20 research outputs found
Group delay in Bragg grating with linear chirp
An analytic solution for Bragg grating with linear chirp in the form of
confluent hypergeometric functions is analyzed in the asymptotic limit of long
grating. Simple formulas for reflection coefficient and group delay are
derived. The simplification makes it possible to analyze irregularities of the
curves and suggest the ways of their suppression. It is shown that the increase
in chirp at fixed other parameters decreases the oscillations in the group
delay, but gains the oscillations in the reflection spectrum. The conclusions
are in agreement with numerical calculations.Comment: 16 pages, 8 figures, submitted to Opt. Com
Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation
We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating (FBG) reflectors and distributed feedback via Rayleigh scattering in a ∼22 km long optical fiber. Twenty two lasing lines with spacing of ∼100 GHz (close to ITU grid) in C-band are generated at Watts power level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution which is almost independent on power. The current set up showing the capability of generating Raman gain of about 100-nm wide giving the possibility of multiwavelength generation at different bands
Turbulent broadening of optical spectra in ultralong Raman fiber lasers
We study the properties of radiation generated in ultralong fiber lasers and find an interesting link between these optical systems and the theory of weak wave turbulence. Experimental observations strongly suggest that turbulentlike weak interactions between the multitude of laser cavity modes are responsible for practical characteristics of ultralong fiber lasers such as spectra of the output radiation
Giant Coulomb broadening and Raman lasing on ionic transitions
CW generation of anti-Stokes Raman laser on a number of blue-green argon-ion
lines (4p-4s, 4p-3d) has been demonstrated with optical pumping from metastable
levels 3d'^2G, 3d^4F. It is found, that the population transfer rate is
increased by a factor of 3-5 (and hence, the output power of such Raman laser)
owing to Coulomb diffusion in the velocity space. Measured are the excitation
and relaxation rates for the metastable level. The Bennett hole on the
metastable level has been recorded using the probe field technique. It has been
shown that the Coulomb diffusion changes shape of the contour to exponential
cusp profile while its width becomes 100 times the Lorentzian one and reaches
values close to the Doppler width. Such a giant broadening is also confirmed by
the shape of the absorption saturation curve.Comment: RevTex 18 pages, 5 figure
Characterization of ultra-long Raman fibre lasers
We present results on characterization of lasers with ultra-long cavity lengths up to 84km, the longest cavity ever reported. We have analyzed the mode structure, shape and width of the generated spectra, intensity fluctuations depending on length and intra-cavity power. The RF spectra exhibit an ultra-dense cavity mode structure (mode spacing is 1.2kHz for 84km), in which the width of the mode beating is proportional to the intra-cavity power while the optical spectra broaden with power according to the square-root law acquiring a specific shape with exponential wings. A model based on wave turbulence formalism has been developed to describe the observed effects
Wave kinetics of random fibre lasers
Traditional wave kinetics describes the slow evolution of systems with many degrees of freedom to equilibrium via numerous weak non-linear interactions and fails for very important class of dissipative (active) optical systems with cyclic gain and losses, such as lasers with non-linear intracavity dynamics. Here we introduce a conceptually new class of cyclic wave systems, characterized by non-uniform double-scale dynamics with strong periodic changes of the energy spectrum and slow evolution from cycle to cycle to a statistically steady state. Taking a practically important example—random fibre laser—we show that a model describing such a system is close to integrable non-linear Schrödinger equation and needs a new formalism of wave kinetics, developed here. We derive a non-linear kinetic theory of the laser spectrum, generalizing the seminal linear model of Schawlow and Townes. Experimental results agree with our theory. The work has implications for describing kinetics of cyclical systems beyond photonics