Author: Fiber-MART.COM

A DWDM system generally consists of five components: Optical Transmitters/Receivers, DWDM Mux/DeMux Filters, Optical Add/Drop Multiplexers (OADMs), Optical Amplifiers, Transponders (Wavelength Converters).

Optical Transmitters/Receivers

Transmitters are described as DWDM components since they provide the source signals which are then multiplexed. The characteristics of optical transmitters used in DWDM systems is highly important to system design. Multiple optical transmitters are used as the light sources in a DWDM system. 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). Lasers create pulses of light. Each light pulse has an exact wavelength (lambda) expressed in nanometers (nm). 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. This device converts the incoming digital signal from electrical (electrons) to optical (photons) form (electrical to optical conversion, E-O). 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. E-O conversion is non-traffic affecting. The format of the underlying digital signal is unchanged. Pulses of light propagate across the optical fiber by way of total internal reflection. At the receiving end, another optical sensor (photodiode) detects light pulses and converts the incoming optical signal back to electrical form. A pair of fibers usually connects any two devices (one transmit fiber, one receive fiber).

DWDM systems require very precise wavelengths of light to operate without interchannel distortion or crosstalk. Several individual lasers are typically used to create the individual channels of a DWDM system. Each laser operates at a slightly different wavelength. Modern systems operate with 200, 100, and 50-GHz spacing. Newer systems support 25-GHz spacing and 12.5-GHz spacing is being investigated. Generally, DWDM transceivers (DWDM SFP, DWDM SFP+, DWDM XFP, etc.) operating at 100 and 50 GHz can be found on the market nowadays.

DWDM Mux/DeMux Filters

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). The output signal of an optical multiplexer is referred to as a composite signal. At the receiving end, an optical drop filter (DeMux filter) separates all of the individual wavelengths of the composite signal out to individual fibers. The individual fibers pass the demultiplexed wavelengths to as many optical receivers. Typically, Mux and DeMux (transmit and receive) components are contained in a single enclosure. Optical Mux/DeMux devices can be passive. Component signals are multiplexed and demultiplexed optically, not electronically, therefore no external power source is required. The figure below is bidirectional DWDM operation. N light pulses of N different wavelengths carried by N different fibers are combined by a DWDM Mux. The N signals are multiplexed onto a pair of optical fiber. A DWDM DeMux receives the composite signal and separates each of the N component signals and passes each to a fiber. The transmitted and receive signal arrows represent client-side equipment. This requires the use of a pair of optical fibers; one for transmit, one for receive.

Bi-Directional DWDM Mux/DeMux Operation

Optical Add/Drop Multiplexers

Optical add/drop multiplexers (i.e. OADMs) have a different function of “Add/Drop”, compared with Mux/DeMuxfilters. Here is a figure that shows the operation of a 1-channel OADM. This OADM is designed to only add or drop optical signals with a particular wavelength. From left to right, an incoming composite signal is broken into two components, drop and pass-through. The OADM drops only the red optical signal stream. The dropped signal stream is passed to the receiver of a client device. The remaining optical signals that pass through the OADM are multiplexed with a new add signal stream. The OADM adds a new red optical signal stream, which operates at the same wavelength as the dropped signal. The new optical signal stream is combined with the pass-through signals to form a new composite signal.

1-Channel DWDM OADM Operation

OADM designed for operating at DWDM wavelengths are called DWDM OADM, while operating at CWDM wavelengths are called CWDM OADM. Both of them can be found on the market now.

DWDM technology is an extension of optical networking. DWDM devices (multiplexer, or Mux for short) combine the output from several optical transmitters for transmission across a single optical fiber. 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. Only one optical fiber is used between DWDM devices (per transmission direction). Instead of requiring one optical fiber per transmitter and receiver pair, DWDM allows several optical channels to occupy a single fiber optic cable. As shown below, by adopting high-quality AAWG Gaussian technology, FS DWDM Mux/Demux provides low insertion loss (3.5dB typical), and high reliability. With the upgraded structure, these DWDM multiplexers and demultiplexers can offer easier installation.

