MXPA01008467A - Laser optimized multimode fiber and method for use with laser and led sources and system employing same - Google Patents

Abstract

A multimode optical fiber (10) having a first laser bandwidth greater than 220 MHz.km in the 850 nm window, a second laser bandwidth greater than 500 MHz.km in the 1300 nm window, a first OFL bandwidth of at least 160 MHz.km in the 850 nm window, and a second OFL bandwidth of at least 500 MHz.km in the 1300 nm window is disclosed.

Description

MULTIMODAL LASER FIBER AND METHOD FOR USING IT WITH LASER AND LED SOURCES, AND SYSTEM THAT USES THE SAME CROSS REFERENCE WITH RELATED REQUESTS This application claims priority of the patent application of E.U.A. with serial number 60/121, 169 filed on February 22, 1999, and the patent application of E.U.A. with serial number 60 / 174,722 filed January 6, 2000, relying on the content thereof and is hereby incorporated herein by reference in its entirety, as is hereby claimed the priority benefit under 35 U.S.C. § 120.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to a multimodal optical fiber and to a method for use with telecommunication systems employing low data transmission rates, as well as systems employing high data transmission speeds, and in particular, to an optical fiber. multimodal and an optimized method for applications designed for newer laser sources, as well as common light emitting diode sources.

Although the present invention is subject to a wide range of applications, it is particularly suitable for use in telecommunication systems designed to transmit data at equal and surplus speeds at one (1) gigabit / second.

ANTECEDENTS OF THE TECHNIQUE The objective of the telecommunications industry is generally to transmit large amounts of information over long distances, in short periods. Over time, it has been shown that this is a moving target that has no apparent end. While the number of users of the systems and the frequency of use of the systems increases, the demands of system resources increase as well. Until recently, data networks have typically operated on local area networks (LANs) that employ relatively low data rates. For this reason, light emitting diodes (LEDs) have been and continue to be the most common light source in these applications. However, while the data rates begin to increase beyond the modulation capacity of the LEDs, the system protocols are migrating from LED sources, and instead, to laser sources. This migration is proven by the recent change towards systems that can provide information at equal speeds exceeding one (1) gigabit / second.

While such transmission speeds will greatly improve the capabilities of the LANs, this creates an immediate concern to the owners of the systems. The multimodal optical fiber currently used in telecommunications systems is designed primarily for use with LED sources and is generally not optimized for use with lasers that will be used to operate systems designed to transmit information at speeds equal to and greater than one (1) gigabit / second. Laser sources require different demands in terms of quality and multimodal fiber design, compared to LED sources. Historically, the core index profile of multimodal fibers has shifted towards high bandwidth production with LED sources, which tends to overfill the core. The combination of the intensity distribution of light from the input pulse of the LED source and the index profile of the fiber produces an overfilled modal weight which results in an output pulse having a relatively uniform rise and fall. Although there are peaks or plateaus that result from small deviations from the near-parabolic ideal index, their magnitude does not affect the performance of the system at low data rates. However, in laser-based systems, the intensity distribution of the source concentrates its energy near the center of the multimodal fiber. As a consequence, small deviations in the profile of the fiber can produce important alterations in the rise and fall of the impulse, which can have an important effect on the performance of the system. This effect may manifest itself in the form of an excessively low broadband such as an excessively high time fluctuation, or both. Although it is possible to correct these deficiencies to some degree by changing the launching condition of the source, such as the out-of-center launch mode conditioning connection conductor or the laser beam expander, it is typically not a practical solution for the operators. owners of the system. A typical field design for a LAN system is designed to cover certain specific link lengths. The standard for the base structure of the field (which travels between buildings) typically has a link length of up to about 2 km. The base structure of the buildings or elevator (which