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A dual-slope-assisted chaotic Brillouin optical correlation domain analysis (DSA-CBOCDA) technique is proposed to improve the measurement accuracy and resolution for static and dynamic strain sensing. By using the gain ratio obtained from two slopes of the Brillouin gain spectrum (BGS), the influence of random fluctuation in chaotic pump power on the measurement result is alleviated. Compared with the previous single-slope-assisted CBOCDA, the measurement accuracy of the DSA-CBOCDA is improved from 25.0 μϵ to 3.9 μϵ for the static strain, and from 28.5 μϵ to 6.2 μϵ for the dynamic strain. Meanwhile, the static strain resolution of 10 μϵ and dynamic strain resolution of 15 μϵ are verified in the experiment. Moreover, the dynamic strain measurement range of 800 μϵ for the proposed DSA-CBOCDA system is also experimentally confirmed, which is approximately fivefold larger than the current DSA-based Brillouin sensing system.

Solar cells can operate at a lower efficiency after a certain temperature, which is caused by a negative thermal coefficient. Therefore, the temperature prediction of photovoltaic (PV) modules is critical to accurately evaluate the efficiency of photovoltaic devices. We propose and experimentally demonstrate a Fuzzy Temperature Difference Threshold Method (FTDTM) based on Raman Distributed Temperature Sensor (RDTS) system for the detection and prediction of PV module temperature. The FTDTM consists of four steps, i.e., division of the universe, establishment of fuzzy relationships, definition of relationship matrix and calculation of predicted temperature. The experimental results show that the proposed RDTS can detect and accurately predict temperature trends by using the FTDTM. When the system window base of the FTDTM is set to 2, the average absolute error of the predicted temperature is 1.08 °C, and the fluctuation range of prediction error is ±3.7 °C. In addition, the experiment studied some factors affecting temperature distribution characteristics of PV modules, including solar radiation intensity, surface dust and inclination angle. We provide a solution for large-scale PV module temperature detection and early warning through RDTS systems with FTDTM.

Chaotic Brillouin optical correlation domain analysis (BOCDA) has been proposed and experimentally demonstrated with the advantage of high spatial resolution. However, it faces the same issue of the temperature and strain cross-sensitivity. In this paper, the simultaneous measurement of temperature and strain can be preliminarily achieved by analyzing the two Brillouin frequencies of the chaotic laser in a large-effective-area fiber (LEAF). A temperature resolution of 1 °C and a strain resolution of 20 µε can be obtained with a spatial resolution of 3.9 cm. The actual temperature and strain measurement errors are 0.37 °C and 10 µε, respectively, which are within the maximum measurement errors.

In order to obtain high stability driving current for chaotic laser and achieve high precision adjustment of chaotic laser driving current and temperature, based on the ADN8810 and ADN8835 chips, we design a chaotic laser drive and temperature control circuit for the chaotic laser. The driving current can be output from 0 to 80 mA, which satisfies the minimum regulation accuracy of 0.01 mA and a linearly adjustable drive capability. The maximum voltage value of the thermoelectric cooler (TEC) terminal can be adjusted internally in the range from 0.5 to 4.5 V to adapt to lasers with different TECs. The maximum current value of the TEC can be adjusted in the range from 0.5 to 4.3 A to protect the laser. The experimental results prove that the stability of the driving current for the circuit output is better than 0.007%, and the maximum fluctuation of the laser temperature is 0.17 ℃ within 2 hours, which can meet the needs of chaotic lasers.

In the field of temperature safety monitoring, it is important to quickly locate the position of temperature anomalies and start to alarm. The multimode fiber (MMF) has a certain temperature hysteresis effect when detecting the surrounding temperature along the sensing fiber, it deteriorates the warning-time of Raman distributed temperature sensor (R-DTS). This paper proposed and experimentally demonstrated an R-DTS with heat transfer functional model to perceive the surrounding temperature in advance. The temperature hysteresis effect of MMF cable in different temperature conditions are studied experimentally. The experimental results show that the temperature change rate of MMF and the surrounding temperature difference maintains a linear relationship after fitting. And this fitting relationship is used to perceive the surrounding temperature anomalies along the MMF for R-DTS system. The experimental results indicate that the warning-time of R-DTS can optimize from 23.4 s to 1.3 s at the temperature condition with 60 °C. It proves that this analytical model of the heat transfer function model can quickly perceive the environment temperature anomalies to avoid the temperature hysteresis effect of MMF at the difference temperature conditions. The research content can be applied in the temperature safety monitoring with high requirements for early-warning time, such as fire monitoring, power cable safety monitoring, and gas pipeline leakage detection.

