Dear all,
I would like to share with you this subject which presents the principle and the common technical indicators of the Optical Splitter.
Like the coaxial cable transmission system, the optical network system also needs to couple, branch, and distribute optical signals, which requires an optical splitter to achieve. Optical splitter, also known as optical splitter, is one of the most important passive devices in the optical fiber link. It is an optical fiber tandem device with multiple input ends and multiple output ends. M × N is commonly used to indicate that a splitter has M input terminals and N output terminals. The optical splitters used in the optical fiber CATV system are generally 1 × 2, 1 × 3 and the 1 × N optical splitter composed of them.
Principle of Optical Splitter
According to the principle, the optical splitter can be divided into two types: fused taper type and planar waveguide type. The fused taper type product is formed by fusing two or more optical fibers on the side; the planar waveguide type is a micro-optical element type product. The photolithography technology forms an optical waveguide on a dielectric or semiconductor substrate to realize the branch distribution function. The two types of beam splitting principles are similar. They change the coupling of the evanescent field between the optical fibers (coupling degree, coupling length) and the fiber radius to achieve branching of different sizes. Conversely, multiple optical signals can be combined into one signal. It's called a synthesizer. Fused cone optical fiber couplers are currently the mainstream manufacturing technology in the market because of their simple manufacturing methods, low prices, easy connection with external optical fibers, and the advantages of resistance to mechanical vibration and temperature changes.
The fusion taper method is to remove two (or more than two) optical fibers with a coating in a certain way, melt under high temperature heating, and simultaneously stretch to both sides, and eventually form a double cone in the heating zone The special waveguide structure can obtain different splitting ratios by controlling the twisting angle of the optical fiber and the length of stretching. Finally, the taper area is cured with a curing glue on the quartz substrate and inserted into the stainless copper tube, which is the optical splitter. In this production process, the thermal expansion coefficient of the cured adhesive is inconsistent with the quartz substrate and the stainless steel tube, and the degree of thermal expansion and contraction is inconsistent when the ambient temperature changes. This situation is likely to cause damage to the optical splitter, especially the optical splitter. The situation is even worse in the wild, which is also the main reason why the optical branch is easily damaged. For the production of more splitters, multiple splitters can be used.
Common Technical Indicators of Optical Splitter
1- Insertion loss
The insertion loss of the optical splitter refers to the number of dB of each output relative to the input optical loss. The mathematical expression is: Ai = -10lg Pouti / Pin, where Ai refers to the insertion loss of the i-th output port; Pouti Is the optical power of the ith output port; Pin is the optical power value of the input.
2- Additional loss
Additional loss is defined as the DB number of the total optical power of all output ports relative to the input optical power loss. It is worth mentioning that for fiber couplers, the additional loss is an indicator that reflects the quality of the device manufacturing process and reflects the inherent loss of the device manufacturing process. The smaller the loss, the better, and it is the evaluation index of the quality of the production. The insertion loss only indicates the output power status of each output port, not only has the inherent loss factor, but also considers the influence of the split ratio. Therefore, the difference in insertion loss between different fiber couplers does not reflect the quality of device fabrication. For 1 * N single-mode standard optical splitter, the additional loss is shown in the following table:
Number of branches 2 3 4 5 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 split ratio is defined as the output power ratio of each output port of the optical splitter. In system applications, the determination of the split ratio is based on the amount of optical power required by the actual system optical node to determine the appropriate split ratio (except for average distribution) The splitting ratio of the optical splitter is related to the wavelength of the transmitted light. For example, when an optical splitting transmits 1.31-micron light, the splitting ratio of the two output ends is 50:50; when transmitting 1.5μm light, it becomes 70: 30 (The reason why this happens is because the optical splitter has a certain bandwidth, that is, the bandwidth of the optical signal transmitted when the split ratio is basically unchanged). So be sure to indicate the wavelength when ordering the optical splitter.
4- Isolation degree
Isolation refers to the isolation capability of one optical path of an optical splitter to optical signals in other optical paths. Among the above indicators, the isolation is more important for the optical splitter. In actual system applications, devices with isolation above 40dB are often required, otherwise it will affect the performance of the entire system.
In addition, the stability of the optical splitter is also an important indicator. The so-called stability means that when the external temperature changes and the working status of other devices changes, the splitting ratio of the optical splitter and other performance indicators should remain basically unchanged. In fact, the stability of the optical splitter depends entirely on the manufacturer's process level. The quality of products from different manufacturers is quite different. In actual applications, I have indeed encountered many inferior optical splitters, which not only deteriorate the performance index quickly, but also have a very high damage rate. As an important component of the optical fiber trunk, you must pay attention when purchasing, not just look at it The price and the price of the optical branch with low technological level must be low.
Reference : https://en.wikipedia.org/wiki/Fiber-optic_splitter
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