travels between floors of a building) typically has a link length of up to about 500 meters. The horizontal link length (which travels between offices on a floor of a building) typically has a link length of up to about 100 meters. Previous and current LAN technology, such as 10 megabit Ethernet, can achieve a transmission with a link length of 2 km with a standard grade multimodal fiber optic. However, the next generation systems that are capable of supporting gigabits / seconds and higher transmission speeds can not achieve all of these link lengths with the standard multimodal fiber currently available. In the 850 nm window, a standard multimodal fiber is limited to a link length of approximately 220 meters. In the 1300 nm window, the standard grade fiber is limited to a link length of only about 550 meters. In this way, the current technology only allows, so much, the coverage of about 2 or 3 lengths of field link. To fully enable a LAN network for gigabit / second transmission speeds, a multimodal fiber is needed that can transmit information on each of the three link lengths. As used herein, an overfilled bandwidth (OFL) is defined as the bandwidth used by the standard measurement technique described in EIA / TIA 455-51 FOTP-51A, "Pulse Distortion Measurement of Multimode Glass Optical Fiber Information Transmission Capacity ", with launch conditions defined by EIA / TIA 455-54A, FOTP54" Mode Scrambler Requirements for Overfilled Launching Conditions to Multimode Fibers ". As used herein, laser bandwidth is defined and measured using the standard measurement technique described in EIA / TIA 455-51 A, FOTP-51 and in any of the following two launch conditions methods. Method (a) is used to determine the 3 dB bandwidth at 1300, and method (b) is used to determine the 3 dB bandwidth at 850 nm. The method (a) used to determine the laser bandwidth of 3 dB at 1300 nm, uses a laser of 1300 nm with a spectral width RMS of 4 nm with a release with a coupled category 5 energy ratio modified by the connection of a conductor of connection of a fiber of simple way, classification in increments, standard of 2 meters, with double wrapping around a mandrel with a diameter of 50 mm. The launching condition is further modified by mechanical compensation of the central axis of the fiber in a simple way from that of the mutimodal fiber, in such a way that a lateral compensation of 4 um is created between the central axis of the core of the connecting conductor of the fiber. fiber in a simple way and the multimodal fiber under test. Note: The category 5 coupled energy relationship is described and measured using the procedures in TIA / EIA 526-14A OFSTP 14 appendix A "Optical Power Loss Measurements of Installed Multimode Fiber Cable Plant". The method (b), which is used to determine the laser bandwidth of 3 dB at 850 nm, uses an OFL release condition of 850 nm with a RMS spectral width of 0.85 nm, as described in EIA / TIA 455-54A FOTP 54, connected to a specially designed multimodal fiber of 1 meter in length having a numerical aperture of 0.208 and a graduated index and alpha profile of 2. Such a fiber can be created by designing a standard multimodal core fiber of 50 μm diameter that has a delta refractive index (delta = n02-nc2 / 2nonc, where n0 = core refractive index and nc = coating refractive index) from 1.3 to a core of 23.5 μm in diameter. Currently, to increase the distance, manufacturers typically change the bandwidth between two windows of wavelength by changing the shape of the refractive index profile. Depending on the elaborate changes, the result is a high OFL bandwidth in the 850 nm window with a low OFL bandwidth in the 1300 nm window, or an OFL bandwidth in 850 nm with a high OFL bandwidth in the 1300 nm window. For example, for a standard FDDI-2% Delta 62.5 um type fiber, the refractive index profile can be adjusted to result in an OFL bandwidth of 1000 MHz.km in 850 nm and 300 MHz.Km to 1300 nm, or can be adjusted to give a result in the OFL bandwidth of 250 MHz.km at 850 nm and 4000 MHz.km at 1300 nm. With such multimodal optical waveguide fibers having standard "alpha" profiles, however, it is not possible to achieve an OFL bandwidth of 1000 MHz.km at 850 nm and 4000 MHz.km at 1300 nm. Typically, the processing tolerances will allow OFL bandwidths of 850 nm / 1300 nm of 6000 MHz.km/300 MHz.km or 200 MHz.km/1000 MHz.km, but not 600MHZ.km/1000MHz.km. However, there is a disconnect between these historical changes in bandwidth, and what is required for gigabit / sec transmission speeds. Because high-speed lasers are the standard light source for LAN networks designed to provide information at speeds exceeding 1 gigabit / sec, a multimodal optical fiber is desired that has an increased bandwidth in both the 850 window nm and 1300 