Alexandr V. Dostovalov

Femtosecond point-by-point inscription of Bragg gratings by drawing a coated fiber through ferrule.

A ferrule-based method of direct fs FBG inscription through protective plastic coating is demonstrated. Fluctuations of fiber core position relative to the writing fs beam are compensated by the developed auto-alignment system. As a result, high-quality FBGs with length from 0.1 to 50 mm are fabricated in polyimide-coated fibers, whose spectra are well described by the theory. The fabricated FBGs have great potential in sensor applications at high temperature and harsh environments both point-action and distributed ones.

Femtosecond Laser Inscription of Long-Period Fiber Gratings in a Polarization-Maintaining Fiber

The method of femtosecond laser inscription by slit-apertured beam is applied for fabrication of long-period fiber gratings in polarization-maintaining Panda-type fiber. Polarization properties as well as ambient refractive index sensitivity are investigated for the inscribed gratings. It is shown that the method allows us to create high-quality element for the use as spectral filter of high-power fiber laser as well as high-temperature sensor.

Quantitative characterization of energy absorption in femtosecond laser micro-modification of fused silica

We present the results of experimental and theoretical study of an energy absorption of femtosecond laser pulse in fused silica. Fundamental and second harmonics of ytterbium laser were used in experiment while general case was considered theoretically and numerically. More efficient absorption at the second harmonics is confirmed both experimentally and numerically. Quantitative characterization of the theoretical model is performed by fitting key parameters of the absorption process such as cross-section of multi-photon absorption and effective electronic collision and recombination times.

Extracavity and external cavity second-harmonic generation in a periodically poled silica fibre

We have studied second-harmonic generation (SHG) of a cw single-frequency ytterbium-doped fibre laser, using a periodically poled silica fibre as a nonlinear medium for frequency conversion. All-fibre external cavity SHG has been investigated for the first time. A twofold increase in second-harmonic power in a fibre ring cavity has been demonstrated and possibilities of further optimising the fibre scheme have been analysed.

Comparative numerical study of energy deposition in femtosecond laser microfabrication with fundamental and second harmonics of Yb-doped laser

We present the results of comparative numerical study of femtosecond laser inscription for fundamental and second harmonic of Yb-doped laser. We have found that second harmonic is more efficient in terms of amount of absorbed energy which leads to lower inscription threshold. Hence this regime is more attractive for applications in femtosecond laser microfabrication. We observed the different size of modified domain on initial pulse energy and different spectrum dynamics during the pulse propagation for fundamental and second harmonics.

Reflection interferometers formed on the single-mode fiber tip

Interferometers formed with thin coatings on the fiber tip and capable of filtering reflected light are proposed. Two types of interferometers are described: those based on a thin metal film and those with a scattering structure implemented in a single-mode fiber. Scattering structures were produced by a femtosecond modification of the single-mode fiber.

Femtosecond core-scanning inscription of tilted fiber Bragg gratings

The results on tilted fiber Bragg gratings (TFBGs) inscription using the method of transverse scanning of the fiber core by a femtosecond laser beam is reported in this paper. As an example, TFBGs consisting of unidirectional and bi-directional grating planes and having a tilt angle up to 9° are created. It is shown that different transverse mode groups of the fiber cladding can be excited with the created structures. The corresponding resonant dips reach the amplitude up to 30 dB that indicates the inscription method efficiency.

Femtosecond-pulse inscription of phase-shifted fiber Bragg gratings for distributed feedback lasers

Fiber Bragg gratings (FBGs) with phase shifts in the structure has a wide field of applications in sensor and laser devices: distributed-feedback and multiwavelength fiber lasers, optical sensors for simultaneous temperature/tension measurements and high-sensitivity ultrasonic detectors, optical signals processing and filtering elements. Advantages of femtosecond (fs) laser inscription technology — modification of non-photosensitive materials, FBG inscription through the fiber plastic coating, high-temperature and radiation resistance of FBGs etc — make the technology attractive to create fiber devices and components with advanced technical features [1].

Femtosecond-pulse inscription of fiber Bragg gratings in multimode graded index fiber

Femtosecond-pulse modification of the refractive index in transparent materials enables the inscription of fiber Bragg gratings with new features and extended capabilities. In this study we present the results of fiber Bragg gratings inscription in Corning 62.5/125 multimode graded index fiber with IR femtosecond laser pulses. The specifics of point-by-point inscription including single and multiple Bragg grating inscription in limited fiber segment as well as different transverse modes excitation/suppression is discussed. Multimode fiber Bragg gratings inscribed with femtosecond radiation are investigated for the first time directly in the Raman fiber laser cavity.

Study of TLIPSS formation on different metals and alloys and their selective etching

Experimental investigation of thermochemical laser-induced periodic surface structures (TLIPSS) formation on metal films (Ti, Cr, Ni, NiCr) at different processing conditions is presented. The hypothesis that the TLIPSS formation depends significantly on parabolic rate constant for oxide thin film growth is discussed. Evidently, low value of this parameter for Ni is the reason of TLIPSS absence on Ni and NiCr film with low Cr content. The effect of simultaneous ablative (with period ≈λ) and thermochemical (with period ≈λ) LIPSS formation was observed. The formation of structures after TLIPSS selective etching was demonstrated.