Theoretical Study Of Deep Ultraviolet Tunable Narrow-band Filter Based On Planar Optical Waveguide

Ultraviolet absorption spectrum analysis is an important method for detecting substances.It has many applications in various marine detection technologies such as marine biochemical sensing and seawater quality analysis.It can be used to detect pollutants,nutrients,biological communities and so on in the water environment-It is of great significance for maintaining the stability of marine ecosystems and improving the ability to predict marine disasters.At present,the commonly used ultraviolet light source is a deuterium lamp light source.The deuterium lamp light source is a typical broadband light source with a main emission wavelength range of 190-400nm.Because pollutants of different water bodies have different absorbances for light of different wavelengths,measurement using a broadband light source will cause a large measurement error for a polluted water body.In order to improve the measurement accuracy,it is necessary to split the ultraviolet broadband light source into a narrow-band light source.The ultraviolet adjustable narrow-band light source can flexibly use the ultraviolet wavelength for measurement according to different types of pollutants in the water body,and can reduce the interference of the excited fluorescence on the measured value of the absorbance of the water body pollutants.Arrayed Waveguide Grating(AWG)based on planar optical waveguide structure has filtering characteristics,and it can turn broadband light into narrow-band light of different wavelengths.The Mach-Zehnder(MZI)optical switch can flexibly select the wavelength passed.The adjustable light source integrated by the AWG and MZI has the advantages of high sensitivity,compact structure,low power consumption and anti-electromagnetic interference.This paper first proposed and designed a new deep ultraviolet tunable narrow-band filter based on AWG and MZI thermo-optic switches in the deep ultraviolet band(210-240nm).It is mixed with deep ultraviolet broadband light source to realize chip-level wavelength tunable narrow-band deep ultraviolet spectrometer.The theoretical design of deep ultraviolet AWG and MZI thermo-optic switch devices was introduced in detail in this paper,mainly in the following aspects:(1)Introduction of the basic theory of the planar optical waveguide.It is explained in detail of the solution process of the characteristic equations of Transverse Electric Mode(TE)and Transverse Magnetic Mode(TM)in the slab waveguide.The method of calculating the effective refractive index of the rectangular waveguide is analyzed.It is obtained of the effective refractive index equation of the rectangular waveguide by the effective refractive index method.(2)The overall structure and performance optimization design of the AWG filter.It is introduced in detail of the working principle of AWG,the performance index of AWG,the choice of optical waveguide material,the choice of single-mode waveguide geometry,the design of optical waveguide structure,the design of AWG parameters,the simulation analysis of AWG,the optimization of AWG and the tolerance analysis.By optimizing the number of arrayed waveguides,taper and offset,the geometric parameters of the AWG device are determined.The performance parameters of the AWG device are:insertion loss is-1.47dB,crosstalk is-29.82dB,3dB bandwidth is 1.87nm and the output channel spacing is 5nm.(3)The overall design of the MZI thermo-optical switching device.It is introduced of the working principle of MZI thermo-optical switch,design of MZI thermal-optical switch,tolerance analysis of MZI thermo-optical switch and thermal field distribution.Through simulation and optimization,the geometric parameters of the MZI thermo-optic switch are determined.The switch length is about 7mm,and the extinction ratio is>23dB.The results show that within the process tolerance range,the performance of the MZI thermo-optic switch does not change much.The air slot structure can effectively limit the thermal field around the waveguide,avoid excessive heat loss into the cladding,and reduce switching power consumption.