On Chip Spectral Analysis Research Based On Photonic Integrated Chip

With the wide applications of spectrum analysis,there is a great requirement for the miniaturization and chipization of spectrum analyzer.Spectrometers based on photonic integrated chips have great advantages in size,weight,and power consumption,which can be applied in many fields such as chemical and biological sensing,spectroscopy,spectral imaging and radio frequency spectrum analysis,etc.In this research field,arrayed waveguide grating(AWG)filter is one of the effective ways to realize on chip spectrum analysis since it is easy to integration and compact in size.In this thesis,different schemes based on AWG for realizing on chip spectrum analysis are introduced with their advantages and disadvantages.Based on the working principle and design processes of AWG,the working principle of the spectrum analysis chip based on two-stage cascaded AWGs is illustrated.Based on the low loss silicon nitride optical waveguide platform,a spectrum analysis chip constructed by a 1×6AWG cascaded with six 1×25AWGs with different center wavelengths was designed.The two-stage AWGs were simulated and optimized,following results are obtained.For the first stage 1×6AWG: the minimum channel insertion loss is1.3dB,the maximum channel insertion loss is 2.5dB,the non-adjacent channel crosstalk is about-24.9dB,and the adjacent channel crosstalk is-27.5dB.For the six 1×25AWGs of the second stage: the minimum channel insertion loss is 3.0dB,the maximum channel insertion loss is 4.4dB,the non-adjacent channel crosstalk is-25.5dB,and the adjacent channel crosstalk is-17.0dB.Then the characteristics of a spectrum analysis chip based on two-stage cascaded AWGs were simulated.The results show that a working wavelength range of 75 nm and a resolution of 0.5 nm can be achieved.For the middle channels,the minimum channel insertion loss is 4.5dB,and the minimum channel crosstalk is-29.0dB.For the edge channels,the maximum channel insertion loss is 9.6dB,and the maximum channel crosstalk is-11.2dB.Finally,according to the simulation results,we found that the first-order AWG has different FSRs at different diffraction orders,while the adjacent channels of the second-order AWG have the same wavelength spacing.Therefore,the insertion loss and crosstalk of the edge channels are relative large.By adjusting the position of the output waveguides of the second-stage AWG to make the wavelength interval of each adjacent channel of the second-stage AWG matching the FSR of the first-stage AWG,the performance optimization of the spectrum analysis chip is realized.After optimization,the minimum channel insertion loss is 4.5dB,the minimum channel crosstalk is-27.4dB;the maximum channel insertion loss is 7.5dB(reduced by 2.1dB),and the maximum channel crosstalk is-18.2dB(reduced by 7.0dB).