A technique of single-longitudinal-mode selection in a fiber laser by means of a fiber multiple-beam reflection interferometer (FRI) has been experimentally demonstrated for the first time. The laser is based on a semiconductor optical amplifier placed in a linear fiber cavity formed by a fiber Bragg grating (FBG), and the FRI generates at 1529.24 nm with output power of 1 mW in single-frequency regime with a linewidth of about 217 kHz and polarization extinction ratio of >30 dB. The FRI technique potentially enables fast tuning (within the FBG bandwidth of ~0.9 nm in our case) by varying the base length of the FRI that can be used in a number of practical applications.

Fiber-based multiple-beam reflection interferometer for single-longitudinal-mode generation in fiber laser based on semiconductor optical amplifier

A two-mirror multiple-beam interferometer with a noninverted response function in reflection is used for the frequency selection and tuning in fiber lasers. The simplest version of the interferometer is based on a thin metal (Troitsky) film. Such a reflection interferometer corresponds to an external (with respect to a fiber) two-mirror cavity that consists of a spherical highly reflective (99.8%) mirror and a plane mirror represented by the thin metal film deposited on the fiber end face. Tuning to the selected frequency is performed due to a variation in the distance between the mirrors.

Reflection interferometer based on the Troitsky thin film for frequency selection in fiber lasers

A new variant of all-fiber multiple-beam interferometer capable to perform narrow-band filtration of a reflected light, with characteristics similar to those for Fabry-Perot interferometer in a transmission, is presented. The interferometer design accompanied with parameters simulation is conducted, the experimental sample is fabricated and the study of its characteristics is undertaken. Experimental results conform the calculations. This variant of reflection interferometer can be used as one of laser cavity mirrors providing frequency selection of low-powered fiber lasers and laser diodes with short linear cavities. We assume, that this device makes it possible to obtain single-frequency operation with fast continuous tuning of a laser wavelength in a wide spectral range.

Multiple-beam reflection interferometer formed in a single-mode fiber for applications in fiber lasers.

Publications on theoretical and experimental studies of multiple-beam reflection interferometers with a “non-inverted” response function in reflection are reviewed. Their operation principles and optical properties are described. The analytical form of recording of the response functions of such interferometers and the method of choosing parameters for controlling the form of the response functions are considered. Results of calculations and experiments are presented.

Multiple-beam interferometers in reflected light with a “non-inverted” response function

Numerical simulation was used to demonstrate the possibility of designing a two-mirror multibeam reflective diffraction interferometer using a single-mode fiber with a cladding. The method is based on the calculation of the multimode and multibeam interference of the cladding modes in the fiber describing the diffraction on a diffuser made in the form of an insert of a different fiber as part of one of the interferometer mirrors. It is shown based on bulk optics that using certain optimization, one can obtain a reflection-response function profile of this interferometer similar to that of the transmission-response function of a Fabry-Perot interferometer.

Numerical simulation of a reflective diffraction fiber interferometer

It is shown that the inclusion of a simple phase grating in the optical scheme of a resonator provides the possibility of performing spectral investigations in reflected light with characteristics of a Fabry-Perot interferometer. The response function of the interferometer is examined, and experimental results are presented.

A reflection interferometer with a noninverted response function based on a phase grating

This paper describes the calculation, fabrication, and experimental investigation of a reflection two-mirror interferometer whose front mirror is asymmetric in reflection and made as a thin-layer diffraction metal structure (Al, Ag) in combination with a dielectric coating (MgF2, ZnS). In reflection, this interferometer creates in the zero diffraction order a transmission-like pattern similar to that produced by an ordinary Fabry-Perot interferometer operating in transmitted light.

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Noninverted interference fringes upon light reflection from a Fabry-Perot interferometer with an asymmetric diffraction mirror

Numerical analysis of the spectral characteristics of a two-layer structure is performed in the processes of fabrication, measurement, and application of this structure as a sensor of the refractive index of the external medium. The effect of environmental conditions and parameters of the metal and dielectric layers on the sensor sensitivity is discussed. The results of model calculations are confirmed by experimental studies.

Spectral properties of a metal–dielectric sensor structure

This paper considers the results of using a two-mirror multiple-beam reflection interferometer (RI) which has a response function in reflection similar to the response function of a Fabry-Perot interferometer in transmission. The two-mirror cavity of the RI included two flat mirrors, one of which was highly reflective, and the other had an asymmetric coefficient of reflection from different sides. The light reflected from the RI was brought to an optical fiber through a collimator lens. The optical fiber, collimator, and RI constituted an integrated fiber RI, which was first used for continuous tuning of the wavelength of an erbium ring fiber laser with a continuous generation in the spectral range 1520–1566 nm.

V. S. Terent’ev

Papers

A reflection interferometer with a noninverted response function based on a phase grating

Noninverted interference fringes upon light reflection from a Fabry-Perot interferometer with an asymmetric diffraction mirror

Numerical simulation of a reflective diffraction fiber interferometer

Spectral properties of a metal–dielectric sensor structure

Frequency selection of the radiation of a fiber laser with a reflection interferometer