nm. Additionally, because LAN networks are barely growing, all the system components needed to cover and / or exceed one gigabit / sec transmission speeds have not yet been completely reduced or practiced, optimized and / or tested. For these reasons, it is not practical to replace existing LAN systems with new LAN systems designed speculatively to cover or exceed such high data rates. Although it may be possible to achieve this result, it probably will not be a preferred or optimal solution, if we continue with such a trajectory of action it will probably result in costly upgrades to the systems and potential rework throughout the system.BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to a multimodal optical fiber that is optimized for high speed laser sources capable of a data transmission of 1.0, 2.5 and 10 gigabits per second while exceeding the link length requirements discussed in previous paragraphs. Additionally, the same multimode optical fiber maintains a sufficiently high OFL bandwidth to support the transmission of information with the 1300 nm and 850 nm LED sources currently used in the LAN systems. Such multimodal fiber optic will allow the present owners of LAN systems to maintain their main LAN systems based on LEDs, while, at the same time it allows them to easily switch to a "gigabit Ethernet system" without having to go through an update of expensive multimodal fiber. As used in the present "gigabit Ethernet system" is defined as a telecommunications system, such as a LAN system, which is capable of transmitting data at equal speeds and / or exceeding one gigabit / sec. Thus, one aspect of the present invention relates to a multimodal fiber having a first laser bandwidth greater than 200 MHz.km in the 850 nm window, a second laser bandwidth greater than 500 MHz.km in the 1300 nm window, a first OFL bandwidth of at least 160 MHz.km in the 850 nm window, and a second OFL bandwidth of at least 500 MHz.km in the 1300 nm window. Such multimodal optical fiber has a variety of uses in the telecommunications industry and is particularly suitable for use in telecommunications systems employing high-speed laser sources. Such a fiber has the additional benefit of providing sufficient OFL bandwidth for the LED sources currently used in major LAN systems. In another aspect, the invention is directed to a multimodal transmission system capable of transmitting data at equal speeds and exceeding one (1) gigabit / second. The multimodal transmission system includes a laser source that transmits at least one (1) gigabit / second of information, and a multimodal optical fiber that communicates with the laser source. The multimodal optical fiber has a first laser bandwidth of at least 385 MHz.km in the 850 nm window that is capable of transporting the information at least 500 m. The multimodal optical fiber also has a second laser bandwidth of at least 746 MHz.km in the 1300 nm window to carry the information at least 1000 m, in addition, the multimodal fiber optic includes the first OFL bandwidths and second high enough to be used with 850 nm and 1300 nm LED sources. Another aspect of the present invention relates to a multimodal optical fiber having a core of 62.5 μm, and a coating that limits the core. The cover has a refractive index lower than the refractive index of the core, and the multimodal optical fiber exhibits a DMD profile, which when measured at a wavelength of 1300 nm includes a first region having a measured average inclination of (r / a) 2 = 0.0 to 0.25 and a second inclination region that has a measured average inclination of (r / a) 2 = 0.25 to 0.50. The inclination of the first region is preferably greater than the inclination of the second region. Most preferably, the inclination of the first region is greater than 1.5 times the inclination of the second region. In a further aspect, the present invention is directed to a method for forming a multimodal optical fiber. The method includes the steps of reacting thermochemically a precursor reagent containing silica and at least one doping reagent to form soot, and supplying the soot to a target in a manner sufficient to produce a glass preform having specified characteristics. The glass preform is extracted in a multimodal optical fiber having 62.5 μm of core region and a coating region which limits the core region. The reaction step includes the selection of a precursor reagent and a doping reagent in accordance with a sufficient soot deposition formula to obtain as a result a multimodal optical fiber exhibiting a DMD profile., which when measured at a wavelength of 1300 nm, has a first average inclination measured over a first region of (r / a) 2 = 0.0 to 0.25, and a second average inclination measured over a second region of (r / a) 2 0.25 to 0.50, the first average