Tag Archives: fiber optic

Introduction Of Specialty Fibers For Optical Communication Systems

Optical fiber communications have changed our lives over the last 40 years. There is no doubt that low-loss optical transmission fibers have been critical to the enormous success of optical communications technology. It is less well known however, that fiber-based components have also played a critical role in this success.

Initially, fiber optic transmission systems were point to point systems, with lengths significantly less than 100 km. Then in the 1980s, rapid progress was made on the research and understanding of optical components including fiber components. Many of these fiber components found commercial applications in optical sensor technology such as in fiber gyroscopes and other optical sensor devices. Simple components such as power splitters, polarization controllers, multiplexing components, interferometric devices, and other optical components proved to be very useful. A significant number of these components were fabricated from polarization maintaining fibers (PMFs). You can buy the PM fiber patch cables from Fiberstore.

Although not a large market, optical fiber sensor applications spurred research into the fabrication of new components such as polarization maintaining components, other components such as power splitters were fabricated from standard multimode (MM) or single-mode telecommunication fiber. In the telecommunication sector, the so-called passive optical network was proposed for the already envisioned fiber-to-the-home (FTTH) network. This network relied heavily on the use of passive optical splitters. These splitters were fabricated from standard single-mode fibers (SMFs). Click here to get the price single mode cable fiber optic. Although FTTH, at a large scale, did not occur until decades later, research into the use of components for telecommunications applications continued.

The commercial introduction of the fiber optical amplifier in the early 1990s revolutionized optical fiber transmissions. With amplification, optical signals could travel hundreds of kilometers without regeneration. This had major technical as well as commercial implications. Rapidly, new fiber optic components were introduced to enable better amplifiers and to enhance these transmission systems. Special fibers were required for the amplifier, for example, erbium-doped fibers. The design of high-performance amplifier fibers required special considerations of mode field diameter, overlap of the optical field with the fiber active core, core composition, and use of novel dopants. Designs radically different from those of conventional transmission fiber have evolved to optimize amplifier performance for specific applications. The introduction of wavelength division multiplexing (WDM) technology put even greater demands on fiber design and composition to achieve wider bandwidth and flat gain. Efforts to extend the bandwidth of erbiumdoped fibers and develop amplifiers at other wavelength such as 1300nm have spurred development of other dopants. Codoping with ytterbium (Yb) allows pumping from 900 to 1090nm using solid-state lasers or Nd and Yb fiber lasers. Of recent interest is the ability to pump Er/Yb fibers in a double-clad geometry with high power sources at 920 or 975 nm. Double-clad fibers are also being used to produce fiber lasers using Yb and Nd.

Besides the amplication fiber, the EDFA (Erbium-Doped Fiber Amplifier) requires a number of optical components for its operation. These include wavelength multiplexing and polarization multiplexing devices for the pump and signal wavelengths. Filters for gain flattening, power attenuators, and taps for power monitoring among other optical components are required for module performance. Also, because the amplifier-enable transmission distance of hundreds of kilometers without regeneration, other propagation propeties became important. These properties include chromatic dispersion, polarization dispersion, and nonlinearities such as four-wave mixing (FWM), self-and cross-phase modulation, and Raman and Brillouin scattering. Dispersion compensating fibers were introduced in order to deal with wavelength dispersion. Broadband coupling losses between the transmission and the compensating fibers was an issue. Specially designed mode conversion or bridge fibers enable low-loss splicing among these thre fibers, making low insertion loss dispersion compensators possible. Fiber components as well as microoptic or in some instance planar optical components can be fabricated to provide for these applications. Generally speaking, but not always, fiber components enable the lowest insertion loss per device. A number of these fiber devices can be fabricated using standard SMF, but often special fibers are required.

Specialty fibers are designed by changing fiber glass composition, refractive index profile, or coating to achieve certain unique properties and functionalities. In addition to applications in optical communications, specialty fibers find a wide range of applications in other fields, such as industrial sensors, biomedical power delivery and imaging systems, military fiber gyroscope, high-power lasers, to name just a few. There are so many linds of specialty fibers for different applications. Some of the common specialty fibers include the following:

