Monthly Archives: January 2015

Advanced Optical Components – Optical Isolator

Connectors and other types of optical devices on the output of the transmitter may cause reflection, absorption, or scattering of the optical signal. These effects on the light beam may cause light energy to be reflected back at the source and interfere with source operation. To reduce the effects of the interference, an Optical Isolator is used. Many laser-based transmitters and Optical Amplifiers use an optical isolator because the components that make up the optical circuit are not perfect.

The optical isolator comprises elements that will permit only forward transmission of the light; it does not allow for any return beams in the fiber transmission routes or in the optical amplifiers. There are a variety of optical isolator types, such as Polarized (dependent and independent), Composite, and Magnetic.

Polarized Optical Isolator

As mentioned, the Polarized Optical Isolator transmits light in one direction only. This is accomplished by using the polarization axis of the linearly polarized light. The incident light is transformed to linearly polarized light by traveling through the first polarizer. The light then goes through a Faraday rotator; this takes the linearly polarized light and rotates the polarization 45 degrees, then the light passes through the exit polarizer. The exit polarizer is oriented at the same 45 degrees relative to the first polarizer as the Faraday rotator is. With this technique, the light is passed through the second polarizer without any attenuation. This technique allows the light to propagate forward with no changes, but any light traveling backward is extinguished entirely.

The loss of backward-traveling light occurs because when the backward light passes through the second polarizer, it is shifted again by 45 degrees. The light then passes through the rotator and again is rotated by 45 degrees in the same direction as the initial tilt. So when the light reaches the first polarizer, it is polarized at 90 degrees. And when light is polarized by 90 degrees, it will be “shut out.” The figures below show the forward- and reverse-transmitted light in a dependent polarized optical isolator.

Forward-Transmitted Light through a Polarized Optical Isolator

Reverse-Transmitted Light through a Polarized Optical Isolator

It should be noted that these figures depict the dependent type of polarized optical isolator. There is also an independent polarized optical isolator. The independent device allows all polarized light to pass through, not just the light polarized in a specific direction. The principle of operation is roughly the same as the dependent type, just slightly more complicated. Tips: The Independent Optical Isolators are frequently used in EDFA Optical Amplifiers.

Composite Optical Isolator

In fact, Composite Optical Isolator is a type of polarization independent isolator used in the EDFA optical amplifier. The EDFA optical amplifier is comprised of Erbium-Doped Fiber, Wavelength-Division Multiplexer, Pumping Diode Laser, Polarization Independent Isolator, and other passive components. Because the polarization independent isolator is composited with the others components into a single EDFA module, it is called a Composite Optical Isolator.

Magnetic Optical Isolator

Magnetic Optical Isolator is another name for polarized optical isolator. The magnetic portion of any isolator is of great importance. As mentioned, there is a Faraday rotator in the optical isolators. The Faraday rotator is a rod composed of a magnetic crystal having a Faraday effect and operated in a very strong magnetic field. The Faraday rotator ensures that the polarized light is in the correctly polarized plane, thus ensuring that there will be no power loss. Here is a figure that shows a basic magnetic optical isolator.

Magnetic Optical Isolator

Optical isolators are used to ensure stabilization of laser transmitters and optical amplifiers as well as to maintain good transmission performance. Ultra speed and large capacity optical fiber trunk systems are expanding as a result of the development of optical amplifiers. In parallel, the demand for optical isolators is increasing. Demand is also expected to increase as LAN and other subscriber fiber optic networks expand. It is therefore imperative that optical isolators be further improved to achieve higher performance, smaller size, and lower price. Luckily, you can now find the best optical isolators solution in Fiberstore, a Manufacturer & Supplier of Fiber Optic Network Solutions focus on Professional Customization.

The Basic Parameters of Passive Optical Network Devices

There are many devices elementary but necessary for the Passive Optical Network (PON) applications that require the transmission, combining, or distribution of optical signals. These passive devices include the Optical Splitter/Coupler, Optical Switch, Optical Attenuator, Optical Isolator, Optical Amplifier, and WDM Filters (CWDM/DWDM Multiplexer) etc. Tips: The passive devices are components that do not require an external energy source.

