|Place of Conferral||北京|
|Keyword||微波光子学 偏振复用 相位编码 微波光子滤器 偏振调制|
Microwave photonics is an interdisciplinary subject involving microwave engineering and photonics technology. Since it can process microwave signals directly in the optical domain, plenty of technologies, such as microwave photonic generation, microwave photonic signal processing and broadband RF receiving and recognizing, based on this subject can benefit from its wide operation bandwidth, low insertion loss and high isolation efficiency. Photonic polarization-division multiplexing is a physical layer method for multiplexing signals carried on the orthogonally polarizied light-waves with the same frequency, which can significantly increase the channel capacity and improve the spectrum efficiency. Therefore, there couldn’t be a better way to melt the PDM technology with microwave photonics to generate a brandnew technology featuring wider processing bandwidth and higher operation frequency. Based on the above, this thesis aims to investigate the novel methods to generate, process, receive and recognize microwave signals using microwave photonic technology based on the polarization-division multiplexing.
In the chapter II, we presents a novel approach to generate a binary phase-coded microwave signal with accurate π-phase shift and large continuous operating bandwidth. In the system, the phase-coding modulation with an accurate π-phase shift has been realized by the joint use of two cascaded polarization modulators (PolMs). The generation of phase-coded microwave signals at 10 GHz, 18 GHz, and 28 GHz has been experimentally demonstrated, which verifies the proposed technique positively. Since there is no use of any optical filters and fiber Bragg gratings (FBGs), this system is rather simple and free from the optical bandwidth limitation problem with operating in a continuous microwave bandwidth as large as limited only by the PolMs (from DC to 40 GHz). Further more，we also demonstrate a technique of generating a binary phase coded microwave pulse based on two cascaded polarization modulators (PolMs). The first PolM (PolM1) followed by an optical band-pass filter is used to generate two phase-locked and polarization orthogonal optical frequencies. The second PolM (PolM2) aims to change their polarization states. A polarizer attached to the output of PolM2 allows only one of the two optical frequencies passing, or combines them with positive/negative phase difference. By changing the voltage level of the electrical modulation signal applied to PolM2, series of binary phase coded microwave pulses are directly generated from a continuous wave microwave signal in the optical domain. In the proposed system, the precise amplitude control or amplification of the modulation signal are avoided. The waveform of the generated pulse is very stable. For a proof-of-concept experiment, a series of 25-GHz pulses with∼2.08-ns pulse duration and∼10.24-ns repetition time is generated. The pulses are phase coded by a 13-bit Barker code.
In chapter III, it focuces on the signal processing unit of the microwave photonic technology. Based on the PDM technology, a widely tunable microwave photonic filter based on polarization processing of non-sliced broadband optical source has been firstly demonstrated, which features single-bandpass response and wide span of operation bandwidth. The BOS is orthogonally polarized by a polarization division multiplexing emulator (PDME) with a tunable time delay between the two polarization states and incident at ±π/4 to one principle axis of a polarization modulator (PolM). The PDME cascaded a PolM and a polarizer realizes a microwave modulation making the phase of the carrier able to be tuned while ±1st sidebands unchanged, which after propagating in a dispersive medium results in a tunable single-bandpass response in the RF domain. We experimentally verified the MPF. By adjusting time delay amount and the optical spectrum bandwidth, the pass-band center frequency wascontinuously tuned from DC to 20GHz and the 3-dB pass-band bandwidth changed while the optical spectrum bandwidth ranges from 1nm to 4nm. Besides, with the combination of the slow light effect in SOA, we present another two-tap complex-coefficient tunable microwave photonic notch filter based on the polarization modulation assisted by a tunable band-pass filter (TBPF). In the proposed filter, the light wave is modulated by the microwave driven signal through the polarization intensity convertor (PIC) that generates two complementary microwave signals with identical amplitudes carried by two orthogonal polarized optical carriers with the same frequency, the complex coefficient is generated from the phase-shifted light wave passing through the SOA in the upper arm. The measured experimental results demonstrated that the notch position of the filter could be tuned in the whole range of the free spectral range (FSR) without changing the shape of the amplitude-frequency response.In chapter IV, we propose and numerically investigate a polarization division multiplexed photonic RF channelizer based on an optical comb. A flat (power rippleo1dB) optical comb with nine lines is generated using two cascaded Mach–Zehnder modulators. The optical comb is split into two paths with one path frequency-shifted by an AOM. Both of the optical combs carry the broadband RF signal via SC-DSB modulation. By combining the two paths using a PBC, a PDM optical comb is obtained, which is then sliced by a FPE, polarization de multiplexed and channelized by WDMs. Compared to the conventional optical comb based channelizers, the key significance of our system is that it releases the trade-off between the measurement range and the accuracy by a factor of 2.
|Subject Area||光电子学 ; 微电子学|
|王辉. 基于偏振复用技术的光子微波\毫米波信号的产生与处理[D]. 北京. 中国科学院研究生院,2014.|
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