Active Fibers: These fibers are doped with a rare earth element such as Er, Nd, Yb or another active element, The fibers are used for optical amplifiers and lasers. Erblium doped fiber amplifiers are a goog example of fiber components using an active fiber. Semiconductor and nanoparticle doped fibers are becoming an interesting research topic.
Polarization Control Fibers: These fibers have high birefringence that can maintain the polarization state for a long length of fiber. The high birefringence is introduced either by asymmetric stresses such as in Panda, and bowtie design. If both polarization modes are available in the fiber, the fiber is called PMF. If only one polarization mode propagates in the fiber while the other polarization mode is cutoff, the fiber is called single polarization fiber.
Dispersion Compensation Fibers: Fibers have opposite chromatic dispersion to that of transmission fibers such as standard SMFs and nonzero dispersion shifted fibers (NZDSFs). The fibers are used to make dispersion compensation modules for mitigating dispersion effects in a fiber transmission system.
Highly Nonlinear Optical Fibers: Fibers have high nonlinear coefficient for use in optical signal processing and sensing using optical nonlinear effects such as the optical Kerr effect, Brillouin scattering, and Raman scattering.
Coupling Fibers or Bridge Fibers: Fibers have mode field diameter between the standard SMF and a specialty fiber. The fiber serves as an intermendiate coupling element to reduce the high coupling loss between the standard SMF and the specialty fiber.
Photo-Sensitive Fibers: Fibers whose refractive index is sensitive to ultraviolet (UV) light. This type of fiber is used to produce fiber gratings by UV light exposure.
High Numerical Aperture (NA) Fibers: Fibers with NA higher than 0.3. These fibers are used for power delivery and for short distance communication applications.
Special SMFs: This category includes standard SMF with reduced cladding for improved bending performance, and specially designed SMF for short wavelength applications.
Specially Coated Fibers: Fibers with special coating such as hermitic coating for preventing hydrogen and water penetration, metal coating for high temperature applications.
Mid-Infrared Fibers: Non-silica glass-based fibers for applications between 2 and 10 micron
Photonic Crystal Fibers (PCFs): Fibers with periodic structure to achieve fiber properties that are not available with conventional fiber structures.

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Detail Of Single Mode And Multi Mode Fiber Optic Cable

Fiber optic cable has become apparent that fiber-optics are steadily replacing copper wire as an appropriate means of communication signal transmission. They span the long distances between local phone systems as well as providing the backbone for many network systems. Other system users include cable television services, university campuses, office buildings, industrial plants, and electric utility companies.

There are three types of fiber optic cable commonly used:  single mode, multimode and plastic optical fiber (POF).  Although fibers can be made out of transparent plastic, glass, or a combination of the two, the fibers used in long-distance telecommunications applications are always glass, because of the lower optical attenuation.  Both multi-mode and single-mode fibers are used in communications, if you need to transmit less data over longer distances, use single mode fiber optic cables. For a greater data capacity over shorter distances, go with multi mode fiber optic cables, with multi-mode fiber used mostly for short distances (up to 500 m),Multi mode is often used for LANs and other small networks. And single-mode fiber used for longer distance links.

Single Mode Fiber: Single Path through the fiber

Single Mode cable is a single stand (most applications use 2 fibers) of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission.  Single Mode Fiber with a relatively narrow diameter, through which only one mode will propagate typically 1310 or 1550nm. Carries higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width.  Single Mode is also referred to as single-mode fiber, single-mode optical waveguide, mono-mode optical fiber and uni-mode fiber. Single-mode fiber gives you a higher rate of transmission, it also can carry the signal up to 50 times farther distance than multimode, at a slightly higher cost.Single-mode fiber has a much smaller core than multimode.

Single Mode fiber is used to connect long distance switches, central offices and SLCs (subscriber loop carriers, small switches in pedestals in subdivisions or office parks or in the basement of a larger building). Practically every telco’s network is now fiber optics except the connection to the home.

Multi Mode Fiber: Multiple Paths through the fiber

Multi-Mode cable has a little bit bigger diameter, with a common diameters in the 50-to-100 micron range for the light carry component (in the US the most common size is 62.5um).Typical multimode fiber core diameters are 50, 62.5, and 100 micrometers.  Multi Mode fiber is used for shorter distances. Most applications in which Multi-mode fiber is used, 2 fibers are used. Multimode fiber gives you high bandwidth at high speeds (10 to 100MBS – Gigabit to 275m to 2km) over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable’s core typically 850 or 1300nm. Long cable runs (Above 3000 feet 914.4 meters in length), the multiple paths of light are believed to cause signal distortion at the receiving end, resulting in lost packets and incomplete data transmission. IPS recommends the use of single mode fiber in all applications using Gigabit and higher bandwidth.

The History of Fiber Optics

Fiber optics, though used extensively in the modern world, is a fairly simple, and relatively old, technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later. Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in 1870: “When the light passes from air into water, the refracted ray is bent towards the perpendicular… When the ray passes from water to air it is bent from the perpendicular… If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be totally reflected at the surface…. The angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, while for diamond it is 23°42′.” Undigested human hairs have also been shown to act as an optical fiber.

Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade. Development then focused on fiber bundles for image transmission. Harold Hopkins and Narinder Singh Kapany at Imperial College in London achieved low-loss light transmission through a 75 cm long bundle which combined several thousand fibers. Their article titled “A flexible fiberscope, using static scanning” was published in the journal Nature in 1954. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastro scope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material.