When working with these passive devices it is important to have a basic understanding of common parameters. Some of the basic parameters that apply to each device are Optical Fiber Type, Connector Type, Center Wavelength, Bandwidth, Insertion Loss (IL), Excess Loss (EL), Polarization-Dependent Loss (PDL), Return Loss (RL), CrossTalk (XT), Uniformity, Power Handling, and Operating Temperature.

Connector Type and Optical Fiber Type

Many passive devices are available with receptacles or fiber optic pigtails. The pigtails may or may not be terminated with a fiber optic connector. If the device is available with a receptacle or connector, the type of receptacle or connector needs to be specified when ordered. You should also note the type of optical fiber used by the manufacturer of the device to ensure it is compatible with the optical fiber used for your application.

Center Wavelength and Bandwidth

Center Wavelength is the nominal operating wavelength of the passive device.

Bandwidth (or bandpass) is the range of wavelengths over which the manufacturer guarantees the performance of the device. Some manufacturers will list an operating wavelength range instead.

Types of Loss

IL is the optical power loss caused by the insertion of a component into the fiber optic system. When working with passive devices, you need to be aware of the IL for the device and the IL for an interconnection. IL as stated by the manufacturer typically takes into account all other losses, including EL and PDL. IL is the most useful parameter when designing a system.
EL may or may not be defined by the manufacturer. EL associated with fiber optic couplers, is the amount of light lost in the coupler in excess of the light lost from splitting the signal. In other words, when a coupler splits a signal, the sum of the power at the output ports does not equal the power at the input port; some optical energy is lost in the coupler. EL is the amount of optical energy lost in the coupler. This loss is typically measured at the specified center wavelength for the device.
PDL is only a concern for Single-Mode passive devices. It is often the smallest value loss, and it varies as the polarization state of the propagating light wave changes. Manufacturers typically provide a range for PDL or define a not-to-exceed number.
RL, short for Return Loss or Reflection Loss, is typically described as this: when a passive device is inserted, some of the optical energy from the source is going to be reflected back toward the source. RL is the negative quotient of the power received divided by the power transmitted.

Tips: IL, EL, PDL, RL are all measured in decibels(dB).

CrossTalk (XT)

XT in an optical device describes the amount of light energy that leaks from one optical conductor to another. XT is not a concern in a device where there is a single input and multiple outputs. However, it is a concern with a device that has multiple inputs and a single output, such as an optical switch. XT is also expressed in dB, where the value defines the difference between the optical power of one conductor and the amount of leakage into another conductor. In an optical switch with a minimum XT of 60 dB, there is a 60 dB difference between the optical power of one conductor and the amount of light that leaked from that conductor into another conductor.

Uniformity

Uniformity is a measure of how evenly optical power is distributed within the device, expressed in dB as well as XT. For example, if a device is splitting an optical signal evenly into four outputs, how much those outputs could vary from one another is defined by uniformity. Uniformity is typically defined over the operating wavelength range for the device.

Power Handing

Power Handling describes the maximum optical power at which the device can operate while meeting all the performance specifications defined by the manufacturer. Power handling may be defined in mW(milliwatt) or dB, where 0 dBm is equal to 1 mW.

Operating Temperature

Operating Temperature describes the range of temperatures that the device is designed to operate in. This can vary significantly between devices, because some devices are only intended for indoor applications while others may be used outdoors or in other harsh environments.

Article Source: http://www.fiberopticshare.com/the-basic-parameters-of-passive-optical-network-devices.html

Fiber Optic Cable Circuit Also Need Lightning Protection

Some time ago a customer bought the fiber optic cable from fs.com, but he asked me if it can be used in frequent areas of lightning and if he needs to lightning protection. Well, As for this problem, I give the customer this explanation.