This work focuses on two meaningful points in green chemistry, one is providing a practical solution for CO2 transformation into a CO2 copolymer, and the other is disclosing the potential application of a CO2 copolymer as a water dispersible binder to overcome the bottleneck in heavy metal free anti-corrosion coatings. For the first point, a CO2-copolymer like CO2-polyol is synthesized from the telomerization of CO2 and propylene oxide using a zinc–cobalt double metal cyanide complex as a catalyst and terephthalic acid as a chain transfer agent. For the second point, for the past 30 years conducting polyaniline, with its unique anti-corrosion behaviour, has been regarded as a heavy metal free anti-corrosion material, but the development of a waterborne polyaniline anti-corrosion coating has encountered an impasse owing to the lack of a compatible binder. Therefore, a water borne cationic polyurethane dispersion (CPUD) was developed for this purpose, in which CO2-polyol was used as a soft segment, and 1,4-butanediol di(3-diethylamino-2-hydroxypropyl alcohol) ether was synthesized as a side-chain cationic extender. Unlike earlier acidic water borne dispersions, this water borne CPUD was near neutral, ensuring good compatibility with an aqueous conducting polyaniline dispersion, and is expected to create significant possibilities for the development of a novel generation of sustainable and eco-friendly metal anti-corrosion materials.

In recent years, optic-fiber sensors have been required to simultaneously measure the structure's crack and environmental temperature in the infrastructure monitoring system. We proposed and experimentally demonstrated a distributed optic-fiber sensor based on the Raman loop configuration and fiber loss characteristic for detecting the temperature and structure's crack. Among them, the Raman loop configuration with reference fiber is proposed to detect the temperature profile along the sensing fiber. It can eliminate the influence of external physical perturbation on the temperature measurement results, and do not require pre-calibration process before measurement. The temperature experimental results show that the temperature accuracy and spatial resolution can reach up to 0.28 °C and 1.2 m with the response time of 1.04 s. In addition, the information of crack is extracted by using the loss characteristics of Stokes, which is based on optical time domain reflectometry. The experiment results indicate that the fiber loss coefficient keeps a good linear variation between the crack ranges of 1.6 mm and 5.6 mm. The studies achieve the temperature and crack measurement only by one fiber.

There is an optical interference noise in the conventional Raman-based fiber-optics distributed sensing, which results in a poor temperature resolution performance. In addition, the traditional whole-fiber demodulation principle complicates the operation steps of the system. In this paper, a novel dynamic difference attenuation recognition (DDAR) principle is operated in the DDP scheme (dual demodulation principle) and the SDP scheme (self-demodulation principle) respectively. It not only helps to eliminate the optical interference noise, but also omits the whole-fiber calibration process. In this experiment, a temperature resolution of 0.30 &deg, C (17.0 km) is achieved through using the DDP scheme based on the DDAR principle, and the measurement time can be shortened to 1.5 s. Meanwhile, a temperature resolution of 0.18 &deg, C (17.0 km) is obtained for the SDP scheme under the DDAR principle. The SNR of DDP and DSP schemes can be optimized to 12.82 dB and 13.32 dB by the proposed DDAR technology. Furthermore, the temperature resolution performance under a large temperature measurement range (0&ndash, 1000 &deg, C) is theoretically analyzed. The results indicate that the temperature responsivity for DDP and SDP schemes are parabolic and linear type respectively, which causes the temperature resolution of the two schemes to show a different trend with the change of temperature. The proposed DDAR method also can improve the temperature resolution in such a large temperature measurement range.

