Research On Integrated Microwave Photonic Delay Lines And Beamforming Chips

By using optical beamforming network（OBFN）technology,transmitting and receiving microwave signals in a specific direction can be achieved and then the communication efficiency can be improved.Compared with traditional electrical beamforming,OBFN system has the advantages of low loss,large instantaneous bandwidth and anti-electromagnetic interference,which shows great potential in many fields such as radar system,radio astronomy and wireless communication.With the developments of integrated photonics,integrated OBFN system has been proposed and drawn more and more attentions.In this thesis,we focus on the integrated optical delay lines,integrated microwave photonic phase shifters and the integrated OBFN chips,which are the key devices in the OBFN systems.The main contents are summarized as below:1.Based on the double strip silicon nitride（Si₃N₄）platform,we designed a cascaded four microring resonators（MRRs）chip,and fabricated in Lionix company.By combining on-resonance and off-resonance delay tuning of the cascade MRRs,continuous optical delay tuning is achieved.The experimental results show that,when the delay bandwidth is set as 10 GHz,5 GHz and 2 GHz,the delay of the cascaded four MRRs can be continuously tuned in the range of 182.9 ps,263.7 ps,and 394.6 ps,respectively.In addition,the measured in-band delay fluctuation is less than 8.5 ps;On the other hand,using the same cascaded four MRRs chip,a high-performance integrated microwave photonic phase shifter is obtained by adjusting the coupling coefficients and resonance wavelengths of the four cascade MRRs.The experimental results show that,it can achieve full phase tuning range of about 400°and low microwave power variations about±1.5 d B with a broad working frequency range of 12 GHz～23 GHz.2.Based on the double strip Si₃N₄ platform,we designed a low loss optical delay line(DL_5bit+MRR)chip,and fabricated in Lionix company,which contains a 5-bit optical switched delay line（OSDL）and a single tunable MRR working at“off-resonance”.The DL_5bit+MRR chip was packaged and optical double sideband modulation link measurements show it can achieve continuous delay tuning in the range of 395.5 ps.In addition,relatively low in-band delay fluctuations of about 4 ps and 1 ps are obtained in 8 GHz and 5 GHz working bandwidths,respectively.Furthermore,the proposed DL_5bit+MRR has a low on-chip loss of 3 d B and the fiber to chip coupling loss is only about 1.06d B/facet.3.According to microwave photonic beamforming system working at 10 GHz,we designed a low loss 1×4 OBFN chip,and fabricated in Lionix company,which contains a 1×4 beam splitter and four 5-bit OSDLs based on the double strip Si₃N₄ platform.According to our experiments,each 5-bit OSDL can achieve 32 delay stages varying from 0 ps to about 130 ps.A low on-chip loss of about 4d B is achieved for each 5-bit OSDL,and a recorded low insertion loss fluctuation of about 0.3 d B is obtained when switching among the 32 delay stages.In addition,the switching power and switching time of the optical switch in the proposed OBFN chip are 270 m W and 109μs,respectively.4.According to microwave photonic beamforming system working at 20 GHz,we designed a compact 4×4 OBFN chip,and fabricated in CUMEC company,which contains four 1×4 beam splitter and sixteen 5-bit OSDLs based on the Silicon on Insulator（SOI）platform.The size of the 4×4 OBFN chip is less than 10 mm×10 mm.According to our experiments,each 5-bit OSDL can achieve 32delay stages varying from 0 ps to about 110 ps.An on-chip loss of about 6 d B is achieved for each 5-bit OSDL,and an insertion loss fluctuation of about 2.7 d B is obtained when switching among the 32delay stages.In addition,the switching power and switching time of the optical switch in the proposed OBFN chip are 35 m W and 17μs,respectively.5.For the silicon OBFN chips based on OSDLs,which contain lots of thermo-optic switches,a spiral optical phase shifter is proposed to replace the straight optical phase shifter and then reduce the switching power.And a quantized pulse voltage driving method is proposed to reduce the switching time of thermo-optic switch.The experimental results show that the designed spiral optical phase shifter can reduce the switching power by 59.4%,and the proposed quantized pulse voltage driving method can reduce the switching time by 85%.