《光纤理论与技术》课件

1、光纤理论与技术哈尔滨工程大学理学院光子科学与技术研究中心2007年3月第1页，共105页。第十一章：发展无限的新型光纤 特种光纤光子晶体光纤第2页，共105页。特种光纤保偏光纤 掺稀土元素光纤 双包层光纤 倏逝场光纤 多芯光纤 红外光纤 纳米光纤第3页，共105页。保偏光纤几何形状引起高双折射 高双折射椭圆芯保偏光纤结构剖面示意图 第4页，共105页。保偏光纤应力诱导高双折射 第5页，共105页。保偏光纤第6页，共105页。掺稀土元素光纤 掺稀土元素光纤是采用某种工艺技术将钕、铒和钇等稀土元素离子单独或混合掺入光纤芯中而制成的。目前主要是掺杂到光纤纤芯中的，但亦有同时掺杂到光纤包层中去的。其掺

2、杂浓度可从1 PPm到0.25 w% 的宽广范围内变化。 第7页，共105页。 纤芯中掺杂稀土元素有 Er、Yb、Nd、Tm、Pr、Er/Yb、Ho等 纤芯直径4mm，NA 0.1 包层直径125mm，形状为圆形掺稀土元素光纤 第8页，共105页。掺稀土元素光纤用这种掺杂光纤可以获得四方面的应用： (1) 激光光纤与光纤放大器； (2) 基于吸收、荧光的分布温度传感； (3) 增大菲尔德常数； (4) 提高克尔效应及非线性光学系数。 第9页，共105页。双包层光纤 双包层光纤及其工作原理 第10页，共105页。 纤芯中掺杂稀土元素有： Er、Yb、Nd、Tm、Pr、Er/Yb、Ho等 单模光纤

3、 ：纤芯小4mm，NA 0.1 纤芯结构分类 大芯多模光纤：纤芯大（30mm），NA大 大模面积（LMA）：纤芯大（30mm ）， NA小（0.1）内包层光纤芯外包层保护层激光输出泵浦光双包层光纤 第11页，共105页。 内包层形状 圆形（同心、偏心） 方形、矩形、六边形、星形 和 D 形 圆形偏心内包层圆形同芯内包层双包层光纤 第12页，共105页。 矩形内包层星形内包层方形内包层D形内包层六边形内包层双包层光纤 第13页，共105页。双包层光纤用包层泵浦的光纤激光特种光纤 第14页，共105页。倏逝场光纤 主要用途：倏逝场光纤生化传感器 电光克尔效应调制器 第15页，共105页。多芯光纤

4、主要用途：密集型光缆光子器件用于图像传递的传像光纤 第16页，共105页。红外光纤方形中空光纤芯红外光纤 第17页，共105页。纳米光纤第18页，共105页。第19页，共105页。第20页，共105页。第十一章：发展无限的新型光纤 特种光纤光子晶体光纤第21页，共105页。ContentsIntroductionWhat is photonic crystal fiber ? Working principle of PCFStructures of photonic crystal fiberCharacteristics of crystal fiberFabrication of cry

5、stal fiberApplications What we have done ?Conclusions第22页，共105页。Introduction Photonic crystal fibers (PCFs) was first demonstrated in 1996 and has generated much attention since then. PCFs are optical fibers that employ a microstructured arrangement of low-index material in a background material of

6、higher refractive index. The background material is often undoped silica and the low index region is typically provided by air voids running along the length of the fiber. 第23页，共105页。Growth trend of publicationsPublication papers cited by SCI from 19962003330+?第24页，共105页。What is photonic crystal fib

7、er ? Photonic crystal fibers, also known as microstructured fibers are a brand new range of optical fibers offering significant new possibilities and functionality within telecommunications and optical components in general. 第25页，共105页。Two categories photonic crystal fiber PCFs may be divided into t

8、wo categories, high index guiding fibers and low index guiding fibers. Similar to conventional fibers, high index guiding fibers are guiding light in a solid core by the Modified Total Internal Reflection (M-TIR) principle. The total internal reflection is caused by the lower effective index in the

9、microstructured air-filled region. 第26页，共105页。Working principle of crystal fiber Low index guiding fibers guide light by the photonic bandgap (PBG) effect. The light is confined to the low index core as the PBG effect makes propagation in the macrostructured cladding region impossible. The strong wa

10、velength dependency of the effective refractive index and the inherently large design flexibility of the PCFs allows for a hole new range of novel properties. Such properties include endlessly single-moded fibers, extremely nonlinear fibers and fibers with anomalous dispersion in the visible wavelen

11、gth region. 第27页，共105页。Working principle of crystal fiberM-TIR is analogous to total internal reflection known from standard optical fibers. It relies on a high index core region, typically pure silica, surrounded by a lower effective index provided by the microstructured region. The effective index

