Bi-doped Fiber Research Articles

Watt-level cladding-pumped bismuth-doped fiber laser operating near 1.31 [formula omitted]m

We report, to the best of our knowledge, the first CW bismuth-doped fiber laser operating at around 1.31 μm with an output power of >1 W utilizing a cladding-pumping configuration with multimode semiconductor laser diodes emitting at a wavelength of 793 nm. The Bi-doped fiber (BDF) serving as an active medium of the laser was based on a pedestal-index design, where P2O5−SiO2 glass core surrounded by P-doped cladding. The BDF construction offers advanced gain characteristics and an increased mode size (∼13 μm). The fiber preform was fabricated by the conventional modified chemical vapor deposition (MCVD) method combined with all gas-phase doping technique. The BDF with low-index polymer coating provided sufficient cladding peak absorption at 750 nm belonging to bismuth active centers associated with phosphorus atoms (BACs-P) that allowed to develop a continuous-wave laser with a linear cavity configuration and enable a maximum slope efficiency of ∼ 4% with respect to the absorbed pump power. In addition, near-field spatial intensity distribution of optical beam has good quality (M2<1.13) and close to Gaussian mode profile in x and y directions. The perspectives for optimization of BDF design and laser system configurations based on such fibers for further power scaling are discussed.

Supermode lasing and light amplification in multicore bismuth-doped fiber

Multicore fibers are promising structures with specific light propagation properties, which can be managed to benefit several applications in optical communications, fiber lasers and amplifiers, high-resolution imaging, and fiber-based sensors. The current use of multicore fibers in laser technology is mainly focused on in-phase coherent beam combining in far-field regions (out-cavity) using bulk optical elements. However, this approach is challenging in terms of the power scalability of all-fiber lasers (intra-cavity), particularly with using low-gain media, where it is needed to provide mode-coupling (supermode propagation) stability along relatively long lengths. Here, we report a conceptual design and fabrication of a multicore bismuth-doped fiber that is capable of achieving light amplification and stable lasing in the E-telecom band inside the cavity using the supermode selection approach. By analysis of experimental and simulation data, it was found that the employment of the proposed design of a Bi-doped fiber provides a considerable advantage over the single-core fiber in terms of laser performance (output power, slope efficiency) in the cladding-pumped configuration. These results open up new opportunities for further advancement of the optical fiber technology towards efficient bismuth-doped fiber-integrated amplifiers and lasers for the O+E+S+C+L+U-telecom bands, which may find important applications, especially for the development of next-generation multiband optical transmission systems.

High-gain ultra-wideband bismuth-doped fiber amplifier operating in the O + E + S band.

We present a double-pass bismuth (Bi)-doped fiber amplifier (BDFA) providing high-gain wideband amplification from 1330 to 1480 nm. A peak gain of 38 dB with 4.7 dB noise figure (NF) was obtained at 1420 nm for a -23 dBm input signal, with >20 dB gain from 1335 to 1475 nm. We achieved 30 and 21.5 dB peak gains with 122 nm (1341-1463 nm) and 140 nm (1333-1473 nm) 6 dB-gain bandwidth for -10 and 0 dBm input signal, respectively. For a 0 dBm signal, the power conversion efficiency (PCE) reached 23.7%, and the in-band optical-signal-to-noise ratio (OSNR) across the wideband BDFA was >44 dB. Also, the absorption and luminescence characteristics have been studied for different Bi-doped phosphosilicate fibers (BPSFs) fabricated in-house.

