1,721,003 research outputs found
Devices based on second-order nonlinear effects in glass fibres
No full textTechniques for the generation of second-order non-linearities in optical fibres are described. Applications to non-linear frequency-optic modulation via the Pockels effect is demonstrated
Cladding-pumped passive harmonically mode-locked fiber laser
Full text linkA passive harmonically mode-locked fiber laser cladding pumped by a broad-area diode-laser array is described. Harmonic mode locking is obtained in a frequency range from 33.3 to 128.6 MHz, where the higher frequency limit is imposed because of insufficient available pump power. The maximum pulse jitter in one cavity round-trip time is between 300 and 50ps in the whole frequency range, and the sidebands in the frequency domain are suppressed by as much as 50dB. 600-fs bandwidth-limited pulses with pulse energies of as much as 20pJ are obtained, giving rise to an average output power as great as 2.5m
Frequency doubling of 1.319µm radiation in an optical fibre by optically written χ(2) grating
No full textFrequency doubling of 1.319µm radiation by an optically-written χ(2) grating in a single-mode optical fibre is reported. A peak power of 25mW at 659nm was generated in 13cm of fibre. Phase matching is achieved by periodic modulation of the nonlinear susceptibility. Third harmonic generation of ultraviolet radiation is shown to be responsible for the creation of defect centres
Poling techniques for optical fibers
No full textNormally, only non-centro-symmetric crystalline materials exhibit second-order optical non-linearities. A material with a large second-order non-linearity is required for use in second-harmonic generation, Pockels modulators and parametric oscillators. Glass, being an amorphous material, exhibits the usual third-order non-linear behaviour, but not second-order effects. However, poling of an optical fibre by simultaneous excitation and orientation of defect centres has recently been demonstrated and leads to the creation of permanent, large second-order non-linearities
Fabrication of low-loss optical fibres containing rare-earth ions
No full textFibres containing rare-earth ions have been produced by an extended MCVD process. The fibres have very high absorption levels in the visible and near infra-red regions, without significantly compromising the low-loss characteristics of the fibre at wavelengths between 950 and 1400 nm
Temperature sensing by thermally induced absorption in a neodymium doped optical fibre
Full text linkAbsorption of 1.06µm radiation in neodymium-doped fibre and subsequent anti-Stokes fluorescence is observed in neodymium-doped fibre at elevated temperatures. The increase in absorption is used as the basis for a distributed temperature sensor over the range 20-800°C. The temperature dependence of fluorescence at 940nm is used in an optical fibre point temperature sensor
Non-linear transmission in germanosilicate fibres at blue/green wavelengths
No full textMany fibre-based devices rely on the ability to transmit light at high intensities down single-mode fibres. Examples are fibre lasers, amplifiers, second-harmonic generators and simple fibre-based high power delivery systems. It is thus important to know whether any non-linear processes exist that could restrict the usefulness of the fibres used in these applications. Brown et al have reported that non-linear effects of this kind do indeed occur at Argon ion wavelengths in germanosilicate fibre, limiting the power that can be delivered to some tenths of a W over only few-metre lengths of single-mode fibre. In this paper we report the chief results of an extensive investigation into this effect in germanosilicate HiBi fibres designed to transmit single-mode blue/green light. These observed non-linearities in the transmission of CW blue/green light cannot be attributed to conventional non-linear processes (such as stimulated Raman or Brillouin scattering) because only short (few-metre) fibre lengths are needed, the thresholds are low, and the effect is insensitive to laser line-width. We have indicated that this non-linear behaviour can be explained by the creation (via two-photon absorption - TPA) and bleaching (via normal absorption) of colour-centres. TPA enables blue/green photons to reach UV energy levels that are sufficient to disrupt the glass matrix, and even though the TPA rate is very low at intensity levels where non-linear transmission is significant, the long path lengths in the fibre, added to the high likelihood of colour-centre formation by quanta at double the photon energy, mean that colour-centres created by TPA can have a dramatic effect on transmission
Second harmonic generation in optical fibres
No full textThe mechanism and properties of high conversion efficiency second harmonic generation in optical fibres is reviewed
Nonlinear transmission and colour-centre dynamics in germanosilicate fibres at 420-540 nm
No full textWe report evidence in support of the view that induced loss and non-linear transmission in pure germanosilicate fibers at blue/green wavelengths are governed by the formation (via two-photon absorption), spontaneous and stimulated transformation and bleaching (via single-photon events) of Ge(1), Ge(2) and Ge(3) colour-centres. Using a tunable pulsed dye laser, the excitation spectrum of the induced absorption, its spectral attenuation and the effects of germania concentration and thermal annealing are investigated
Dynamics of color-center induced nonlinear transmission in GeO<sub>2</sub>-SiO<sub>2</sub> fibres
No full textWe show that the predominant factor limiting high power transmission in the blue/green spectral region in germanosilicate core fibres is the creation of germania-related color-centres via two-photon absorption
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