We proposed and experimentally demonstrated a distributed optic-fiber sensor based on the Raman loop configuration and fiber loss characteristic for detecting the temperature and structure's crack. Among them, the Raman loop configuration with reference fiber is proposed to detect the temperature profile along the sensing fiber. It can eliminate the influence of external physical perturbation on the temperature measurement results, and don't require pre-calibration process before measurement. This proposed method improves the engineering applicability of optic-fiber sensors. In addition, the information of crack is detected by using the fiber loss characteristics based on OTDR technology.

CO2 based waterborne polyurethane (CO2-WPU), especially high CO2 content one, suffered from the poor flexibility at low temperature due to high content of rigid carbonate segment. Here a microphase separation idea was proposed by introducing poly(butyl acrylate) (PBA) as soft phase to toughen CO2-WPU via an organic solvent free route, i.e., the polymerizable butyl acrylate acted as a pseudo-solvent during CO2-WPU prepolymer synthesis, it then experienced radical polymerization after formation of CO2-WPU, and finally forming a material with multi-phase structure. Benefiting from the separation of soft PBA phase and hard CO2-WPU phase in micro-size, a 368% increase in elongation at break (eb) and nearly 65 times increase in toughness at -10 °C was observed when PBA loading increased from blank to 65 wt%. As a comparison, the tensile strength (σm) and eb of the PBA/CO2-WPU blending film at room temperature was only 4.4 MPa and 383% when PBA loading was 50 wt%, while the PBA/CO2-WPU multi-phase film showed σm of 18.8 MPa and eb of 489%, respectively. The toughening effect was attributed to the more uniform micro-phase separation structure caused by molecular level inter-migration between PBA and CO2-WPU during preparation process.

We report a novel passively mode-locked quantum-well laser, which have an asymmetric colliding pulse mode-locked structure. The saturable absorber (SA) multi-quantum wells (MQWs) of the laser have bandgap, which is gradually varied along the ridge direction realized by selective area growth technique, forming a broadband absorber. As a result, light pulses are obtained at a repetition frequency of 226 GHz with a minimum pulse width of 605 fs under an appropriate current bias. Because of the continuous variation of the SA MQW bandgap, the SA absorption peak covers a wide range of wavelength, which makes the device more immune to SA bandgap change resulted from SA reverse bias or light absorption-induced heating of the SA, compared with traditional MQW mode-locked lasers.

An elevated-temperature dispersing (ETD) strategy was developed to disperse prepolymers at 80 °C for producing waterborne CO2-based polyurethane (CO2-WPU) in a whole-procedure organic solvent-free route. The obstacle of high viscosity challenging the traditional prepolymer-dispersing process was overcome, and the concern of significant NCO loss at high temperature was eliminated because prepolymer dispersion ensured >90% NCO retention. The particle size of the typical CO2-WPU emulsion lay between 45 nm and 70 nm, and it showed excellent stability even after centrifugation for 30 min at 3000 rpm. The dried CO2-WPU film showed not only good mechanical performance with a tensile strength of 54.3 MPa and elongation at break of 641%, but also excellent hydrolysis resistance owing to the unique structure of the CO2-polyol. This ETD strategy showed clear feasibility for commercial polyether or polyester oligomerols. It avoids the cooling step and solvent-removal procedure required in a traditional prepolymer-dispersing process, thereby greatly shortening the preparation period and reducing energy consumption.

A novel temperature demodulation method which eliminates the unstable of incident light on Raman distributed temperature sensors (RDTS) is presented. This method based on the incident light fluctuation compensation algorithm which optimizes the temperature measurement errors for RDTS. Besides, compared to convention temperature-distance display method, the temperature three-dimensional (3D) display technology can realize the fibre model 3D display. Experimental results indicate that the temperature measurement error is optimized by using the presented method. This paper provides a solution for accurate measurement of temperature as well as temperature 3D display along the sensing fibre for RDTS systems.

