What Is An Optical Fiber Coupler? What Is The Principle And Use Of Optical Fiber Coupler?

As we all know, optical network systems also need to couple, branch, and distribute optical signals, so this requires fiber couplers to achieve. So, what is the fiber coupler, and what is the principle and use of the fiber coupler?

What is an optical fiber coupler?

1. Alias: Optical fiber coupler, also known as optical fiber adapter, also known as optical fiber flange.

2. Definition: A detachable (movable) connection device between optical fiber and optical fiber, which precisely connects the two end faces of the optical fiber so that the light energy output of the transmitting optical fiber can be coupled to the receiving optical fiber to the maximum extent, and its involvement in the optical link to minimize the impact on the system.

3. Classification: Classified according to optical fibers

SC fiber coupler: Applied to SC fiber interface, if 8 thin copper contact plates, it is an RJ-45 connector, if one copper column, it is an SC fiber interface.

LC fiber coupler: applied to LC fiber interface, connector connecting SFP module, commonly used in routers.

FC fiber coupler: Applied to the FC fiber interface, generally used on the ODF side.

ST Fiber coupler: Applied to ST fiber interface, often used in fiber distribution frames.

What is the principle and use of an optical fiber coupler?

Optical network systems also need to couple, branch, and distribute optical signals, which requires fiber couplers to achieve. An optical fiber coupler, also known as an optical splitter, splitter, is one of the most important passive devices in optical fiber links, is a fiber optic junction device with multiple inputs and multiple outputs, commonly used M×N to indicate that a splitter has M inputs and N outputs.

Optical splitters used in optical fiber CATV systems are generally 1×2, 1×3, and 1×N optical splitters composed of them.

1. Principles

It can be divided into two kinds: fused taper type and planar waveguide type. The fused taper type is made by side welding of two or more optical fibers. A planar waveguide is a micro-optical component product, which uses lithography technology to form an optical waveguide on a medium or semiconductor substrate to realize branch distribution function.

These two types of optical splitting principles are similar, they change the extinction field between the optical fiber coupling (coupling degree, coupling length) and change the optical fiber radius to achieve the different sizes of the branch amount, and conversely, you can also combine multiple optical signals into one signal called a synthesizer. The fused cone fiber coupler has become the mainstream manufacturing technology in the market because of its simple production method, cheap price, ease of connection with external fiber as a whole, and can withstand mechanical vibration and temperature changes.

The fusion tapering method is to distract two (or more) optical fibers that remove the coating layer in a certain way, melt under high-temperature heating, stretch to both sides at the same time, and finally form a special waveguide structure in the form of a double cone in the heating region, by controlling the Angle of the fiber torsion and the length of the stretch, different spectral proportions can be obtained.

Finally, the taper area is solidified on the quartz substrate with solidifying glue and inserted into the stainless copper tube, which is the optical splitter. This production process is inconsistent with the thermal expansion coefficient of the solidified adhesive and the quartz substrate and stainless steel tube, and the degree of thermal expansion and contraction is inconsistent when the ambient temperature changes, which is easy to cause damage to the optical splitter, especially when the optical splitter is placed in the field, which is also the main reason for the optical splitter to be damaged. Splitter production for more routes can be composed of multiple splits.

2. Common technical indicators

(1) Insertion loss.

The insertion loss of the optical splitter refers to the dB number of each output relative to the input light loss, and its mathematical expression is: Ai=-10lg Pouti/Pin, where Ai refers to the insertion loss of I input outlet; Pouti is the optical power of the I-th output port; Pin is the optical power value at the input end.

(2) Additional loss.

Additional loss is defined as the total optical power of all output ports relative to the number of DB of input optical power loss. It is worth mentioning that for the optical fiber coupler, the additional loss is an indicator of the quality of the device manufacturing process, reflecting the inherent loss of the device production process, the smaller the loss, the better, is an assessment indicator of the quality of the production.

The insertion loss only represents the output power status of each output port, which not only has the inherent loss factor but also considers the influence of the spectral ratio. Therefore, the difference in insertion loss between different fiber couplers does not reflect the quality of the device. The additional loss of the 1*N single-mode standard optical splitter is shown in the following table:

Number of branches 2 3 45 6 7 8 9 10 11 12 16 Additional loss DB 0.2 0.3 0.4 0.45 0.5 0.55 0.6 0.7 0.8 0.9 1.0 1.2

(3) Spectral ratio.

The spectral ratio is defined as the output power ratio of each output port of the optical splitter. In system applications, the spectral ratio is indeed determined according to the amount of optical power required by the actual system optical node (except for the average distribution). The spectral ratio of the optical splitter is related to the wavelength of the transmitted light. For example, when an optical branch transmits 1.31 microns of light, the spectral ratio of the two output terminals is 50:50; When transmitting 1.5μm of light, it becomes 70:30 (this is the case because the optical splitter has a certain bandwidth, that is, the bandwidth of the transmitted optical signal when the spectral ratio is basically unchanged). Therefore, it is necessary to specify the wavelength when ordering the optical splitter.

(4) Isolation degree.

Isolation refers to the ability of a certain optical path of an optical splitter to isolate optical signals in other optical paths. Among the above indicators, the isolation degree is more significant for the optical splitter, and devices with an isolation degree of more than 40dB are often required in practical system applications, otherwise, the performance of the entire system will be affected.

In addition, the stability of the optical splitter is also an important indicator, the so-called stability means that when the external temperature changes, the working state of other devices changes, the optical splitter's spectral ratio and other performance indicators should basically remain unchanged, in fact, the stability of the optical splitter completely depends on the process level of the manufacturer, the product of different manufacturers, the quality disparity is quite large.

In practical applications, I do encounter a lot of poor quality optical splitters, not only do the performance indicators deteriorate fast, but also the damage rate is quite high, as an important device in the optical fiber trunk, the purchase must pay attention to, can not look at the price, the optical splitter price of low process level is certainly low.

In addition, uniformity, return loss, directivity, and PDL all occupy a very important position in the performance index of optical splitter.

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