The recent results on the new laser material – Bi-doped glasses and optical fibers are reviewed. First, luminescence properties of various Bi-doped glasses are discussed. At last the results of investigations of Bi-doped fiber lasers covering a wavelength range of 1150 – 1550 nm are presented.

https://iopscience.iop.org/article/10.1002/lapl.200910025/pdf

Bi-doped fiber lasers

Germania-glass-based core silica glass cladding single-mode fibers (/spl Delta/n up to 0.143) with a minimum loss of 20 dB/km at 1.9 /spl mu/m were fabricated by the modified chemical vapor deposition (MCVD) method. The fibers exhibit strong photorefractivity with the type-IIa-induced refractive-index modulation of 2/spl times/10/sup -3/. The Raman gain of 300 to 59 dB/(km/spl middot/W) was determined at 1.07 to 1.6 /spl mu/m, respectively, in a 75 mol.% GeO/sub 2/ core fiber. Only 3 m of such fibers are enough for the creation of a 10-W Raman laser at 1.12 /spl mu/m with a 13-W pump at 1.07 /spl mu/m. Raman generation in optical fiber at a wavelength of 2.2 /spl mu/m was obtained for the first time.

Germania-based core optical fibers

Over the past two decades, fiber laser technologies have matured to such an extent that they have captured a large portion of the commercial laser marketplace. Yet, there still is a seemingly unquenchable thirst for ever greater optical power to levels where certain deleterious light-matter interactions that limit continued power scaling become significant. In the past decade or so, the industry has focused mainly on waveguide engineering to overcome many of these hurdles. However, there is an emerging body of work emphasizing the enabling role of the material. In an effort to underpin these developments, this paper reviews the relevance of the material in high power fiber laser technologies. As the durable material-of-choice for the application, the discussion will mainly be limited to silicate host glasses. The discussion presented herein follows an outward path, starting with the trivalent rare earth ions and their spectroscopic properties. The ion then is placed into a host, whose impact on the spectroscopy is reviewed. Finally, adverse interactions between the laser lightwave and the host are discussed, and novel composition glass fiber design and fabrication methodologies are presented. With deference to the symbiosis required between material and waveguide engineering in active fiber development, this review will emphasize the former. Specifically, where appropriate, materials-based paths to the enhancement of laser performance will be underscored.

/pdf/materials-for-optical-fiber-lasers-a-review-2n45z3gaeq.pdf

Materials for optical fiber lasers: A review

We demonstrate a high-efficiency random lasing in a 850 m span of a phosphosilicate fiber. Random distributed feedback owing to the Rayleigh backscattering in the fiber enables narrowband generation with output power of up to 7.3 W at the Stokes wavelength λS = 1308 nm from 11 Wof the pump power at λP = 1115 nm. The laser demonstrates unique generation efficiency. Near the generation threshold, more than 2 W of output power is generated from only 0.5 W of pump power excess over the generation threshold. At high pump power, the quantum conversion efficiency defined as a ratio of generated and pump photons at the laser output exceeds 100%. Itis explained by the fact that every pump photon is converted into the Stokes photon far from the output fiber end, while the Stokes photons have lower attenuation than the pump photons.

/pdf/high-efficiency-generation-in-a-short-random-fiber-laser-3qvj85mzom.pdf

High-efficiency generation in a short random fiber laser

Cascaded lasing provided by Raman gain (at 1115-nm pumping) and random distributed feedback (via Rayleigh backscattering) in a 1.65-km phosphosilicate fiber is studied. Output power for the second Stokes component (1398 nm) exceeds 5 W at pump power of 11 W. In contrast to conventional cascaded Raman laser with high-Q cavity for the intermediate first Stokes component, there is no cavity here and no cavity losses, correspondingly. Longitudinal power distribution is shown to be quite different also. As a result, the efficiency of pump to 2nd Stokes wave conversion is not influenced by the intermediate stage and depends only on the integral attenuation in the fiber. Herewith, the number of generated 2nd Stokes photons at the output may even exceed the absorbed pump photons due to the lower attenuation of Stokes waves.

High-efficiency cascaded Raman fiber laser with random distributed feedback.

Characteristics of one-cascade (106 ⇒ 124 µ m) and two-cascade (106 ⇒ 124 ⇒ 148 µ m) phos- phorus-doped fiber Raman lasers are studied The cavities of both lasers are formed by Bragg gratings written directly in the active fiber Double-cladding Yb 3+ and Nd 3+ ion fiber lasers with λ ~ 106 µ m were employed for pumping These lasers were pumped, in their turn, by diode laser arrays with λ ~ 098 µ m (Yb) and λ ~ 081 µ m (Nd) The efficiency of the one-cascade laser with an unprecedentedly short length of 50 m was as high as 65% with 48-W pump radiation applied to the input of the laser The maximum efficiency of the two-cascade Raman fiber laser was 40% Gratings directly written in the active fiber reduced concentrated losses in laser cavities, which allowed the laser length to be decreased and the lasing threshold power of Raman fiber lasers to be low- ered

/pdf/highly-efficient-one-and-two-cascade-raman-lasers-based-on-16qrkpdu7z.pdf

Highly efficient one- and two-cascade Raman lasers based on phosphosilicate fibers

Summary form only given Lasers based on high P/sub 2/O/sub 5/-doped fibers can potentially have a higher efficiency than Raman fiber lasers (RFL) based on standard Ge-doped fibers An increase of phosphorus content in the fiber core gives rise to an increase of the Raman gain coefficient Despite a rise of optical losses, heavily P/sub 2/O/sub 5/-doped fibers enable one to develop extremely efficient Raman lasers A two-cascaded Raman laser based on a P/sub 2/O/sub 5/-doped fiber with the frequency shift of 1330 cm/sup -1/ per cascade and with Bragg gratings written directly in the P/sub 2/O/sub 5/-doped fiber demonstrated the highest ever achieved efficiency in RFL

1480 nm two-cascaded highly efficient Raman fiber laser

Strong photosensitivity of antimony oxide doped fibers under irradiation at 193 nm

Stress changes in hydrogenated phosphorous-doped fibers after Bragg grating inscription have been measured. Fibers with three different drawing tensions have been investigated. The core stress was found to increase independently of the initial stress state.

UV-induced stress changes in phosphorous-doped fibers drawn at different drawing tensions

Optical loss in a hydrogen-loaded phosphorus-doped fiber treated with a 193
nm ArF eximer laser light was studied. It follows from the experiments that additional
optical losses in the region of 1.0-1.6 µn must remain negligible after writing a Bragg
grating. Absorption spectra of the phosphorus-doped fiber after hydrogen loading and
UV-irradiation differ strongly from that of a germanium-doped fiber.

Y.V. Larionov

Papers

Highly efficient one- and two-cascade Raman lasers based on phosphosilicate fibers

1480 nm two-cascaded highly efficient Raman fiber laser

Strong photosensitivity of antimony oxide doped fibers under irradiation at 193 nm

UV-induced stress changes in phosphorous-doped fibers drawn at different drawing tensions

Influence of hydrogen loading and UV irradiation on optical properties of phosphorus-doped fibers