solators Circulators
Isolators & Circulators
solator: Definition An isolator is a device that allows light to pass along a fibre in one direction but not in the opposite direction
Isolator: Definition • An isolator is a device that allows light to pass along a fibre in one direction but not in the opposite direction
Application coupling a laser to a fibre Reflected light can cause instability in the laser and cause many undesirable effects high speed communication system optical amplifiers fibre ring cavity
Application • coupling a laser to a fibre. Reflected light can cause instability in the laser and cause many undesirable effects. • high speed communication system • optical amplifiers • fibre ring cavity
The Faraday Effect Light travelling within the material has its plane of polarisation (electric and magnetic field vectors)rotated by an amount depending on the length and he strength of the magnetic field the most important aspect is that the effect is asymmetric materials: YIG(Yttrium-Iron-Garnet
The Faraday Effect • Light travelling within the material has its plane of polarisation (electric and magnetic field vectors) rotated by an amount depending on the length and the strength of the magnetic field. • the most important aspect is that the effect is asymmetric. • materials : YIG (Yttrium-Iron-Garnet)
Simple Isolator Forward Direction Polarising filter Polarising filter Faraday Rotator (rotated 45 degrees) (vertical) Electric Field Electric Field Direction Direction Reverse direction Electric Field Electric Field Direct irection
Simple Isolator
Problem The isolator is plarization-dependent incoming light randomly polarised will lose 50% of its power If the signal is polarised and the orientation is wrong then we can lose all of the signal if the polarisation varies with time the variations will be translated into variations in attenuation serious noise!
Problem • The isolator is plarization-dependent • incoming light randomly polarised will lose 50% of its power! • If the signal is polarised and the orientation is wrong then we can lose all of the signal. • if the polarisation varies with time the variations will be translated into variations in attenuation:serious noise!
Polarisation Independent isolator separating the incoming ray into its two orthogonal polarisations processing them separately and then re-combining them at the output
Polarisation Independent Isolator • separating the incoming ray into its two orthogonal polarisations • processing them separately • and then re-combining them at the output
磁环 n out 偏振分光镜YG 玻片 (互易) (a)正向 磁环 out 偏振分光镜YG <玻片 (互易) (b)反向
Practical confiquration
Practical configuration
Circulator: Definition Light entering at any particular port(say port 1)travels around Port the circulator and Port 3 exits at the next port (say port 2). Light Port 1 entering at port 2 Port 4 leaves at port 3 and So on
Circulator: Definition • Light entering at any particular port (say port 1) travels around the circulator and exits at the next port (say port 2). Light entering at port 2 leaves at port 3 and so on