What is a PLC Divider?
2019-10-01
Divider is an integrated waveguide optical power distribution device based on quartz substrate. It has the characteristics of small size, wide working wavelength range, high reliability and good spectral uniformity. It is especially suitable for connecting local and terminal devices in passive optical networks (EPON, BPON, GPON, etc.) and realizing optical signal splitting. At present, there are two types: 1 *N and 2 *N.
According to the principle, the splitter can be divided into two types: the fused taper type and the planar waveguide type. The fused taper type products are formed by side fusion of two or more optical fibers. The planar waveguide type is a micro-optical component type product, which uses photolithography technology to form optical waveguides on dielectric or semiconductor substrates to realize branch distribution function. The principle of these two types of spectroscopy is similar. They can achieve different branching quantities by changing the coupling degree and length of the evanescent field between the fibers and the radius of the fibers. On the other hand, they can combine multiple optical signals into one signal called synthesizer. Fused taper fiber coupler has become the mainstream manufacturing technology in the market due to its simple fabrication method, low price, easy connection with external optical fibers, and resistance to mechanical vibration and temperature changes.
Fused tapering method is to remove two (or more) coated optical fibers by perturbing them in a certain way, melt them at high temperature and stretch them to both sides at the same time.By controlling the twisting angle and the stretching length of the optical fibers, different light-splitting ratios can be obtained. Finally, the taper region is solidified with curing glue on the quartz substrate and inserted into the stainless copper tube, which is the optical splitter. Because the thermal expansion coefficient of the curing adhesive is different from that of quartz substrate and stainless steel tube, the degree of thermal expansion and contraction is not the same when the ambient temperature changes. This situation easily leads to the damage of optical splitter, especially when the optical splitter is placed in the field, which is also the main reason for the damage of optical splitter. For the production of multiplexers with more routes, it can be composed of multiple dividers.
PLC shunt is fabricated by semiconductor technology (photolithography, etching, development, etc.). Optical waveguide arrays are located on the upper surface of the chip, and the shunting function is integrated on the chip, i.e. to realize 1, 1 bisection on one chip. Then, the multi-channel optical fiber arrays at the input and output ends of the chip are coupled and packaged separately.
Advantages
(1) Loss is insensitive to light wavelength and can meet the transmission needs of different wavelengths.
(2) The spectrum is uniform, and the signal can be evenly distributed to users.
(3) Compact structure, small size, can be directly installed in the existing various handover boxes, without leaving much installation space.
(4) There are many shunt channels for a single device, which can reach more than 32 channels.
(5) The lower the cost of multi-channel, the more the number of branches, the more obvious the cost advantage.
Shortcomings
(1) Component fabrication process is complex and the technology threshold is high. At present, chips are monopolized by several foreign companies, and few domestic enterprises can produce large quantities of packaging.
(2) Compared with the fused taper shunt, the cost is higher, especially in the low-channel shunt.
(3) Fused tapered fiber splitter editing
Fused tapering technology is to tie two or more optical fibers together, then melt and stretch on the taper machine, and real-time monitor the change of the spectral ratio. After the spectral ratio reaches the requirements, the melt stretching is completed. One end of the fused taper retains one optical fiber (the rest is cut off) as the input end, and the other end serves as the multi-channel output end. At present, the mature taper drawing process can only be pulled below 1 x 4 at a time. More than 1*4 devices are connected together by multiple 1*2 devices. It is encapsulated in the shunt box as a whole.
Main advantages
(1) The taper coupler has more than 20 years of history and experience, equipment and processes need only be used, develop funds are only a few tenths or even a few percent of the cost of PLC.
(2) Only quartz substrates, optical fibers, heat shrinkable pipes, stainless steel pipes and less glue can be easily obtained from raw materials, and the total cost is not more than one dollar. The investment depreciation cost of machines and instruments is less, and the cost of low-channel shunts such as 1 *2, 1 *4 is lower.
(3) The spectral ratio can be monitored in real time according to the need, and the unequal splitter can be made.
Main shortcoming
Loss is sensitive to optical wavelength, and devices are usually selected according to wavelength. This is a fatal defect in the process of three-in-one operation, because the optical signal transmitted by three-in-one transmission has 1310 nm, 1490 nm, 1550 nm and other wavelength signals.
Editor of Technical Indicators
(1) Insertion loss.
The insertion loss of optical splitter refers to the dB number of each output relative to the input light loss. Its mathematical expression is: Ai=-10lg Pout/Pin, where Ai refers to the insertion loss of the first output port; Pout is the optical power of the first output port; Pin is the optical power value of the input port.
(2) Additional loss.