The field of tunnel fire detection requires a Raman distributed temperature sensor (RDTS) with high-accuracy and visual localization. A novel temperature demodulation method to improve the temperature measurement accuracy of the RDTS systems is presented. This method is based on the optical dynamic difference compensation algorithm, which can eliminate the optical power fluctuation. In addition, the visual localization technology is presented by using the longitudinal lining model (LLM) of a three-dimensional (3D) temperature display, which enhances the engineering application of RDTS in tunnel fire detection. Experimental results indicate that the temperature measurement accuracy is optimized from 7.0 &deg, C to 1.9 &deg, C at the sensing distance of 18.27 km by using the presented method. We provide a solution for temperature field monitoring as well as fire visual localization of the tunnel through RDTS systems.

Though cationic waterborne polyurethane (CWPU) has been regarded as an important environmental friendly material, it is hampered by poor water resistance due to incorporation of excessive hydrophilic groups to assure the stability of water dispersion. Here UV-curing in combination with terminal hydrophilicity induced dispersion strategy was employed to prepare water-resistant CWPU from CO2-polyol which was an oligoethercarbonate diol from telomerization of propylene oxide and CO2. In this system, multiple vinyl ether side chains were incorporated on CWPU backbone using 3-allyloxy-1,2-propanediol as functional chain extender to achieve efficient UV curing, and a small amount of terminal hydrophilicity was designed to ensure the stable dispersion of CWPU. The typical UV-cured CWPU film reached water absorption equilibrium at 72 h, maintaining water absorption rate as low as Ca. 5.8% even immersed in water for 240 h. Moreover, compared with traditional polyester and polyether polyols from petroleum resources, UV-cured CWPU from CO2-polyol not only used partially sustainable raw material like CO2, but also provided excellent water resistance in corrosive media for a long time (tensile strength retention above 90% for 336 h) due to hydrolysis resistant structure like carbonate and ether units in CO2-polyol.

The Raman optical time-domain reflectometry (ROTDR) uses the Raman backscattering signal of an optical pulse to obtain environmental information along the sensing fiber, with the pulse width limiting spatial resolution to the meter level in current systems. To solve this problem, we propose a chaos ROTDR system to eliminate the superposition effect of Raman backscattering response caused by pulse width. Here, the chaotic laser is applied as the sensing source instead of a conventional laser. For the random amplitude characteristics of the chaotic laser in time series, the chaotic Raman backscattering signal of individual points along the sensing fiber can be obtained, so that the millimeter-evel spatial resolution is realized. Firstly, the propagation equation of the chaotic Raman backscattering signal is established. Subsequently, the most relevant factors impacting the performance of spatial resolution and the signal-to-noise ratio (SNR) could be addressed based on two methods proposed in this study: one is the time-domain differential reconstruction (TDDR), and the other is the short-scale time-domain correlation compression (SSTDCC). Finally, the spatial resolution of 5 mm and temperature sensitivity of 0.1 K are achieved, which is an unprecedented breakthrough compared to the state-of-the-art technology.

Multiwavelength laser arrays with 25-GHz channel spacing have been fabricated by upper separate confinement heterostructure (SCH) layer selective area growth (SAG) technique. The reconstruction equivalent chirp (REC) technique is used to introduce an equivalent phase shift into the grating structure, so that a high single longitude mode yield of lasers can be ensured. Because different emission wavelengths are realized through thickness modulation of the upper SCH layer by SAG, the sampling period in the REC technique is the same for all the lasers in an array, which may alleviate the effects of the facet phase on the emission wavelength. The fabricated laser arrays have less than 0.051 nm standard deviation of wavelength deviations. Only conventional photolithography process is needed, helping to lower the fabrication cost of the laser arrays.

UV-curable waterborne polyurethanes (CO 2 -UV-WPUs) with CO 2 -polyols as soft segment were firstly synthesized. In addition to the good mechanical performance, the coexistence of carbonate and ether moieties in soft segment assured the excellent hydrolysis resistance of CO 2 -UV-WPU compared with polybutylene adipate glycol based waterborne polyurethane (PBA-UV-WPU). Its retention of tensile strength reached 88% after 15 h immersion in 1.5% sodium hydroxide solution, while that of PBA-UV-WPU completely lost its mechanical property. The double bond density primarily governed the mechanical performance of CO 2 -UV-WPU, when it increased from 0.93 mmol/g to 2.4 mmol/g, the tensile strength increased from 29 MPa to 67 MPa, while elongation at break decreased from 150% to 9.6%, accompanied by the reduction of maximum water swelling percentage from 26.7% to 14.5%. The introduction of CO 2 -polyol as soft segment not only created a route to produce UV-curable waterborne polyurethane from CO 2 , but also provided polyurethane with novel value-added performance like good hydrolysis resistance. Moreover, the thermal/mechanical performance and hydrophilicity of CO 2 -UV-WPUs could be conveniently adjusted by controlling molecular weight of CO 2 -polyols, ensuring the application feasibility of CO 2 -UV-WPU.