A variety of other image transmission applications soon followed.

In 1880 Alexander Graham Bell and Sumner Tainter invented the ‘Photo phone’ at the Volta Laboratory in Washington, D.C., to transmit voice signals over antical beam. It was an advanced form of telecommunications, but subject to atmospheric interferences and impractical until the secure transport of light that would be offered by fiber-optical systems. In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, also proposed the use of optical fibers for communications in 1963, as stated in his book published in 2004 in India. Nishizawa invented other technologies that contributed to the development of optical fiber communications, such as the graded-index optical fiber as a channel for transmitting light from semiconductor lasers. The first working fiber-optical data transmission system was demonstrated by German physicist Manfred Börner at Telefunken Research Labs in Ulm in 1965, which was followed by the first patent application for this technology in 1966. Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), making fibers a practical communication medium. They proposed that the attenuation in fibers available at the time was caused by impurities that could be removed, rather than by fundamental physical effects such as scattering. They correctly and systematically theorized the light-loss properties for optical fiber, and pointed out the right material to use for such fibers — silica glass with high purity. This discovery earned Kao the Nobel Prize in Physics in 2009.

NASA used fiber optics in the television cameras sent to the moon. At the time, the use in the cameras was classified confidential, and only those with the right security clearance or those accompanied by someone with the right security clearance were permitted to handle the cameras.

The crucial attenuation limit of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zima working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. Such low attenuation ushered in optical fiber telecommunication. In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 25 miles (40 km) long.
Attenuation in modern optical cables is far less than in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70–150 kilometers (43–93 mi). The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or eliminating optical-electrical-optical repeaters, was co-developed by teams led by David N. Payne of the University of Southampton and Emmanuel Desurvire at Bell Labs in 1986. Robust modern optical fiber uses glass for both core and sheath, and is therefore less prone to aging. It was invented by Gerhard Bern see of Schott Glass in Germany in 1973.

The emerging field of photonic crystals led to the development in 1991 of photonic-crystal fiber, which guides light by diffraction from a periodic structure, rather than by total internal reflection. The first photonic crystal fibers became commercially available in 2000. Photonic crystal fibers can carry higher power than conventional fibers and their wavelength-dependent properties can be manipulated to improve performance.

Source: fiber optic cable manufacturer

The difference between copper and fiber optics?

Although the fiber optic cables may look like traditional copper cables, we should always bear in mind that inside fiber cables are fragile glass fibers which can be broken easily if not properly treated.

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Disadvantages of Fiber Optics?

The science of fiber optics has its advantages and disadvantages. Though there are more advantages than disadvantages, they still are there. One of the largest disadvantages is the overall price of manufacturing and installation of the fiber optic system. Not only is a large amount of glass wire needed for one of these systems, but expensive transmitters and receivers are needed to move the data it carries. Setting up the wires and splicing them also comes at a large expense and also with a great degree of difficulty.

Related fiber optics products:
Fiber optical cables, fiber optic patch cord, fiber optic pigtail

What are Fiber Optic Attenuators

Fiber optic attenuators are used in applications where the optical signal is too strong and needs to be reduced. For example, in a multi-wavelength fiber optic system, you need to equalize the optical channel strength so that all the channels have similar power levels. This means to reduce stronger channels’ powers to match lower power channels.

The attenuation level is fixed at 5 dB, which means it reduces the optical power by 5dB. This attenuator has a short piece of fiber with metal ion doping that provides the specified attenuation.

There are many different mechanisms to reduce the optical power, this picture shows another mechanism used in one type of variable attenuator. Here variable means the attenuation level can be adjusted, for example, it could be from 1 dB up to 20dB.

Fiber optic attenuators are usually used in two scenarios.

The first case is in fiber optic power level testing. Attenuators are used to temporarily add a calibrated amount of signal loss in order to test the power level margins in a fiber optic communication system.

In the second case, attenuators are permanently installed in a fiber optic communication link to properly match transmitter and receiver optical signal levels.

Optical attenuators are typically classified as fixed or variable attenuators.

Fixed attenuators have a fixed optical power reduction number, such as 1dB, 5dB, 10dB, etc.

Variable attenuators’ attenuation level can be adjusted, such as from 0.5 dB to 20dB, or even 50dB. Some variable attenuators have very fine resolution, such as 0.1dB, or even 0.01dB.

This slide shows many different optical attenuator designs.

The female to female fixed attenuators work like a regular adapter. But instead of minimizing insertion loss, it purposely adds some attenuation.

The female to female variable attenuators are adjustable by turning a nut in the middle. The nut adjusts the air gap in the middle to achieve different attenuation levels.

The male to female fixed attenuators work as fiber connectors, you can just plug in your existing fiber connector to its female side.

