DWDM Technology and DWDM Channel Guide

Author Yana

Date 09/30/2022

This article will introduce you to what DWDM is, including how DWDM works, What is the DWDM channel spacing, the advantages of the DWDM system, and provide a DWDM ITU grid for reference.

What is DWDM?

DWDM (Dense Wavelength Division Multiplexing) multiplexes the optical wave coupling into a single optical fiber, allowing two or more optical wavelength signals to transmit information through different optical channels simultaneously in the same optical fiber, thus providing bandwidth more effectively. DWDM is a technology used to improve the bandwidth of the existing optical fiber backbone network.

A multiplexer and demultiplexer are to be placed at both ends of the optical fiber to realize the coupling and separation of different optical waves. Specifically, in the transmission end, various optical signals are combined by a multiplexer and then coupled to one fiber cable. At the receiving end, the optical carriers of various wavelengths are separated by a demultiplexer. The working diagram of WDM technology is shown below.

WDM Working Diagram

DWDM Channel Spacing

The DWDM channel spacing is 0.4/0.8/1.6nm (50/100/200 GHz grid) and DWDM enables 40 channels, 80 channels, and 160 channels over one fiber. With the help of EDFA, the DWDM system can work in the range of thousands of kilometers.

Why the DWDM channel spacings are 0.4nm, 0.8nm, and 1.6nm? The following explains the counting process of DWDM channel spacing.

c = The speed of light =299,792,458m/sec

λ = wavelength

f = frequency

In physics, c=λf, that is λ=c/f

As ITU-T defined, in a 100GHz 40-wave system, each channel spacing is 0.1THz (100GHz), f1~f40 are 192.10THz, 192.20THz, 192.30THz…196.00THz.

When f1=192.10THz, λ1=c/f1=299,792,458m/sec / 192.10THz = 1560.61nm

When f2=192.20THz, λ2=c/f2=299,792,458m/sec / 192.20THz = 1559.79nm

When f3=192.30THz, λ2=c/f3=299,792,458m/sec / 192.30THz = 1558.98nm

When f4=192.40THz, λ2=c/f4=299,792,458m/sec / 192.40THz = 1558.17nm

…

λ1-λ2 = 1560.61nm-1559.79nm = 0.82nm

λ2-λ3 = 1559.79nm-1558.98nm = 0.81nm

λ3-λ4 = 1558.98nm-1558.17nm = 0.81nm

…

Therefore, it can be inferred that the frequency interval and wavelength interval are very close to a linear relationship. In 100GHz frequency spacing, the wavelength spacing is very close to 0.8nm. Similarly, in 50GHz frequency spacing, the wavelength spacing is very close to 0.4nm, and in 200GHz frequency spacing, the wavelength spacing is very close to 1.6nm.

DWDM Channel Chart - ITU Grid

ITU G694.1 defines the standard DWDM wavelength range. The complete channel grid for 100GHz DWDM and 50GHz DWDM is shown below.

