Valery A. Kozlov

All-fiber coherent beam combining of fiber lasers

One half of a 2x2 fused taper single-mode fiber coupler is used for the all-fiber spatial and spectral beam combining of two fiber lasers.

Polarization effects in a high-birefringence elliptical fiber laser with a Bragg grating in a low-birefringence fiber

The polarization characteristics of a fiber laser cavity that combines a high-birefringence Er(3+)-doped elliptical core fiber with a Bragg grating fabricated in a low-birefringence (Low-Bi) fiber are studied. It is shown that, by use of an adequate length of Low-Bi fiber and an intracavity polarization controller, the dependence of the fiber lasers state of polarization on the pumps state of polarization can be altered. This fiber laser cavity design allows for the realization of a double-frequency, orthogonally polarized single-mode fiber laser source insensitive to the polarization parameters of the pump source.

Optical Waveguide Evanescent-Field Amplifiers

We briefly describe the recent development of the optical evanescent-field amplifiers including the solid-state integrated-optic and fiber-optic devices. Application of these amplifiers to the optical communication systems is discussed.

Single-mode-fiber to thin film optical waveguide couplers using bulk laser crystals

Optical fiber-to-thin film optical waveguide couplers have been studied experimentally as the base for in-line fiber- optic active components. Laser active crystals have been used in a planar structure as active substrate or active core for fiber-optic active components design.

Fiber optic systems for diode-pumped solid state lasers

Radial nonsymmetrical fiber endface microlenses original fabrication technique has been used for high efficient pump laser diode radiation coupling (up to 93% without AR coating) into the standard optical fibers and for the form of a pump power diagram at the output fiber endfaces. Nd:GdVO4 laser (2.5 mm crystals length) parameters with semiconfocal (output mirror curvature radius 10 cm) and monolith plane mirrors cavities have been measured for different pump diagrams formed by plane endfaces, spherical microlenses, and Selfoc lenses. Compact diode-pumped solid state lasers may be used in optical communications, optical storage, medicine, and other applications. Diode laser (DL)-optical fiber coupling gives several advantages for these pumping systems -- a possibility to combine several DLs radiation, a remote DLs mounting, small size and electrical safety of the laser heads, simple schemes of active crystals cooling, axial symmetry of the pumping beam for longitudinal geometry. In general, high coupling efficiency between a semiconductor light source and optical fiber may be achieved by the use of microlens, formed on the endface of the fiber. In this case bulk optical components between DL and optical fiber are not needed. In addition, the only reflection surface exists in this coupling technique. Different techniques for producing microlenses on a fiber endface have been developed. For example, tapered hemispherical lenses, melted, etched, and polished lenses are commonly used for this coupling. However, all types of such techniques produce in general radial symmetry lenses: therefore, they do not provide efficient coupling between a round fiber core and a nonsymmetrical DLs radiation. In this paper we demonstrate the fabrication technique of fiber endface radial nonsymmetrical microlenses with radii curvature from few micrometers to few tens micrometers by grinding/polishing process. This process may be used for producing different nonspherical microlenses (cylindrical, elliptical, hyperbolic, etc.) to efficient coupling DLs radiation into single-mode or multimode optical fibers and for producing microlenses (including spherical) on the output fiber endface to form a diagram of a pumping power.

Laser diode optical fiber pumping system for solid state lasers

New fabrication technique of fiber endfaces microlenses (spherical, cylindrical, elliptical, hyperbolic, etc.) by grinding/polishing process has been developed. The coupling efficiency of laser diodes radiation in the range of 90 - 93% has been obtained. Fiber-diode-pumped Nd:GdVO4 laser output power dependence on pump power diagram at the fiber output has been investigated.

Comparison of spectroscopic and laser properties of Cr4+:YxLu3-xAl5O12 crystals

We present a spectroscopic and lasing investigations of the Cr4+:YxLu3-xAl5O12 crystals, a new laser materials for the infrared region of spectrum. The laser action on the Cr4+:Y1.5Lu1.5Al5O12 crystal is demonstrated. The Cr4+:YxLu3-xAl5O12 saturable absorber Q-switch for a diode side-pumped Nd:GdVO4 laser is performed.

Passive Q-switching of a fiber optic module-pumped Nd:GdVO laser with LiF:F crystals

Passive Q-switching of optical fiber-diode-pumped Nd:GdVO4 laser by special developed LiF:F2- crystals have been realized. Pulse duration of 15-100 ns and pulse repetition rate of 5-200 kHz have been obtained.

Evanescent field thin-film optical amplifier

An evanescent field integrated optics amplifier for 1,07-1,34 μm spectral band have been proposed and demonstrated. The amplifier is a silicon oxide thin - film waveguide on an laser active LiF:F2- color center crystalline substrate. The measured gain was - 1 OdB for the mode propagating length 2 cm. Solid state integrated optics lasers and amplifiers, whose rapid development was inspired by successes in waveguide lasers and amplifiers, have several important features that can make them preferable in various applications. The possibility to incorporate these components into integrated optics circuits, developed technology for crystal growth and processing, simple pumping schemes (including by laser diodes), flexibility in using different active ions to achieve the desired goals make them attractive for many . researches. Currently these lasers/amplifiers are usually made by in-diffusion of active ions into crystalline materials and glasses, as well as by ion implantation and epitaxial growth 1. We propose a rather new concept of integrated optics amplifier, which employs a passive waveguide on a substrate of active material. When light propagates through the waveguide, part of it propagates in the substrate as an evanescent field. The portion is defined by the waveguide parameters, the wavelength and the mode index. Using a standard pumping scheme one can amplify the portion that propagates in the active substrate and, therefore, the entire mode. The advantage of this amplifier is relatively simple planar fabrication technology and the possibility to utilize various pumping sources and schemes.