With its excellent characteristics of stability and high polarization crosstalk, polarization-maintaining optical devices lead the development of cutting-edge products in high-speed optical networks. This is in line with the development of optical networks and should be regarded as a new technological breakthrough. PSUMAI technology has a high-quality and experienced team in this field. The research on polarization-maintaining devices started early. We used the technical experience accumulated by Guangyue people for many years to make the technical level of pusmai ahead of other peers. Since they developed N*N series polarization-maintaining device products. As far as we know, other domestic counterparts are still stuck in the process development of 1*2 and 2x2.

There is a long history of demand and research on polarization-maintaining fibers and polarization-maintaining devices. Only limited by system cost and device manufacturing difficulty, polarization-maintaining devices have not received widespread attention and sufficient improvement for a long time.
　　
　　Due to the ellipticity and residual stress that are difficult to overcome in the production of ordinary optical fibers, as well as the unavoidable influence of external forces and magnetic fields during use, ordinary optical fibers will randomly change the phase difference of the two degenerate modes transmitted in them to make them polarized. state changes randomly. The power penalty caused by system noise such as PDL and PMD reduces the sensitivity of the system, especially in the occasions requiring demultiplexing interference, the ordinary optical fiber system is stretched, and no satisfactory results can be obtained, which reflects its limitations.

　　
Since the direction of the random stress generated by the applied stress, the defect itself and the residual stress randomly changes the polarization state of the transmitted light, then if the inherent stress larger than these forces and the direction is constant is introduced into the fiber, the applied stress, the defect itself and the residual stress will be reduced. The induced birefringence can be neglected, then the transmitted light whose polarization direction is parallel or orthogonal to the internal intrinsic stress direction will always maintain its polarization state.
　　
　　Many scholars and engineers have devoted a lot of energy to the development and production of polarization-maintaining devices, making the production of polarization-maintaining devices more and more mature; but overall, production still lags behind research; Continuous improvement, in most of the current use cases, polarization-maintaining devices can meet the needs. The development direction of polarization-maintaining devices is high extinction ratio, insensitivity to the environment, stable and reliable device performance, smaller size, and lower cost. The following briefly introduces the status and uses of several polarization-maintaining devices:
　　
　　1. Polarizing beam combiner (PBC): 
　　PBC is the abbreviation of Polarization Beam Combiner, which means polarization beam combiner, also called polarization multiplexer. The mechanism of the device is based on birefringent prisms, polarizing films, and photonic crystals. The general principle is to combine two linearly polarized beams with orthogonal polarization directions into one beam, or vice versa. Among them, the polarizing film type PBC has the largest volume and the highest cost, and it is an indisputable fact that it will soon be eliminated from the market. Photonic crystal is not yet mature, its ease of use still needs to be practiced, and its reliability still needs to be studied; however, as an emerging technology, its bright prospects are worth looking forward to. The most common use of PBC is to enhance pumping and eliminate polarization dependence in distributed FRA. sources are combined. The current optical communication system mainly develops a wider band and develops in the direction of denser wavelengths. There is even a demand for DWDM with 50GHZ and 25GHZ wavelength intervals. In fact, the blind pursuit of wavelength density will dramatically increase the system cost; and coherent optical communication and polarization multiplexing will be a good means to increase the system capacity. If PBC is used for polarization multiplexing, even two optical carriers with identical wavelengths can be transmitted in the same fiber without interfering with each other, which is equivalent to increasing the system capacity by 2 times. In this regard, there are researchers at home and abroad doing useful work. Using the PBC in reverse is a polarizing beam splitter, also known as a polarization demultiplexer. Since this type of device has a polarizing effect during beam splitting, the device can also be used as a polarizer, and its excellent device index, IL < 0.3dB, ER > 28dB.

Based on this device, IPBC and IPBS are developed. They are a common isolator synthesized in one device, and have the functions of PBC and PBS at the same time, and play the role of suppressing reflected light for upstream systems or light sources. For extremely demanding systems, the dual-stage IPBC/S is a good choice, with peak isolation up to 60dB.

