This PDF file contains the front matter associated with SPIE Proceedings Volume 9043 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

With the development of ultrahigh speed optical communications, optical sampling oscilloscope is a promising candidate for the optical performance monitoring. In this paper, a periodically poled lithium niobate based optical sampling oscilloscope is demonstrated. In the optical sampling oscilloscope, the bit rate adaptive method and chirp Z transform synchronization method are adopted to realize bit rate transparency. The optical sampling is completed by the sum frequency generation effect in periodically poled lithium niobate waveguide. The sampled signal is processed by FPGA based digital signal processing hardware, the eye diagram and parameters such as Q factor are measured. Intensity modulated optical signals with symbol rate from 1.0~25Gbaud are measured with our optical sampling oscilloscope. The experimental results are compared with that measured with Agilent 86100A wide bandwidth optical to electronic (O/E) oscilloscope and EXFO PSO-100 optical sampling oscilloscope. The measurement results of our oscilloscope are much closer to Agilent 86100A oscilloscope. Besides, our optical sampling oscilloscope has the advantage of faster measurement speed and higher synchronization accuracy due to the novel methods we proposed. The operation stability is also measured for our optical sampling oscilloscope, and the steady state can be maintained for several hours.

Advanced modulation formats, such as DPSK, DQPSK, QAM, have become the mainstream technologies in the optical network over 40Gb/s, the DPSK format is the fundamental of all advanced modulation formats. Optical buffers, as a key element for temporarily storing packets in order to synchronization or contention resolution in optical nodes, must be adapted to this new requirement. Different from other current buffers to store the NRZ or RZ format, an all-optical buffer of storing DPSK packets based on nonlinear polarization rotation in SOA is proposed and demonstrated. In this buffer, a section of PMF is used as fiber delay line to maintain the polarization states unchanged, the driver current of SOA is optimized, and no amplifier is required in the fiber loop. A packet delay resolution of 400ns is obtained and storage for tens rounds is demonstrated without significant signal degradation. Using proposed the new tunable DPSK demodulator, bit error rate has been measured after buffering for tens rounds for 10Gb/s data payload. Configurations for First-in First-out (FIFO) buffer or First-in Last-out (FILO) buffer are proposed based on this buffer. The buffer is easy control and suitable for integration. The terminal contention caused by different clients can be mitigated by managing packets delays in future all-optical network, such as optical packet switching network and WDM switching network.

We present a narrow linewidth laser by optical feedback from a high-finesse F-P cavity. The cavity transmission feeds back to the laser diode by the external ring path. With a low servo bandwidth system, the feedback phase is compensated for maintaining the optical feedback operation. The linewidth of the optical feedback laser is reduced to 100 Hz, and the laser frequency noise in frequency range of 1 Hz to 10 kHz is suppression over 50 dB. It experimentally demonstrates the excellent characteristics of optical feedback technique.

A 1×4 optical splitter based on annealed proton exchanged (APE) waveguides is designed and fabricated. The beam propagation method and refractive index profile of APE waveguide are analyzed numerically. The symmetry of the optical splitter is reformed and optimized by adding straight waveguide in the cascaded Y-branch structure. The relationship between the length of the straight waveguide and the beam-slipper coefficient is obtained. The function of the 1×4 optical splitter is simulated by the commercial software BeamProp (RSoft). And the result indicates that the output uniformity of the optical splitter is improved when the length of the straight waveguide is 1935μm. Furthermore, the polarization-maintaining is gained in the 1×4 optical splitter since only the TE mode can propagate in the APE waveguide in X-cut LiNbO₃ crystal. Finally, the optical splitter is fabricated and tested experimentally and the results show good agreement with the simulation.

Terahertz transmission of several metallic mesh structures is studied based on the finite differential time domain (FDTD) method. The terahertz filtering properties of these metallic meshes are analyzed by the numerical simulation. The shape and size dependence of terahertz transmission of these metallic structures are illustrated. The numeric results show that the terahertz transmission of these metallic meshes have various frequency selectivity. The design of terahertz filters for the different resonance frequencies is presented based on the above simulation. This work provides a good reference for the design and manufactures of terahertz filter.

