Modified Talbot interferometer for fabrication of fiber-opticgrating filter over a wide range of Bragg wavelength and bandwidth usinga single phase mask

A technique involving a compact apparatus that combines the phase mask and two-beam interferometric techniques is presented. It involves the use of a phase mask to diffract the ultraviolet (UV) beam and a cylindrical lens combined with a pair of mirrors to produce two symmetric virtual line sources of UV light. Bragg wavelength and bandwidth of the fiber gratings can be controlled with a simple translation of the fiber and/or the phase mask. Using a 40-mw continuous-wave frequency-doubled argon-ion laser at 244 mm and a single phase mask, a series of chirped fiber gratings with the Bragg wavelength in a wide range around 600 nm and 1300 nm are fabricated in hydrogen-loaded ordinary fibers     

单偏振双波长非保偏有源掺杂光纤激光器

利用宽带保偏光纤光栅(PFBG)、普通有源光纤和窄带普通光纤光栅构成独立的谐振腔,且窄带普通光纤光栅的中心波长分别与保偏光纤光栅的一个反射峰波长对准,可以输出稳定的双波长/单波长的单偏振激光.利用这一思想,制成了基于非保偏有源掺杂光纤的单偏振双波长光纤激光器.实验结果表明,双波长同时激射时的激光消光比为46.7 dB,单波长激光的消光比为59.6 dB,滤波出单波长测量其偏振度为98.5%.这种激光器在微波光子领域可用于在光域产生微波.     

基于3×3耦合器的马赫-曾德尔干涉仪的光纤光栅波长解调技术

介绍了一种基于3×3和2×2光纤耦合器构成的非平衡马赫-曾德尔干涉仪的波长解调方案。理论分析和数据对比表明,相对于由两个2×2光纤耦合器构成的马赫-曾德尔干涉仪,本干涉仪具有宽谱的灵敏度、能跟踪波长的变化方向和相位展开的优点。实验方案用于测量固定在悬臂梁上的传感光纤布拉格光栅(FBG)的峰值波长变化,获得了±1 pm的静态波长解调精度,在10 Hz处的动态分辨率为27 n/εHz。相位展开算法使得应变测量范围达到了2014με,对应的相位变化为3.22π。     

带状光纤多波长阵列光栅刻写工艺研究

为了实现一次性在八芯带纤上不同波长阵列光纤光栅刻写,采用专门设计的带纤夹具夹持光纤,使用电控位移平台对带状光纤整体施加拉力,利用相位掩膜工艺对光纤逐根曝光,采用扫描写入的方法进行汉明切趾,仅用单一相位模板就实现了八芯带纤上不同波长阵列布喇格光纤光栅刻写。刻栅过程由电脑编程控制,中心波长、波长间隔以及切趾方式可以灵活调整。结果表明,获得的光栅其3dB带宽为0.2nm、波长间隔为0.5nm、波长偏差小于50pm、反射率达到80%~85%。此种带状光纤多波长阵列光栅刻写工艺是完全可行的。     

波长可切换窄线宽单频掺镱光纤激光器（特邀）

基于光纤环形激光器,设计出由三端口环形器、偏振控制器、未泵浦保偏掺镱光纤和光纤布拉格光栅组成的滤波器件作为高精度滤波器对谐振腔内的模式个数进行抑制,通过调谐偏振控制器,在保偏掺镱光纤内形成的梳状光谱和动态光栅,实现了窄线宽、单、双波长可切换单频掺镱光纤激光器。单波长运行时,在1064.37 nm处测得激光器输出线宽346 Hz,光信噪比大于50 dB,30 min内该激光器波长及功率的不稳定性均在0.01 nm和0.2 dB范围内。通过调节偏振控制器,单波长和双波长可以实现互相切换,双波长分别位于1064.156 nm和1065.236 nm。该技术为超窄线宽激光器的双波长输出提供了新的途径。     

A four-element fiber grating sensor array with phase-sensitivedetection

A four-element, time-division multiplexed, fiber grating sensor array operating between the wavelengths of 1280 and 1310 nm was constructed and tested. The array consists of a 1300-nm edge-emitting LED that illuminates four gratings spaced five meters apart. Each grating in the array reflects a spectrally narrow-band (0.3-0.5 mn) wavelength region. Measurand-induced changes in the grating period change the wavelength of the light reflected by each grating. The wavelength shifts are converted to phase changes by routing the reflected signal through a nearly path balanced fiber Mach Zehnder interferometer. The minimum detectable strain was measured to be as low as 2 nanostrain/√(Hz) for frequencies greater than 10 Hz     

Computer control of fiber Bragg grating spectral characteristicsusing a thermal head

