基于镀铜长周期FBG的波长可调谐环形光纤激光器

将采用化学镀铜膜技术封装的长周期光纤光栅（LPFG）串人环形腔中,设计了一种新颖的波长可调谐掺Er3＋光纤激光器（EDFL）。铜镀膜（化学涂镀）的LPFG在激光器环腔中用作带阻滤波器,利用恒电流源调节LPFG所处温度场,影响LPFG透射谱,改变激光器环形腔增益最高点,实现输出激光波长的可调谐。在LPFG环境温度调谐20...     

A Highly Sensitive Fiber-Optic Refractive Index Sensor Based on an Edge-Written Long-Period Fiber Grating

A novel long-period fiber grating (LPFG) is edge-written without any destructive damage on the fiber based on the thermal shock and rapid cooling effects of the high-frequency CO₂ laser pulses exposure method in this letter. The refractive index disturbance induced by high-frequency CO₂ laser pulses mainly occurs in the edge region of the fiber cladding rather than in the fiber core. An edge-written LPFG with a resonant peak of ~18 dB is obtained using a standard telecommunication fiber. The experimental results show that such a novel LPFG structure has much higher refractive index sensitivity over conventional LPFGs side-written, which can be used as a refractive index sensor, or a tunable filter and modulator by controlling the refractive index sensitive film which is coated on the cladding of such an LPFG.     

双信道解复用长周期光纤光栅的实验研究

长周期光纤光栅是近几年出现的一种波长选择滤波器件。利用其波长选择损耗特性,提出将之用于1310nm/1550nm波分复用系统的解复用。采用电弧熔融刻槽的方法,制备了长周期光纤光栅。并通过控制电弧放电过程和光栅的周期长短及周期数,得到了较为理想的谱特性。结果显示,其通道插入损耗能够小于0.5dB,20dB损耗阻带带宽可达15nm,信道隔离度估计约25dB。     

声光调制光纤器件及其应用

综述了近年来光纤中声光耦合的研究及其一些应用。由PZT产生的弹性声波在光纤上传播,导致光纤周期性的微弯,引起光纤内模式耦合。其作用类似于长周期光栅,但又因为声波的频率、振幅随着施加的RF信号的频率和振幅的改变而改变,因而相对长周期光栅来讲有着灵活、可调的优点。根据声波对光纤共振波长的调谐特性,可以做出很多性能优异的光器件,如频移器,窄带和超宽带的可调滤波器,可调光衰减器,光开关等。     

高频CO2激光脉冲写入的新型长周期光纤光栅及其在光通信中的应用

报道了一种利用频率为几千赫兹的高频CO2激光脉冲的热冲击效应制作长周期光纤光栅的新技术。实验中，作者首次发现这种新型的长周期光纤光栅具有一些独特的光学特性，比如弯曲特性和横向负载特性等，这主要是因为用高频CO2激光脉冲写成的长周期光纤光栅的横截面折射率分布不对称所致。基于这种新型长周期光纤光栅，设计了一种用于减小掺铒光纤放大器噪声系数的ASE噪声滤波器和平坦掺铒光纤放大器增益谱的增益均衡器，此外，还利用这种新型长周期光纤光栅独特的弯曲和压力特性，研究设计了两种用于动态平坦掺铒光纤放大器增益谱的动态增益均衡器。     

Tunable notch filter using a thermooptic long-period grating

This paper proposes a tunable notch filter using a thermooptic long-period grating and investigates it theoretically. This notch filter is in the form of an integrated optical device and is based on a simple structure as compared with existing integrated optical notch filters. The thermooptic grating denotes a thermooptic index perturbation induced by periodic heaters. The attenuation of a resonance band in the transmission spectrum of the proposed notch filter can be controlled by adjusting the electric power applied to the periodic heaters. Employing the heat transfer theory and the coupled-mode theory, the proposed filter is designed and analyzed. The paper also presents analytic expressions for the temperature change due to a heater and the coupling coefficients due to the thermooptic grating. This filter may have potential as a compact dynamically controllable device like a tunable gain flattening filter.     

