Shipborne Underwater Acoustic Communication System and Sea Trials with Submersible Shenhai Yongshi

The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-cone directional transducer and a horizontal-toroid one is installed on the mothership. Improved techniques are proposed to combat adverse channel conditions, such as frequency selectivity, non-stationary ship noise, and Doppler effects of the platform’s nonlinear movement. For coherent modulation, a turbo-coded single-carrier scheme is used. In the receiver, the sparse decision-directed Normalized Least-Mean-Square soft equalizer automatically adjusts the tap pattern and weights according to the multipath structure, the two receivers’ asymmetry, the signal’s frequency selectivity and the noise’s spectrum fluctuation. The use of turbo code in turbo equalization significantly suppresses the error floor and decreases the equalizer’s iteration times, which is verified by both the extrinsic information transfer charts and bit-error-rate performance. For noncoherent modulation, a concatenated error correction scheme of nonbinary convolutional code and Hadamard code is adopted to utilize full frequency diversity. Robust and lowcomplexity synchronization techniques in the time and Doppler domains are proposed. Sea trials with the submersible to a maximum depth of over 4500 m show that the shipborne communication system performs robustly during the adverse conditions. From the ten-thousand communication records in the 28 dives in 2017, the failure rate of the coherent frames and that of the noncoherent packets are both below 10%, where both synchronization errors and decoding errors are taken into account.

Conceptual design and RCS performance research of shipborne early warning aircraft

In order to improve the survivability of the aircraft,conceptual design and radar cross section（RCS） performance research are done. The CATIA software is used to design the 3D digital model of the shipborne early warning aircraft, and some measures are taken to reduce the RCS characteristics of the early warning aircraft at the same time. Based on the physical optics method and the equivalent electromagnetic flow method,the aircraft＇s RCS characteristics and strength distribution characteristics are simulated numerically, and compared with the foreign advanced shipborne early warning aircraft. The simulation results show that under the X radar band, when the incident wave pitching angle is 0？, compared with the foreign advanced shipborne early warning aircraft, the forward RCS average value of the conceptual shipborne early warning aircraft is reduced to 24.49%, the lateral RCS average value is reduced to 5.04%, and the backward RCS average value is reduced to 39.26%. The research results of this paper are expected to provide theoretical basis and technical support for the conceptual design and the stealth design of the shipborne early warning aircraft.

Electro-Optical Effect Measurement of Thin-Film Material Using PM Fiber Mach-Zehnder Interferometer

A polarization-maintaining （PM） fiber Mach-Zehnder （MZ） interferometer has been established to measure the EO effect of very thin film materials with optical anisotropy. Unlike a common MZ interferometer, all the components are connected via polarization-maintaining fibers. At the same time, a polarized DFB laser with a maximum power output of 10mW is adopted as the light source to induce a large extinction ratio. Here,we take it to determine the electro-optical coefficients of a very thin superlattice structure with GaAs, KTP, and GaN as comparative samples. The measured EO coefficients show good comparability with the others.

Estimation of sea clutter inherent Doppler spectrum from shipborne S-band radar sea echo

Measurement of shipborne radar sea echo is instrumental in collecting the sea clutter data in open sea areas.However,the ship movement would introduce an extra Doppler component into the spectrum of the sea clutter,so the sea clutter inherent spectrum must be estimated prior to investigating the sea clutter Doppler characteristics from the shipborne radar sea echo.In this paper we show some results about a shipborne sea clutter measurement experiment that was conducted in the South China Sea in a period between 2017 and 2018;abundant clutter data have been collected by using a shipborne S-band clutter measurement radar.To obtain the sea clutter inherent Doppler spectrum from these data,an estimation method,based on the mapping relationship between the shipborne clutter spectrum and the inherent clutter spectrum,is proposed.This method is validated by shipborne clutter data sets under the same measuring conditions except for the ship speed.Using this method,the characteristics of the Doppler spectrum lineshapes in the South China Sea are calculated and analyzed according to different sea states,wave directions,and radar resolutions,which can be instrumental in designing the radar target detection algorithms.

Electro-optical properties cholesteric liquid of polymer stabilized crystal film＊

Liquid crystals （LCs） and polymers are extensively used in various electro-optical applications. In this paper, normal mode polymer stabilized cholesteric LC film is prepared and studied. The effects of chiral dopant and monomer concentrations on the electro-optical properties, such as contrast ratio, driving voltage, hysteresis width and response time, are investigated. The reasons of electro-optical properties influenced by the concentrations of the materials are discussed. Through the proper material recipe, the electro-optical properties of polymer stabilized cholesteric LC film can be optimized.

