Co-doped Optical Fiber Research Articles

Exploring the potential of a bismuth-erbium-vanadium co-doped optical fiber as a stable Q-switcher in the 1550 nm region

This paper experimentally demonstrates the ability of a bismuth-erbium-vanadium co-doped optical fiber as a saturable absorber (BEV-FSA) to generate stable Q-switched pulses in the 1550 nm region. The laser cavity delivered passively Q-switched pulses exploiting an erbium-ytterbium co-doped double-clad fiber (DC-EYDF) as the laser gain medium while maintaining an all-fiber cavity configuration. The output parameters of the laser such as output power, repetition rate, pulse duration, and pulse energy have been studied in detail with the variation of pump power. The output spectrum centered at 1550.86 nm throughout the experiment. The system produced stable pulses with a minimum pulse width of 1.83 µs with a pulse energy≈0.4µJ at the highest pump power of 2.31 W. The highest achievable repetition rate was 47.5 kHz with an of SNR≈53dB.

Experimental study on activating bismuth active centers in bismuth/erbium co-doped optical fiber by ionizing radiations

Post-treatments by ionizing radiations have been proposed previously for regulating the properties of bismuth/erbium co-doped optical fiber (BEDF). In this work, the effects of common ionizing radiations (i.e. gamma ray, electron beam and mixed γ/neutron) on Bismuth Active Centers (BACs) in BEDF have systematically been investigated. Our experimental results show obvious BAC activation by ionizing radiation – evident from the increase in saturable absorption at 830 nm that is closely associated with the BAC responsible for the desirable near infrared (NIR) emissions. This radiation induced BAC activation has been confirmed from the emission of BAC associate with silica (BAC-Si). The saturation pump power of the BAC-Si emission in all irradiated samples is found higher than that in pristine (or non-irradiated) samples. In addition, the effect on emission by different radiation is found in the order of gamma ray > mixed gamma/neutron > electron beam. On the other side, we have also observed significant radiation induced unsaturable loss that can affect the pumping efficiency and Figure of Merit (FOM).

Investigation of Thermal Sensing in Fluoroindate Yb3+/Er3+ Co-Doped Optical Fiber

An investigation of fluoroindate glass and fiber co-doped with Yb3+/Er3+ ions as a potential temperature sensor was assessed using the fluorescence intensity ratio (FIR) technique. Analysis of thermally coupled levels (TCLs-2H11/2 and 4S3/2), non-thermally coupled levels (non-TCLs-4F7/2 and 4F9/2), and their combination were examined. Additionally, the luminescent stability of the samples under constant NIR excitation using different density power at three different temperatures was carried out. The obtained values of absolute sensitivity (0.003 K-1-glass, 0.0019 K-1-glass fiber 2H11/2 → 4S3/2 transition) and relative sensitivity (2.05% K-1-glass, 1.64% K-1-glass fiber 4F7/2 → 4F9/2 transition), as well as high repeatability of the signal, indicate that this material could be used in temperature sensing applications.

Improved Fluorescence and Gain Characteristics of Er-Doped Optical Fiber with PbS Nanomaterials Co-Doping.

Er-doped optical fiber (EDF) with ultra-broad gain bandwidth is urgently needed given the rapid advancement of optical communication. However, the weak crystal field of the host silica glass severely restricts the bandwidth of traditional EDF at 1.5 μm. In this study, we theoretically explored the introduction of PbS nanomaterials in the silica network assisted with the non-bridging oxygen. This can significantly increase the crystal field strength of Er3+ ions in the local structure, leading to their energy level splitting and expanding the fluorescence bandwidth. Additionally, the PbS/Er co-doped optical fiber (PEDF) with improved fluorescence and gain characteristics was fabricated using modified chemical vapor deposition combined with the atomic layer deposition technique. The presence of PbS nanomaterials in the fiber core region, which had an average size of 4 nm, causes the 4I13/2 energy level of Er3+ ions to divide, increasing the fluorescence bandwidth from 32 to 39 nm. Notably, the gain bandwidth of PEDF greater than 20 dB increased by approximately 12 nm compared to that of EDF. The obtained PEDF would play an important role in the optical fiber amplifier and laser applications.

Broadband high-gain Tm3+/Ho3+ co-doped germanate glass multimaterial fiber for fiber lasers above 2 µm.

