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Photodarkening and photoinduced index changes are reported for the first time to our knowledge in tantalumdoped silica optical fibers exposed to KrF excimer laser emission at 248 nm. The UV absorption of the tantalum-doped preform features the tail of a strong absorption band below 200 nm. The 248-nm-induced absorption in the UV also features the tail of a band below 200 nm. Photodarkening at 900 nm shows signs of saturation after several excimer pulses and some recovery after each pulse. Using an external holographic writing technique at 248 nm, we also formed Bragg gratings at 1.55 μm in these fibers. The grating growth saturated after several pulses and displayed a fast decay component when writing was performed with a higher pulse rate. The decay is well fitted by a stretched exponential with β = 0.35.

We demonstrate for the first time a 1.49-μm Er3+:Yb3+co-doped silica fiber laser with fiber Bragg grating feedback, pumped with a diode-pumped Nd:YLF laser at 1.047 μm, which can be used for remote pumping of EDFAs. We examine both the potential and limitations of this laser as a high power source and point out how an efficient, high power laser could be realized. The maximum demonstrated output power, 21 mW, was limited by the cavity losses, by the strong ASE at the peak gain wavelength 1.535 μm, and by a “bottleneck effect” in the energy transfer between ytterbium and erbium with a corresponding reduced pump absorption at higher pump powers. By overcoming these limitations an output power in excess of 500 mW with 1 W of pump power is predicted.

A new technique has enabled us to resolve the strong UV absorption spectrum in UV-exposed germanosilicate preforms. Our results show, for the first time to our knowledge, that the large photoinduced absorption changes between 165 and 300 nm (~700 dB/mm at 195 nm has been observed) can account for ~3 × 10^−4 of index change at 1.5 μm. The thermal-annealing dynamics of the photoinduced absorption changes also resemble those of fiber gratings, evidence that the color-center model of photosensitivity plays an important role in the photoinduced index changes in UV-written fiber gratings. We also find that the photoinduced absorption changes depend linearly on germania (i.e., germanium dioxide) concentrations in the preforms, and their exposure-time dependence can be fitted with a stretched-exponential function.

A low-insertion-loss, all-single-mode fiber, wavelength-division-multiplexing filter comprising a four-port polished coupler and a strong fiber grating is demonstrated. The device operates in a novel way by a process we call grating-frustrated directional coupling. A fiber grating, present in only one half of the coupler, frustrates the transference of power to the other half within a narrow wavelength range. The performance of a prototype device—a 1535-nm channel-dropping filter with 0.7-nm bandwidth, 70% peak transmission, and 13-dB isolation—shows great promise for wavelength-division-multiplexing and line-filtering applications.

We report what is to our knowledge the first fiber distributed-feedback laser using a single Bragg grating at 1.5 μm written directly into a 2-cm-long Er^3+-doped fiber codoped with Yb^3+. We obtained robust single-frequency operation by either using one end reflector or locally heating the center of the grating to create the necessary phase shift.

A new type of internally written grating filter is proposed and demonstrated in single-mode optical fibers. A photoinduced rocking birefringence is created by polarization interference between two counterpropagating and orthogonal linear-polarization modes at 514.5 nm. This birefringent grating has the correct submicrometer pitch for efficient phase-matched reflection of a linearly polarized mode into the orthogonally polarized counterpropagating mode. The phenomenon represents a new form of holography in which the image (the orthogonal counterpropagating mode) is reconstructed by scattering off a hologram consisting of a periodic birefringence.

The dispersion of picosecond pulses on reflection from efficient photorefractive fiber gratings is explored experimentally. Unlike simple measurements of reflectivity, this approach allows both the amplitude and the phase of the grating response to be probed as a function of frequency.

We propose a new method for the simultaneous interrogation of conventional two-beam interferometers and Bragg grating sensors. The technique employs an unbalanced Mach–Zehnder interferometer illuminated by a single low-coherence source, which acts as a wavelength-tunable source for the grating and as a path-matched filter for the Fizeau interferometer, thus providing a high phase resolution output for each sensor. The grating sensor demonstrates a dynamic strain resolution of ~0.05?μ?/Hz at 20 Hz, while the interferometric phase resolution is better than 1?mrad/Hz at 20 Hz, corresponding to an rms mirror displacement of 0.08 nm.

The spectral behaviour of two superimposed fibre gratings having different Bragg wavelengths (850 and 1300 nm) with respect to strain and temperature has been studied. The results show that the ratio of sensitivity at two Bragg wavelengths is dependent on strain and temperature, which can be used for simultaneous measurement of these parameters using a single sensing element.

A new approach for the interrogation of a large number of fiber-optic grating sensors is proposed and demonstrated for a small number of sensors in which signal recovery is achieved by matching a receiving grating to its corresponding sensor. This technique is demonstrated for both quasi-static and periodic measurands, and the resolution achieved for a single sensor–receiving grating pair for quasi-static strain is 4.12 μ∊.

Gratings with as high as 2.4% reflection efficiency written by a 20-ns single excimer pulse at 248 nm have been demonstrated for the first time to our knowledge in Ce^3+-doped fibers. The grating strength is shown to increase with Ce^3+ concentration under the same writing conditions. Investigation of the grating decay at elevated temperatures has revealed several different time constants, showing that several different types of mechanism may be involved. Part of the grating was found to be stable for >10 h at 600°C.

That tumors in general are not subject to invasion by bacteria, other than those of the pyogenic group, is well known. The simultaneous occurrence of carcinoma and tuberculosis in an organ or tissue is occasionally reported, but the invasion of other tumors by the tubercle bacillus is very unusual. This is especially true of uterine myomata which are seldom involved in even the most extensive tuberculous infections of the adjacent mucosa. The case here reported is of interest not merely on account of the rarity of the condition, but also because of the absence of tuberculosis in the mucosa of the general uterine cavity with but a slight lesion in one tube. The tuberculosis of the myoma and that of the tube were secondary to tuberculosis of the lung, but apparently independent of one another and due to infection through the blood stream. As a fairly exhaustive review of the

The authors report a highly-efficient, short, robustly single-frequency and linearly polarised Er3+:Yb3+ codoped fibre laser with fibre-grating Bragg reflectors. An output power of 19 mW for 100 mW of 980 nm diode pump power and a slope efficiency relative to a launched pump power of 55% is demonstrated. The RIN of the laser was < –157 dB/Hz and the laser linewidth was 300 kHz.

For the first time the production of Bragg fibre gratings written by single excimer laser pulses as the fibre is being drawn is demonstrated. Reflectivities approaching 100% have been obtained, demonstrating the feasibility of online mass production.

The first demonstration is reported of highly reflecting fibre Bragg gratings written holographically by a single 20ns excimer laser pulse; reflection efficiencies of 65% combined with 1nm bandwidths at 1550nm have been obtained. Single-pulse gratings with FWHM bandwidths of 0.05nm (6GHz) have also been produced, to the authors' knowledge the narrowest reported to date.