Tunable Bragg gratings for fiber lasers

A tuning method of a fiber Bragg grating by the bending compression-tension is considered. With this method, a relative tuning range of the resonance wavelength of the grating of about 5% has been obtained. The changes in the shape of the spectrum and in the grating reflectivity during the tuning process are studied. The reflectivity of the fiber Bragg grating has been found to considerably increase with increasing degree of compression. It is shown that such an increase is caused by compression-induced changes in the refractive index modulation amplitude in the grating. The fiber Bragg grating developed has been applied for tuning the radiation wavelength of an ytterbium fiber laser. The tuning range of the laser has been found to be 45 nm around the central wavelength 1080 nm.     

The ultra narrow-band fiber grating filter

In this paper, we propose an ultra narrow band fiber grating filter which is composed of two optical circulators and two fiber Bragg gratings (FBG). Through numerical simulation and experiment investigation, a narrow-band output spectrum with 1064 nm center wavelength and 0.017 nm bandwidth is obtained. It may find a certain application in the fields of free space optic communication, laser tuning and so on as we believe.     

Incorporation of a fiber Bragg grating to improve the efficiency of a 1580-nm-band tunable fiber ring laser

An efficient and tunable 1580-nm-band erbium-doped fiber ring laser is achieved by injection of amplified spontaneous emission in a conventional band by a fiber Bragg grating into the gain medium. The insertion of the fiber Bragg grating reduces the lasing threshold to 25%. The tuning range is 1560-1610 nm; the side-mode suppression ratio is better than 65 dB.     

73-nm tuning of a double-clad Yb<Superscript>3+</Superscript>-doped fiber laser based on a hybrid array

We report on a wide wavelength tuning in a double-clad ytterbium-doped fiber laser. The laser cavity consists of an array of broadband high-reflection fiber Bragg gratings and a bulk grating as the output coupler and wavelength selection element. The proposed fiber laser configuration combines a low intracavity loss of the fiber Bragg grating mirrors with a wide wavelength tuning of the bulk gratings. We demonstrate a >70-nm wavelength tuning range, limited only by the available fiber Bragg gratings.     

Highly reliable strain-tuning of an Erbium-doped fiber laser for the interrogation of multiplexed Bragg grating sensors

The authors implemented a tunable linear cavity Erbium-doped fiber (EDF) laser for the interrogation of multiplexed fiber Bragg grating sensors (BGS). A high-strength single-pulse draw-tower fiber Bragg grating (FBG) was used as the mechanically tunable element enabling the rapid wavelength sweeping of the laser center wavelength. A simple algorithm to process the noisy acquired data and identify the peak of the BGS spectra was employed. For the first time, this type of configuration was used to reliably interrogate at least three fiber Bragg grating sensors with a standard wavelength spacing between the Bragg wavelengths of 3 nm, without risk of breaking the stretched fiber, using an FBG with a simple PZT driven mount as the tuning elements.     

Wavelength-tunable, passively mode-locked fiber laser based on graphene and chirped fiber Bragg grating

We demonstrate a wavelength-tunable, passively mode-locked erbium-doped fiber laser based on graphene and chirped fiber Bragg grating. The saturable absorber used to enable passive mode-locking in the fiber laser is a section of microfiber covered by graphene film, which allows light-graphene interaction via the evanescent field of the microfiber. The wavelength of the laser can be continuously tuned by adjusting the chirped fiber Bragg grating, while maintaining mode-locking stability. Such a system has high potential in tuning the mode-locked laser pulses across a wide wavelength range.     

一种新颖的光纤光栅温度调谐装置的原理与实验研究

提出了一种新颖的光纤光栅温度调谐方案，并将按此方案制作的调谐装置命名为双肩梁，详细分析了其原理.设计制作了一套双肩梁调谐装置，并对其进行了实验研究.实验中得到了0.436nm/℃的温度调谐效率，把所用光纤光栅的温度灵敏度提高了50倍之多.调谐具有很好的线性和可重复性.该装置最大的优点在于它突破了以往热调谐方法中驱动材料热膨胀系数的限制，使得温度调谐效率可以根据实际需要进行灵活设计，从而具有很大的灵活性.该装置在激光器调谐、高灵敏度温度传感以及传感解调等领域有着很大的潜在应用价值. 关键词： 光纤光栅 调谐 双肩梁 温度调谐     

