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Three single-mode fibers have been drawn from each of four MCVD-made pure-silica-core F-doped-silica-cladding preforms, the drawing parameters (temperature, speed, and tension) being varied among the fibers in a controlled fashion. The initial optical loss spectra in the range 200-1700 nm as well as radiation-induced attenuation (RIA) spectra in the near-IR range under γ-irradiation to 82 kGy (7.6 Gy/s) are measured in the fibers. RIA is found to increase significantly with increasing the drawing temperature and to increase much less with increasing the speed and tension. The mechanism of the strong drawing temperature effect on RIA is argued to be associated with a rise in the fiber silica fictive temperature, which, in turn, enhances the concentration of strain-assisted radiation-induced self-trapped holes.

An all-fiber ultrafast dissipative soliton laser at 1.3 microns based on phoshosilicate fiber doped with bismuth is presented. A nonlinear optical loop mirror containing high-germanium fiber with high nonlinearity and large positive dispersion was used. The scheme yields 11.3 ps pulses with energy of 1.7 nJ at repetition rate of 3.5 MHz. By means of bismuth-doped fiber amplifier and diffraction gratings compressor, the pulses were amplified up to 8.5nJ and compressed down to 530 fs. To achieve best results the optimal bismuth active fiber was chosen according to the investigated dependence of the gain coefficient on bismuth active centers concentration in phosphosilicate fibers.

For the near IR spectral region from 1150 to 1800 nm, including the ranges from 1250 to 1500 nm and 1600 to 1800 nm where efficient rare-earth-doped fiber lasers don’t exist, bismuth-doped optical fibers are promising active materials. The last two spectral ranges are of great interest for some applications, in particular for optical fiber communication. Earlier, we developed Bi-doped fiber lasers and optical amplifiers operating in the first of these spectral ranges. Here, we report new results on the development of bismuth-doped optical fibers and fiber lasers for a spectral range of 1600-1800 nm.

We describe composite optical fibers with rare-earth co-doped phosphate-glass core in a silica-glass cladding. High RE-ion concentrations in the phosphate core of the composite fiber allow fiber length reduction in comparison with silica fibers. The silica cladding provides high mechanical strength and protects the phosphate core from air moisture while making it easier to splice with silica fibers.

We have studied the photodarkening effect in fiber preforms with an ytterbium-doped aluminosilicate glass core. The room-temperature stable Yb2+ ions formation in the glass matrix under both UV- and NIR-pumping irradiation was revealed by the method of absorption spectra analysis and the fluorescence spectroscopy technique. Comparative studies of preforms and crystals samples luminescence spectra, obtained under UV-excitation, were performed. A general mechanism of Yb2+ ions and aluminium oxygen-hole centers (Al-OHC) formation as a result of photoinduced process of Yb3+ ions excitation to "charge-transfer state" (CTS) was found for both Yb:YAG crystal and aluminosilicate glass.

A germanium-doped silica-core fiber with an active region in the form of a thin ring of silica doped with bismuth ions was fabricated. Bismuth doping in the ring surrounding the core allows to stabilize bismuth in silica glass, and it does not impose any restrictions on the composition of the core. The bismuth concentration in the ring is less than 0.2 wt.%. The GeO2 concentration in the core is more than 15 mol.%. A high germanium concentration in the core allows to shift the zero dispersion wavelength to 1860 nm and to obtain a high nonlinear refractive index (n2 more than 3,2*10-20 m2/W). Spectroscopic investigations were carried out in the visible and near infrared (800-1700 nm) spectral range. Despite the small concentration of bismuth, we observed the absorption and luminescence characteristic bands, confirming the presence of bismuth active centers in silica glass. Upon pumping at 1350 nm the on/off gain spectrum was measured on a 20-m fiber. The gain was observed throughout investigated range of 1430-1530 nm. The maximal gain of ~9.5 dB was obtained near 1430 nm. The results of the spectroscopic investigations of the fiber with a thin active Bi-doped ring showed prospects of the creation and application of such fiber type for laser and nonlinear optics.

Although singlemode fiber lasers become a mature technology, enhancements, in terms of output power, spatial beam quality, bend insensitivity are still required. A major trend is to increase the active core area to increase the thresholds of nonlinear effects while ensuring a transverse singlemode beha vior. Actually, increasing the active ions’ concentration is also demanded since it allows a drastic reduction of the fiber length, everything being equal. Two non-exclusive strategies are laid out to overcome fiber laser limitations. On the one hand, it is demonstrated that surrounding a highly multimode active core by a properly designed microstructured cladding, exhibiting specific resonant features, allows the fiber laser to be operated in the singlemode regime. On the other hand, a large mode area photonic bandgap fibre is shown to lead to a transverse singlemode fibe r laser with very good lasing efficiency. Keywords: Fiber laser, all-solid microstructured cladding, photonic bandgap fiber.

