Thin-film lithium niobate heterointegrated photodetector

Integrated optics is one of the frontiers of photonics research, focusing on on-chip integrated active devices, passive devices and on-chip integrated photonic systems, which are widely used in optical communications, microwave photonics and other fields. As an important integrated photonic platform, thin film lithium niobate has the advantages of strong mode field binding, small device size, high nonlinear efficiency, and wide transparent window. Based on the thin-film lithium niobate integrated photonic platform, many compact integrated photonic devices with excellent performance have emerged, such as high-performance electro-optical modulators, broadband optical frequency combs, and high-efficiency frequency shifters.

The next generation of mobile communication technology (6G) will make full use of low, medium and high full spectrum resources, with peak rates of Tbit/s. As an important physical layer foundation of the next generation of mobile communication technology, optical fiber communication system is the core link of massive data access, aggregation and transmission. The thin-film lithium niobate integrated platform has realized electro-optical modulators with large bandwidth (100 GHz) and low half-wave voltage (100 mV), which is one of the realization paths of ultra-large capacity optical fiber communication in the future.

However, lithium niobate materials are difficult to achieve laser generation and photodetection, so the on-chip integration of light source and photodetector is a major challenge for thin-film lithium niobate integration platforms. Among them, the on-chip integration of high-performance photodetectors is essential for the thin-film lithium niobate integration platform.

Recently, the team of Professor Yan Lianshan and Professor Xie Xiaojun from the School of Information Science and Technology of Southwest Jiaotong University successfully developed a high-speed and efficient thin-film lithium niobate heterogeneous integrated photodetector with a 3-dB bandwidth of 110 GHz and a responsivity of 0.4 A/W using a heterogeneous integration process and wafer-level compound tape-out process.

Figure 1: Schematic diagram of a thin-film lithium niobate heterointegrated photodetector

The research results were published online in Light: Advanced Manufacturing under the title “Ultra-wideband Waveguide-coupled Photodiodes Heterogeneously Integrated on a Thin-film Lithium Niobate Platform.” Southwest Jiaotong University is the first completion unit, and Professor Xie Xiaojun and Professor Yan Lianshan, are the corresponding authors of the paper. Zeng Zhongming, a researcher at the Suzhou Institute of Nanotechnology and Nanobionics, Chinese Academy of Sciences, provided valuable support for this work, and the nanoprocessing platform of the Suzhou Institute of Nanonics, Chinese Academy of Sciences provided important process platform support. This work is funded and supported by the National Key Research and Development Program.

This work first etched to form thin-film lithium niobate optical waveguides and passive devices, and then bonded indium phosphide wafers with thin-film lithium niobate wafers. After the bonding wafer is thinned, the device table structure is formed by dry etching and wet etching, and the device electrode structure is formed by SU-8 photoglue exposure, development, metal plating and stripping, and finally sliced and polished to prepare a thin film lithium niobate heterogeneous integrated photodetector.

Figure 2: Preparation process of thin-film lithium niobate heterointegrated photodetector

Source: Light: Advanced Manufacturing 4, 30 (2023)

By optimizing the device epitaxial layer structure, passive waveguide structure, and metal electrode structure, the 110 GHz 3-dB bandwidth and 0.4 A/W responsivity are realized.

To further verify the performance of the device, the device was applied to a digital signal receiving system to achieve error-free reception of 32 Gbaud four-level pulse amplitude modulation signals.

Figure 3: Performance indicators of thin-film lithium niobate heterointegrated photodetector

Source: Light: Advanced Manufacturing 4, 30 (2023)

This work breaks through the bottleneck of high-speed and efficient signal detection of thin-film lithium niobate platform, lays the foundation for the development of large-scale, multi-functional, high-performance thin-film lithium niobate photonic integrated chips, and is of great significance in ultra-high-speed optical communications, high-performance integrated microwave photonics and other applications. (Source: Advanced Manufacturing WeChat public account)

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