A and bias voltage of 15 V, which is about 50% higher than that of the compared device without CuOx/Cu buffer layer. The highest efficiency is achieved to be 5.9 cd/A at 11.6 V with 3 400 cd/m2, which is almost twice as high as that of the compared device.

Abstract:The temperature characteristics of near infrared surface plasmon resonance (SPR) sensors with Kretschmann configuration are studied theoretically and experimentally. The experimental results match with the numerical simulations in the temperature range from 10 °C to 40 °C. With the increase of temperature, the resonance angle for gas increases slightly, but that for aqueous solution decreases obviously. No matter the dielectric layer is gas or aqueous solution, the resonance peaks are both broadened.

Abstract:High-performance and tensile-strained germanium (Ge) p-i-n photodetector is demonstrated on Si substrate. The epitaxial Ge layers were prepared in an ultrahigh vacuum chemical vapor deposition (UHV-CVD) system using low temperature Ge buffer technique. The devices were fabricated by in situ doping and using Si as passivation layer between Ge and metal, which can improve the ohmic contact and realize the high doping. The results show that the dark current of the photodetector with diameter of 24 μm is about 2.5×10-7 μA at the bias voltage of –1 V, and the optical responsivity is 0.1 A/W at wavelength of 1.55 μm. The 3 dB bandwidth (BW) of 4 GHz is obtained for the photodetector with diameter of 24 μm at reverse bias voltage of 1 V. The long diffusion time of minority carrier in n-type Ge and the large contact resistance in metal/Ge contacts both affect the performance of Ge photodetectors.

Abstract:The 885 nm direct pumping directly into the 4F3/2 emitting level of Nd3+ is applied on an Nd:Lu0.15Y0.85VO4 crystal. The maximum output power of 2.8 W for continuous wave (CW) operation is obtained. For Q-switched operation, the maximum average output power is 1.2 W with pulse repetition of 23.69 kHz and pulse width of 35 ns at the pump power of 27.9 W. The high-quality fundamental transverse mode can be observed owing to the reduction of thermal effect for Nd:Lu0.15Y0.85VO4 crystal by 885 nm direct pumping.

Abstract:We report the fabrication and optical properties of sub-micrometer-thick Ge20Sb15Se65 chalcogenide rib waveguides. The radio-frequency (RF) magnetron sputtering method is used to deposit 0.83 μm-thick films. A protective layer of SU-8 is employed to prevent the attack of the alkaline developer, and CHF3 is used as the etching plasma for reactive ion etching (RIE). Finally, the resulted rib waveguides with smooth sidewalls and vertical pattern profiles are rendered. The propagation losses for 4 μm-wide waveguides are measured to be 0.7 dB/cm for transverse electric (TE) modes and 0.68 dB/cm for transverse magnetic (TM) modes at 1 550 nm via the cutback method.

Abstract:We propose an approach to generate optical triangular-shaped pulse train with tunable repetition rate using quadrupling radio frequency (RF) modulation and optical grating dispersion-induced power fading. In this work, a piece of chirped fiber Bragg grating (FBG) is employed as the dispersive media to remove the undesired 8th harmonic in optical intensity. Thus, the generated harmonics of optical intensity can be corresponding to the first two Fourier components of typical periodic triangular pulses. This work also analyzes the impacts of the extinction ratio and the bias voltage drift on the harmonic distortion suppression ratio. After that, the value of the extinction ratio and the range of the bias voltage drift can be obtained. The advantage of this proposal is that it can generate high order frequency-multiplexed optical pulses train which can be applied in all optical signal processing and other fields.

Abstract:To facilitate the efficient support of quality-of-service (QoS) for promising free-space optical (FSO) communication systems, it is essential to model and analyze FSO channels in terms of delay QoS. However, most existing works focus on the average capacity and outage capacity for FSO, which are not enough to characterize the effective transmission data rate when delay-sensitive service is applied. In this paper, the effective capacity of FSO communication systems under statistical QoS provisioning constraints is investigated to meet heterogeneous traffic demands. A novel closed-form expression for effective capacity is derived under the combined effects of atmospheric turbulence conditions, pointing errors, beam widths, detector sizes and QoS exponents. The obtained results reveal the effects of some significant parameters on effective capacity, which can be used for the design of FSO systems carrying a wide range of services with diverse QoS requirements.

Abstract:In this paper, the optimum supercontinuum (SC) spectrum generation in a dispersion decreasing fiber is presented. Three normalized parameters for the pump pulse and SC fiber are introduced. It is found that the shape of an SC spectrum is uniquely specified by the input soliton order, the normalized dispersion slope and the normalized effective fiber length. For a pumping condition with a given input soliton order and a given normalized dispersion slope, by optimizing the normalized effective fiber length, the residual spectral peak in the SC spectrum can be suppressed effectively, and a broad SC spectrum with optimum spectral flatness can be obtained.

Abstract:We present an all-digital demodulation system of interferometric fiber optic sensor based on an improved arctangent-differential-self-multiplying (arctan-DSM) algorithm. The total harmonic distortion (THD) and the light intensity disturbance (LID) are also suppressed, the same as those in the traditional arctan-DSM algorithm. Moreover, the lowest sampling frequency is also reduced by introducing anti-aliasing filter, so the occupation of the system memory is reduced. The simulations show that the improved algorithm can correctly demodulate cosine signal and chirp signal with lower sampling frequency.

Abstract:In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening, and the spectrum standard deviation is calculated by an auto-correlation method. A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal. The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz. The suspension of carbon particles is driven by a syringe pump. The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation. The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans. The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to 8.4 mm/s. The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.

Abstract:A novel fiber Bragg grating (FBG) rain gauge is proposed in this paper to achieve high precision rainfall measurement. One core sensitive FBG, a temperature compensation FBG and a mechanical transition system construct this novel FBG rain gauge. Sensing principle of this FBG rain gauge is explained in detail, and its theoretical calculation model is also established, which shows that the relationship between center wavelength of sensitive FBG and external rainfall has very good linearity. To verify its detection performance, the calibration experiment on one prototype of this FBG rain gauge is carried out. After experiment data analysis, the detection precision of this FBG rain gauge is 15.4 μm which is almost two orders of magnitude higher than that of the existing rainfall measurement device. The experimental data confirm that this FBG rain gauge can achieve rainfall measurement with high precision.

Abstract:Nitric oxide (NO) and nitric oxide synthase (NOS) have an important role in pain signaling transmission in animal models. Low-level laser therapy (LLLT) is known to have an analgesic effect, but the mechanism is unclear. The aim of the study is to investigate the influence of LLLT on NO release and NOS synthesis in dorsal root ganglion (DRG) neurons, in order to find whether LLLI can ameliorate pain through modulating NO production at the cellular level. The results show that in stress conditions, the laser irradiation at 658 nm can modulate NO production in DRG neurons with soma diameter of about 20 μm in a short time after illumination, and affect NOS synthesis in a dose-dependent manner. It is demonstrated that LLLT might treat pain by altering NO release directly and indirectly in DRG neurons.

Abstract:Determination of light absorption distribution in the prostate tissue irradiated by diffusing light source is important for the treatment planning. In this paper, a three-dimensional (3D) optical model of human prostate is developed, and the light absorption distribution in the prostate tissue is estimated by Monte Carlo simulation method. Light distribution patterns including 3D distributions in the tissue model irradiated by two diffusing light sources are obtained and compared. Also, the impacts of length and energy of cylinder diffusing light source on the irradiance volume are demonstrated. Those results will be significant for the nondestructive qualitative assessments of photodosimetry in biomedical phototherapy.

Abstract: