Simulation of Brillouin gain properties in a double-clad As_2Se_3 chalcogenide photonic crystal fiber

The Brillouin gain properties in a double-clad As_2Se_3 photonic crystal fiber(PCF)are simulated based on the finite-element method(FEM).The results indicate that the Brillouin gain spectrum(BGS)of our proposed chalcogenide PCF exhibits a multipeaked behavior and has a high Brillouin gain coefficient.We also find that a larger size of inner cladding air holes will lead to a more pronounced second peak in the BGS.On the other hand,the size of the outer cladding has nearly no effect on the BGS behavior.Through these results,one can tailor the Stimulated Brillouin scattering effect in PCFs for a wide range of applications.     

Characterization of stimulated Brillouin scattering in small core microstructured chalcogenide fiber

We report a full modal characterization of the stimulated Brillouin scattering (SBS) properties in small core As₂Se₃-based chalcogenide photonic crystal fibers (PCFs). Our results include the calculation of Brillouin gain spectrum (BGS), Brillouin gain coefficient (g_B), Brillouin frequency shift (BFS) by taking into account the contribution of the higher-order acoustic modes. We show that for a highly nonlinear PCF having a 2-μm hole-to-hole pitch and a 0.5-μm hole diameter, a Brillouin gain coefficient g_B = 5.91 10^? 9 m.W^? 1 is obtained around the acoustic frequency of 8.19 GHz, which is more than 340 times larger than that of the same PCF made with silica glass. We demonstrate that the BGS of small core PCF structures show strong SBS and multipeaked behavior, with a presence of a second peak, when decreasing the core diameter which is to be attributed to the higher-order acoustic modes. We designed small core PCFs with tailored Brillouin response for a wide range of applications.     

Slow-light delay enhancement in small-core pure silica photonic crystal fiber based on Brillouin scattering

We demonstrate that we realize large-delay slow light based on stimulated Brillouin scattering in a short length of our fabricated small-core photonic crystal fiber (PCF). The cavity effect from the partially reflective splices in the end of the PCF enhances slow-light delay significantly. Our experiments show that large slow-light delay can be easily realized in a very short length of the PCF with a moderate pump power. Up to a one-half pulse-width delay is achieved in only 50 m of PCF in a single pump segment.     

Brillouin gain spectrum characterization in Ge-doped large-mode-area fibers

The dependence of Brillouin gain spectrum (BGS) characteristics, including the Brillouin frequency shift (BFS) and the BGS bandwidth, on germanium concentration in large-mode-area Ge-doped passive fibers is investigated theoretically and experimentally. The simulation results show that the BFS is inversely proportional to GeO₂ concentration, and the BGS bandwidth initially increases with the augment of GeO₂ concentration, and then decreases. The BGSs of four fibers with core diameters of 10 μm and 20 μm for different GeO₂ concentrations are compared experimentally. Experimental results demonstrate that with the same core diameter, the variations of BFS and BGS bandwidths with GeO₂ concentration accord with the simulation results. Additionally, the BGS characteristics of three large-mode-area passive fibers with diameters of 10 μm, 25 μm, and 30 μm are measured, which confirm that the increasing of the fiber diameters will cause the BGS bandwidth to broaden. We believe that these results can provide valuable references for modulating the high-power narrow-linewidth fiber lasers and Brillouin fiber amplifiers.     

液芯光纤中基于多线抽运调制的带宽可控平顶布里渊增益谱

提出在CS₂/CCl₄混合介质液芯光纤中利用多线抽运调制 技术实现带宽可控平顶布里渊增益谱的方法, 理论研究了抽运光谱线间距、谱线强度和芯液介质混合比对布里渊增益谱的影响, 得到了带宽可控平顶增益谱的条件. 结果表明, 采用一个强度或相位调制器, 基于单频和多频调制技术产生2–9条抽运光谱线, 通过控制谱线间距和各谱线强度比, 并改变CS₂体积分数, 获得了增益带宽在50 MHz–2 GHz 范围内可控的平顶增益谱. 该方法操作简便、带宽调控范围大, 可用于高增益低畸变布里渊放大, 满足微弱光信号探测和慢光系统的应用需求. 关键词： 受激布里渊散射 布里渊增益谱 多线抽运调制 液芯光纤     

Observation of stimulated Brillouin scattering in polymer optical fiber with pump-probe technique

Stimulated Brillouin scattering (SBS) in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm core diameter was experimentally observed for the first time, to the best of our knowledge, at 1.55 μm wavelength with the pump-probe technique. Compared to spontaneous Brillouin scattering previously reported, the Brillouin gain spectrum (BGS) was detected with an extremely high signal-to-noise ratio, even with a short POF (1 m) and scrambled polarization state. We also investigated the BGS dependences on probe power and temperature, which indicate that SBS in a POF measured with this technique can be utilized to develop high-accuracy temperature sensing systems.     