A key advantage to DWDM is that it’s protocol and bitrate independent. DWDM-based networks can transmit data in IP, ATM, SONET, SDH and Ethernet. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel. Voice transmission, email, video and multimedia data are just some examples of services which can be simultaneously transmitted in DWDM systems. DWDM systems have channels at wavelengths spaced with 0.4 nm spacing.

DWDM is a type of Frequency Division Multiplexing (FDM). A fundamental property of light states that individual light waves of different wavelengths may coexist independently within a medium. Lasers are capable of creating pulses of light with a very precise wavelength. Each individual wavelength of light can represent a different channel of information. By combining light pulses of different wavelengths, many channels can be transmitted across a single fiber simultaneously. Fiber optic systems use light signals within the infrared band (1 mm to 400 nm wavelength) of the electromagnetic spectrum. 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.

When you’re planning a new network cable installation or considering upgrades to an existing network, you might want to consider using fiber optic cables.

Network fiber cables have some definite advantages over copper cables.

1. Greater Bandwidth

Copper cables were originally designed for voice transmission and have a limited bandwidth. Fiber optic cables provide more bandwidth for carrying more data than copper cables of the same diameter. Within the fiber cable family, singlemode fiber delivers up to twice the throughput of multimode fiber.

2. Faster Speeds

Fiber optic cables have a core that carries light to transmit data. This allows fiber optic cables to carry signals at speeds that are only about 31 percent slower than the speed of light—faster than Cat5 or Cat6 copper cables. There is also less signal degradation with fiber cables.

3. Longer Distances

Fiber optic cables can carry signals much farther than the typical 328-foot limitation for copper cables. For example, some 10 Gbps singlemode fiber cables can carry signals almost 25 miles. The actual distance depends on the type of cable, the wavelength and the network.

4. Better Reliability

Fiber is immune to temperature changes, severe weather and moisture, all of which can hamper the connectivity of copper cable. Plus, fiber does not carry electric current, so it’s not bothered by electromagnetic interference (EMI) that can interrupt data transmission. It also does not present a fire hazard like old or worn copper cables can.

5. Thinner and Sturdier

Compared to copper cables, fiber optic cables are thinner and lighter in weight. Fiber can withstand more pull pressure than copper and is less prone to damage and breakage.

6. More Flexibility for the Future

Media converters make it possible to incorporate fiber into existing networks. The converters extend UTP Ethernet connections over fiber optic cable. Modular patch panel solutions integrate equipment with 10 Gb, 40 Gb and 100/120 Gb speeds to meet current needs and provide flexibility for future needs. The panels in these solutions accommodate a variety of cassettes for different types of fiber patch cables.

7. Lower Total Cost of Ownership

Although some fiber optic cables may have a higher initial cost than copper, the durability and reliability of fiber can make the total cost of ownership (TCO) lower. And, costs continue to decrease for fiber optic cables and related components as technology advances.

When installing fibre optic cable, care must be taken to ensure that the cable is not bent, stretched or deformed. The best case is that the fibre core will break and be faulty, the worst case is that the fibre optic core will be deformed or damaged and cause signal distortion that results in intermittent faults.

Two types of fibre optic cable

In data networking, two types of cable are in common use — single mode (SMF) and multimode (MMF). The core is embedded in a layer of cladding that helps to protect and strengthen the cable.

Fibre breakage

The glass core in a fibre optic cable is fragile. It is slightly thicker than a human hair but made of glass (more rarely, a plastic material may be used for multi-mode). Manufacturers have been able to design and manufacture the core material to be somewhat elastic and resilient to bending. Single mode fibre uses a special type of glass that is extruded into a solid medium to protect it. MMF is made from glass but being thicker (at 50 µm compared to 9 µm), is more robust. Because of this, SMF is more sensitive to breakage than MMF.

When the core is stretched or bent beyond a certain point, the core will physically break into two parts. The cladding and buffer around the cable core helps to prevent damage. The glass core has some space to protect against movement, thermal expansion/shrinking, and for installation.

When the cable’s physical integrity is compromised, two outcomes are possible. The best case is that two pieces of the core are not physically aligned and no laser light will propagate. Something that is broken can be located and fixed.