Bi-doped glass optical fibers are a very promising active laser medium. Luminescence of Bi-doped glasses takes place in a spectral region of 1100-1500 nm [2], where no fiber lasers (or any other efficient lasers) exist. The glasses have very broad luminescence bands (200-400 nm) and long lifetime (200-700 μs). The Bi absorption bands are situated in a spectral region of 500-1100 nm where long-lived high-brightness laser diodes developed for the pumping of lasers and amplifiers are available. Besides, strong luminescence has been observed in a variety of glass compositions. However, up to 2005 there had been no reports on the fabrication of Bi-doped optical fibers. The first Bi-doped optical fibers were fabricated in 2005 [5,6] and that year the first Bi-doped fiber laser was constructed [7]. In this paper 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. Then we describe the Bi-doped silica-based optical fiber fabrication by MCVD technique and the absorption and luminescence properties of the fibers. At last the results of investigations of high-power Bi-doped fiber lasers are presented.

The delivery or generation of high power in optical fibre requires the increase of the core size to increase the threshold of nonlinear effects and the damage threshold. However the bend loss strongly limits the increase of the effective area (A eff ). All-solid photonic bandgap fibres are attractive for the delivery of power since they can be made singlemode whatever the core diameter is. Moreover the silica core can be doped with rare-earth ions. A Bragg fibre is a bandgap fibre composed of a low index core surrounded by N concentric layers of high and low index. We have fabricated Large Mode Area Bragg fibres by the MCVD process. These Bragg fibres present a ratio A eff /λ 2 close to 500. A first Bragg fibre, defined by N = 3 and an index contrast between the cladding layers Δn = 0.01, exhibits a measured critical bend radius R c close to 16 cm (bend loss equal to 3 dB/m). Increasing the index contrast Δn leads to a tighter field confinement. The field distribution of the guided mode strongly decays in the periodic cladding and is thus less sensitive to bending. We propose here the design of an improved Bragg fibre with a very large index contrast Δn = 0.035 which leads to a dramatic reduction of the bend loss. The critical bend radius was measured to be lower than 3 cm. This fibre is less bend sensitive than an equivalent solid core fibre, either a step-index fibre or a photonic crystal fibre.

applications. 2 im laser sources are potentially usefull for a variety of atmosoheric, space applications and medicalequipment. 2 trn fiber laser based on the thulliurn 3F4 —3H6 transition has been demonstrated [1]. In Ref. [2] Yb:Tmfiber laser has been reported, in which the optical pump excites the Tm ions indirectly, via energy transfer from Ybions. Investigation of processes of nonradiative energy transfer between Yb3 and Tm ions in a fiber core glass isnot only of pure scientific interest but also of significant practical one since such processes can define the essentialparameters of lasers based on such fibersWe have studied the processes ofnonradiative energy transfer between Yb3 and Tm ions in alumosilicatefibers.

The fast mode of optical discharge propagation in optical fibres was observed. In contrast to the known fibre fuse effect such optical discharge propagation is accompanied by fibre cracks and velocity reaches≈3km/s under the intensity 40W/ μm 2 .

The influence of hydrostatic densification of the parameters of the 3.15-eV luminescence and on the efficiency of photocoloration of germanosilicate glass is investigated. A four-fold decrease of the luminescence intensity under excitation at both 5 eV and 3.7 eV is revealed after 19% densification of the glass. A mechanism of relaxation of excitation of germanium oxygen-deficient centers is proposed based on the model of bistable oxygen vacancy. This mechanism explains the high sensitivity of the 3.15-eV luminescence to strain and temperature quenching.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Academy of Sciences of the USSR,117942 Moscow, 38 Vavilov street, phone number 135- 82 -96.AbstractThe necessity to take into consideration the absorption by free carriers in silverand thallium halides for the evaluation of minimal optical losses in these materials andfibers from them in the range 2 - 25Jnm is pointed out for the first time. It is shownthat the absorption by free carriers exceeds for 1 - 2 orders the previous minimal lossevaluations and its value is found to be 10-1 - 10-2 dB /km.IntroductionRecently there has been a considerable growth of interest in the materials whose hightransparence range lies within the middle infrared. It is the possibility of obtaining thematerials with ultimate low losses

A new type of halide glasses, based on coordination compounds of the chlorides, bromides and heavy metals have been proposed. The formation of the halide glasses and their property will be discussed on the basis of suggested sheme of cluster compound formation. The paper also deals with the fabrication of silver and thallium halide fibers with axial-symmetric index profile by extrusion;the starting billet has the same cross-sectional profile.The resultant step-index and quasi gradient -index profile fibers had optical losses from 0.4 to 1.0 dB/m at 10.6 μm and good mechanical properties. Also we studied the mechanical properties of new waveguides extruded from AgBr-AgI and KRS-13-AgI solid solution crystals and numerically calculated the optical losses induced by silver colloides in AgHal-materials. The UV-resistance of silver halide fibers of different composion have been investigated. This losses depend on composion and state of fiber.

