Applications of Polarization Maintaining Fiber
01 Fiber Optic Gyroscope
One of the typical applications of polarization-maintaining fibers is to fabricate sensing fiber loops in fiber-optic gyroscopes
02 Fiber Laser
Polarization-maintaining fibers are widely used in fiber lasers due to their special polarization properties. Laser polarization-maintaining fibers can be divided into ytterbium-doped, thulium-doped, erbium-ytterbium co-doped polarization-maintaining fibers, large mode field area ytterbium-doped polarization-maintaining photonic crystal fibers, passive matching polarization-maintaining fibers, etc. .
03 Current Transformer (FOCT)
Similar to fiber optic gyroscopes, the application of polarization-maintaining fibers in current transformers also constitutes a sensing fiber loop. But the difference between the two is that the sensing fiber ring here can be composed of a rotating polarization-maintaining fiber, and the entire system uses the Faraday magneto-optical effect, that is, the magnetic field generated by the current-carrying conductor will cause the polarization state of the light transmitted in the fiber ring to be changed. Rotation occurs. Since the current in the current-carrying conductor is proportional to the generated magnetic field, the magnitude of the current can be calculated by monitoring the polarization rotation angle of the light.
04 Integrated optics
Integrated Optics is an important application of polarization maintaining fibers. Lithium niobate (LiNbO3) modulator is a typical integrated optical device. Titanium dioxide-doped waveguides are diffused in the lithium niobate chip, and the pigtails of the polarization-maintaining fibers provide a stable polarization state and are aligned with the chip's birefringence axis. The functionality of the device is based on the Pockels effect: when a voltage is applied to the electrodes, the refractive index of the substrate changes in proportion to this voltage, and the resulting change in the effective optical path length can be used to generate interference, according to doped titanium dioxide The precise design of the waveguides can be manipulated to provide modulation of phase, frequency or amplitude, or even switch optical power between channels.
05 Optical fiber flow sensor
Polarization-maintaining fibers can also be used in other types of fiber-optic sensing systems. For example, Laser Doppler Velocimetry, which is used for flow velocity measurement, determines the flow velocity of air or blood in blood vessels by measuring the Doppler frequency shift of light scattered by the fluid.
06 Medical application
In medicine, doctors can use special catheters or "guide wires" to diagnose patients with coronary heart disease. This is known as OCT (Optical Coherence Tomography, optical coherence tomography. OCT uses low-coherence (broadband) light , polarization-maintaining fiber also plays an important role in it, and surgeons can distinguish the relationship between blood vessel wall and blood vessel occlusion through OCT, which is conducive to further surgical treatment.
07 Substance composition detection
Taking advantage of the characteristics that a specific substance will react with a certain material or adsorb to each other, polarization-maintaining fiber can also be used for substance composition detection. Taking hydrogen detection as an example, the palladium metal layer (Pd layer) will absorb hydrogen and expand, which will cause the change of the birefringence B of the polarization-maintaining fiber to which it adheres. By detecting this change, it is possible to analyze whether the gas contains hydrogen and its content. .