A less common case is that core materials will be partially aligned after the break and pass a partial signal. The network may or may not work due to the drop in laser power.

Intermittent operation may occur as the cable expands/shrinks with temperature, vibration or movement and the core loses alignment or the gap expands to reduce laser power to a non-functional level.

A fibre optic cable relies on complete internal reflection — and this scenario still supports that — but a substantial amount of signal power can be lost at this interface, plus reflections at the break/air interface will have secondary effects.

Cracking of the fibre core

It is also possible that the fibre core might be damaged instead of broken. For SMF, the glass might only crack and cause imperfection in the medium, which would reduce signal propagation and cause reflections. MMF is more likely to be damaged by flexing and cause power loss. In the case of graded fibre, this is quite damaging to the signal as it will be badly distorted.

Best and worst cases

When working with fibre optic patch leads, it is common for people to trap them in doors or stretch them by pulling on them. While patch leads are designed to be more flexible compared to the cabling used in risers, they are still susceptible to breakage in the best case. Best case means that the cable doesn’t work; worst case is when the fibre core is partially damaged and likely to cause intermittent operation.

Intermittent is much worse than broken. Another reason for replacing cables is that the fibre connectors are dirty, scratched or faulty and new cables will improve the power level received. Cleaning the cables and SFP (Small Form-Factor Pluggable) connectors can also resolve intermittent problems.

In my opinion, that’s why replacing the cable often fixes intermittent problems in a network. It is very hard to test or confirm a faulty fibre optic patch lead. A faulty patch lead can cause waveform deformation through propagation distortion or power loss through a cracked or misaligned core. And according to the temperature fluctuation, ambient vibration by fans and coolers, or just being moved, the network might have problems.

The image below shows a fibre optic patch where the rack door has been pressing on the patch where the strain relief ends, and rather obviously, the bend radius has been severely compromised. While patch cables are fairly robust, this cable is faulty when the door is closed but working when the door is open.

That’s worse than just broken.

The CWDM are by and large in view of thin coat channel innovation which is the type of item fall under the WDM class. There arrived in a total scope of Class-8 CWDM Mux-Demuxand also OADM that stands for Optical Add Drop Multiplexer units with a specific end goal to meet a wide range of necessities and system arrangements.

Likewise, it has across the board applications that require the Channel CWDM. Some of them include: Gigabit and 10G Ethernet, Fiber Channel, ATM, ESCON, in Metro total, SDH/SONET, and CATV and so forth. Presently, we should talk about the accompanying components and utilizations of Channel CWDM that settle on it an ideal decision for all. The CWDM Mux / Demux items give up to 16-channel or even 18-channel Multiplexing on a solitary fiber. Standard CWDM Mux/Demux bundle sort include: ABS box bundle, LGX pakcage and 19″ 1U rackmount.

Highlights

The loss of insertion quality creates from the presentation of a gadget into the optical fiber is by and large lesser in CWDM than alternate gadgets; this produces short inclusion costs.

Channel-8 CWDM is dependably very steady and solid in the meantime. Not at all like every other sort of WDM class, the Channel CWDM has higher dependability.

The CWDM items are typically Epoxy free on optical way; this prompts better working and Epoxy free condition while the execution.

In CWDM, the channel segregation is very high. This expanded seclusion prompts better and successful outcomes.

Applications

WDM and Access Organize: As these channel sorts are the piece of WDM class, these have their best application in the WDM and also Access systems.

Line Observing: These items have their incredible use in line checking. This guarantees there is no crash on a similar line of some other range or frequency.

Cellular Application: The CWDM channel arrangements have their utilizations and applications additionally in the Cellular area, and advances as the unequaled panacea for some different parts and ventures.

Telecommunication: The broadcast communications devours Channel-8 CWDM at an incredible rate. It needs to utilize these items for the straightforward transmission of signs and utilization of the filaments for the same.

Aside from every one of the elements and applications, the capacity of CWDM is additionally to unravel the deficiency of fiber and straightforward transmission of exchange while lessening the charges of system building. This is the motivation behind why the Channel CWDM and LGX CWDM Mux and DeMux Module have a matter of extraordinary heights in the realm of fiber optics, flag transmission and multiplexing and so forth.