Why do we need fiber optic isolator?

Posted on March 13, 2014 by admin

Why do we need fiber optic isolator?

Light can be reflected back and forth. This is also true in fiber optic communication networks. But in fiber optic networks, most of the reflections are harmful to the stability of the system which is especially true for lasers.

Laser is essentially a resonant cavity between two semi-transparent mirrors. The lasing process happens between these two mirrors. The lasing process is very delicate and can be easily interfered. If back-reflected and scattered light enters into the laser, the lasing process will fluctuate and the output power of the laser will fluctuate.

So that is where fiber optic isolator comes to play. Optical isolators are devices that transmit light only in one direction. They play a vital role in fiber optic systems by stopping back-reflection and scattered light from reaching sensitive components, particularly lasers.

How do optical isolators work?

The inside workings of optical isolators depend on polarization. An isolator is composed of a pair of linear polarizers and a Faraday rotator.

The two linear polarizers are oriented so the planes in which they polarize light are 45¡ã apart. The Faraday rotator sits between these two polarizers. The Faraday rotator rotates the plane of the polarization of light by 45¡ã in a single direction no matter the light traveling direction, may it be from the first polarizer(left) or the second polarizer(right).

So if the light goes from the first polarizer to the second polarizer (from left to right). The Faraday rotator will rotate the polarized light from the first polarizer by 45¡ã which exactly matches the polarization plane of the second polarizer. So the light will go through with minimum loss.

But if the light goes from the second polarizer to the first polarizer (from right to left). The Faraday rotator will rotate the polarized light from the second polarizer also by 45¡ã. But since it rotates the light as the same direction as from left to right, this time when the rotated light gets to the first polarizer, the polarization planes of the polarized light and the first polarizer are 90¡ã cross. So all light are blocked and no light will go through.

From above mentioned principles, you see that fiber optic isolators transmit light only in one direction and they work like a one way street.

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Polarization Maintaining Fiber Components

Posted on March 10, 2014 by admin

What is polarization?

Light waves consist of oscillating electric and magnetic fields. These two fields are perpendicular to each other and to the direction of light traveling. We call the electric field plane as the light’s polarization.

Sunlight and many other ordinary light is made of many light waves, each with their electric and magnetic fields oriented randomly. If all waves’ electric fields were aligned parallel to each other, we call this light linearly polarized.

* Polarization’s effect on optical fibers

Polarization does not really matter in multimode fibers but it can be crucial in single mode fibers especially for long distance and high speed rate fiber communications. Why? Let me explain it below.

Technically speaking, single mode fibers actually have two modes traveling in it. These two modes have orthogonal polarization and perfect single mode fibers cannot differentiate between them. These two modes are functionally identical and light energy can shift easily between these two polarization modes.

However, fiber’s geometry is not perfect. As a result, these two modes actually travel along the fiber at slightly different speeds. The effect is called PMD (polarization mode dispersion). The slight speed difference can cause problems in high speed fiber optic links such as 10Gbit/s and 40Gbit/s.

* Polarization maintaining fibers come to the rescue!

Polarization maintaining fibers are special kinds of single mode fibers, they are also commonly called PM fibers or Panda PM fibers.

PM fibers have built-in asymmetry which is also called birefringence. The refractive index of PM fiber differs for the two polarizations and this effect prevent light energy from coupling between two polarizations.

PM fibers can transmit light in a single polarization if the input light polarization is aligned to one of its two birefringence axes. And that is why they are called polarization maintaining fibers.

* The applications of polarization maintaining fibers

PM fibers are rarely used for long distance transmission because of their expensive price and higher attenuation than single mode fiber. They are commonly used for telecommunication applications, fiber optic sensing and interferometry.

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Polarization Maintaining Fiber Components

Posted on March 6, 2014 by admin

* What is polarization?

Light waves consist of oscillating electric and magnetic fields. These two fields are perpendicular to each other and to the direction of light traveling. We call the electric field plane as the light’s polarization.

Sunlight and many other ordinary light is made of many light waves, each with their electric and magnetic fields oriented randomly. If all waves’ electric fields were aligned parallel to each other, we call this light linearly polarized.

* Polarization’s effect on optical fibers

Polarization does not really matter in multimode fibers but it can be crucial in single mode fibers especially for long distance and high speed rate fiber communications. Why? Let me explain it below.

