Fiber Optic Attenuator Overview

As we all know, a fiber optic amplifier is often installed where optical signals are weak and need to be enlarged. But what if there is too much power level of an optical signal which should be reduced? To solve this issue, fiber optic attenuator comes into being. Fiber optic attenuator or optical attenuator is a passive device utilized to decrease the power rate of the optical signal either in free space or in an optical fiber without appreciably distort the waveform. This article will give an overview of optical attenuator to make you better understand it.

The Importance of Fiber Optic Attenuator

Many people may think that the bigger the optical signal, the better the performance. Actually, either too little or too much power can cause high bit error rates. Too much power can make the receiver amplifier saturate, while too little will cause noise problems as it interferes with the signal. For example, in DWDM system, multiple wavelength channels arriving at a node may pass through different paths and experience different losses, their powers need to be equalized before entering the optical amplifier to get flat since the gain of each channel depends on the power level of the other channels. So in this case, a fiber optic attenuator is required to control the power level of optical signals.

How Does a Fiber Optic Attenuator Work?

The power reduction is done by means such as absorption, reflection, diffusion, scattering, deflection, diffraction, and dispersion, etc. The fiber optic attenuator usually works by absorbing the light, like sunglasses absorb extra light energy. Using this working principle, fiber optic attenuators typically have a working wavelength range in which they absorb all light energy equally, and should not reflect the light or scatter the light in an air gap which could cause unwanted back reflection in the fiber system. This kind of principle is more popular in the design of optical attenuator, since it is simple and can effectively reduce the optical signal power. The following picture shows the absorptive principle of optical attenuator.

Types of Fiber Optic Attenuator

Optical attenuator is widely used in fiber optic communications, either to test power level margins by temporarily adding a calibrated amount of signal loss, or to be installed permanently to properly match the levels of a transmitter and a receiver. There are two commonly used types, including fixed attenuator and variable attenuator.

Fixed attenuator, as its name shows, is designed with an unchanging level of attenuation that is ideal for attenuating single-mode fiber connectors in various applications. It can be theoretically designed to provide any amount of attenuation that is desired and be set to deliver a precise power output. This type of optical attenuator is utilized in structure for two distinct types of services. On the first type, it is used to regulate the channels in order to set up a recognized level of signal. On the second type, this mechanism is used to match the impedance and also as a shield to avoid the contact with two different device. A LC fixed fiber optic attenuator is shown in the image below.

Different from fixed attenuator, variable attenuator can offer a wide range of attenuation values with flexible adjustment which is generally used for testing and measurement or equalizing the light power among different channels in EDFAs. This type of optical attenuator can be divided into stepwise variable attenuator and continuously variable attenuator. The former one can change the attenuation of the single in known steps such as 0.1 dB, 0.5 dB, or 1 dB, while the latter one can allow the operators to adjust the attenuator to accommodate the changes required quickly and precisely without any interruption to the circuit. Like fixed attenuator, both these two types of variable attenuators are available with regular connectors, like LC, SC or FC. Here is a LC to LC variable fiber optic attenuator.

Conclusion

As an indispensable passive optical component in WDM networks, fiber optic attenuator is designed to control the power level of optical signals more precisely. We have discussed the importance, working principle and commonly used types of fiber optic attenuator. Hope you can have a better understanding of it.

WDM Network

CWDM

CWDM (Coarse Wavelength Dense Multiplexing) is a method of combining multiple signals on laser beams at various wavelengths for transmission along fiber optic cables. CWDM uses five or six wavelengths which are from 1270 nm to 1610 nm with a channel spacing of 20 nm. The channel width itself is 13 nm, and the remaining 7 nm is designed to secure the space to the next channel. This 20nm intervals allows the use of low-cost, uncooled lasers for CWDM. CWDM is technologically simpler and easier to implement than DWDM, and it addresses traffic growth demands without overbuilding the infrastructure. But the wavelengths it can support are limited, so it is suitable for a short distance transmission.

DWDM

DWDM is the abbreviation of dense wavelength division multiplexing, which is a type of WDM systems. It works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. DWDM can maintain a more stable wavelength than CWDM, because it has a more dense wavelength intervals which can support more than 80 channels at present, and each channel can carry 2.5Gbps light signal. This allows DWDM to be suitable for long distance optical transmission. As it costs higher than CWDM, it is not available for the use of normal people.

