Fiber Optic Blog

Understanding the characteristics of different fiber optic cables types aides in understanding the applications for which they are used. Operating a fiber optic system properly relies on knowing what type of fiber is being used and why. There are two basic types of fiber cables: multimode fiber optic cable and single-mode fiber optic cable. Multimode fiber is best designed for short transmission distances, and is suited for use in LAN systems and video surveillance. Single-mode fiber is best designed for longer transmission distances, making it suitable for long-distance telephony and multichannel television broadcast systems.

Multimode Fiber

Multimode fiber cables, the first to be manufactured and commercialized, simply refers to the fact that numerous modes or light rays are carried simultaneously through the waveguide. Modes result from the fact that light will only propagate in the fiber core at discrete angles within the cone of acceptance. This fiber type has a much larger core diameter, compared to single-mode fiber, allowing for the larger number of modes, and multimode fiber is easier to couple than single-mode optical fiber. Multimode fiber may be categorized as step-index or graded-index fiber. Multimode Step-index Fiber Figure 2 shows how the principle of total internal reflection applies to multimode step-index fiber. Because the core’s index of refraction is higher than the cladding’s index of refraction, the light that enters at less than the critical angle is guided along the fiber.

Three different lightwaves travel down the fiber. One mode travels straight down the center of the core. A second mode travels at a steep angle and bounces back and forth by total internal reflection. The third mode exceeds the critical angle and refracts into the cladding. Intuitively, it can be seen that the second mode travels a longer distance than the first mode, causing the two modes to arrive at separate times. This disparity between arrival times of the different light rays is known as dispersion, and the result is a muddied signal at the receiving end. For a more detailed discussion of dispersion, see “Dispersion in Fiber Optic Systems” however, it is important to note that high dispersion is an unavoidable characteristic of multimode step-index fiber. Multimode Graded-index Fiber Graded-index refers to the fact that the refractive index of the core gradually decreases farther from the center of the core. The increased refraction in the center of the core slows the speed of some light rays, allowing all the light rays to reach the receiving end at approximately the same time, reducing dispersion.Figure 3 shows the principle of multimode graded-index fiber. The core’s central refractive index, nA, is greater than that of the outer core’s refractive index, nB. As discussed earlier, the core’s refractive index is parabolic, being higher at the center. As Figure 3 shows, the light rays no longer follow straight lines; they follow a serpentine path being gradually bent back toward the center by the continuously declining refractive index. This reduces the arrival time disparity because all modes arrive at about the same time. The modes traveling in a straight line are in a higher refractive index, so they travel slower than the serpentine modes. These travel farther but move faster in the lower refractive index of the outer core region.

Single-mode Fiber

Single-mode fiber allows for a higher capacity to transmit information because it can retain the fidelity of each light pulse over longer distances, and it exhibits no dispersion caused by multiple modes. Single-mode fiber also enjoys lower fiber attenuation than multimode fiber. Thus, more information can be transmitted per unit of time. Like multimode fiber, early single-mode fiber was generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that of the cladding rather than graduated as it is in graded-index fiber. Modern single-mode fibers have evolved into more complex designs such as matched clad, depressed clad and other exotic structures.

Single-mode fiber has disadvantages. The smaller core diameter makes coupling light into the core more difficult. The tolerances for single-mode connectors and splices are also much more demanding. Single-mode fiber has gone through a continuing evolution for several decades now. As a result, there are three basic classes of single-mode fiber used in modern telecommunications systems. The oldest and most widely deployed type is non dispersion-shifted fiber(NDSF). These fibers were initially intended for use near 1310 nm. Later, 1550 nm systems made NDSF fiber undesirable due to its very high dispersion at the 1550 nm wavelength. To address this shortcoming, fiber manufacturers developed, dispersion-shifted fiber(DSF), that moved the zero-dispersion point to the 1550 nm region. Years later, scientists would discover that while DSF worked extremely well with a single 1550 nm wavelength, it exhibits serious nonlinearities when multiple, closely-spaced wavelengths in the 1550 nm were transmitted in DWDM systems. Recently, to address the problem of nonlinearities, a new class of fibers were introduced. These are classified as non zero-dispersion-shifted fibers (NZ-DSF). The fiber is available in both positive and negative dispersion varieties and is rapidly becoming the fiber of choice in new fiber deployment. For more information on this loss mechanism, see the article “Fiber Dispersion.”

One additional important variety of single-mode fiber is polarization-maintaining (PM) fiber. All other single-mode fibers discussed so far have been capable of carrying randomly polarized light. PM fiber is designed to propagate only one polarization of the input light. This is important for components such as external modulators that require a polarized light input. Figure 7 shows the cross-section of a type of PM fiber. This fiber contains a feature not seen in other fiber types. Besides the core, there are two additional circles called stress rods. As their name implies, these stress rods create stress in the core of the fiber such that the transmission of only one polarization plane of light is favored. Single-mode fibers experience nonlinearities that can greatly affect system performance.

Fibers are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line-of-sight path. In some buildings, optical fibers route sunlight from the roof to other parts of the building (see nonimaging optics). Optical fiber illumination is also used for decorative applications, including signs, art, toys and artificial Christmas trees. Swarovski boutiques use optical fibers to illuminate their crystal showcases from many different angles while only employing one light source. Optical fiber is an intrinsic part of the light-transmitting concrete building product, LiTraCon.

