In-Fibre Bragg Gratings (FBGs)
In-Fibre Bragg Gratings (FBGs)
What is FBG? An in-fibre Bragg grating is constructed by varying the refractive index of the core lengthwise along the fibre Light of the specified wavelength traveling along the fibre is reflected from the grating back in the direction from which it came Wavelengths which are not selected are passed through with little or no attenuation
• An in-fibre Bragg grating is constructed by varying the refractive index of the core lengthwise along the fibre. • Light of the specified wavelength traveling along the fibre is reflected from the grating back in the direction from which it came. • Wavelengths which are not selected are passed through with little or no attenuation. What is FBG?
Fiber Bragg Grating 200 um Long-period grating 500 nm Bragg grating 125um Cladding 8 Core 1 mm to 1500 mm Singlemode fibre Regions with higher refractive index than that of core’s
Fiber Bragg Grating ~ 500 nm (Bragg grating) ~ 200 µm (Long-period grating) 125 µm 8 µm 1 mm to 1500 mm Singlemode fibre Core Cladding Regions with higher refractive index than that of core’s
It works like this Input signal 4IIIIIIID Selected NON. Sooted Wavelengh wawdengshs resonant wavelengths are reflected back toward the source non-resonant wavelengths are transmitted through the device without loss The centre wavelength is given by =2n eff
It works like this • resonant wavelengths are reflected back toward the source • non-resonant wavelengths are transmitted through the device without loss. • The centre wavelength is given by: = 2neff
Principle of Operation 辑辑菲 The grating forms an electromagnetic resonant circuit. Power from the forward direction is coupled into the resonant circuit and then reflected back. Non-resonant wavelengths are not afected very much
Principle of Operation The grating forms an electromagnetic resonant circuit. Power from the forward direction is coupled into the resonant circuit and then reflected back. Non-resonant wavelengths are not affected very much