Research On Optical Communication Beamsplitters Based On Subwavelength Gratings

With the continuous development of the scale of high speed optical communication and integrated optical path,higher and higher requirements of basic optical component performance are put forward.The subwavelength grating has the advantages of small size,easy integration,simple structure,easy etching preparation and so on.Through reasonable selection of grating structure parameters,various optical devices with different functions can be obtained.For example,the deflector that can control the propagation direction of incident light,the lens that can converge the incident light,the optical power beam splitter that can realize energy separation,the lens that can improve the laser coupling efficiency,and so on.The use of subwavelength gratings to design higher performance devices has broad prospects.This paper designs and optimizes two beam splitting devices by analysing the principles and characteristics of the subwavelength grating.The specific reasearch results are as follows:1.We propose a method of designing polarization-stabilized subwavelength grating.The polarization-stabilized subwavelength grating can be applied in the position of light source resonator to increase the output ratio of single-polarized light.The working principle of the device is equivalent to the polarization beam splitter.We combine the calculation results of the transmittance of different polarization states,and then edit the relevant programs to filter out the required structural data.Finally the simulation software is used to verify the effect that the device can achieve high transmission of TE light and high reflection of TM light.2.We propose the subwavelength grating polarization beam splitter with beam deflection function.The mixed polarized light with the wavelength of 1550 nm is obliquely incidented on the upper grating with Bragg angle to achieve the beam splitting.Then the nonperiodic subwavelength grating is setted on the propagation path of each single polarized light to control the direction of light propagation.Modeling in the simulation software COMSOL verify that the structure can achieve polarization beam splitting and vertical light output,and the polarization extinction ratio reach 14.0 d B.This structure is helpful for improving the coupling efficiency with other devices.3.We have proposed two types of one dimensional convergence subwavelength grating 1×4 power beam splitters,transmission type and reflection type.These two components can simplify the device structure and reduce energy loss are all designed by wavefront phase control principle and the splicing method.Through the simulation four convergent beams with equal optical power can be obtained.The transmittance of the transmissive structure is 92.67%,and the reflectivity of the reflective structure is 70.97%.Reflective convergence subwavelength grating 1×4 optical power beam splitter with the focal length of 100 ?m is designed according to the existing conditions.The actual structure is prepared according to the layout exposure and etching of the silicon wafer,and a test system is built with other members of the research group.The test results show four light field peaks,which indicates the device can achieve four-way beam splitting,and the total reflectance is 64.6%.