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【Objective】The use of random mapping and traditional constellations in Optical-Orthogonal Frequency Division Multiplexing (O-OFDM) - Index Modulation (IM) system cannot reach the optimal Bit Error Rate (BER) performance. Therefore, a step-by-step optimal signal mapping method is proposed based on the optimal selection of active sub-carriers and the optimal rotation of constellation to improve the BER performance of O-OFDM-IM system.【Methods】At the transmitter side, the method firstly selects the optimal combination of active subcarriers based on the channel state information and the channel norm maximization criterion. Then considering ∂=0.5° as the step size, an exhaustive search algorithm is used to obtain the optimal constellation by using the channel state information. Next, the optimal constellation graph obtained by rotation is loaded on the active sub-carrier for signal transmission. At last, the Maximum Likelihood (ML) detection algorithm is used to recover the original signal at the receiver to minimize the system error probability.【Results】The results show that at the condition of BER=10-4 and strong turbulence, the Signal to Noise Ratio (SNR) is improved by about 1.45 dB when the modulation order is 16 in (4, 2) system. In addition, with the increase of turbulence intensity, the improvement of BER performance is more obvious. For example, when the BER=10-4 the SNR of the (4, 2) system at 8 Quadrature Amplitude Modulation (QAM) is improved by about 1.35 dB in strong turbulence and 1.2 dB in weak turbulence.【Conclusion】Based on the known channel state information, a step-by-step optimal signal mapping method for O-OFDM-IM is proposed in this paper, which can effectively improve the BER performance of the system in strong turbulence channels.

In the field of optical communication, laser and its modulation bandwidth and modulation rate are very important for optical wireless communication. There are two main modulation modes for semiconductor laser signal: internal modulation and external modulation. These two modulation technologies have their own characteristics and are suitable for different fields of optical fiber communication. Internal modulation laser, also known as direct modulation laser, has become a cost-effective light source for the Fifth Generation Mobile Communication Technology (5G) fronthaul and data center because of its high-speed transmission and low cost. There is no additional Chirp of light source in external modulation laser, so the Composite Second Beat (CSB) distortion caused by fiber dispersion can be effectively overcomed. On the basis of reviewing the development history of communication laser and its modulation technology, this paper introduces the work and main progress made by Xi’an University of Technology in this field. This paper discusses the internal and external factors of nonlinear distortion of semiconductor laser, simulates the effects of various parameters of response characteristics, linearization compensation method and power control system on the output light source of light emitting device, and analyzes the influence of temperature fluctuation on the output power of laser and modulation device. Based on the basic theory of refractive index ellipsoid and numerical analysis, the variation trend of emitted light intensity with temperature is discussed under the longitudinal and transverse modulation, respectively. The results show that the variation trend of outgoing light intensity with temperature under longitudinal modulation is only related to the refractive index of Lithium Niobate (LN) crystal. Under transverse modulation, the variation trend of outgoing light intensity with temperature is affected not only by the refractive index of the crystal, but also by the crystal size and its expansion coefficient. Therefore, the special size crystal can be used to improve the temperature stability of the electro-optic modulator.

为提高蛋白基Pickering乳液稳定性，采用美拉德反应制备乳清分离蛋白（WPI）-葡聚糖（Dex）接枝物，然后利用该接枝物制得蛋白基固体颗粒，再与中链甘油三酯制备Pickering乳液，考察WPI-Dex接枝物对蛋白基固体颗粒乳化活性、乳化稳定性和蛋白基Pickering乳液乳析指数的影响，以及Pickering乳液在不同pH、加热温度、贮藏时间下粒径的变化。结果表明：扫描电镜观察到共价接枝Dex将WPI形貌结构由球状转变为片状，十二烷基硫酸钠-聚丙烯酰胺凝胶电泳证实干法美拉德反应成功制备了WPI-Dex接枝物；与WPI相比，WPI-Dex接枝物的乳化活性和乳化稳定性分别增加了57.8%和138.5%；WPI和WPI-Dex接枝物Pickering乳液贮藏30 d时的乳析指数分别为52.3%和36.0%，WPI-Dex接枝物使Pickering乳液的乳析稳定性提高了31.2%；WPI-Dex接枝物Pickering乳液具有良好的pH稳定性、热稳定性和贮藏稳定性。综上，蛋白质糖基化接枝修饰是提高天然蛋白质Pickering乳液稳定性的有效方法。In order to improve the stability of protein-based Pickering emulsion, Maillard reaction was used to prepare the whey protein isolate(WPI)-dextran(Dex) conjugate. The WPI-Dex conjugate was used to prepare protein-based solid particles, and then Pickering emulsion was prepared with medium-chain triglyceride. The effects of the WPI-Dex conjugate on the emulsification activity, emulsion stability of protein-base solid particles and creaming index of Pickering emulsion were investigated, as well as the change of diameter of Pickering emulsion under different pH, heating temperature and storage time. The results showed that scanning electron microscopy (SEM) observed the covalently grafted Dex transformed the morphologic structure of WPI from globular to flake. The WPI-Dex conjugate was successfully prepared by the dry state Maillard reaction, which was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Compared with WPI, the emulsification activity and emulsion stability of WPI-Dex conjugate increased by 57.8% and 138.5%, respectively. The creaming indexes of WPI and WPI-Dex conjugate Pickering emulsion stored for 30 d were 52.3% and 36.0%, respectively, and the creaming stability of WPI-Dex conjugate Pickering emulsion increased by 31.2%. WPI-Dex conjugate Pickering emulsion had good pH stability, thermal stability and storage stability. In conclusion, the glycosylation graft modification of protein is an effective method to improve the stability of natural protein Pickering emulsions.