Wavelength Division Multiplexing (WDM) is an optical fiber transmission technology that allows multiple light wavelengths (or colors) to be used to send data over the same medium. A single fiber can carry two or more colors of light, and in a single optical waveguide, multiple signals can be carried at different wavelengths, or frequencies, of the spectrum.

Early fiber optic transmission systems used simple pulses of light to transmit information across glass fibers. Light blinking switches represent numbers one and zero. The actual light can be of almost any wavelength -- from about 670 nanometers to 1550 nanometers. In optical fiber transmission, WDM technology uses multiple optical wavelengths to send data on the same medium.

In the 1980s, fiber-optic datacom modems used low-cost LEDs to emit near-infrared pulses placed on low-cost fiber optics. As the need for information increases, so does the need for bandwidth. Early SONET systems used 1310-nanometer lasers to transmit 155Mb/s data streams over long distances.

But this capacity is quickly exhausted. Advances in optoelectronic components have led to the design of systems that can transmit multiple wavelengths of light simultaneously on a single optical fiber, significantly increasing the capacity of optical fibers. Thus, WDM technology was born. Multiple high bit rate data streams, such as 10Gb/s, 40Gb/s, 100Gb/s, 200Gb/s, and most recently 400Gb/s and 800Gb/s, each carrying different throughputs, can all be carried over a single fiber for multiplexing.

There are now two types of WDM:

Coarse WDM (CWDM for short): CWDM is defined as a WDM system with less than eight active wavelengths on an optical fiber. CWDM is used for short-distance communication and therefore uses wavelengths with a wide frequency range, which are spread over large distances. The standardized channel spacing can accommodate the wavelength drift of the laser due to thermal changes during operation. CWDM is a compact and cost-effective option when spectral efficiency is not an important requirement.

Dense wavelength division multiplexing (Dense WDM, DWDM for short): DWDM is defined in units of frequency. The wavelength interval of DWDM is more compact, and more channels can be placed on one optical fiber, but the cost of implementation and operation is higher. DWDM is suitable for optical

A system with more than eight active wavelengths on a fiber. DWDM can finely slice the spectrum, putting more than 40 channels into the C-band frequency range.

Suppliers using DWDM have found various techniques to squeeze 40, 88 or 96 fixed-spaced wavelengths into the fiber's C-band spectrum. Traditional DWDM line systems use wavelength selective switches (WSS) designed with fixed 50GHz or 100GHz filters. These fixed-grid line systems can accommodate channels from earlier generations of coherent transceivers that require less than 50 GHz or 100 GHz of light spectrum (depending on the filters used). Now, networks with high-bandwidth applications and continuous bandwidth growth are facing capacity depletion and are turning to C+L-band solutions, which also utilize the L-band spectrum of optical fiber, potentially doubling the capacity of optical fiber.

As optical networks evolve to meet today's ever-increasing bandwidth demands, so does the reliance on next-generation programmable coherent technologies to maximize fiber capacity and reduce cost-per-bit transmission. To take full advantage of these advantages requires a flexible mesh line system that can accommodate these high baud rate channels such as 800G wavelengths that require more than 100GHz of spectrum.

WDM is a fiber optic transmission technology that uses multiple wavelengths of light to send data over the same medium.

In fact, today's next-generation coherent modems are so smart and programmable that even more constellation and baud rate options are considered by the modem, making extremely fine-grained adjustments possible. Today, flexible channel plans are achievable, enabling anything from 64 x 75GHz channels, or for higher, 40-45 channels at 800G line rate – leveraging flexible mesh (or meshless) architectures , supporting channels with a minimum size of 37.5GHz and adjustable increments of 6.25GHz - to accommodate any current or future channel.

When these DWDM systems are enhanced with Erbium Doped-Fiber Amplifiers (EDFAs) and Raman amplification—two technologies that enhance high-speed communication performance—the operating range of these systems can be extended to digital thousand kilometers. Robust for a channel-dense system

To operate, high-precision filters are required to strip specific wavelengths without interfering with adjacent wavelengths. DWDM systems must also use precision lasers, which operate at a constant temperature to keep the channel accurate.

One of the best features of deploying DWDM on a flexible mesh photonic line system is signal independence—the ability to support multiple generations of transceivers regardless of format, bit rate, symbol rate, etc. As a result, many networks designed for 10 and 40Gb/s are now carrying 200Gb/s lanes, and many networks that have deployed flexible mesh capabilities are now even carrying 400Gb/s or even 800Gb/s signals!

Gezhi provides comprehensive DWDM solutions to meet customers' needs, from edge to core, covering a range of flexible platforms.