相移长周期光纤光栅的透射谱特性及其切趾优化

应用耦合模理论和传输矩阵法计算模拟了均匀长周期光纤光栅的透射谱，采用不同的切趾函数对其进行了切趾优化，通过比较得出了最佳的切趾函数。分析了引入多个丌相移的相移长周期光纤光栅的透射谱结构，发现其具有一个通带、两个阻带的滤波特性。着重分析了相移个数，引入位置等参数对谱结构的影响。除运用传统的高斯函数折射率切趾方法对透射谱进行优化外，尝试了一种新型的长度切趾方法，达到了较好的优化效果。该方法的易实现性为切趾相移长周期光纤光栅的实际制作带来了方便。     

基于长周期光纤光栅的增益平坦滤波器的研制

文中主要介绍了用长周期光纤光栅(L PFG) 制作增益平坦滤波器( GFF) 时要注意的一些技术性问题,其中包括光敏光纤的选择、光纤模式的选择、写光栅的曝光强度、波长漂移量的预留。     

基于非对称形变的全光纤宽阻滞滤波器的制作

本文提出的基于长周期光纤光栅（LPFG）的全光纤宽阻带滤波器的制做方法，基本原理是在光纤纤芯中引入周期性的非对称形变，从而使光纤纤芯的折射率发生周期性变化；提出了两种实现光纤纤芯非对称形变的方法，进而制做出阻带中心波长分别为1310nm和1550nm的全光纤宽阻带滤波器插入损耗分别小于0.8dB和1.4dB，后向反射损耗小于-70dB。这样的器件可用于提高WDM系统的隔离度。     

Gain-flattening filter using long-period fiber gratings

We propose a novel structure for a gain-flattening filter, in which a conventional long-period fiber grating (LPFG) and a phase-shifted LPFG are written closely. The transmission characteristics are investigated in the case of a closely arranged configuration. For the fabrication of a phase-shifted LPFG, a UV-trimming method to control the amount of the phase shift is examined theoretically and experimentally. Finally, a 67-mm-long LPFG gain-flattening filter designed for an erbium-doped fiber amplifier is fabricated and the measured spectrum is shown     

Temperature-sensitive mechanical LPFG using contractive force of heat-shrinkable tube

A novel temperature-sensitive mechanical long period fiber grating (LPFG) fabricated utilizing the photo-elastic effect is proposed. Our proposed LPFG consists of a telecommunication optical fiber, a metric screw, and the heat-shrinkable tube, which are commercially available. The heat-shrinkable tube and the metric screw are used to obtain the grating along the single-mode fiber. The gratings are achieved by pressing the optical fiber between the heat-shrinkable tube and the metric screw due to the contractive force of its tube. By changing the temperature, the resonance loss is tuned due to the thermal expansion of the heat-shrinkable tube. Operating mechanism of thermally tunable characteristics of our LPFG are also described from a viewpoint of the coupling coefficient.     

基于色散光纤环级联结构的可调谐带通微波光子滤波器

提出并验证了一种宽调谐带宽的带通微波光子滤波器设计方案。该滤波器借助可调谐光纤光栅Sagnac环对宽带光源进行均匀切割,产生波长间隔可调的连续光载波作为滤波器的抽头,结合色散光纤环级联结构,实现滤波器的可重构性。研究结果表明,在光电调制器和光电探测器的频率带宽足够大的情况下,当光纤光栅Sagnac环的臂长差在0.50~8.28mm内变化、可调谐光纤延迟线的最小变化步长为0.01mm时,该方案能够实现滤波器中心频率在8.0506~1333.2000GHz内调谐,调谐步长为161.01MHz,边瓣抑制比达到27dB。     

A novel tunable gain equalizer based on a long-period fiber grating written by high-frequency CO/sub 2/ laser pulses

A novel tunable gain equalizer based on the long-period fiber grating (LPFG) induced by high-frequency CO/sub 2/ laser pulses is demonstrated, for the first time, to our knowledge. Both the resonant wavelength and the resonant peak amplitude of the novel LPFG have a good linearity with temperature and transverse load, respectively. The wavelength and the peak amplitude of the gain equalizer can be tuned by the means of adjusting temperature and transverse load independently, showing that this tunable equalizer is a practical approach to realizing dynamic gain equalization in erbium-doped fiber amplifier systems.     