High-gain Tm3+/Ho3+ co-doped optical fibers are urgently desired for high-repetition-rate mode-locked fiber lasers at >2 µm. Here, Tm3+/Ho3+ co-doped germanate glass with low hydroxyl (OH-) content was prepared by the conventional melt-quenching method combined with the reaction atmosphere procedure (RAP) dehydration technique. The doping concentrations of Tm2O3 and Ho2O3 are 2.5 mol.% (7.1 wt.%) and 0.25 mol.% (0.7 wt.%), respectively. Thanks to the high Tm3+ doping (7.1 wt.%) and low energy transfer efficiency (19.8%) between Tm3+ and Ho3+ ions, it enables achieving broadband and high-gain performance in the 2 µm region. Then a silicate-clad Tm3+/Ho3+ co-doped germanate core multimaterial fiber was successfully drawn by using the rod-in-tube method, which has a broadband amplified spontaneous emission (ASE) with a full width at half-maximum (FWHM) of 247.8 nm at 2 µm. What is more, this new fiber has a high gain per unit length of 4.52 dB/cm at 1.95 µm. Finally, an all-fiber-integrated passively mode-locked fiber laser was built by using this broadband high-gain fiber. The mode-locked pulses operate at 2068.05 nm, and the fundamental repetition rate is up to 4.329 GHz. To the best of our knowledge, this is the highest fundamental repetition rate for the all-fiber passively mode-locked fiber laser above 2 µm. These results suggest that the as-drawn multimaterial fibers with broadband high-gain characteristics are promising for high-repetition-rate ultrafast fiber lasers.

Broadband mid-infrared amplified spontaneous emission from Er/Dy co-doped fluoride fiber with a simple diode-pumped configuration

Er3+/Dy3+ co-doped double-clad ZBLAN optical fiber has been used to obtain amplified spontaneous emission (ASE) broadband light sources cladding-pumped by 980-nm multimode laser diode (LD) sources. It has been demonstrated that mid-infrared broadband emission extending from 2515 to 3735 nm was obtained by energy transfer between Er3+ and Dy3+. We experimentally investigated the optimum design of Er3+/Dy3+ co-doped ZBLAN fiber in terms of ion concentration, fiber length, pumping configuration, and pumping power. The ASE output power was more than 2.5 mW when the LD pump power was set at 5 W. To assess its potential for gas sensing applications, the fabricated ASE light source was used to successfully detect methane gas with concentrations at 1% and 5%. The simple and stable construction of our ASE light source is suitable for practical purposes.

Wearable and Fully-Portable Smart Garment for Mechanical Perturbation Detection With Nanoparticles Optical Fibers

This paper presents the development of a wearable smart textile for mechanical perturbation assessment during gait based on distributed optical fiber sensor system using the transmission-reflection analysis (TRA). In this case, magnesium and erbium co-doped optical fiber is employed as a high scattering medium, which results in high spatial resolution for the technique (in the order of a few millimeters). The optical fiber was embedded in a garment and controlled displacements at predefined locations on the garment were applied, where the simultaneous assessment of displacement amplitude and location was obtained using a slope-assisted technique. In the proposed technique, the slope inverses of the transmission-reflection curves are correlated with the displacement applied on the fiber, where a determination coefficient (R2) of 0.996 was obtained. Then, the sloped-normalized reflection (or backscattered) response is used on the disturbance location estimation with relative errors as low as 3.7%. The on-body application tests show an inherent insensitivity of the proposed smart garment to body movement due to natural gait movements, indicating the feasibility of the proposed approach on detecting only the transverse induced mechanical perturbations. In the wearable tests, the sensor system shows high correlation (R2 higher than 0.98) in the tests with different volunteers (subjected to similar displacements at predefined locations) and millimeter-accuracy on the disturbance location estimation.

