Doped Silica Glass Research Articles

Hollow core optical fibres with comparable attenuation to silica fibres between 600 and 1100\u2009nm

For over 50 years, pure or doped silica glass optical fibres have been an unrivalled platform for the transmission of laser light and optical data at wavelengths from the visible to the near infra-red. Rayleigh scattering, arising from frozen-in density fluctuations in the glass, fundamentally limits the minimum attenuation of these fibres and hence restricts their application, especially at shorter wavelengths. Guiding light in hollow (air) core fibres offers a potential way to overcome this insurmountable attenuation limit set by the glass’s scattering, but requires reduction of all the other loss-inducing mechanisms. Here we report hollow core fibres, of nested antiresonant design, with losses comparable or lower than achievable in solid glass fibres around technologically relevant wavelengths of 660, 850, and 1060 nm. Their lower than Rayleigh scattering loss in an air-guiding structure offers the potential for advances in quantum communications, data transmission, and laser power delivery.

Short-length CW laser of Nd[formula omitted] heavily doped single-mode silica glass fiber fabricated by zeolite method

We constructed a CW fiber laser using a 40-mm-long Nd3+ heavily doped silica glass single-mode fiber (Nd-SMF). Its core glass was fabricated by the zeolite method, and its Nd2O3 doped density was measured as 1.25 wt%. Nd-SMF also demonstrated laser oscillation. The laser power reached 19.7 mW and its slope efficiency and laser threshold were 14.6% and 22.0 mW, respectively. Such a short single-mode fiber will help us easily make a high repetition rate over GHz and a compact oscillator with adequate saturable absorbers. An Nd-SMF laser has the potential to achieve laser miniaturization and high repetitive pulsed oscillation.

Evaluation of Flat Gain with RAMAN-Thulium Doped Silica Glass Fiber Hybrid Optical Amplifier in Some Band Spectrum for Super Dense Wavelength Division Multiplexing System

The performance of RAMAN-TDSGF hybrid optical amplifier (HOA) has been examined in the context of gain and noise figure (NF) for 400 × 10 Gbps super dense wavelength division multiplexing (SD-WDM) system. Characteristics of this novel HOA has also compared with RAMAN-EDFA-RAMAN, RAMAN-EDFA and RAMAN-RAMAN HOA for the range of 1530 nm to 1665, and 1530 nm to 1586 nm respectively. Best rating in terms of maximum gain of 35.9 dB and noise figure of 3.2 dB have recorded from RAMAN-TDSGF HOA with the variation of 0.025 dB than the other HOAs. Moreover this paper also has shown the worst response from RAMAN-RAMAN HOA for super dense optical communication system.

Remote Measurements of X-Rays Dose Rate Using a Cerium-Doped Air-Clad Optical Fiber

Cerium doped silica glasses are attractive materials for radiation dosimetry. In this article, Ce-doped air-clad optical fiber has been fabricated for real-time X-ray dose rate measurements through the radioluminescence (RL) signal. The structural properties of the obtained material were studied using Raman spectroscopy. The presence of Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions inside the sol-gel-derived silica core was confirmed using photoluminescence (PL) measurements. This optical fiber, with a high numerical aperture, was tested as active and guiding material in an all-fibered remote X-ray dosimeter configuration. We demonstrated that the response dependence of RL versus dose rate is linear from 52 mGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s up to at least 1.5 Gy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s, allowing to monitor the dose rate evolution during an irradiation run. The presented results confirm the potentialities of this microstructured optical fiber to monitor ionizing radiations in harsh environments. They also pave the way toward an alternative to the widely used approach that uses scintillator material at the end of a transport's optical fiber.