光纤光栅选频掺Yb3+双包层光纤激光器

利用相位掩模法，在D形内包层掺Yb3+双包层光纤一端直接写制出Bragg光栅，用作双包层光纤激光器的输出腔镜.试验得到了线宽为0.196nm，波长为1058.2nm，最高输出功率为570mW的稳定激光输出，解决了激光器中模式竞争造成的输出不稳定现象.从速率方程出发，对激光器的输出功率与抽运功率、光栅反射率的关系以及最佳光纤长度进行了理论分析，结果与实验符合很好. 关键词： 双包层光纤光栅 掺Yb3＋双包层光纤激光器 相位掩模 速率方程     

A linearly-polarized tunable Yb-doped fiber laser using a polarization dependent fiber loop mirror

A Ytterbium-doped linearly-polarized fiber laser is constructed with a polarization maintaining fiber Sagnac loop mirror. The fiber loop mirror made of polarization maintaining fiber coupler has a polarization dependent reflectivity, which provides the necessary polarization discrimination between the slow and fast axes. With a fiber Bragg grating written in normal polarization maintaining fiber as an output coupler, laser output of up to 5.6 W at 1070 nm is generated with a polarization extinction ratio of > 20 dB and an overall efficiency of 55%. The broadband polarization dependent reflection of the fiber loop mirror offers advantages of easy spectral tuning and simple linearly-polarized laser generation.     

High-Q, tunable, photonic microwave single passband filter based on stimulated Brillouin scattering and fiber Bragg grating filtering

We experimentally demonstrate a single passband, photonic microwave bandpass filter scheme based on stimulated Brillouin scattering (SBS) in optical fiber. A single side band (SSB)-modulated probe and a single frequency, tunable pump beam that have been produced by the combination of conventional Mach-Zehnder modulators and fiber Bragg grating filters, are used for the generation of SBS phenomenon in a 1-km long highly nonlinear dispersion-shifted optical fiber. Using the proposed scheme a single microwave passband with a ∼26 MHz bandwidth is readily achieved over a radio frequency tuning range from 1.3 to 9.3 GHz. The maximum Q-factor is measured to be ∼360.     

光纤光栅选频掺Yb3+双包层光纤激光器

利用相位掩模法 ,在D形内包层掺Yb3 双包层光纤一端直接写制出Bragg光栅 ,用作双包层光纤激光器的输出腔镜 .试验得到了线宽为 0 196nm ,波长为 10 5 8 2nm ,最高输出功率为 5 70mW的稳定激光输出 ,解决了激光器中模式竞争造成的输出不稳定现象 .从速率方程出发 ,对激光器的输出功率与抽运功率、光栅反射率的关系以及最佳光纤长度进行了理论分析 ,结果与实验符合很好     

Influence of uniaxial crystal material cladding on reflectivity and dispersion of uniform fiber Bragg grating

The fiber Bragg grating with cladding made of uniaxial crystal material whose optical axis is parallel to the axis of fiber Bragg grating proposed in the paper published in 2003 was investigated again and an error was corrected in the calculation, its effective index, reflectivity and dispersion were examined using coupled-mode theory and numeric solution. The calculated results indicate that no low frequency cutoff phenomenon exists in the HE₁₁ mode, more power is transmitted by the core of the fiber with cladding made of isotropic material, the reflectivity of the fiber Bragg grating with cladding made of uniaxial crystal material is much higher than that with cladding made of isotropic material, the parameter K_cl, i.e., the ratio of the extraordinary to the ordinary ray refractive index, has a stronger impact on the reflectivity, Bragg wavelength and the dispersion of this kind of fiber Bragg grating when it varied from 1.00 to 1.01 than in other regions. This means that the characteristics of the fiber Bragg grating with uniaxial crystal cladding can be changed through adjusting K_cl while keeping its length, periodicity and the other parameters as constants.     