Optical fiber is also used in imaging optics. A coherent bundle of fibers is used, sometimes along with lenses, for a long, thin imaging device called an endoscope, which is used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures. Industrial endoscopes (see fiberscope or borescope) are used for inspecting anything hard to reach, such as jet engine interiors. Many microscopes use fiber-optic light sources to provide intense illumination of samples being studied.

In spectroscopy, optical fiber bundles transmit light from a spectrometer to a substance that cannot be placed inside the spectrometer itself, in order to analyze its composition. A spectrometer analyzes substances by bouncing light off of and through them. By using fibers, a spectrometer can be used to study objects remotely.

An optical fiber doped with certain rare earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. Rare-earth doped optical fibers can be used to provide signal amplification by splicing a short section of doped fiber into a regular (undoped) optical fiber line. The doped fiber is optically pumped with a second laser wavelength that is coupled into the line in addition to the signal wave. Both wavelengths of light are transmitted through the doped fiber, which transfers energy from the second pump wavelength to the signal wave. The process that causes the amplification is stimulated emission.

Optical fibers doped with a wavelength shifter collect scintillation light in physics experiments.

Optical fiber can be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment. Examples of this are electronics in high-powered antenna elements and measurement devices used in high voltage transmission equipment.

The iron sights for handguns, rifles, and shotguns may use short pieces of optical fiber for contrast enhancement.

Ethernet Is a Protocol

While eight-conductor Ethernet cables with RJ-45 plugs are extremely common (these are the cables that look like over-sized phone cords), Ethernet itself is a protocol standard that defines the way that bits of information travel over a particular medium. The two most common cabled versions of Ethernet are traditional copper cables and fiber-optic cables.

Patch Cables

Most standard copper Ethernet cables are referred to as patch cables. However, ordinary phone cords can be considered patch cables, as well as the RCA and HDMI cables that connect a home TV and stereo system together.

Types

Different Ethernet cables have different names, with “patch cables” being the most common. Some of the differences include the length of the cable as well as the purpose. For example, an Ethernet connection that is designed for speed and/or great distance can be referred to as a “backbone” or “long haul,” even though it may use the exact same type of copper cable that a patch cable uses.

Fiber optic cables have been instrumental in advancing technological communication. Fiber optics today stretch across oceans and bring Internet connection to remote locations. They provide more reliable service for land-line phones than traditional wires. Although their manufacture can be complex, you can install fiber optic connections very easily. The process involves gluing bare fiber optic cable to a connector and then heating the connector to seal it.

1. Strip the plastic jacket at the end of the fiber optic cable. Optic cable ends have jackets to prevent any damage in shipping from the manufacturer. Clamp the plastic jacket, using a fiber optic stripper tool, which has a designated slot to fit the size of a fiber optic jacket. Squeeze the handles of the stripper like pliers. Pull the jacket away from the fiber optic cable.

2. Open the back chamber of the epoxy glue gun by twisting off the back cap. Insert the epoxy glue tube into the chamber and squeeze lightly. You will only need a few ounces of glue for the task. Screw the cap back on the epoxy glue gun chamber.

3. Inject epoxy glue into the fiber optic connector socket. Each fiber optic connector has two sockets on each side of it to form the connection. Insert the glue gun into the connector socket. Press and hold the trigger to insert the glue. The glue should spot should not be larger than an eye pupil.

4. Insert one fiber optic cable end into the connector sockets. Hold the cable in the socket and count to 10. Let go of the fiber optic cable and connector. Check that the cable stays in position once you let go of it.

5. Place the new fiber optic connection into an an epoxy curing oven. Turn on the oven and turn the timer knob to six minutes. Insert the fiber optic connector attached to the cable into one of the curing oven slots. Press the start button on the oven. Pull out the connector from the oven slot. Wiggle the connector end to test the stability of the connection. If it seems fragile, reinsert the connector into the oven and cook it for a few more minutes. Repeat steps three to five to seal the fiber optic connector on both sides.

1000M Gigabit Ethernet Media Converter Description:

1000M adaptive fast Ethernet optical Media Converter is a new product used for optical transmission via high-speed Ethernet. It is capable of switching between twisted pair and optical and relaying across 1000 Base-Tx and 1000Base-FX network segments, meeting long-distance, high-speed and high-broadband fast Ethernet work group users’ needs, achieving high-speed remote interconnection for up to 100 km’s relay-free computer data network. With steady and reliable performance, design in accordance with Ethernet standard and lightning protection, it is particularly applicable to a wide range of fields requiring a variety of broadband data network and high-reliability data transmission or dedicated IP data transfer network, such as telecommunication, cable television, railway, military, finance and securities, customs, civil aviation, shipping, power, water conservancy and oilfield etc, and is an ideal type of facility to build broadband campus network, cable TV and intelligent broadband FTTB/FTTH networks.

1000M Gigabit Ethernet Media Converter Features:

In accordance with Ethernet standards IEEE802.3, 1000Base-TX and 1000Base-FX

Supported Ports: SC for optical fiber; RJ45 for twisted pair

Auto-adaptation rate and full/half-duplex mode supported at twisted pair port

Auto MDI/MDIX supported without need of cable selection

Up to 6 LEDs for status indication of optical power port and UTP port

External and built-in DC power supplies provided

Up to 1024 MAC addresses supported

512 kb data storage integrated, and 802.1X original MAC address authentication supported

Conflicting frames detection in half-duplex and flow control in full duplex supported

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.