Study On Er³⁺-Yb³⁺ Co-doped Fluorosilicate Glass Microsphere Laser

Whisper gallery mode(WGM)microsphere cavity is an important microcavity resonant optical device,which has a number of advantages,such as high-quality factor(10⁷-10⁹)and ease of fabrication etc.It has great potential applications on the fields of low threshold microlasers and high sensitivity optical sensors.In order to achieve a microcavity laser at visible wavelength range,fluorosilicate glass based optical microsphere resonator structure was designed and fabricated.The photophysical and lasing performance of the fluorosilicate glass microsphere laser was also investigated.First,Er³⁺-Yb³⁺ion co-doped Si O₂-KF-Zn F₂fluorosilicate glass samples were prepared by a traditional melt-quenching method.The Si O₂-KF-Zn F₂glass system has a good glass-forming ability and a high up-conversion luminescence efficiency.The desired concentration of Er³⁺-Yb³⁺ions were determined by measuring the up-conversion photoluminescence spectra of the glass samples.Next,Er³⁺-Yb³⁺co-doped fluorosilicate glass fiber samples was prepared by using a pulling method from a melting glass sample.Then a CO₂laser was used to fabricate the fluorosilicate glass microspheres by heating,tapering and melting Er³⁺-Yb³⁺co-doped fluorosilicate glass fibers,the diameters of the fabricated microsphere samples are around 50-150?m.In this work,tapered silica fiber was selected as the coupling waveguide to deliver the light from pump laser and fluorosilicate microsphere and also collect the output signal.Tapered silica fibers were prepared by employing a homemade elongation machine.The minimum diameter of the tapered fiber is about 2.24?m and the loss is about 0.3 d B.The transmission spectrum of fluorosilicate glass microspheres in the frequency domain was measured using a tunable 1550 nm narrow linewidth laser.The Q value of the fluorosilicate glass microspheres was calculated to be as high as 1.29×10⁶approximately.Under the excitation of a 980 nm laser diode,single-mode green laser emission was observed in the Er³⁺-Yb³⁺co-doped fluorosilicate glass microsphere with a diameter of 58?m.The central wavelength of the green laser is at 545.57 nm and the threshold pump power is circa52.5?W.In addition,tunable visible up-conversion luminescence from green to red color was also observed in the Er³⁺-Yb³⁺co-doped fluorosilicate glass microsphere with a diameter of110?m.In summary,fluorosilicate glass demonstrated in this work represent a new type of compound glass system which exhibits excellent optical properties in up-conversion photoluminescence.The optimization of the fluorosilicate glass material properties with regard to the envisioned application demands an understanding of the key concepts describing their local structures at different wavelengths.Because of the inevitable losses and nanocrystallization of fluorosilicate glass during the fabrication process of melting or annealing,the synthesis and elemental analytical characterization present important and critical challenges.