ITU Channel	Wavelength (nm)	Freq(THz)	ITU Channel	Wavelength (nm)	Frequency (THz)
1	1577.03	190.1	41	1544.53	194.1
2	1576.2	190.2	42	1543.73	194.2
3	1575.37	190.3	43	1542.94	194.3
4	1574.54	190.4	44	1542.14	194.4
5	1573.71	190.5	45	1541.35	194.5
6	1572.89	190.6	46	1540.56	194.6
7	1572.06	190.7	47	1539.77	194.7
8	1571.24	190.8	48	1538.98	194.8
9	1570.42	190.9	49	1538.19	194.9
10	1569.59	191	50	1537.4	195
11	1568.11	191.1	51	1536.61	195.1
12	1567.95	191.2	52	1535.82	195.2
13	1567.13	191.3	53	1535.04	195.3
14	1566.31	191.4	54	1534.25	195.4
15	1565.5	191.5	55	1533.47	195.5
16	1564.68	191.6	56	1532.68	195.6
17	1563.86	191.7	57	1531.9	195.7
18	1563.05	191.8	58	1531.12	195.8
19	1562.23	191.9	59	1530.33	195.9
20	1561.41	192	60	1529.55	196
21	1560.61	192.1	61	1528.77	196.1
22	1559.79	192.2	62	1527.99	196.2
23	1558.98	192.3	63	1527.22	196.3
24	1558.17	192.4	64	1526.44	196.4
25	1557.36	192.5	65	1525.66	196.5
26	1556.55	192.6	66	1524.89	196.6
27	1555.75	192.7	67	1524.11	196.7
28	1554.94	192.8	68	1523.34	196.8
29	1554.13	192.9	69	1522.56	196.9
30	1553.33	193	70	1521.79	197
31	1552.52	193.1	71	1521.02	197.1
32	1551.72	193.2	72	1520.25	197.2
33	1550.92	193.3	73	1519.48	197.3
34	1550.12	193.4	74	1518.71	197.4
35	1549.32	193.5	75	1517.94	197.5
36	1548.51	193.6	76	1517.17	197.6
37	1547.72	193.7	77	1516.4	197.7
38	1546.92	193.8	78	1515.63	197.8
39	1546.12	193.9	79	1514.86	197.9
40	1545.32	194	80	1514.09	198

ITU Channel	Wavelength (nm)	Freq(GHz)	ITU Channel	Wavelength (nm)	Frequency (GHz)
1	1577.03	190.1	40.5	1544.92	194.05
1.5	1576.61	190.15	41	1544.53	194.1
2	1576.2	190.2	41.5	1544.13	194.15
2.5	1575.78	190.25	42	1543.73	194.2
3	1575.37	190.3	42.5	1543.33	194.25
3.5	1574.95	190.35	43	1542.94	194.3
4	1574.54	190.4	43.5	1542.54	194.35
4.5	1574.13	190.45	44	1542.14	194.4
5	1573.71	190.5	44.5	1541.75	194.45
5.5	1573.3	190.55	45	1541.35	194.5
6	1572.89	190.6	45.5	1540.95	194.55
6.5	1572.48	190.65	46	1540.56	194.6
7	1572.06	190.7	46.5	1540.16	194.65
7.5	1571.65	190.75	47	1539.77	194.7
8	1571.24	190.8	47.5	1539.37	194.75
8.5	1570.83	190.85	48	1538.98	194.8
9	1570.42	190.9	48.5	1538.58	194.85
9.5	1570.01	190.95	49	1538.19	194.9
10	1569.59	191	49.5	1537.79	194.95
10.5	1569.18	191.05	50	1537.4	195
11	1568.11	191.1	50.5	1537	195.05
11.5	1568.36	191.15	51	1536.61	195.1
12	1567.95	191.2	51.5	1536.22	195.15
12.5	1567.54	191.25	52	1535.82	195.2
13	1567.13	191.3	52.5	1535.43	195.25
13.5	1566.72	191.35	53	1535.04	195.3
14	1566.31	191.4	53.5	1534.64	195.35
14.5	1565.9	191.45	54	1534.25	195.4
15	1565.5	191.5	54.5	1533.86	195.45
15.5	1565.09	191.55	55	1533.47	195.5
16	1564.68	191.6	55.5	1533.07	195.55
16.5	1564.27	191.65	56	1532.68	195.6
17	1563.86	191.7	56.5	1532.29	195.65
17.5	1563.45	191.75	57	1531.9	195.7
18	1563.05	191.8	57.5	1531.51	195.75
18.5	1562.64	191.85	58	1531.12	195.8
19	1562.23	191.9	58.5	1530.72	195.85
19.5	1561.83	191.95	59	1530.33	195.9
20	1561.42	192	59.5	1529.94	195.95
20.5	1561.01	192.05	60	1529.55	196
21	1560.61	192.1	60.5	1529.16	196.05
21.5	1560.2	192.15	61	1528.77	196.1
22	1559.79	192.2	61.5	1528.38	196.15
22.5	1559.39	192.25	62	1527.99	196.2
23	1558.98	192.3	62.5	1527.6	196.25
23.5	1558.58	192.35	63	1527.22	196.3
24	1558.17	192.4	63.5	1526.83	196.35
24.5	1557.77	192.45	64	1526.44	196.4
25	1557.36	192.5	64.5	1526.05	196.45
25.5	1556.96	192.55	65	1525.66	196.5
26	1556.56	192.6	65.5	1525.27	196.55
26.5	1556.15	192.65	66	1524.89	196.6
27	1555.75	192.7	66.5	1524.5	196.65
27.5	1555.34	192.75	67	1524.11	196.7
28	1554.94	192.8	67.5	1523.72	196.75
28.5	1554.54	192.85	68	1523.34	196.8
29	1554.13	192.9	68.5	1522.95	196.85
29.5	1553.73	192.95	69	1522.56	196.9
30	1553.33	193	69.5	1522.18	196.95
30.5	1552.93	193.05	70	1521.79	197
31	1552.52	193.1	70.5	1521.4	197.05
31.5	1552.12	193.15	71	1521.02	197.1
32	1551.72	193.2	71.5	1520.63	197.15
32.5	1551.32	193.25	72	1520.25	197.2
33	1550.92	193.3	72.5	1519.86	197.25
33.5	1550.52	193.35	73	1519.48	197.3
34	1550.12	193.4	73.5	1519.09	197.35
34.5	1549.72	193.45	74	1518.71	197.4
35	1549.32	193.5	74.5	1518.32	197.45
35.5	1548.91	193.55	75	1517.94	197.5
36	1548.52	193.6	75.5	1517.55	197.55
36.5	1548.11	193.65	76	1517.17	197.6
37	1547.72	193.7	76.5	1516.78	197.65
37.5	1547.32	193.75	77	1516.4	197.7
38	1546.92	193.8	77.5	1516.02	197.75
38.5	1546,52	193.85	78	1515.63	197.8
39	1546,12	193.9	78.5	1515.25	197.85
39.5	1545.72	193.95	79	1514.87	197.9
40	1545.32	194	79.5	1514.49	197.95

