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Using coupled mode approach, we perform an analytical investigation of hot carrier effects (HCEs) of pump wave on (steady-state and transient) Brillouin gain coefficients of magnetoactive doped semiconductors. The threshold condition for exciting transient stimulated Brillouin scattering phenomenon is estimated. Numerical calculations are made for n-InSb crystal—CO2 laser system. Efforts are made to obtain enhanced values of Brillouin gain coefficients and lower threshold intensity by suitably choosing plasma and cyclotron frequencies around resonances. HCEs of intense pump wave modify the momentum transfer collision frequency of carriers and consequently the nonlinearity of the Brillouin medium, which in turn (1) lowers threshold intensity, (2) enhances Brillouin gain coefficients, (3) shifts the enhanced Brillouin gain spectrum toward smaller values of magnetic field, and (4) widens the range of magnetic field at which peak of Brillouin gain spectrum (around resonance) occurs. The inclusion of HCEs in the analysis leads to better understanding of laser-semiconductor interactions and validate the possibility of chosen Brillouin medium as a potential candidate material for the fabrication of widely tunable and efficient Brillouin amplifiers and oscillators. [ABSTRACT FROM AUTHOR]

Brillouin light scattering describes the diffraction of light waves by acoustic phonons, originating from random thermal fluctuations inside a transparent body, or by coherent acoustic waves, generated by a transducer or from the interference of two frequency-detuned optical waves. In experiments with optical fibers, it is generally found that the spontaneous Brillouin spectrum has the same frequency dependence as the coherent Brillouin gain. We examine the origin of this similarity between apparently different physical situations. We specifically solve the elastodynamic equation, giving displacements inside the body, under a stochastic Langevin excitation and in response to a coherent optical force. It is emphasized that phase matching is responsible for temporal and spatial frequency-domain filtering of the excitation, leading in either case to the excitation of a Lorentzian frequency response solely determined by elastic loss. [ABSTRACT FROM AUTHOR]

Presented here are the selected optical, physical, and Brillouin-related properties of a novel silica-clad, strontium aluminosilicate (SrAlSi) glass optical fiber produced using the molten core method. The Brillouin gain coefficient was found to be 0.11 × 10−11 m/W, which is about 20 × lower than conventional silica glass optical fibers. The SrAlSi core fiber also has a near-zero temperature coefficient of Brillouin frequency shift (–0.064 MHz/K) and can be considered athermal for all intents and purposes. Additional physical and Brillouin properties of the individual glass components are deduced through the use of an additive model. As a highlight, strontia (SrO) is found to have a large negative Pockels photoelastic coefficient of p12 = – 0.245. Various other bulk properties, such as the acoustic velocity, refractive index, mass density, thermo-optic, and thermo-acoustic, as well as strain-optic and strain-acoustic coefficients are provided. [ABSTRACT FROM PUBLISHER]

The notion that Stimulated Brillouin Scattering (SBS) is primarily defined by bulk material properties has been overturned by recent work on nanoscale waveguides. It is now understood that boundary forces of radiation pressure and electrostriction appearing in such highly confined waveguides can make a significant contribution to the Brillouin gain. Here, this concept is extended to show that gain enhancement does not require nanoscale or subwavelength features, but generally appears where optical and acoustic fields are simultaneously confined near a free surface or material interface. This situation routinely occurs in whispering gallery resonators (WGRs), making gain enhancements much more accessible than previously thought. To illustrate this concept, the first full-vectorial analytic model for SBS in WGRs is developed, including optical boundary forces, and the SBS gain in common silica WGR geometries is computationally evaluated. These results predict that gains 104 times greater than the predictions of scalar theory may appear in WGRs even in the 100 μm size range. Further, trapezoidal cross-section microdisks can exhibit very large SBS gains approaching 102 m-1W-1.With resonant amplification included, extreme gains on the order of 1012 m-1W-1 may be realized, which is 108 times greater than the highest predicted gains in linear waveguide systems. [ABSTRACT FROM AUTHOR]