We have demonstrated a passively mode-locked fiber laser with a composite cavity structure for repetition rate control. An optical delay line is used to control the length so that the lengths of the main cavity and the sub-ring cavity are accurately co-prime. Using this method we have obtained 46th harmonic pulses with a fundamental repetition of 17.39MHz. The fundamental mode-locking is substantially suppressed. The SNR of rf spectrum is higher than 45 dB. Stable 800MHz repetition rate mode-locked pulses in duration of 14.27 ps are generated. The detuning phenomenon appears when two cavity’s lengths are not matched. A larger pump power is required to maintain the oscillation.

The slow light is always at the cost of the signal distortion when the periodic rectangular signal propagates in Erbium-doped fiber (EDF), which is confirmed by the implemented simulations and measurements. A new definition of Fundamental Harmonic Fractional Delay (FHFD) is proposed based on the fundamental harmonic phase delay with the consideration of signal distortion to evaluate the slow light effect. The influences of signal power, modulation depth and duty ratio on slow light effect are studied, and the relationship between Fundamental Harmonic Fractional Delay (FHFD) and Total Harmonic Distortion (THD) is given.

This paper proposed a novel algorithm to obtain a wanted amplifier gain spectrum in order to get a flat gain within a wide gain band for the first time. In this method three pumps with different power and frequency space are composed to one pump unit which is optimized with a pre-specified gain ripple. We have been able to generate an optimum compensated spectrum for the EDFA or FOPA in less than 50 iterative optimizing steps resulting in less than 0.5dB gain ripple.

A passively mode-locked ytterbium-doped all fiber laser has been demonstrated based on the nonlinear polarization rotation technique in a all normal dispersion cavity. By optimizing the coupling ratio and position of the output coupler, stable mode-locked pulses is generated with an average power of 200 mW at a repetition rate of 3.3 MHz, and corresponding to single pulse energy of 60 nJ. The slope efficiency of power is as high as 68%.

In this paper, we report the design and fabrication of an uncooled infrared (IR) focal plane array (FPA) on quartz substrate and the wafer-level vacuum packaging for the IR FPA in view of an optical readout method. This FPA is composed of bi-material cantilever array which fabricated by the Micro-Electro Mechanical System (MEMS) technology, and the wafer-level packaging of the IR FPA is realized based on AuSn solder bonding technique. The interface of soldering is observed by scan electron microscope (SEM), which indicates that bonding interface is smooth and with no bubbles. The air leakage rate of packaged FPA is measured to be 1.3×10^-9 atm·cc/s.

In recent years, with the development of the Flat-Field Holographic Concave Grating, they are adopted by all kinds of UV spectrometers. By means of single optical surface, the Flat-Field Holographic Concave Grating can implement dispersion and imaging that make the UV spectrometer system design quite compact. However, the calibration of the Flat-Field Holographic Concave Grating is very difficult. Various factors make its imaging quality difficult to be guaranteed. So we have to process the spectrum signal with signal restoration before using it. Guiding by the theory of signals and systems, and after a series of experiments, we found that our UV spectrometer system is a Linear Space- Variant System. It means that we have to measure PSF of every pixel of the system which contains thousands of pixels. Obviously, that's a large amount of calculation .For dealing with this problem, we proposes a novel signal restoration method. This method divides the system into several Linear Space-Invariant subsystems and then makes signal restoration with PSFs. Our experiments turn out that this method is effective and inexpensive.

The increasing demand of network traffic requires new research centers; improve their communications networks, due to the excessive use of mobile and portable devices wanting to have greater access to the network by downloading interactive content quickly and effectively. For our case analyze optical network link through simulation results assuming a DWDM (Dense wavelength Division Multiplexing) optical link, considering the nonlinearity phenomenon FWM (Four Mixed Wavelength) in order to compare their performance, assuming transmission bit rates to 2.5 Gbps and 10 Gbps, using three primary wavelengths of 1450 nm, 1550 nm and 1650 nm for the transmission of information, whose separation is 100 GHz to generate 16 channels or user information. Tests were conducted to analyze optical amplifiers EDFAs link robustness at a maximum distance of 200 km and identify parameters OSNR, SNR and BER, for a robust and effective transmission

