In fiber preparation, the birefringence (B) is artificially made large, or the fiber whose beat length λ is as short as millimeters, referred to as PM fiber or HB fiber, high birefringence fiber. From the perspective of polarization optics, if a general single-mode fiber is regarded as an isotropic medium, the high birefringence fiber is equivalent to a uniaxial crystal with a large birefringence.
In fiber preparation, the birefringence (B) is artificially made large, or the fiber whose beat length λ is as short as millimeters, referred to as PM fiber or HB fiber, high birefringence fiber. From the perspective of polarization optics, if a general single-mode fiber is regarded as an isotropic medium, the high birefringence fiber is equivalent to a uniaxial crystal with a large birefringence. High birefringence fiber is also called polarization maintaining fiber. In fact, the fiber can maintain the polarization only when the polarization direction of the input linearly polarized light is transmitted along the main axis of the fiber. Injection in other directions cannot keep the polarization direction unchanged during transmission. The output light must be elliptically polarized light.
There are two ways to manufacture PM fiber:
(1) Asymmetrical stress is applied outside the core to make the refractive index of the core asymmetry. The main types of fibers that belong to this type of fiber are elliptical cladding fiber, bow tie type fiber and panda type fiber;
(2) It is an elliptical core fiber, which utilizes the asymmetry of the core geometry. The beat length of this kind of fiber is slightly longer, but the thermal stability is correspondingly better than that of the stressed fiber.
PM optical fiber has very important applications in optical fiber communication and optical fiber sensing technology.
Direction of development
Polarization-maintaining optical fiber will have greater market demand in the next few years. With the rapid development of new technologies in the world and the continuous development of new products, polarization-maintaining optical fibers will develop in the following directions:
(1) Use the new technology of photonic crystal fiber to manufacture a new type of high-performance polarization maintaining fiber;
(2) Develop temperature-adaptive polarization-maintaining optical fiber to meet the requirements of aerospace and other fields;
(3) Develop various rare earth-doped polarization-maintaining fibers to meet the needs of optical amplifiers and other device applications;
(4) Develop fluoride polarization-maintaining fiber to promote the development of fiber optic interference technology in the field of infrared astronomy technology;
(5) Low-attenuation polarization-maintaining fiber: With the continuous improvement of single-mode fiber technology, loss, material dispersion and waveguide dispersion are no longer the main factors affecting fiber communication, and the polarization mode dispersion (PMD) of single-mode fiber has gradually become The most serious bottleneck restricting the quality of optical fiber communication is particularly prominent in high-speed optical fiber communication systems of 10 Gbit/s and above. In order to solve the problem of the deterioration of transmission system performance caused by PMD, a solution to compensate PMD is generally adopted. However, PMD is very sensitive to environmental conditions such as temperature, and slight disturbances of the light source wavelength, and will change randomly over time. All bring difficulties to PMD compensation of optical fiber communication system. If the low-attenuation polarization-maintaining fiber can be successfully developed, it will provide a new solution to the PMD problem in the high-speed transmission system;
(6) Use Kerr effect and Faraday rotation effect to manufacture polarized light devices
Polarization maintaining fiber
Polarization-maintaining optical fiber transmits linearly polarized light and is widely used in various fields of the national economy such as aerospace, aviation, navigation, industrial manufacturing technology and communications. In the interferometric fiber sensor based on optical coherent detection, the use of polarization-maintaining fiber can keep the linear polarization direction unchanged, improve the coherent signal-to-noise ratio, and achieve high-precision measurement of physical quantities. As a special type of optical fiber, polarization maintaining fiber is mainly used in sensors such as fiber optic gyroscopes, fiber optic hydrophones, and fiber optic communication systems such as DWDM and EDFA. Because fiber optic gyroscopes and fiber optic hydrophones can be used in military inertial navigation and sonar, they are high-tech products, and polarization-maintaining fiber is its core component, so polarization-maintaining fiber was once included in the list of embargoes against China by western developed countries. Some domestic optical fiber production companies have been able to produce.