The effects of doping in the multiquantum well (MQW) active region on the properties of InP-based long wavelength deep ridge transistor lasers (TLs) are numerically studied. Doping in the MQWs is shown to lead to a decrease of the slope efficiency and a notable increase of the current gain of the TLs, which makes MQW doping a useful tool for facilitating the design of TLs. When there are nonradiative recombination centers on the exposed MQW side walls of the TLs, doping in the MQWs is found to be able to enhance the performance of the TLs by reducing the threshold current and increasing the current gain greatly. With doping in the MQWs, the carrier diffusivity is decreased, making the defects less effective in consuming the carriers. The results show that doping in the MQWs helps to obtain high-quality TLs. The reduced carrier diffusion that results from doping also helps to improve the quality of a normal diode laser in case a deep ridge structure is needed.

A novel Rayleigh noise suppression method is proposed to improve temperature accuracy and resolution for Raman distributed fiber-optics sensors. The proposed temperature demodulation method can eliminate temperature measurement inaccuracy caused by Rayleigh noise. The experimental results indicate that the temperature accuracy is optimized from 6.2°C to 1.7°C at a sensing distance of 9.1 km by using the proposed method, and the temperature resolution leads to about 1.5°C improvement compared with the tradition demodulation method at a sensing distance of 10.0 km. The proposed method provides a robust and reliable high performance for long sensing ranges.

We present the fabrication of a low-cost multiwavelength laser array monolithically integrated with a passive optical combiner for optical line terminals (OLTs) in wavelength-division multiplexing (WDM) passive optical networks (PONs). By combining the upper separate confinement heterostructure layer selective area growth technique and the bundle integrated guide technique, both multiwavelength emission with highly uniform spacing and low-loss passive-waveguide material can be obtained in a single metal–organic chemical vapor deposition (MOCVD) growth step, which greatly simplifies the fabrication of the device. A prototype laser array, which has four distributed feedback (DFB) laser elements and a multimode interference coupler as combiner, is successfully fabricated. The shallow ridge structure of the DFB lasers and the deep ridge structure of the passive waveguides are obtained by a single dry etching step, which further eases the device fabrication. The properties of the device are measured and discussed. The results indicate that our method is promising for fabricating cost-effective OLT light sources for WDM-PONs.

Amorphous poly(propylene carbonate) (PPC) is brittle at room temperature, but the studies related to the toughening of PPC is rare. Herein, two types of polyurethane (PCO2PU) synthesized from a CO2-based diol and toluene diisocyanate were used as rubbery particles to toughen PPC. The notched impact strength of PPC increased from 20.8 J m−1 to 54.2 J m−1 at a PCO2PU loading of 20 wt%, comparable with that of neat nylon 6, and reached 228.3 J m−1 at a PCO2PU loading of 30 wt%, 10.9 fold that of neat PPC and even higher than bisphenol A polycarbonate. Matrix yielding as well as cavitation was observed during the impact process, which was responsible for the increase of impact strength. Moreover, the toughening efficiency was related with the carbonate content of PCO2PU, and the transition of fracture behavior from brittle to ductile occurred when the PCO2PU with a weight average diameter of 0.20 μm was uniformly dispersed in PPC substrate.

A novel passively mode-locked quantum-well laser, which saturable absorber (SA) has gradually varied bandgap, is fabricated. Light pulses are obtained at a repetition frequency of 226 GHz with a minimum pulse width of 605 fs under an appropriate mono current bias.