Space division multiplexing in multicore fibers is one of the most promise technologies in order to support transmissions of next-generation peta-to-exaflop-scale supercomputers and mega data centers, owing to advantages in terms of costs and space saving of the new optical fibers with multiple cores. Additionally, multicore fibers allow photonic signal processing in optical communication systems, taking advantage of the mode coupling phenomena. In this work, we numerically have simulated an optical MIMO-OFDM (multiple-input multiple-output orthogonal frequency division multiplexing) by using the coded Alamouti to be transmitted through a twin-core fiber with low coupling. Furthermore, an optical OFDM is transmitted through a core of a singlemode fiber, using pilot-aided channel estimation. We compare the transmission performance in the twin-core fiber and in the singlemode fiber taking into account numerical results of the bit-error rate, considering linear propagation, and Gaussian noise through an optical fiber link. We carry out an optical fiber transmission of OFDM frames using 8 PSK and 16 QAM, with bit rates values of 130 Gb/s and 170 Gb/s, respectively. We obtain a penalty around 4 dB for the 8 PSK transmissions, after 100 km of linear fiber optic propagation for both singlemode and twin core fiber. We obtain a penalty around 6 dB for the 16 QAM transmissions, with linear propagation after 100 km of optical fiber. The transmission in a two-core fiber by using Alamouti coded OFDM-MIMO exhibits a better performance, offering a good alternative in the mitigation of fiber impairments, allowing to expand Alamouti coded in multichannel systems spatially multiplexed in multicore fibers.

In this paper influence of high-precision optical inline dispersion compensation and ideal electric domain dispersion compensation in 100Gbit/s coherent detection polarization division multiplexing quadrature phase shift keying (PDMQPSK) system are studied by numerical simulation. The results show that the system performance of the system without optical inline dispersion compensation is significantly better than the system with high-precision inline dispersion compensation, and the system with ideal electric domain dispersion compensation is more suitable for long-distance transmission. We also try to search the optimal ratio of inline dispersion compensation in high-precision optical inline dispersion compensation system. We discover that there is not the ratio that can make the performance of the highprecision optical inline dispersion compensation system significantly better than the other ratio in a certain range of inline dispersion compensation ratio. Furthermore, the performance of the high-precision inline dispersion compensation system is obviously worse than the ideal electric domain dispersion compensation system when the ratio is optimal, and the performance is a little better than the performance when the ratio is 100%.

Real-time Orthogonal Frequency Division Multiplexing Passive Optical Network (OFDM-PON) has been extensively studied at home and abroad in recent years. In this paper, we realize a real-time OFDM transmitter system and introduce Savitzky-Golay filter to smooth the transmitted signal into the communication system. Firstly, the architecture of the real-time OFDM-PON was proposed in which a Xilinx V5 FPGA is used to generate the OFDM signal and a S-G filter is used to smooth the signal and weaken the noise. At the receiver, we use MATLAB to recover the signal and simulate the constellation diagram and bit error rate. What’s more, this paper introduces the basic principle of S-G filter and analysis the performance of the filter when it is used in an OFDM system. In conclusion, the simulation results show that the S-G filter implemented in the real-time OFDM-PON system is easy to realize that it can reduce the complexity of the system and bit error rate at the same time. As a result, it is proofed to be suitable for the real-time OFDM-PON system.

Trellis-coded pulse-amplitude modulation (TC-PAM) is applied in visible light communication (VLC) system using RGB-LED. Based on natural modulation, we propose a modified modulation to yield performance enhancement. Further, a decoding method of combing soft-decision Viterbi algorithm with most significant bit (MSB) decoding is developed. Finally, the results of Monte-Carlo simulation are presented to verify the best modulation and decoding method among the mentioned modulation and decoding techniques.