Technically speaking, single mode fibers actually have two modes traveling in it. These two modes have orthogonal polarization and perfect single mode fibers cannot differentiate between them. These two modes are functionally identical and light energy can shift easily between these two polarization modes.

However, fiber’s geometry is not perfect. As a result, these two modes actually travel along the fiber at slightly different speeds. The effect is called PMD (polarization mode dispersion). The slight speed difference can cause problems in high speed fiber optic links such as 10Gbit/s and 40Gbit/s.

* Polarization maintaining fibers come to the rescue!

Polarization maintaining fibers are special kinds of single mode fibers, they are also commonly called PM fibers or Panda PM fibers.

PM fibers have built-in asymmetry which is also called birefringence. The refractive index of PM fiber differs for the two polarizations and this effect prevent light energy from coupling between two polarizations.

PM fibers can transmit light in a single polarization if the input light polarization is aligned to one of its two birefringence axes. And that is why they are called polarization maintaining fibers.

* The applications of polarization maintaining fibers

PM fibers are rarely used for long distance transmission because of their expensive price and higher attenuation than single mode fiber. They are commonly used for telecommunication applications, fiber optic sensing and interferometry.

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Polarization Maintaining Fiber Components On Sale

Posted on March 5, 2014 by admin

What Are Fiber Optic Circulators? Fiber Optic Communication Tutorial Series
The optical circulator has similar function and design as the optical isolator. An optical circulator is an nonreciprocal passive device that directs light sequentially from port 1 to port 2, from port 2 to port 3, and so on in only one direction. The operation of a circulator is similar to that of an isolator except its constructions is more complex. Like the isolator, its uses polarization to do its job.

The typical construction of an circulator consists of a number of walk-off polarizers, half-wave plates and Faraday rotators. Typically an optical ciruclator has three or four ports.

A variety of circulators are available commercially. They have low insertion loss, high isolation over a wide wavelength range, minimal polarization dependent loss, and low polarization mode dispersion.

The typical insertion loss of an isolator is about 0.6dB, channel isolation is over 40dB, optical return loss is over 50dB and polarization dependent loss is lower than 0.1dB.

The applications of optical ciruclators

In advanced optical communication systems, circulators are used for bi-directional transmissions, WDM networks, fiber amplifier systems, and for optical time domain reflectometer (OTDR) measurements.

Optical circulators are essential compoents of optical communication systems. They enable the routing of light from one optical fiber or waveguide to another based upon the direction of light propagation.

More information

Optical ciruculators extend the basic idea behind an optical isolator and add more functionality to the device. A circulator does not disgard the backward propagating light, as an isolator does, but directs it to another port, thus resulting in a three-port device in the simplest configuration. More ports can be added if one wants to redirect light coming from the third port to a fourth port. Even six ports circulators exist which direct light to different ports in a circular fashion depending on which port light enters.

You may guess that with the increasing of ports, the design becomes increasingly complex. You are absolutely correct on that guess. A second layer of complexity is added for polarization-independent circulators because they must split the incoming light from any port into its orthogonally polarized components and process each component separately.

In general, a circulator requires a large number of parts. The most important component in a polarization independent circulator is the beam displacer. Beam displacer is made from a strongly birefringent medium such that it displaces the orthogonally polarized components spatially by different amounts.

In spite of their complexity, optical circulators are available commercially in a relatively compact size with fiber pigtails on each end. Insertion losses are also very acceptable for such complex devices.

Optical circulators have found many applications in designing lightwave systems. A example could be a three-port circulator used with a fiber grating to realize a narrowband bandpass filter working in transmission. The circulator coverts the device into a transmission filter for all practical purposes..
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Wholesale Polarization Maintaining Fiber Components

Posted on March 4, 2014 by admin

Optical fibers are designed for many different application scenarios. To understand the different applications, it is important to understand the properties of different fiber types.

Two major types of optical fibers exist for communication system: multimode fiber and single mode fiber. The difference between them is that multimode fiber can carry many modes of light rays while single mode fiber can only carry one mode of light ray. This is a big difference. This fact determines that multimode fiber can only be used in short distance link, usually within a few hundred meters, while single mode fiber is used on much longer, usually 40~120km, distance. Based on this fact, it is now easier to understand that multimode fiber is used in LAN network and video surveillance while single mode fiber is used in long distance telephony applications.

