whats the difference between coarse wavelenght divsion multiplexing and dense wavelenght divsion multiplexing?

Answer 1

CDWM works on a 20nm channel spacing typically in the 1500nm- 1600nm space for telecommunication allowing for about 16channels down a single fibre.

DWDM works on a much smaller channel spacing (0.8nmspacing I believe) in the 1500nm-1565nm range for C band and 1570nm - 1605nm range for L-band with a potential for 40 channels (or possibly more) down a single fibre.

At this point the main difference is cost vs. bandwidth. CWDM would result in significanlty lower bandwidth, but because the lasers/ filters and receivers are far less sofisticated then DWDM components the CWDM components would cost significantly less.

Answer 2

In course multiplexing, the wavelength of each laser is separated by a wide margin (i.e. 1.2 micron, 850 nm, 670 nm -- only 3 or 4 frequencies). There are fewer lasers working each fiber optic line, so fewer signals may be transmitted on each line.

In dense multiplexing, they try an pack as many lasers as possible down one fiber optic line. Each laser is tuned to a wavelength just outside the bandwidth of the previous one. I.E. 1.2 micron, 1 micron, 980 nm, 960 nm, 940 nm, ... 660 nm (about 15 of them) A lot more lasers means more signals can be transmitted down one fiber.

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