QSFP-40G-CWDM4 VS QSFP-40G-PSM4 solution comparison

      The 40G QSFP+ LR optical module contains two different types: QSFP-40G-CWDM4 and QSFP-40G-PSM4, respectively, the former is transmitted in the link using WDM, and the latter is transmitted using multiple parallel fibers.
1. QSFP-40G-CWDM4
      CWDM (Coarse Wavelength Division Multiplexing): Coarse Wavelength Division Multiplexing (CWDM) enables simultaneous transmission of multiple signals of different wavelengths over a single fiber.
      QSFP-40G-CWDM4 adopts dual LC interfaces, and the module adopts Coarse Wavelength Division Multiplexing (CWDM), in which the four typical wavelengths of 1271nm, 1291nm, 1311nm and 1331nm at the transmitting end will be merged into a single path through the built-in MUX of the optical module, and then eventually transmitted to the remote end through the LC optical fiber, and after receiving the optical signals at the receiving end, they can be transmitted through the DEMUX. After receiving the optical signals of the four wavelengths of the combined wave, the receiver will separate the 10G optical signals of the four different wavelengths into the corresponding channels through DEMUX, as shown in the figure below:

Figure 1 QSFP-40G-CWDM4 signaling diagram

2. QSFP-40G-PSM4
      PSM4 (Paralell Single Mode 4 lanes): 4-channel parallel single mode fiber transmission, each independent optical signal is transmitted in a separate fiber;
      QSFP-40G-PSM4 adopts MPO interface, the four independent 10G signals inside the module enter into the corresponding parallel optical fiber after electrical/optical conversion, and each optical fiber transmits one 10G signal, as shown in the following figure:

Figure 2 QSFP-40G-PSM4 signaling diagram

      From the application point of view of the optical module: QSFP-40G-PSM4 module internal function structure is relatively simpler, the cost of optical module is lower, but the MPO patch cable cost is higher, especially for long-distance transmission; QSFP-40G-CWDM4 module is relatively more costly, but the use of ordinary double LC patch cable, patch cable cost is very low, more suitable for long-distance cabling. The specific choice of that program needs to be made by the customer according to the actual situation. The specific choice of that program needs to be evaluated by the customer according to the actual transmission requirements.
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