Advantages of DWDM System

WDM technology has developed rapidly in recent years as it has the following advantages:

Make full use of the bandwidth resources of optical fiber. Fiber has huge bandwidth resources (low-loss band). WDM provides several times to dozens of times or even hundreds of times transmission capacity over an optical fiber than that of single wavelength transmission, so it greatly increases the fiber transmission capacity of the fiber optic communication system.

Supports different types of signals at the same time. Since the different wavelength channels in the WDM system are independent, various data rate signals and various types of signals can be transmitted, such as PDH and SDH signals, digital signals, analog signals, and mixed transmission of multiple services (audio, video, data), etc.

Reduce line costs. Since WDM technology enables multiple wavelengths to be multiplexed and bidirectional transmitted over one single fiber, a large number of optical fiber cables can be saved, especially in long-distance and high-capacity transmission. In addition, it is convenient to expand the capacity of the existing fiber communication system without great modification.

Reduce the ultrahigh-speed requirements of devices. With the continuous increase of the transmission rate, many optical devices have limitations in speed. WDM technology can reduce the performance requirements of some devices while achieving large-capacity transmission.

Provide high flexibility of networking. DWDM can adjust the network structure without changing the optical cable facilities based on optical wavelength division multiplexing technology. Therefore, it has great flexibility and freedom in the design of optical fiber communication networks.

QSFPTEK provides DWDM system products and solutions, including DWDM optical modules, DWDM Mux Demux and OTN solution, welcome to consult our sales and tech team via [email protected].