A new method of pulse signal de-noising based on wavelet transform and coherent averaging method is proposed. Pulse signal is complex and weak, generally submerged by the interference of baseline drift, motion artifact and high frequency noise. Consequently, it’s difficult to measure the heart rate by processing only one single-channel pulse signal, especially when the noise frequency and the pulse signal frequency are in the same frequency range. In this paper, multichannel pulse signal processing based on wavelet transform and coherent averaging is proposed to solve the above problem. First, the detail coefficients and approximation coefficients of each channel signal are obtained by N layer wavelet decomposition, then reconstructing the signal with high layers coefficients as the high frequency noises always exist in low layers coefficients. In this way we can filter out the high frequency interference. Second, the centerline of the upper and lower envelope curve obtained by cubic spline estimation is subtracted from each reconstructed signal so as to eliminate the baseline drift completely. Finally, the heart rate is acquired with the coherent averaging method which results in the noise being offset each other and the pulse signal being enhanced in the frequency range of pulse wave. The pulse signal and three kinds of noise signals simulated with the superposition of different frequency sin signal were analyzed, besides the experiment of six channel pulse signals measured simultaneously based on PhotoPlethysmoGraphy (PPG) were conducted. The simulation and experiment results showed that this method was superior to the traditional single channel.

Briefly compare the polarization rotation speed of Mach-Zehnder interferometer, lithium crystal, LCD and semiconductor optical amplifier (SOA), etc. Then propose a program of high-speed ternary optical multiplier based on SOA’s nonlinear polarization rotation. Finally, the theoretical analysis and simulation research of SOA’s nonlinear polarization rotation indicate that the ternary optical multiplier is one of the possible options to achieve high-speed optical computing, and may be widely applied to optical computer.

We have proposed the component parameters measuring method based on the differential confocal focusing theory. In order to improve the positioning precision of the laser differential confocal component parameters measurement system (LDDCPMS), the paper provides a data processing method based on tracking light spot. To reduce the error caused by the light point moving in collecting the axial intensity signal, the image centroiding algorithm is used to find and track the center of Airy disk of the images collected by the laser differential confocal system. For weakening the influence of higher harmonic noises during the measurement, Gaussian filter is used to process the axial intensity signal. Ultimately the zero point corresponding to the focus of the objective in a differential confocal system is achieved by linear fitting for the differential confocal axial intensity data. Preliminary experiments indicate that the method based on tracking light spot can accurately collect the axial intensity response signal of the virtual pinhole, and improve the anti-interference ability of system. Thus it improves the system positioning accuracy.

In this paper, total harmonic distortion (THD) of phase generated carrier demodulation algorithm by digital arctangent approach (PGC-DAT algorithm) is analyzed. THD due to the deviations of modulation depth and carrier phase delay is investigated both theoretically and experimentally. The analytical expression of THD as the function of carrier modulation depth, signal amplitude, initial phase and deviations of modulation depth and carrier phase delay has been derived. According to our analysis, the maximum THD for different initial phases exists, which reaches the peak value when the signal amplitude is close to 1.2 rad. The best modulation depth to minimize the maximum THD is 2 rad. Finally, an experimental system is set up with the mean THD below -60 dB. The analytical expression of THD derived in this paper agrees well with the experimental results.

In order to study the practical applicabality of the 3rd-order distributed Raman amplifier (DRA) in Cable Antenna Television (CATV) system, the structure of the 3rd-order DRA is put forward firstly, and the effect of higher order simulated Raman scattering is investigated. Moreover a simulated 3rdorder DRA-CATV system over 120 km fiber is set up to study its performance of 16-QAM as the main digital signal. In order to compare the performances, a simulated 1st-order DRA-CATV system is also set up. Simulation results indicate that the bit error rate (BER) of 16-QAM in the 3rd-order DRACATV system is lower than that in the 1st-order DRA-CATV system. The theory results are beneficial to apply a higher-order Raman pumping (HOP) DRA for the future experiment.

This paper presents a novel intelligent fiber-optic video surveillance system based on voice-leading, namely take the fiber grating as a trigger leading to intelligently dispatch the video camera (active or dormancy). And to simultaneously receive the video signal and leading signal under a single receiver, make full use of the power difference between the two signals. The proposed method is validated through the experimental system. Experimental results show that the system is error-free for a 30 km transmission.