We present a new technique for arbitrarily controlling the temperature distribution in fiber Bragg gratings (FBG's) to control their spectral characteristics. A thermal head consisting of a microheater array, driven with computer control signals is used as a controlling device. Various spectral characteristics including a chirped grating and a transmission filter are demonstrated using a single unchirped grating. An effective improvement in response time constant of thermal control was observed on bonding of the fiber grating to thermal head (18 ms), in comparison to that without bonding (40 ms). The measured results did not show any hysterisis. Reliability studies of this technique are also reported. The same technique is further used for the dual wavelength operation of an Er-doped fiber laser     

Fabrication and characterization of annealed proton exchanged long period waveguide grating in x-cut LiNbO3

In this paper, a long-period waveguide grating was fabricated in x-cut lithium niobate substrate by patterned annealed proton exchange waveguide fabrication process. The waveguide mode characteristic was evaluated using a charge-coupled device (CCD) camera. It shows that the waveguide is single mode transmission at a wavelength of 1 550 nm. The transmission spectra of the long period waveguide gratings were measured by optical spectrum analyzer (OSA) and show an extinction ratio of ~17 dB and a 3 dB bandwidth of ~10 nm at the resonant wavelength. The resonant wavelength moves toward to the long wavelength direction as the waveguide width-difference increases in the same period, and also shifts toward to the long wavelength direction with the increase of the period in the case of the same waveguide width-difference. The method of fabricating a long period waveguide grating based on a patterned annealed proton exchange technique simplifies the fabrication process, and at the same time, reduces the fabrication cost.     

掺镱双包层光纤光栅激光器输出特性的研究

通过对泵浦源LD的温度控制,研究了不同温度对泵浦源波长以及光纤激光器输出特性的影响。利用熔接在掺镱双包层光纤两端的光纤光栅作为光纤激光器的谐振腔,采用锥度光纤耦合的方法实现了5.1W的单模激光输出,输出波长1100nm,最大转换效率63%。     

Wavelength-interleaved OADMs incorporating optimized multiple phase-shifted FBGs for fiber-radio systems

We demonstrate that a single fiber Bragg grating (FBG)-based optical add-drop multiplexer can be used to improve the optical spectral efficiency in a mm-wave WDM-fiber wireless network. The technique employs wavelength interleaving in conjunction with optical single-sideband modulation, together with a single multiphase-shifted fiber Bragg grating. Wavelength optical add-drop features are also demonstrated using the grating, and our results show the performance of the novel grating in terms of channel isolation and add-drop functionality. We perform simulations to optimize placement of the phase shifts when an apodization profile is applied to the grating, in an attempt to minimize in-band and out-of-band transmission-amplitude ripples. Experiments are performed using cascade configurations both with the apodized gratings with optimal phase-shift positions and with the original unoptimized gratings. The experimental results demonstrate how these novel gratings can be used in fiber-radio networks incorporating multiple optical add-drop multiplexers.     

基于光纤Bragg光栅的光纤激光器实验研究

利用熔接在掺Yb^3＋双包层光纤两端的光纤Bragg光栅作为光纤激光器的谐振腔．用中心波长为976nm的半导体激光器（LD）为泵浦源,对D型内包层掺Yb^3＋双包层光纤进行泵浦,实现了25W的单模激光输出,输出波长为1085．6nm,峰值半宽（FWHM）为0．3nm,以及总体68％光-光转换效率。     

Tuning Bragg wavelength by writing gratings on prestrained fibers

Bragg gratings at a specific wavelength are made using an excimer KrF laser and a phase mask. The wavelength can be varied for fine tuning and multiplexing applications by straining the optical fiber during UV illumination. When the strain is removed, the grating formed is at a smaller wavelength than that dictated by the phase mask for the unstrained fiber. This technique was demonstrated by writing two gratings located at the same point in the optical fiber. The transmission from the first grating was used as a means for in situ absolute wavelength tuning. The second grating made with approximately 0.2% axial strain was at 1534.54 nm. Once the grating was made, the strain was removed from the fiber leaving the second grating tuned to 1532.04 nm, a wavelength shift of 2.5 nm     

Postfabrication wavelength trimming of fiber Bragg gratings writtenin H2-loaded fibers

A postfabrication technique for writing fiber Bragg gratings in H ₂-loaded fiber with precise wavelength control is reported. The grating wavelength is highly stable and less than a 0.01-nm shift was observed after storing at room temperature for two months. This technique allows 1 nm of wavelength trimming and significantly enhances the grating thermal stability     

Long-phase error-free fiber Bragg gratings

Stitching errors in the phase mask degrade the spectral response of fiber Bragg gratings fabricated with the phase mask technique. We successfully fabricated a stitching error-free phase mask and applied it to the fabrication of fiber Bragg gratings (FBGs). The gratings have no observable excess sidelobes in the reflectivity and show excellent wavelength selectivity     

