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Research On Key Techniques Of Tunable Optoelectronic Oscillator

Posted on:2015-04-15Degree:MasterType:Thesis
Country:ChinaCandidate:C L JiangFull Text:PDF
GTID:2308330473451540Subject:Optical engineering
Abstract/Summary:PDF Full Text Request
Microwave signal source with high-quality is the foundation of all microwave application fields. The phase noise and stability of microwave signal directly affects the performance of the microwave system. Compared with traditional microwave oscillators, the phase noise of optoelectronic oscillator(OEO) does not worsen when the frequency is increasing. This meets the growing demand for phase noise character in various microwave systems. As a new method to generate microwave signal based on photonics techniques, OEO can generate spectrally pure microwave signal with high-quality and ultralow phase noise in both optical and electrical domain simultaneously, and its oscillation frequency ranges from a few MHz to a hundred GHz. Usually, the microwave signal is not only required to be high-quality but also to be frequency tunable in the application areas like wireless communications, radar, signal processing and measurement techniques. Therefore, it is very essential to research the frequency tunability of OEO.First, the significance and development of tunable OEO is described. Then the oscillation threshold, oscillation frequency, oscillation amplitude and the spectrum is analyzed in detail. Based on two microwave photonic phase shifter, three different tunable OEO is designed: 1 by inserting a vector sum phase shifter into the basic OEO structure, the frequency can be tuned in a small range; 2 by using a chirped grating and dual-loop structure, the electrical band-pass filter is replaced, and the frequency is tuned from 8 GHz to 12 GHz with a vector sum phase shifter in simulation; 3 consisted by a dual-drive Mach-Zehnder modulator, a tunable microwave amplifier and a 90° hybrid coupler, a microwave photonic phase shifter independent of frequency is realized. While changing the phase of the loop, the frequency is tuned in a range of 1.48 MHz.In the experimental study, the use of a voltage tuning band-pass filter can obtain a tunable OEO. Because the center frequency of the filter is nearly linear with the voltage, the oscillation frequency varies from 97.4 MHz to 114.9 MHz when the voltage is set from 1 V to 2.4 V. Another tunable OEO is achieved with a microwave photonic filter(MPF). This MPF is made of a phase modulator and an optical tunable band-pass filter. A single oscillation of 9.38 GHz is obtained by adjusting the loop-gain carefully and the side mode suppression ratio(SMSR) is close to 50 dB. When the bandwidth of the optical filter is tuned, the center frequency of the MPF is changed and so the oscillation frequency becomes to 9.04 GHz. Finally, the OEO with a small tuning range based on vector sum phase shifter is proved by experiment. The amplitude ratio of two optical signals can be tuned by a variable optical attenuator, in open-loop measurement, two output port of the coupler achieve phase shift of 37.5 ° and 29.4 ° respectively. In close-loop measurement, one port realizes a continuous tuning range from 74.1 MHz to 80.4 MHz; another port realizes a continuous tuning range from 78.7 MHz to 74.5 MHz, but for further tuning the frequency hops to 85.6 MHz.
Keywords/Search Tags:microwave photonics, optoelectronic oscillator, frequency tunable, phase shifter
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