Suitable cable barrier property makes its lightning protection is not so obvious as coax and open cable circuit. And in the process of rapid development of fiber optic cables, safety grounding is often misunderstood and even forgotten. With a large number of adoptions of optical fiber cable, the situation of the fiber optical cable circuit from lightning often occurs these years. Fiber optic cable circuit has a great deal of capacity and the easiest links that be lightning struck is buried links, and it is also difficult to repair, so once it is in trouble, will cause huge losses. This page mainly introduces the fiber optic cable circuit lightning protection.

Fiber optic cable has no electrical conductivity, can protect from impact current, but in order to male high capacity optical cables from environmental events, fiber optic cables must have armored cable components and when electric line close to short and a lighting strike, people will feel current ac or surge current, harm the safety or damage the link road equipment. Related product: adss fiber.

Lightning has the trend to find the minimum impedance path to bleed thundercloud charge opposite charges neutralize underground. When lightning the land or buildings, lightning point potential while the cable extends to the very far, far end can be regarded as a potential 0, so the potential of lightning strikes near the cable is also regarded as 0. Such colony formation and fiber optic cable between the lightning point of great potential difference, the potential difference exceeds the compressive strength of Jiang Lei point between the outer sheath of the cable will breakdown the outer sheath formed from lightning point to the metal components arc channel, so a lot of lightning current flock to the cable, causing serious damage to the cable. ? It is the time to use optical fiber cable st termination kit. Cable lines in the construction inevitably damage PE (polyethylene) jacket, another rat-bite, external staff may cause the cable exposed metal components. These points will be easy to expose a strong electrical charge is introduced or lightning cable, causing damage.

According to relevant data show that in the following cases, cable lines susceptible to lightning strikes:

Metal sheaths, strengthen the core or the insulation lower copper cable.
Mutation terrain, soil resistivity changes in the larger area.
Cable trees or tall buildings with a single gauge are not enough time.

According to the above analysis, the same cable line to be concerned about its main work. Fiber optic cable lines for lightning protection, can target local weather and terrain and other natural conditions, a targeted manner. After analysis of a few lightning cable, I found that the cable line construction and maintenance should pay attention to the following questions.

First, as for aerial cables, one of the outdoor fiber optic cable, the connector box usually has to the structure of the core can be broken even, whether using electrical connected or disconnected, metal pressure plate structure is superior to the self-contained bolt connection, and the self-contained horizontal hole is better than vertical slot structure, it is a problem that should be paid attention to when choosing connector box.

Second, for underground cable lines protection, first of all, station grounding method, in the joint of the metal part of the cable shall be connected, the relay length of cable, moisture proof layer, strengthens core armored layer connected state.In both ends (station), the wrong layer, reinforcement, they can moisture proof layer should be through the arrester grounding.

Some Developments that May Occur in the Fiber Amplifier

This page will focus on fiber optic amplifiers?application, and obviously, the introduction of EDFA in a long distance network has been the first, application identified by several telecom’s operators. I just think EDFA’s advantage is that using the existing cable from 565 Mbit/s systems. Into a 2400 Mbit/s without any additional electronic requirement, maybe this is one of the cost/performance ratio advantage of the optical amplifier versus the conventional technologies. Other applications arise from those countries where the telecommunication network infrastructures are poor, or even non existing. In such a situation the possibility to reach a distance in the order of 200km at 140 or 565 Mbit/s makes the use of EDFA more competitive.

Optical amplification has been already successfully tested in various laboratories and field trials in Europe, North America and Japan. Worldwide standards authority is still working on the standardization of EDFA optical amplifier. Major telecom manufactures already supply line terminals with integrated optical amplifier functions. As far as the future submarine links are concerned, it is expected that in a few years, because of optical amplification, the electronical of today submerged repeaters, will be amended by replacing all optical amplifiers.

Well, an example of the power budget calculations at 2400 Mbit/s is given in the annex, where an EDFA system composed by a power amplifier and a pre-amplifier has been considered. In combination with a dispersion shifted submarine fiber optic cable, it belongs to outdoor fiber optic cable. Junction Networks. The massive introduction of SDH systems, and the forecast use of it on the existing cables, has made the use of EDFA technologies achievable also in the junction networks area. In Europe, North America and Japan, this possibility will be limited to the intercity applications.

