Doped Silica Fiber Research Articles

Crystal field effects of Al doping on the Stark splitting and gain bandwidth of erbium doped silica fibers

In this study, erbium-doped silica fibers (EDFs) with different Al/Er ratios were prepared by high-temperature source combined with the modified chemical vapor deposition (MCVD) method. The effects of different Al/Er ratios on the gain performance of erbium-doped silica fiber amplifiers (EDFA) were investigated. The EDFA demonstrated in this paper achieves a maximum gain of 45 dB at 1560 nm when the signal power is −20 dB, while the bandwidth of 20 dB gain is up to 68 nm (1532∼1600 nm). Additionally, the effect of Al doping on the crystal field around the Er ion was analyzed and the Stark energy level distribution of the Er ions was further derived. Our approach offers a feasible solution for C + L band amplification from the perspective of Stark effect and crystal field analysis.

Simulation of solar-pumped multicore Nd3+-doped silica fiber lasers

Simulation of solar-pumped multicore Nd3+-doped silica fiber lasers

Single-frequency DBR lasing by integrating FBGs into germanium-free photosensitive highly Yb3+-doped silica fibers

Monolithic distributed Bragg reflector (DBR) cavity which directly integrates fiber Bragg gratings (FBGs) into the photosensitive RE-doped fibers is a promising configuration in constructing compact and efficient single frequency fiber lasers (SFFLs). Yet, the doping level of rare-earth (RE) ions has generally to be sacrificed in the classical Ge-photosensitized RE-doped silica fibers because of the dramatic refractive index increase caused by the introduction of Ge. Here, we demonstrate an approach to realize the trade-off between photosensitivity and RE doping concentration. We validate that the addition of a small amount of cerium (0.37wt.%) instead of Ge could photosensitize Yb3+-doped silica fiber (YDF), while maintaining fiber numerical aperture (NA) at 0.12 under a high 2.5-wt.% Yb doping level. Based on the short monolithic DBR cavity constructed by this germanium-free photosensitive highly YDF, a 1064 nm fiber laser with a 48.6% slope efficiency and an over 200 mW power on two orthogonally polarized modes could be realized. Further stable and linear-polarized 1064 nm SFFL is also demonstrated in a designed monolithic polarization maintaining cavity with an output power of 119 mW and an efficiency of 26.4%. Our results provide an alternative way to develop photosensitive highly RE-doped fibers towards monolithic laser cavity application.

A novel Nd3+-doped fiber fabricated by curable nanocomposites for 916 nm laser

In this work, a novel Nd3+-doped silica fiber preform was fabricated by the UV-curable nanocomposite technology combined with the solution doping method. The preform sample had a great homogeneity with a doping concentration of 1.14 wt% Nd3+ ions and 2.51 wt% Al3+ ions. The obtained Nd3+-doped core glass provided a relatively large emission cross section (∼0.84 pm2) and a long lifetime (373 μs) of 916 emission. On this basis, by using an 808 nm laser diode as the pump source, lasing at 916 nm was achieved from a 4 cm long fabricated Nd3+-doped silica fiber, with the corresponding slope efficiency of ∼13.6 %. Notably, only 2 cm-short created fiber alone was enabled for 916 nm lasing generation. Our results indicated that the created Nd3+ doped fiber by the novel approach has unique advantages and potential for compact short-cavity 0.9 μm laser applications.

Quantum storage of 1650 modes of single photons at telecom wavelength

To advance the full potential of quantum networks one should be able to distribute quantum resources over long distances at appreciable rates. As a consequence, all components in such networks need to have large multimode capacity to manipulate photonic quantum states. Towards this end, a photonic quantum memory with a large multimode capacity, especially one operating at telecom wavelength, remains an important challenge. Here we optimize the preparation of atomic frequency combs and demonstrate a spectro-temporally multiplexed quantum memory in a 10-m-long cryogenically cooled erbium doped silica fibre. Our multiplexing storage has five spectral channels - each 10 GHz wide with 5 GHz separation - with up to 330 temporal modes in each, thus resulting in a simultaneous storage of 1,650 modes of heralded single photons with a 1000-fold increasing in coincidence detection rate with respect to single mode storage. Our results could pave the way for high speed quantum networks compatible with the infrastructure of fibre optical communication.

