What they say is a paper recently published in Science [1]. In the research, the team used high-energy erbium ion implantation for doping in the ultra-low loss silicon nitride integrated optical waveguide with the maximum length of 0.5 meters. This rare earth ion implantation technology was verified in thin film materials in 199 1 year by Alberto Polman, a professor at Bell Laboratories at that time (now working at the Dutch National Institute of Atomic and Molecular Studies). While ensuring the uniformity of ion doping, the team achieved an atomic doping concentration as high as 0.3%, and the overlap factor of erbium ion distribution and optical mode field was as high as 50%, which was obvious compared with other rare earth ion doping methods.
After high temperature annealing, the waveguide after ion implantation still maintains the ultra-low background optical loss of less than 5 dB per meter, which is equivalent to the optical signal background loss of less than 50% in a 1 meter-long optical waveguide. The research group used the pump light with the wavelength of 1480 nm (about 245 MW) and achieved the maximum optical power conversion efficiency of nearly 60%.
The amplification performance of related devices is not only equivalent to that of the most advanced silicon-based heterojunction semiconductor optical amplifier, but also reaches the level of some commercial erbium-doped fiber amplifiers. In addition, they also demonstrated the selective ion implantation technology, which proved the feasibility of arbitrarily defining erbium-doped regions on the chip, and thus prepared passive functional devices that can realize both optical gain units and low loss on the same integrated photonic chip, providing a technical basis for realizing large-scale and complex monolithic integrated active photonic chips.
In application, one of its most direct application prospects is to realize a high-performance waveguide optical amplifier with extremely compact size. In some application scenarios sensitive to equipment size and weight, such as data centers, mobile devices, airborne and satellite-borne devices, it will replace the desktop optical amplifier.
In addition, the device can be integrated with other on-chip photonic functional devices on the same photonic chip to realize more complex and highly integrated functional devices and systems, such as low-noise lasers, wavelength tunable lasers and photonic radar engines. To meet the research and application requirements of important fields such as optical communication, integrated microwave photonics and quantum information storage.
Among them, Dr. Liu Yang, Ph.D. student Qiu Zheru and Ph.D. student Ji Xinru are the main authors of the paper. Two former colleagues, Dr. and Dr., also participated in this work. The former is currently working in Nanjing University of Aeronautics and Astronautics, and the latter is currently working in Shenzhen International Quantum Research Institute.
The topic of this paper is "An Erbium-doped Amplifier Based on Photonic Integrated Circuit", which has been reported by Science since its publication.
An urgent problem: to achieve high performance and low crosstalk optical signal amplification in integrated photonic chips.
According to reports, erbium-doped fiber amplifier, as a device that can directly amplify weak optical signals, is widely used in long-distance optical fiber communication networks and various fiber lasers. Erbium-doped fiber amplifier is realized by implanting Er ions into the core of the fiber, so that the optical signal in the communication band can be directly amplified under the excitation of the pump light source.
In recent twenty years, the integrated photonic chip technology has developed rapidly, and the size and power consumption of photonic signal processing devices have also been greatly reduced. However, it is always a difficult problem to realize high performance and low crosstalk optical signal amplification in integrated photonic chips.
The team directly injected high-concentration rare earth erbium ions into the integrated photonic chip, and realized the integrated optical waveguide amplifier, which achieved the same performance as the commercial optical fiber amplifier for the first time, and solved the key problems of integrated high-power optical amplifier, low-noise laser, high-pulse power mode-locked laser and other important photonic devices.
Its research background should start from the 1980s. At that time, internationally renowned photonics experts, Sir D.N. Payne of the Optoelectronic Center of the University of Southampton, England, and Bell Laboratories physicist Emmanuel de Suwell and other researchers invented erbium-doped fiber amplifier, and its birth was a revolutionary breakthrough in optical fiber communication technology.
The optical fiber invented by Gao Kun, a Chinese physicist and Nobel Prize winner in physics, laid the foundation for optical communication. However, it is only after the optical fiber amplifier replaces the traditional electric repeater with limited performance that the optical communication technology can develop rapidly, and people can communicate with the rest of the world through long-distance and transoceanic optical fiber communication networks all over the world.
Rare earth ions, such as erbium, ytterbium and thulium. They have a unique 4f shell electronic structure, which makes them have an excited state lifetime of several milliseconds in the host material, which is beneficial to realize the inversion of particle number and thus amplify the optical signal. At the same time, the millisecond long excited state lifetime can greatly reduce the crosstalk between optical signals in different bands, so that optical signals with multiple wavelengths can be amplified in one amplifier, which greatly increases the channel capacity.
At present, the noise figure of commercial fiber amplifier can be very close to the limit noise performance (3 dB) of non-phase sensitive optical amplifier determined by quantum mechanics. Because of these characteristics, the fiber amplifier based on rare earth ion doping has become an ideal gain medium in optical communication technology.
In addition, fiber amplifier plays a vital role in almost all fiber laser applications, such as fiber sensing, frequency measurement, laser radar, laser processing and other applications. In the most accurate atomic clock in the world, the optical frequency comb is the key component to convert optical frequency into radio frequency, and the optical fiber amplifier doped with rare earth ions is also used.
It is precisely because of the performance advantages and great success in application of fiber amplifier based on rare earth ions that the realization of waveguide amplifier based on rare earth ions on integrated photonic chips has naturally become an important research goal, which will be of great significance to the development of integrated photonics and can fill the gap of low-noise optical amplification technology on integrated photonic chips.
In the past 30 years, many teams in the world have tried to develop waveguide amplifiers doped with rare earth ions. For example, in the 1990s, Bell Laboratories carried out pioneering research on erbium-doped waveguide amplifiers. However, due to the limitations of large volume, high loss and incompatibility with modern integrated photonic chip micro-nano processing technology, the related research gradually stopped.
In recent ten years, with the rapid development of integrated photonics and the continuous improvement of device processing technology, researchers have renewed their interest in realizing erbium-doped waveguide amplifiers on mainstream integrated photonic materials platforms. Previously, some teams have prepared erbium-doped alumina and erbium-doped lithium niobate amplifiers.
However, the reported output power of integrated photonic waveguide amplifier is much lower than 1 MW (