Recent advances in the communications industry have focused on metro and access networks as they address storage area network (SAN), video on demand (VOD), high definition television (HDTV), smart home, teleconferencing and more. Bandwidth crisis.
The new fiber optic cable has been able to transmit the entire optical communication band, including O-band, E-band, S-band, C-band, L-band and U-band, while network service providers are planning investments for the next five years.
The optical devices used in these new applications vary and the test methods differ from each other, but in most cases these methods are not actually used. Now that the output of optical devices continues to soar, it is necessary to study more practical test methods. It is a good way to measure the performance of an optical device over the entire band on the same test platform. The results of the full-band test provide network service providers with the assurance that they can optimize future passive optical network (PON), coarse wavelength division multiplexing (CWDM) networks, and are backward compatible.
There are two main types of passive optical components in a PON network. One is a wavelength division multiplexer/demultiplexer, and the other is a 1×N or 2×N optical splitter, where N can be 4, 8, 16 or 32. The wavelength division multiplexer/demultiplexer can be used in "triplexers", taking the device as an example. Its main function is to separate and combine the optical signals of three wavelengths in the PON network. The three wavelengths are 1310 nm, 1490 nm, and 1550 nm, respectively.
Because these devices are used in different locations on the PON network, their testing requirements are different. For example, a wavelength division multiplexer/demultiplexer (optical filter) is required to satisfy sufficient isolation between different passbands, and the expectation of a 1×N or 2×N optical splitter is optical division. The road is as uniform as possible in each optical band. Despite the different requirements for these devices, it is desirable to be able to understand the response of these devices to the entire spectrum. The ITU-TBPON standard G.983 states this by requiring the optical device to be used to mark at least two indicators in the two optical bands: 1260 nm to 1360 nm and 1480 nm to 1580 nm. Used in optical network terminals (ONUs) and optical line terminals (OLTs), respectively.
For the optical power budget, there is a well-known parameter that is 1 dB margin. For a PON network, this means that it can extend the range and coverage of the extra. For example, in the 1310nm band, the fiber loss is 0.35dB/km, and the extra loss of 1dB means that the network's extension is reduced by 2.8km. In some cases, it can seriously affect the potential benefits of the communications infrastructure. Therefore, it has become very important to accurately determine the parameters of optical devices in a PON network.
Figure 1. Typical measurement results for a 1x32 optical splitter
Figure 1a shows the insertion loss (IL) test results and Figure 1b shows the polarization dependent loss (PDL) test results. As can be seen from the figure, the insertion loss test is relatively easy to achieve over a wide range of wavelengths, while the polarization dependent loss (PDL) test is not so simple.
Figures 1a and 1b show the insertion loss (IL) test and the polarization (polarization) dependent loss (PDL) test, respectively, and test the output ports of a 1 x 32 optical splitter. From the test results we can see the consistency of the device at each wavelength. While most device manufacturers already have the ability to test insertion loss over a wide range of wavelengths, it does not necessarily mean they can perform polarization-dependent loss testing at full-band. PDL testing is often done for only a few wavelengths. This can lead to underestimation of PDL inconsistencies when used in a full-band environment.
Today, coarse wavelength division multiplexing (CWDM) networks have been widely used in storage area networks (SANs) and metropolitan area networks, and are considered a "low-cost CWDM" technology. Although people are still discussing whether CWDM devices are really cheap to manufacture, the wavelength configuration standard for CWDM only defines 16 wavelengths, which limits the number of wavelengths actually used, and also limits the update, which in turn affects system maintenance. the cost of.
The most commonly used are 4 wave and 8 wave devices. These devices need to be tested in the wavelength range of 1460 nm to 1620 nm according to the actual configuration (possibly S band, C band or L band). The measured spectral width is 100 nm to 160 nm. . For a 16-wave optical device, it is required to test in the wavelength range of 1260 nm to 1620 nm. Since the filter needs to ensure that the isolation of adjacent channels is at least 45~55dB, it is not easy to find the best test method, that is, to ensure a wide spectral range, a large dynamic range, and both wavelength and loss tests. Very accurate method. In CWDM or PON systems, the accuracy required for device testing is 50 pm or the sampling resolution is 100 pm, which is 5 pm for DWDM. Compared with the DWDM network, although the wavelength accuracy requirements of the PON network and the CWDM network are not so strict, the requirements for the accuracy of the loss test are very strict.
