Photoluminescence properties of solid-state Tb3+ doped NaY(MoO4)2

A cost-effective ultra-dense wavelength-division-multiplexed passive optical network（UD-WDM PON） with speed of 12.5 Gbit/s and channel spacing of 12.5 GHz is proposed and demonstrated. The distributed feedback（DFB） lasers modulated in 4-level pulse amplitude modulation（4-PAM） format are used for downstream links, and the reflective semiconductor optical amplifiers（RSOAs） together with an optical frequency comb modulated in quadrature phase shift keying（QPSK） format are used for upstream links. We can achieve the error-free transmission of the upstream signals with speed of 12.5 Gbit/s even after 20 km single-mode fiber（SMF）. The power penalty obtained by using the frequency comb generator instead of a tunable laser is around 0.5 d B. By using 11 DFB lasers and a set of intensity and phase modulators, it is possible to provide the seed light for 297 optical network units（ONUs） within the C-band.     

Measurement of frequency stability in tunable lasers by using an F-P interferometer

A method for measuring the frequency stability of tunable laser is proposed by using confocal Fabry-Perot（F-P）interferometer.The F-P interferometer is used to get the output frequency of the laser as a reference,and the method eliminates the need of an independent optical source as a frequency reference.Using this technique,the frequency stability of the tunable external-cavity diode laser（ECDL）is measured to be 2.26×10~（-9）with an integration time of 20 ms.     

Reconfigurable WDM-PON empowered by a low-cost 8-channel directly modulated laser module

A 10 Gbit/s 16-km-long reconfigurable wavelength-division-multiplexing passive optical network (WDM-PON) is presented empowered by a low-cost multi-channel directly modulated laser (DML) module. Compared with the case using discrete devices in conventional scheme, the proposed DML module provides a cost-effective solution with reduced complexity. The clear eye diagram and the bit error rate (BER) of less than 2×10-7 with a sensitivity of ?7 dBm are obtained. Due to the special packaging design, the crosstalk between channels under condition of simultaneous operation can be negligible.     

A variable coefficient microwave photonic filter based on multi-wavelength fiber laser and Mach-Zehnder interferometer

A microwave photonic filter（MPF） with variable coefficient is proposed and demonstrated, which is constructed by a multi-wavelength fiber laser and Mach-Zehnder interferometer（MZI）. Through changing the slope characteristics of Mach-Zehnder interference spectrum adjusted by optical variable delay line（OVDL）, the conversion from phase modulation（PM） to intensity modulation（IM） is realized. The multi-wavelength fiber laser with Lyot-Sagnac optical filter has variable wavelength spacing. So the designed filter has a variable number of taps and tap weights. As a result, the tunable range of passband center frequency is 2.6 GHz. The reconfigurability of MPF can be also realized by adjusting the output of fiber laser.     

Testing content addressable memories with physical fault models

Content addressable memory （CAM） is widely used and its tests mostly use functional fault models. However, functional fault models cannot describe some physical faults exactly. This paper introduces physical fault models for write-only CAM. Two test algorithms which can cover 100% targeted physical faults are also proposed. The algorithm for a CAM module with N-bit match output signal needs only 2N＋2L＋4 comparison operations and 5N writing operations, where N is the number of words and L is the word length. The algorithm for a HIT-signal-only CAM module uses 2N＋2L＋5 comparison operations and 8N writing operations. Compared to previous work, the proposed algorithms can test more physical faults with a few more operations. An experiment on a test chip shows the effectiveness and efficiency of the proposed physical fault models and algorithms.     

A channel estimation algorithm for optical orthogonal frequency division multiplexing systems

A simple channel estimation （CE） scheme, which is pilot-aided with just a little number of pilots inserted in the first half part of the subcarriers, is proposed and simulated for resisting the fiber dispersion in optical orthogonal frequency division multiplexing （OFDM） systems. The simulation results verify that the receiver sensitivity is improved by 2-3 dBm for bit error rate （BER） of 10^-3 with the proposed CE algorithm than that with other kinds of CE algorithms based on linear square principle. The good constellation performance for a 40 Gbit/s transmission system can be also obtained by the proposed scheme.     

Characteristic analysis of a novel F-P interferometer based on a pair of FBGs with built-in LPFGs

The transmission characteristics of a Fabry-Pérot (F-P) interferometer based on a fiber Bragg grating (FBG) pair with a built-in long-period fiber grating (LPFG) are theoretically analyzed, and the shift of transmission interference fringe as a function of environmental refractive index is acquired. The influence of the lengths of F-P cavity, LPFG and FBG on the transmission characteristics of the proposed interferometer has been numerically investigated, and the simulation results indicate that the sensitivity of refractive index reaches 2.27 × 10-6 for an optical spectrum analyzer (OSA) with a resolution of 1 pm.     