Additional loss is defined as the sum of optical power at all output ports and the number of DB losses relative to the input optical power. It is worth mentioning that for optical fiber couplers, the additional loss is an index reflecting the quality of the device manufacturing process and the inherent loss of the device manufacturing process. The smaller the loss, the better it is, it is an evaluation index of the quality of the device manufacturing. The insertion loss only represents the output power of each output port, not only has the inherent loss factor, but also takes into account the influence of the spectral ratio. Therefore, the difference of insertion loss between different fiber couplers can’t reflect the quality of device fabrication. For 1*N single-mode standard optical splitters, the additional losses are shown in the following table:
Bifurcation number 23 4 5 6 7 8 9 10 11 12 16
Additional loss DB 0.20.30.40.45 0.50.55 0.6 0.7 0.8 0.9 1.0 1.2
(3) Spectrum ratio.
The splitting ratio is defined as the output power ratio of each output port of the optical splitter. In system application, the splitting ratio is to determine the appropriate splitting ratio (except for the average distribution) according to the amount of optical power required by the actual optical node of the system. The splitting ratio of the optical splitter is related to the wavelength of the transmitted light, for example, when an optical splitter is in the system. When 1.31 micron light is transmitted, the ratio of the two output ports is 50:50; when 1.5 micron light is transmitted, it becomes 70:30 (the reason for this is that the optical splitter has a certain bandwidth, that is, the bandwidth of the transmitted optical signal when the ratio of the two output ports is basically unchanged). So when making optical splitters, we must specify the wavelength.
(4) Isolation.
Isolation is the ability of one optical path of an optical splitter to isolate optical signals in other optical paths. Among the above indicators, isolation is more important for optical splitters. In practical system applications, devices with isolation of more than 40 dB are often need, otherwise the performance of the whole system will be affected. In addition, the stability of the optical splitter is also an important index. The so-called stability means that when the external temperature changes and the working state of other devices changes, the optical splitter's spectral ratio and other performance indicators should remain basically unchanged. In fact, the stability of the optical splitter depends entirely on the technological level of the manufacturer. The quality of the products from the same manufacturer is quite different. In practical application, I do encounter a lot of poor quality optical splitters, not only the performance indicators deteriorate quickly, but also the damage rate is quite high. As an important component of optical fiber trunk, we must pay attention to it when choosing and purchasing. We can not only look at the price, but also the price of optical splitter with low technology level is certainly low. In addition, uniformity, echo loss, directivity and PDL all play an important role in the performance of optical splitters.
According to the principle, the splitter can be divided into two types: the fused taper type and the planar waveguide type. The fused taper type products are formed by side fusion of two or more optical fibers. The planar waveguide type is a micro-optical component type product, which uses photolithography technology to form optical waveguides on dielectric or semiconductor substrates to realize branch distribution function. The principle of these two types of spectroscopy is similar. They can achieve different branching quantities by changing the coupling degree and length of the evanescent field between the fibers and the radius of the fibers. On the other hand, they can combine multiple optical signals into one signal called synthesizer. Fused taper fiber coupler has become the mainstream manufacturing technology in the market due to its simple fabrication method, low price, easy connection with external optical fibers, and resistance to mechanical vibration and temperature changes.
Fused tapering method is to remove two (or more) coated optical fibers by perturbing them in a certain way, melt them at high temperature and stretch them to both sides at the same time.By controlling the twisting angle and the stretching length of the optical fibers, different light-splitting ratios can be obtained. Finally, the taper region is solidified with curing glue on the quartz substrate and inserted into the stainless copper tube, which is the optical splitter. Because the thermal expansion coefficient of the curing adhesive is different from that of quartz substrate and stainless steel tube, the degree of thermal expansion and contraction is not the same when the ambient temperature changes. This situation easily leads to the damage of optical splitter, especially when the optical splitter is placed in the field, which is also the main reason for the damage of optical splitter. For the production of multiplexers with more routes, it can be composed of multiple dividers.
PLC shunt is fabricated by semiconductor technology (photolithography, etching, development, etc.). Optical waveguide arrays are located on the upper surface of the chip, and the shunting function is integrated on the chip, i.e. to realize 1, 1 bisection on one chip. Then, the multi-channel optical fiber arrays at the input and output ends of the chip are coupled and packaged separately.
Advantages
(1) Loss is insensitive to light wavelength and can meet the transmission needs of different wavelengths.
(2) The spectrum is uniform, and the signal can be evenly distributed to users.
(3) Compact structure, small size, can be directly installed in the existing various handover boxes, without leaving much installation space.
(4) There are many shunt channels for a single device, which can reach more than 32 channels.
