Manual The Fundamentals of Signal Transmission: Optical Fibre, Waveguides and Free Space

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Bandwidth measures the data-carrying capacity of an optical fiber. It is expressed as the product of the data frequency and the distance over which data can be transmitted at that frequency. For example a fiber with a bandwidth of MHz km can transmit data at a rate of Mhz for 1 km or at a rate of 20 MHz for 20 km. Step-index fibers have a typical bandwidth of 20 MHz km. In a multimode graded-index fiber the core has an index of refraction that decreases as the radial distance from the center of the core increases. As a result, the light travels faster near the edge of the core than near the center.

Different modes therefore travel in curved paths with nearly equal travel times. This greatly reduces the spreading of optical pulses. Graded-index fibers therefore have bandwidths which are significantly greater than step-index fibers. Typical core diameters of graded-index fibers are 50, Graded-index fibers are often used in medium-range communications applications, such as local area networks.

A fan of rays injected into a graded-index fiber is brought back into focus, before it diverges again. A ray will travel along an approximately sinusoidal path. The wavelength of this sinusoidal path is called the pitch of the fiber. If a graded-index fiber is cut to have a length of one quarter of the pitch of the fiber, it can serve as an extremely compact lens, called a GRIN lens.

Light exiting a fiber can be collimated into a parallel beam when the output end of the fiber is connected to the GRIN lens. Because its properties are set by its length, this graded-index lens is referred to as a quarter-pitch or 0. Focusing of the fiber output onto a small detector or focusing of the output of a source onto the core of a fiber can be accomplishing by increasing the length of the GRIN lens to 0.

Such an arrangement is useful for coupling sources to fibers and fibers to detectors. Here z is the direction of propagation, and q is an integer. Many fiber parameters can be expressed in terms of V. The first subscript, m, gives the number of azimuthal, or angular nodes in the electric field distribution. The second subscript, n, gives the number of radial nodes. Output patterns are symmetric about the center of the beam and show bright regions separated by dark regions the nodes that determine the order numbers m and n. The zero field at the outer edge of the field distribution is counted as a node.

When the V number is less than 2. When the V number is greater than 2. A large number of modes are supported by these fibers.

Optical Communication: Its History and Recent Progress

The amount of light carried by each mode is determined by the launch conditions. The attenuation of some large-angle modes is much higher than that of other modes, but after the light has propagated a considerable distance, a stable mode distribution develops. To generate a stable mode distribution even with only a short length of fiber, mode filtering is accomplished through mode scrambling. A series of bends is introduced into the fiber. These bends couple out the light in the large-angle modes with the high attenuation and distribute the remaining light among the other guided modes.

Mode scrambling permits repeatable, accurate measurements of fiber attenuation to be made in the laboratory, even with short lengths of fiber. A single mode fiber only allows light to propagate down its center and there are no longer different velocities for different modes. A single mode fiber is much thinner than a multimode fiber and can no longer be analyzed using geometrical optics.

Because the single-mode fiber propagates only the fundamental zero-order mode, modal dispersion, the primary cause of pulse overlap, is eliminated.

ISBN 13: 9780340705766

Thus, the bandwidth of a single-mode fiber is much higher than that of a multimode fiber. Pulses can be transmitted much closer together in time without overlap. Because of this higher bandwidth, single-mode fibers are used in all modern long-range communication systems. Single-mode fibers have a typical bandwidth of GHz km.

When laser light is coupled into a fiber, the distribution of the light emerging from the other end reveals if the fiber is a multimode or single mode fiber. Light emerging from a multi-mode fiber Light emerging from a single-mode fiber Optical fibers are used widely in the medical field for diagnoses and treatment. Optical fibers can be bundled into flexible strands, which can be inserted into blood vessels, lungs and other parts of the body. An endoscope is a medical tool carrying two bundles of optic fibers inside one long tube.

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One bundle directs light at the tissue being tested, while the other bundle carries light reflected from the tissue, producing a detailed image. Endoscopes can be designed to look at regions of the human body, such as the knees, or other joints in the body. Signals lose strength as they propagate through the fiber. This is known as beam attenuation. Attenuation is measured in decibels dB.

