optic coupler

why people are not interested in optics
is there questions about optics

now tell me about the light guidance in optical fiber?
in manufacturing of optic fiber coupler with fusion the laser power is coupled in fiber that is twisted on and than back.and continuously one to another ?

Please try to study from:
https://www.edaboard.com/viewtopic.php?t=61112

light guidance in optical fiber because of the index difference of core and cladding. This difference introduces reflection follows the snellius law
cladding's index is lower than core's , so the light comes to cladding will be refracted leaves the normal line.

Noemally, light is travelled in optical fiber has some leaky mode to shell layer of them. so when we paralled two fiber and twisted them before fusion. leaky mode of two fiber will become one and distance between two core is closer. so light path in one core can leak to another and become to coupling mode.