inclination being greater than the second average inclination. The multimodal optical fiber of the present invention results in several advantages over multimodal optical fibers known in the art. One of these advantages is that the multimodal optical fiber of the present invention is fully compatible for use with high-speed laser sources, as well as LED sources. In this way, the multimodal optical fiber of the present invention can be used with conventional local area networks employing LED sources, and can be used with Gigabit Ethernet Systems, which employ high-speed laser sources. In addition, the multimodal optical fiber of the present invention eliminates the need for costly frequently used connection conductors for conditioning to allow operation in the 1300 nm operation window for the Gigabit Ethernet System protocol. For many multimodal optical fibers, a conditioning connection conductor is used to move the energy away from the center of the multimodal fiber to avoid defects in the centerline profile that are typically obtained from some processing procedures. Because the preferred multimodal optical fiber of the present invention is made using the external vapor deposition (OVD) method, the preferred multimodal optical fiber of the present invention has reduced defects in the centerline profile. In this way, a mode conditioning connection conductor is no longer needed to enable operation in the 1300 nm operation window and the preferred fiber of the present invention, thus allowing a centered or slightly launch diverted due to indeterminate tolerances in the connector, obtaining ease of installation and use. Additionally, the multimodal optical fiber of the present invention optimizes laser performance with a variety of laser sources, including, but not limited to, 780 nm Fabry-Perol lasers, 850 nm Vertical Cavity Surface Emitting (VCSELs) lasers, lasers of 1300 nm, of Fabry-Perot, and transmitters of low cost of 1300 nm contemplated for the future. The multimodal optical fibers of the present invention are also designed to support operations of 2.5 and 10 gigabits / second over important link lengths when used with a high performance laser in more advanced telecommunications systems. Additional features and utilities of the present invention will be set forth in the detailed description below, and in part will be readily apparent to those skilled in the art from said description, or will be recognized by practice of the invention as described herein. , including the detailed description below, the claims, as well as the accompanying drawings. It should be understood that both the general description made and the following detailed description are merely exemplary of the invention, and were created to provide a general description or structure for understanding the nature and character of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute a part of the present specification. The drawings illustrate various embodiments of the invention, and together with the description, function to explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a preferred embodiment of a multimodal optical fiber of the present invention. Figure 2 is a DMD profile curve of the multimodal optical fiber of Figure 1 measured at 1300 nm. Figure 3 is a DMD profile curve of the multimodal optical fiber of Figure 1 measured at 850 nm.

Figure 4 is a DMD profile curve of a second preferred embodiment of a multimodal optical fiber of the present invention measured at 1300 nm. Figure 5 is a graph showing the DMD profile curve of the multimodal optical fiber of Figure 1, and the DMD profile curve for a second preferred multimodal optical fiber measured at 1300 nm. Figure 6 shows the bandwidth of the optical fiber of Figure 1 for a variety of laser sources. Figure 7 is the curve of the refractive index profile of the first preferred embodiment of the multimodal optical fiber of the present invention, having the DMD profile of Figure 2. Figure 8 is the profile curve of the index of refraction of the second preferred embodiment of the multimodal optical fiber of the present invention, having the DMD profile of Figure 4.