Another consequence of this difference is the information carrying capability difference between these two types of fibers. Single mode fiber can carry hundreds times of more information than multimode fiber.

Now let’s examine the fiber types in detail.

Multimode fiber

Light ray travels in the fiber core at discrete angles within its acceptance cone. Multimode fiber has 50um or 62.5um diameter core, which is much larger than a 9um diameter single mode fiber core. Thus a large number of modes (light rays injected into the fiber at different angles) can be coupled into multimode fiber.

Now let’s look at two light rays that travel along a multimode fiber. One light ray travels straight down the fiber core center which is the shortest path. A second light ray travels at a steep angle and bounces back and forth by the fiber core side wall (a phenomenon called total internal reflection) while traveling down the fiber length which is a longer path than the first light ray.

Since the second light ray travels a longer path than the first light ray, they arrive at the fiber end at separate time (the second light arrives later than the first). This disparity between arrival times of the different light rays is called dispersion. The consequence of this disparity is a muddied signal at the receiving end. In order to properly receive the signal, the signal must run at a slower rate and that is why multimode fiber’s bandwidth is limited.

Single mode fiber

Single mode fiber, on the other hand, only accepts one light ray, which is the first light ray that travels straight down the fiber core center. So there is no arrival time disparity between different fiber modes which makes a cleaner signal at the receiving end. This is the reason why single mode fiber can run signals at much higher speed resulting in its much higher bandwidth.

Single mode fiber does have some disadvantages though. The smaller fiber core diameter makes it much harder to couple light into the fiber. This increases the manufacturing cost of many single mode fiber optic components such as isolator, attenuator, etc. The tolerances for single mode connectors, mechanical splices are also much more demanding.

One important variety of single mode fiber is polarization maintaining fiber, or also called PM fiber. PM fiber carries only one polarization (the light’s electronic field direction) of the light. PM fiber’s major applications include coherent communication system and electro-optic modulators which serves as a light transmitter in high speed fiber optic system.

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Polarization Maintaining Fiber Components On Sale

Posted on March 3, 2014 by admin

Bathrobes are used by millions of people in the world. Choose the best kind of bathrobe for you according to your taste.

Bathrobes are also called dressing gowns. They are typically robes worn after taking a bath or swimming in the pool. Bathrobes are usually worn at home where there is privacy because usually the user is wearing nothing underneath it. They are worn to preserve modesty or to keep the wearer warm whenever there is no urgent need to be fully dressed.

As with dressing gowns, bathrobes are open in the front and are closed with a belt put over the nightgowns when rising from the bed. Men started to wear robes too on a regular basis from the banyan, an 18th century custom as a means of orientalist imitation. A type of cotton kimono called the “Japanese Yukata” is worn as outdoor summer clothing and a bathrobe. There are various types of bathrobes available in the market today. Bathrobes are now categorized into the type of weaving and the type of textile used.

Styles of Bathrobe Fabrics

Bathrobes are made out of different fabrics. These are cotton, wool, microfiber and silk.

Cotton is perhaps the most widely used fabric in the world. It is a natural fiber primarily consists of cellulose. In textile manufacturing, cotton is perhaps the generally used fiber. Due to cellulose polarization, bathrobes made of cotton easily absorb water. Cotton bathrobes are mostly used in the pool, beach or after taking a shower. Bathrobes made of this material are suited in temperate climates since cotton absorbs perspiration.

Wool is a type of material suitable in colder countries. It is thick and could absorb heat well. It is comfortable to wear on winter or spring.

Microfiber is a synthetic material made of polyester or cellulose. It can be woven into different types of clothing in order to substitute for the natural fiber cloth. Modern types of microfibres are enhanced to maximize water absorption and breathe ability. Bathrobes made of microfibre are soft and lightweight just like silk bathrobes. It is usually thin in and much like a strand of hair.

