An inline optical isolator is a passive magneto-optic device that only allows light to travel in one direction, with fiber optic pigtail in two ports. Isolators are used to protect a source from back reflections or signals that may occur after the isolator. It is mainly used in EDFA, ASE light source and other equipment to isolate the influence of reverse light on the light source. As we all know, an isolator’s function is based on the Faraday Effect. An inline isolator works in the best bandwidth according to different central wave band, not for all spectrum from 1260nm to 1620nm. Let us tell you the reason of that.
The core material of inline optical isolator is; Birefringent crystals and; Faraday rotators, which have an significant effect on the Isolation, Insertion loss, PMD.
First of all, the core parameters of birefringent crystals are the direction of the optical axis and the coating. The direction of the optical axis is independent of the wavelength. The coating is easily satisfied by the design of the film parameters for all bandwidth.
So the key to the question is in the Faraday rotators. The core parameters of Faraday rotator are the rotation angle, coating and the absorption of light energy by the material itself. In terms of rotation angle, in different bandwidth, the same faraday rotators has different change of angle of rotation. It has a large distance from the normal size of Birefringent crystal 45°. (The actual rotation angle is >60.4°), Due to the large difference between the relative optical axis of 45° from the birefringent crystal, the deflection angle of the forward birefringent light (o light and e light) is too large, and the deflection angle of the reverse birefringent light is too small, resulting in full bandwidth isolation In the short-wave and long-wave positions, the insertion loss becomes larger and the isolation becomes smaller, so it cannot be used in the system. So we always make customed optical isolators based on our customers' requirement.
We can realize the function of ultra-long bandwidth isolator according to the characteristics of the optical rotation angle of the optical rotator and through the cooperation of the optical axis angle of the wedge plate.
