Effect of Ce2O3 on the 1.53 μm spectroscopic properties in Er3+-doped tellurite glasses

Er3+/Ce3+co-doped tellurite-based glasses with composition of TeO 2-Zn O-Na2O are prepared by high-temperature melt-quenching technique.Effects of Ce2O3 content on the 1.53μm band fluorescence spectra and fluorescence lifetime of Er3+are measured and investigated.It is found that the tellurite glass containing Ce2O3 with molar concentration of 0.25%exhibits an increment of 13%in 1.53μm fluorescence intensity and an increment of 15%in the 4I13/2 level lifetime.The results indicate that the prepared tellurite-based glass with a suitable Er3+/Ce3+codoping concentration is an excellent gain medium applied for broadband Er3+-doped fiber amplifier(EDFA)pumped with a980 nm laser diode.     

Influence of Yb2O3 on the 1.53 μm spectroscopic properties in Er3+/Ce3+ co-doped TeO2-WO3-Na2O-Nb2O5 glasses

The Yb2O3 component was introduced into the Er3+/Ce3+ co-doped tellurite glasses with the composition of TeO2-WO3-Na2O-Nb2O5 to study the effect of Yb3+ on the 1.53 μm spectroscopic properties of Er3+. The X-ray diffraction (XRD) curve and Raman spectrum were measured to investigate the structure nature of synthesized tellurite glasses. The absorption spectrum, upconversion emission spectrum and fluorescence spectrum were measured to evaluate the improved effect of Yb3+ concentration on the 1.53 µm band fluorescence of Er3+. Results of the measured 1.53 µm band fluorescence intensity show a significant improvement with the increase of Yb3+ concentration, while the total quantum efficiency reveals a similar increasing trend. The results of the present work indicate that Er3+/Ce3+/Yb3+ tri-doped tellurite glass has good prospect as a promising gain medium applied for the 1.53 µm broadband amplifier.     

Structure and spectroscopic properties of Er3+/Ce3+ co-doped TeO2-Bi2O3-TiO2 glasses modified with various WO3 contents for 1.53 μm emission

The Er^3＋/Ce^3＋ co-doped tellurite-based glasses （TeO2-Bi2O3-TiO2） modified with various WO3 contents are prepared using conventional melt-quenching technique. The X-ray diffraction （XRD） patterns and Raman spectra of glass sam- ples are measured to investigate the structures. The absorption spectra, the up-conversion emission spectra, the 1.53 /am band fluorescence spectra and the lifetime of Er3＋：4113/2 level are measured, and the amplification quality factors of Er3＋ are calculated to evaluate the effect of WO3 contents on the 1.53 μm band spectroscopic properties. With the in- troduction of WO3, it is found that the prepared tellurite-based glasses maintain the amorphous structure, while the 1.53 μm band fluorescence intensity of Er3＋ is improved evidently, and the fluorescence full width at half maximum （FWHM） is broadened accordingly. In addition, the prepared tellurite-based glass samples have larger bandwidth qual- ity factor than silicate and germanate glasses. The results indicate that the prepared Er3＋/Ce3＋ co-doped tellurite-based glass with a certain amount of WO3 is an excellent gain medium applied for the 1.53 μm band Er3＋-doped fiber ampli- fier （EDFA）.     

Performance of Er3+-doped chalcogenide glass MOF amplifier applied for 1.53 μm band

A model of Er3＋-doped chalcogenide glass （GasGe20Sb10S65） microstructured optical fiber （MOF） amplifier under the excitation of 980 nm is presented to demonstrate the feasibility of it applied for 1.53 μm band optical communications. By solving the Er3＋ population rate equations and light power propagation equations, the amplifying performance of 1.53 μm band signals for Er3＋-doped chalcogenide glass MOF amplifier is investigated theoretically. The results show that the Er6＋-doped chalcogenide glass MOF exhibits a high signal gain and broad gain spectrum, and its maximum gain for small-signal input （-40 dBm） exceeds 22 dB on the 300 cm MOF under the excitation of 200 mW pump power Moreover, the relations of 1.53 μm signal gain with fiber length, input signal power and pump power are analyzed. The results indicate that the Er3＋-doped Ga5Ge20Sb10S65 MOF is a promising gain medium which can be applied to broadband amplifiers operating in the third communication window.     