In connection with the subscriber loop network design, a similar range of products is drawn up by the worldwide industry for the next generation of CATV systems. It is CATV amplifier. In a near future optical transmitters with Booster Amplifier? integrated in the same equipment, will need to be able to transmit up to 60/80 television channels simultaneously, in a cluster of 200/300 subscribers each. The figure showed a?Booster EDFA Optical Amplifier.

Although CATV amplifier housing employed in current CATV networks is designed to accommodate a return path amplifier, most of today’s CATV system have unactivated return channels. Roughly 20 percent of today’s CATV systems use some fiber optic links to bypass slow amplifier chains in the trunk portion of the network. Service is typically provided to residences and apartments, with relatively limited business locations connected to CATV networks. Similar applications product has WDM amplifier. In-line amplifier, just differ in the range of applications. There is usually only a single CATV operator in a given service area, with nascent competition from microwave and direct broadcast satellite service providers. Television receives only background antennas that are 1 to 2 meters in diameter are used by a small fraction of residential customers. With the fast developments of fiber optical amplifiers, I am very bullish on the trend of it, hope it can be dragged out more widely features and bring more benefits to people.

One Small Problem When We Choose the Fiber Patch Cable

There is a common phenomenon that people are always able to distinguish different types of interfaces easily after corresponding to the given pictures, but when we choose the fiber patch cable, such as the polishing type also confused them, it shows UPC or APC, also confused us, recently I finally understand it and share my ideas with you.

First we can look from the definition, the above are acronyms for the following:

- UPC – Ultra Physical Contact
- APC – Angled Physical Contact

Only from the words we can have a simple understanding of them, in order to have a deeper understanding, there i named a few examples for you. Usually when we hear about the description like “fiber patch lc apc lc upc”, “e2000 fc apc”, “sc apc to sc upc single mode 9 125 simplex fiber optic patch cord cable”, what do this words apc upc mean? Then we will give you explanations. In Fiberstore, We use different color to distinguish them, the blue is UPC connector and the green is APC connector, shown as the figure.

In fact, it stands for the polish style of fiber optic core and connect the copper connector of copper cable as medium, and we need to know that the connections between the fiber optic connector and the ceramic core. Different fiber optic connector ring’s size, length and polished style is different, different polish of the fiber optic connector rings result in different performance, mainly on the back reflection. Generally, UPC is 50dB or higher and APC is 60dB or higher. All insertion loss of that they should be less than 0.3dB and the lower insertion loss is, the better performance they have, it is the reason why UPC connector is more widespread than APC. At the same time, there is a point we need to pay attention to, we all know that fiber optic cables can be divided into single mode and multimode fiber cables, but single mode fiber optic cables can be with UPC or APC polished connectors, while multimode fibers are not made with APC connectors. When we talk about the insertion loss, fiber optic attenuators have to be mentioned, it also has the diffent db to choose, as for the more knowledge about it, please always pay close attention to.

Fiberstore, you know, it offers kinds of fiber cables to choose, the different connector series all available for UPC/APC version, and we can also provide SM, MM, OM3 cables, simplex and duplex option, 0.9mm, 2.0 mm, 3.0mm cable diameter for choose, as for the fiber length, it can be customized according to your requirements.

The More and More Mature Fiber Optic Cables Transmission Technology

Fiber optic media are any network transmission media that generally use glass, or plastic fiber in some special cases, to transmit network data in the form of light pulses. Within the last decade, optical fiber has become an increasingly popular type of network transmission media as the need for higher bandwidth and longer spans continues.

Fiber optic technology is different in its operation than standard copper media because the transmissions are “digital” light pulses instead of electrical voltage transitions. Very simply, fiber optic transmissions encode the ones and zeroes of a digital network transmission by turning on and off the light pulses of a laser light source, of a given wavelength, at very high frequencies. The light source is usually either a laser or some kind of Light-Emitting Diode (LED). The light from the light source is flashed on and off in the pattern of the data being encoded. The light travels inside the fiber until the light signal gets to its intended destination and is read by an optical detector.