Design and implementation of the optical fiber control and transmission module in multi-channel broadband digital receiver

An optical fiber control and transmission module is designed and realized based on Virtex-7 field programmable gata array （FPGA）, which can be applied in multi-channel broadband digital receivers. The module consists of sampling data transfer submodule and multi-channel synchronous sampling control submodule. The sampling data transmission in 4× fiber link channel is realized with the self-defined transfer protocol. The measured maximum data rate is 4.97 Gbyte/s. By connecting coherent clocks to the transmitter and receiver endpoints and using the self-defined transfer protocol, multi-channel sampling control signals transferred in optical fibers can be received synchronously by each analog-to-digital converter （ADC） with high accuracy and strong anti-interference ability. The module designed in this paper has certain reference value in increasing the transmission bandwidth and the synchronous sampling accuracy of multi-channel broadband digital receivers.     

Wavelet-denoising technique in near-infrared methane detection based on tunable diode laser absorption spectroscopy

A novel wavelet denoising （WD） assisted wavelength modulation technique is proposed for improving near-infrared de- tection performance on methane concentration based on tunable diode laser absorption spectroscopy （TDLAS）. Due to the ability of multi-level analytical resolutions both in time- and frequency-domains, the noise contained in the differen- tial signal is greatly suppressed. Sensor mechanical part, optical part and electrical part are integrated, and a portable detection device is finally developed. Theory and formulations of the WD-assisted wavelength modulation technique are presented, and experiments are carried out to prove the normal function on the extraction of the second harmonic （2j） signal from severely polluted differential signal by using the technique. By virtue of WD＇s suppression on noises, the sensing characteristics on CH4 concentration are improved, and the limit of detection （LOD） is decreased from 4× 10-6 （without WD processing） to 10-6. The proposed technique can also be used for the measurement on the concentration of other gases with corresponding near-infrared distributed feedback lasers.     

Statics characteristics of two Bose-Einstein condensate dark solitons trapped in an optical lattice

The statics characteristics of two coupled Bose-Einstein condensate （BEC） dark solitons trapped in an optical lattice are investigated with the variational approach. It is found that the interaction between a ‘kink＇ and an ‘anti-kink＇ with opposite phase gradients is effectively repulsive, and the optical lattice can be controllably used to produce a pair of static BEC dark solitons. Its effect depends on the initial location of the BEC dark solitons, the lattice amplitude and wave number.     

Experimental measurement of scintillation index of vortex beams propagating in turbulent atmosphere

A microwave photonic link(MPL)with high spurious-free dynamic range(SFDR)is proposed and analyzed.The optical carrier is divided equally into two paths.The path 1 is modulated by radio frequency(RF)signals in a Mach-Zehnder modulator(MZM),and the phase of path 2 is controlled before the combination with path 1.By properly adjusting the phase difference of the two paths with the optical phase shifter,the third-order intermodulation distortion(IMD3)can be significantly suppressed.A proof-of-concept simulation is carried out.The results show that a reduction of 40 d B in the IMD3 and an improvement of 21.1 d B in the SFDR are achieved as compared with the conventional MZM-based MPL.The proposed MPL shows the advantages of simple structure,low cost and high efficiency.     

Optimal energy efficiency capacity under joint design of sensing and transmission duration for cognitive radio system

Due to its opportunistic spectrum sharing capability, cognitive radio （CR） has been proposed as a fundamental solution to alleviate the contradiction between spectrum scarcity and inefficient utilization of licensed spectrum. In CR system （CRS）, to efficiently utilize the spectrum resource, one important issue is to allocate the sensing and transmission duration reasonably. In this paper, the evaluation metric of energy efficiency, which represented the total number of bits that were delivered with per joule of energy consumed, is adopted to evaluate the proposed scheme. We study a joint design of energy efficient sensing and transmission durations to maximize energy efficiency capacity （EEC） of CRS. The tradeoff between EEC and sensing and transmission durations are formulized as an optimization problem under constraints on target detection probability of secondary users （SUs） and toleration interference threshold of primary users （PUs）. To obtain the optimal solution, optimizing sensing duration and transmission duration will be first performed separately. Then, a joint optimization iterative algorithm is proposed to search the optimal pair of sensing and transmission durations. Analytical and simulation results show that there exists a unique duration pair where the EEC is maximized, and that the EEC of the proposed joint optimization algorithm outperforms that of existed algorithms. Furthermore, the simulation results also reveal that the performance of the proposed low complexity iterative algorithm is comparable with that of the exhaustive search scheme.     

Novel Scheme of All-optical AND Gate Based on Fabry-Perot Semiconductor Optical Amplifier

A novel scheme of all-optical AND gate based on a Fabry-Perot semiconductor optical amplifier （FP-SOA） is proposed and its feasibility is verified by simulation. Using this scheme, all-optical AND gate can be realized with the extinction ratio of 10 dB. The influence of pulse interval and pulse width on the extinction ratio is also investigated.     

Optimal design of a multi-mode interference splitter based on SOI

In this paper, the multimode waveguide lengths and the output port locations of a SOI （silicon on insulator） material-based 1×4 MMI （multimode interference） optical splitter are optimized by means of FD-BPM （finite difference - beam propagation method）. An improved 1×4 MMI optical splitter is designed. Compared with an usual optical splitter, a smaller loss 0. 12dB and a better output port power uniformity 0.11dB are achieved for the optical signal transmission.     