Enhancement of fluorescence emission and signal gain at 1.53 µm in Er3+/Ce3+ co-doped tellurite glass fiber

Er3+/Ce3+ co-doped tellurite glasses with composition of TeO2-GeO2-Li2O-Nb2O5 were prepared using conventional melt-quenching technique for potential applications in Er3+-doped fiber amplifier (EDFA). The absorption spectra, up-conversion spectra and 1.53 µm band fluorescence spectra of glass samples were measured. It is shown that the 1.53 µm band fluorescence emission intensity of Er3+-doped tellurite glass fiber is improved obviously with the introduction of an appropriate amount of Ce3+, which is attributed to the energy transfer (ET) from Er3+ to Ce3+. Meanwhile, the 1.53 µm band optical signal amplification is simulated based on the rate and power propagation equations, and an increment in signal gain of about 2.4 dB at 1 532 nm in the Er3+/Ce3+ co-doped tellurite glass fiber is found. The maximum signal gain reaches 29.3 dB on a 50 cm-long fiber pumped at 980 nm with power of 100 mW. The results indicate that the prepared Er3+/Ce3+ co-doped tellurite glass is a good gain medium applied for 1.53 µm broadband and high-gain EDFA.     

Profile-broaden ultraviolet lasing from whispering gallery mode cavity in crown-like zinc oxide

Based on the transfer matrix method,a detailed theoretical and numerical study on double-phase-shifted fiber Bragg grating(FBG)is investigated.Temporal responses of the double-phase-shifted FBG to optical pulse are analyzed and the influence of the two phase-shifts’position on the reflected output pulse is evaluated.Results demonstrate that very different temporal pulse waveforms can be achieved by adjusting the length ratio(α=L2/L1).Specifically,a transform-limited Gaussian input optical pulse can be shaped into flat-top square pulse(α=1.81)or two identical optical pulse sequences(α=1.93).     

Enhancement of nonlinear optical phenomena from crown-like nanostructure zinc oxide based on whispering gallery mode

Whispering gallery mode （WGM）-enhanced nonlinear optical phenomena from crown-like nanostructure zinc oxide （ZnO） samples are observed. The samples are synthesized by vapor-phase transport method. The morphology and crystal struc- ture are examined and characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD） and high-resolution transmission electron microscopy （HRTEM）, and they are excited by femtosecond laser pulses with cen- tral wavelengths of 355 nm, 800 nm and 1150 nm, respectively. The typical stimulated emission presents a red shift com- pared with spontaneous emission, which is observed under the excitation of 355 nm with a relatively low threshold. The ultraviolet （UV） frequency up-conversion emission is obtained when the excitation pulse wavelengths are selected as 800 nm and 1150 nm, respectively. The peak position and the relationship between the emission intensity and excitation inten- sity demonstrate that the UV up-conversion photoluminescence （PL） is induced by two- and three-photon absorptions. The PL characteristics and their WGM-enhanced mechanism are investigated.     

波导耦合回音壁模式光学微球腔结构耦合特性分析

提出了一种耦合微球和波导系统的有效方法,并在数值和实验上进行了论证.为了研究微球腔和波导系统的耦合特性,首先通过耦合模理论研究了这个系统的2D模型.通过有限时域差分法设计了一个数值仿真系统.在快速傅里叶变换(FFT)处理样本数据后,得到了波长范围从600 nm到1 000 nm的相对强度谱曲线和传输谱曲线.在实验中,采用熔融单模光纤顶端的方法制得了石英材料微球腔.采用热拉技术制得了锥形光纤,用来作为激发微球腔中回音壁模式的波导.测试了这个微球腔-锥形光纤耦合系统,通过优化微球腔与锥形光纤的相对位置得到其品质因数高达2.3×106,耦合效率高达92.5%.这些耦合特性可以很好地用理论结果解释.这些特性表明了其在实际微腔传感和微型激光器中极具潜力.     

Thermally induced whispering gallery mode laser in MEH-PPV solutions

We report on thermally activated whispering gallery laser modes of a solution of MEH-PPV conjugated polymer supported by a silica optical fiber. The viscosity of the polymer solution gives place to a thin shell of the gain solution around the fiber driven by capillary action. Whispering gallery modes (WGMs) are thermally induced by a decrease in the refractive index of the polymer solution under intense optical pumping. The laser emission is produced because the evanescent waves of the WGMs couple the surrounding gain medium. These results support the use of conjugated polymers in optofluidic laser systems and highlight the importance of physicochemical properties, such as viscosity and optically induced heating, on the performance of the devices.     

