Research Of Delay Lines Based On Silicon Waveguide Bragg Grating

Microwave photonics is a discipline that uses optical devices and technologies to generate,transmit,process and detect radio frequency signals.The radio frequency signal processing method based on microwave photonics can process ultra-wideband signals,and flexibly tailor the radio frequency response according to requirements.The processed signals can also transmit in low loss optical fibers.Microwave photonics has the advantages of both microwave technology and optical technology,which is one of the important solutions to cope with the bandwidth bottleneck in communication systems.As one of the important components of microwave photonics,optical delay lines play an important role in the fields of phased array antenna,microwave photonic filter and so on.However,the current integrated optical delay lines have drawbacks such as small bandwidth,discrete delay adjustment and small feature size.To deal with these problems,this thesis focuses on the theory and application of chirped Bragg grating delay lines.The main contents are as follows:(1)The mainstream integrated optical delay line schemes are introduced in detail,the advantages and disadvantages of these schemes are analyzed.The calculation methods of optical waveguide are briefly introduced.The working principle of Bragg gratings are analyzed using coupled mode theory,and some important parameters such as coupling coefficient are derived.(2)The contradirectional coupling chirped Bragg grating is analyzed in detail.Based on the analysises,a four-channel optical delay network was proposed and demostrated,the measured dispersion coefficients were 10.35,4.00,-4.32 and-14.38 ps/nm with 7 nm available bandwidth.The corresponding scanning angle was calculated,from-33.9 degree to 36.4 degree by changing the operation wavelength.(3)Chirped Bragg gratings based on multimode waveguide were proposed,which uses gradual duty cycle to achieve chirp and mismatch apodization to suppress delay ripples.Two chirped Bragg gratings with a length of 1.192 mm with positive and negative dispersion coefficient are fabricated and measured,the effectiveness of mismatch apodization was verified.For the chirped grating with positive dispersion coefficient,a delay of 22.9 ps is achieved,the amplitude of delay ripples is about 2.5 ps,the unit delay loss is 0.17 d B/ps and the delay related loss is 0.052 d B/ps.For the chirped grating with negative dispersion coefficient,a delay of 17.7 ps is realized,the unit delay loss is 0.1 d B/ps and the delay related loss is 0.019 dB/ps.