Control of temperature dependent viscosity for manufacturing of Bi-doped active fiber

Bi-activated photonic materials are promising for various applications in high-capacity telecommunication, tunable laser, and advanced bioimaging and sensing. Although various Bi-doped material candidates have been explored, manufacturing of Bi heavily doped fiber with excellent optical activity remains a long-standing challenge. Herein, a novel viscosity evolutional behavior mediated strategy for manufacturing of Bi-doped active fiber with high dopant solubility is proposed. The intrinsic relation among the evolution of Bi, reaction temperature and viscosity of the glass system is established. Importantly, the effective avenue to prevent the undesired deactivation of Bi during fiber drawing by tuning the temperature dependent viscosity evolution is built. By applying the strategy, for the first time we demonstrate the success in fabrication of heavily doped Bi active fiber. Furthermore, the principal fiber amplifier device is constructed and broadband optical signal amplification is realized. Our findings indicate the effectiveness of the proposed temperature dependent viscosity mediated strategy for developing novel photonic active fiber, and they also demonstrate the great potential for application in the next-generation high-capacity telecommunication system.

E-band telecom-compatible 40 dB gain high-power bismuth-doped fiber amplifier with record power conversion efficiency

Multi-band transmission is one of the key practical solutions to cope with the continuously growing demand on the capacity of optical communication networks without changing the huge existing fiber base. However, ultra-broadband communication requires the development of novel power efficient optical amplifiers operating beyond C- and L-bands, and this is a major research and technical challenge comparable to the introduction of the seminal erbium-doped fiber amplifiers that dramatically changed the optical communication sector. There are several types of optical fibers operating beyond C- and L-bands that can be used for the development of such amplifiers, specifically the fibers doped with neodymium, praseodymium, thulium, and bismuth. However, among these, Bi-doped fibers are of special interest as the most promising amplification medium because, unlike the others, different Bi-associated active centers allow amplification in an enormous band of overall width of 700 nm (1100–1800 nm). Such spectral coverage can be obtained by using different host materials, such as aluminosilicate, phosphosilicate, silica, and germanosilicate glasses. Here, we report a novel Bi-doped fiber amplifier with record characteristics for E-band amplification, including the highest power conversion efficiency among telecom-compatible E-band amplifiers reported to date. This bismuth-doped fiber amplifier (BDFA) features a maximum gain of 39.8 dB and a minimal noise figure of 4.6 dB enabled by 173 m Bi-doped fiber length. The maximum achieved power conversion efficiency of 38% is higher than that of L-band Er-doped fiber amplifiers. This performance demonstrates the high potential of BDFA for becoming the amplifier of choice in modern multi-band optical communication networks.

Cladding-pumped laser and amplifier for E- and S-bands based on multimode bismuth-doped graded-index fibers: toward "watt-level" output power.

In this Letter, we investigated the potential scalability of output power of a cladding-pumped laser and a power amplifier (booster) based on a multimode Bi-doped fiber (BDF) using the mode-selection approach. We fabricated the multimode double-clad graded-index (GRIN) fiber with a confined Bi-doped germanosilicate glass core with a diameter of ≈30 and ≈60 µm. Using femtosecond (fs) inscription technology with high spatial resolution, Bragg gratings of a special transverse structure allowing the selection of low-order modes were written into the core of BDFs. The operation features of the cladding-pumped multimode bismuth-doped GRIN fiber lasers with the inscribed Bragg gratings with various reflection coefficients were investigated. In addition, the behavior of the output power and the beam quality (M2 parameter) of the optical radiation of the developed devices was studied. The CW laser and booster operating at nearly 1.45 µm with maximum output powers of ≈0.8 and ≈1 W, respectively, based on the 60-µm-core BDF under pumping by multimode laser diodes at 808 nm were developed, which are, to the best of our knowledge, the most powerful cladding-pumped BDF devices to date. Near single-mode lasing (M2 <1.3) is demonstrated for a 30-µm-core fiber. The experimental data open new possibilities to achieve higher powers in cladding-pumped BDF sources, which are more cost-effective compared to core-pumped counterparts.

Formation of E-band luminescence-active centers in bismuth-doped silica fiber via atomic layer deposition.