Evaporation characteristics of Er3+-doped silica fiber and its application in the preparation of whispering gallery mode lasers.

In this work, the concentration of rare-earth ions in doped silica whispering gallery lasers (WGLs) is controlled by evaporation. The fabrication of WGLs is used to experimentally evaluate the evaporation rate (mol/μm) and ratio (mol/mol) of erbium and silica lost from a doped fiber during heating. Fixed lengths of doped silica fiber are spliced to different lengths of undoped fiber and then evaporated by feeding into the focus of a CO2 laser. During evaporation, erbium ions are precipitated in the doped silica fiber to control the erbium concentration in the remaining SiO2, which is melted into a microsphere. By increasing the length of the undoped section, a critical point is reached where effectively no ions remain in the glass microsphere. The critical point is found using the spectra of the whispering gallery modes in microspheres with equal sizes. From the critical point, it is estimated that, for a given CO2 laser power, 6.36 × 10-21 mol of Er3+ is lost during the evaporation process for every cubic micron of silica fiber. This is equivalent to 1.74 × 10-7 mol of Er3+ lost per mol of SiO2 evaporated. This result facilitates the control of the doping concentration in WGLs and provides insight into the kinetics of laser-induced evaporation of doped silica.

Actively pulse shaped linearly polarized nanosecond hybrid Ho3+ and Tm3+-doped silica fiber & Ho3+:YAG MOPA at 2048 nm

Ho3+:YAG amplifiers are able to efficiently scale pulse energy at wavelengths far shorter than the main emission peak. For 24 W input power at 2048 nm a signal output power of 81.6 W is reached, resulting in 5.3 dB gain.

Amplification at 2.3-µm in 1.9-µm thulium-doped silica fiber laser

A high-power 1.9-µm Tm3+-doped silica fiber laser generates 7.3-dB of gain at 2.3 µm when cladding- pumped with 207 W of power at 793 nm. We attribute the 2.3-µm gain to the transition 3H4 → 3H5 of Tm3+.

Monolithic ultrashort-cavity DBR gain-switched thulium doped fiber laser made by high-precision femtosecond laser direct-writing

We demonstrate a novel monolithic ultrashort-cavity distributed Bragg reflector (DBR) gain-switched thulium doped silica fiber laser. Commercial heavily thulium doped non-polarization-maintaining silica fiber was selected as the gain medium. Monolithic linear laser resonator, which includes a pair of uniform fiber Bragg gratings (FBGs) with a space of 1.0-mm inbetween, was inscribed in the thulium fiber by femtosecond-laser point-by-point (PbP) writing method. The reflectivity of either FBG is close to 100 % and the effective cavity length is calculated to be 3.5 mm. Such an ultrashort-DBR-cavity fiber laser exhibited high Q factor and low cavity loss, allowing the efficient utilization of pump power within the millimeter-long cavity. Single-longitudinal, linearly polarized, gain-switched TDFL at 2003 nm, with a recorded shortest pulse duration of 4.3 ns, a repetition rate of 50 kHz, a maximum peak power of 500 W, and single pulse energy of 2.14 μJ, has been realized, benefitted from the ultrashort cavity length.

Development of pedestal-free large mode area fibers withTm3+ doped silica nanostructured core.

We present the pedestal-free thulium doped silica fiber with a large nanostructured core optimized for fiber lasers. The fiber is composed of over 6 thousand thulium doped silica nanorods with a diameter of 71 nm each which form a nanostructured step-index core. We study the influence of non-continuous distribution in nanoscale active areas on gain, beam quality, and fiber laser performance. The proof-of-concept fiber is effectively single mode for wavelength above 1.8 µm. We demonstrate the performance of the fiber in a laser setup pumped at 792 nm. Single mode laser emission with a slope efficiency of 29% at quasi-continuous output power of 4 W with M2 = 1.3 at the emission spectrum 1880-1925 nm is achieved.