Fusion splicing small-core photonic crystal fibers and single-mode fibers by repeated arc discharges

We demonstrate a novel method for low-loss splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) by repeated arc discharges using a conventional fusion splicer. An optimum mode field match at the interface of PCF-SMF and an adiabatic mode field variation in the longitudinal direction of the small-core PCF can be achieved by repeated arc discharges applied over the splicing joint to gradually collapse the air holes of the small-core PCF. This method is simple and offers a practical solution for light coupling between small-core PCFs and SMFs.     

Photopolymer microtips for efficient light coupling between single-mode fibers and photonic crystal fibers

A novel method for light coupling between single-mode fibers (SMFs) and small-core photonic crystal fibers (PCFs) is demonstrated. The method is based on growing photopolymer microtips directly on the end faces of SMFs. The shape and size of the tips can be controlled by adjusting the laser power and the exposure time for polymerization to match the mode field to the small-core PCFs. A 5 dB improvement in coupling efficiency between a SMF and a commercial small-core, highly nonlinear PCF is experimentally demonstrated. This compact and efficient butt-coupling method is particularly suitable for PCF gas sensor applications.     

光子晶体光纤中布里渊散射声波模式特性的分析

推导了光子晶体光纤中声波微小位移波动方程; 研究了泵浦波长以及纤芯折射率对声波模式的影响; 应用石英圆柱模型研究了小芯径光子晶体光纤中纤芯直径对布里渊声波模式色散的影响. 结果表明在光子晶体光纤中, 纵向声波和横向声波共同作用产生质点声场, 两者相互耦合将产生混合声波模式; 可以通过改变泵浦波长或光子晶体光纤纤芯折射率来改变参与布里渊散射(BS) 过程的声波模式的传播常数; 随着光子晶体光纤(PCF) 纤芯直径的增大, 声波模式耦合程度得到加强, 相速度呈减小趋势, 且同一传播常数下, 声波模式数呈增多趋势; 随着泵浦波频率的增大, 声波相速度减小.     

Optical refractometer based on large-core air-clad photonic crystal fibers

A large-core air-clad photonic crystal fiber-based sensing structure is described, which is sensitive to refractive index. The sensing head is based on multimodal interference, and relies on a single-mode/large-core air-clad photonic crystal fiber (PCF)/single-mode fiber configuration. Using two distinct large-core air-clad PCF geometries-one for refractive index measurement and the other for temperature compensation, it was possible to implement a sensing head sensitive to refractive index changes in water as induced by temperature variations. The results indicated the high sensitivity of this sensing head to refractive index variations of water, and a resolution of 3.4×10(-5) refractive index units could be achieved.     

Dependence of the brillouin frequency shift on strain and temperature in a photonic crystal fiber

The dependence of the Brillouin frequency shift on strain in a photonic crystal fiber (PCF) was measured at a wavelength of 1320 nm for the first time to the authors' knowledge. Together with measurements of the dependence of the Brillouin frequency shift on temperature in the PCF, we demonstrate the feasibility of the highly precise simultaneous measurement of temperature and strain by use of the PCF in a distributed Brillouin sensing system with a spatial resolution of 15 cm.     

Brillouin scattering spectrum in photonic crystal fiber with a partially germanium-doped core

The Brillouin scattering spectrum in a photonic crystal fiber (PCF) with a partially Ge-doped core is measured with a pump-probe technique at a wavelength of 1320 nm. One main peak and four subpeaks are observed. The main peak has a Lorentzian shape with the bandwidth deltanuB = 66 MHz. Its intensity is six times higher than that from a standard single-mode fiber measured under the same conditions, which is consistent with the ratio of (1/Aeff(PCF))/(1/Aeff(SMF)), where Aeff is the effective area of the fibers. The temperature coefficient for the main peak is 0.96 MHz/degrees C. We believe that the subpeaks are caused by an interaction between light-wave and guided modes of longitudinal acoustic waves in the graded-Ge-doped region, the silica region, and the microstructured cladding. An analysis of the guiding and antiguiding properties of the PCF for acoustic waves is presented.     

Investigation on threshold power of stimulated Brillouin scattering in photonic crystal fiber

We have developed a theoretical approach to simulate stimulated Brillouin scattering (SBS) generation in photonic crystal fiber (PCF). The threshold condition for the SBS occurrence has been derived as a function of fiber parameters and input pump power. A particular emphasis is given to the influence of the input pump power and fiber length on the Brillouin gain in the PCF. To assess threshold pump power accurately, the pump depletion effect has been included by employing the 1% criterion. This simulation can anticipate the Brillouin threshold gain value precisely. The threshold gain varies from 14 to 18 depending on the PCF length.     