Silk is a type of fabric also commonly used in making bathrobes. It is a lustrous and fine fiber. It is mainly composed of fibroin. Secretions of silk worms or insect larvae forms into an elastic and strong thread produce this so-called fibroin. The cost of producing this material is very expensive thus making silk bathrobes more expensive than the usual cotton bathrobes. Silk robes are lightweight and think like the microfibre robes. This type of robe is not recommended for wet places or environments primarily because the fabric lacks the polarity and surface area needed to absorb water. Silk robes are traditional and a very popular choice in women for it is not worn after showers or baths.

Weave Styles of Bathrobes

There is the flannel, a woven fabric is very soft to touch. It is loosely made from spun yarn usually wool or cotton. Velour is a design with cut loops. Bathrobes made of velour are commonly made with terrycloth inside for the terrycloth absorbs the water faster and more efficiently than velour. This weave style gives bathrobes a luxurious feeling for it makes this garment soft to touch.

Terry is a type of pile fabric commonly woven from cotton. On both sides of the bathrobe, it has uncut loops. The denser and longer the loops are, the spongier the garments are.

Waffle fabric has a distinctive grid-like appearance. A type of waffle called “pique” may be applied in velour, silk, cotton as well as any other fabrics..
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Polarization Maintaining Fiber Components On Sale

Posted on February 28, 2014 by admin

An optical time domain reflectometer or OTDR for short is a high tech tool used in the fiberoptic industry. An optical time domain reflectometer measures the time and intensity of light which is reflected through a fiber optic cable. OTDRs can find faults, breaks, bends and splices in fiber optic cables. This enables a technician to measure the quantity of light loss as well as identify the exact point at which the loss is occurring.

Light loss in fiber cable is a serious issue because it can hamper or completely stop data transmission. With so many communications networks dependent on fiber optic cabling to transmit data, having a way to quickly diagnose problems means repairs can occur much more rapidly leading to less network downtime.

An OTDR works by injecting a series of optical pulses through the fiber which are reflected back to the injection point and measured for deviations or aberrations in the light wave. Based on the measurement of the deviation the trouble spot can usually be precisely located.

Some critics of OTDR systems point out that they can produce inaccurate measurements if two faults are located close to each other. There is also the potential issue of faulty measurements which can sometimes occur if the optical pulse has to travel a great distance. However with the proper training a technician can compensate for these issues and interpret the readings correctly.

All things considered when used correctly an optical technician will find an optical time domain reflectometer to be an invaluable instrument in the daily course of troubleshooting, repairing and maintaining fiber optic networks..
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Polarization Maintaining Fiber Components

Posted on February 27, 2014 by admin

The characteristics of asbestos are why it has been incorporated into hundreds of commercial products. Properties such as incombustibility, high-tensile strength, resistance to corrosion, sound-proofing and thermal insulation are only some of the reasons why this material has been widely used by the construction industry.

The application of this component in many roofing materials has been thought to be hazardous to human health by causing several respiratory problems due to its friability, which is its capacity to crumble. The United States Environmental Protection Agency (EPA) regulates products containing more than one percent of asbestos and has separated the construction material into friable and non-friable substances. This is based on the amount of silicate fibers (dust) that are released when the substances are damaged or disturbed. Since this is quite hazardous, it is important to determine if the roofing material on a residence contains this hazardous substance.

Identifying Asbestos in Roofs

If a house was built before the 1980’s, it more than likely contains some type of asbestos materials, according to many experts from the Occupational Safety and Health Administration (OSHA). Only microscopic laboratory testing (polarized light microscopy) can confirm the presence of the substance when it is cut, sawed, and disturbed. It comes in various colors, depending on how it was used. The more common colors are white, brown, metallic blue, brown-yellow, and green.

Because of the technology used to manufacture asbestos now, it is easy to detect and distinguish it upon a visual inspection; however, a microscope is still needed to determine the type, presence, and amount of the substance.

Products with Asbestos

There are several products that may contain these hazardous fibers. This includes the following: roofing felt; asphalt shingles; roofing tiles; siding shingles; clapboards; sprayed ceiling coatings; troweled coatings; textured paints; ceiling tiles; and spackle.

Exposure to asbestos fibers is very risky as they are considered to be a carcinogen; inhalation of the dust is extremely harmful to human health. Therefore, it is imperative to identify any materials that may possibly contain this substance.