Monolithic 2-µm single-frequency linearly-polarized gain-switched distributed feedback fiber laser by femtosecond laser direct-writing.

We report a single-frequency, linearly polarized gain-switched, distributed feedback (DFB), 2-µm thulium doped silica fiber laser (TDFL), with an effective cavity length of 2.5 mm. The cavity is based on a heavily thulium doped non-polarization-maintaining silica fiber and composed of a π-phase-shifted fiber Bragg grating (FBG) with a total FBG length of 35 mm. The DFB FBG was written by femtosecond-laser point-by-point (PbP) method. In-band pumping scheme is chosen with a 1550 nm nanosecond pulsed erbium-doped silica fiber laser pump. Single-longitudinal, linearly polarized, gain-switched TDFL at 2002 nm, with a recorded shortest pulse duration of 4.7 ns, a repetition rate of 20 kHz, a maximum peak power of 170 W, and single pulse energy of 0.8 µJ, has been obtained, benefitting from the ultrashort DFB cavity made by the femtosecond laser direct-writing method.

High ytterbium concentration Yb/Al/P/Ce co-doped silica fiber for 1-µm ultra-short cavity fiber laser application.

We demonstrate a high ytterbium concentration Yb/Al/P/Ce co-doped silica fiber by conventional modified chemical vapor deposition (MCVD) technology and solution doping process. The fiber has a Yb concentration of about 2.5 wt%, and the corresponding core absorption coefficient is measured to be ∼1400 dB/m at 976 nm. The gain coefficient was measured to be approximately 1.0 dB/cm. It is found that the Yb/Al/P/Ce co-doped silica shows a lower photodarkening-induced equilibrium loss of 52 dB/m at 633 nm than the Yb/Al/P co-doped silica fiber of 117 dB/m. Using the heavily Yb3+-doped silica fiber, a compact and robust ultrashort cavity single-frequency fiber laser was achieved with a maximum output power of 75 mW and a linewidth of 14 kHz. Furthermore, a compact passively mode-locked fiber laser (MLFL) with a repetition rate of 1.23 GHz was also proposed using our developed Yb-doped fiber. The laser properties of the proposed lasers were systematically investigated, demonstrating the superior performance of this fiber in terms of photodarkening resistance and ultrashort-cavity laser application. Furthermore, utilizing an all-fiber structure based on silica-based fiber offers the significant advantage of high stability and reliability.

Волоконные лазеры с солнечной накачкой без первичного концентратора.

We studied solar pumped fiber lasers without primary concentrator. A model of solar sidepumped Nd3+ doped silica fiber lasers was developed using photon tracing method. Theabsorbed power distribution, possible losses and the pumping efficiency are estimated using the model. We analyzed the estimated paramters and drawed conclutions which have many suggests for improved design of solar pumped fiber lasers. The absorption efficiency of a fiber solar laser without a primary concentrator or sun tracker was calculated to be 0.2% for a 190 m fiber. The output power of the fiber laser is 40 mW, and the conversion efficiency from sunlight to laser light is calculated to be 0.06%. The developed model allows one to estimate the overall efficiency, output power and absorption distribution of Nd3+ fiber lasers without focusing optics, enabling various investigative comparisons.

Enhanced fluorescence and gain characteristics of PbS doped silica fiber with PbSe nano-semiconductor co-doping

A PbS/PbSe nano-semiconductor co-doped silica fiber (PbS/PbSe DSF) was prepared and the enhancement mechanism of fluorescence and gain characteristics were investigated. PbS/PbSe DSF showed the broadband luminescence ranging from 1000 nm to 1380 nm, and the fluorescence intensity at 1160 nm and 1300 nm was enhanced by 15.8 dB and 14.6 dB, respectively. The on–off gain of PbS/PbSe DSF is 13.7–18.9 dB in the range of 1100–1350 nm and the net gain is 10.7–14.5 dB under 980 nm pumping. Simultaneously, based on density functional theory (DFT), local structural models of PbS/PbSe co-doped fiber materials were built, and the study showed that the introduction of PbSe increased the absorption at 969 nm and the corresponding emission in the range of 1100–1400 nm. Moreover, microstructural characterization showed the presence of high-density nanoparticle distribution in the core of PbS/PbSe DSF, indicating that the PbSe co-doping may have changed the local field environment of PbS deposition and increased the crystallinity, which finally improved the fiber performance. The results indicate that the proposed PbS/PbSe DSF is a potential gain material with important research value in areas such as active fiber amplifiers.