On the pre-amplified linear cavity multi-wavelength Brillioun-erbium fiber laser with low SBS threshold highly nonlinear photonic crystal fiber

An efficient multi-wavelength Brillouin-erbium fiber laser utilizing low stimulated Brillouin scattering threshold highly nonlinear photonic crystal fiber (PCF) is presented. A Fabry-Perot pre-amplified Brillouin pump configuration was used which consists of 100 m PCF and 10 m erbium doped fiber (EDF). Up to 28 output channels with SNR of more than 20 dB could be generated with modest pump power.     

A low-threshold multiwavelength Brillouin fiber laser with double-frequency spacing based on a small-core fiber

We demonstrate multiwavelength Brillouin fiber lasers (MWBFLs) with double-frequency spacing based on a small-core fiber (SCF) and a standard single-mode fiber (SMF), which have core diameters of 5 and 8.8 μm, respectively. Experimental results show that the SCF-based MWBFL exhibits a higher laser output power and a lower pump threshold. The output powers of the SCF-based MWBFL are > 1.4 times those of the SMF-based MWBFL. Moreover, the threshold power required to generate each channel of the SCF-based MWBFL is 59% that of the SMF-based MWBFL. When the same pump power of 180 mW is injected, the number of laser channels generated for the SCF-based MWBFL is 13, which is twice that generated for the SMF-based MWBFL. In addition, the SCF-based MWBFL exhibits good wavelength tunability from 1535 to 1565 nm and temporal stability over an hour.     

High-power tunable single-frequency single-mode erbium:ytterbium codoped large-core fiber master-oscillator power amplifier source

We present a cladding-pumped single-frequency, single-mode erbium:ytterbium codoped fiber master-oscillator power amplifier source generating up to 151 W of continuous-wave output power at 1563 nm with 33% slope efficiency and 20 dB gain. This source was also tunable and had a stable operation range of 1546 to 1566 nm at an output power level in excess of 125 W. The doped fiber exploited a large-core design for improved power handling and mitigation of stimulated Brillouin scattering. There was no sign of having stimulated Brillouin scattering even at the highest power. Despite a large core (V = 12), the output beam was nearly diffraction limited (M2 = 1.1). The source showed slight rollover at over 100 W of output power because of the onset of emission from ytterbium, centered at 1060 nm.     

Photonic crystal ber-based multi-wavelength Brillouin ber laser with dual-pass ampli cation con guration

A simple technique for achieving a stable, room temperature and multi-wavelength lasing with narrow linewidth is demonstrated using Brillouin ber laser (BFL) with a 100-m-long photonic crystal ber (PCF) in conjunction with a dual-pass configuration. A broadband ber Bragg grating (FBG) operating in the C-band region is incorporated at the end side of the setup to allow a dual-pass operation. The proposed BFL can operate at any wavelength depending on the Brillouin pump wavelength and the FBG’s reflection region used. With a Brillouin pump (BP) of 15.7 dBm, approximately 7 Stokes and 4 anti-Stokes lines are obtained with a line spacing of 0.08 nm.     

Brillouin characterization of holey optical fibers

We report the results of detailed measurements on the Brillouin frequency shift (BFS), gain bandwidth, and gain coefficients of several small-core holey optical fibers (HFs) of both uniform and axially varying structural characteristics and compare these with measurements on more conventional fibers. Our measurements show that the BFS of HFs is first-order proportional to the modal index for light propagating along the fiber and is thus extremely sensitive to its precise structural parameters. Our results highlight the possibility of using distributed Brillouin scattering measurements to perform nondestructive structural characterization of HFs, and the possibility of producing Brillouin-suppressed HFs using controlled structural variation along the fiber length.     

Applications of Nonlinear Effects in Highly Nonlinear Photonic Crystal Fiber to Optical Communications

Unique dispersion characteristics and enhanced nonlinearity make the small-core photonic crystal fiber (PCF) an ideal candidate for nonlinear optical devices to telecommunication applications. Some technical reasons behind great research interest of highly nonlinear PCFs in optical communication components are reviewed. Nonlinear effects in highly nonlinear PCFs and their research progress are presented. Several typical applications including WDM sources, optical amplification, optical switching, wavelength conversion, optical regeneration and all-optical demultiplexing etc are introduced, together with state-of-the art performances. Some new possible applications and future prospects are discussed.     

Influences of pump wavelength and environment temperature on the dual-peaked Brillouin property of a small-core microstructure fiber

The influences of the pump wavelength and temperature on the dual-peaked Brillouin property of a piece of a small-core microstructure fiber are investigated using the heterodyne method. The experimental results indicate that the dispersion characteristics of the acoustical modes participating in the Brillouin scattering are formed by the coupling of two acoustical modes with different acoustical field distributions. The influence of the pump wavelength can contribute to the variation of the acoustical mode wave vectors. On the other hand, the influence of the environment temperature can contribute to the shift of acoustical mode dispersion map by the variation of the material mechanical parameters and thermal expansion. The model and experiment results demonstrate that the height ratio of the two Brillouin peaks can be controlled by adjusting the pump wavelength or environment temperature.