In this study, a Si defect structure was added into the silica network in order to activate the bismuth and silica structure active center. TD-DFT theoretical simulations show that the Bi and Si ODC(I) models can excite the active center of the E-band at 1408 nm. Additionally, the Bi-doped silica fiber (BDSF) with improved fluorescence was fabricated using atomic layer deposition (ALD) combined with the modified chemical vapor deposition (MCVD) technique. Some tests were used to investigate the structural and optical properties of BDSF. The UV-VIS spectral peak of the BDSF preform is 424 cm-1, and the binding energy of XPS is 439.3 eV, indicating the presence of Bi° atom in BDSF. The Raman peak near 811 cm-1 corresponds to the Bi-O bond. The Si POL defect lacks a Bi-O structure, and the reason for the absence of simulated active center from the E-band is explained. A fluorescence spectrometer was used to analyze the emission peak of a BDSF at 1420 nm. The gain of the BDSF based optical amplifier was measured 28.8 dB at 1420 nm and confirmed the effective stimulation of the bismuth active center in the E-band.

Tunable ultra-broadband multi-band NIR emission in Bi-doped aluminogermanate glasses and fibers via controllable Al2O3 content for broadband amplifiers

The tunable ultra-broadband multi-band NIR emission of Bi-doped germanate glass and fiber can be achieved via constructing various glass local network environments with steerable Al2O3 content and show potential applications in broadband amplifiers.

Ultra-Wideband Amplification in Telecom Bands with Bi-Doped Multi-Layered Glass Fibers

Ultra-Wideband Amplification in Telecom Bands with Bi-Doped Multi-Layered Glass Fibers

Research on High Absorption Germanosilicate Bi-Doped Fiber and Its Gain Performance

Research on High Absorption Germanosilicate Bi-Doped Fiber and Its Gain Performance

Bi-doped fiber amplifiers in the E + S band with a high gain per unit length.

We present a bismuth (Bi)-doped fiber amplifier (BDFA) operating in the 1400-1480 nm range using 35 m of Bi-doped germanosilicate fiber. A maximum gain of 23 dB for an input signal of -23dBm at 1440 nm has been achieved, which, to the best of our knowledge, is the highest gain per unit length of 0.66 dB/m reported for a BDFA. The 3 dB bandwidth is measured to be 40 nm (1415-1455 nm), and the gain coefficient is 0.2 dB/mW. A further temperature dependence study of BDFA across the temperature range of -60°C to 80°C also showed a negligible effect of temperature on the E + S band BDFA gain.

Random Laser Operating at Near 1.67 µM Based on Bismuth-Doped Artificial Rayleigh Fiber

A narrow-linewidth bismuth-doped fiber laser (BDFL) with the random cavity and operational wavelength at 1.67 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m was demonstrated. The laser cavity was formed by an array of weakly reflecting fiber Bragg gratings inscribed in the active fiber core directly during the fiber drawing process. Taking into account the performed analysis of optical and laser properties, the viability of this approach as applied to Bi-doped fibers with high-GeO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> -SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> glass core is shown, even despite the high sensitivity of bismuth active centers (BACs) to laser irradiation, i.e. processing does not lead to the destruction of the BACs. The maximum output power of the developed BDFL in a simple linear configuration with the use of 200 m-long bismuth-doped active fiber was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 20 mW at room temperature when pumped by Er-Yb fiber laser at a wavelength of 1568 nm and the total power of 450 mW. The achieved width of the laser emission line was narrower than 0.02 nm. We studied the laser behavior in various configurations, and it was revealed that the laser wavelength can vary within the spectral range of 1.669–1.674 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m in dependence on the length and the ambient temperature of the active fiber. It was most likely caused by inhomogeneous distribution of the written gratings structures along the active fiber length that was induced due to the peculiarities of the used active fiber, namely, a significant core ellipticity. In addition, we demonstrated the possibility of the output power scalability of this type of lasers by using a homemade Bi-doped fiber power amplifier. As a result, the optical power of the random BDFL was increased up to 240 mW.

