Dynamic population gratings in rare-earth-doped optical fibres

Abstract

Dynamic Bragg gratings can be recorded in rare-earth (e.g. Er, Yb) doped optical fibres by two counter-propagating mutually coherent laser waves via local saturation of the fibre optical absorption or gain (in optically pumped fibres). Typical recording cw light power needed for efficient grating formation is of sub-mW–mW scale which results in characteristic recording/erasure times of 10–0.1 ms. This review paper discusses fundamental aspects of the population grating formation, their basic properties, relating wave-mixing processes and also considers different applications of these dynamic gratings in single-frequency fibre lasers, tunable filters, optical fibre sensors and adaptive interferometry.

Polarization of the fluorescence excited in erbium-doped fibers in 1490–1570nm spectral range

“…The excited state spatial migration is widely discussed in connection with efficiency of the resonant frequency up-conversion in EDF [8][9][10] and of the optical pumping in Er, Yb co-doped fibers [7,11]. Spatial migration of excitation can also be an important factor contributing to the experimentally observed in EDF reduction of efficiency of population Bragg gratings [12][13][14].…”

Double-frequency Brillouin fiber lasers

“…It has 95% main reflectivity peak at 1547.37 with a fullwidth at half-maximum (FWHM) of ~0.07 nm. During laser operation the optical waves traveling in the unpumped fiber section in opposite directions interfere into a standing wave that causes inscription of the population inversion gratings in the fiber providing highly-selective reflection of the inscribing light through two-wave mixing effect [23]. The efficiency of this process depends on the light power, therefore the grating reflectivity peak is more pronounced at the laser resonance frequency L ν .…”

“…The first laser configuration is stabilized through self-injection locking mechanism [22] implemented to the laser cavity with DFB semiconductor pump laser. Second configuration comprises a nonlinear fiber mirror based on the population inversion dynamical gratings induced in low-absorbed Er-doped fiber [23] through the refractive index change effect [24]. In both cases, once the pump laser gets a resonance with the ring laser cavity, the growing optical feedback forces the DFB pump laser, in the first case, and the nonlinear fiber mirror, in the second case, to operate the cavity resonance frequency.…”

Polarization insensitive homodyne detection of optical phase modulation by two-wave mixing in saturable Er-doped fiber

“…In general, the fiber gratings under consideration were of the amplitude type because they were associated with local saturation of the fiber optical absorption or gain in the bright fringes of the recording interference pattern (for a general discussion of such gratings, see the recent review paper [10] and the corresponding references therein). However, in some special cases, the phase component of the recorded dynamic grating can be comparable to the amplitude component as in an EDF at 1492 nm [11], or even exceed it significantly as in the Yb-doped fiber (YDF) at 1064 nm [12].…”

“…The characteristic time of the population grating formation typically represent some fraction of the spontaneous relaxation time s 0 of the meta-stable level and descends with an increase of the recording light power [10]. This means that in EDF with s 0 10 ms, suppression of the slow phase and polarization fluctuations with frequencies below 100 Hz is obviously possible.…”