| With the advent of the information age,communication networks have become increasingly demanding in terms of high-speed,high-capacity,and diversity of services.Dense Wavelength Division Multiplexing(DWDM)technology can effectively expand network capacity and enhance the system's anti-jamming capability.The requirements of multiple broadband services on the flexibility and interactivity of communication networks can be achieved through ROF technology.Combining ROF technology with DWDM technology can solve the problem of network transmission capacity and multiple service requirements at the same time.However,when the number of channels of a dense wavelength division multiplexing system is increased,the available system bandwidth is not increased,and thus a narrower line width of the light source is required to satisfy the smaller channel wavelength interval.Therefore,developing a multi-carrier light source with dense wavelength division multiplexing system with high wavelength control accuracy and high stability is one of the keys to increase system capacity and improve transmission quality.There are many technical solutions for generating a multi-carrier light source,and the generation scheme of the multi-carrier light source based on the external light modulator is widely used because its structure is simple and stable,and the frequency spacing of the multi-carrier light source can be changed.The second chapter introduces the principle of the relevant external modulator and its mathematical model.The generation scheme of a multi-carrier light source based on a single external modulator and multiple external modulators is introduced separately and the results are analyzed.Based on the analysis results in Chapter 2,the third chapter proposes a multi-carrier light source generation scheme that can generate low flatness,multiple subcarriers,and a large spectrum width.The structure of this generation scheme is mainly composed of a cascade of Mach-Zehnder modulators,electro-absorption modulators,and phase modulators.The three modulators are driven simultaneously by a single RF signal to obtain a low-flattened multi-carrier light source with an adjustable frequency interval.When the frequency of the driving signal is 18 GHz,the obtained multi-carrier lightsource has a flatness of 0.086 dB and a spectrum width of 540 GHz with a sub-carrier number of 31.The paper also analyzes the effect of Mach-Zehnder modulator's upper and lower arm bias voltage difference,electro-absorption modulator's chip factor and modulation index on the number of subcarriers,flatness and spectrum width of the generated multi-carrier light source.Based on the multi-carrier light source with adjustable frequency interval proposed in Chapter 3,Chapter 4 designs two DWDM-ROF systems based on the multi-carrier light source structure,which are respectively a single millimeter wave output mode DWDM-ROF system design.DWDM-ROF system design with optional frequency output millimeter wave.Both system designs can achieve 15 downlink signal transmissions under the condition of 31 subcarriers generated by a multi-carrier light source.The first system design can obtain 15 60 GHz millimeter wave signals after the base station beat frequency.The second system design adds a digital optical switch matrix structure to the first system design,which can simultaneously achieve 5 kinds of frequency millimeter wave output,increasing the flexibility of the system.Finally,the performance of the two systems was simulated and analyzed.The results show that after40 km of optical fiber link transmission,it still has good system performance.In addition,the influence of the flatness of the multi-carrier light source on the millimeter-wave power fluctuation generated by the DWDM-ROF system is also analyzed.It is found that the fluctuation of the millimeter-wave power will increase as the flatness increases.Therefore,the good flatness of the multi-carrier light source can improve the stability of the DWDM-ROF system. |
PDF Full Text Request