With its help, it is no longer difficult to integrate the processing of optoelectronic devices

This paper was selected for the cover of the journal Laser and Photonics Review Courtesy of Lanzhou University

Professor Tian Yonghui of the School of Physical Sciences and Technology of Lanzhou University and Professor Anan Yonghui of the Royal Melbourne Institute of Technology in Australia. Mitchell’s research group and Shanghai Jiao Tong University Professor Su Yikai’s research group cooperated to deposit a layer of silicon nitride on the surface of the thin film lithium niobate wafer, using the traditional etching technology to only etch the silicon nitride layer to form a sub-wavelength grating waveguide, which effectively coped with the challenge of the difficult processing of thin-film lithium niobate integrated optoelectronic devices, reduced the device size, improved the chip integration, and successfully realized a small-size, high-performance optical mode and polarization processor device based on the waveguide.

Recently, the relevant results were published in the International Optical Journal “Laser and Photonic Review” under the title of “Thin Film Lithium Niobate Integrated Sub-wavelength Grating for Pattern and Polarization Manipulation”, and was selected as the cover of the current issue. Han Xu, a doctoral student at the School of Physical Sciences and Technology of Lanzhou University, is the first author, Tian Yonghui is the corresponding author, and Dr. Ren Guanghui of the Royal Melbourne University of Technology is the co-corresponding author of the paper.

Silicon nitride is an ideal auxiliary material, with a refractive index similar to lithium niobate, through a reasonable design waveguide structure so that most of the light field in the silicon nitride-lithium niobate heterogeneous waveguide can still be limited to the lithium niobate layer, so as to exert its excellent optical properties to achieve electro-optical, acousto-optic and optical nonlinear devices. More importantly, silicon nitride is a CMOS process compatible material, and the mature micro-nano processing process can easily realize the processing and production of silicon nitride layers, which helps to achieve large-scale integration of lithium niobate integrated optoelectronic chips. This work is another important breakthrough made by the collaborative team in the field of integrated optoelectronic devices based on the silicon nitride-thin film lithium niobate platform, further illustrating and demonstrating the advantages of the platform.

The work is based on a sub-wavelength grating waveguide, an optical microstructure consisting of periodicly arranged waveguide units with a period much smaller than the input wavelength. Using spatial mode filters and polarizers as examples, the team demonstrated the regulation of spatial and polarization modes through optical microstructures on a thin-film lithium niobate platform. Through the analysis of the optical mode and polarization characteristics of different crystalline axes of lithium niobate in thin films, the cooperative team made TE1 mode-on filters and TE2 mode-on filters on the Z axis of lithium niobate crystallography, and made TM polarizers on the Y axis of lithium niobate crystallography. The experimental results show that the insertion loss of the device at 1550 nm is less than 3.1dB, and the ratio of mode and polarization extinction is higher than 30dB, and the device shows a large operating bandwidth. It is worth mentioning that all devices are only about 50 μm long, which is much smaller than the same type of device previously reported on the material platform. (Source: China Science Daily Wen Caifei Faisa)

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