We propose and experimentally demonstrate a novel auto-correction method for improving temperature stability in long-range Raman distributed fiber temperature sensors. The proposed method is based on multi-stage constant temperature control and dynamic gain calibration technology, which can suppress the unstable photoresponsivity and noise of a system. The experimental results indicate that the temperature stability is optimized from ±12.6°C to ±7.2°C at the sensing distance of 30 km for multimode fiber using this method.

We propose a transistor laser with a current confinement aperture (a-TL) formed in a reverse junction layer in the middle of emitter ridge. The a-TLs are studied numerically in comparison with the deep ridge TLs. Data show that in a-TLs, the effects of nonradiative recombination centers on the side walls of the emitter ridge can be reduced greatly due to the confinement of carrier flow in the center region of the emitter ridge. Furthermore, the reverse junction layer can be used as an etching stop layer for the emitter ridge formation, which facilitates both the design and the fabrication of the device. Together with the fact that in a-TLs, the effects of p-type material are alleviated effectively by placing the multi-quantum wells above the base layer, high performance can be expected, especially for long-wavelength devices.

A transistor laser (TL), having the structure of a transistor with multi-quantum wells near its base region, bridges the functionality gap between lasers and transistors. However, light emission is produced at the expense of current gain for all the TLs reported up to now, leading to a very low current gain. We propose a novel design of TLs, which have an n-doped InP layer inserted in the emitter ridge. Numerical studies show that a current flow aperture for only holes can be formed in the center of the emitter ridge. As a result, the common emitter current gain can be as large as 143.3, which is over 15 times larger than that of a TL without the aperture. Besides, the effects of nonradiative recombination defects can be reduced greatly because the flow of holes is confined in the center region of the emitter ridge.

Temperature effect of dendrimer/graphite nanosheets/polypyrrole (dendrimer/NanoGs /PPy) interface material has been investigated by molecular dynamics (MD) simulation to reveal its work mechanism as molecular thermoswitch (temperature sensitive switch). Interfacial energy, structure and thermoswitch mechanism were studied in temperature range of 300–440 K. Effective interaction, uniform distribution and appropriate coating of interfaces lead to the high compatibility at 360 K. Incompact and weak coating interfaces result in steady and low compatibility at 340 K and 400 K, respectively. The dendrimer/NanoGs/PPy interface material working as a thermoswitch is realized by geometry change of dendrimer driven by its interfacial interactions with PPy and NanoGs at various temperatures.

Interfaces of graphite nanosheet/AgCl/Polypyrrole (NanoG/AgCl/PPy) composite have been researched by atomistic and mesoscale simulations. The results showed that the three-component nanocomposites were formed on the basis of van der Waals interfacial interactions between two components (except between NanoG and AgCl). PPy played a key role of adhesive, which combine with NanoG and AgCl separately through strong advantaged interfaces. So the three-components could form nanocomposite as a whole in mesoscale. Quantitative analysis of density and potential distributions of NanoG/AgCl/PPy composites showed that they had proper potential interfaces and uniform distribution. The NanoG well dispersed in PPy matrix, and the matrix was decorated by core–shell nanoparticles with AgCl as the core and PPy as the conducting shell.

We report a widely tunable distributed Bragg reflector (DBR) laser, in which InGaAsP with 1.4 μm wavelength emission wavelength is butt-jointed as the DBR material. A Ti thin film heater is integrated in the DBR section of the device. With the help of the tuning effect of the heater, an over 20nm wavelength tuning range is obtained.

Transistor lasers (TLs) with n-doped quantum wells (QWs), which own low threshold current, are reported in this paper. The exposed side walls of QWs introduce amounts of recombination centers, which damages the properties of deep ridge TLs greatly. It is found that the heavily doping in quantum wells can effectively alleviate this effect. Assuming that the surface recombination is 106 cm/s, the light output power and current gain of common emitter configurations as functions of varying doping concentration and ridge width are studied. With doping concentration of 1018 cm−3 and ridge width of 2µm, the threshold current of TLs can be reduced from more than 100 mA to 31 mA and current gain can be increased from 0.1 to 2.4.