Brillouin fiber laser with ultranarrow linewidth of 30 Hz is demonstrated for the first time without phase locking loop, the laser operates single longitudinal mode, while mode selection is achieved by a Fabry-Perot interferometer and a section of coreless fiber with Farday rotation mirror through optical phase conjugation, the Brillouin gain is provided by a 25-km fiber. The output linewidth is a factor of 100 reductions comparing with pump laser. Moreover, the laser exhibits an ultralow-frequency noise (<;15 Hz/Hz1/2 at 10 Hz). The proposed laser configuration provides an ideal tool to achieve linewidth reduction of any laser from kilohertz level to subhundred hertz with lower frequency noise. [ABSTRACT FROM PUBLISHER]

This paper reports a vector Brillouin optical time-domain analyzer based on heterodyne detection and IQ demodulation algorithm. This approach employs an acousto-optic frequency shifter to generate a single-frequency reference, which simplifies the probe spectrum and directly features the Brillouin gain and phase shift compared with the phase modulation. In addition, the proposed IQ demodulation algorithm makes signal processing easy to implement and allows fast and real-time demodulation. A proof-of-concept experiment is carried out in an ~1.6-km standard single-mode fiber consisting of two different sections of fibers. Both the Brillouin gain and phase-shift spectrograms are successfully measured with an ~2-m spatial resolution. The temperature dependence values of the Brillouin gain and phase-shift spectra are also measured, and the temperature dependence values of the Brillouin frequency shift show excellent linearity larger than 0.999 and almost identical slopes of 1.166 and 1.159 MHz/°C, respectively. [ABSTRACT FROM PUBLISHER]

The linearity of stimulated Brillouin scattering (SBS) is studied in detail for the first time. A closed-form expression which measures the linearity of an SBS system is derived. This expression allows one to design the region of linear operation, and the amount of Brillouin gain of an SBS system, by altering some basic system parameters. The theory presented is experimentally verified using an SBS-based microwave photonic filter structure. The effect of the length of the Brillouin medium on the linearity of the filter is investigated, and a 9.7 dB extension in the dynamic range is demonstrated by reducing the length of the fibre used as the Brillouin medium, from 25 to 0.57 km, while the filter stopband rejection level remains 30 dB. [ABSTRACT FROM PUBLISHER]

Using electromagnetic treatment, a detailed analytical investigation of stimulated Brillouin scattering (SBS) has been made for a semiconducting crystal in the presence of an external magnetostatic field. The effect of piezoelectricity (β) and magnetic field $(\vec{B}_0)$ has been introduced through equation of motion of lattice vibration and Lorentz force, respectively. The analysis is applied to both cases viz. non-piezoelectric (β = 0) and piezoelectric (β ≠ 0) in the absence (B0 =0) and the presence (B0 ≠ 0) of external magnetostatic field. The numerical estimates are made for n-type InSb crystals, taken as representative III–V semiconductor, duly shined upon by pulsed 10.6 μm CO2 laser. The inclination of applied magnetostatic field with respect to the direction of propagation of pump beam is found to augment the gain coefficient for the onset of stimulated Brillouin scattering. Moreover, the SBS gain coefficient increases with increasing scattering angle and results in a maximum value for the backscattered mode. The backward Brillouin gain is found to be nearly 104 times larger than forward gain when β ≠ 0 and B0 = 10T. The analysis also suggests the possibility of observing optical phase conjugation reflectivity as high as 106 in the weakly piezoelectric doped semiconductors with moderate magnetostatic field. The numerical estimation suggests that piezoelectric doped III–V semiconductors in the presence of magnetic field are candidate materials for fabrication of cubic nonlinear devices. [ABSTRACT FROM AUTHOR]

A frequency domain approach to distributed fiber-optic Brillouin sensing is presented and numerically analyzed. In this technique, both measurements and signal processing are performed in the frequency domain. We use an integral equation which directly relates the Brillouin gain to the Brillouin signal in the frequency domain in order to develop a new technique for the quantitative reconstruction of temperature-strain profiles along an optical fiber. The reconstruction is achieved by minimizing a cost function representing the error between the measured and the model data. Such a minimization is effectively performed by representing the unknown (temperature-strain) profile with a finite number of parameters. Numerical results confirm the effectiveness of the proposed approach and its stability with respect to measurement errors. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrate a perfectly orthogonal optical single-sideband signal generation technique using stimulated Brillouin scattering. By using both the Brillouin gain and loss, a perfectly orthogonal optical single-sideband signal is achieved. In addition, the modulation depth of the single-sideband signal is adjustable by separately tuning the gain and loss for the optical carrier. [ABSTRACT FROM PUBLISHER]