Vanadium oxide (VOx) films were deposited onto well cleaned glass substrates by bipolar pulsed reactive magnetron sputtering at room temperature. Dependence of the structure, composition, optical and electrical properties of the films on the pulsed power’s duty cycle has been investigated. The results from the X-ray diffraction (XRD) analysis show that there was no remarkable change in the amorphous structure in the films with duty cycle can be observed. But chemical analysis of the surface evaluated with x-ray photoelectron spectroscopy (XPS) indicates that decrease the duty cycle favors to enhance the oxidation of the vanadium. The optical and electrical properties of the films were characterized by spectroscopic ellipsometry and temperature dependent resistivity measurements, respectively. The evolution of the transmittance, optical band gap, optical constants, resistivity and temperature coefficient of resistance (TCR) of the deposited films with duty cycle was analyzed and discussed. In comparison with conventional DC sputtering, under the same discharge atmosphere and power level, these parameters of the VOx films can be modified over a broad range by duty cycle. Therefore adjusting the duty cycle during deposition, which is an effective way to control and optimize the performances of the VOx film for various optoelectronic devices applications.

Layered cobalt oxide thin films with tilted structures exhibit large light-induced transverse voltage signals due to the transverse thermoelectric effect and have great potential applications in uncooled broad-band light detectors. In this paper, we investigated the photoresponse in c-axis tilted Bi₂Sr₂Co₂O_y thin films coated with a layer of nano-structured silver light absorber by using a 532 nm continuous wave laser as the incident light. The incidence direction of the laser beam was directly perpendicular to the sample surface. The laser spot was located at the centre position between the two electrodes and its diameter was about 2 mm. The induced lateral voltage signals were recorded using a 2400 Keithley source meter. Open-circuit voltage signals were observed when the sample surface was illuminated by the 532 nmradiation. Appropriate lateral size and thickness of the nano-structured silver layer can increase the photo-thermal-electric conversion efficiency in this photoresponse process due to the effective absorption of the light at the absorption layer, leading to the improvement in voltage sensitivity. The result offers important guidance of designing the light absorption layer for high performance broad-band light detectors based on the light-induced transverse voltage effect.

In recent years,tunable optical delay line has attracted much research interest for its applications in optical communications,optical signal processing and optical control of phased array antennas in microwave communications. Compared with optical delay line based on slow light techniques, all-optical wavelength conversion followed by signal propagation in a dispersive medium presents an alternative approach to control the delay time because it is simpler and more controllable. In this paper, a tunable optical delay line with a large time delay up to 650ps based on four-wave mixing (FWM) wavelength conversion in 420m high nonlinearity fiber (HNLF) and dispersion in 8km standard single mode fiber (SMF) is experimentally demonstrated.Our experimental results are in good agreements with the principle.

Fast optimization algorithms of the design of diffractive optical elements (DOEs) for beam shaping are often based on fast Fourier transform (FFT), and the demand of the sampling theorem must be met when FFT is used to calculate the light intensity. Limited by the fabricating technology, the pixel size of a DOE cannot be too small. For beam shaping in Fresnel diffraction domain, given that the sampling interval of a DOE is fixed, if the diffraction distance is too short, all FFT algorithms would not meet the demand of the sampling theorem, and then the results of beam shaping would become worse. In this paper, the disadvantages of the FFT algorithms in near Fresnel diffraction domain are discussed, and an area division method is proposed for the DOEs design. The simulation and experimental results show the validity of the proposed area division method.

T-APPM is combined of TCM (trellis-coded modulation) and APPM (Amplitude-Pulse-position modulation) and has broad application prospects in space optical communication. Set partitioning in standard T-APPM algorithm has the optimal performance in a multi-carrier system, but whether this method has the optimal performance in APPM which is a single-carrier system is unknown. To solve this problem, we first research the atmospheric channel model with weak turbulence; then a modified T-APPM algorithm was proposed, compared to the standard T-APPM algorithm, modified algorithm uses Gray code mapping instead of set partitioning mapping; finally, simulate the two algorithms with Monte-Carlo method. Simulation results showed that, when bit error rate at 10^-4, the modified T-APPM algorithm achieved 0.4dB in SNR, effectively improve the system error performance.

A photonic crystal fiber (PCF) with high nonlinearity and flattened dispersion is designed. The structure of PCF is in a hexagon lattice. The larger air holes in the outer rings are used to confine the light field into the core region to enhance the nonlinearity, and the flattened dispersion can be achieved by adjusting the diameters of six smaller air holes in the first ring. By optimizing the sizes of the smaller and larger holes, the PCF can achieve high nonlinearity of 19 W^-1km^-1 and low dispersion of 80.96 ps/(nm·km) with the fluctuation dispersion range of 8.49 ps/(nm·km) within the wavelength range of 1400 to 1800 nm. The PCF designed can find important applications in effectively realizing Raman soliton self-frequency shift and generating supercontinuum.

