A PM fiber coupler is a special type of optical fiber coupler.
It is based on selectively coupling light with different polarization states (such as horizontal polarization and vertical polarization) within the fiber. In optical fibers, light can be decomposed into different polarization modes, and a PM fiber coupler can distinguish and handle the interactions between these polarization modes.
Through special structural designs, such as waveguide structures or stress-induced birefringence, the polarization propagation characteristics of light are modified to achieve coupling functions.
It is not simply power coupling, but also involves the conversion and recombination of polarization modes. For instance, it can couple light of one polarization state into another fiber port in a certain proportion, and during this process, the polarization state distribution of the light may be changed.
Typically, a PM fiber coupler uses fiber materials with birefringent properties or specially shaped fiber waveguide structures. For example, a panda-type polarization-maintaining fiber has a core and cladding shape designed to preserve the polarization state of light. During the coupler fabrication process, this structural characteristic is leveraged to achieve precise polarization mode coupling.
The fabrication process requires high-precision microprocessing techniques. Even small structural deviations can lead to instability in polarization states or errors in coupling ratios. For instance, in the fabrication of a coupler using a fused taper process, factors such as the taper length, diameter, and alignment accuracy of the two fibers can influence the polarization mode coupling effect.
In high-speed optical fiber communication systems, it is a key component for polarization multiplexing technology. By using a PM fiber coupler, signals with different polarization states can be processed and transmitted separately, thus increasing the communication system's capacity. For example, in 100Gbps and higher-speed optical communication links, polarization multiplexing technology, in conjunction with a PM fiber coupler, effectively utilizes the bandwidth resources of optical fibers.
It can be an important component in polarization-sensitive optical fiber sensors. In optical fiber sensors that measure physical quantities such as stress, temperature, or magnetic fields, a PM fiber coupler can detect changes in the light's polarization state caused by variations in external physical factors, enabling the measurement of the physical quantity being sensed.
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