Demultiplexing of interferometrically interrogated fiber Bragggrating sensors using Hilbert transform processing

The peak reflectance wavelengths of gratings with reflectance maxima separated by less than 2 nm can be accurately determined through a demultiplexing method based on Hilbert transforms of interferograms. We demonstrate a wavelength demultiplexing of three fiber Bragg gratings (FBG's) with less than 4 pm crosstalk and repeatability and less than 19 pm uncertainty. We anticipate that a large number of gratings can be demultiplexed with a single broadband source and a single receiving interferometer, provided that the interferogram is sampled at accurate intervals slightly above the Nyquist rate     

Operation of diode laser pumped Tm3+ ZBLAN upconversionfiber laser at 482 nm

Lasing at 482 nm is observed in Tm³⁺-doped ZBLAN glass fiber pumped with single-mode InP semiconductor diode lasers. Up to 5 mW of 482 nm light is obtained with <40 mW of absorbed pump power from a single 1135 nm pump diode laser. The optimum pump wavelength is measured to be 1135-1340 nm. More efficient laser operation is observed in fiber with 2500 ppm Tm³⁺ compared to 1000 ppm Tm³⁺ because of the reduced length of the fiber laser cavity possible with increased doping. Improved slope efficiencies are also demonstrated when the fiber laser is co-pumped with up to 5 mW from a 1220 nm diode laser. The relative intensity noise (RIN) of the fiber laser displays a maximum of -90 dB/Hz at relaxation oscillation frequencies of a few tens of kHz. The measurement of RIN is limited by shot-noise of -152 dB/Hz above 2 MHz. At higher frequencies, self mode-locking was observed in the fiber laser, which may indicate the existence of saturable absorbers in the fiber core. The presence of such bleachable absorbers is indicated by the observed increase in threshold after upconversion lasing at 482 mm     

基于实时校准技术的光纤光栅传感解调系统

报道了一种采用实时校准技术的数字化光纤光栅传感解调方案。解调系统利用锯齿波电压信号和数字相位同步信号控制可调谐光纤法布里一珀罗(TFFP)滤波器，对光纤光栅传感器阵列进行扫描式寻址，同时采用非测量环境中的参考光栅和数字温度计提供精确的参考波长，并由高速数字信号处理器(DSP)实时校准滤波器的波长读取值，很好地消除了滤波器渊谐的温度漂移、非线性和蠕动性引起的测量误差。结果表明，实验系统的波长寻址范围为1520～1570nm，扫描频率为100Hz，波长测量分辨率为5pm，应变测量分辨率为4．13με。     

8-wavelength DBR laser array fabricated with a single-step Bragggrating printing technique

An 8-wavelength distributed Bragg reflector (DBR) array for narrow channel wavelength division multiplexing (WDM) has been fabricated with a new technique for printing first-order Bragg gratings using a phase mask and a conventional incoherent source. All the distributed gratings were printed in a single photolithographic step with a slightly modified mask aligner. The DBR's excellent wavelength control for channels separated by as little as 0.8 nm is described. Many advanced photonic devices relying on gratings like quarter-wave shifted distributed feedback (DFB) lasers and wavelength division multiplexing (WDM) components can potentially be manufactured with this technique in a simple and cost-effective way     

基于重叠光栅的双波长掺铒光子晶体光纤激光器

提出了一种基于光纤重叠光栅的双波长光子晶体光纤激光器。激光器采用线形腔结构,掺铒光子晶体光纤为激光器的增益介质,反射率均高于99%的光纤重叠光栅用作激光器的波长选择器件。基于增益均衡技术,抑制谐振腔内的模式竞争,在室温下获得了稳定的双波长激光同时输出。实验结果表明:其3 dB线宽小于0.02 nm,30 dB线宽小于0.25 nm,SMSR为54.34 dB,双波长激光的中心波长间隔为0.932 nm。该双波长激光器输出的双波长激光具有较好的稳定性。     

机械可调的相移长周期光纤光栅

介绍了一种利用机械应力在普通单模光纤(SMF)中产生相移长周期光纤光栅(LPFGs)的简单方法。通过光弹效应，用有凹槽的平板制作LPFGs；用螺丝控制2个凹槽平板之间的距离，可以得到不同的相移值，实现了相移值的连续可调。光栅的传输光谱可以通过所加外力实现调谐，谐振峰强度的可调谐范围达到了16dB。该方法对于光栅光谱的调谐有很大的灵活性，可应用于掺Er光纤放大器(EDFA)的增益平坦。