The in-line patch cable type variable attenuators work as regular patch cables, but your can adjust its attenuation level by turning the screw.

For precise testing purposes, engineers have also designed instrument type variable attenuators. These instrument type attenuators have high attenuation ranges, such as from 0.5 dB to 70dB. They also have very fine resolution, such as 0.01dB. This is critical for accurate testing.

Source: fiber optic cable manufacturer

What is Single-mode optic fiber

Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics. Instead, it must be analyzed as an electromagnetic structure, by solution of Maxwell’s equations as reduced to the electromagnetic wave equation. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. As an optical waveguide, the fiber supports one or more confined transverse modes by which light can propagate along the fiber. Fiber supporting only one mode is called single-mode or mono-mode fiber. The behavior of larger-core multi-mode fiber can also be modeled using the wave equation, which shows that such fiber supports more than one mode of propagation (hence the name). The results of such modeling of multi-mode fiber approximately agree with the predictions of geometric optics, if the fiber core is large enough to support more than a few modes.

The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. Instead, especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave.

The most common type of single-mode fiber has a core diameter of 8–10 micrometers and is designed for use in the near infrared. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with core diameters as small as 50 micrometers and as large as hundreds of micrometers. The normalized frequency V for this fiber should be less than the first zero of the Bessel function J0 (approximately 2.405).

Related fiber optic products:

The History about fiber optics

Fiber optics, though used extensively in the modern world, is a fairly simple, and relatively old, technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later. Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in 1870: “When the light passes from air into water, the refracted ray is bent towards the perpendicular… When the ray passes from water to air it is bent from the perpendicular… If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be totally reflected at the surface…. The angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, while for diamond it is 23°42′.” Unpigmented human hairs have also been shown to act as an optical fiber.

Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade. Development then focused on fiber bundles for image transmission. Harold Hopkins and Narinder Singh Kapany at Imperial College in London achieved low-loss light transmission through a 75 cm long bundle which combined several thousand fibers. Their article titled “A flexible fibrescope, using static scanning” was published in the journal Nature in 1954. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material.

A variety of other image transmission applications soon followed.

In 1880 Alexander Graham Bell and Sumner Tainter invented the ‘Photophone’ at the Volta Laboratory in Washington, D.C., to transmit voice signals over an optical beam. It was an advanced form of telecommunications, but subject to atmospheric interferences and impractical until the secure transport of light that would be offered by fiber-optical systems. In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities.Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, also proposed the use of optical fibers for communications in 1963, as stated in his book published in 2004 in India. Nishizawa invented other technologies that contributed to the development of optical fiber communications, such as the graded-index optical fiber as a channel for transmitting light from semiconductor lasers. The first working fiber-optical data transmission system was demonstrated by German physicist Manfred Börner at Telefunken Research Labs in Ulm in 1965, which was followed by the first patent application for this technology in 1966.Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), making fibers a practical communication medium. They proposed that the attenuation in fibers available at the time was caused by impurities that could be removed, rather than by fundamental physical effects such as scattering. They correctly and systematically theorized the light-loss properties for optical fiber, and pointed out the right material to use for such fibers — silica glass with high purity. This discovery earned Kao the Nobel Prize in Physics in 2009.

NASA used fiber optics in the television cameras that were sent to the moon. At the time, the use in the cameras was classified confidential, and only those with the right security clearance or those accompanied by someone with the right security clearance were permitted to handle the cameras.

The crucial attenuation limit of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. Such low attenuation ushered in optical fiber telecommunication. In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 25 miles (40 km) long.

Attenuation in modern optical cables is far less than in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70–150 kilometers (43–93 mi). The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or eliminating optical-electrical-optical repeaters, was co-developed by teams led by David N. Payne of the University of Southampton and Emmanuel Desurvire at Bell Labs in 1986. Robust modern optical fiber uses glass for both core and sheath, and is therefore less prone to aging. It was invented by Gerhard Bernsee of Schott Glass in Germany in 1973.

The emerging field of photonic crystals led to the development in 1991 of photonic-crystal fiber, which guides light by diffraction from a periodic structure, rather than by total internal reflection. The first photonic crystal fibers became commercially available in 2000. Photonic crystal fibers can carry higher power than conventional fibers and their wavelength-dependent properties can be manipulated to improve performance.

Related fiber optic products: fiber optic patch cord, fiber optic patch panel, fiber optic connector

About Optical fiber

An optical fiber (or optical fibre) is a flexible, transparent fiber made of glass (silica) or plastic, slightly thicker than a human hair. It can function as a waveguide, or “light pipe”, to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

Optical fibers typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those that only support a single mode are called single-mode fibers (SMF). Multi-mode fibers generally have a wider core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,050 meters (3,440 ft).

Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together, either mechanically or by fusing them with heat. Special optical fiber connectors for removable connections are also available.