LR6 alkaline battery.Introduction to CWDM Passive Module Test Solution

　　The price of CWDM system is much lower than that of DWDM system. Because CWDM has small power, small size and easy use, the cost of supporting facilities, personnel training and later maintenance is lower. Compared with optical cable engineering: the use of CWDM equipment is quick to open, low cost, and convenient for later network upgrades. You can directly add the required signals or replace higher-speed products without changing the optical fiber links. The network upgrade is simple and reduces the network cost. Upgrade costs. At present, DWDM technology has been widely used in long-distance high-speed optical communication systems such as national backbone networks and submarine optical cable communication systems. However, due to its complex technology and high cost, DWDM is not suitable for use in metropolitan area networks and access networks. Different from the DWDM system, the CWDM system uses a distributed feedback (DFB) laser and a broadband optical filter without a cooler. Therefore, the CWDM system has the following advantages: low power loss, small size and low cost. The launch of the CWDM system on the market enables it to replace the DWDM system in metropolitan area networks and access networks. Currently, most CWDM systems operate in the range from 1470nm to 1610nm, with a channel spacing of 20nm. The current technologies for making CWDM include thin film filters (ThinFilmFilter, TFF) and all-fiber couplers (AllFiberCoupler). Regardless of the manufacturing method of CWDM devices, there is the same very important issue: testing of technical indicators. These indicators include insertion loss, channel bandwidth, isolation, passband flatness and other important indicators. Since CWDM covers a very wide wavelength range (>140nm), the test is relatively complex. The test methods include the following: 1. Use white light source as the test light source

　　Advantages: The wavelength coverage of white light source is very wide. Disadvantages: The power density of the white light source is very small, <-55dBm/nm, so the isolation index test can only reach about 20dB, which is difficult to meet the requirements.

　　2. Advantages of using 1550nm LED light source as the test light source: LED light source has a wider wavelength coverage and is cheaper. Disadvantages: The power density of the LED light source is small, in the range of -40~-50dBm/nm, so the isolation index test can only reach about 20~30dB. Of course, if the spectrometer uses a high-sensitivity scanning method, it can also reach 30~40dB. However, there is a problem of low test efficiency (it takes about 5 minutes to scan a channel).

　　3. Advantages of using tunable laser as test light source: pDL, return loss and other indicators can also be tested. Disadvantages: Generally, the wavelength of a single tunable laser cannot cover the required range of CWDM, so two are needed; in addition, a higher-end tunable laser must be selected, otherwise the isolation index of a general tunable laser can only be measured due to the influence of ASE. About 30dB. In addition, the test speed is slow, the efficiency is low, the cost is high, and the test curve is easily affected by pDL.

　　4. Advantages of using S+C+L broadband light source (SLD) as the test light source: high test efficiency and intuitive results (recommended first choice). http://www.opeak.com.cn

　　5. Using ASE-C+L broadband light source as the test light source, and then scanning with a spectrometer has the following advantages: high test efficiency, intuitive results, and moderate cost. It is the most commonly used test solution. The ASE-C+L broadband light source approximately covers the wavelength range of 1520~1620nm. In this range, the optical power density is approximately 3 orders of magnitude greater than that of the LED light source (refer to Figure 1). Therefore, the isolation index of CWDM can be measured to more than 50dB. . Disadvantages: The light in the 1470~1520 band is weak, but it still has some light. Its optical power density is equivalent to that of the LED light source. The isolation index can be measured to about 20~30dB. Of course, high-sensitivity scanning methods can also be used to improve the test isolation. Spend.

　　Note: The above describes the measurement method for CWDM modules. Similar measurement methods can also be used for CWDM thin film filters, CWDM fiber couplers and other devices, which should be simpler.

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