基于相移光纤光栅的布拉格波长解调原理的分析

提出了一种基于相移光纤光栅(phase shifted fiber grating)的布拉格波长解调技术，相移光纤光栅在反射谱阻带中能打开线宽极窄的一个或多个通透窗口，而且窗口位置随所加相移量的大小呈线性变化。实验中应用电流调谐相移量以实现布拉格波长的解调。选用最大波长偏移量为2nm的相移光纤光栅进行调谐滤波，温度的测量范围可达到200℃，应变的测量范围可达到2000μs。实验表明利用相移光纤光栅进行布拉格波长解调，取得了预期的效果，为布拉格波长解调技术提出了新的思路。     

All-optical control of Bragg grating in semiconductor-coated D-shaped fiber

A Bragg grating was fabricated in a D-shaped fiber that was subsequently coated with an alpha-Si:H semiconductor film. The reflected spectrum was optically controlled by means of evanescent coupling, shifting to shorter wavelengths with increased control-light power. The effective nonlinearity of the fiber was 2.0 x 10(-10) cm(2)/W . The device was optically tuned by 4.3 x 10(-4) nm/mW , leading to 54% (>3-dB) depth modulation for 230 mW of power.     

Oscillation wavelength of fiber Bragg grating semiconductor lasers

Based on the physical fact that a laser containing a gain medium with homogenous line broadening oscillates at the wavelength which requires the smallest threshold gain due to the mode competition effect, after taking into account the wavelength-depended reflectivity distribution profile of a fiber Bragg grating, the oscillation wavelength λ_l of fiber Bragg grating semiconductor lasers has been investigated theoretically. The results show that the laser oscillation wavelength λ_B is not fixed at the Bragg reflection wavelength λ_l of fiber Bragg grating, and the offset between λ_B and λ_l depends on the reflectivity distribution profile of fiber Bragg grating and the gain profile of semiconductor gain medium.     

Tunable dual-wavelength fiber laser based on a polarization-maintaining fiber Bragg grating and a Hi-Bi fiber optical loop mirror

We demonstrate experimentally the operation of a linear cavity dual-wavelength fiber laser using a polarization maintaining fiber Bragg grating (PM-FBG) as an end mirror that defines two closely spaced laser emission lines. The PM-FBG is also used to tune the laser wavelengths. The total tuning range is ∼8 nm. The laser operates in a stable dual-wavelength mode for an appropriate adjustment of the cavity losses for the generated wavelengths. The high birefringence (Hi-Bi) fiber optical loop mirror (FOLM) is used as a tunable spectral filter to adjust the losses. The FOLM adjustment was performed by the temperature control of the Hi-Bi fiber.     

Enhanced thermal and magnetic actuations for broad-range tuning of fiber Bragg grating based reconfigurable add drop devices

We demonstrate two new approaches to broad-range tuning of fiber Bragg grating devices: amplified thermal tuning and programmable magnetic tuning. The thermal-strain tuning approach employs a novel configuration to amplify thermally induced wavelength shifts by use of a negative thermal-expansion component. The magnetic-strain tuning approach allows programmable and latchable wavelength shifts through magnetic interactions that induce controlled strain on the fiber grating. The advantages and disadvantages of these two techniques are contrasted.     

Millimeter-wave pulse generation based on pulse reshaping using superstructure fiber Bragg grating

A novel optical approach is proposed to generate millimeter wave (MMW) pulse signal based on the pulse reshaping of superstructure fiber Bragg grating (SSFBG). In our scheme, one input pico-second Gaussian pulse is transformed into n Gaussian pulses by the SSFBG reshaping firstly, and then the pulse train is replicated to form a required frequency modulation MMW optical pulse envelope by the linear chirped fiber Bragg grating (LCFBG) or other highly dispersive element. The high-speed photodetector (PD) and band-pass filter can transform the MMW optical pulse into an MMW pulse signal ultimately. Depending on this scheme, MMW signals with frequency up to 10 GHz can be easily generated by the completed fiber components.     

Simultaneous measurement of strain and temperature based on a fiber Bragg grating combined with a high-birefringence fiber loop mirror

We present an all-fiber sensor for simultaneous measurement of temperature and strain. The sensing head is formed by introducing a fiber Bragg grating into a high-birefringence fiber loop mirror that acts as a Mach-Zehnder interferometer for temperature and strain discrimination. A sensing resolution of ±1 °C in temperature and ±21 με in strain has been experimentally achieved over a temperature range of 60 °C and strain range of 600 με.