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

⦁ 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
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 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, please contact us via email: sales@moduletek.com

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