We present a birefringent Yb-doped tapered double-clad fiber with a record core diameter of 96 µm. An impressive gain of over 38 dB was demonstrated for linearly polarized CW and pulsed sources at a wavelength of 1040 nm. For the CW regime the output power was70 W. For a mode-locked fiber laser a pulse energy of 28 µJ with 292 kW peak power was reached at an average output power of 28 W for a 1 MHz repetition rate. The tapered double-clad fiber has a high value of polarization extinction ratio at 30 dB and is capable of delivering the linearly polarized diffraction-limited beam (M² = 1.09).

The efficiency of a new method for calculating the spectrum and attenuation coefficient of leaky electromagnetic modes is demonstrated with multilayer planar optical waveguides the guiding properties

Nuclear industry may benefit from the implementation of Optical Fiber Sensor (OFS) technology. This is obvious if the OFS integrates features that meet specific nuclear sensing needs, such as distributed dose monitoring in underground radioactive waste disposals. The use of radiation sensitive fibers for dosimetry has already been proposed in literature. In this paper, we report on our gamma irradiation of such dedicated Ge-P co-doped and pure P-doped optical fiber, fabricated by the Fiber Optic Research Center in Moscow. We show that after a careful selection of the wavelength at which the radiation-induced attenuation is measured, it is possible to reconstruct the dose within 20% accuracy by means of a linear model or a second order polynomial, depending on the temperature.

A fiber-optic refractometer for various liquids with refractive indices in the range from 1.33 to 1.43 has been manufactured and tested. The sensor is based on a thin silicon oxynitride (Si₃N_4-xO_x) film coated thinned optic fiber section (taper) obtained in a multimode all-silica optical fiber by chemical etching of the reflective cladding. The film was deposited on the cylindrical surface of the thinned fiber by the surface plasma chemical vapor deposition method (SPCVD). Lossy mode resonance (LMR) was observed in the transmission spectrum of the coated taper at a wavelength dependent on the refractive index of the liquid in which the taper was immersed. We tested the obtained sensors in distilled water, isopropyl alcohol, dimethylformamide, and their aqueous solutions. It was found that with the help of the SPCVD, one can obtain a set of sensors in a single deposition run with the dispersion of sensitivity and spectral position of LMR no more than 5%. Maximum sensitivity of the manufactured sensors to surrounding media refractive index (SMRI) variation exceeds 1090 nm/RIU, which is the highest value recorded to date for a sensor with a non-oxide coating.

Short tapered fiber sections 3–10 mm in length and 12–20 microns in diameter were fabricated through the partial etch removal of the outer silica cladding. ZnTe and Bi ₂ Te ₃ crystalline films 1–60 nm thick were subsequently applied to the surface of the tapered fiber sections using metalorganic chemical vapor deposition. Transmission spectra of the taper were recorded within the wavelength region of 1–1.6 μ m at regular intervals whilst the deposition. Strong decreases in transmission in relatively narrow spectral bands were observed. The results can be applied to lossy mode resonance fiber sensors and passively mode-locked pulsed fiber laser designs.

The results of the rigorous calculation of mode fields in double adiabatic, single-mode etched-out optical fiber tapers coated with thin indium tin oxide films are discussed in the context of their application as environment refractive index sensors. It is shown that at only two particular thicknesses covering the homogeneous section of the taper ITO film about 100 nm and 177 nm, the lossy mode resonance is observed in the wavelength range of 1.50–1.55 µm. Moreover, the sensitivity of a sensor based on a 177 nm coating is significantly higher, and the resonance width is significantly lower than that of a sensor with a 100 nm coating. Optimal from the viewpoint of the figure of merit, values for the diameter of a homogeneous section of the etched fiber are defined.