河北师范大学：《电动力学》课程教学资源（PPT课件讲稿）第七章 光波导技术（7.5.3）Isolators Circulators

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