We present an InP-based distributed Bragg reflector (DBR) laser transmitter which has a wide wavelength tuning range and a high chip output power for wavelength division multiplexing passive optical network (WDM-PON) applications. By butt-jointing InGaAsP with 1.45µm emission wavelength as the material of the grating section, the laser wavelength can be tuned for over 13nm by the DBR current. Accompanied by varying the chip temperature, the tuning range can be further enlarged to 16 nm. With the help of the integrated semiconductor optical amplifier (SOA), the largest chip output power is over 30mW. The electroabsorption modulator (EAM) is integrated into the device by the selective-area growth (SAG) technique. The 3dB small signal modulation bandwidth of the EAM is over 13 GHz. The device has both a simple tuning scheme and a simple fabrication procedure, making it suitable for low cost massive production which is desirable for WDM-PON uses.

We report continuous-wave (CW) operation up to 20 °C of 1.5-μm wavelength npn-InGaAsP/InP multiple quantum well (MQW) transistor laser (TL) with a deep-ridge structure. With CW laser emission, the common emitter current gain of the device can be over 3.5, which is significantly larger than those of the previously reported long wavelength TLs. It is found that at low base current, the laser operation occurs on the first excited state of the MQWs. At high base current, however, the device shows stimulated emissions on the ground state transition. The trend is contrary to what has been observed in the GaAs based TLs and is explained by the change of carrier flow at different base currents.

Modifications of poly(vinyl alcohol) (PVA) can improve the properties and performance of poly(vinyl acetate) (PVAc) emulsions stabilized with these modified colloids. Water resistance and toughness of the emulsions as wood adhesives can be achieved through chemical reactions of the hydroxy groups of the colloid with various modifiers. The chemical changes can be carried out either in the preparation of PVA through hydrolysis of copolymers of vinyl acetate and other monomers, or by the reaction of modifiers with PVA aqueous solutions. The modified PVAc emulsions show better properties than those of the conventional emulsions in performance tests and applications. The modified colloids are becoming increasingly used in the manufacture of PVAc emulsions in the adhesive industry, because of their advantages over emulsions made using conventional (unmodified) PVA. The trend of current research is to introduce more functionality into the colloid, so that the traditional protective colloids can be modified to function as crosslinkers and chain transfer agents.

Various modifications of polyvinyl acetate emulsion wood adhesive were made and their performance evaluated in standard tests. The results are interpreted in the context of adhesion theories and the chemical structures of the polymers and wood. The adhesion of the polymers to wood and the cohesive strength of the polymers are the two predominant factors determining the performance of the adhesives. Adhesive strength in thermosetting resins is enhanced by irreversible chemical reactions that create extensive networks within the adhesive layer and strong bonds to the wood substrate, leading to strong and durable joints that passed all of the performance evaluation tests. Most of the PVAc emulsions exhibited good adhesive performance in the dry state, but failed in water soak and boiling water immersion tests since their adhesion and cohesion are mainly based on weaker physical interactions. Emulsions with (hard) core‐(soft) shell morphology and correspondingly high glass transition temperatures gave poor performance under all conditions.

Poly (vinyl acetate)‐based emulsion polymer/isocyanates (EPI) structural wood adhesives were prepared and their performance benchmark tested according to the specifications of the Japanese JAS‐111 standard. The changes of the glass transition temperature of the cured emulsions relative to unmodified poly(vinyl acetate) emulsion, measured using differential scanning calorimetry, indicated the chemical structure changes resulting from modification of poly(vinyl acetate) emulsion. The EPI adhesives showed excellent water resistance and near‐colourless gluelines in wood joints, ease of application and additional significant advantages over other types of wood adhesives. The performance test results are interpreted on the basis of the viscoelastic behaviour of free‐standing adhesive films. Other types of crosslinkers were used in the study to compare with the isocyanate hardeners.

