Simulation Research On All-optical Analog-to-Digital Conversion System

The analog-to-digital converter is an important part of the communication system and is a bridge connecting the analog signal and the digital signal.Since the electronic analog-to-digital conversion system is limited by electronic devices,it is difficult to keep up with the requirements of high-speed and high-precision analog-to-digital conversion.Therefore,the realization of analog-to-digital conversion by optical means has become a research hotspot in recent years.At present,there are many methods for all-optical analog-to-digital conversion.Among them,the scheme based on intensity modulator and phase modulator has the advantages of simple implementation principle and mature device.Therefore,the all optical analog-to-digital conversion using intensity modulation and phase modulation is adopted to design two systems.Then the systems were simulated and the performance was analyzed.The main work of the thesis is as follows:In this thesis,based on the principles of the intensity quantization and the phase shift quantization,an all-optical analog-to-digital conversion scheme of intensity-phase quantization is proposed.In the intensity quantization,the period multiplication of the electro-optical modulation curve is required for increasing the quantization bit rate.In the phase shift quantization,the number of quantization channels is doubled for increasing the 1-bit quantization precision,which make the system too complicated.The above two problems can be solved by combining two quantization schemes.The 6-bit quantization precision in the all-optical analog-to-digital conversion system for a 2.5GHz sinusoidal signal with 50Gbit/s sampling pulse is implemented by simulation,and the effective quantization bit rate of 5.8918bit is obtained.By means of joint quantization,adding two intensity modulators in the 4-bit phase-shifted optical quantization scheme can improve the quantization accuracy by 2 bits without significantly increasing the complexity of the system.The performance of the system was analyzed.For the intensity-phase joint quantization scheme,the quantized voltage range is limited by the half-wave voltage of the electro-optic modulator.Although the quantization accuracy is improved,it is difficult to narrow the quantized voltage range.In order to solve this problem,the all-optical analog-to-digital conversion scheme based on cascaded asymmetric Mach-Zehnder electro-optic modulator is designed.A 5 bit quantization accuracy system for a 2.5 GHz sinusoidal with 50 Gbit/s sampled pulse is implemented by simulating.The optical comparator is used to enable all-optical decision.Compared with the intensity quantization system or phase quantization system,the quantization bit rate is increased,and the devices used in the system are reduced as much as possible.And the noise generated by the electronic comparators is also avoided.At the same time,the limitation of the quantized voltage range in the intensity-phase joint quantization scheme is also solved.In the simulation,the quantization precision of 4.9928bit,which is very close to the theoretical value of 5bit,is obtained.The errors performance of the scheme are analyzed.