The Properties And Applications Of Diffraction Gratings

Since twenty-first Century,the information process of human society has been accelerated,and the volume of data processing and transmission has increased dramatically.At present,the main carrier of data processing and transmission of information in human society is integrated circuits.However,with the increasing integration of electronic devices,it is becoming more and more difficult to integrate more transistors on unit area chips,and Moore's law is becoming more and more difficult to maintain.People turn their attention to integrated photonic chip.Although silicon has mature CMOS processing technology as a very successful integrated circuit material,so silicon has become an integrated photonics leading material platform.At present,silicon based optical devices are mainly developed for specific needs,and then the interconnection between components is realized through optical fibers or waveguides.So many silicon-based photonic devices have been designed.These devices provide a guarantee for efficient transmission and controlling of light.As an important diffractive optical element,grating has unique diffraction properties.It has important applications in coupling,mode conversion and filtering.Based on the grating structure,this paper has completed two aspects of the work.First,a vertical coupler based on double-layer grating is designed.Second,the grating is introduced on the solar cell to improve the ability of trapping photon.(1)The vertical coupler.The current integrated optical path is connected mainly through fiber to connect optical devices,achieving the purpose of optical interconnection.The efficient coupling between optical fiber and chip has a great application prospect.The mode mismatch caused by the scale gap between fiber and waveguide seriously reduces the coupling efficiency.The traditional rectangular grating is difficult to realize absolute coupling vertically.Therefore,this paper designs a coupler structure based on dual-layer grating and achieves high vertical coupling efficiency through consecutive grating diffraction.In principle,the coupler overcomes the weakness of the single layer grating,which has strong back reflection.By placing the two gratings up and down,the deviation of the light propagating direction comes up to 90 degrees.By designing reasonable structure parameters,the vertical coupler achieves the coupling efficiency of fifty-eight percent and 60nm bandwidth calculated by 2db attenuation in 1500-1600nm bandwidth.(2)The application of grating structure in improving solar cell's ability to trap light.Solar energy is a clean and renewable energy.The efficient development of solar energy has always been the focus of research.The solar cell is a device that uses the photovoltaic effect to convert light into electricity directly.The principle of generation is that:the ground state electrons of the special material jumps when absorbing the photon energy,and the transition electrons are injected into the guide band of the semiconductor.Therefore,we can improve the efficiency of carrier generation and the efficiency of battery conversion by "confining" the light in the molecular layer.We designed a grating structure based on diffraction grating,which successfully improves the conversion efficiency of the battery by introducing a grating into the cell film.When the grating period is 750nm,the duty cycle is 0.65 and injection light wavelength in range of 3 50nm and 850nm,the solar cell of this structure achieves 19.7%conversion efficiency.