WDM / DWDM Pilot Tone Modulation
The Pilot Tone Modulation refers to: in a wavelength division multiplexing system, a small amplitude low-frequency sine or cosine modulation is superimposed on the transmitting end for each wavelength as a mark, and different wavelengths are marked with different frequencies. When this low-frequency sine or cosine signal is superimposed on the light wavelength, there is a modulation amplitude for the top of the light wavelength, so it can also be called a top-adjusted signal.
The low-speed on-channel signal based on the Pilot Tone Modulation is sometimes called a low-frequency dither signal, sometimes called pilot tone modulation.
The low-frequency top-adjusting signal is used to mark the optical channel. The top-adjusting signal is superimposed on the original signal and enters the optical network for transmission, but the frequency of the top-adjusting signal should be in the frequency band of the information channel. In order to avoid interference with data information, its frequency It must be lower than the minimum cutoff frequency of the data channel, but at the same time, in order to avoid the influence of the dynamic characteristics of the EDFA gain, its frequency must not be too low. Therefore, the frequency of the tuning signal is mostly between 10KHz and 1 MHz. Different optical carriers are distinguished by the top-adjusting signals of different frequencies, and different optical carriers are identified by detecting the frequency of the top-adjusting signals, so this belongs to an analog tag technology. This signal is a frame signal instead of a byte. It should contain the frame preamble, frame header, frame conformance, and frame tail. The information carried should be: the information of this wavelength, the ROADM node where the sender is located, and the domain where it is And destination ROADM nodes. The monitoring channel is added to the low-frequency end of the information channel. The generation of the top-adjustment signal can allow the use of low-speed devices in the existing network to complete the generation and detection of the top-adjustment signal without the need for proprietary hardware. Using the top-adjusting signal as the wavelength label technology, the generation and addition of labels and the implementation of detection are relatively simple.
In a WDM / DWDM network, for each signal that needs to be transmitted, the network management system needs to assign it a unique frequency of the top-adjusting signal, and different transmission signals assign different frequencies of the top-adjusting signal. Reasonable planning, can establish a correspondence table of wavelength channel and label frequency in the whole network. The receiving end can obtain the corresponding optical wavelength connection information by detecting the frequency of the top-adjustment signal, and then can detect the wavelength by tracking the label.