P in and P out refer to the optical power going in and coming out of the fiber. Losses may be substantially higher for lower quality reflective surfaces, rendering it even more likely that the input signal will not be accurately transmitted to the preselected output fiber.

Another drawback concerns the relative cost of the device disclosed in the ' patent. Reflective mechanisms, especially those having good quality reflective surfaces, are typically expensive and as such, tend to increase the initial cost of the switching mechanism. Furthermore, periodic maintenance or cleaning of the reflective surface is required to maintain optical performance of the reflective mechanism and ensure maximum light transmission from the input fiber to the preselected output fiber.

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Fiber-optic cable - Wikipedia

It is one object of the present invention to provide an opto-mechanical switching device which does not require extensive alignment between an input fiber and a plurality of output fibers. It is another object of the present invention to provide an opto-mechanical switching device which does not require expensive reflective mechanisms for transmitting an optical input to a predetermined output fiber. It is a more specific object of the present invention to provide an opto-mechanical switching device which employs a re-directing fiber to accurately and efficiently transmit an optical input to a predetermined output fiber.

It is yet another object of the present invention to provide a method for switching an optical signal between a plurality of output fibers using a re-directing fiber. In one preferred form, the present invention provides an opto-mechanical switching device for selectively switching an optical input between a plurality of output fibers. The opto-mechanical switching device includes a re-directing fiber adapted to receive the optical input.

The re-directing fiber is selectively positionable to transmit the optical input to a predetermined one of the plurality of output fibers.

The Fundamentals of Signal Transmission: Optical Fibre, Waveguides and Free Space

A method for switching an optical input between a plurality of output fibers is also provided. Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein:.

Optical fiber cables, how do they work? - ICT #3

With reference to FIG. Opto-mechanical switching device 10 is shown to include a separator member 12 , a plurality of output fibers 14 , an output fiber connector 16 , a re-directing fiber 18 , a re-directing fiber housing 20 and a drive mechanism With additional reference to FIG. In the particular embodiment illustrated, separator member 12 is an annular plate and the plurality of holes 30 are spaced apart around the circumference of a circle formed concentrically about the central axis 34 of opto-mechanical switching device The plurality of output fibers 14 are conventional fiber optic cables that are positioned in the holes 30 in the separator member 12 and fixedly coupled thereto by a conventional securing means such as an adhesive.

The distal end 40 of the plurality of output fibers 14 is coupled to output fiber connector 16 in a manner that is well known in the art. Output fiber connector 16 permits opto-mechanical switching device 10 to be quickly and accurately coupled to an optical circuit not shown without the need for aligning opto-mechanical switching device 10 to fiber optic cable elements of the optical circuit.

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Re-directing fiber 18 is shown in the particular embodiment illustrated to include a first portion 50 which is generally coincident with the central axis 34 , a second portion 52 which is generally parallel to the first portion 50 and radially outwardly offset therefrom, and a third or central portion 54 which extends between the first and second portions 50 and Re-directing fiber 18 is molded into or otherwise fixedly coupled to re-directing fiber housing Re-directing fiber housing 20 is therefore operable for maintaining the shape of the re-directing fiber 18 as well as protecting the re-directing fiber 18 from contact with foreign objects which would tend to abrade the sides of the re-directing fiber Drive mechanism 22 is coupled to re-directing fiber 18 and is selectively operable for moving the re-directing fiber such that the second portion 52 of the re-directing fiber 18 is aligned to the proximal end 60 of a predetermined one of the plurality of output fibers In the particular embodiment illustrated, drive mechanism 22 includes a conventional stepper motor 64 and a conventional controller Stepper motor 64 may be a permanent magnet or variable reluctance type stepper motor, with the angular resolution of each step preferably correlating to the angular spacing between the holes 30 in the separator member Stepper motor 64 includes a housing 70 that is fixedly coupled to separator member 12 in a predetermined radial relationship.