Calculation of radiation from a quasi-optical reflector antenna for whispering gallery mode

We propose a method to calculate the radiation characteristics of a quasi-optical reflector antenna for whispering gallery mode called Vlasov's antenna. Correction of the shape of the reflector, which was a parabolic cylinder in the original paper by Vlasov et al. (1975), is performed using wave-normal rays. The radiation field is calculated by means of an image source which is obtained with the geometrical optics. Some numerical results show that the radiated beam is gaussian-like in far zone. A scheme of high-power application (500kW, 106·4GHz, TE_12,2) to a beam transmission system is also presented     

A whispering gallery mode strain sensor based on microtube resonator

A novel whispering gallery mode (WGM) strain sensor based on microtube has been proposed, where perceiving strain variations are reported via the dynamical regulation of a whispering gallery mode. The WGMs in the microtube resonator were evanescently excited by a micro-nano fiber fabricated by the fusion taper technique. The structural changes of microtubes under axial strain were simulated with finite element software, and the effect of microtube wall thickness on strain sensitivity was systematically studied through experiments. The experimental results show that the strain sensitivity of thin-walled microtube is found to be 1.18 pm/με and the Q-factor in the order of 4.4×104. Due to its simple fabrication and easy manipulation as well as good sensing performance, the microtube strain sensor has potential applications in high-sensitivity optical sensing.     

An improved design for quasi-optical mode conversion of whispering gallery mode gyrotron radiation

Results are reported of a theoretical and experimental investigation of a quasi-optical mode converter for the transformation of whispering gallery mode gyrotron output into a linearly polarized Gaussian like beam. The mode converter consists of a helically cut waveguide launcher, similar to that originally proposed by Vlasovet al, followed by a focusing mirror. Theoretical results using aperture field methods indicate that the length of the waveguide launcher is of critical importance in providing a confined radiation pattern. Experimental results on the radiation pattern were obtained for several launcher lengths using a 0.6 MW, 149 GHz pulsed gyrotron operating in the TE_16,2 mode. Radiation pattern results for the optimum launcher length agree well with theoretical calculations using the Stratton-Chu aperture radiation theory for unperturbed waveguide modes. A mirror focusing in the azimuthal direction was designed by a geometrical optics approach to focus the radiation coming from the launcher. Good focusing with 91.4% efficiency (power in the focused beam divided by gyrotron power) was found experimentally using the combined launcher and mirror with the pulsed gyrotron. These results indicate that quasi-optical antennas are useful for transforming high order, high frequency gyrotron modes into directed beams in free space.     

Experimental study of a high efficiency quasi-optical mode converter for whispering gallery mode gyrotrons

A mode converter for whispering gallery mode gyrotrons has been designed and experimentally demonstrated. Experiments were performed on a megawatt power level, 3μs pulsed gyrotron operating in the TE_16,2,1 whispering gallery mode at 146 GHz. The gyrotron cavity employs a non-linear uptaper to minimize radial mode conversion. About 99% of the output power is in the TE_16,2 mode. The quasi-optical converter consists of a helically cut Vlasov-type waveguide launcher and a reflector. The doubly curved reflector, designed using geometric optics and vector diffraction theory, was built to focus the full radiation pattern to a small, gaussian-like focal spot. Of the power incident in the TE_16,2 mode, 96% is directed by the launcher and reflector to a gaussian-like focal spot in the far field. Small fractions of other modes were found to form distinct focal spots in the far field. Analysis of the power in the other focal spots allows for a good quantitative measurement of gyrotron output mode content, potentially on a single shot basis.     

Laser-tuned whispering gallery modes in silica microbubble resonator integrated with iron oxide particles

A 473-nm-laser-tuned whispering gallery mode(WGM) silica microbubble resonator integrated with iron oxide particles is demonstrated in this paper. Owing to the photo-induced thermal effect, the WGM resonance wavelength could be tuned by adjusting laser power density of the illuminating light absorbed by the iron oxide particles. A wavelength tuning sensitivity of 0.03 nm/(mW·mm^-2) and a tuning range of 0.18 nm are experimentally achieved. Moreover, the influence of ambient temperature on the WGM spectral characteristics is experimentally studied, and a silica-microbubble-based reference scheme is demonstrated to compensate for the temperature-caused resonance wavelength variation. The proposed laser-tuned microresonator has great potential in optical modulation and high-precision optical filtering applications.     

Modelization of the whispering gallery mode in microgear resonators using the Floquet-Bloch formalism

In this paper, a two-dimensional (2-D) method describing the whispering gallery mode in a microgear resonator is presented. The microgear is a microdisk surrounded by a circular grating. The method, which is based on the Floquet-Bloch formalism, analytically describes the field within the disk and outside the grating. On the other hand, the field within the grating is calculated using a finite-difference scheme in polar coordinates. Matching the boundary conditions, it is possible to work in a forced oscillation regime or in a free oscillation regime (laser mode). The resonant wavelength and quality factor can then be deduced. Compared to the coupled mode theory and to 2-D finite-difference time-domain computations, the method is faster and more accurate. Moreover, a polarization effect of the microgear is demonstrated. The TE polarization experiences a Q-factor improvement contrary to TM polarization. Finally, microgear structures prove to be more efficient than micro flowers.