双波长啁啾相移光纤光栅

理论研究并实验验证了一种含有两段π相移的啁啾相移光纤光栅.采用F矩阵对啁啾相移光纤光栅进行计算并分析了该光栅的谱特性.含有两段π相移的啁啾相移光纤光栅可以在普通啁啾光栅透射谱阻带中产生双波长透射峰,透射峰位置直接取决于光栅中π相移的位置,透射峰的线宽和透射峰的波长间隔没有关系,仅随着啁啾率的增大而增大.采用带相位掩模的逐点扫描法对含有两段π相移的双波长啁啾相移光栅进行了制作,获得波长间隔为8 nm的双波长透射谱的光栅器件.该光栅的消光比和3 dB谱线宽分别为20 dB和0.08 nm,实验结果和理论设计一致.     

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser's peak powers can get 3.1 mW above and have a good stability.     

Thermally switchable and discretely tunable comb filter with a linearly chirped fiber Bragg grating

We propose and experimentally demonstrate a novel switchable and discretely tunable comb filter based on a thermally induced linearly chirped fiber Bragg grating. Experimentally we achieved a thermally induced optical bandpass filter that has eight switchable passband peaks with peak separations of 1.6 and 3.2 nm, a very narrow bandwidth (as small as 10 pm) of each peak, a tunable range of 16.5 nm, and a greater than 25 dB rejection ratio. Two spectral peaks separated by only 0.8 nm were also obtained with this comb filter. This filter provides the unique advantages of an all-fiber structure, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, low polarization sensitivity, simple structure, ease of fabrication, and low cost.     

Solgel grating waveguides for distributed Bragg reflector lasers

Solgel grating waveguides and their application to the fabrication of external-cavity distributed Bragg reflector (DBR) lasers are demonstrated. A new composition of aluminosilicate material is developed for the fabrication of single-mode waveguides and Bragg reflectors. An average loss of <0.2 dB/cm is measured in the single-mode waveguides at 1550 nm. The reflectors show filtering greater than 97% near 1530 nm, with a bandwidth of ~0.6 nm . The Bragg reflectors are used as feedback resonators for DBR lasers. Single-mode lasing with a sidemode suppression of better than 25 dB is demonstrated.     

Fabrication of Dual-Wavelength Fiber Bragg Grating with a Longitudinal Stretch

A method of fabricating dual-wavelength fiber Bragg grating with a uniform phase mask is demonstrated. Theoretical analysis and numerical simulation using Matrix method are given. The moving exposing technique is adopted. Good control over the grating’s reflectivity and the separation of the two Bragg wavelengths is enabled by adjusting the stretch, the length of the grating, and the exposure. A grating with two equal transmission peaks of 19.5 dB is obtained by using this method, and the separation of the two Bragg wavelengths is 0.78 nm. Translated from Chinese Journal of Quantum Electronics, 2005, 22(1) (in Chinese)     

Improved stabilization of a 1.3 microm femtosecond optical frequency comb by use of a spectrally tailored continuum from a nonlinear fiber grating

We report significant enhancement (+24 dB) of the optical beat note between a 657 nm cw laser and the second-harmonic generation of the tailored continuum at 1314 nm generated with a femtosecond Cr:forsterite laser and a nonlinear fiber Bragg grating. The same continuum is used to stabilize the carrier-envelope offset frequency of the Cr:forsterite femtosecond laser and permits improved optical stabilization of the frequency comb from 1.0 to 2.2 microm. Using a common optical reference at 657 nm, a relative fractional frequency instability of 2.0 x 10(-15) is achieved between the repetition rates of Cr:forsterite and Ti:sapphire laser systems in 10 s averaging time. The fractional frequency offset between the optically stabilized frequency combs of the Cr:forsterite and Ti:sapphire lasers is +/-(0.024 +/- 6.1) x 10(-17).     

High extinction ratio in-fiber polarizers based on 45 degree tilted fiber Bragg gratings

We report a near-ideal in-fiber polarizer implemented by use of 45 degrees tilted fiber Bragg grating structures that are UV inscribed in hydrogenated Ge-doped fiber. We demonstrate a polarization-extinction ratio of 33 dB over a 100-nm operation range near 1550 nm. We further show an achievement of 99.5% degree of polarization for unpolarized light with these gratings. We also theoretically investigate tilted grating structures based on the Green's function calculation, therein revealing the unique polarization characteristics, which are in excellent agreement with experimental data.     