Pump-induced photobleaching and thermal dependent recovery of BAC-Si in Bi/Er co-doped optical fiber by 830 nm laser irradiation

The pump-induced bleaching effects upon the luminescence of Bi/Er co-doped optical fiber (BEDF) under 830 nm pumping have been investigated. The BEDF was continuously irradiated for 9 h at room temperature (RT) under 830 nm pumping, and the emission intensity of bismuth active centers (BACs) had decreased partially. Especially, the emission intensity of BAC associated Si (BAC-Si) monotonously had reduced with irradiation time and hardly recovered to the initial level at RT after 91 h since pumping off. The pump-induced bleaching of BAC-Si in BEDF under 830 nm pumping was also studied with different irradiation intensities, and the result indicates that the photobleaching of BAC-Si is a single-photon process. In addition, thermal dependent recovery had been investigated. It was found that the emission intensity of BAC-Si in bleached BEDF can be enhanced even more than the initial level (∼5%) at low temperature while that is reduced further by high-temperature treatment. The underlying mechanism of the partially reversible photobleaching effect at RT was also discussed. All these results are conducive to having a deep insight into the nature of BACs and provide an alternative way to enhance the luminescence intensity of irradiated BEDF.

Transmission–Reflection Analysis in high scattering optical fibers: A comparison with single-mode optical fiber

Transmission–Reflection Analysis (TRA) is an inexpensive technique used in distributed monitoring systems for single perturbation tracking. However, TRA is limited to long distance applications (~km), since it has poor spatial resolution (~m) when combined to standard silica fibers. This paper proposes the use of a magnesium and erbium co-doped optical fiber in conjunction with the TRA technique. The goal is to improve spatial resolution and accuracy for detection of loss-inducing disturbances along the sensing fiber. Bending losses are induced at several points of the fiber spaced at 50 cm over a 5.4 m fiber length, where each curve is clearly identified with a maximum hysteresis of 1.65%. The localization of a strong disturbance with an estimated accuracy of ±0.8 mm near the source end and ±7.2 mm near the fiber end is analytically demonstrated. Regarding weak disturbances, the proposed approach is vulnerable to noisy measurements. However, the response accuracy has been estimated up to ±36.7 mm.

Eye safe emission in Tm3+/Ho3+ and Yb3+/Tm3+ co-doped optical fibers fabricated using MCVD-CDS system

The RE-co-doped silica optical fibers emitting in the eye-safe spectral range are still attractive for new applications like LIDAR, pollution monitoring, navigation, and free-space optical communication. High gain and beam quality of fiber sources based on large mode area (LMA) active fibers can be fabricated by the well-known Modified Chemical Vapor Deposition (MCVD) technology improved by the chelate doping system. Considering silica matrix, the most interesting co-dopants in the region above 1400 nm are thulium and holmium. In the paper Tm3+/Ho3+ and Yb3+/Tm3+ co-doped silica optical fibers (refractive index and rare earth distribution profile, luminescence) are presented. Their respective emission spectra has been measured over the range 1550–2150 nm for Tm3+/Ho3+ (exc. at 796 nm) and 1600–2100 nm for Yb3+/Tm3+ (exc. at 976 nm). A wide luminescent spectrum has been recorded from RE co-doping of silica glass during the MCVD process and we were able to achieve the appropriate and uniform concentration for getting the conditions of energy transfer. The fabrication and characterization of Tm3+/Ho3+ and Yb3+/Tm3+ co-doped optical fibres are presented. The analysis of luminescence spectrum changes vs. fibre length has shown that there is Amplified Spontaneous Emission (ASE) at 1960 nm in Yb3+/Tm3+ co-doped optical fibre. The possibilities of obtaining novel constructions of RE co-doped optical fibers for eye-safe emission region will be also shown.

Analysis of uncoated LPGs written in B-Ge doped fiber under proton irradiation for sensing applications at CERN

In this contribution, a complete dissertation concerning the behavior of a Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser and exposed to proton irradiation during a recent extensive campaign performed at the European Organization for Nuclear Research (CERN) with a fluence of 4.4·1015 p∙cm−2 is provided. The experimental results have been thus combined for the first time to the best of our knowledge with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the ultra-high dose proton exposure. From the correlation between experimental and numerical analysis, the irradiation exposure was found to induce a maximal variation of the core effective refractive index of ~1.61·10−4, responsible of a resonance wavelength red shift of ~44 nm in correspondence of the highest absorbed radiation dose of 1.16 MGy. At the same time, a relevant decrease close to ~0.93·10−4 in the refractive index modulation pertaining to the grating was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The effect of the proton beam on the spectral response of the LPG device and on the optical fiber parameters was assessed during the relaxation phases, showing a partial recovery only of the wavelength shift without any relevant change in the dip visibility revealing thus a partial recovery only in the refractive index of the core while the reduction of the refractive index modulation observed during the irradiation remained unchanged.

