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Soliton-like thermal shock-waves in optical fibres: Origin of periodic damage tracks
No full textThe periodic damage track left after the passage of a soliton-like thermal shock-wave along an optical fibre is shown to arise through mode focusing in the thermal lens created by the shock-wave
Single-mode fibre grating written into Sagnac loop using photosensitive fibre: transmission filters
No full textFibre-based narrow band filters are of great importance in wavelength division multiplexing. Although narrow band reflection filters have been reported using in-fibre distributed grating reflectors, no experimental reports have been published so far of transmission filters
UV-induced refractive index changes in germanosilicate fibres
No full textPhoto-induced guided index changes approaching at both 633nm and 1.55µm, measured using a simple interferometric technique, are reported in germanosilicate single-mode optical fibres exposed to 266nm from the side
Enhanced photorefractivity in germanosilicate fibres: Effects of bleaching with 488nm Light
No full textPermanent index changes, Δn, of the order of 10-4 at 633 nm are induced in germanosilicate optical fibers by exposure to light at 488,266, and 240 nm. This photorefractivity has great potential in the fabrication of efficient grating-based devices for a wide range of WDM and lasing applications. It has been explained in terms of alterations in the UV absorption spectrum yielding (through the Kramers-Kronig relation) almost dispersion-free Δn values between 500 nm and 1.5 µm. The predominant cause is the movement of electrons from broken oxygen deficient Ge-Si bonds (associated absorption peak at 240 nm) to Ge(2) traps (when occupied by an electron an absorption peak appears at 213 nm) (see Fig. 1). The Ge-Si bonds can be broken by single-photon absorption of 240-or 266-nm light (permitting gratings of any period to be fabricated by side writing), or (much more slowly) by two-photon absorption (TPA) of 488-nm light. However, an undesirable side effect of 266-nm treatment is that the absorption induced for approximately the same Δn value is some two orders of magnitude larger than that obtained with 488-nm light (30 dB/m at 633 nm). This absorption is attributed to the creation of Ge(1) color centers, with a broad absorption peak centered at 281 nm and extending into the visible (Fig. 1). Because the balance between bleaching and trapping at Ge(1)and Ge(2) dopant sites is different for 266-nm light, it seemed possible that the population of Ge(1) centers could be depleted by 488-nm light, perhaps even enhancing the induced Δn
Optical damage in fibres: the fibre fuse
No full textWe demonstrate experimentally that catastrophic breakdown in the cores of optical fibres can be initiated thermally at modest optical intensities, forming periodic damage tracks uniform over several centimetres. The dynamics of this breakdown are investigated
Solitary thermal shock-waves and optical damage in optical fibres
No full textThermally-induced catastrophic optical breakdown is clearly of great importance for fiber-based laser-light delivery systems. Fiber core can be destroyed irreparably at rates of 1 m/s by breakdown that starts at a locally heated point and travels back towards the laser; that the damage tracks left behind are often elegantly uniform and periodic is only a slight recompense. Breakdown can occur at relatively modest intensities (we have recorded 2.8 mW/µm in a multimode fibre at blue/green wavelengths), and has been observed in many different fibres at both Ar+ and Nd:YAG laser wavelengths. We initiate the effect by heating the fibre with a small flame whilst the laser light is propagating within it. A solitary thermal shock-wave is created which propagates along the fibre towards the laser, leaving the core permanently damaged and unable to guide light. Associated with this shock-wave is a bright spot of side-scattered light which can be observed propagating along the fibre; for this reason we have named the effect the "fibre-fuse". Similar thermal shock-waves have previously been seen in gases ("laser-induced deflagration waves"
Single-mode tapers as 'fibre fuse' damage circuit-breakers
No full textThe 'fibre fuse' thermal damage effect can destroy kilometres of fibre at relatively modest laser powers. A low-loss tapered region strategically placed in a single-mode fibre can act as a thermal circuit breaker. thereby halting the damage propagation and protecting the fibre 'upstream' from the taper
Photoinduced refractive-index changes in germanosilicate fibres
Full text linkPhotoinduced guided index changes approaching 10-4 in the range 488-784 nm, measured using a simple interferometric technique, are reported in germanosilicate single-mode optical fibers exposed to the 488-nm line of an Ar+ laser running multifrequency. The wavelength dependence and dynamics of the writing process are characterized, and the material dispersion of the induced Δn(λ) is shown to be weak. The effect is placed in the context of related research on color centers in these fibers, and two different mechanisms are proposed that lead to quantitative estimates in rough agreement with the measured Δn values
Rocking filter formation in photosensitive high birefringence optical fibres
No full textParent et al. observed that the refractive index changes induced in optical fibres by Hill grating formation (at 488 and 514.5 nm) were birefringent. A wavelength filter, formed in a simple and novel way by exposing high birefringence fibre to linearly polarised 488nm light, is reported. Narrow bandwidth operation and high conversion efficiencies are achieved experimentally between the two orthogonal polarisation states of the fibre
UV-induced refractive index changes in Ce<sup>3+</sup>-doped fibres
No full textAn optically-induced index change of 1.4 x 10-4 has been observed when Ce3+-doped fibres were subjected to UV light at 266nm. The effect is comparable with that observed in Ge-doped fibres with the potential of being improved with higher dopant-level
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