193 nm excimer laser-induced color centers in Yb3+/Al3+/P5+-doped silica glasses

Yb3+, Yb3+/Al3+, and Yb3+/P5+ co-doped silica glasses, as well as pure silica, Al3+, and P5+ single-doped silica glasses, were prepared using a sol–gel method combined with high-temperature sintering. The glasses were irradiated with a 193 nm ArF excimer laser for different durations. The species of the 193 nm laser-induced color centers were identified by radiation-induced absorption (RIA), in-situ photoluminescence (PL), and continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopic techniques. To obtain the RIA and CW-EPR characteristics of each color center, the Gaussian decomposition of RIA and the line-shape simulation of the CW-EPR spectra were performed. The formation mechanism of the color centers was correlated with the glass microscopic structure, which was obtained by nuclear magnetic resonance (NMR) spectroscopy. The results show that the oxygen hole center and the Yb2+ ion pairs are primarily responsible for the radiation-induced darkening, and their formation is highly dependent on the charge balance between the Yb3+ ion and its ligand. This work provides insights into the underlying mechanism of pump light and/or external radiation-induced optical losses in Yb3+-doped silica fibers.

Optical properties of Er3+ heavily doped silica glass fabricated by zeolite method

We successfully fabricated heavily Er3+-doped silica glasses (ErZSG) by a zeolite method and measured their optical properties such as absorption, fluorescence and excitation spectra, and lifetime. The samples’ lifetime was measured as 4.26±0.02 msec at 9,600 wtppm. In order to reveal the quantum efficiency η, we also examined the radiative lifetimes of the ErZSGs by Judd-Ofelt analysis, and then the quantum efficiency was evaluated to be 45.1±3.3% at 9,600 wtppm, which is a high enough value for constructing a short-length laser oscillator. The ErZSG-based short-length laser oscillator is an attractive light source for such applications as medicine, biology, and metrology, and it is especially promising as a light source of LiDAR.

Spectroscopic properties of Sm3+ and CdS co-doped in sol-gel silica glass

Sm 3+ - doped silica glass co-doped with CdS nanoparticles have been prepared by sol-gel method. FTIR spectra of the samples at different annealing temperatures show the gradual removal of hydroxyl group. XRD pattern shows crystalline nature of the silica host along with CdS peak. The optical absorption and fluorescence properties have been investigated using Judd-Ofelt theory. The Judd-Ofelt intensity parameters have been obtained from the absorption spectrum following the trend Ω 2 &gt; Ω 4 &gt; Ω 6 and the large value of Ω 2 indicates covalency of the rare earth bonding. Under excitation with 370 nm, photoluminescence peaks have been observed in the green, yellow, orange and red region as a result of radiative relaxation from the 4 G 5/2 state.

Optical multi-stability in a nonlinear high-order microring resonator filter

We theoretically analyze and experimentally demonstrate optical bi-stability and multi-stability in an integrated nonlinear high-order microring resonator filter based on high-index contrast doped silica glass. We use a nonlinear model accounting for both the Kerr and thermal effects to analyze the instability behavior of the coupled-resonator based filter. The model also accurately predicts the multi-stable behavior of the filter when the input frequency is slightly detuned. To understand the role of the intracavity power distribution, we investigate the detuning of the individual rings of the filter from the optical response with a pump–probe experiment. Such a measurement is performed scanning the filter with a low-power probe beam tuned a few free spectral ranges away from the resonance where the pump is coupled. A comprehensive understanding of the relationship between the nonlinear behavior and the intracavity power distribution for the high-order microring resonator filter will help the design and implementation of future all-optical switching systems using this type of filter.

Third-harmonic generation in CMOS-compatible highly doped silica micro-ring resonator.

We present the first demonstration of visible emission from highly doped silica glass micro-ring resonators (MRRs) through a third-harmonic generation (THG) nonlinear process. We obtain green light conversion efficiency of 2.7×10-5 W-2 in a MRR with loaded Q-factor of 1.4×106 pumped in the telecom band. A thermal nonlinear model is developed to account for the in-cavity power dependence of the resonance detuning. Using the extracted thermal nonlinear coefficients, the measured TH resonance shift is calibrated by subtracting the thermal nonlinear-induced phase mismatch to obtain the theoretical threefold wavelength relationship along with the measured cubic power relationship.