Room-temperature operation of widely tunable loss filter

A widely tunable and room-temperature operational loss filter based on a long-period fibre grating (LPFG) fabricated in a B/Ge codoped fibre is reported. The filter exhibits extremely high temperature sensitivity. A maximum spectral shift of -48.1 nm from 10 to 40°C is achieved, corresponding to a thermal tuning efficiency of 1.6 nm/°C. This value is increased by more than one order of magnitude compared with the LPFGs fabricated in standard telecom fibre and even twice that of a LPFG with sensitivity enhanced by a special polymer     

Synthesis of Flat-Top Bandpass Filters Using Two-Band Rejection Long-Period Fiber Gratings

We propose a synthesis method based on the genetic algorithm for designing flat-top bandpass filters using two-band rejection long-period fiber grating (LPFG) filters. In the proposed method, the LPFG structure constructed by concatenating the two-band rejection filters is used as the initial parameter to easily design good flat-top bandpass filters in a wavelength range.     

Strain-induced thermally tuned long-period fiber gratings fabricated on a periodically corrugated substrate

This paper reports the characteristics of a strain-induced thermally controlled loss-tunable long-period fiber grating (LPFG) fabricated on a prepatterned corrugated substrate. Periodic microbending at the fiber-substrate interface induces mode coupling between the core and asymmetrical cladding modes that yields narrow-band attenuation as large as -25 dB. Several parameters that affect the performance of the tunable LPFG, such as the diameter of the etched fiber, number of grating periods, curing condition, and thermal expansion properties of the bonding materials, are investigated. This paper also demonstrates the integration of an on-chip thin-film microheater that also functions as a temperature sensor for the LPFG.     

Electromagnetic crystal (EMXT) waveguide band-stop filter

An electromagnetic crystal (EMXT) with a bandgap around 35 GHz is used as the top and/or bottom walls of a rectangular waveguide. Because of its bandgap, such an EMXT waveguide is a very effective band-stop filter with the rejection band centered at 35 GHz. More than 70 dB of isolation for the rejection band and less than 2 dB of insertion loss for the pass band are measured. Finite element simulation of the EMXT band-stop filter agrees very well with measurements. Using tunable EMXT walls, a band-stop filter with adjustable center frequency and bandwidth can also be realized.     

Acoustooptic Tunable Gap-Type Bandpass Filter With a Broad Stopband

We demonstrate a novel all-fiber gap-type tunable bandpass filter configuration that consists of a broadband hollow optical fiber (HOF) acoustooptic tunable filter (AOTF) concatenated with a narrowband single-mode fiber (SMF)-AOTF. Owing to the unique mode coupling properties of HOF-AOTF and SMF-AOTF, a narrow passband channel of a full-width at half-maximum (FWHM) of ~4 nm could be formed in a broad stopband platform of a 90-nm FWHM successfully. In this scheme, the center wavelength and rejection efficiency of both passband and stopband were found to be flexibly tunable by adjusting the frequency and the voltage of radio-frequency signals applied to individual acoustic transducers.     

High-temperature sensitivity of long-period gratings in B-Gecodoped fiber

We report an investigation of thermal properties of long-period fiber gratings (LPFGs) of various periods fabricated in the conventional B-Ge codoped fiber. It has been found that the temperature sensitivity of the LPFGs produced in the B-Ge fiber can be significantly enhanced as compared with the standard telecom fiber. A total of 27.5-nm spectral shift was achieved from only 10°C change in temperature for an LPFG with 240-μm period, demonstrating a first ever reported high sensitivity of 2.75 nm/°C. Such an LPFG may lead to high-efficiency and low-cost thermal/electrical tunable loss filters or sensors with extremely high-temperature resolution. The nonlinear thermal response of the supersensitive LPG was also reported and first explained     

Tuning and wavelength switching erbium-doped fiber ring lasers by controlled bending in arc-induced long-period fiber gratings

In this paper, we report a simple method for the production of an all-fiber, tunable and wavelength switchable erbium-doped fiber ring laser (EDFRL). We use the shift in resonance wavelength and notch-depth of arc-induced long-period fiber gratings (LPFGs) when it is subject to controlled bend to suppress some wavelength gain and promote lasing in a selective way in a fiber laser system. By changing the bending radius, the operating wavelength of the EDFRL can be tuned from 1526 to 1538 nm and then switched and tuned from 1568 to 1557 nm. The maximum separation measured between laser lines was ～42 nm. This is one of the highest laser separations reported in a wavelength switching operation of an EDFL using a single LPFG as wavelength selective filter.