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In this work, long high-quality fiber Bragg gratings with phase shifts in the structure are inscribed directly in the optical fiber by point-by-point technique using femtosecond laser pulses. Phase shifts are introduced during the inscription process with a piezoelectric actuator, which rapidly shifts the fiber along the direction of its movement in a chosen point of the grating with a chosen shift value. As examples, single and double π phase shifts are introduced in fiber Bragg gratings with a length up to 34 mm in passive fibers, which provide corresponding transmission peaks with bandwidth less than 1 pm. It is shown that 37 mm π -phase-shifted grating inscribed in an active Er-doped fiber forms high-quality DFB laser cavity generating single-frequency radiation at 1550 nm with bandwidth of 20 kHz and signal-to-noise ratio of >70 dB. The inscription technique has a high degree of performance and flexibility and can be easily implemented in fibers of various types.

The concept of random lasers exploiting multiple scattering of photons in an amplifying disordered medium in order to generate coherent light without a traditional laser resonator has attracted a great deal of attention in recent years. This research area lies at the interface of the fundamental theory of disordered systems and laser science. The idea was originally proposed in the context of astrophysics in the 1960s by V.S. Letokhov, who studied scattering with “negative absorption” of the interstellar molecular clouds. Research on random lasers has since developed into a mature experimental and theoretical field. A simple design of such lasers would be promising for potential applications. However, in traditional random lasers the properties of the output radiation are typically characterized by complex features in the spatial, spectral and time domains, making them less attractive than standard laser systems in terms of practical applications. Recently, an interesting and novel type of one-dimensional random laser that operates in a conventional telecommunication fibre without any pre-designed resonator mirrors–random distributed feedback fibre laser–was demonstrated. The positive feedback required for laser generation in random fibre lasers is provided by the Rayleigh scattering from the inhomogeneities of the refractive index that are naturally present in silica glass. In the proposed laser concept, the randomly backscattered light is amplified through the Raman effect, providing distributed gain over distances up to 100 km. Although an effective reflection due to the Rayleigh scattering is extremely small (∼0.1%), the lasing threshold may be exceeded when a sufficiently large distributed Raman gain is provided. Such a random distributed feedback fibre laser has a number of interesting and attractive features. The fibre waveguide geometry provides transverse confinement, and effectively one-dimensional random distributed feedback leads to the generation of a stationary near-Gaussian beam with a narrow spectrum. A random distributed feedback fibre laser has efficiency and performance that are comparable to and even exceed those of similar conventional fibre lasers. The key features of the generated radiation of random distributed feedback fibre lasers include: a stationary narrow-band continuous modeless spectrum that is free of mode competition, nonlinear power broadening, and an output beam with a Gaussian profile in the fundamental transverse mode (generated both in single mode and multi-mode fibres). This review presents the current status of research in the field of random fibre lasers and shows their potential and perspectives. We start with an introductory overview of conventional distributed feedback lasers and traditional random lasers to set the stage for discussion of random fibre lasers. We then present a theoretical analysis and experimental studies of various random fibre laser configurations, including widely tunable, multi-wavelength, narrow-band generation, and random fibre lasers operating in different spectral bands in the 1–1.6 μm range. Then we discuss existing and future applications of random fibre lasers, including telecommunication and distributed long reach sensor systems. A theoretical description of random lasers is very challenging and is strongly linked with the theory of disordered systems and kinetic theory. We outline two key models governing the generation of random fibre lasers: the average power balance model and the nonlinear Schrodinger equation based model. Recently invented random distributed feedback fibre lasers represent a new and exciting field of research that brings together such diverse areas of science as laser physics, the theory of disordered systems, fibre optics and nonlinear science. Stable random generation in optical fibre opens up new possibilities for research on wave transport and localization in disordered media. We hope that this review will provide background information for research in various fields and will stimulate cross-disciplinary collaborations on random fibre lasers.

Reflection properties of a fiber Bragg grating (FBG) inscribed in a multimode fiber strongly depend on the transverse profile of FBG. Point-by-point FBG fabrication by IR femtosecond pulses with highly nonlinear refraction index variation as a function of intensity within the focal spot offers an opportunity to tailor the FBG transverse profile with high spatial resolution. In this paper we review our recent results on the femtosecond inscription of FBGs in multimode fibers, study of their spectral and mode-selective properties as well as applications for mode selection in multimode and multicore fiber lasers.

Digital planar holograms (DPH) are successfully fabricated for the first time by nanoimprint lithography (NIL). A state-of-the-art UV-NIL process is developed by combining both advantages of step and repeat technology at low pressure for high-throughput and imprinting of spin-coated resist films for easy pattern transfer. The nanofabrication process is used in order to replicate DPH structures, composed of multi-million lines grating, into silicon dioxide waveguide core. Optical performances of nanospectrometers chips are in agreement with simulations.

BEAMETR technique is developed for robust operator independent measurement of electron beam sizes in two coordinates. This method involves software and a specially designed pattern-sample. In this paper, we report the fabrication of this sample and the demonstration of beam size and shape measurements for different Scanning Electron Microscopes and operating conditions (voltage, aperture, astigmatism) with a good consistency. Electron Beam Lithography system (100keV) was used for patterning; proximity correction was applied to improve pattern quality. In this chip version, the minimum feature linewidth was 20nm after lift-off.

Effects of intensity interactions (pump power depletion and sequential saturation of cascade generation) have been studied in a two-stage phosphosilicate Raman fiber laser in experiment and modeling. An analytical model of the laser which takes into account power variation along the fiber and spectral broadening of the first Stokes wave has been developed that describes experimental data both qualitatively and quantitatively. Good agreement between calculated and experimental values of the thresholds, differential efficiency for the first and the second Stokes waves and saturation levels for the residual pump and the first Stokes wave powers is demonstrated.