The optical attenuator is one of the indispensable test instruments for optical fiber communication equipment detection (such as optical power meter measurement, optical power attenuation, receiver sensitivity measurement, etc.). With the continuous development of optical fiber communication technology, optical fiber communication equipment and device manufacturers are increasingly demanding performance indicators for optical attenuators. Here we discuss the principle of optical attenuators. The principle of the optical attenuator is shown in Figure 1. The incident light is collimated by the fiber collimator, attenuated by two attenuator plates, and then passed through the fiber collimator into the output fiber. Among the two attenuators, one is a fixed attenuator, and the attenuation varies from 0db to 50db in 10db steps, and the other is a continuous attenuator. The attenuation varies from 0db to 15db, through two attenuators. Combining can achieve a continuously variable optical attenuator in the range of 0db to 60db. In Fig. 1, the optical attenuator piece and the optical axis are maintained at a certain angle. This installation method is not only that the reflected light of the front and rear surfaces of the optical attenuating piece is staggered, thereby avoiding the influence of the interference phenomenon on the optical test system, and effectively preventing the same. The reflected light returns to the incident end, increasing the previous return loss specification. The optical attenuator requires light weight, small volume, high precision, good stability, and convenient use. It can be divided into fixed, graded, and continuously adjustable. Variable optical attenuators (VOAs) have a wide range of applications in optical communications, and their primary function is to reduce or control optical signals. We have introduced a new type of continuously adjustable, large attenuation coefficient laser energy attenuator. The device is simple in structure, small in components, small in size, easy to manufacture, low in cost, and easy to integrate with other devices. Variable fiber attenuators are typically used for testing and measurement, but are also widely used in EDFAs to equalize the optical power between different channels. The variable fiber attenuator is fabricated from an attenuating fiber doped with metal ions to adjust the optical power to the desired level. If most of the external material has a refractive index greater than its mode effective refractive index, this mode can add some of the radiated optical power. If the attenuation index of the external material can be adjusted to a controllable level, such as thermo-optic, electro-optic or acousto-optic, devices with controlled attenuation are achievable. Fixed optical attenuators are used in the principle that fiber optic systems may use multiple functions. Fixed fiber attenuators are adapter-style tools that are ideal for attenuating single-mode fiber connectors in a variety of applications. It has two major categories, line and plug. The picture below is from left to right. The line type looks like a normal fiber patch cord; it is connected by a fiber optic cable to two connectors of the specified type. The plug-type attenuator looks like a large-head fiber optic connector with a male connector and a female connector, like the same type of common connector, such as FC, ST, SC and LC. Fixed optical attenuators are typically constructed in the form of movable connectors that enable connection to fiber optic lines. In addition, a certain thickness of the metal film is also plated on the end face of the fiber, and a few micrometers of air gap is left in the light path to obtain a fixed attenuation. This is a male-female device for different connector designs (LC/SC/FC/ST/MU), PC, UPC or APC grinding (APC optional tapered or stepped ferrule), attenuation values: 1~30dB, wavelength: single mode 1310um, 1550um or dual wavelength; multimode 850um or dual wavelength, with dust cap. Yin-yang fiber attenuator features: metal ion-attenuating fiber to achieve attenuation effect, high power resistance, light source weight, small size, high precision, good stability, various forms, easy to use; the last point is the application range of fiber attenuator : Optical distribution frame, optical network system, high-speed optical fiber transmission system, cable television (CATV) system, long-distance trunk dense wavelength division multiplexing (DWDM) system, optical add/drop multiplexer (OADM). At present, the market for optical attenuators is getting larger and larger, and in passive devices, the output is second only to connectors, couplers, and the like. Since the optical fixed attenuator has the advantages of low cost, stable performance, and ease of use, its market is larger than the variable optical attenuator. And because of the flexibility of optical variable attenuators, market demand is still growing steadily. Attenuators are one of the most important passive devices in optical communication systems and have broad application prospects. In recent years, some large optical device companies in foreign countries are still developing various new high-performance optical attenuator products in order to obtain optical attenuators with higher performance, smaller size and more suitable price. Attenuator with fixed attenuation and attenuator with adjustable attenuation, use: 1. Balance the gain of each wavelength signal for the BA front end; 2. In the line, the power control of the WDM system; 3. Closed loop output power control; 4. Power detection at the optical detection end. 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Principle of optical attenuator Classification of Fiber Attenuators 1. Variable Fiber Attenuators