The new fiber optic cable has been able to transmit the entire optical communication band, including O-band, E-band, S-band, C-band, L-band and U-band, while network service providers are planning investments for the next five years.
The optical devices used in these new applications vary and the test methods differ from each other, but in most cases these methods are not actually used. Now that the output of optical devices continues to soar, it is necessary to study more practical test methods. It is a good way to measure the performance of an optical device over the entire band on the same test platform. The results of the full-band test provide network service providers with the assurance that they can optimize future passive optical network (PON), coarse wavelength division multiplexing (CWDM) networks, and are backward compatible.
There are two main types of passive optical components in a PON network. One is a wavelength division multiplexer/demultiplexer, and the other is a 1×N or 2×N optical splitter, where N can be 4, 8, 16 or 32. The wavelength division multiplexer/demultiplexer can be used in "triplexers", taking the device as an example. Its main function is to separate and combine the optical signals of three wavelengths in the PON network. The three wavelengths are 1310 nm, 1490 nm, and 1550 nm, respectively.
Because these devices are used in different locations on the PON network, their testing requirements are different. For example, a wavelength division multiplexer/demultiplexer (optical filter) is required to satisfy sufficient isolation between different passbands, and the expectation of a 1×N or 2×N optical splitter is optical division. The road is as uniform as possible in each optical band. Despite the different requirements for these devices, it is desirable to be able to understand the response of these devices to the entire spectrum. The ITU-TBPON standard G.983 states this by requiring the optical device to be used to mark at least two indicators in the two optical bands: 1260 nm to 1360 nm and 1480 nm to 1580 nm. Used in optical network terminals (ONUs) and optical line terminals (OLTs), respectively.
For the optical power budget, there is a well-known parameter that is 1 dB margin. For a PON network, this means that it can extend the range and coverage of the extra. For example, in the 1310nm band, the fiber loss is 0.35dB/km, and the extra loss of 1dB means that the network's extension is reduced by 2.8km. In some cases, it can seriously affect the potential benefits of the communications infrastructure. Therefore, it has become very important to accurately determine the parameters of optical devices in a PON network.
Figure 1. Typical measurement results for a 1x32 optical splitter
Figure 1a shows the insertion loss (IL) test results and Figure 1b shows the polarization dependent loss (PDL) test results. As can be seen from the figure, the insertion loss test is relatively easy to achieve over a wide range of wavelengths, while the polarization dependent loss (PDL) test is not so simple.
Figures 1a and 1b show the insertion loss (IL) test and the polarization (polarization) dependent loss (PDL) test, respectively, and test the output ports of a 1 x 32 optical splitter. From the test results we can see the consistency of the device at each wavelength. While most device manufacturers already have the ability to test insertion loss over a wide range of wavelengths, it does not necessarily mean they can perform polarization-dependent loss testing at full-band. PDL testing is often done for only a few wavelengths. This can lead to underestimation of PDL inconsistencies when used in a full-band environment.
Today, coarse wavelength division multiplexing (CWDM) networks have been widely used in storage area networks (SANs) and metropolitan area networks, and are considered a "low-cost CWDM" technology. Although people are still discussing whether CWDM devices are really cheap to manufacture, the wavelength configuration standard for CWDM only defines 16 wavelengths, which limits the number of wavelengths actually used, and also limits the update, which in turn affects system maintenance. the cost of.
The most commonly used are 4 wave and 8 wave devices. These devices need to be tested in the wavelength range of 1460 nm to 1620 nm according to the actual configuration (possibly S band, C band or L band). The measured spectral width is 100 nm to 160 nm. . For a 16-wave optical device, it is required to test in the wavelength range of 1260 nm to 1620 nm. Since the filter needs to ensure that the isolation of adjacent channels is at least 45~55dB, it is not easy to find the best test method, that is, to ensure a wide spectral range, a large dynamic range, and both wavelength and loss tests. Very accurate method. In CWDM or PON systems, the accuracy required for device testing is 50 pm or the sampling resolution is 100 pm, which is 5 pm for DWDM. Compared with the DWDM network, although the wavelength accuracy requirements of the PON network and the CWDM network are not so strict, the requirements for the accuracy of the loss test are very strict.
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