What Is an Optical Attenuator?

An optical attenuator is a device used to attenuate optical power. It is mainly used for optical fiber system index measurement, short-distance communication system signal attenuation, and system test.

Chinese name: Optical attenuator
Foreign name: optical attenuator

Features: Requires light weight, small size and high accuracy
main products: Adjustable optical attenuator
Precautions: Keep the environment clean and dry

Optical Attenuator Introduction

Optical attenuator is a very important passive component of fiber optics.It can attenuate the optical signal energy according to the requirements of users. . At present, a series of optical attenuators have been widely used in the field of optical communications, bringing convenience to users.

An optical device that can be inserted into an optical path and can attenuate the optical signal power according to a set requirement. Use it to adjust the power of the optical signal transmitted by the optical communication system or test system, so that the system reaches a good working state. It is also commonly used to detect the sensitivity and dynamic range of optical receivers.

Optical attenuators can be divided into fixed attenuators, stepped adjustable attenuators, continuously adjustable attenuators, and continuous and stepped combined attenuators. Its main performance parameters are attenuation and accuracy.

Metal film is usually evaporated or sputtered on a glass substrate or a doped glass with high absorption is used to make the attenuation film. The required attenuation can be obtained by controlling the thickness of the coating or the amount of doped glass and its thickness. It is also possible to make the attenuator by using the coupling loss when two sections of fiber are docked.

Optical Attenuator Features

Optical attenuators require light weight, small size, high accuracy, good stability, and easy use. It can be divided into fixed, variable, and continuously adjustable.

The working principle of the serial optical attenuator

3.1 : Optical attenuator 3.1 The optical attenuator is classified as:

Optical attenuator:

1. Displacement type optical attenuator:

Lateral displacement type optical attenuator

Vertical displacement optical attenuator

2. Attenuating sheet optical attenuator

3.Intelligent optical attenuator

In serialized optical attenuators, different types of optical attenuators have different principles.

3.2 Optical Attenuator 3.2 Working Principle of Displacement Optical Attenuator

The displacement optical attenuator uses the principle that the attenuation of the optical fiber changes with its centering accuracy. When the optical fiber is docked, a certain displacement occurs between the optical fibers to achieve the purpose of attenuating a certain amount of optical energy. Lateral displacement method and longitudinal displacement method can be used.

3.3 Optical Attenuator 3.3 Types of Fixed Fixed Attenuator

Displacement type fixed attenuators can be divided into converter type and converter type.

(1) Converter-type optical fixed attenuatorConverter-type optical fixed attenuator has stable performance, both ends are converter interfaces, and the attenuation is divided into five types: 5, 10, 15, 20, and 25 dB. For use with various types of connectors, you only need to remove the converter in the connector and replace it with the same type of optical attenuator to achieve the purpose of attenuating the optical signal. According to different ports, there are several types:

Converter light: FC type, SC type, ST type

Fixed attenuator: FC-SC type, FC-ST type, SC-ST type

(2) Converter type optical fixed attenuator

One end of the converter-type optical fixed attenuator is a connector plug, and the other end is a converter port. Its performance is stable, and the attenuation is divided into 5, 10, 15, 20, 25 dB. When in use, you only need to insert a conversion optical attenuator of the same type at the connector to achieve the purpose of attenuating optical signals in the line. According to different ports, there are several types:

SC FC type, ST FC type, SC ST type

Converter type fixed attenuator: ST SC type, FC SC type, FC ST type

C type, SC type, ST type

3.4 Optical Attenuator 3.4 Attenuation Sheet Optical Attenuator

The attenuator-type optical attenuator directly fixes an attenuator with absorption characteristics in the optical path to achieve the purpose of attenuating optical signals. The attenuation sheet is made by an absorption glass sheet or a method of plating an absorption film on a glass substrate. Attenuating sheet-type optical attenuators can be divided into step-type two-wheel variable optical attenuators and continuous variable attenuators.

3.5 Optical Attenuator 3.5 Stepped Double Wheel Variable Optical Attenuator

The structure of the stepped two-wheel variable optical attenuator is shown in Figure 1. The collimator uses a parallel optical path.Two attenuation disks with a fixed attenuation are inserted into the optical path.Each attenuation disk is equipped with six attenuation plates of 0, 5, 10, 15, 20, and 25 dB. By rotating these two discs, different attenuation plates on the two discs can be combined with each other to obtain ten levels of attenuation of 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 dB. Of course, if you want to obtain step attenuators in other attenuation ranges, you can easily achieve the desired purpose by changing the filter and position on the attenuation disk accordingly.

Figure 1.Structure of a stepped dual-wheel variable optical attenuator

3.6 Optical Attenuator 3.6 Continuously Variable Optical Attenuator

The overall structure and working principle of the continuous variable optical attenuator are similar to the two-wheel stepped variable optical attenuator (as shown in Figure 2). But it is a combination of a step attenuator and a continuously changing attenuator.The attenuation of the step attenuator is 0, 10, 20, 30, 40, 50 dB. 0 ~ 15dB, so the total attenuation adjustment range is: 0 ~ 65dB. In this way, through the combined effect of the coarse file of the step attenuator and the fine file of the variable attenuator, the goal of continuous attenuation of light energy can be achieved.

Figure 2 Structure of a two-wheeled continuous variable optical attenuator

3.7 Optical Attenuator 3.7 Intelligent Optical Attenuator

The technology of step-type double-wheel and double-wheel continuous variable optical attenuator is very mature, and its performance is very stable. It is very common to use, but because the mechanical knob is used to adjust the attenuation and the dial reading, it affects the accuracy. The intelligent optical attenuator can overcome this deficiency. The intelligent optical attenuation principle block diagram is shown in Figure 3.

Figure 3 Schematic diagram of intelligent optical attenuator

It controls the micro motor through the circuit, drives the rack, translates the filter, and then feeds back the actual attenuation signal detected by the data encoding disk to the circuit for correction, so as to achieve the purpose of automatic driving, automatic detection and display of the optical attenuation . Therefore, the intelligent optical attenuator has the characteristics of high accuracy, continuously adjustable attenuation, small volume, easy to carry, and simple and convenient to use. The attenuation unit of the intelligent optical attenuator uses the principle shown in Figure 4. Compared with the previous attenuator, except that the filter is changed to a continuously changing neutral filter, the other components in the attenuation unit are the same. Since the absorption efficiency of the used filter changes linearly with the translation direction of the filter, when the motor moves the filter along a direction perpendicular to the optical path, the purpose of attenuating the optical signal is achieved.

Figure 4 Schematic diagram of the attenuation unit of the intelligent optical attenuator

Optical Attenuator Performance

At present, the market for optical attenuators is growing. Among the passive devices, their output is second only to connectors and couplers. Because the fixed optical attenuator has the advantages of low price, stable performance and easy use, its market is larger than the variable optical attenuator. Due to its flexibility, the market demand for optical variable attenuators is still steadily increasing. Attenuators are one of the most important passive components in optical communication systems, and have a wide range of applications. In recent years, some large foreign optical device companies are still developing various new high-performance optical attenuator products in order to obtain higher performance, smaller size, and more affordable optical attenuators.

Main Products of Optical Attenuator

Adjustable optical attenuators are commonly used in optical measurements. When measuring the sensitivity of an optical receiver, it is usually placed at the input of the optical receiver to adjust the received optical power. When using an optical attenuator, keep the environment clean and dry, and wear a protective cap when not in use. Handle with care when moving, avoid collision.