The output signal of an optical multiplexer is referred to as a composite signal. Multiple wavelengths (all within the 1550 nm band) created by multiple transmitters and operating on different fibers are combined onto one fiber by way of an optical filter (Mux filter). Generally, DWDM transceivers (DWDM SFP, DWDM SFP+, DWDM XFP, etc.) operating at 100 and 50-GHz can be found on the market nowadays. Newer systems that support 25-GHz spacing and 12.5-GHz spacing are being investigated. Modern systems operate with 200, 100, and 50-GHz spacing. Each laser operates at a slightly different wavelength. Several individual lasers are typically used to create the individual channels of a DWDM system. A pair of fibers usually connect any two devices (one transmit fiber, one receive fiber).ĭWDM systems require very precise wavelengths of light to operate without interchannel distortion or crosstalk. At the receiving end, another optical sensor (photodiode) detects light pulses and converts the incoming optical signal back to electrical form. Pulses of light propagate across the optical fiber by way of total internal reflection. The format of the underlying digital signal is unchanged. Electrical ones and zeroes trigger a light source that flashes (e.g., light = 1, little or no light =0) light into the core of an optical fiber. This device converts the incoming digital signal from electrical (electrons) to optical (photons) form (electrical to optical conversion, E-O). In an optical-carrier-based system, a stream of digital information is sent to a physical layer device, whose output is a light source (an LED or a laser) that interfaces a fiber optic cable. Each light pulse has an exact wavelength (lambda) expressed in nanometers (nm). Incoming electrical data bits (0 or 1) trigger the modulation of a light stream (e.g., a flash of light = 1, the absence of light = 0). Multiple optical transmitters are used as the light sources in a DWDM system. The characteristics of optical transmitters used in DWDM systems is highly important to system design.
Transmitters are described as DWDM components since they provide the source signals which are then multiplexed. Frequencies of light in the optical range of the electromagnetic spectrum are usually identified by their wavelength, although frequency (distance between lambdas) provides a more specific identification.Ī DWDM system generally consists of five components: Optical Transmitters/Receivers, DWDM Mux/DeMux Filters, Optical Add/Drop Multiplexers (OADMs), Optical Amplifiers, Transponders (Wavelength Converters). Fiber optic systems use light signals within the infrared band (1mm to 750nm wavelength) of the electromagnetic spectrum. By combining light pulses of different wavelengths, many channels can be transmitted across a single fiber simultaneously. Each individual wavelength of light can represent a different channel of information. Lasers are capable of creating pulses of light with a very precise wavelength. A fundamental property of light states that individual light waves of different wavelengths may coexist independently within a medium. DWDM systems have channels at wavelengths spaced with 0.4nm or 0.8nm spacing.ĭWDM is a type of Frequency Division Multiplexing (FDM). Voice transmission, email, video and multimedia data are just some examples of services that can be simultaneously transmitted in DWDM systems. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel. DWDM-based networks can transmit data in IP, ATM, SONET, SDH and Ethernet. With the upgraded structure, these DWDM multiplexers and demultiplexers can offer easier installation.Ī key advantage of DWDM is that it's protocol and bitrate independent. As shown below, by adopting high-quality AAWG Gaussian technology, FS DWDM Mux/Demux provides low insertion loss (3.5dB typical), and high reliability. Instead of requiring one optical fiber per transmitter and receiver pair, DWDM allows several optical channels to occupy a single fiber optic cable. Only one optical fiber is used between DWDM devices (per transmission direction).
At the receiving end, another DWDM device (demultiplexer, or Demux for short) separates the combined optical signals and passes each channel to an optical receiver.
DWDM devices (multiplexer, or Mux for short) combine the output from several optical transmitters for transmission across a single optical fiber. DWDM technology is an extension of optical networking.