CWDM Mux/Demux

CWDM Mux/Demux is a passive device which is very reliable and simple to use. These devices are designed to multiplex multiple CWDM channels into one or two fibers. The common configuration is 4, 8, 16 and 32 channels. These modules multiplex the light signal outputs from four or more electronic devices, and send them over a single optical fiber, then finally demultiplex the signals into separate, distinct signals for output into electronic devices at the end of the fiber optic cable.

Fiber Optic Splitter

Fiber optic splitter, also called beam splitter, is a type of technology which takes a single optic signal instead of an electrical signal and divides it into multiple signals to send data from one place to another. It is used in passive optical network (PON) as a key component to divide the power of the light over multiple fibers. A single fiber optic splitter can be used in the GPON network. Note that optical splitter can also be employed in the central office alongside the OLT or in the basement of a building for a multiple dwelling unit (MDU) installation. Optical splitters are manufactured commonly in two types according to working principle—FBT (Fused Biconical Taper) splitter and PLC (Planar Lightwave Circuit) splitter. Each type has its own performance.

Fiber Optic Attenuator

Fiber optic attenuator is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. It is usually used when the signal arriving at the receiver is too strong and hence may overpower the receiving elements. To achieve power loss, technologies including air-gap, absorption, scattering and interference filter are often used for the attenuator products. Fiber optic attenuators can take a number of different forms, and are typically classified as fixed and variable attenuators. Furthermore, according to different types of connectors, there are LC, SC, ST, FC, MU, E2000 attenuators, etc.

FTTH

FTTH is the the acronym of fiber-to-the-home, which is an installation and use of optical fiber to provide unprecedented high-speed internet access from a central point directly to individual buildings such as residences, apartment buildings and businesses. In FTTH deployment, families and officers can both utilize the network in an easier way. FTTH dramatically increases the connection speeds available to computer users compared with technologies now used in most places. Certainly, FTTH is one of the fastest growing applications worldwide.

PON

PON (Passive Optical Network) is a technology in fiber optic communication which implements a point-to-multipoint architecture (P2MP), where unpowered fiber optic splitters are used to enable a single optical fiber to serve multiple end-points such as customers instead of providing individual fibers between the central office and the customers. A PON system consists of an optical line termination (OLT) at the communication company’s office, and a number of optical network units (ONU) near end users. Depending on the termination of the PON, the system can be divided into fiber-to-the-home (FTTH), fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), etc.

CWDM SFP+ Transceiver

CWDM SFP+ transceiver (Coarse Wavelength Division Multiplexing Small Form Factor Pluggable) also known as SFP 10G CWDM transceiver is based on the popular SFP transceiver. It can reach a maximum speed of 11.25 Gbps and is commonly used in 10G Ethernet but also as 8x fiber channel or 4x fiber channel speed. CWDM SFP+ commonly comes in three versions including LR, ER and ZR. The LR has 10dB power budget while the ER has 15 dB and ZR 24 dB.

Fiber Media Converter

Fiber media converter is a simple network equipment which can connect two dissimilar media types such as twisted pair with fiber optic cables. And it supports a number of different data communication protocols such as Ethernet, Fast Ethernet, Gigabit Ethernet, Serial Datacom interfaces, and so on. Fiber media converter is an essential part of fiber networking because it has long distance operation, high bandwidth capacity and it reliably makes fiber optics the most desired channel for data communication. The types of fiber media converter ranges from small independent equipment to PC card converter and high-end mouth density chassis.

Fiber Patch Panel

Fiber patch panel, also called fiber distribution panel, is an integrated unit for fiber cable management to terminate the fiber optic and provide access to the individual fiber for cross connection. There are two main types of fiber patch panels. One is a wall-mounted device, and the other is a rack-mounted panel. Fiber patch panel helps network technicians in minimizing the clutter of wires when setting up fiber optic cables, organizing and distributing the optical cables and the branches.