Electro-optical dual modulation on resistive switching behavior in BaTiO3/BiFeO3/TiO2 heterojunction

The novel BaTiO3/BiFeO3/TiO2 multilayer heterojunction is prepared on a fluorine-doped tinoxide(FTO) substrate by the sol–gel method. The results indicate that the Pt/Ba TiO3/BiFeO3/TiO2/FTO heterojunction exhibits stable bipolar resistive switching characteristic, good retention performance, and reversal characteristic. Under different pulse voltages and light fields, four stable resistance states can also be realized. The analysis shows that the main conduction mechanism of the resistive switching characteristic of the heterojunction is space charge limited current(SCLC) effect. After the comprehensive analysis of the band diagram and the P–E ferroelectric property of the multilayer heterojunction, we can deduce that the SCLC is formed by the effect of the oxygen vacancy which is controlled by ferroelectric polarizationmodulated change of interfacial barrier. And the effective photo-generated carrier also plays a regulatory role in resistance state(RS), which is formed by the double ferroelectric layer Ba TiO3/BiFeO3 under different light fields. This research is of potential application values for developing the multi-state non-volatile resistance random access memory(RRAM) devices based on ferroelectric materials.

Experimental study of electro-optical-switched pulsed Nd:YAG laser

We report the specification of a compact and stable side diode-pumped Q-switched pulsed Nd：YAG laser. We ex- perimentally study and compare the performance of the pulsed Nd：YAG laser in the free-running and Q-switched modes at different pulse repetition rates from 1 Hz to 100 Hz. The laser output energy is stabilized by using a special configu- ration of the optical resonator. In this laser, an unsymmetrical concave-concave resonator is used and this structure helps the mode volume to be nearly fixed when the pulse repetition rate is increased. According to the experimental results in the Q-switched operation, the laser output energy is nearly constant around 70 mJ with an FWHM pulse width of 7 ns at 100 Hz. The optical-to-optical conversion efficiency in the Q-switched regime is 17.5%.

Electro-Optical Properties of Carbon Nanotubes Obtained by High Density Plasma Chemical Vapor Deposition

In this work, we studied the electro-optical properties of high-aligned carbon nanotubes deposited at room temperature. For this, we used the High Density Plasma Chemical Vapor Deposition system. This system uses a new concept of plasma generation: a planar coil is coupled to an RF system for plasma generation. This was used together with an electrostatic shield, for plasma densification, thereby obtaining high-density plasmas. The carbon nanotubes were deposited using pure methane plasmas. Three methods were used for the surface modification of the sample: reference substrate (silicon wafer only submitted to a chemical cleaning), silicon wafer with surface roughness generated by plasma etching, silicon wafer with a thin iron film and silicon wafer with diamond nano powder used as precursor materials. For each kind of silicon wafer surface, the carbon nanotubes were deposited with two different deposition times (two and three hours). The carbon nanotubes structural characteristics were analyzed by Atomic Force Microscope and Scanning Electronic Microscope. The carbon nanotubes electrical characteristics were observed by Raman Spectroscopy and the carbon nanotubes electro-optical properties were analyzed by current vs voltage electrical measurements and photo-luminescence spectroscopy measurements. The photoelectric effect in the carbon nanotubes were determined by photo-induced current measurements. In this work, we obtained carbon nanotubes with semiconductor properties and carbon nanotubes with metallic properties. The electro-optical effects depend strongly on the substrate preparation and the deposition parameters of the carbon nanotubes. The carbon nanotubes are high aligned and show singular properties that can be used for many applications.

Electro-optical properties of high birefringence liquid crystal compounds with isothiocyanate and naphthyl group

Liquid crystal（LC） compound with isothiocyanate and naphthyl group is an attractive high birefringence LC material,and can be used in optical devices. In this paper, the electro-optical properties of a series of this type of LC compounds were investigated. The melting points and enthalpy values of these LC compounds were higher than those of corresponding compounds with the phenyl group. These compounds exhibited high birefringence with a maximum value of 0.66. Fluorine substitution in the molecular almost does not affect the birefringence value. When these LC compounds with the naphthyl group were dissolved in a commercial LC mixture, the electro-optical properties depending on temperature were investigated. In the low-temperature region, LC mixtures with the naphthyl-group LC compounds exhibited higher viscosity than pure commercial LCs. In the high-temperature region, viscosity values very closely approached each other. When response performance was investigated, figure-of-merit（FoM） values were measured. The Fo M values of LC mixtures containing LC compounds with naphthyl group were lower than those of reference benzene LCs in the low-temperature region. However, in the high-temperature region, the results were reversed. These isothiocyanate LC compounds with naphthyl group can be applied in special fast-response LC device, particularly the ones used under high-temperature conditions.