12、 of such a fiber can, in the simple case, be approximated by standard a step index fiber, with a high index core and a low index cladding. However, the refractive index of the microstructured cladding in PCFs exhibits a wavelength dependency very different from pure silica - an effect which allows P

13、CFs to be designed with a complete new set of properties not possible with standard technology. Step index fiber 第28页，共105页。Working principle of crystal fiberPhotonic crystal fiber As an example, the strong wavelength dependence of the refractive index allow design of endlessly single-moded fibers,

14、where only a single mode is supported regardless of optical wavelength. Furthermore, it is possible to alter the dispersion properties of the fibers, thereby making it possible to design fibers with an anomalous dispersion at visible wavelengths.More complex index structures can also be constructed

15、by utilizing arrangements of holes of different size in various periodic or unperiodic structures. In addition, highly asymmetric core fibers can be fabricated thereby creating fibers with very high level of birefringence. 第29页，共105页。Working principle of crystal fiberPhotonic bandgap fibers are base

16、d on physical mechanisms fundamentally different from the M-TIR guiding fibers. The bandgap effect can be found in nature, where the beautiful and bright colors that are seen in butterfly wings are the result of naturally occurring periodic microstructures. The SEM picture at the lower left shows th

17、e microstructure on a butterfly wing. The structure size is in the order of a few microns. In a PBG fiber, the core is created by introducing a defect in the PBG structure (e.g. an extra air hole), thereby creating an area where the light can propagate. 第30页，共105页。Working principle of crystal fiberA

18、s the light can only propagate at the defect region, a low index guiding core has been created. This is not possible in standard fibers, and the low index guiding of PBG fibers therefore opens a whole new set of possibilities. In this way, it is possible to guide light in air, vacuum or any gas comp

19、atible with the fiber material. Especially the possibility for guiding in air or vacuum has attracted much attention, as it might hold the key to transmission fibers with extremely low losses. 第31页，共105页。Working principle of crystal fiber The different guiding mechanisms. (A) Conventional total inte

20、rnal reflection (TIR); this occurs when the wave vector component in the direction of propagation lies in the range kn2 kn1. (B) PBG guidance when the light is evanescent in the air regions; this can only occur when lies in the same range as in (A); the process is one of frustrated tunneling, that i

21、s, the cladding resonators are out of resonance with the core waveguide and hence tunneling is prevented. 第32页，共105页。Working principle of crystal fiber (C) PBG guidance when the light is propagating in all subregions of the fiber; this can only occur when lies in the range kn2, the underlying mechan

22、ism being a Bragg PBG.第33页，共105页。PBG PCF第34页，共105页。Basic explanation 第35页，共105页。Vector analysis of PCF fiber第36页，共105页。Structures of crystal fiberTypical honeycomb based PCF structure 第37页，共105页。Air-guiding PCFLow bend loss: unnoticeable 3mm radiusLow Fresnel reflection: 10-4Reduced nonlinearitiesPo

23、tential ultra-low loss transmission第38页，共105页。Structures of crystal fiber第39页，共105页。Structures of crystal fiber第40页，共105页。1.7 m Core Highly Nonlinear FiberFEATURES:- Small mode field area- Zero dispersion in the visible wavelength range- Bending insensitive APPLICATIONS:- Continuum generation- Four-

24、wave mixing- Raman amplification第41页，共105页。15 m Core Large Mode Area Fiber FEATURES: - Handles very high power levels without nonlinearities- Low fiber loss APPLICATIONS: -High power delivery 第42页，共105页。High Numerical Aperture PCFHigh numerical aperture (NA): up to 0.7Large core areaLow nonliearitie

25、s第43页，共105页。Double Cladding PCF Extremely high NA for the pump core/inner cladding.Large mode area for signal mode signal: high power delivery, low nonlinearity, and a good overlap between pumping and signal area (high pump efficiency)第44页，共105页。Highly Nonlinear Polarization Maintaining Fiber FEATUR

26、ES: - Polarization Maintaining- Small mode field area- Zero dispersion in the visible wavelength range- Bending insensitive APPLICATIONS: - Continuum generation- Four-wave mixing- Raman amplification 第45页，共105页。Endlessly Single-Mode FiberEndlessly single-mode large mode area PCF can handle up to 20

27、times more power than conventional fiber and is made entirely from un-doped silica glass.第46页，共105页。Endlessly Single-Mode FiberActual unit cell in the photonic crystal with Its circular approximation Variation of Veff with /for various relative hole diameters d/. The dashed line marks Veff = 2.405,

28、the cutoff V value for a step-ndex fiber第47页，共105页。Chromatic Dispersion 第48页，共105页。Anomalous dispersion第49页，共105页。Supercontinuum GenerationSuper continuum generation in a 75cm length of PCF. The fiber is pumped with 100fs, 680nm pulse. The pulse energy is 1nJ.第50页，共105页。Loss properties3.2 dB/km at 1

