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Research On Microwave Photonic Phase Shifter Used In Optically Controlled Phased-Array

Posted on:2012-03-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:P F QuFull Text:PDF
GTID:1118330335453018Subject:Microelectronics and Solid State Electronics
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Microwave photonic phase shifter (MWPPS) is a photonic device which is used to tune the phase of a microwave signal in optical domain. It have drawn much attention in both military and satellite communications due to the advantage of compact size, light weight, high operating frequency and large simultaneous band. It plays an important role in optically controlled phased-array antenna (OCPAA) for optical beam forming network (OBFN). And it can overcome the electronic-bottleneck and tune the phase of high frequency signal in millimeter-wave band even in~THz domain by taking advantage of microwave and photonics.In this dissertation, OCPAA was firstly introduced and then the basic concept, functionality and design rule of the MWPPS were elaborated in detail. The main body of this dissertation can be divided into two parts. In the first part, two different kinds of millimeter-wave band MWPPS, i.e., sideband-modulation based MWPPS and orthogonal vector sum method (VSM) based MWPPS, were theoretically demonstrated. The second part is the experimental study of two VSM-MWPPSs, i.e., discrete MWPPS and integrated MWPPS.In chapter 2, a tunable wide band microwave photonic phase shifter based on sideband technology was designed in SOI waveguide for the first time. This MWPPS consists of a Fabry-Perot (F-P) filter, a phase modulation region (PMR), and distributed Bragg reflectors (DBRs). Firstly, the two sidebands-based microwave signals in optical domain were separated by the F-P filter Then the reflector was designed to~100% reflect the transmitted wave came from the F-P filter. Finally, the PMR was set in the middle to modulate the phase of the transmitted wave by thermo-optics effect. For this device, it was demonstrated that the linear microwave phase shift of 0~2πcould be achieved in an ultra-wide band (38 GHz~1.9 THz) by a refractive index (RI) variation of 0~10×10-3.The tuning resolution was about 6.92°/℃.The phase response is frequency-independent and its output power is constant.In chapter 3, for the first time to our knowledge, orthogonal VSM was proposed to transfer the traditional bulk VSM MWPPS to integrated one which is very important for large-scale OCPAA. This integrated VSM MWPPS consists of a 1×2 variable optical power splitter (VOPS), an optical switch (OS), two mode order convertor-multiplexers (MOCMs) and fixed time delay lines (FTDLs).The 1×2 VOPS and OS were successfully designed in SOI rectangular waveguides based on symmetrical directional coupler (SDC). And the 0th to 1st and 0th to 2nd MOCMs were designed based on asymmetrical directional coupler (ADC). Finally, the fixed time delay of 6.25 ps and 18.75 ps were achieved in a distance of 4617μm due to the large group velocity difference between different modes in SOI multimode waveguides. By operating the VOPS and OS, the microwave phase shift of 0~2πcould be achieved by a refractive index (RI) variation of 0~15×10-3 for 40 GHz signal. The corresponding tuning resolution was about 1.64°/℃.In chapter 4, the discrete MWPPSs for 10 GHz were experimentally studied. Firstly, the feasibility of broadband source based VSM-MWPPS was studied. Then, four-branch structure VSM-MWPPS was constructed and measured. By combining two adjacent branch while keeping the other branches in off-state, the phase shift of 0~π/2 can be achieved. The phase shift of 0~2πcan be realized by four combinations. The corresponding maximum power variation in each combination is about 3 dB. The maximum power variation in frequency-sweep is about 3.6 dB.The two-branch structure VSM-MWPPS was then constructed to simplify the four-branch structure. The fixed time delay between the two branches is 48ps. The measured phase shift of this device ranged from 0 to 175°. By combining the reversal characteristic of the Mach-Zehnder LiNbO3 intensity modulator, the phase shift of 180°to 355°was achieved. The total phase shift range is near 360°. The maximum power variation is less than 20 dBAt the end of this chapter, multicarrier-modulation based VSM-MWPPS was constructed which can be used in long haul OCPAA systems. Two carriers of the wavelengths of 1530 nm and 1560 nm were multiplexed and then modulated by a 10 GHz microwave signal. A 52 m-long SMF-28 fiber was used to introduce a time delay of 25 ps between the two carriers due to the dispersion in SMF-28 fiber. Finally, a measured phase shift of 0 to 90°was achieved by tuning the optical power of the carriers. The maximum power variation is about 7 dB.In chapter 5, for the first time to our knowledge, an integrated asymmetrical Mach-Zehnder structure VSM-MWPPS for 10 GHz based on broadband optical source was designed in small cross-section SOI rib waveguides and then studied experimentally.0 to near 360°phase shift can be achieved by using the reverseal characteristic of the intensity modulator. Four sub-components, i.e., Y-branch power splitter, waveguide true time delay lines, waveguide variable optical attenuators and Y-branch power combiner were integrated in SOI rib waveguides. In experiment, the masks of the device and the electrode were firstly fabricated. Then the Inductively coupled plasma (ICP) processing, which is a key technology for fabricating SOI rib waveguides, was studied in detail. The optimum conditions of ICP etching were obtained. And the device was also fabricated.Finally, some important parameters of the integrated VSM-MWPPS were measured: the propagation loss is about 7.6 dB/cm, the coupling loss is about 5.5 dB/cut, the pure bending loss is about 2 dB/90°, the effective refractive index is about 3.42558, the group index is about 3.5893, the group delay between the two delay lines is about 48 ps, the corresponding fixed phase difference between the two branches is about 172.8°for 10 GHz MW signal, and the maximum power variation at frequency-sweep state is about 2.2 dB.
Keywords/Search Tags:Phase shifter, Microwave photonics, OCPAA, SOI
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