Stepper motor 64 also includes an output member 72 that is rotatable about the central axis Controller 68 is coupled to stepper motor 64 and causes stepper motor 64 to rotate output member 72 to a predetermined rotational position. Alternatively, drive mechanism 22 may include a conventional servo motor or other rotary actuator which permits a rotational output member to be accurately positioned in a plurality of predetermined radial positions. It will be appreciated that virtually any component that performs the function of precisely rotating the fiber housing 20 to precise angular positions could be used to form the drive mechanism In operation, an opto-mechanical switching device 10 is mounted in a desired location, an input fiber 74 is aligned to the first portion 50 of the re-directing fiber 18 and the output fiber connector 16 is coupled to a fiber optic circuit.

As those skilled in the art will understand, the gap between the input fiber 74 and the first portion 50 of the re-directing fiber 18 as well as the respective gaps between the second portion 52 of the re-directing fiber 18 and the proximal end 60 of the plurality of output fibers 14 are preferably controlled to be both uniform and as small as possible to prevent contact between the ends of the fibers while maximizing signal transmission between the respective fibers.

Those skilled in the art will also understand that signal transmission between the respective fibers can be maximized through proper preparation of the ends of the fibers e. Input fiber 74 provides an optical input signal that is received by the first portion 50 of re-directing fiber The optical input signal is transmitted through the re-directing fiber 18 where it exits the second portion 52 of the re-directing fiber 18 , and then enters the proximal end 60 of a first one of the plurality of output fibers 14 e.

When switching is required, controller 68 causes the stepper motor 64 to rotate re-directing fiber 18 to a precise, predetermined position such that the second portion 52 of the re-directing fiber 18 is aligned to the proximal end 60 of a preselected second one of the plurality of output fibers 14 e. Advantageously, this approach does not rely on reflective mechanisms. As such, total internal reflection results in a loss in efficiency of only about 1 percent or less, thus substantially increasing the reliability with which data may be accurately transmitted to an output fiber.

Furthermore, as the re-directing fiber housing 20 and the separator member 12 cooperate to align the second portion 52 of the re-directing fiber 18 to the proximal ends 60 of the plurality of output fibers 14 , the cost associated with the process of aligning fibers is substantially reduced, with the only necessary field alignment being between the first portion 50 of the re-directing fiber 18 and the input fiber While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims.

In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.

Effective date : Year of fee payment : 4. Year of fee payment : 8. An opto-mechanical switching device for selectively switching an optical input between a plurality of output fibers. The re-directing fiber is disposed within a re-directing fiber housing. The re-directing fiber housing is selectively positionable via a stepper motor to transmit the optical input to a predetermined one of the plurality of output fibers. TECHNICAL FIELD The present invention generally relates to optical switches and more particularly to an optical switch and a switching method therefor for the switching of an optical signal through the use of a selectively positionable re-directing fiber.

What is claimed is: 1. An opto-mechanical switch for selectively switching an optical input signal from an input fiber optic cable between a plurality of output fiber optic cables, the opto-mechanical switch including a discrete re-directing fiber optic cable that is spaced apart from both the input and output fiber optic cables, the re-directing fiber optic cable being adapted to receive the optical input signal, the re-directing fiber optic cable mounted within a housing, the re-directing fiber optic cable and the housing being selectively positionable to transmit the optical input signal to a predetermined one of the plurality of output fiber optic cables, wherein the re-directing fiber optic cable is distinct from the input fiber optic cable and the output fiber optic cables.

The opto-mechanical switch of claim 1 , further comprising a separator member for spacing the plurality of output fiber optic cables apart and positioning each of the plurality of output fiber optic cables in a predetermined position. The opto-mechanical switch of claim 2 , wherein the separator member spaces the plurality of output fiber optic cables apart around a circumference of a circle.


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The opto-mechanical switch of claim 3 , further comprising a drive mechanism for rotating the re-directing fiber optic cable about a central axis that extends through a center point of the circle. The opto-mechanical switch of claim 4 , wherein the drive mechanism includes a stepper motor. The opto-mechanical switch of claim 4 , wherein the drive mechanism has a housing that is fixedly coupled to the separator member and an output member that is coupled to the re-directing fiber optic cable.