29、550 nm7.1 dB/km at 850 nm 2 km length fiber第51页，共105页。Macro-bending loss properties第52页，共105页。Highly birefringent propertiesBeat length = 0.4 mmAt wavelength 1540 nm第53页，共105页。Fabrication of crystal fiberFabrication of PCF, like in conventional fiber fabrication, starts with a fiber preform. PCF pre

30、forms are formed by stacking a number of capillary silica tubes and rods to form the desired air/silica structure. 第54页，共105页。Fabrication of crystal fiberThis way of creating the preform allows a high level of design flexibility as both the core size and shape as well as the index profile throughout

31、 the cladding region can be controlled. This is very useful for fabrication of e.g. polarization maintaining fibers with highly asymmetric core regions, where multiple of the capillary tubes is replaced with solid silica rods. 第55页，共105页。Fabrication of crystal fiberWhen the desired preform is constr

32、ucted, it is drawn to a fiber in a conventional high-temperature drawing tower and hair-thin photonic crystal fibers are readily produced in kilometer lengths. Through careful process control, the air holes retain their arrangement all through the drawing process and even fibers with very complex de

33、signs and high air filling fraction can be produced. 第56页，共105页。Fabrication of PCF第57页，共105页。Fabrication of crystal fiberFinally, the fibers are coated to provide a protective standard jacket that allows robust handling of the fibers. The final fibers are comparable to standard fiber in both robustn

34、ess and size and can be both striped and cleaved using standard tools. 第58页，共105页。Applications of PCF Fiber delivery of very high-power light, single- mode from UV to infrared;2. Dispersion compensation ;3. White light (supercontinuum) sources ;4. Wavelength converters ;5. Hollow transmission fibers

35、 ;6. Multi-core fiber couplers ;7. Pulse shapers ;第59页，共105页。Applications of PCF Chemical sensors with long interaction lengths ;9. Temperature-insensitive PM pigtails ; Gyroscope fibers-athermal, and highly birefringent 11. Pressure and temperature sensors ; High Aeff and PM fibers for single-mode

36、interconnects ;13. Mode converters 第60页，共105页。High-power light delivery 第61页，共105页。White-light supercontinuum generation experiment第62页，共105页。White-light supercontinuum generationPropagation lengths 40 cm, 1.3 m, and 2.6 m第63页，共105页。Wavelength converter 第64页，共105页。Wavelength converterOutput spectra

37、for different values of incident peak power第65页，共105页。This fiber guided pink light (core 14 microns in diameter) Using air core as the medium almost entirely eliminates optical nonlinearities so the nonlinear power threshold can be more than 1000 times higher than that of a conventional fiber. Hollo

38、w Core Bandgap Fiber第66页，共105页。Multicore PCF and Multicore couplerApplications:1.Strain sensor;2.Temperature sensor3.Pressure sensor第67页，共105页。Dispersion compensation第68页，共105页。PCF using as gas sensor第69页，共105页。Testing result of acetylene gas第70页，共105页。Acoustic wavelength-shift modulator第71页，共105页。T

39、win core PCF fiber as temperature sensor 第72页，共105页。“I tried to think of something different, something nobody else had thought of ” -Philip St. John Russell 第73页，共105页。The idea of Photonic crystal fiber 第74页，共105页。Microstructured fiber used as an atom waveguide第75页，共105页。Coaxial periodic optical fi

40、ber第76页，共105页。Segmented cladding fiber第77页，共105页。Air suspended core fiber for producing efficient evanescent field devices 第78页，共105页。What we have done ?Invention patents about plastic photonic crystal fiber designResearch on mode field distribution and dispersion characteristics of photonic crystal

41、 fiberSimulation of highly birefringent PCF Splice loss estimation of PCF/SMFAnalysis for tapered photonic crystal fiberAnalysis of combination structured photonic crystal fibers第79页，共105页。Hollowly plastic photonic crystal fiber design and fabrication technique第80页，共105页。Basic equations第81页，共105页。Cr

42、oss section of the PCF with a pitch of 2.3 第82页，共105页。Contour maps of the energy distribution of fundamental mode第83页，共105页。Three dimensional mode field distributions 第84页，共105页。Energy distribution of central axis 第85页，共105页。V parameter of a PCF versus the normalized frequency 第86页，共105页。Effective i

43、ndex of a PCF versus the normalized frequency 第87页，共105页。Effective index of a PCF versus wavelength 第88页，共105页。Dispersion as a function of wavelength 第89页，共105页。Dispersion as a function of wavelength 第90页，共105页。Propagation constant vs the wavelength 第91页，共105页。Modeling of Highly Birefringent PCF The

44、 cross-section of the PCF and electric field vectors of the y-polarized fundamental mode. Dependence of modal birefringence on the size of holes.第92页，共105页。The mode field diameter and half divergence angle as a function of wavelength for various d2/. The dashed and solid lines corresponds to x and y directi