Highly Efficient O-Band Rectangular Pulse Emission in a Figure-of-Nine Bismuth-Doped Fiber Laser

Highly efficient rectangular pulse emission is significant in high energy O-band applications due to the zero dispersion of standard telecom optical fiber in the second telecommunication window. The rectangular pulse emission offers the peak power clamping, which avoids wave-breaking and maintains the fundamental repetition frequency with arbitrarily widened temporal pulse width of ultrafast laser at high pump powers. The current technology in the O-band rectangular pulse emission achieves the maximum pulse energy of ∼30 nJ with an efficiency of ∼1.06%. Here, we fabricated a single-mode bismuth-doped phosphosilicate optical fiber by the modified chemical vapour deposition technique. The Bi-doped phosphosilicate optical fiber was characterized by a peak absorption of ∼0.6 dB/m at 1250 nm and a high gain coefficient of ∼0.22 dB/m at 1320 nm. These parameters contribute to the generation of rectangular pulse with a pump power threshold of ∼227.7 mW in a figure-of-nine laser cavity. The maximum pulse energy was achieved as ∼197.7 nJ, whereas the laser efficiency is ∼14.3%. We presented an O-band rectangular pulse emission with the highest pulse energy and efficiency as compared to previous studies, whilst its all-fiber laser setup is robust and feasible for high pulse energy applications.

17-dB Net Gain of Broadband Single-Mode Cr-Doped Crystalline Core Fiber Fabricated by Small Core

A record net gain of 17-dB has been demonstrated in a 300-nm broadband single-mode Cr-doped crystalline core fiber (CCF) with a 19-μm core diameter and 18-cm fiber length. The gain-per-unit-length of the CCF, which is an impressive 94 dB/m, is significantly higher than that currently achieved in other rare-earth doped fiber amplifiers, such as Er and Bi-doped fibers. This high gain was achieved by matching the transmission mode between CCF and single mode fiber for improving the coupling efficiency. We controlled precisely the conical molten-zone in the growth process, as well as the optimization of the Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> concentration through thermal annealing and polarization pumping techniques. We also measured the noise figures of several core diameters, finding that the 19-μm core diameter CCF exhibited a noise figure 4.2 dB lower than the previous 25-μm core diameter CCF. This result is important because it indicates that the smaller diameter CCF is capable of providing even better signal-to-noise ratios. And the error-floor free data transmission of the CCF was successfully demonstrated at a rate of 10 Gb/s. This is an important achievement because it shows that the CCF has the potential to be used in high-speed communication applications.

Tailoring optical properties of bismuth-doped germanosilicate fibers for E/S band amplification

Bismuth-doped germanosilicate optical fibers can operate in the E-,S-,C-,L- and U- telecommunication bands, depending on the pumping wavelength. However, the unclear origin of bismuth NIR luminescence limits the field progress. Herein, we focus on E- and S-band optical properties and demonstrate, for the first time, that number density of bismuth active centers (BACs) with a characteristic absorption at ∼1400 nm and, consequently, luminescence and gain in the E- and S-band, can be considerably tailored and increased through glass composition, preform and fiber fabrication conditions. Contrary to previous studies that pointed to low GeO2 content, ∼5 mol%, to present luminescence in this spectral region, we found that, increasing the Ge content in the glass matrix actually enhances the luminescence and the gain. Our study provides new insights into the nature of these BACs and prospects for tailoring spectroscopic properties in Bi-doped germanosilicate optical fibers for E- and S-band fiber amplification.

Cladding pumped bismuth-doped fiber amplifiers operating in O-, E-, and S-telecom bands.

Bismuth-doped fibers (BDFs) are considered nowadays as an essential part of the development of novel optical amplifiers, which can provide a significant upgrade to existing fiber optic telecommunication systems, securing multiband data transmission. In this paper, a series of BDF amplifiers (BDFAs) for O-, E-, and S-telecom bands based on a cladding pumping scheme using low-cost multimode semiconductor laser diodes at a wavelength of 0.7-0.8 µm were demonstrated for, it is understood, the first time. The developed BDFAs are characterized by a high peak gain of >25-30 dB in the corresponding telecom bands and a relatively low noise figure of 5-6 dB. Comparative analysis shows that most of the parameters of cladding pumped BDFAs are close to those of the best core pumped ones. This research opens up new opportunities for utilizing Bi-doped fibers as a key element of cost-effective and ready-to-work BDFAs for various practical applications.

