INFORMATION TECHNOLOGY

Above 10W! Micro-nano fiber high-power continuous optical transmission


Recently, the team of Associate Professor Guo Xin and Professor Tong Limin of Zhejiang University and Associate Researcher Li Yuhang of Tsinghua University have cooperated to achieve high-power (above 10W) continuous optical single-mode transmission of silicon oxide micro-nano fiber, which is 30 times higher than the previous highest experimental value, and predict that the optical damage threshold of micro-nano fiber is higher than 70W. Based on the high-power continuous optical transmission of micro-nano fibers, the research team realized the high-speed driving of microdroplet light in air and efficient nonlinear optical frequency conversion. This research is expected to expand micro-nano fiber technology to the demand area of high-power applications.

The study was published in Light: Science & Applications under the title “High-power continuous-wave optical waveguiding in a silica micro/nanofibre.”

Jianbin Zhang, a doctoral student at the School of Optoelectronic Science and Engineering, Zhejiang University, and Kang Yi, a master’s student, are the co-first authors of the paper, and Associate Professor Guo Xin and Professor Limin Tong from the School of Optoelectronic Science and Engineering of Zhejiang University and Yuhang Li, associate researcher at the Department of Precision Instruments of Tsinghua University, are co-corresponding authors of the paper.

Micro-nano fiber is a one-dimensional optical waveguide with a diameter close to or less than the vacuum wavelength of the transmitted light, which is generally prepared by the standard glass fiber by physical stretching method at high temperature, and has the characteristics of low transmission loss, strong light field constraint ability, high proportion of evictile field, enhanced surface field, large range of waveguide dispersion and excellent mechanical properties. In recent years, as a miniaturized fiber optics platform, micro-nano fiber has received extensive attention and in-depth research in the fields of optical near-field coupling, optical sensing, nonlinear optics, atomic optics, fiber lasers and photomechanics, showing unique advantages and application prospects. In the applications of micro-nano fiber-based fiber lasers, nonlinear optics and photodynamic interaction, improving the optical power of the conduction mode in micro-nano fibers is one of the effective ways to improve the output power, nonlinear frequency conversion efficiency and photodynamic response of lasers.

However, limited by factors such as light source power, coupling efficiency and optical loss, the highest single-mode transmission power (continuous optical power or average power of pulsed light) of micro-nano fiber has been reported to be 0.4W [AIP Adv. 4, 067124 (2014)]。 In order to meet the application requirements of high-power transmission of micro-nano fibers, it is important to greatly improve the continuous optical transmission power of micro-nano fibers and study the optical damage threshold of micro-nano fibers.

In this paper, the research team studied the wave-guided loss mechanism of silicon oxide micro-nano fiber, carried out high-precision design, preparation and surface ultra-clean protection of micro-nano fiber and its thermal insulation transition zone, greatly reduced the loss factors such as coupling input loss and surface scattering, and successfully realized the high-power continuous optical transmission of silicon oxide micro-nano fiber at a wavelength of 1.55μm. As shown in Figure 1, the experimental system adopts the all-fiber connection method to realize the optical input and output at both ends of the micro-nano fiber.

Figure 1: Experimental setup for high-power continuous optical transmission of micro-nano fiber.

The results show that in an ultra-clean environment, a micro-nano fiber with a diameter of 1.1 μm can stably transmit continuous light with a power of up to 13W for a long time, and there are no abnormal scattering points and damage on the surface, and the optical transmittance remains above 95% (Figure 2). Compared with the previously reported single-mode transmission maximum power value of 0.4W of micro-nano fiber, the transmission optical power of micro-nano fiber in this study is increased by 30 times.

Figure 2: Optical transmittance (a) and surface scattering photo (b) of micro-nano fibers transmitting high-power continuous light.

In order to further explore the limit of optical power transmission, the research team knotted the micro-nano fiber into a junction-type resonator, measured the temperature of the micro-nano fiber when transmitting high-power continuous light by using the resonant peak shift of the resonant cavity, and estimated that the optical damage threshold of the micro-nano fiber was higher than 70W (Figure 3). By studying the photoluminescence spectrum and transmission spectrum of micro-nano fibers, the research team speculates that the optical damage of micro-nano fibers is mainly due to surface defects (such as oxygen defect centers, oxygen suspension bonds, etc.) and water molecules absorbed during the fiber drawing process.

Figure 3: Schematic diagram of micro-nano fiber optical damage threshold measurement.

Based on the high-power transmission light field of micro-nano fibers, the research team achieved high-speed photodynamic driving of 10 μm droplets in air attached to micro-nano fibers (Figure 4a). When the input optical power is 2.2W, the droplet can move up to 2.1mm s-1, which is 10 times faster than the previously reported microfiber light-driven particles (Figure 4b). In addition, by precisely controlling the diameter of the waist region of the micro-nano fiber and tuning the input optical wavelength, efficient nonlinear optical frequency conversion under continuous optical excitation, including second harmonic generation and third harmonic generation, was successfully achieved (Figure 4c). When the input power of the micro-nano fiber is 11.3W, the second harmonic conversion efficiency is 8.2×10-8, and the third harmonic conversion efficiency is 4.9×10-6. Due to the high power transmission, high-precision quasi-phase matching and long nonlinear interaction length of micro-nano fibers in this study, the second harmonic conversion efficiency under continuous light excitation in this study is higher than the frequency conversion efficiency under pulsed light excitation previously reported.

Figure 4: Experimental results of microdroplet photodynamic drive (a,b) and nonlinear optical frequency conversion (c) based on continuous optical high-power transmission of microfiber fiber.

In this paper, continuous optical high-power single-mode transmission of up to 13W in silicon oxide micronano fiber is reported, and the transmission power limit above 70W is predicted. Based on the high-power continuous optical transmission of micro-nano optical fiber, the high-speed optical drive of microdroplets in the air and the efficient nonlinear optical frequency conversion are successfully realized. The above research results are expected to expand micro-nano fiber optics and technology to high-power applications, and develop new frontier technologies in nonlinear optics, photomechanics, fiber lasers, biomedical photonics and other aspects based on micro-nano fibers. (Source: LightScience Applications WeChat public account)

Related paper information:https://doi.org/10.1038/s41377-023-01109-2

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