Fundamental Studies On Ultra-broadband Multimode Near-infrared Emission Bi-doped Glasses And Optical Fibers

Bismuth（Bi）doped glass fiber materials exhibit tunable ultra-broadband near-infrared（NIR）luminescence（800-1800 nm）,and gradually become a new direction in the field of broadband gain materials for optical communications.However,the development of Bi-activated glass and fiber materials still have the following problems:Firstly,the source of NIR luminescence of Bi ions has not been clarified,the emission centers are sensitive to the environment and exhibit variability,and while lacking an effective regulation mechanism.Secondly,Bi-activated glasses and fibers have an unsatisfied emission efficiency,are more common in single-band emission,and have a narrow bandwidth in the long communication band,which is difficult to achieve to efficient and ultra-broadband NIR luminescence with stable coexistence of multiple centers.Thirdly,Bi fibers are mostly found in silica-based optical fibers drawn at high temperature,and there is a lack of Bi-doped glass components suitable for low-temperature preparation.Fourthly,Bi-doped glasses and fibers are commonly used in optical amplifiers and lasers,and its single application cannot make full use of its broadband luminescence characteristics.In order to solve these problems,a series of Bi-doped multi-component glasses are systematically designed,prepared and studied,and their optical applications are explored,and the research results obtained in this paper are as follows:1.Expanding the emission bandwidth of Bi-doped multi-component glass:through simple component controlling,that is,selecting the appropriate glass network modifier（alkaline earth metal oxide）species（Ba O）,optimizing the content of glass network modifier（Ba O）（10 mol%）,reducing the content of glass network intermediate（Al₂O₃）（<15 mol%）,and seeking the appropriate Bi₂O₃ doping concentration（<0.1 mol%）to adjust the degree of glass structural polymerization,local charge distribution,and the number and distribution of structural defects,thereby creating a glass network environment suitable for the stable coexistence of multi-Bi active centers,and ultra-broadband multi-mode NIR emission was realized in Bi-doped multi-component glass,with emission peaks at 1154（Bi⁺）,1265（Bi⁰）,924 and 1516 nm（Bi and germanium oxygen-deficient centres,BGODCs）,emission coverage of 850-1630 nm,and FWHM of 532 nm.In addition,such ultra-broadband Bi multi-mode NIR emission exhibits excellent thermal stability.In subsequent studies,this structural regulation strategy is expected to serve as a simple and universal method to prepare ultra-broadband Bi-activated gain materials.2.Enhancing emission intensity of Bi-doped multi-component glass:The metal reduction strategy was used to achieve efficient multi-mode NIR emission of low-concentration Bi-doped multi-component glass.In view of the effect of Al₂O₃ on the NIR luminescence mode of Bi ions,the effect of adding Al powder to Al₂O₃-free and Al₂O₃-containing multi-component glass on the NIR luminescence behavior of multimodal Bi was studied.For glass samples without Al₂O₃,the addition of Al powder can construct a local reduction environment,which can not only effectively reduce high-valence inactive Bi ions to low-valent Bi luminescence centers（Bi⁰）,but also induce the generation of more oxygen vacancies,thereby effectively increasing the number of Bi⁰ and BGODCs,thereby greatly enhancing the ultra-broadband multi-mode luminescence of low-concentration Bi-doped glass.In glass samples containing Al₂O₃,the sample typically exhibits a weaker single-band emission of 1148 nm（Bi⁺）when Al powder is not introduced.After introducing an appropriate amount of Al powder,not only can more low-cost Bi near-infrared emission centers be reduced,but also more oxygen vacancies can be generated,thereby inducing the generation of BGODCs,which significantly increases the number and type of Bi emission centers,thereby giving glass samples efficient ultra-broadband multi-mode luminescence.Finally,multimodal NIR emission enhanced by metal reduction also has excellent thermal stability.In addition,this metal reduction strategy can also be extended to other multi-component glass systems,and a variety of metal elements have the same effect.This also provides a simple and universal method to achieve efficient multi-mode NIR luminescence of Bi-doped multi-component glass,which lays the foundation for the subsequent preparation of multi-mode luminescence doped multi-component glass fiber and the development of broadband amplifiers and tunable lasers.3.Realizing low-temperature preparation and on-off gain of Bi doped multi-component glass fibers:Bi-doped multi-component glass fiber with ultra-broadband multi-mode NIR luminescence was successfully drawn by rod-in-tube method.The fiber diameter is 125μm,the core diameter is 10μm,and there is no crystallization phenomenon after the glass is drawn into the fiber.Meanwhile,the optical fiber has ultra-broadband multi-mode NIR emission that is similar to core glass.The transmission loss of the fiber at 1310 nm was measured by the cut-back method as 6.35 d B/m.The optical path of fiber gain test was built,and under the 808 nm laser pumping,the fiber had an ASE（Amplified Spontaneous Emission）spectrum of 1000-1600 nm and a peak value of 1300 nm.Subsequently,with a gain fiber of10 cm,an on-off gain of 7.4 d B of 1310 nm was achieved at a signal optical power input of-75 d Bm at a pump power of 230 m W.By switching the signal light source to a broadband light source with multiple wavelength outputs,the on-off gains of multiple signal wavelengths of 1288,1395,1510 and 1585 nm are achieved,reaching 4.5,5.3,8.4 and 3.6 d B,respectively.These results are of great significance for promoting the development of Bi-doped multi-component fiber amplifiers and tunable lasers.4.The research of Bi doped multi-component glass in NIR LED light source was carried out:Using the NIR luminescence characteristics of Bi-doped multi-component glass with broadband tunable and effective broadband absorption in the blue light region,the research of all-inorganic broadband tunable NIR LED devices used by Bi-doped glass as blue light pumping was systematically carried out,as well as its potential applications in various aspects.Firstly,the tunable emission of Bi-doped germanate glass in NIR I and NIR II region was successfully realized by introducing Al₂O₃,and the corresponding NIR I gc-LEDs and NIR II gc-LEDs（glass converted light emitting diode）light sources were prepared.At a drive current of 320 m A,the output power of the two NIR LED light sources is 48.4 m W and 179.5 m W,respectively.Subsequently,its potential applications in night vision,biological penetration,and food inspection were demonstrated,and it was found that NIR II gc-LEDs containing more organic functional group information and deeper tissue penetration depth are more conducive to infrared spectroscopy applications.Secondly,the ultra-broadband NIR gc-LEDs light source was successfully constructed by using Bi-doped glass with ultra-broadband multi-mode NIR emission,and the actual output power can reach 111.75 m W at a driving current of 320 m A,and the operating temperature is only 61.3°C.Moreover,we demonstrated the potential application of the device in night vision,biological tissue penetration and imaging,non-destructive testing,information anti-counterfeiting and food inspection.These results are expected to open a new chapter in glass as an ultra-broadband NIR LED light source for the next generation of NIR spectroscopy applications.