Stimulated Brillouin Scattering Frequency Research Articles

Distributed static and dynamic detection of an acoustic wave in a Brillouin random fiber laser

The interaction of random laser and gain medium is important to understand the noise origin in random fiber lasers. Here, using the optical time domain reflectometry method, the time-resolved distributed acoustic wave generated by a Brillouin random fiber laser (BRFL) is characterized. The dynamic property of the acoustic wave reflects the gain dynamics of the BRFL. The principle is based on the polarization-decoupled stimulated Brillouin scattering (SBS)-enhanced four-wave mixing process, where the probe light experiences maximum reflection when the phase match condition is satisfied. Static measurements present exponentially depleted Brillouin gain along the gain medium in the BRFL, indicating the localized random SBS frequency change in the maximum local gain region, which varies with time to contribute random laser noise as revealed in the dynamic measurement. The SBS-induced birefringence change in the Brillouin gain fiber is approximately 10 − 7 to 10 − 6 . The phase noise of the BRFL is observed directly inside the random laser gain medium for the first time via time and spatially varied acoustic wave intensity. By counting the temporal intensity statistical distribution, optical rogue waves are detected near the lasing threshold of the BRFL. Different temporal intensity statistical distribution at high and low gain positions is found, which is caused by the SBS nonlinear transfer function and localized gain. The distributed characterization methods in the paper provide a new platform to study the interaction of random lasers and gain medium, giving us a new perspective to understand the fundamental physics of the random lasing process and its noise property.

High-Temperature Sensitivity in Stimulated Brillouin Scattering of 1060 nm Single-Mode Fibers.

With the rapid advancement of Yb-doped fiber lasers (YDFL) whose output wavelength is near 1060 nm, passive fibers to carry the high optical power at the spectral range are also gaining significant importance. Stimulated Brillouin scattering (SBS) in the passive fibers connecting components in the lasers, especially, can set a fundamental limit in the power handling of YDFL systems. We experimentally analyzed SBS characteristics of passive single mode fibers (SMF) at a wavelength of 1060 nm. For two types of SMFs (Corning HI1060 and HI1060Flex), the Brillouin frequency (νΒ), its linewidth (ΔνΒ), and their variations with respect to the input laser power and the surrounding temperature were experimentally measured, along with the SBS threshold power (Pth). The optical heterodyne detection method was used to identify temperature-dependent SBS characteristics of fibers, and we found SMFs at λ = 1060 nm showed a temperature sensitivity in SBS frequency shift more than 40% higher than in conventional SMFs operating in C-band. Detailed procedures to measure the SBS properties are explained, and a new potential of 1060 nm SMF as a distributed temperature sensor is also discussed.

Photonic millimeter-wave ultrawideband signal generation using frequency upconversion based on the stimulated Brillouin scattering effect

We present a novel and simple scheme for photonic generation of a millimeter-wave ultrawideband (UWB) signal free of low-frequency components that is implemented by using a stimulated Brillouin scattering (SBS)-based frequency-doubling method. A dual-parallel Mach-Zehnder modulator is incorporated to generate appropriate optical sidebands and an optical carrier carrying the UWB signal. Then the single-sideband modulation is realized based on the successive SBS frequency shifting process. Eventually, a UWB signal is upconverted to twice the frequency of the radio frequency signal. To vindicate the feasibility of the proposed scheme, an experiment is carried out, and it turns out that a UWB signal with a bandwidth of 7GHz is upconverted to 21.75GHz. The spectrum of the generated signal meets well with the Federal Communications Commission mask.

Tunable Dual-Passband Microwave Photonic Filter Based on Stimulated Brillouin Scattering

A novel ultra-narrow dual-passband microwave photonic filter (MPF) with wide tunability based on stimulated Brillouin scattering (SBS) is presented. The proposed dual-passband MPF is implemented via the usage of carrier suppressed modulation of an electrooptic modulator (EOM). The passband separation of the dual-passband filter is determined by the oscillation radio frequency (RF) that is applied onto the EOM, where the frequency change of the RF oscillator results in two times the bandpass frequency shift with a central frequency that is symmetric with respect to the SBS frequency shift. A complete theoretical model based on the combined effects of the Brillouin gain and loss in a dual-wavelength Brillouin pump structure is presented to characterize the filter RF responses. Experimental results show a widely tunable dual-passband MPF that has an ultra-narrow bandwidth of 20.1MHz with over 35 dB out-of-band rejection ratio and a 20-3-dB bandwidth shape factor of 2.5.

Frequency spacing switchable multiwavelength Brillouin erbium fiber laser utilizing cascaded Brillouin gain fibers.

A new hybrid Brillouin erbium fiber laser scheme that employs cascaded multiple Brillouin gain fibers in a ring cavity to realize multiwavelength laser output with switchable frequency spacing is proposed and experimentally investigated. The multiple frequency downshifting processes introduced by multiple stimulated Brillouin scattering (SBS) effects in one round-trip of the cavity make it possible to realize multiwavelength output with frequency spacing that is an integer multiple of the SBS frequency shifting. With two cascaded SBS fibers, the frequency spacing can be switched between single and double SBS frequency shifting by properly adjusting the Brillouin pump power. Multiwavelength outputs with triple or quadruple SBS frequency spacing are also demonstrated by employing three or four SBS gain fibers, respectively.