Preparation and Microstructural,Structural,Optical and Electro-Optical Properties of La Doped Pmn-Pt Transparent Ceramics

Transparent relaxor ferroelectric ceramics of the system lanthanum modified lead magnesium niobate have been investigated for a variety of electro-optic properties could make these materials alternatives to (Pb,La)(Zr,Ti)O3. However, a study that relates the properties in function stoichiometric formula, it has not been analyzed heretofore. Therefore, in this work the effect of A-site substitution of La+3 in the characterization microstructural, structural, optical and electro-optical on (1-x)[Pb(1-3/2y)Lay(Mg1/3Nb2/3)O3]-xPbTiO3 and (1-z)[(1-x)Pb(Mg1/3Nb2/3)O3+xPbTiO3]+zLa2O3 has been performed. It was observed that the properties according to the stoichiometric formula and the PT had a maximum whose behavior was related to the addition of lanthanum in each stoichiometries.

Model of Airflow Field on the Deck for Shipborne Helicopter Flight Dynamics Analysis

For the research of helicopter/ship dynamic interface,the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter.The steady flow is calculated by computational fluid dynamics(CFD)method,while the stochastic flow is composed of the compensation velocity derived from ship motion and turbulence above the deck.The accuracy of the proposed flow field model is verified by comparing the helicopter response in the proposed flow field with the results calculated by US Army′s Military Specifications(MIL)model which is commonly used in engineering.Meanwhile,it also shows the proposed flow field model is more appliable to flight dynamics analysis of shipborne helicopter.On that the basis,ship deck flow field is simulated at different sea conditions by adjusting the wind speed on the deck,mother ship movement and shipboard turbulence,etc.And helicopter angular rate response is calculated.The results show that the difference of dynamic stability between helicopter′s roll and pitch leads to the facts that the influence of above factors on the helicopter′s roll angular rate response is greater than that of pitch angular rate,that the frequency and amplitude of mother ship roll motion are much greater than those of pitch motion,and that the disturbance caused by roll motion on the air has greater influence on the helicopter response.The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.

Shipborne aerosol IR decoy modulated by laser

Working principles, features, current situation and future development of the aerosol IR decoys are summarized in this paper, and a new type aerosol IR decoy——aerosol IR decoy modulated by laser is emphasized. The simulation results show that compared with the traditional IR decoys, the late-model aerosol IR decoy effectively enhances the capability of protecting targets and countermining IR guidance weapons. It is a new direction of aerosol IR decoys.

Electro-optical properties and(E,F) phase diagram of fluorinated chiral smectic liquid crystals

Fluorinated smectic liquid crystals each with a biphenyl benzoate rigid core are investigated. Molecular structures of the studied compounds have difference only in fluorine position and the length of the carbon chain. Dielectric relaxation study and electro-optical measurements are carried out with the classical SSFLC geometry. The field-induced phase transitions are studied and the（E,T） phase diagram is established.

Analysis of electro-optical intensity modulator for bunch arrival-time monitor at SXFEL

A bunch arrival-time monitor(BAM) based on an electro-optical intensity modulation scheme is currently under development at Shanghai Soft X-ray Free-Electron Laser to meet the high-resolution requirements for bunch stability. The BAM uses a radio frequency signal generated by a pickup cavity to modulate the reference laser pulses in an electro-optical intensity modulator(EOM), and the bunch arrival-time information is derived from the amplitude change of the laser pulse after laser pulse modulation.EOM is a key optical component in the BAM system.Through the basic principle analysis of BAM, many parameters of the EOM are observed to affect the measurement resolution of the BAM system. Therefore, a systematic analysis of the EOM is crucial. In this paper, we present two schemes to compare and analyze an EOM and provide a reference for selecting a new version of the EOM.

Electro-optical Properties of Liquid Crystal Composite Materials

The liquid crystal composite materials consist of microdroplets of liquid crystals which are spontaneously formed in a matrix of a polymer at the time of its polymerization. The director configuration in liquid crystal droplets, the model of orientation of droplets, and the contrast ratios of a cell are investigated. Droplet size, spacing and distribution are readily controlled in these materials to allow optimization of displays based upon electrically controlled light scattering from the liquid crystal droplets. Preliminary experimental and theoretical studies of the light scattering and electro-optic response of new material show that these materials can offer new features suitable for large area displays and light valves.

