This paper presents a microwave photonics method for the instantaneous frequency measurement of microwave signals, based on the generation of a two-frequency laser radiation in the Mach -Zehnder modulator with a difference frequency equal to the measured, and the "frequency -amplitude" conversion in the π-phase-shifted fiber Bragg grating. Frequency measurement occurs in two ranges: 0.3 -3 GHz in the passband of the FBG and 3 -30 GHz in its reflection band. Using the specific conversion of two-frequency radiation in the π-phase-shifted fiber Bragg grating allowed us to obtain measuring characteristics, that are independent of the amplitude fluctuations of the optical carrier and to organize additional circuit for monitoring the spectral characteristics of the used elements to reduce measurement inaccuracy caused by their temperature instability.

This work presents a fabricated silica few-mode microstructured optical fiber (MOF) with a special six GeO2-doped core geometry, an outer diameter of 125 µm (that corresponds to conventional commercially available telecommunication optical fibers), and improved induced twisting up to 500 revolutions per 1 m (under a rotation speed of 1000 revolutions per meter with a drawing speed of ~2 m per minute). The article discusses some technological aspects and issues of manufacturing the above-described twisted MOFs with complicated structures and geometry as GeO2-doped silica supporting elements for them. We present results of some measurements performed for fabricated samples of chiral silica six-GeO2-doped-core few-mode MOFs with various orders of twisting and both step and graded refractive indexes of “cores”. These tests contain research on MOF geometrical parameters, attenuation, and measurements of the far-field laser beam profile.

No abstract

No abstract

This work presents designed and fabricated silica few-mode optical fiber (FMF) with induced twisting 10 and 66 revolutions per meter, core diameter 11 µm, typical “telecommunication” cladding diameter 125 µm, improved height of quasi-step refractive index profile and numerical aperture 0.22. Proposed FMF supports 4 guided modes over “C”-band. We discussed selection of specified optical fiber parameters to provide desired limited mode number over mentioned wavelength range. Some results of tests, performed with pilot samples of manufactured FMF, are represented, including experimentally measured spectral responses of laser-excited optical signals, that comprise researches and analysis of few-mode effects, occurring after fiber Bragg grating writing.