　　
　　2. Polarization-Maintaining Coupler:
　　Currently commercially available polarization-maintaining couplers are mainly based on the fusion cone method, thin-film waveplate spectroscopy, and prism spectroscopy. The key to making a coupler by the fusion cone method is the alignment and control of the stress axis, so the cost of the fusion cone system is very high, but I am glad that domestic manufacturers have produced this type of polarization-maintaining coupler, breaking the foreign monopoly on this technology. The advantages of the fusion cone coupler are that the additional loss is low and the volume is small; but the fusion cone type polarization-maintaining coupler has always become a potential hidden danger due to the existence of its stress region, the key parameter of the device, that is, the extinction ratio. , and is sensitive to temperature. In this regard, more detailed work is still needed to improve. The thin film wave plate spectroscopic technology, relying on mature coating technology and micro-optical processing technology, has produced stable and reliable products. Prism spectroscopy is a newly emerging technology. Its biggest advantage is that the extinction ratio is very high. Compared with the previous two methods, prism spectroscopy is generally 3~5dB higher, becoming the leader in polarization maintaining couplers. Regardless of the type, any splitting ratio can be done. The most widely used field of this kind of device is optical fiber sensing, which measures specific physical quantities through demultiplexing interference; it is also used for power division in polarization-maintaining systems and power/wavelength monitoring in light sources.
　　
　　3. PM 80um small cladding fiber product series:

Compared with the 125um cladding diameter polarization maintaining fiber, the 80um cladding diameter fiber has more advantages: its smaller size can save system space; its lower bending loss can make the system miniaturized; its bending internal stress is smaller, and it can be Ensure long-term reliability of the system. For the optical fiber coiling that is inevitably used in fiber optic gyroscopes, 80um fiber provides fatigue resistance far better than 125um fiber, and the working life is much longer than that of 125um system. For aerospace navigation and some aircraft that need to measure their own angular rate, nothing is more important than stability and reliability. It can be said that the 80um cladding diameter fiber is tailor-made for fiber optic gyroscopes. It is better to use a polarization-maintaining system for fiber optic gyroscopes, but some manufacturers also choose a non-polarization-maintaining system based on cost and integration difficulties. Related passive devices mainly include couplers, isolators, polarizers, etc. For gyroscope light source, there is also 80um wavelength division multiplexer.

80um small cladding fiber devices are also used in Doppler velocimeters, holographic detectors, hydrophones, etc.　　
　　4. Introduction to other PM devices:

Polarizer: It can polarize the input light of any polarization state. This type of device, the all-fiber single-polarization fiber polarizer has the best characteristics.

Polarization-maintaining wavelength division multiplexer: In principle, any two or more wavelengths can be combined and demultiplexed. This type of device is currently the most common type of thin-film filter, and there are also cone-fused and Bragg grating types. .

Polarization-maintaining circulator: In general, the polarization-maintaining circulator has only one optical axis, such as the slow axis works and the fast axis is cut off or vice versa, but even so, normal use is sufficient.

Polarization-maintaining isolator: In addition to the functions of ordinary isolators, this type of device adds a polarization-maintaining function. The fast and slow axes can work at the same time or both of them can be selected.

Almost all common optical fiber devices can produce polarization-maintaining devices with similar functions; as for polarization-maintaining Faraday rotators, polarization-maintaining Faraday mirrors, polarization-maintaining jumpers, and composite devices that integrate multiple functions, It will not be described in detail here.　　

　　SHENZHEN PUSMAI Technology Co.,Ltd taking the development of polarization-maintaining devices as one of the means to serve the society, actively promoting the development of polarization-maintaining devices, making their products increasingly mature and quite impressive, becoming the manufacturer with the most complete polarization-maintaining products in the world, and occupying a high position in the competition of many products Get ahead. The popularization and promotion of polarization-maintaining devices requires the sincere cooperation of more colleagues in the industry and more attention and research. It is believed that polarization-maintaining devices can make their due contributions to the development of human science and technology.