Spectroscopic investigations on Se/RE doped sol gel derived silica matrices

Selenium and rare earth ions co-doped inorganic luminescence silica matrices are synthesized through sol gel route. The incorporation of cubic Se quantum dots within the porous silica frame is confirmed from TEM analysis. The successful entrapment of green as well as blue color emitters within the silica frame generates evident luminescence bands in the visible region. Obtained Se/Tb3+ ions doped silica glasses give characteristic sharp emission peaks of terbium ions at 488 nm, 543 nm, 584 nm, 619 nm wavelength under UV excitations. A broad blue emission band from selenium nanodots centered at 421 nm wavelength is observed in the emission spectrum. Colorimetric studies are done with the aid of 1931 chromaticity diagram. CIE indices of the co-doped glasses are found to lie in between the CIE indices of selenium doped silica glasses (0.18, 0.21) and terbium doped silica glasses (0.28, 0.46). For a fixed concentration of Se and terbium in silica glasses, tunable luminescence without shift in peak wavelength is observed under the excitation wavelength of 340 nm to 380 nm. Varying blue to green luminescence intensity ratio (B/G) with the excitation wavelength reveals the possibility of tunable emission of the glassy matrix for their applicability in solid lighting systems.

1.8μm fluorescence characteristics of Tm3+ doped silica glasses and fiber prepared by the glass phase-separation technology

We report Tm3+ doped silica glasses and fiber prepared from mesoporous silica glass by glass phase-separation technology. The Judd–Ofelt parameters and radiation properties of Tm3+ doped silica glasses were calculated and evaluated according to the recorded absorption spectrum. The absorption and emission cross-section, gain spectra and fluorescence lifetime were analyzed. Tm3+ doped large-core double-cladding fiber with a core NA of 0.08 was fabricated by the rod-in-tube method. The measurements show that the fiber has a Tm3+ concentration of 10300 ppm by weight and excellent homogeneity in the fiber core. The 1.8 μm luminescence properties were investigated. It is suggested that the Tm3+ doped silica glass prepared by glass phase-separation technology can be a potential fiber core material to achieve 2 μm fiber laser.

Manufacture and spectroscopic analysis of Tm3+-doped silica glass and microstructure optical fiber through the laser sintering technique

We demonstrated how a Tm3+-doped silica glass rod was successfully manufactured by the laser sintering technique and made into a Tm3+-doped microstructure optical fiber by the stack-capillary-draw method. Based on the absorption spectrum, the core glass shows outstanding spectroscopic properties through Judd-Ofelt analysis. The fiber core-cladding structure was preserved completely without any crystallization in the core. Besides, a self-built fiber laser at 1.95 μm produces 740 mW output power with a slope efficiency of 16.73%. The results prove that our laser sintering technique is a promising preparation method to acquire fiber materials for a 2.0 μm laser.

Variations in the linear and nonlinear refractive indices of chalcogenide glass thin films for photonic applications

In this paper, we report the variations in linear and nonlinear refractive indices of Ge20Ga5Sb10S65, Ge20Ga5Sb10Se65, Ge25Sb10S65 and, Ge16As24S60 chalcogenide glass thin films. The linear refractive index (n) has been determined and analyzed by the Swanepoels method and the Wemple-DiDomenico model(WDD). The theoretical formulation by Fournier and Snitzer has been used to study the nonlinear refractive index (n2) which is compared with the modified Boling model. The compositional dependence of various parameters such as the optical band gap(Eg), linear refractive index, extinction coefficient(k), optical conductivity(σ) and dielectric parameters(εr, εi) was also analyzed. Results on variations of linear and nonlinear refractive indices are interpreted on the basis of the optical polarizability of the materials. The n2 of the prepared chalcogenide glass thin films are found to be two orders greater than that of pure and doped silica glasses which make them ideal candidates for all-optical networks.

