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Why GE CWDM products using uncooled lasers don't support industrial temperature applications

Time: 2023-06-26

      ⦁ Background.
      GE CWDM products using uncooled lasers are only supported for commercial temperature applications, and this article briefly analyzes why.
      ⦁ International standards related to CWDM products
      In the ITU-T Recommendation G.694.2 standard, the center wavelength and channel bandwidth of CWDM products are defined.
      There are 18 wavelengths in total: 1271, 1291, 1311, 1331, 1351, 1371, 1391, 1411, 1431, 1451, 1471, 1491, 1511, 1531, 1551, 1571, 1591, and 1611 nm, with a spacing of 20 nm, and a channel bandwidth of ±6.5 nm permitted for the center wavelength.

Table 1 Center wavelength of CWDM products defined by ITU-T G.694.2

G.6942 Nominal central wavelengths (nm)for spacing of 20 nm
1271
1291
1311
1331
1351
1371
1391
1411
1431
1451
1471
1491
1511
1531
1551
1571
1591
1611

      ⦁ Temperature characteristics of DFB laser
      The center wavelength of a DFB laser increases with increasing temperature and decreases with decreasing temperature.
      Checking the datasheets of DFB CWDM devices from vendors such as AOI, BROADCOM, and Hisense Optoelectronics, the lasers have a typical wavelength/temperature coefficient of 0.09 nm/°C, and a center wavelength range of ±3 nm at room temperature of 25°C.

Table 2 Center wavelength as well as range nominal for AOI 2.5G CWDM TO

Part Number Center wavelength minimum(nm) Center wavelength(nm) Center wavelength maximum(nm)
DFB-1470-T5-2.5-A7-A-A-M787 1467 1470 1473
DFB-1490-T5-2.5-A7-A-A-M787 1487 1490 1493
DFB-1510-T5-2.5-A7-A-A-M787 1507 1510 1513
DFB-1530-T5-2.5-A7-A-A-M787 1527 1530 1533
DFB-1550-T5-2.5-A7-A-A-M787 1547 1550 1553
DFB-1570-T5-2.5-A7-A-A-M787 1567 1570 1573
DFB-1590-T5-2.5-A7-A-A-M787 1587 1590 1593
DFB-1610-T5-2.5-A7-A-A-M787 1607 1610 1613
  NOTE : ALL wavelength ate tested in T=25℃,P0=5mW,CW mode

      Taking the wavelength of 1470nm as an example, it can be calculated that at a high temperature of 85°C, the center wavelength limit value reaches 1473+0.09*(85-25)=1478.4nm, which exceeds the maximum value of the center wavelength defined by the ITU, which is 1471+6.5=1477.5nm.
      From the above analysis, the main reason why CWDM products using uncooled lasers cannot meet industrial grade applications is that the center wavelength of DFB lasers changes drastically with temperature, and at the extreme high temperature point, the wavelength exceeds the bandwidth of the CWDM channel defined by ITU-T G.694.2.
      If industrial temperature support is required, we can provide GE-CWDM products with cooled lasers.
      Moduletek Limited provides commercial temperature GE-CWDM using uncooled lasers and industrial temperature GE-CWDM products with cooled lasers!
      If you have any questions about the above content, you can contact us by Email : web@moduletek.com

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