Thermally aggravated photo-bleaching of BAC-Al in bismuth/erbium co-doped optical fiber.

The thermal effect upon the photo-bleaching of bismuth/erbium co-doped optical fiber (BEDF) containing Al has been investigated. The photo-bleaching effects of aluminum related bismuth active center (BAC-Al) in BEDF are studied from room temperature (RT) up to 350°C under the irradiation of a 980nm laser. No visible bleaching of the luminescence associated with BAC-Al was observed at RT, but significant bleaching appeared at higher temperatures above 150°C under the same irradiation power. The underlying mechanism of significant thermal aggravation of photo-bleaching is discussed, and its impact needs to be considered in the design and application of optical amplifiers and lasers using Al-doped BEDF.

Spectroscopic study of the radiation hardening of bismuth/erbium co-doped optical fiber (BEDF) by hydrogen loading

Targeting the improved performance and the potential implementation in terrestrial and space applications, radiation hardening of bismuth/erbium co-doped optical fiber (BEDF) by hydrogen loading has been investigated. It is evident that gamma radiation induced absorptions (RIAs) exist in BEDFs with and without H2 loaded. Thereinto, RIA of BEDF with H2 loaded is greatly suppressed. Particularly, RIA of H2 loaded BEDF at 620 nm is over 40 dB/m lower than that of BEDF without H2 loaded after 35.6 Gy gamma irradiation. Due to the RIA, the bismuth active center (BAC) emission spectra of all irradiated BEDFs are reduced. But the decrement of H2 loaded BEDF is ~1 dB less than that of the counterpart. Although the change of the BAC-Si concentration by gamma radiation is unnoticeable via the comparison of the absorption and emission spectra, the results in this work demonstrate that H2 loading is an effective radiation hardening method for potential applications of bismuth doped optical fiber (BDF) and BEDF in radiative environment.

Effects of quenching and cooling upon near infrared luminescence of Bi/Er co-doped optical fiber

The effects of thermal quenching and low-temperature cooling upon near infrared (NIR) luminescence of Bi/Er co-doped optical fiber (BEDF) are investigated by comparing the emission spectrum in different states. The experimental results indicate NIR luminescence has been significantly enhanced by quenching with appearance of two new luminescent centers at ∼ 950 and 1230 nm, which are believed to be associated with two different bismuth active centers (BAC-Ge and BAC-Al2). Furthermore, when the quenched fiber is immersed in liquid nitrogen for cooling, the luminescence from 900 to 1500 nm is further enhanced while the luminescence of Er3+ peaked at 1536 nm is decreased. To find out the optimal cumulative effect of quenching and cooling, the experiment of quenching and cooling are repeated multiple times. It is found that the highest luminescence intensity for the band 1000-1360 nm in BEDF is achieved at the second experiment. These results not only exhibit more intrinsic information of the spectral properties of BACs in Bi-doped fibers, but also provide a new way to control the formation of BACs, obtaining broader and higher luminescence.

Ultraviolet Irradiation Effects on luminescent Centres in Bismuth-Doped and Bismuth-Erbium Co-Doped Optical Fibers via Atomic Layer Deposition

The effects of ultraviolet irradiation on luminescent centres in bismuth-doped (BDF) and bismuth/erbium co-doped (BEDF) optical fibers were examined in this study. The fibers were fabricated by modified chemical vapor deposition combining with atomic layer deposition method. The fibers were exposed to irradiation from a 193 nm pulsed wave argon fluoride laser, and an 830 nm wavelength laser diode pump source was employed for excitation. The experimental results showed that, for the BDF, the transmission loss was slightly reduced and the luminescence intensity was increased at the bismuth-related active aluminum centre (BAC-Al). Then, for the BEDF, the transmission loss was increased a little and the luminescence intensity was also increased at the BAC-Al centre. However, the luminescence intensity was decreased at approximately 1420 nm of the bismuth-related active silica centre (BAC-Si) for all fiber samples. One possible formation mechanism for luminescence intensity changes was probably associated with the valence state transfer of bismuth ions. The other possible mechanism was that the ArF-driven two-photon process caused luminescence changes in BAC-Al and BAC-Si. It was very important to reveal nature of luminescence properties of Bi-doped and Bi/Er co-doped optical fiber.