All-Silica Fiber Ultra-Flat 2-3 μm Supercontinuum Source Based on Highly Nonlinear Silica Fiber

In this letter, we demonstrated an all-silica fiber 1.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.2 ~\mu \text{m}$ </tex-math></inline-formula> supercontinuum (SC) source based on germanium-doped highly nonlinear fibers (HNLF). By optimizing the length of HNLF, as the pump injected into the HNLF increased to 6 W, a 4.12 W broadband SC source extending from 1516 to 3182 nm was obtained. The 3 dB spectrum bandwidth was up to 1022 nm ranging from 1855 nm to 2877 nm, and the 1 dB bandwidth was up to 878 nm covering from 1959 nm to 2837 nm. To the best of our knowledge, this is the flattest SC in the 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3 ~\mu \text{m}$ </tex-math></inline-formula> region based on doped silica fiber to date.

Radiation Sensitive Long-Period Fiber Grating Based on Tb-Doped Silica Fiber

We demonstrate a radiation sensitive long-period fiber grating (LPG) based on terbium (Tb)-doped silica fiber, fabricated by dual-sided CO2 laser exposure. At a total dose of 6.0 ± 0.2 kGy of gamma radiation, the maximum radiation-induced resonance wavelength shift (RIRWS) of LPG in Tb-doped silica fiber is up to 3.98 nm, which is much higher than that of 1.14 nm in standard single-mode fiber. To characterize the degree of modification of fibers by radiation, we calculate the radiation-induced refractive index change (RIRIC), which is as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.05\times 10^{-5}$ </tex-math></inline-formula> for Tb-doped silica fiber, approximately 276.3% of that of standard single-mode fiber. In addition, the growth of RIRWS with increasing cladding mode order is analyzed, and the theoretical and experimental RIRWS of LPG are compared. This new type of LPG has great promise in the field of high-dose radiation sensing, such as dose monitoring in nuclear reactors, particle collision experiments, and so on.

Aggregation of ODC(I) and POL Defects in Bismuth Doped Silica Fiber

First-principles calculations were used to simulate the aggregation of the peroxy chain defect POL and the oxygen vacancy defect ODC(I). Defect aggregation's electronic structure and optical properties were investigated. The two defects were most likely to accumulate on a 6-membered ring in ortho-position. When the two defects are aggregated, it is discovered that 0.75 ev absorption peaks appear in the near-infrared band, which may be brought on by the addition of oxygen vacancy defect ODC(I). We can draw the conclusion that the absorption peak of the aggregation defect of ODC(I) defect and POL is more prominent in the near infrared region and visible light area than ODC(I) defect and POL defect.

High-power, high-efficiency single-frequency DBR fiber laser at 1064 nm based on Yb3+-doped silica fiber.

A high-power, high-efficiency single-frequency fiber laser at 1064 nm was demonstrated based on a distributed Bragg reflector (DBR) all-silica-fiber configuration. A single-frequency laser with an output power of 642 mW and slope efficiency of 66.4% with respect to absorbed pump power was achieved from a 1.2-cm-long commercially available Yb3+-doped silica fiber. To the best of our knowledge, this is the highest single-frequency laser power and efficiency obtained from the DBR all-silica fiber laser. The work presented here paves the way for the development of high-power, robust, and cost-effective single-frequency Yb3+-doped all-silica fiber lasers.

High-Peak-Power Pulsed Single-Frequency Fiber MOPA Based on Yb3+-Doped Silica Fiber

High-Peak-Power Pulsed Single-Frequency Fiber MOPA Based on Yb3+-Doped Silica Fiber

Preparation of Highly Tm3+-Doped Silica Fibers and Study of 2.0 μm Laser Performance

Preparation of Highly Tm3+-Doped Silica Fibers and Study of 2.0 μm Laser Performance