Fiber optic cables are optimized for one or more wavelengths of light. The wavelength of a particular light source is the length, measured in nanometers (billionths of a meter, abbreviated “nm”), between wave peaks in a typical light wave from that light source. You can think of a wavelength as the color of the light, and it is equal to the speed of light divided by the frequency. In the case of Single-Mode Fiber (SMF), many different wavelengths of light can be transmitted over the same optical fiber at any one time. This is useful for increasing the transmission capacity of the fiber optic cable since each wavelength of light is a distinct signal. Therefore, many signals can be carried over the same strand of optical fiber. This requires multiple lasers and detectors and is referred to as Wavelength-Division Multiplexing (WDM).

Typically, optical fibers use wavelengths between 850 and 1550 nm, depending on the light source. Specifically, Multi-Mode Fiber (MMF) is used at 850 or 1300 nm and the SMF is typicallyused at 1310, 1490, and 1550 nm (and, in WDM systems, in wavelengths around these primary wavelengths). The latest technology is extending this to 1625 nm for SMF that is being used for next-generation Passive Optical Networks (PON) for FTTH (Fiber-To-The-Home) applications. Silica-based glass is most transparent at these wavelengths, and therefore the transmission is more efficient (there is less attenuation of the signal) in this range. For a reference, visible light (the light that you can see) has wavelengths in the range between 400 and 700 nm. Most fiber optic light sources operate within the near infrared range (between 750 and 2500 nm). You can’t see infrared light, but it is a very effective fiber optic light source.

Above: Multimode fiber is usually 50/125 and 62.5/125 in construction. This means that the core to cladding diameter ratio is 50 microns to 125 microns and 62.5 microns to 125 microns. There are several types of multimode fiber patch cable available today, the most common are multimode sc patch cable fiber, LC, ST, FC, ect.

Tips: Most traditional fiber optic light sources can only operate within the visible wavelength spectrum and over a range of wavelengths, not at one specific wavelength. Lasers (light amplification by stimulated emission of radiation) and LEDs produce light in a more limited, even single-wavelength, spectrum.

WARNING: Laser light sources used with fiber optic cables (such as the OM3 cables) are extremely hazardous to your vision. Looking directly at the end of a live optical fiber can cause severe damage to your retinas. You could be made permanently blind. Never look at the end of a fiber optic cable without first knowing that no light source is active.

The attenuation of optical fibers (both SMF and MMF) is lower at longer wavelengths. As a result, longer distance communications tends to occur at 1310 and 1550 nm wavelengths over SMF. Typical optical fibers have a larger attenuation at 1385 nm. This water peak is a result of very small amounts (in the part-per-million range) of water incorporated during the manufacturing process. Specifically it is a terminal –OH(hydroxyl) molecule that happens to have its characteristic vibration at the 1385 nm wavelength; thereby contributing to a high attenuation at this wavelength. Historically, communications systems operated on either side of this peak.

When the light pulses reach the destination, a sensor picks up the presence or absence of the light signal and transforms the pulses of light back into electrical signals. The more the light signal scatters or confronts boundaries, the greater the likelihood of signal loss (attenuation). Additionally, every fiber optic connector between signal source and destination presents the possibility for signal loss. Thus, the connectors must be installed correctly at each connection. There are several types of fiber optic connectors available today. The most common are: ST, SC, FC, MT-RJ and LC style connectors. All of these types of connectors can be used with either multimode or single mode fiber.

Most LAN/WAN fiber transmission systems use one fiber for transmitting and one for reception. However, the latest technology allows a fiber optic transmitter to transmit in two directions over the same fiber strand (e.g, a passive cwdm mux using WDM technology). The different wavelengths of light do not interfere with each other since the detectors are tuned to only read specific wavelengths. Therefore, the more wavelengths you send over a single strand of optical fiber, the more detectors you need.

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