The results on the designing of the first diode laser spectrometers for the middle IR region using crystalline fibers from KRS-5 or KRS-13 are presented. The advantages of the fiber diode laser spectrometers and gas monitors provide the simplification of their constructions and the substantial widening of their applications without the deterioration of spectral resolution 0.005 cm-1.

Crystalline fibers are considered as the most promising fibers for the region 5÷20 μm. The relation of optical and mechanical characteristics of fibers with parameters of the initial crystals and their extrusion is shown. The mechanisms of optical losses including those induced by ∝ - or UV-radiation are discussed together with the optical damage of fibers, induced by continuous or pulsed radiation of CO2-laser.

The paper deals with the investigation of optical and mechanical properties of polycrystalline fibers from silver and thallium halide crystals. The dependence of the fiber properties on the fabrication conditions as well as the influence of the stretching stresses and UV irradiation on the optical losses and also their resistance to the pulsed CO 2 -laser radiation are discussed. The fabrication of the first AgCl-cladded KRS-13 fibers isreported.

KRS-5 and chalcogenide glass fibers have been developed with optical losses of several hundreds of dB/km at CO-and CO2-lasers wavelengths.

The achievement of compact, reliable and multifunctional surgical CO 2 laser units with specialized beam delivery systems opens new prospects for extending the clinical use of lasers.

Some promising materials for mid-IR fibers with low losses have been fabricated and investigated. Among them germanium dioxide glass, chalcogenide glasses and thallium halide crystals.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The results on the investigation of optical and mechanical properties of polycrystalline IR fibers from the point of view of their application in power delivery for laser surgery are discussed in the talk.

We have considered the mechanism of plastic deformation of T1 and Aq halide crystals under extrusion of polycrystalline fibers. The influence of the extrusion parameters on the structure as well as on the optical and mechanical properties of the fabricated fibers is examined.

The continuous expanding of CO 2 laser applications in medicine needs not only compact, reliable and multifunctional surgical CO 2 laser units, but also specialized beam delivery systems, which are essential to extend the clinical use of lasers. Our effort for improving the surgical CO 2 laser units was directed to : a) developing compact CO 2 laser scalpels, reliable and more suitable for the surgical operating theatre by using high performance with low maintenance average power sealed-off CO 2 lasers; b) designing specialized electronic circuits to increase the protection degree against uncontrolled irradiation by technical failures or wrong manipulation; c) extending the operating regimes, i.e. continuous wave, laser pulses with pre-established length and laser pulses with variable repetition frequency. The beam delivery systems used with our surgical CO 2 lasers units included opto-mechanical articulated arms, IR fiber optic cables and laser microscope adaptors. Coupling different CO 2 laser scalpels, beam delivery systems and terminals, we have tested these surgical laser units in neurosurgery, otolaryngology,,ophthalmology and microvascular lympho-venous anastomosis. The most significant data recorded by us on the interaction of laser radiation with living matter are shortly reviewed.

We report measurements of damage threshold and transparency of quartz fibers for the λ= 248, 308 and 351 nm radiation. Thresholds and specific energy for tissue photoablation have been determined for these wavelengths. Results of clinical applications of UV fiber laser scalpels for angioplasty and extirpation of tumours from bronchi are discussed.

The extinction coefficients of SeH and SH groups were measured for Se, As-Se and As-S glasses. The As-S and As-Se glass fibers were drawn from the melt with low optical losses: As-Se fiber - 76 dB/km at 4.4μm and 96 dB/km at 5.2 μm, As-S fiber - 44 dB/km at 2.5μm. The mechanical strength of fibers was also measured.

Investigations of optical losses in silicone-clad fibers immersed into water have shown that water diffusion through the reflecting cladding results in the loss increase, which is of a reversible character. Such fiber can easily be integrated in an optical fiber cable; water penetration can then be localised by the back-scattering method.

