Absorption-emission cross-section ratio for Er³⁺ doped fibres at 1.5µm

The ratio of absorption to emission cross-section is determined for Er3+ doped fibres. This parameter, essential in modelling optical amplifiers, is found to be significantly different from previously published values. Reasons for this are discussed

Fabrication and development of polarisation maintaining fibres using gas phase etching

Polarisation-maintaining fibres are of considerable interest in the field of optical fibre sensors because of their ability to transmit either of the two orthogonal li early polarised modes over long distances - an extinction ratio of 20dB in 5km of PANDA fibre has been reported (Hosaka et a1 (I)). The fibres owe their polarisation holding performance to the high levels of birefringence designed into the structure. Although the form birefringence of an elliptical core can be used (Dyott et a1 (2)), the fibres are usually made birefringent by doping the silica on either side of the core with materials having different expansion coefficients. The resulting fibre has a birefringence proportional to the anisotropic stress across the core, whose magnitude depends upon the expansion coefficient mismatch and fibre geometry. In this paper, the optimum structure for a polarisation-maintaining fibre is first designed and then a process to make it is described together with typical performance figures. Finally, two techniques are described to enhance the already high levels of birefringence obtainable, and experimental results are given which show how short lengths of fibre can be used as a high extinction polariser, while long lengths of fibre can be used for the transmission of linearly polarised light aligned to one of the axes only - the other linearly polarised mode being suppressed

High-power erbium-doped-fibre amplifiers operating in the saturated regime

Highly saturated, erbium-doped fiber amplifiers can be employed as efficient power amplifiers. Differential pump-to-signal conversion efficiencies of 59% (quantum efficiency of 93%) can be obtained, resulting in 54 mW (+17.3 dBm) of amplified signal for only 100 mW of pump power at 978 nm. In addition, these amplifiers are shown to have virtually-flat spectral-gain characteristics with a 1 dB bandwidth in excess of 38 nm

Pump excited-state absorption in Er-doped fibres

Ground-state and excited-state absorption spectra covering the wavelength range of 450-1050 nm are presented for erbium-doped silica fibers with four different core codopants: GeO2, GeO2/B2O3, GeO2/P2O5, and Al2O3. It is shown that the host glass influences the excited-state absorption spectra and that P2O5- or Al2O3-codoped fibers are the preferred choice for 514.5-, 655-, or 807-nm pump wavelengths owing to reduced pump excited-state absorption. However, excited-state absorption is still significant at the 807-nm wavelength. Pump wavelengths of 524, 532, and 980-nm appear ideal because of the strong ground-state absorption and lack of excited-state absorption

Coiled-birefringent-fiber polarizers

Experimental results are presented that illustrate the excellent reproducibility and thermal stability of fiber polarizers made by coiling highly birefringent bow-tie fibers. The effective extinction ratio of the polarizer when used in a fiber-optic gyroscope is shown to be 62 dB

Absorption and emission cross-section of Er³⁺ doped silica fibres

A detailed set of measurements is presented on determining the emission and absorption cross sections of Er3+ doped fibers for the 4 I 13/2 to 4 I 15/2 transition. Two techniques are employed: the Füchtbauer-Ladenberg analysis, based on spectroscopic data; and a more direct technique involving optical saturation of the transition. The cross sections, and in particular their ratio, are significantly different for the two techniques. Possible reasons for this are discussed, and we conclude that the Füchtbauer-Ladenberg approach is inappropriate in this situation

Bend behaviour of polarising optical fibres

Experimental results are presented which show how both bend radius and the orientation of the fibre in the bend considerably affect the single-polarisation operation of bow-tie fibres

Performance of bow-tie polarising fibres

Differential bending loss between the two polarised modes is shown to be a necessary condition for truly single-polarisation operation in highly-birefringent fibres. The very high polarisation extinction ratios obtainable make the fibre ideally suited to many applications requiring transmission of polarised ligh

Single-polarisation operation of highly birefringent bow-tie fibres

Experimental results show that bow-tie fibres with high levels of stress-induced birefringence can be operated such that they support only a single linearly polarised mode. Under these conditions the loss of the fibre is 5 dB/km for the guided mode and 55 dB/km for the suppressed mode. For short-length operation as a polariser, extinction ratios as high as 50 dB/m have been obtained

An Extended X-ray Absorption Fine-Structure Study Of The Rare-Earth Sites In A Neodymium Doped Glass

The local environment around the metal sites in a Nd doped aluminosilicate glass has been determined using extended x-ray absorption fine structure. Detailed fitting of the spectrum reveals an average Nd coordination of 4.5 +/- 1 oxygen atoms at 2.15 angstrom and 4.5 +/- 2 oxygen atoms at 2.44 angstrom; a second shell, containing silicon atoms, is centred at 3.7 angstrom. It is suggested that all the oxygen atoms are nonbridging