Superstrate index control of waveguide grating reflectivity

Control of reflectivity of a relief grating in a high-index film overlaid on a monomode glass waveguide was achieved by adjustment of the superstrate refractive index with liquids. Weak gratings reflecting at 1531 nm were inscribed by UV laser ablation. The grating reflectivity was measured as the ratio of the transmission outside the reflection band, at 1536 nm, to that at the Bragg wavelength. Reflectivity with an air superstrate was <0.3 dB for both polarizations. In the TE polarization the grating strength increased to 20.5 dB after application of a liquid of index 1.45. In the TM polarization the strength increased to 27 dB with a superstrate index of 1.50. Good agreement was found with a theoretical model based on beam propagation.     

光纤光栅外腔半导体激光器的高频调制特性

报道了光纤光栅外腔激光器瞬态特性的理论分析,引入了一个适用于外腔情况的等效光子寿命,模拟计算表明,要获得高于2．5GHz的调制速率,光纤光栅外腔的长度必须短于4cm范围,对所研制的光纤光栅外腔激光器进行了高频调制测量,得到了在1GHz下的单模激光输出,边模抑制比在40dB以上,3dB动态线宽为0．1nm左右,20dB动态线宽为0．3nm。     

Superchirped moiré grating based on an acousto-optic superlattice with a chirped fiber Bragg grating

A superchirped moiré grating has multiple superimposed chirped Bragg gratings. We show that a superchirped moiré grating can be formed in an acousto-optic superlattice with a chirped fiber Bragg grating. There are multiple transmission peaks related to Fabry-Perot resonance in the transmission spectrum. The peak spacing is varied by the acoustic frequency. The proposed devices can be used as tunable multiple-passband transmission filters and switches.     

基于高双折射光纤布拉格光栅的自动增益控制掺铒光纤放大器

掺铒光纤非均匀展宽引起的空间烧孔现象导致单波长激光并不能完全控制放大器增益,提出了一种新颖的自动增益控制掺铒光纤放大器的结构:即采用高双折射光纤布拉格光栅产生抽运光,其写制光栅的波峰对应的波长分别为1549.3 nm和1549.83 nm,波长间隔为0.53 nm。通过调整偏振控制器,就实现了单激光或双激光的增益控制。这种设计增益控制范围为40 nm(1530~1570 nm),当输入功率在-40~-15 dBm的动态范围内,双激光增益控制的掺铒光纤放大器的平均增益和噪声系数分别约为22.22 dB和8.69 dB,而它们的漂移分别被钳制在0.69 dB和1.51 dB。系统性能测试表明:双激光控制掺饵光纤放大器在稳定性方面比单激光有着明显的优势。     

A stable dual-wavelength fiber laser with tunable wavelength spacing using a polarization-maintaining linear cavity

We propose and experimentally demonstrate a stable dual-wavelength erbium-doped polarization-maintaining (PM) fiber laser with tunable wavelength spacing using an all-PM linear cavity that makes use of two reflection peaks from the PM fiber Bragg grating (PM-FBG). Experimental results show stable dual lasing lines with a wavelength separation of ∼0.22 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. By applying axial strain to the PM-FBG, the center wavelengths of the two lasing lines can be tuned over several nanometers and the wavelength separation between the lasing lines can also be tuned to as small as 0.05 nm, which, to our knowledge, is the smallest wavelength spacing ever obtained from a stable room-temperature dual-wavelength fiber laser. The proposed laser configuration has the advantages of simple structure, low loss, stable dual-wavelength operation and a very small lasing linewidth of ∼5 kHz . PACS 42.55.Wd; 42.81.-i; 42.81.Gs     

Microwave generation using an all polarization-maintaining linear cavity dual-wavelength fiber laser with tunable wavelength spacing

A stable dual-wavelength erbium-doped fiber laser with a linear cavity is formed by a polarization-maintaining uniform fiber Bragg grating (PM-FBG) and a polarization-maintaining linearly chirped fiber Bragg grating (PM-LCFBG), both of which were fabricated on a high-birefringence (Hi-Bi) fiber. Experimental results show stable dual-wavelength lasing operation with a wavelength separation of ∼0.22 nm, which can be tuned down to as small as 0.05 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room-temperature. Microwave signal at frequency of 9.41, 18.03 and 27.46 GHz is achieved by heterodyned the output lasing wavelengths on a photodetector.     