Results on the growing of single-crystal sapphire and heavy metal halide fibers from the melt by Stepanov's method (capillar technique) are reported. In order to minimise the optical losses due to surface imperfections single-crystal halide graded-index fibers with the total diameter between 0.2 and 1.2 mm and length up to 7-8 m were grown. The pre-sence of a crystalline cladding allowed to lower the surface scattering losses of graded-index fibers down for 5-10 times in comparison with unclad fibers.

Different types of memories on the base of fiber optic round circuits of the data recirculation are presented. The main physical aspects of their creating necessary for the construction of various systems for the signal processing and optical computing are con-sidered. The first system for the analog and parallel digital signals processing on the base of a multichannel digital fiber optic memory and a microcomputer has been constructed. For the ultrafast data processing we have suggested and studied a block scheme of the optical memory operating on ultrashort light pulses - solitons. It is shown that in the fiber memory devices operating on solitons with Raman amplification the nonlinear filtering of the noise and soliton components of the field as well as the long-time data storage without noise accumulation can be realized.

The mechanisms of light scattering losses ∝ s in fibers fabricated by plastic deformation of silver and thallium halide crystals have been analysed. It was found that the power index 7 in the loss dependence on wavelenght λ(∝ s ~λ -7 ) continuosly changes in the range -0.5 s and η by evolution of the micropores distribution and by exsistence of vacancy excess in fibers. The average diameter D of effective micropores and their concentration N are determined from the spectra We observed these micropores in KRS-5 and KRS-13 polycrystalline fibers.

A new design of Y-type end-fused single-mode fiber directional couplers has been suggest ed, and its optimum parameters with which it is possible to obtain losses of 0,5-1 dB have been determined. Cross-talk attenuation between reverse channels exceeds 60 dB. It has been found by experiments that transmission coefficients of the developed couplers are stable at wavelength variations. Furthermore, Y-type directional couplers maintain polarization state of the propagating radiation. Simple Michelson interferometer based on Y-type fiber optic directional couplers with a new optical fringe visibility registration system for the narrow linewidth( uV) = 10 kHz - 1 MHz) analysis of the single-frequency lasers has been created.

Chalcogenide glass optical fibers with optical losses of 0.3-1 dB/m in the 3.5-7 I'm wavelength region have been obtained. The fibers optical properties as well as the dependence of their optical losses on low temperature and time have been investigated.© (1986) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

UV and gamma induced colour centres in germanium -doped silicaglass and fibersV.B.Neustruev, A.N.Guryanov *, E.M.Dianov, V.F.Khopin; V.M.Kim,V.M.Mashinsky, M.V.Romanov, V.A.Tikhomirov **General Physics Institute, Academy of Sciences of the USSR38 Vavilov Street, Moscow 117942, USSR* Institute of Chemistry, Academy of Sciences of the USSR49 Tropinin Street, Gorky 603600, USSR** Institute of Nuclear Physics, Moscow State UniversityMoscow 119899, USSRABSTRACTInduced optical losses and paramagnetic Ge(n)- centres have been investigated in germaniumdoped silica glass and optical fibers after gamma- and UV- irradiation. It has been foundthat all the excitations created the similar effects. By means of selective photoexcitationGe(1 and 3)- centres were identified in optical spectra presumably as the induced absorptionbands at 4.4 eV and 6.2 eV, respectively. Moreover, for Ge(1)- centre photobleaching takesplace under 266 nm excitation. In optical fibers we have observed no difference in X- andUV- induced loss spectra in the wavelength range from 480 nm to 1900 nm. We have foundpartial reversibility of the photo -colouration.The comparison of samples prepared by MCVD, VAD and PCVD techniques has been made. Theorigin of the dominant colour centres and their contributions to the irradiative inducedlosses are discussed.1. INTRODUCTIONInitial and induced absorption spectra of Ge -doped silica glass differ f om those ofpure silica by strong UV- absorption bands caused by Ge _colour centres (CC).£-5 Complex242 nm -band increases at more reductive conditions,1,294 thereby it is assumed that Ge -CCare caused by oxygen deficiency in the first coordination sphere of Ge -atom.There is noconventtional model of Ge -CC. The two -fold coordinated Ge atom 6, oxygen vacancy? and Ge +-centre' are discussed as versions.Properties of Ge -CC as well as their changing after irradiation have been discussed ina great number of papers.6'899,10 Paramagnetic E'(Ge)- centres (or Gekn)- centres) have beenobserved after ionizing irradiation 11,11, including photoexcitation 1). A lot of datahave been reported on the radiation damage of Ge -doped silica -core optical fibers in visibleand near -infrared spectral regions. -4 -16 Several papers have be n published on the photo

The polarization properties of the monomode fibers with low and high birefringence were investigated using the radiation sources of various spectrum widths. The gyroscopes on the base of fibers with low birefringence were investigated.