Optical isolator is a passive optical components allows only one-way passage of light, its working principle is based on Faraday rotation of non-reciprocity. Echo reflected through the optical fiber can be well isolated optical isolator. The main advantage of the optical isolator Faraday magneto-optical effect of the crystal. Optical isolator characteristics are: forward low insertion loss, high reverse isolation, high return loss.

 Its role is to prevent adverse effects after the optical path of the light generated due to various reasons the light source and the optical system to produce transmission. For example, between the semiconductor laser source and the optical transmission system mounting an optical isolator, the reflected light can reduce the adverse effects on the stability of the spectral output of the light source is largely generated. In the high-speed direct modulation, direct detection optical fiber communication systems, backward transmitted light will produce additional noise, the system's performance degradation, which also requires an optical isolator to eliminate. Both ends of the optical fiber amplifier doped fiber isolator mounted glazing can improve the stability of the fiber amplifier, without it, after the reflected light will enter the signal source (laser), causing volatility in the signal source. In the long haul coherent optical communication system, installed at some distance an optical isolator can reduce the power loss caused by stimulated Brillouin scattering by.

 Optical isolator Schematic
 A wide variety of optical isolators, optical isolators including online, free-space optical isolator and the like. The domestic part of 1310/1480 / 1550nm polarization independent optical isolator interior design process for single-mode fiber of two orthogonal polarization states are treated to ensure that the entire device is independent of the polarization characteristics. Unipolar device having low insertion loss, two-stage device has a high optical isolation, suitable for different applications, mainly used in fiber amplifiers, fiber lasers.

 Isolator Application of Fiber Lasers
 Compared with the common optical fiber communication systems use lower power optical isolator at higher laser power, optical isolator design and production also showed some differences, which is in the design and development of high-power devices the main problem to be solved.

 Optical element injury problem at a high power density of the laser radiation. This problem is not the high- power optical isolator exist, that is, other high-power optical devices design and production process is also to face. In order to solve this problem.

 First, the need to ensure the production and testing of products in good environmental cleanliness and choose a higher damage threshold optics and optical film, of course, this was also the product cost constraints. Because the tiny particles in the air if you adhere to the optical surface will greatly reduce the laser damage threshold of optical surfaces, these tiny particles absorb the laser is relatively large, easily lead to energy concentration near the particle, resulting in damage to the optical surface of the film and even surface damage, pitting in the surface of the element leaving the pits even device failure.

 Secondly, because under normal circumstances the optical elements inside the damage threshold is much higher than the laser damage threshold of its surface, the laser power density of the surface of the element will determine the ability of the entire device laser induced damage, especially in the case of pulsed Work even more so. Then you can try to make by optically converting optical element surface spot size expanding ways to improve the damage threshold, for example, expanded core optical fiber method, and a beam expander lens optical fiber method is to use this principle to work, or width by a laser pulse stretching method disguised reduced laser power density, concentrated in space and time, can effectively improve product performance laser resistance by avoiding laser energy.

 Thermal effects of high power devices and thermal design. Because of the high power devices operating at higher power, compared with the low-power devices, and more easily heat will inevitably be affected by temperature rise, so the performance of the device by the thermal characteristics and thermal design of a more serious impact. Optical properties of the optically active crystal usually easily affected by temperature, if during device operation due to the accumulation of the absorbed laser energy and cause the internal temperature to rise to a larger, will make the crystal rotation angle of the polarization plane of the light deviates from the rotation caused by the normal noticeable performance degradation, serious and even cause damage to the device.

 Further, the permanent magnets at high temperatures are also more prone to the field weakening and demagnetization phenomenon, irreversible loss of the magnetic field even, so the stability of high Wendui Yong magnets is unfavorable; and, in the case of extremely high optical power of the optical element a larger temperature rise due to the heat from the internal surface of the transfer, the internal temperature necessarily higher than the temperature of the surface thereof, so that the temperature gradient and thermal stress occurs inside the optical element, the refractive index of the center of the beam cross-section of the interior and the magnitude of change in refractive index of different edge, which appeared in the refractive index difference, that is, the emergence of a lens effect, which will change the propagation characteristics of the beam, resulting in a serious decline in the quality of the beam, seriously affect the normal operation of the device even cause damage.

 Therefore, we must take effective measures to reduce the absorption of laser light and effective heat dissipation. Reduce the absorption of the laser light absorption coefficient requires selection of a smaller optical materials, reducing the light transmission distance elements in the interior design rational structure, efficient heat dissipation requirements may arise where it accumulated in the heat to provide effective heat transfer path and cooling, the power size can take passive cooling or active cooling method. Megawatt class optical isolator design on the use of optical crystal shape slats to improve the cooling temperature control capability of the device.

 Magnetic field design high power isolator. Another key high-power optical isolator design of the magnetic field and the magnet design and selection. Under normal circumstances, the use of opto-isolators are magnetic rotation effect to work, it must be applied in the optical crystal suitable magnetic field. To save energy and ease of use, strong permanent magnet materials are generally used to generate the required magnetic field, when the magnetic field of the magnet and the selection and design is very important to the performance and cost of the device greatly affected. Under normal circumstances require a strong uniform magnetic field in a space optical crystal, so it can reduce the size of optical crystals, higher performance and low cost, so it requires no significant increase in the volume of the device case design choices suitable magnets for strong uniform magnetic field. Specific design by selecting the magnetic strong magnet, and the use of appropriate shape and volume to achieve the desired magnetic field.

  Assembly technology for high power isolator. High power optical isolator requires long-term stability in harsh environments, which the device structure and assembly process put forward a very high demand. A well-designed structure and assembly process can effectively reduce the optical components of internal stress, thereby enhancing the performance and stability of the product so that the device can be a long-term stable and reliable work. Isolator structure design mainly need to solve two problems: first, the assembly of optical components requires reliable, effective cooling temperature; followed by the need solid and reliable assembly strong permanent magnets, with the improvement of magnet design and manufacturing capabilities of the device multiple magnets may use a combination of more complex shapes to provide a strong uniform magnetic field, and a strong magnetic force between the magnets requires assembly process design appropriate method to reliably magnet assembly and requested that the assembly process will not result in damage to the magnets or demagnetization. These need to accumulate and improve in practice.

  2015, 1997 million dollars global fiber laser market size of about isolator, an increase of 5.65% over 2014 to $ 18.9 million year on year. Meanwhile, the expected market size in 2016 will reach $ 21.63 million, an increase of 8.28%. The future, as domestic enterprises to develop high-power isolator, growth in the domestic market will be higher than the international market.

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