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FIBER OPTIC - Coggle Diagram

- - - - The modulating region is mainly within the cladding of the optical fibre.
        
        The cladding is normally removed and replaced with a material which is sensitive to the measurand.
        
        Chemical and biochemical sensors are typical examples of this type of sensor.
- - - - :explode:FIBRE BRAGG GRATING
        (Mohd Farid Izuan Bin Azmi)
        
        Theory
        • The Bragg wavelength of an FBG is given as
        
        𝑛𝑒𝑓𝑓 is the effective refractive index
        𝛬 is the grating period of the fibre core.
        
        How FBG is produced?
        FBG are made by laterally exposing the core of a single-mode fiber to a periodic pattern of intense laser light.
        
        The exposure produces a permanent increase in the refractive index of the fiber’s core, creating a fixed index modulation according to the exposure pattern.
        
        This fixed index modulation is called a grating.
        
        • The change in the Bragg wavelength, caused by changes in strain, temperature and wavelength can be written as :
        + +
        
        •The changes in Bragg wavelength for a given change in temperature are given as:
        where is an effective strain-optic constant, and the standard value is 0.213
        
        •
        Parameters for standard optical fibre (silica):
        p11=0.113
        p12=0.252
        Poisson's ratio,v,=0.16
        n=1.482
        
        • The changes in Bragg wavelength for a given change in temperature are given as:
        
        ɛ, thermo-optic coefficient = (8.60e-6)°C-1
        𝛼,thermal expansion coefficient =(0.55e-6)°C-1
        ∆𝑇, temperature change (in °C)
        
        Transmission & reflection spectrum of FBG
        
        • For efficient and highly sensitive temperature sensor, it is desired to have high Peak Reflectivity (stronger reflectivity).
        • A uniform FBG bandwidth and reflectivity depend on
        grating length (L) and grating strength (∆nac)
        
        Schmeatic Diagram of FBG
        
        Principle
        :• The input spectrum from a broadband source is sent to the FBG through a 2x2 coupler.
        • The transmission spectrum is missing wavelengths that match the Bragg wavelengths of the FBG'S.
        • The transmission spectrum is missing wavelengths that match the Bragg wavelengths of the FBG'S.
        • Changes in measurements at each FBG move the reflected wavelength in the same way.
- - - - equation for calculate loss
        
        equation for calculate total power loss
      - ::explode:Other losses :explode:
        
        1. Connectors : joints that may be disconnected & remated. (0.5 -1.0 dB)
        
        2. Splices : permanent joints. (0.1 dB)
        
        3. Terminations : source fibre coupling point (2-3 dB) & fibre - PD coupling point (negligible)
        
        4. Non linear scattering losses : stimulated Brillouin scattering , stimulated Raman scattering
  - - - :explode: Effect of dispersion on different fibres :explode:
      - :explode:Types of dispersion :explode:
        
        1. Modal dispersion ( Intermodal dispersion)
        2. Material dispersion
        3. Wavelength dispersion
        4. Polarization mode dispersion (PMD)
        
        Equation for time delay expression for modal dispersion
        
        Equation for Maximum bit rate , B
        
        Equation for Maximum signal bandwidth
        
        1 more item...
        
        Equation for expression for pulse spreading due to modal dispersion
        
        Equation for time delay due to intermodal dispersion in MMGI
        
        Equation for material dispersion & waveguide dispersion
        
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- - - - POYNTING S/VECTOR
        
        units: Joules per square meter per sec
      - IRRADIANCE
        
        units: W/m^2
    - - frequency & wavelength is related by the velocity of light formula
      - velocity of light according to the Maxwell's equation