Comparative study of oscillator strengths in dye and metal doped silica glasses

In the present study sol gel silica glasses doped with rhodamine dye (Rh6G) and transition metals like silver, copper and iron were prepared at room temperature through sol gel route. The molar concentrations of dye and metal are varied and synthesized to get a uniform dye and metal doped clusters in silica matrices. Structural characterization is performed by SEM and XRD on doped silica glasses. SEM micrographs reveal the size of particles to be 10-50μm. The amorphous structures of the glasses are confirmed by XRD. The absorption spectra are monitored and analyzed. The absorption spectra of fluorescent dye doped sol gel silica glasses are found within the limit of 400-600 nm and the absorption spectra of different metal doped glasses are in the range of 250-350nm. Oscillator strengths of dye doped and metal doped glasses are calculated and compared. Oscillator strength of rhodamine dye doped silica glasses is comparatively higher than the other doped glasses. Silver is seen to have high oscillator strength among the metal doped silica glasses.

CMOS-compatible high-index doped silica waveguide with an embedded silicon-nanocrystal strip for all-optical analog-to-digital conversion

Passive all-optical signal processors that overcome the electronic bottleneck can potentially be the enabling components for the next-generation high-speed and lower power consumption systems. Here, we propose and experimentally demonstrate a CMOS-compatible waveguide and its application to the all-optical analog-to-digital converter (ADC) under the nonlinear spectral splitting and filtering scheme. As the key component of the proposed ADC, a 50&#x00A0;cm long high-index doped silica glass spiral waveguide is composed of a thin silicon-nanocrystal (Si-nc) layer embedded in the core center for enhanced nonlinearity. The device simultaneously possesses low loss (0.16&#x00A0;dB/cm at 1550&#x00A0;nm), large nonlinearity (305&#x2009;&#x2009;W&#x2212;1/km at 1550&#x00A0;nm), and negligible nonlinear absorption. A 2-bit ADC basic unit is achieved when pumped by the proposed waveguide structure at the telecom band and without any additional amplification. Simulation results that are consistent with the experimental ones are also demonstrated, which further confirm the feasibility of the proposed scheme for larger quantization resolution. This demonstrated approach enables a fully monolithic solution for all-optical ADC in the future, which can digitize broadband optical signals directly at low power consumption. This has great potential on the applications of high-speed optical communications, networks, and signal processing systems.

Enhanced luminescence properties of Eu3+-doped high silica glass by Ag nanoparticles

Eu3+ and Ag nanoparticles (Ag-NPs) doped high silica glass (HSG) was synthesized by absorbing and sintering porous glass. The effect of localized surface plasmon resonance (LSPR) of Ag-NPs on absorbance, luminescence properties and decay curves was investigated. The results indicate that Ag-NPs are effectively doped into HSG. The surface plasmon coupling can be formed between the Eu3+ ions and the Ag-NPs surface because the broad absorption band of Ag-NPs overlaps with the excitation peaks of Eu3+. The profiles of the excitation and emission spectra were not affected by Ag-NPs. By optimizing the Ag concentration, the emission intensity and quantum yield (QY) of HSG-Eu3+-0.1%Ag are significantly higher than those of HSG-Eu3+. Plasmon-enhanced luminescence can occur through enhancement of local electromagnetic field and radiative decay rate.

