EE-566 PresentationFiber Bragg Grating: IntroductionSlide 3Fiber Bragg Grating: TheorySlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Fiber Bragg Grating: Theory – Blazed GratingFiber Bragg Grating: Theory – Chirped GratingFiber Bragg Grating: ManufacturingSlide 14Fiber Bragg Grating: ManufacturingSlide 16Slide 17Fiber Bragg Grating: ManufacturersFiber Bragg Grating: ManufacturersSlide 20Slide 21Fiber Bragg Gratings - ApplicationSlide 23Slide 24Slide 25Slide 26Slide 27Slide 28Fiber Bragg Gratings – Application, WDMSlide 30Slide 31Fiber Bragg Gratings – ReferencesEE-566 PresentationTopic: Fiber Bragg GratingsPresented By: Eric GlauberDate: 10/29/03Fiber Bragg Grating: Introduction•The Fiber Bragg Grating (FBG) is a fiber optic passive component exhibiting basic functional attributes of reflection and filtering.•FBG’s are relatively simple to manufacture, small in dimension, low cost and exhibit good immunity changing ambient conditions and EM radiation.•FBG’s have replaced bulk optic mirrors & beam splitters in equipment which increases system stability and portability.Fiber Bragg Grating: IntroductionTelecommunicationsFiber LasersFiber AmplifiersFiber FiltersDispersion Compensators Optical Fiber Phase ConjugatorWDM–Multiplexers–DemultiplexersSensorsStrain SensorsTemperature SensorsChemical SensorsAccelerometersFBG’s are commercially used in the areas of Telecommunications and Sensors:Fiber Bragg Grating: Theory1978 – Hill et. all•Phenomenon of photosensitivity in optical fibers•Exposed Ge-doped core fibers to intense light at 488 or 514 nm•Induced permanent refractive index changes to the core.Fiber Bragg Grating: Theory•FBG is a longitudinal periodic variation of the index of refraction in the core of an optical fiber.•The spacing of the variation is determined by the wavelength of the light to be reflected.BraggBraggFiber Bragg Grating: TheoryThe Bragg Condition is the result of two requirements:1. Energy Conservation: Frequency of incident radiation and reflected radiation is the same.2. Momentum Conservation: Sum of incident wave vector and grating wave vector equal the wave vector of the scattered radiation. K + ki = kfThe resulting Bragg Condition is: B = 2neff•The grating reflects the light at the Bragg wavelength (B) • B is a function of the grating periodicity () and effective index (neff). •Typically; B= 1.5 m, = 0.5mFiber Bragg Grating: Theory•The spectral component reflected (not transmitted) typically has a bandwidth of 0.05 – 0.3 nm.A general expression for the approximate Full Width Half Maximum bandwidth of a standard grating is given by (S = grating parameter (.5 to 1), N = numbers of grating pains):Δλ =λ B S( (Δn/2n0)2 + (1/N)2 )1/2 1570 1572 1574 1576 1578-40-30-20-100L o s s i n d B Wavelength in nm Reflection TransmissionFiber Bragg Grating: Theory•The shift in Bragg Wavelength with strain and temperature can be expressed using:B = 2n({1-(n2/2)[P12 – (P11 + P12)]}+ [ + (dn/dT)/n]TWhere: = applied strainPi,j = Pockel’s coef. of the stress-optic tensor = Pisson’s ratio = coef. of thermal expansion T = temperature change[P12 – (P11 + P12)] ~ 0.22•The shift in Bragg Wavelength is approximately linear with respect to strain and temperature.Fiber Bragg Grating: Theory•The measured strain response at a constant temperature is found to be:(1/B)B/  = 0.78 x 10-6-1•Sensitivity Rule of thumb at B = 1300nm:0.001nm/Fiber Bragg Grating: Theory•The measured temperature response at a constant strain is found to be:(1/B)B/ T = 6.67 x 10-6 oC-1•Sensitivity Rule of thumb at B = 1300nm:0.009nm/ oCFiber Bragg Grating: Theory – Blazed Grating•Bragg grating planes are tilted at an angle to the fiber axis.•Light which otherwise would be guided in the fiber core, is coupled into the loosely bound, guided cladding or radiation modes.•The bandwidth of the trapped out light is dependent on the tilt angle of the grating planes and the strength of the index modulation.•As shown above, the vector diagram is a result of the conservation of momentum and conservation of energy requirement. The results of applying the law of cosines yealds: Cos(θb) = ׀K ׀/2 vFiber Bragg Grating: Theory – Chirped Grating•Bragg grating has a monotonically varying period as illustrated above.•These gratings can be realized by axially varying either the period of the grating or the index of refraction of the core or both.•The Bragg Condition becomes: λB = 2neff(z)Λ(z)•The simplest type of chirped grating is one which the grating period varies linearly with axial length: Λ(z) = Λ0 + Λ(z)Fiber Bragg Grating: Manufacturing1989 Meltz et. all.•Grating written into core by holographic side exposure method•Exposure with two beam interference pattern of UV light at 244nm•Focal spot is approx. rectangular, 4mm L X 125  m W.Fiber Bragg Grating: ManufacturingSplit Beam Interferometer MethodFiber Bragg Grating: ManufacturingInterference patternGratingCoreø 9µmCladdingø 125µmLaserBeamLaserBeamFiber Fiber Bragg Grating: ManufacturingNovel interferometer technique using a right angled prism.Inherently more stable -because beams are perturbed similarly by any prism vibration.Fiber Bragg Grating: ManufacturingPhase Mask Technique.•UV is diffracted into –1,0,1 orders by relief grating.•Input mask is wavelength specific.•Different B require different phase masks.Fiber Bragg Grating: ManufacturersManufacturers:•Advanced Optics Solutions GMBH•Blue Road Research•3M Optical OEM Systems•Alcatel Optronics•Boeing•Gould Fiber Optic•MPB Communications•OZ Optics Limited•TeraXion Inc.•Oxford Lasers Inc.•Thorlabs