(5) The lower the cost of multi-channel, the more the number of branches, the more obvious the cost advantage.
Shortcomings
(1) Component fabrication process is complex and the technology threshold is high. At present, chips are monopolized by several foreign companies, and few domestic enterprises can produce large quantities of packaging.
(2) Compared with the fused taper shunt, the cost is higher, especially in the low-channel shunt.
(3) Fused tapered fiber splitter editing
Fused tapering technology is to tie two or more optical fibers together, then melt and stretch on the taper machine, and real-time monitor the change of the spectral ratio. After the spectral ratio reaches the requirements, the melt stretching is completed. One end of the fused taper retains one optical fiber (the rest is cut off) as the input end, and the other end serves as the multi-channel output end. At present, the mature taper drawing process can only be pulled below 1 x 4 at a time. More than 1*4 devices are connected together by multiple 1*2 devices. It is encapsulated in the shunt box as a whole.
Main advantages
(1) The taper coupler has more than 20 years of history and experience, equipment and processes need only be used, develop funds are only a few tenths or even a few percent of the cost of PLC.
(2) Only quartz substrates, optical fibers, heat shrinkable pipes, stainless steel pipes and less glue can be easily obtained from raw materials, and the total cost is not more than one dollar. The investment depreciation cost of machines and instruments is less, and the cost of low-channel shunts such as 1 *2, 1 *4 is lower.
(3) The spectral ratio can be monitored in real time according to the need, and the unequal splitter can be made.
Main shortcoming
Loss is sensitive to optical wavelength, and devices are usually selected according to wavelength. This is a fatal defect in the process of three-in-one operation, because the optical signal transmitted by three-in-one transmission has 1310 nm, 1490 nm, 1550 nm and other wavelength signals.
Editor of Technical Indicators
(1) Insertion loss.
The insertion loss of optical splitter refers to the dB number of each output relative to the input light loss. Its mathematical expression is: Ai=-10lg Pout/Pin, where Ai refers to the insertion loss of the first output port; Pout is the optical power of the first output port; Pin is the optical power value of the input port.
(2) Additional loss.
Additional loss is defined as the sum of optical power at all output ports and the number of DB losses relative to the input optical power. It is worth mentioning that for optical fiber couplers, the additional loss is an index reflecting the quality of the device manufacturing process and the inherent loss of the device manufacturing process. The smaller the loss, the better it is, it is an evaluation index of the quality of the device manufacturing. The insertion loss only represents the output power of each output port, not only has the inherent loss factor, but also takes into account the influence of the spectral ratio. Therefore, the difference of insertion loss between different fiber couplers can’t reflect the quality of device fabrication. For 1*N single-mode standard optical splitters, the additional losses are shown in the following table:
Bifurcation number 23 4 5 6 7 8 9 10 11 12 16
Additional loss DB 0.20.30.40.45 0.50.55 0.6 0.7 0.8 0.9 1.0 1.2
(3) Spectrum ratio.
The splitting ratio is defined as the output power ratio of each output port of the optical splitter. In system application, the splitting ratio is to determine the appropriate splitting ratio (except for the average distribution) according to the amount of optical power required by the actual optical node of the system. The splitting ratio of the optical splitter is related to the wavelength of the transmitted light, for example, when an optical splitter is in the system. When 1.31 micron light is transmitted, the ratio of the two output ports is 50:50; when 1.5 micron light is transmitted, it becomes 70:30 (the reason for this is that the optical splitter has a certain bandwidth, that is, the bandwidth of the transmitted optical signal when the ratio of the two output ports is basically unchanged). So when making optical splitters, we must specify the wavelength.
(4) Isolation.
Isolation is the ability of one optical path of an optical splitter to isolate optical signals in other optical paths. Among the above indicators, isolation is more important for optical splitters. In practical system applications, devices with isolation of more than 40 dB are often need, otherwise the performance of the whole system will be affected. In addition, the stability of the optical splitter is also an important index. The so-called stability means that when the external temperature changes and the working state of other devices changes, the optical splitter's spectral ratio and other performance indicators should remain basically unchanged. In fact, the stability of the optical splitter depends entirely on the technological level of the manufacturer. The quality of the products from the same manufacturer is quite different. In practical application, I do encounter a lot of poor quality optical splitters, not only the performance indicators deteriorate quickly, but also the damage rate is quite high. As an important component of optical fiber trunk, we must pay attention to it when choosing and purchasing. We can not only look at the price, but also the price of optical splitter with low technology level is certainly low. In addition, uniformity, echo loss, directivity and PDL all play an important role in the performance of optical splitters.
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