Dosimetric response of fabricated Ge-doped optical fibres in computed tomography RQT beam quality x-ray beams

Novel germanium (Ge)-doped silica glass fibres tailor-made in Malaysia are fast gaining recognition as potential media for thermoluminescence (TL) dosimetry, with active research ongoing into exploitation of their various beneficial characteristics. Investigation is made herein of the capability of these media for use in diagnostic imaging dosimetry, specifically at the radiation dose levels typically obtained in conduct of Computed Tomography (CT). As a first step within such efforts, there is need to investigate the performance of the fibres using tightly defined spectra, use being made of a Philips constant potential industrial x-ray facility, Model MG165, located at the Malaysian Nuclear Agency Secondary Standards Dosimetry Lab (SSDL). Standard radiation beam qualities (termed RQT) have been established for CT, in accord with IEC 61267: 2003 and IAEA Technical Reports Series No. 457: 2007. A calibrated ionisation chamber has also been utilised, forming a component part of the SSDL equipment. The fabricated fibres used in this study are 2.3 mol% flat fibre (FF) of dimensions 643 × 356 μm2 and 2.3 mol% cylindrical fibre (CF) of 481 μm diameter, while the commercial fibre used is 4 mol% with core diameter of 50 μm. The dopant concentrations are nominal preform values. The fibres have been irradiated to doses of 20, 30 and 40 milligray (mGy) for each of the beam qualities RQT 8, RQT 9 and RQT 10. For x-rays generated at constant potential values from 100 to 150 kV, a discernible energy-dependent response is seen, comparisons being made with that of lithium fluoride (LiF) thermoluminescence dosimeters (TLD-100). TL yield versus dose has also been investigated for x-ray doses from 2 to 40 mGy, all exhibiting linearity. Compared to TLD-100, greater sensitivity is observed for the fibres.

Tm3+ Tellurite-Modified-Silica Glass Thin Films Fabricated Using Ultrafast Laser Plasma Doping

Thin glass films have been produced by implanting Tm3+ doped and Tm3+/Er 3+ codoped tellurite glasses into silica substrates using ultrafast laser plasma doping for the first time. The resulting glass films had thicknesses of up to 2 μm, refractive indices of 1.5–1.65 and exhibited photoluminescence in the 1.5–2.1 μm wavelength region when excited with 808 nm and 976 nm laser diodes. The OH− content of the silica glass substrate was also found to have an effect on the Tm3+: 3F4 photoluminescence lifetime in the modified thin glass film layer, with the high OH− containing substrate exhibiting a shorter lifetime. Through optimization of the femtosecond laser ablation parameters, we have produced crack-free thin films of Tm3+ doped tellurite-modified silica glass layers with good thickness uniformities of ±10 nm, and the refractive index of the modified layer is up to 13% higher than the bare substrate material.

Multiple luminescence spanning the UV to NIR regions of Tm3+-doped silica glass microspheres pumped by 1527 nm

Fluorescence spectra of Tm3+-doped silica glass microspheres under excitation of a continuous wave diode laser at 1527 nm were investigated. It showed rich upconversion emissions from the high-energy states of Tm3+ ions, which spanned from the ultraviolet (UV) to near-infrared (NIR). Analysis indicated that the purple light emission came from a six-photon upconversion process. What's more, a broadband fluorescence emission was observed in a wavelength range of 620–935 nm. The high power density was a main advantage by confining the light in the microsphere cavities. The multiple fluorescence upconversion emissions of Tm3+-doped silica glasses under ∼1550 nm excitation may open a new door to explore the future visible light communication technology.

Fabrication and Gamma-Ray Irradiation Effect on Optical and Mechanical Properties of Germano-Silicate Glass Fibers with Inner Cladding of B and F Doped Silica Glasses

ABSTRACTThe effect of glass composition, pure silica glass, boron-doped and fluorine-doped silica glasses of inner cladding, in the germano-silicate glass core fibers on optical and mechanical properties upon the γ-ray irradiation was investigated. Enhanced radiation hardening at 1,550 nm was found in both the B- and F-doped fibers after the γ-ray irradiation with dose-rate of 1.25 kGy/h. The radiation-induced attenuation (RIA) was found to increase in the order of the B-doped fiber, the F-doped fiber, and the silica fiber. While no major influence on the refractive index of the fibers after the γ-ray irradiation was found, the residual stress was slightly changed.