Essential Safety Reminders

Not ALL asbestos-containing products are dangerous, according to the Environmental Protection Agency (EPA). Exposure is less likely to happen if the material is in good condition; however, if the products are disturbed due to repairs and renovations, it will more than likely lead to the fibers being released and put the occupants of the home at risk. To avoid this possibility, asbestos-containing products should be maintained in good condition. In addition, remember that when the product is damaged or disturbed, prompt isolation of the area should be done and the location should also be isolated to avoid disturbing the substance. After this has been accomplished, an inspector should be contacted immediately for a consultation..
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Polarization Maintaining Fiber Components On Sale

Posted on February 26, 2014 by admin

What Are Fiber Optic Circulators? Fiber Optic Communication Tutorial Series
The optical circulator has similar function and design as the optical isolator. An optical circulator is an nonreciprocal passive device that directs light sequentially from port 1 to port 2, from port 2 to port 3, and so on in only one direction. The operation of a circulator is similar to that of an isolator except its constructions is more complex. Like the isolator, its uses polarization to do its job.

The typical construction of an circulator consists of a number of walk-off polarizers, half-wave plates and Faraday rotators. Typically an optical ciruclator has three or four ports.

A variety of circulators are available commercially. They have low insertion loss, high isolation over a wide wavelength range, minimal polarization dependent loss, and low polarization mode dispersion.

The typical insertion loss of an isolator is about 0.6dB, channel isolation is over 40dB, optical return loss is over 50dB and polarization dependent loss is lower than 0.1dB.
In advanced optical communication systems, circulators are used for bi-directional transmissions, WDM networks, fiber amplifier systems, and for optical time domain reflectometer (OTDR) measurements.

Optical circulators are essential compoents of optical communication systems. They enable the routing of light from one optical fiber or waveguide to another based upon the direction of light propagation.

More information

Optical ciruculators extend the basic idea behind an optical isolator and add more functionality to the device. A circulator does not disgard the backward propagating light, as an isolator does, but directs it to another port, thus resulting in a three-port device in the simplest configuration. More ports can be added if one wants to redirect light coming from the third port to a fourth port. Even six ports circulators exist which direct light to different ports in a circular fashion depending on which port light enters.

You may guess that with the increasing of ports, the design becomes increasingly complex. You are absolutely correct on that guess. A second layer of complexity is added for polarization-independent circulators because they must split the incoming light from any port into its orthogonally polarized components and process each component separately.

In general, a circulator requires a large number of parts. The most important component in a polarization independent circulator is the beam displacer. Beam displacer is made from a strongly birefringent medium such that it displaces the orthogonally polarized components spatially by different amounts.

In spite of their complexity, optical circulators are available commercially in a relatively compact size with fiber pigtails on each end. Insertion losses are also very acceptable for such complex devices.

Optical circulators have found many applications in designing lightwave systems. A example could be a three-port circulator used with a fiber grating to realize a narrowband bandpass filter working in transmission. The circulator coverts the device into a transmission filter for all practical purposes..
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What is polarization mode dispersion Fiber

Posted on February 25, 2014 by admin

What is polarization mode dispersion Fiber

1. Polarization mode and polarization mode dispersion (PMD)

In single mode fibers, light pulses are actually composed of two distinct polarization modes. The electric field vector of the two modes are perpendicular to one another, or called orthogonal. Normally the two polarization modes behave just the same in the fiber which means they can not be distinguished.

But that is only the theory with a perfect symmetrical fiber and no outside force on the fiber. Since the world is not perfect and neither is the fiber, these two polarization modes do behave differently in real world fibers.

Stresses within the fiber, and outside forces applied to the fiber cause the refractive index of glass to differ slightly for these two polarization modes. This phenomenon is called birefringence.

Birefringence makes these two polarization modes travel at slightly different speed. This speed difference broadens lightwave signal just as other dispersions and this fact is called Polarization Mode Dispersion (PMD).

2. PMD and its impact on single mode fiber optic systems

The potential effects of polarization mode dispersion became significant only a few years ago when high speed fiber optic digital communication systems came to play, such as the 40Gbit/s systems.

Polarization mode dispersion (PMD) is smaller in magnitude than other types of dispersions, but it is more difficult to compensate for, at least until now. PMD becomes a problem in systems with data rates higher than 2.5Gbit/s. PMD makes more challenge to sending higher data rates over long distance..
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