Four different approaches were taken to improve the water resistance of poly(vinyl acetate) (PVAc) emulsion adhesives. The improved wood adhesives were tested according to the ISO 9020 standard. Tensile storage modulus (E’) and glass transition temperature of the polymer films were measured using dynamic mechanical thermal analysis to quantify the influence of different approaches on those variables. Gel fraction and swelling ratio of the polymer film were measured to evaluate internal crosslink density. The experimental results showed that blending melamine/urea/formaldehyde (MUF) resin with PVAc emulsions modified the water resistance considerably and the film had a high E’ since an interpenetrating network‐type structure was formed in the polymer. The advantages and limitations of each modification were assessed on the basis of comparison of the results.

Fillers with different chemical properties were used to study their effects on poly(vinyl acetate) (PVAc) emulsion wood adhesives. The elastoplastic behaviour of the filler treated PVAc emulsions was studied using differential scanning calorimetry and dynamic mechanical thermal analysis. The results show that the glass transition temperature (Tg) of the polymer is not changed significantly by the addition of the fillers, while the tensile modulus is changed together with the hardness and stiffness. The viscosity of the emulsions and their performance on wood surfaces are greatly affected by fillers. Fillers with high oil‐absorption capacity increase viscosity to a greater extent. The acidity of the fillers influences the setting time for bonding of the emulsions to wood, and the water resistance, since some chemical reactions can take place during curing.

We report a widely tunable distributed Bragg reflector (DBR) laser, in which InGaAsP with 1.4- $\mu \text{m}$ photoluminescence wavelength is butt-jointed as the DBR section material. A titanium (Ti) thin-film heater is integrated in the DBR section of the device. With the help of the tuning effect of the heater, an over 20-nm wavelength tuning range is obtained. The DBR laser is a promising light source for future wavelength division multiplexing passive optical networks.

2-Furyloxirane(FO) with purity of over 99% was prepared in 80% yield by epoxidation of furfural with trimethylsulfonium chloride and potassium hydroxide in acetonitrile/water solution. Polymerization of FO was realized using tri-isobutyl aluminum (Al(i-Bu)3) as catalyst, when Al(i-Bu)3 concentration was 0.009 mol/L, poly(2-furyloxirane)(PFO) with M n of 3.4 kg/mol and a polydispersity index of 1.5 was obtained in yield of 88% after polymerization at 25 °C for 48 h. The corresponding PFO showed glass transition temperature (T g ) of Ca. 1 °C and 5 wt% thermal decomposition temperature(T d ) of 260 °C. The obtained PFO was almost 100% head-to-tail structure, and it was a good plasticizer and thermal stabilizer for poly(propylene carbonate)(PPC), an alternate copolymer of propylene oxide and carbon dioxide. For PFO/PPC polyblend with PFO loading of 2 wt%, its T d increased by 50 °C from 214 °C of pure PPC to 264 °C, while its elongation at break increased from 13% of pure PPC to 29%.

A novel design of a two-mode de/multiplexer (DE/MUX) based on multimode interference (MMI) couplers is presented. Instead of the phase shifter (PS) in the shape of a narrow strip waveguide, which needs tight design and fabrication requirements, a tilted joint is used as a PS in the proposed device, so that the effects of the fabrication errors of the PS on the performance of the device can be reduced greatly. Simulations show that while the size of the device is as small as 39.54 μm, which is more compact than other MMI-based DE/MUX, the fabrication tolerance is larger than ±25 nm. Within the entire C-band wavelength range, the de-multiplexing crosstalk of the device is lower than -28 dB and the insertion loss is below 1.0 dB.

We present an InP based distributed Bragg reflector (DBR) laser transmitter which has a wide wavelength tuning range and a high chip output power for wavelength division multiplexing passive optical network (WDM-PON) applications. By butt-jointing InGaAsP with 1.45 µm emission wavelength as the material of the grating section, the laser wavelength can be tuned for over 13 nm by the DBR current. Accompanied by varying the chip temperature, the tuning range can be further enlarged to 16 nm. With the help of the integrated semiconductor optical amplifier (SOA), the largest chip output power is over 30 mW. The electroabsorption modulator (EAM) is integrated into the device by the selective-area growth (SAG) technique. The 3 dB small signal modulation bandwidth of the EAM is over 13 GHz. The device has both a simple tuning scheme and a simple fabrication procedure, making it suitable for low cost massive production which is desirable for WDM-PON uses.