Recently, the Russell Center for Advanced Lightwave Science of Hangzhou Institute of Optics and Fine Mechanics, the United Nations University of Science and Technology Hangzhou Institute for Advanced Studies, the Shanghai Institute of Optics and Precision Mechanics of the Chinese Academy of Sciences, and Ifibo (Ningbo) Optoelectronics Technology Co., Ltd. published their latest Резултатите от изследванията в международното най-високо оптично списание „Optica“ и за първи път постигнаха високоефективността, висококачествеността и високото едномодово чистота гъвкаво предаване на близо до вата, стотици фемтосекунди, 2 . 8 µm Band Band Pulses във холоко-кокосни кристални фибри (Hollow-Core PCF). Този резултат не само осигурява ефективно решение на недостатъците на средните инфрачервени ултрабързи импулси при предаване, но също така поставя основата за разширяване на средните инфрачервени лазерни приложения
High-power mid-infrared ultrafast broadband light sources have important applications in advanced spectroscopy, material fine processing, medical surgery, and remote sensing. The limitations of laser transmission have hindered the further expansion of mid-infrared laser applications. In traditional transmission methods, the absorption of various gas molecules in the spatial optical path causes deformation of the output light spot and deterioration of pulse quality. Solid mid-infrared optical fiber has serious nonlinear accumulation, which causes serious distortion of the output time-frequency signal. To solve this problem, the research team used a self-made single-hole eight-ring structure Hollow-core PCF (length 5 m) to transmit mid-infrared ultrafast pulses. Thanks to the advantages of low transmission loss, low nonlinear effect accumulation and support for rapid vacuum extraction of Hollow-core PCF, the team not only solved the problems caused by traditional transmission methods, but also successfully achieved efficient transmission with an overall efficiency of >70%.
During the experiment, the experimenters used a self-built mid-infrared pulse fiber laser as the light source and a 5 m long Hollow-core PCF as the transmission medium. The two ends of the Hollow-core PCF were fixed in the air chamber so that the Hollow-core PCF could be evacuated using a vacuum pump. After the vacuum was drawn (the entire extraction process took less than 1 minute, and the gas pressure was drawn to ~10 mbar), the team successfully achieved an overall laser efficiency of > 70%, a Gaussian spot output that was close to the diffraction limit, and the entire system showed excellent stability. In addition, the spectral shape of the output in the frequency domain was basically consistent with the input. In the time domain, due to the small amount of waveguide dispersion of the hollow-core PCF (-2.04 fs2/mm @ 2.8 μm), the pulse width was widened from the input 117 fs to 404 fs. Subsequently, the experimenters added Ge and ZnSe positive dispersion materials to compensate for the negative dispersion introduced by the hollow-core PCF, coupling lens and air chamber window, and obtained an output with a pulse width of 98 fs (close to the transformation limit pulse width of 96 fs), with a peak power of 170 kW. In addition, the experimenters also used the autocorrelation trace to estimate that the output fundamental mode energy accounted for >95%.
The experimenters also compared the transmission scheme with the spatial optical path of the same length and the solid-core fluoride fiber. The results show that during the transmission of ultrafast pulses in solid-core fluoride fibers, the nonlinear effect is too strong, resulting in time-domain splitting of the pulses and an obvious spectral redshift, which verifies the unique advantages of hollow-core photonic crystal fibers in the transmission of high-peak power mid-infrared ultrafast pulses. The experiment achieved high-efficiency, high-fidelity and high-single-mode purity mid-infrared laser flexible transmission technology, laying a good foundation for the application of broadband mid-infrared ultrafast light sources in spectroscopy, infrared countermeasures and remote усещане .
The relevant research results were published in the top journal of lasers and optoelectronics, Optica, with the title "Flexible delivery of broadband, 100 fs mid-infrared pulses in the water-absorption band using hollow-core photonic crystal fiber". Lin Wei, a joint doctoral student of Shanghai Institute of Optics and Fine Mechanics and University of Science and Technology of China Hangzhou Institute of Разширените технологии и Ли Зекинг, докторска студент от Института по оптика и фина механика в Шанхай, са авторите на сътрудничеството, а Хуанг Джипг, Джианг Син и Панг Менг от Ръсел Център са съвместни автори .}}}}}}}}}}}}}}}})
Фигура 1. Експериментална настройка и резултати . (a) Експериментален оптичен път . обектив, покрит CAF2 плано-конвексичен обектив; HWP, Полувъвена чиния; QWP, плоча на четвърт вълна; FM, огледало за огъване; FTIR, инфрачервен спектрометър за трансформация на Фурие; AC, autocorrelator. (b) SEM image of the fiber structure. (c) Loss spectrum measured using the truncation method, the shaded area represents the measurement uncertainty (orange, left axis), and the calculated dispersion curve (blue, right axis). (d) Output power through a 5-meter-long Кухо-ядро PCF . (E) Използване на 30 mm ZnSe и 5 mm GE материали, е постигнат импулсен изход с близост, ограничена от трансформация импулсна ширина от 98 fs .
Figure 2. Comparison of different transmission modes. (a) Normalized absorption spectrum of water vapor. (b) Direct laser output (gray) and transmission spectrum in the spatial optical path (purple), transmission spectrum of hollow-core PCF in air (green), and transmission spectrum of hollow-core PCF in vacuum (red). The right side shows the enlarged spectrum in the range of 2.7-2.8 μm. (c) Raman soliton generation in a solid-core fluoride fiber. The FTIR spectrum is on the left and the autocorrelation trace is on the right.