Demonstration of an ultra-high frequency picosecond pulse generator using an SBS frequency comb and self phase-locking

We propose a method to generate phase-locked pulses in the picosecond regime by using Stimulated Brillouin Scattering (SBS). The phase-locked comb is generated using only long length of fiber and a single frequency CW pump laser. We show that there is a phase relationship between multiple Stokes peaks in a cavity, which directly leads to pulsing without the need to add a mode-locking component. This generates highly coherent pulses in the order of ~10 ps. The repetition frequency, which is very stable is in the order of tens of GHz, is based on the SBS frequency shift and has a linear dependence with temperature (1 MHz/°C). Such a laser could therefore be used in high-speed optical clocks and optical communication system. This system allows the pulses to be generated at any wavelength by simply changing the pump wavelength.

Stimulated Brillouin scattering generation in ns pulsed double-cladding fiber amplifier

This paper proposes a study both in theory and experiment on the phenomenon of stimulated Brillouin scattering (SBS) in a double-cladding fiber amplifier. The distortion characteristic of the 200-ns is observed through a stationary coupled-wave SBS model including the second-order Stokes wave for double-cladding fiber amplifier. The first-order Stokes wave is amplified during backward propagation to such an intense peak power that it can generate second-order Stokes wave. The stochastic aspect of pulse distortion induced by SBS is also experimentally demonstrated in the single frequency 200ns pulse amplifier with 12-m Yb3+ doped double-cladding fiber. The backward SBS pulse is observed when the pulse peak power is up to 3.3W, and the pulse width of SBS is narrower than that of the input signal. In the meantime, to overcome the difficulty of the pulse spectrum measurement, a novel method is put forward to measure the SBS frequency shift using the F–P interferometer with free spectral rang of 30G, showing a good agreement with the theoretical estimation. SBS is the main factor that limits the output pulse peak power in the amplification of the single-frequency pulse.

Photonic generation of microwave/millimeter‐wave sources without cavity or modulation using fiber stimulated Brillouin scattering

AbstractA simple photonic scheme is presented to generate microwave/mm‐wave sources by utilizing the optical heterodyne technique between an optical carrier and its Stokes light coming from stimulated Brillouin scattering (SBS) in optical fibers. Stable microwave sources with the frequencies of about 10.56 and 21.71 GHz are experimentally realized using the first‐ and second‐order SBS frequency shifts based on standard single‐mode fibers. This scheme is laser cavity or modulation free and of frequency‐multiplied capacity to achieve higher microwave and millimeter‐wave sources. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1203–1206, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24285

Measurement of the SBS gain of radiation in glasses

A method for determining the specific gain under conditions of stimulated Brillouin scattering (SBS) is proposed, which is based on measuring the amplification of a Stokes beam with an inhomogeneous spatial intensity distribution in a sample used as an SBS amplifier. Under the same experimental conditions, the values of the SBS gain are obtained for the new phosphate glass KGSS 0180 (g = 1.9 cm/GW) and for the GLS 22 (g = 1.4 cm/GW), K8 (g = 1.3 cm/GW), and KU2 (g = 1.5 cm/GW) glasses, which are widely used in laser systems. The SBS frequency shift of radiation with a wavelength of 1.054 μm (14.57±0.02 GHz) and the hypersonic velocity (5030 m/s) have been determined for the KGSS 0180 glass by optical heterodyning. The relaxation time of hypersound in the noted media is estimated.

Formation of high-quality XeCl laser radiation in a cavity with an SBS mirror

An experimental investigation was made of a XeCl laser with a cavity formed by a semitransparent plane mirror and a stimulated-Brillouin-scattering (SBS) medium. Spatial and spectral selection by the SBS mirror resulted in the formation of narrow-band highly directional radiation representing a superposition of converging and diverging beams. Each beam was amplitude-modulated at intervals of time corresponding to two round trips through the cavity and it consisted of a set of spectral lines 0.3 cm-1 wide, distributed over an interval of two SBS frequency shifts. About 30% of the energy of each beam was within the diffraction angle. The total output energy was 10 mJ when the pulse duration was 120 ns.

Observation and compensation of frequency detuning in high-reflectivity Brillouin enhanced four-wave mixing

Details of the frequency relationships among interacting beams in Brillouin enhanced four-wave mixing (BEFWM) are examined. A new technique using two individually injection-seeded single-mode lasers allows for precise control and knowledge of the relative wavelengths of the interacting beams. This is compared with the standard frequency-shifting technique employing a single laser in conjunction with stimulated Brillouin scattering (SBS) frequency shifters. A continuously tunable frequency difference ranging over many gigahertz is achieved, resulting in a valuable tool for the investigation of nondegenerate four-wave mixing processes such as BEFWM. Two variations of BEFWM are studied: ωpump1 − ωpump2 = 0 with noncollinear pumps; and ωpump1 − ωpump2 = ωSBS with collinear pumping. Resonance spectra of BEFWM gain versus probe–pump frequency shift show a significant detuning in the frequency for the gain maximum from the expected Brillouin shift for the former case. When the probe–pump frequency is tuned in compensation for this detuning, improvements in BEFWM phase conjugation are realized in comparison with more conventional techniques using SBS frequency shifting.