Overview of WDM Network

WDM networks are networks that deploy optical WDM fiber links where each one carries multiple wavelength channels. WDM is the acronym of Wavelength Division Multiplexing, which is a technology that multiplexes several signals over a single optical fiber by optical carriers of different wavelengths which use a laser or a LED. There is a multiplexer and a demultiplexer at the either end of the WDM. A multiplexer is at the transmitting end to combine several signals together, and a demultiplexer is at the receiving end to split the signals apart. WDM systems are popular in fiber optic network as they allow to be expanded by simply upgrading the multiplexer and demultiplexer at each end. And with the help of WDM, there is no need for us to overhaul the backbone network regardless of several generations of technology development.

Types of WDM

According to the differences of channel space, there are mainly two kinds of WDM techniques. One is DWDM and the other is CWDM. DWDM is the abbreviation of Dense Wavelength Division Multiplexing, which is a technology that can put data from different sources together on an optical fiber, with each signal carried at the same time on its own separate light wavelength. DWDM has so dense wavelength intervals that it can multiplex more than 80 separate wavelengths or channels of data into light stream transmitted on a single optical fiber. Each channel can carry 2.5Gbps light signals, and up to 200 billion bits can be delivered a second by the optical fiber. Therefore, DWDM can maintain a more stable wavelength than CWDM and it can be used for long distance optical transmission. But it is a high-cost device and energy consumption that it is not suitable for ordinary people.

CWDM (Coarse Wavelength Division Multiplexing) is an economical technology to save fiber resources through transmitting multiple wavelengths on one optical fiber and it is a multiplexing technology for city and access network. Transmission is realized using five or six wavelengths between 1270nm and 1610nm with a 20nm interval. CWDM is a low-cost system because of its uncooled modulating laser which only consumes 0.5W power, and its cost only takes up 30% of the DWDM expense. Therefore, CWDM is available for the applications in a short distance, high bandwidth and areas with dense access points. It can be used in cable television networks, where different wavelengths are applied for the downstream and upstream signals.

Commonly Used Devices in WDM Network

Optical Splitter

Today, network technology develops fast, the advent of fiber optic splitter is magnificent in helping users maximum the performance of optical network circuits. Fiber optic splitter also called as beam splitter is used in passive optical network (PON) which can split an incident light beam into two or more light beams, and vice versa. It is suitable for the maintenance of long-haul network, cable TV ATM circuit or local area/metro area network, and it also can be used for FTTx/PON applications. Generally, PLC splitter and FBT splitter are the two commonly used types.

Optical Amplifier

With the demand for longer transmission length, optical amplifiers have become an essential component in long-haul fiber optic systems. An optical amplifier is a device which can amplify an optical signal directly, without the need to convert it to electricity signal first. It may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed. Optical amplifier can be used in both linear and non linear modes of operation. Commonly used types of optical amplifier are semiconductor laser amplifiers and fiber amplifiers.

Optical Attenuator

In data communication, receiving either too much or too little optical power will cause high bit error rates. In order to solve this problem, using an optical attenuator is a good solution. An optical attenuator is a passive device used to reduce the power level of an optical signal either in free space or in an optical fiber without appreciably distorting the waveform. Optical attenuator is widely used in fiber optic communications, either to test power level margins by temporarily adding a calibrated amount of signal loss, or installed permanently to properly match the levels of a transmitter and receiver. There are two commonly used types, including fixed attenuator and variable attenuator.

CWDM Mux/Demux

CWDM Mux/Demux is a passive device which is very reliable and simple to use. These devices are available with various of wavelength combinations, usually from 1270nm to 1610nm with 20nm intervals. And based on different applications, a CWDM Mux/Demux module can be designed into different channels. A typical four channel Mux/Demux module can be used to multiplex four different wavelengths onto one fiber which means four different data can be transmitted over the same fiber at the same time. And Mux/Demux modules are integrated in an entirety. In general, CWDM Mux/Demux products can be used in fields, like all enterprises and carrier with fiber optic infrastructure, connecting field offices to central office, and so on.

DWDM Mux/Demux

DWDM Mux/Demux is designed to multiple DWDM channels into one or two fibers. The common configuration is 4, 8, 16, and 40 channels, or 50G DWDM Mux/Demux. These modules multiplex the light signal outputs from four or more electronic devices passively and send them over a single optical fiber, then demultiplex the signals into separate, distinct signals for input into electronic devices at the end of the fiber optic link.

WDM network is an important part in fiber optic communication, and there are a number of devices in a WDM network. This is a brief introduction about WDM network in this article. Hope it can give users a general knowledge of WDM network.