Nanjing University \”Nature\” published in the latest developments of optical micro-nano: high performance metallic sodium plasmon Component

I. Introduction results

Surface plasmon is excited by light with a new metal element formed by the interaction of free electrons, because of its binding capability and light field subwavelength scales break the diffraction limit transmission characteristics, and in the micro-nano photonic integrated photonic device, the field of super-resolution imaging with broad application prospects. General plasmonic components such as a laser, and the like cavity, wherein the sub-micron size can be small, deep submicron, while the plasmon waveguide may be even as small as nanometers. However, due to plasmon excitation oscillation electronic participation, and thus loss due to the Joule heat would be applied to components plasmon bottleneck. For micro-nano devices and photonic integrated chips, finding the target metal band low-loss optical materials become researchers in the field for many years efforts. Previously, it has been hoping to noble metals (silver, gold, etc.), lower compared to other metals, silver, gold loss, good stability. Especially in recent years, single-crystal thin film process such that the loss of silver breakthrough is further reduced, to develop optical frequency band stimulated plasma components hope. However, for most devices still higher, the silver intrinsic loss, plus the cost of the noble metal preparation and other factors, a noble metal components to application plasmon is still a great challenge. For the noble metal with respect to the transmission characteristics of the alkali metal, represented by sodium closer to an ideal model of the free electron gas, and the interband transition smaller losses, it is considered possible to have a lower optical loss. However, since the active chemical properties of sodium metal and harsh preparation conditions, based on experimental sodium metal components of the Exploration plasmon rarely reported. Recently, Nanjing University, Zhu Xi, Zhou Lin, Zhu Shining research team and Maren Min, Cai Shandeng Georgia Tech Research Group of Peking University cooperation, sodium metal films and has made the study of plasmon important breakthrough in photonic devices. They use the sodium metal having a low melting point (97.72 degrees C) characteristics, developed a unique spin coating process the liquid metal, sodium metal film made, for the first time discloses a film excellent in optical band metallic sodium or the like from the excimer characteristics. The results confirmed that the free electron relaxation time noble metal sodium is approximately twice the fundamental conductive metal silver, sodium and the like from the quality factor plasmon waveguide also provides significant benefits over traditional. On this basis, they have developed a sodium communication band optical pump lasers at room temperature lasing threshold of only 140 kilowatts per square centimeter, to create the nano plasmon laser lasing threshold temperature low grade and the like. The use of effective packaging process, and the like prepared from sodiumComponent plasmon is stable and good performance.

Second, the prepared graphics Introduction

Sodium metal film is sodium plasmon Component first problem to be solved, as shown, a spin coating process the liquid metal binding development team controlled cooling technology 1 , both high efficiency and low cost, the successful plasmon sodium metal film structural quality like. Theoretical calculations and experimental results show that the free electron relaxation time sodium films deposited about 0.42 picoseconds, the quality factor (Figure of Merit) -1 / 2 has obvious advantages in the near infrared. Preparation of alkali metal thin film break plasmon photonic device is a low loss, and the like developed technical basis.

南京大学《Nature》刊登微纳光学最新进展:金属钠基高性能等离激元器件
FIG 1 metal ion such as sodium plasmon prepared and measured dielectric constant film.

The research team transmission characteristics Na surface plasmon polaritons quantitatively studied. 2a, the both ends of the nano-pillar array as a spatial light coupling structure and the like is coupled into the waveguide surface plasmon and coupled out by measuring the propagation distance of the different signal intensity (signal intensity drops initial value 1 / e propagation distance) may implement quantitative calibration of the propagation length. The results show that sodium plasmon band in the near infrared (e.g., 1500 nm), surface – SiO2 interface propagation length up to 200 microns. In addition, the unique benefit of greater lateral dispersion characteristic electromagnetic localization effect, sodium plasmon waveguide having a pattern and a smaller size. In the near infrared, sodium waveguiding quality factor is more than twice metallic silver.

南京大学《Nature》刊登微纳光学最新进展:金属钠基高性能等离激元器件
FIG sodium 2 – plasmon waveguide structure and from the characterization of silica.

Based on this research team developed a further sodium plasmon functional device. Nm laser light source is a one chip integrated core photonic devices, smaller size, higher modulation speed, low power laser capable of operating at room temperature and its development has been the goal. For example, to achieve optical interconnect features lasers requires close scale electronic devices on the electronic chip, the power consumption should be less than the electrical interconnection. However, miniaturization of the conventional laser is restricted by the optical diffraction limit, only small feature sizes on the order of light wavelength. Introduction of a metal micro-nano structures, by surface plasmon auxiliary light source can not only break the optical diffraction limit, Reduced feature size, but also to enhance light interacts with matter, reduce the lasing threshold and the power of the laser device.

南京大学《Nature》刊登微纳光学最新进展:金属钠基高性能等离激元器件
FIG. 3 sodium plasmon nano laser structures, laser mode field analysis and laser spectroscopy

The research team designed and fabricated metal based – insulator – semiconductor composite micro-nano laser device structure (FIG. 3). Experimental results show that the combination of a low-loss plasmon sodium InGaAsP quantum well structure with high quality factor of the structures, can effectively reduce ohmic losses and radiation losses of the entire device, and the like at room temperature sodium prepared plasmon laser lasing threshold is about 140 kilowatts per square centimeter (FIG. 4), to create the same type of nano low laser threshold.

南京大学《Nature》刊登微纳光学最新进展:金属钠基高性能等离激元器件
FIG sodium 4-yl plasmon laser nanometer laser spectroscopy

It is worth mentioning, due to effective protection package, the laser device 6 under normal circumstances months later still maintained a good performance. Meanwhile, a research team sodium accelerated aging test in the device under high temperature and high humidity, the preparation of Na-proof plasmon components have very good tolerance.

Third, the opportunities and challenges

effectively reduce the alkali metal plasmonic material optical loss, a new search path for the small-scale research and polishing material coupling interaction space-time. Sodium represented in the NIR alkali metal exhibits excellent characteristics plasmon, to provide low loss to explore a new way of plasmon photonic material; low-loss, high-performance components sodium plasmon plasmon integrated application solid step in the direction of show and so on. At the same time the alkali metal and low loss characteristics intrinsic limit has yet to be excavated in depth, with the future development of technology to enhance the quality of the material, combined with an alkali metal unique electrochemical properties, will provide for the development of new plasmon function device new opportunities, which has a milestone. 2020 May 27, relevant research results \”stable high performance sodium-based near-infrared plasmon components\” (Stable, high-performance sodium-based plasmonic devices in the near infrared) in the title, published online in \”Nature\” magazine, (Nature581,401-405 (2020)); graduate Wang Yang, Yu Jian Yu, Mao Yifei and Chen Ji is tied for first author, Zhu Xi, Maren Min, Zhou Lin and Zhu Shining as co-corresponding author. The study funded by the National R & D program focused on \”nanotechnology\” key projects, the National Natural Science Foundation. Nanjing University, Peking University, Georgia Institute of Technology, Industry and Commerce of Zhejiang University and other researchers involved in cooperative units. Links: https://www.nature.com/articles/s41586-020-2306-9

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