This paper presents the design and numerical simulation of the double H-shaped metallic periodic structure based on finite difference time domain (FDTD) method in terahertz frequency range. The double H-shaped structure unit cell consists of two H structures overlapped in the same plane. Numerical simulation results show that the double H-shaped structure results in a distinct and strong transmission trap in 0.2～3.0THz range. The position and the full wave at half maximum (FWHM) of transmission trap are changed with different structure size. The surface current distribution of structure is numerical simulated, which clarifies the frequency selection mechanism of the transmission spectra.

A specialty optical taper is proposed for receiving optical signal. According to the geometrical optics, the coupling efficiency for different shape curve is analyzed, such as piecewise function type, parabola type, and linear type. The relationship between the different large endface radius, small endface radius, taper length, refractive index and coupling efficiency is analyzed, respectively. By comparing the input and output light energy of specialty optical taper, the coupling efficiency can be analyzed in experiment. The experimental results are in good accordance with the theoretical data. For the ±1.5 mm radial displacement, the coupling efficiency can be more than 50% in different directions, respectively. Finally, the errors are also given.

Thermal effect of diode-pumped solid-state lasers (DPSSL) based on YAP/Tm:YAP composite crystal is studied by using of finite element method (FEM). It is found that the peak temperature in a composite rod decreases to less than 80% of that in a non-composite crystal. Thermal stress of composite rod is obviously reduced to less than 70% comparing with non-composite crystal. It is also demonstrated that length of thermal lens unchanged with increasing of un-doped crystal length, which means that beam quality of composite laser wouldn’t be improved by non-composite crystal. Therefore, it is concluded that using composite crystal would benefit for the properties of temperature and heat stress while insignificance for beam quality of DPSSL.

The Microchannel plate (MCP) is the main noise source of low-level light (LLL) image intensifier. Material and the whole manufacturing process of MCP have great impact on the noises of MCP. In this paper, based on the physical mechanisms of MCP, noises of MCP are classified scientifically. By using the data obtained from the actual production and the process test, the regression equation of the noise figure of MCP is derived, and the theoretical model of MCP noise figure is established, including the background noise figure model caused by the dark current of the MCP primarily about the time of the alkali corrosion technic, the ion feedback induced noise figure model caused by the patterns of the MCP channel wall primarily about the time and temperature of the hydrogen reduction technic, and the electronic scattering noise figure model caused by the open area ratio of the MCP primarily about the time of the alkali corrosion technic. Guided by the theoretical model of noise figure, the methods of suppressing noises of MCP are obtained and the technics are optimized. Taking advantage of the new techniques, the noise figure of the third generation MCP has been reduced to below 1.8.

Affected by atmospheric turbulence and multipath transmission, inter-symbol interference (ISI) is generated, and communication speed is limited in the channel of non-line-of-sight ultraviolet (NLOS UV) communication. Thus, MIMO space division multiplexing (MIMO-SDM) technology has a significant effect to reduce co-channel interference, fading and improve the transmission rate. Combined with characteristics of UV channel and noise, model of UV communication MIMO channel and channel capacity is developed, and the application of SDM technology based on vertical bell laboratories layered space-time coding (V-BLAST) is investigated. Also bit error rate (BER) performances with zero-forcing (ZF), minimum mean square error (MMSE) detection algorithm are obtained. Simulation results show that the capacity of UV communication MIMO channel is related to the number of transmit and received antennas , and channel SNR. And the BER performance with MMSE detection algorithm is better than ZF detection algorithm.

A novel asymmetric wide-coupled waveguide structure is put forward. We optimize the thickness of N-type waveguide and cladding through theoretical calculation of this structure, and adopt LP-MOCVD to grow the designed semiconductor lasers. The fabricated 980nm laser with 1200μm cavity length has a threshold current of 590mA, slope efficiency of 0.96W/A. When the operating current is 2.6A, the output power is 2000mW and the far field divergence angle is 16.1° (vertical) by 10.2° (horizontal). Experimental results indicate that the novel asymmetric wide-coupled waveguide structure can achieve high power output, effectively reduce the vertical far field divergence angle and improve the beam quality of the device.