Effects of thermal treatment on photoluminescence properties of bismuth/erbium co-doped optical fibers

Abstract The effects of thermal annealing on the photoluminescence (PL) properties of bismuth/erbium co-doped multicomponent optical fiber (BEDFs) in a temperature range of from room temperature (RT) up to 1100 °C are clarified by PL, Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) measurements. When pumped by an 830 nm laser diode, the fiber exhibits a broad near-infrared (NIR) emission band consisting of three distinctive peaks at the wavelengths of 1100, 1420 and 1530 nm, originating from different luminescence centers, viz., Al-related, Si-related bismuth active centers (BACs) and Er3+, respectively. The relative emission intensities of the BACs and Er3+ vary in distinctively different manners with thermal treatment temperature are comprehensively studied. Three temperature regions, i.e., RT ∼ 300 °C, 300–800 °C, and 800–1100 °C can be distinguished accordingly. The instability of the BACs, formation of non-luminous bismuth centers and crystallization of the fiber are proposed to account for the thermal effects on the PL behaviors of the different luminescent centers in the fiber. A first-ever piece of information is also given concerning the PL reversibility of the various luminescence centers in the BEDFs.

Broadband stimulated emission generation in Er3+/Tm3+/Ho3+ codoped optical fiber rod

We demonstrate the broadband stimulated emission generation in the Er3 + / Tm3 + / Ho3 + codoped optical fiber rod (ETHOFR). The absorption spectra, broadband emission, energy level, electron transition process, and optical stimulated emission of this codoped material are analyzed. Broadband spectrum amplification from 1.7 to 2.1 μm is observed when ETHOFR is excited by 793-nm laser diode (LD). The optical gain shows similar wavelength in dependence on luminescence properties. This material holds potential in the application of weak optical signal amplification.

Development of Bi/Er co-doped optical fibers for ultra-broadband photonic applications

Targeting the huge unused bandwidth (BW) of modern telecommunication networks, Bi/Er co-doped silica optical fibers (BEDFs) have been proposed and developed for ultra-broadband, high-gain optical amplifiers covering the 1150–1700 nm wavelength range. Ultrabroadband luminescence has been demonstrated in both BEDFs and bismuth/erbium/ytterbium co-doped optical fibers (BEYDFs) fabricated with the modified chemical vapor deposition (MCVD) and in situ doping techniques. Several novel and sophisticated techniques have been developed for the fabrication and characterization of the new active fibers. For controlling the performance of the active fibers, post-treatment processes using high temperature, g-radiation, and laser light have been introduced. Although many fundamental scientific and technological issues and challenges still remain, several photonic applications, such as fiber sensing, fiber gratings, fiber amplification, fiber lasers, etc., have already been demonstrated.

Photo-bleaching mechanism of the BAC-Si in bismuth/erbium co-doped optical fibers.

Photo-bleaching of the silica-related bismuth active center (BAC-Si) in bismuth/erbium co-doped optical fibers is investigated. By analyzing dynamic spectral characteristics of BAC-Si, the photo-bleaching of the BAC-Si is found to be linked to the escape of an excited electron from the bismuth site in the BAC-Si. This mechanism of BAC-Si bleaching linked to an escaping excited electron is further confirmed with both photo-bleaching experiments by different laser pump wavelengths and a potential energy model describing the loss of an excited electron. Additionally, the temperature effect on the photo-bleaching, which is in good agreement with the above findings, is observed and discussed.

Optical properties of the Yb/Er co-doped silica glass prepared by laser sintering technology

Yb/Er co-doped silica glass is the critical core material in the fabrication for Yb/Er co-doped optical fiber. In this paper, we demonstrate the novel laser sintering technology for making the Yb/Er co-doped silica glass rod, and analyze its physical and optical properties. The experimental results show that the fabricated silica glass is amorphous, and Yb3+/Er3+ ions uniformly distribute in the glass matrix. The material presents very good emission property around 1535 nm, and the calculation result of the gain cross section also indicates the good gain property at the emission band. Moreover, the Judd-Ofelt analysis results show that the material has very attractive spectroscopic parameters. These results can be used as good reference for the fabrication of Yb/Er co-doped optical fibers used for high-power fiber lasers in the future.