Chirped pulse amplification with a nonlinearly chirped fiber Bragg grating matched to the Treacy compressor

We demonstrate a fiber chirped pulse amplification system that uses an engineered nonlinearly chirped fiber Bragg grating stretcher dispersion matched to the Treacy compressor. The seed pulses at 1558 nm are stretched to 720 ps, amplified by more than 50 dB to 6.5-microJ energy, and recompressed to 940 fs. After almost 1000 times compression the pulses are within 30% of the bandwidth limit and have a contrast ratio of better than 30 dB.     

Tunable microwave photonic notch filter using a dual-wavelength fiber laser with phase modulation

A novel tunable microwave photonic notch filter using a phase-modulated dual-wavelength fiber laser is presented. A stable dual-wavelength erbium-doped fiber laser with a linear cavity is formed by a polarization-maintaining uniform fiber Bragg grating (PM-FBG) and a polarization maintaining linearly chirped fiber Bragg grating (PM-LCFBG), both of which were fabricated on a high-birefringence (Hi-Bi) fiber. It is found that a stable room-temperature dual-wavelength operation can be achieved due to the presence of two reflection peaks arising from the orthogonal states of polarization (SOP) of the PM-FBG. Experimental results show stable dual-wavelength lasing operation with a wavelength separation of ∼0.36 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. The dual-wavelength fiber laser is combined with a phase modulator and a segment of single-mode fiber (SMF) as a dispersive device to form a tunable microwave photonic notch filter. By stretching the PM-FBG to tune the wavelength separation of the dual-wavelength fiber laser, a tunable microwave photonic notch filter with various free spectral ranges (FSRs) and a rejection ratio greater than 35 dB was developed.     

All-Fiber Spectroscope with Second-Order Fiber Bragg Grating for Rotational Raman Lidar

Owing to the second-order fiber Bragg grating possessing narrower reflectivity bandwidth than first-order, an all-fiber spectroscopic filter with several second-order fiber Bragg gratings and optical fiber couplers in the visible region is designed to extract interest rotational Raman spectra. Considering the inference fringe visibility of inscribing fiber Bragg grating and the fiber core index dispersion effect, numerical simulations are made by the improved mathematical model based on an exponential photorefractive dynamic, and its simulative results show better agreement with the experimental data. We propose an all-fiber spectroscopic configuration, which could balance lidar sensitivity against signal-to-noise ratio for optimizing remote sensing performance by fiber Bragg gratings serially. Simulative results show that the thumb principle for fabricating second-order fiber Bragg grating is the increasing gratings length, and that this all-fiber spectroscope can achieve >70 dB suppression to elastic scattering and efficiently extract the rotational Raman signal for profiling atmospheric temperature.     

Stable Dual-Wavelength Oscillation of an Er-Doped Fiber Ring Laser at Room Temperature

We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23 nm and mutually orthogonal polarization stages was achieved by utilizing the polarization hole-burning effect. An amplitude variation of less than 0.7 dB over an 80 s period was obtained for both wavelengths.     

Stable Dual-Wavelength Oscillation of an Er-Doped Fiber Ring Laser at Room Temperature

We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23 nm and mutually orthogonal polarization stages was achieved by utilizing the polarization hole-burning effect. An amplitude variation of less than 0.7 dB over an 80 s period was obtained for both wavelengths.     

Gain Efficient L-band EDFA With Dynamic Gain Equalization

A gain efficient L-band erbium-doped fiber amplifier with dynamic gain equalization is presented. Using a single fiber Bragg grating and a static equalizer, the gain is clamped at 27dB with less than 0.5dB variations over 35nm.