This paper presents a new optical structure which achieves super-resolution by means of changing the complex amplitude of light wave. It also establishes the numerical simulation of the structure. Placed in front of the aperture of optical system, this new structure can modulate the light wave by changing the amplitude transmittance, and also make the central maximum of the Airy Pattern narrower to achieve super-resolution. We analyze modulation effects of many kinds of transmittance function. The numerical simulated result shows that the central maximum of the Point Spread Function (PSF), modulated by transmittance function whose edge value is greater than central value, becomes narrower than that of the idea optical system. It is also concluded that this optical structure is insensitive to different wavelength compared with the phase shifting apodizer, which brings about less chromatic dispersion. This conclusion is extremely useful to realize the super-resolution.

Theoretical analysis as well as system simulation of a NRZ/RZ (NRZ and duty cycle 33% 50% 66% RZ) shaped APPM (2×4 and 4×4) modulated scheme for gamma-gamma distribution turbulent free-space optical communication is done. Results show lower BER in RZ scheme especially with duty cycle 33%, however the NRZ scheme has higher frequency efficiency. So both BER performance and frequency efficiency can be synthetically considered to choose a proper scheme according to simulation results.

This paper designs and implements one kind of automatic mode-locked system. It can adjust a passively mode-locked fiber laser to keep steady mode-locked states automatically. So the unsteadiness of traditional passively mode-locked fiber laser can be avoided. The system transforms optical signals into electrical pulse signals and sends them into MCU after processing. MCU calculates the frequency of the signals and judges the state of the output based on a quick judgment algorithm. A high-speed comparator is used to check the signals and the comparison voltage can be adjusted to improve the measuring accuracy. Then by controlling two polarization controllers at an angle of 45degrees to each other, MCU extrudes the optical fibers to change the polarization until it gets proper mode-locked output. So the system can continuously monitor the output signal and get it back to mode-locked states quickly and automatically. States of the system can be displayed on the LCD and PC. The parameters of the steady mode-locked states can be stored into an EEPROM so that the system will get into mode-locked states immediately next time. Actual experiments showed that, for a 6.238MHz passively mode-locked fiber lasers, the system can get into steady mode-locked states automatically in less than 90s after starting the system. The expected lock time can be reduced to less than 20s after follow up improvements.

We establish and describe a physical transmission channel analysis model combining with the mode coupling and differential mode group delay theory over the weakly guiding graded-index few-mode optical fiber with special design base on the positive and negative few-mode fiber segment cascade structure. Numerical simulations illustrate the relationship between the differential mode group delay and bit error rate under the condition of weakly mode-coupling. The model can be a basic formalism for analyzing and controlling of mode coupling/dispersion induced by distortion, in the given optical multiple-input multiple-output scheme over FMFs.

There’s some key problems of transmission of multi—service mixed signals in fibers for C—RAN, so the influence of dispersion and crosstalk on transmission of mixed signals is researched. Besides, the evolution of multi—service signals is theoretically analyzed. A scheme for transmitting mixed signals is proposed, by which the optical carrier will filtered. The carrier loading mixed RF signals are modulated by direct modulation. Then mixed signals will be transmitted. Mixture transmission of LTE signals and random radio signals is simulated, obtained the maximum transmission distance of signals at which signals can keep high-quality, with the help of the analysis of performance of the transmission system. This transmission distance can meet the demand of access networks, which means that the proposed scheme is available.

This paper presents a signal processing technique of chatter detection for boring bar based on the Hilbert–Huang Transform (HHT). HHT is suitable for the analysis of non-stationary and non-linear signals. The flow of HHT for processing chatter signal and the principle are introduced. Two kinds of signals from strain gauge and FBG sensor are compared by HHT. The signals are decomposed into several intrinsic mode functions (IMFs) using empirical mode decomposition (EMD). The Hilbert transform is then applied on each IMF to obtain the instantaneous frequencies with time and their amplitudes. Finally, the marginal and the Hilbert spectrums of strain signals were produced using selected IMFs. The results show that the HHT-based strain signal analysis can also be considered as a simple and reliable method for chatter vibration detection.