Energy-Efficient Mapping for 3D NoC Using Logistic Function Based Adaptive Genetic Algorithms

The problem of mapping application tasks is one of key issues in 3D Network on chip （3D NoC） de- sign. A novel Logistic function based adaptive genetic al- gorithm （LFAGA） is proposed for energy-aware mapping of homogeneous 3D NoC. We formulate the mapping prob- lem and show the Standard genetic algorithm （SGA）. The LFAGA is presented in detail with the goal of obtaining higher convergence speed while preventing the premature convergence. Experimental results indicate that the pro- posed LFAGA is more efficient than previously proposed Chaos-genetic mapping algorithm （CGMAP）. In the ex- periments, a randomly generated task graph of size 27 is mapped to a 3D NoC of size 3×3×3, the convergence speed of LFAGA is 2.55 times faster than CGMAP in the best condition. When the task size increases to 64 and the 3D NoC size extends to 4×4×4, LFAGA is 2.31 times faster compared to CGMAP. For the NoC sizes in the range from 3×3×2 to 4×4×4, solutions obtained by the LFAGA are consistently better than the CGMAP. For example, in the experiment of size 4×4×4, the improvement of final result reaches 30.0% in term of energy consumption. For a real application of size 3×4×2, 18.6% of energy saving can be achieved and the convergence speed is 1.58 times faster than that of the CGMAP.     

Diode-end-pumped Nd:YVO4/LBO lasers with 4.2W continuous-wave output at 457 nm

A continuous-wave （CW） 457 nm blue laser operating at the power of 4.2 W is demonstrated by using a fiber coupled laser diode module pumped Nd： YVO4 and using LBO as the intra-cavity SHG crystal. With the optimization of laser cavity and crystal parameters, the laser operates at a very high efficiency. When the pumping power is about 31 W, the output at 457 nm reaches 4.2 W, and the optical to optical conversion efficiency is about 13.5% accordingly. The stability of the output power is better than 1.2% for 8 h continuously working.     

A novel two-stage spectral compression structure employing a logarithmic DIF interconnected with an HNLF-NOLM

A novel two-stage spectral compression structure which employs a logarithmic dispersion increasing fiber （DIF） in- terconnected with a highly nonlinear linear fiber-nonlinear optical loop mirror （HNLF-NOLM） is proposed and dem- onstrated by numerical simulation. The numerical simulation is implemented by solving the generalized nonlinear SchrOdinger equation using split-step Fourier method, where the soliton number is in the range of 0.5≤N≤1.4. The re- suits show that the spectra are well-compressed and low-pedestal, and the maximum spectral compression ratio （SCR） can reach 10.93 when N=l.4.     

Time-domain modified DFT modulated filter banks for multi-carrier transceiver systems

A time domain designing method is proposed for discrete Fourier transform （DFT） modulated filter banks （DFT-FBs） for application in multi-carrier transceiver systems. Instead of using the time-reversed pair limitation between the transmitting /receiving filter pair, the receiving filters in the proposed filter banks are derived from transmitting filters in accordance with the Moore-Penrose generalized inverse matrix. It can be freely obtained to design the transmitting prototype filter, which mainly affects the level of spectral containment. Furthermore, the symbol error rate （SER） performance of the proposed filter bank based trans-multiplexer with one tap equalizer is investigated in ideal channel and multi-path channel environments respectively. Simulation shows that the proposed approach can achieve significant SER reductions when square root raised cosine （RRC） prototype filter is used for comparing with the orthogonal frequency division multiplexing （OFDM） and the general DFT-FBs based applications.     

A dual-wavelength erbium-doped fiber laser with widely tunable wavelength spacing

A stable dual-wavelength erbium-doped fiber laser （EDFL） with tunable wavelength spacing and equalized output power is proposed and experimentally demonstrated. The fiber laser uses two fiber Fabry-Perot tunable filters （FFP- TFs） as the wavelength filter. The main cavity is divided into two sub-cavities with imbalance cavity losses through a 30/70 optical coupler. The tunable wavelength spacing can be achieved by changing the center wavelength of the filters and the equalized dual-wavelength output power can be achieved by properly controlling the variable optical attenuator （VOA） inserted in the lower-loss cavity.     

A band-pass microwave photonic filter based on Lyot-Sagnac filter and cascaded optical structures

A band-pass microwave photonic filter（MPF）based on Lyot-Sagnac filter and two cascaded optical structures is demonstrated.In the experiment,a stabilized and tunable multi-wavelength optical source is obtained by slicing the broadband optical source（BOS）with a Lyot-Sagnac filter.A standard single-mode fiber（SMF）and a fiber ring resonator are cascaded to improve the mainlobe-to-sidelobe suppression ratio（MSSR）and Q-factor of the filter.The analysis shows that MSSR and Q-factor are improved by reducing the split ratio of the coupler or increasing the length of fiber in fiber ring resonator.The results have significant guidance for MPF design by choosing appropriate devices and parameters.Based on the analyses,a band-pass filter with MSSR of 53.54 dB and Q-factor of 4048 is achieved by choosing the split ratio of0.01,the length of SMF of 30 km and the length of fiber in fiber ring resonator of 152.27 cm.