A Study On Photonic Generation And Transmission Of Microwave And Millimeter-wave Signals

From 1970 s, the rapid rise of optoelectronics and optical fiber communication and the development of microwave technology make the two independent subjects have more and more connections. In recent years, with the increasing development of wireless communication technology, the requirements of information transmission rate are much higher. The result is that existing frequency bands can not meet the growing requirements of the transmission rate. Microwave and millimeter-wave band has a bandwidth of several hundreds of GHz, but is very hard to be distributed over long distance due to its huge transmission loss. Furthermore, high frequency, low phase noise and frequency tunable microwave and millimeter-wave signals are very costly or impossible to be generated in the electrical domain. Therefore, photonic generation of high frequency, low phase noise and frequency tunable microwave and millimeter-wave signal, and fiber transmission of microwave and millimeter-wave signal have attracted extensive attentions from researchers all over the world because of its unique advantages. In this thesis, first, a brief introduction to the basic concepts, the development, and the major research topics of microwave photonics is made; second, the basic theoretical knowledge of optical external modulation, optoelectronic oscillator and fiber dispersion is discussed; then, theoretical analyses, simulations and experiment studies are made for photonic generation of microwave and millimeter-wave signal and fiber transmission of microwave and millimeter-wave signal. Our research findings are as follows:1. Three Mach-Zehnder modulator(MZM) based microwave and millimeter-wave signal generation approaches with frequency multiplication are proposed and studied by simulation. Using a single MZM, frequency multiplication factor(FMF) is limited to 2(if optical filtering is employed, FMF can reach 4), while using cascaded MZMs, parallel MZMs, or novel three-arm MZM, FMF can be increased significantly(up to 18) without using optical filtering. As a result, high frequency microwave and millimeter-wave signal can be generated using low frequency oscillators, which greatly reduces the cost of the system. The advantage also includes its easy frequency tuning, which only needs to change the frequency of the input oscillator.2. A frequency-mutiplying optoelectronic oscillator(OEO) with a tunablemultiplication factor is proposed and experimentally studied. Low phase noise microwave and millimeter-wave signal can be generated without optical filtering using our method, and the FMF can be 4, 6 or 8 by changing the modulation index and the bias points of the modulators. As far as we know, it is the largest FMF achieved in an OEO compared with an FMF of 4 using optical filtering in the previous work. The advantage of microwave and millimeter-wave signal generation using OEO is that it does not need an input oscillator, and its phase noise performance is only determined by the Q factor of the OEO. Very low phase noise performance can be achieved by using a very long OEO loop.3. Two photonic approaches to generating phase-coded microwave waveforms are proposed. Using a single polarization modualtor(Pol M), an ultra-wide frequency tunable binary phase-coded microwave waveform generation method is proposed and experimentally studied. The method is very simple and the main device is only a Pol M. By chaging the bias point of the Pol M using a coding signal, a phase-coded microwave waveform at the fundamental or doubled frequency is generated. Compared with the previous work, it features a much simple architechture and very large frequency tunable range, as well as its capability of generating doubled frequency phase-coded microwave signal, which increases the working bandwidth of the approach further more. Another phase-coded microwave waveform generation approach is based on a dual-parallel Mach-Zehnder modulator(DP-MZM), where the DP-MZM functions as an optical wavelength convertor. The original optical wavelength is modulated by a coding signal and then combined with the shifted optical wavelength from the DP-MZM, so two optical wavelengths with a wavelength space determined by the input microwave signal are obtained. Applying the optical wavelengths to a photodetector(PD), a binary or quaternary phase-code microwave is generated. The approach has good reconfigurability and wide frequency tunable range, which is mainly limited by the bandwidth of the DP-MZM.4. Two MZM based radio-over-fiber(ROF) systems, which realize the transmission of microwave and millimeter-wave signal over optical fiber, are proposed and studied by simulation. The first one is based on a three-arm MZM. By introducing a DC bias on one arm of the three-arm MZM, the fiber dispersion is compensated and the influence of fiber dispersion is eliminated. The second one is a duplex ROF link using cascadedMZM. Its downlink realizes frequency 12-tupling and wavelength reuse is incorporated in the uplink, which greatly reduces the requirement of the frequency of the oscillator and no optical source is needed for the uplink. Thus, the cost of the system is reduced.5. A method for microwave vector signal transmission over an optical fiber based on IQ modulation and coherent detection is proposed and experimentally studied. For multi-input multi-output(MIMO) system and ROF wavelength-division-multiplexed passive-optical network(ROF-WDM-PON), it is sometimes required that different data signals carried by microwave carriers with an identical frequency are transmitted over a single optical fiber. Using the proposed method, two microwave and millimeter-wave vector signals with an identical carrier frequency can be transmitted using a single carrier, which greatly increases the spectral efficiency and decreases the cost of the system.