We proposed an ultra-broadband multi-sized PbS quantum dots(QDs) fiber amplifier based on a symmetric fused tapered coupler. The 2x2 tapered fiber coupler was coated with a mixture of PbS QDs in two different sizes. By using the multisized PbS QDs as the gain medium, a maximum bandwidth of 400 nm (1200~1600 nm) has been achieved under evanescent wave excitation. In addition, with a 70 mW of 980 nm pump, we obtained a small signal gain of greater than 14 dB in this region.

An improved phase retrieval algorithm for optical anti-counterfeiting mask is proposed which combines the G-S algorithm with the simulated annealing algorithm. The proposed algorithm takes full advantage of the respective advantages of the G-S algorithm and the simulated annealing algorithm. In the scheme, the redesigned simulated annealing algorithm is used to control the times of iterations to achieve global searching, which makes the G-S algorithm to jump out automatically when the program is trapped in local optimal solution. The computer simulation results show that the proposed algorithm improves the quality of decoded image obviously compared with the traditional G-S algorithm, and reduces the running time of the program greatly.

Due to the development of micro-electronics in the field of multi-element optical detectors and fiber optics in the communication technology, fiber spectroradiometer now are widely used in photometry and radiometry. For most of time, the measurement environment may differ greatly from the experimental condition where calibration is made. Mistake may arise in the measurement process. An investigation of the characteristics of the fiber spectroradiometer is presented here, such as the plug and pull of the fiber optics, the bandwidth, the integration time and linearity, and short time stability. Experiments show that the bandwidth can significantly affect the accuracy of the measurement. Different from the conventional big-size scanning spectroradiometer, the measurement ability of the fiber spectroradiometer should be restricted in some application field. In measuring the spectra with multiple peaks, appropriate bandwidth spectroradiometer should be used.

Ultrashort pulse sources are important in the field of industry processing. With its excellent linear and nonlinear optical characteristics, graphene and single-walled carbon nanotubes(SWCNTs) have been proven to be two attractive materials to generate nanosecond, picosecond and femtosecond laser pulses. They have a lot of advantages, such as lower saturation intensity, larger saturable-absorption modulation depth, higher damage threshold, sub-picosecond recovery time. Graphene and SWCNTs were deposited on the fiber end facets by the optically driven deposition method. By utilizing two different staurable absorbers, we study the performance of three different lasers. Two Er-doped Q-switched optical fiber lasers were constructed by constructing graphene and SWCNTs separately into the ring cavity as saturable absorber. Different performances of the two fiber lasers were investigated by the physical characteristics of the two different materials. Stable pulses generated by a passively mode-locked fiber laser was obtained when two saturable absorbers were inserted into the resonator cavity of a fiber laser at the same time, the repetition rate of 8 MHz which agree with the length of the cavity proved the mode-locked state of the laser. This first time ever trial shows excellent output properties for its long time stable operation.

Time-stretch technique has been researched for a long time and many implementations with different performance have been proposed. In this paper, we utilize phase modulation and optical coherent detection (PM-CD) to implement photonic time-stretch analog-to-digital converter. In this implementation scheme, only one optical source is used to ensure the coherence of the modulated signal and the reference signal. Besides, envelope removing technique is also employed to remove the Gaussian envelope contained in the stretched radio frequency (RF) signal. As a proof of its feasibility, this paper presents a brief analysis of the time-stretch technique and the implementation of the PM-CD system we proposed. A comprehensive mathematical model for the PM-CD combining with envelope removing technique is developed and a numerical simulation is also presented. Simulation results show this technique can not only slow down the high frequency RF signal but also recover the stretched RF signal with little distortion. The most important point is the phase error in PM-CD, the nonlinearity of the photodetector (PD) and the pulse-to-pulse variations can be eliminated at the same time. This technique is an improvement compared to the previously proposed PM-CD time-stretch analog-to-digital converter.

Illuminance distribution of LED spherical arrays is studied by theoretical analysis and simulation. The optimal layout of the LED spherical array is founded by changing the angle, the ball radius, and the power of different LED. The uniformity of illumination of the LED spherical array is verified, which is better than LED planar array. In addition, the illuminance distribution of indoor ground surface illuminated by LED spherical array with different parameters and the related curves are obtained. The LED spherical array mentioned in this paper can be useful in the application of indoor visible light communication.