Output Power Saturation Effect in Cladding-Pumped Bismuth-Doped Fiber Lasers

In this article, output power characteristics of cladding-pumped lasers based on bismuth-doped phospho- and germanosilicate core glass fibers were thoroughly studied and analyzed. The developed lasers are capable of providing the output power of several hundred milliwatts with the slope efficiency close to 1%. The output power saturation for the Bi-doped germanosilicate fiber laser and absence of the saturation regime for the Bi-doped phosphosilicate fiber one was found. This effect is explained by a relatively long relaxation time of bismuth active centers (BACs), namely a non-radiative transition from the higher-lying pump level to the upper laser (metastable) level in the corresponding energy levels diagram. The experimentally obtained data are in good agreement with the results of numerical simulation. In addition, it was investigated that the relaxation time of the BACs from the higher-lying level can have a significant impact on the laser efficiency and the achieved output power. The consequences caused by the saturation effect is possible to overcome with dual-wavelength pumping (combining cladding-pumping at 808-nm wavelength and core-pumping at a wavelength in the range of 1930 – 2040 nm), which provides both the BACs excitation and the stimulated relaxation of BACs from the excited (pump) state to the upper laser level. Using this approach the output power of the Bi-doped fiber laser was increased by almost two times.

1.3/1.4 µm dual-wave band dissipative soliton resonance in a passively mode-locked Bi-doped phosphosilicate fiber laser.

We report the 1.3/1.4 µm dual-wave band dissipative soliton resonance (DSR) in a passively mode-locked bismuth-doped phosphosilicate fiber (Bi-PSF) laser. The low-water-peak Bi-PSF with two bismuth active centers associated with silicon and phosphorus supports the O+E-band gain. Using a 1239 nm home-made Raman fiber laser as pump source and nonlinear amplifying loop mirror for initiating mode-locking, stable DSR operation at 1343 and 1406 nm is achieved with the spectral bandwidth of 12 and 16 nm. The pulse duration with the pump power increases from 62 to 270 ps with a repetition frequency of 4.069 MHz. The average power is 11.05 mW corresponding to the maximum energy of 2.7 nJ. This is, to the best of our knowledge, the first demonstration of a mode-locked fiber laser in the ∼1.38 µm water absorption band and the O+E dual-wave band operation for applications in all-spectral-band communications, bio-medical imaging, and terahertz difference frequency generation.

Research progress on ultra-broadband luminescence of Bi-doped glass and fiber (invited)

Research progress on ultra-broadband luminescence of Bi-doped glass and fiber (invited)

(INVITED) Bi-doped optical fibers and fiber amplifiers

Bismuth (Bi)-doped aluminosilicate, phosphosilicate, germanosilicate and high (⩾50 mol%) germanosilicate fibers have shown luminescence around 1.15 μm, 1.3 μm, 1.45 μm and 1.7 μm, respectively. Bi-doped fibers have paved the way for developing optical amplifiers and fiber lasers in the wavelength region of 1150–1500 nm and 1600–1700 nm, where it can serve a wide range of applications in astronomy, imaging, medicine and advanced optical communications. However, spectroscopic study is required to understand the nature of near-infrared (NIR)-emitting Bi active centers (BACs) to improve the efficiency of Bi-doped fiber amplifiers and lasers. In this paper, we review the luminescence properties of Bi-doped glasses as well as Bi-doped fibers with aluminosilicate, phosphosilicate, and germanosilicate glass hosts. Absorption and emission cross-sections of Bi-doped phosphosilicate fibers are reported. In addition, we review the current state of the art of Bi-doped fiber amplifiers development in the second telecom window (O-band) and in the E-band and S-band for the next-generation high-capacity optical communications.