Synthesis and electro-optic properties of fluorine-containing polyimide

The fluorine-containing organic polymer was synthesized from 3, 3＇, 4, 4＇-Bisphenyltetracarboxylic （BPDA）, and 2,2-Bis （3-amino-4-hydroxyyphenyl） hexafluoropropane （6FHP）. It is a first-step preparation of a preimided hydroxy-containing polyimide, followed by the covalent bonding of an active chromophore, dispersed red 19 （DR19）, onto the backbone of the polyimide via the Mitsunobu reaction. The nonlinear optical （NLO） containing polyimide was synthesized. The differential scanning calorimeter （DSC）and thermal gravimetric analysis （TGA） exhibited Tg and the temperature Tg at which 5 % mass losses occurring of polymer were 248 and 309 ℃, respectively. A reflective electro-optic （EO） modulator using this polymer was fabricated. The optical nonlinearities were determined to be d33 = 5. 209×10^-9 esu （poling voltage of 3.6 kV, 205 ℃） and d33 =7. 418×10^-9esu （poling voltage of 3. 8 kV, 210 ℃） by the second harmonic generation method in in-situ condition at a fundamental wavelength of 1 064 nm. The EO coefficients 733 of the polymer layer in the EO modulator were determined to be 2. 182 pm/V （poling voltage of 3.6 kV, 205 ℃） and 3. 107 pm/V （poling voltage of 3.8 kV, 210 ℃） at 1064 nm by an attenuated-total-reflection （ATR） method.

A High-Performance Silicon Electro-Optic Phase Modulator with a Triple MOS Capacitor

We propose and analyze a novel Si-based electro-optic modulator with an improved metal-oxide-semiconductor （MOS） capacitor configuration integrated into silicon-on-insulator （SOl）. Three gate-oxide layers embedded in the silicon waveguide constitute a triple MOS capacitor structure, which boosts the modulation efficiency compared with a single MOS capacitor. The simulation results demonstrate that the Vπ Lπ product is 2. 4V · cm. The rise time and fall time of the proposed device are calculated to be 80 and 40ps from the transient response curve, respectively,indicating a bandwidth of 8GHz. The phase shift efficiency and bandwidth can be enhanced by rib width scaling.

Mach-Zehnder Electro-Optic Polymer Modulator with C orona Poled Core Layer

A Mach-Zehnder(MZ) electro-optic(EO) modulator are real iz ed,with three optical layers as polymer materials.The functional layer is the co rona poled crosslinkable polyurethane.The ridge waveguide is fabricated by using the spin-coating,poling,photolithography and oxygen reactive ion etching(RIE) techniques.The mode and the modulation properties of these devices are demonstra ted in a micron control system,while the light source works at the wavelength of 1 31 or 1 55 micron.

High-power electro-optic switch technology based on novel transparent ceramic

A novel high-power polarization-independent electro-optic switch technology based on a reciprocal structtire Sagnac interferometer and a transparent quadratic electro-optic ceramic is proposed and analyzed theoretically and experimentally. The electro-optic ceramic is used as a phase retarder for the clockwise and counter-clockwise polarized light, and their po- larization directions are adjusted to their orthogonal positions by using two half-wave plates. The output light then becomes polarization-independent with respect to the polarization direction of the input light. The switch characteristics, including splitter ratios and polarization states, are theoretically analyzed and simulated in detail by the matrix multiplication method. An experimental setup is built to verify the analysis and experimental results. A new component ceramic is used and a non- polarizing cube beam splitter （NPBS） replaces the beam splitter （BS） to lower the ON/OFF voltage to 305 V and improve the extinction ratio by 2 dB. Finally, the laser-induced damage threshold for the proposed switch is measured and discussed. It is believed that potential applications of this novel polarization-independent electro-optic switch technology will be wide, especially for ultrafast high-power laser systems.

Recent progress in integrated electro-optic frequency comb generation

Optical frequency combs have emerged as an important tool enabling diverse applications from test-and-measurement,including spectroscopy,metrology,precision distance measurement,sensing,as well as optical and microwave waveform synthesis,signal processing,and communications.Several techniques exist to generate optical frequency combs,such as mode-locked lasers,Kerr micro-resonators,and electro-optic modulation.Important characteristics of optical frequency combs include the number of comb lines,their spacing,spectral shape and/or flatness,and intensity noise.While mode-locked lasers and Kerr micro-resonators can be used to obtain a large number of comb lines compared to electro-optic modulation,the latter provides increased flexibility in tuning the comb spacing.For some applications in optical communications and microwave photonics,a high degree of integration may be more desirable over a very large number of comb lines.In this paper,we review recent progress on integrated electro-optic frequency comb generators,including those based on indium phosphide,lithium niobate,and silicon photonics.