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES A refractive index profile for a multimodal optical fiber is described, which is optimized for applications that use newer laser sources, as well as the most common LED sources. The alpha index of the refraction profiles describes a profile shape that can vary continuously with the radius. In the present invention, the refractive index profile preferably includes at least two regions having at least "alpha" exponents commonly referred to by the symbol (a), so that the index profile uniformly changes from an alpha or alphas optimized for one or more laser sources (at one or more wavelengths) near the center of the profile to an alpha or alphas optimized for the LEDs (at one or more wavelengths) near the outside of the profile. A multimodal optical fiber having such an index profile extends both distance and data rate capacity beyond those documented for telecommunication systems capable of delivering information at equal speeds or exceeding one (1) gigabit / second. Because laser sources have "light traces" smaller than LEDs, it has been found that the outer portion of the profile can be optimized in accordance with the requirements of OFL bandwidth (typically 160-200 MHz. Km at 850 nm and 500+ MHz. Km at 1300 nm, for multimodal fibers having 62.5 um cores), while simultaneously optimizing the internal portion of the profile for the requirements of laser bandwidth and source characteristics. It is believed that this is the first profile that is simultaneously optimized for both the large light tracing LEDs and the small light tracer lasers in both 130 mm and 850 nm windows. Because the laser light trace at 1300 nm is even smaller than those of the laser sources with short wavelength (SX), the internal profile requirements are preferably determined by the SX bandwidth requirements. It has been found that the high laser bandwidth in short wavelength (for example, with CD lasers at 780 nm or VCSEL at 850 nm), as well as long wavelength (for example with Fabry-Perot lasers at 1300 nm or 1500 mn) can be achieved when the internal profile is adequately optimized. An important feature of the optimized index profile is that it provides a high OFL bandwidth at 1300 nm with LED sources so that the adjustment to the overall profile to achieve superior performance with lasers is small and / or in areas of the profile that are not affect the performance of the OFL bandwidth. This also requires that alpha (r) be a uniform function of r, without abrupt transitions. The present invention is directed to a multimodal optical fiber having an index profile specifically designed to provide high bandwidth and low temporal fluctuation with typical short wavelength lasers (e.g., 780, 850 or 980 nm) and lasers of long wavelength (eg, 1300 nm or 1500 nm) while maintaining a sufficiently high bandwidth and low jitter when legacy LED sources are used at 1300 nm and 850 nm. The index profile of the multimodal optical fiber of the present invention can be described in several ways. First, in a multimodal fiber with M modes, the output pulse can be described, Psai¡da (t) = ΔPm d (tm-tpr0m), where the mode més has a relative power Pm and a mode delay tm relative to tprom =? Pmtm /? Pm average. The OFL or laser bandwidth is determined from the amplitude of the Fourier transform of Psa? Da (t) and is optimized if all the tm are equal. The mode delays tm are determined by the index profile and the operating wavelength. The modal power Pm depends on the characteristics of the source (the specific laser, LED etc). The multimodal fibers of the present invention are preferably designed to meet the OFL or laser bandwidth requirements for most, and most preferably, all commonly used sources. For example, the fiber requirements may be that the OFL bandwidth is greater than 160MH.km and 500 MHz.km with LED sources at 850 nm and 1300 nm, respectively, and that the laser bandwidth is greater than 385MHz. .km and 746MHz.km with VCSEL laser source at 850 nm and Fabry-Perot at 1300mn, respectively. A second way of writing the fiber index profile refers to a direct measurement of the refresh rate of the kerman content of the core. Typical multimodal fibers are designed to have a spare index that varies as a function of radial position and is proportional to the content of gemania. This index profile, n (r) is described by the following function: For r < a, n (r) = n? (1-2? (r / a) 8) 0-5 where ni is the value of the index at the center of the nucleus, r is the radial position, a is the radius of I Core liner interface, g is the profile shape parameter, and? is defined as:? = (n12-n02) / 2n12 where the value of the index is not in the interface of the coating core. This profile description is common in the literature with the exponent "g" frequently denoted as alpha (a). Those skilled in the art use both terms interchangeably without confusion. For purposes of the present invention, the profile of the index is defined as follows: For 0 < r < a, n (r) = n? (1-2? (R / a) 9 (r)) 5 where g (r) is a profile shape parameter that changes continuously with the radius, so that the OFL and laser bandwidth objectives described previously in the first index profile description method are met. The relative power of the near-center modes is greater for the laser sources than for the LED source, and higher for the long-wavelength laser (eg Fabry-Perot laser at 1300nm) than for the laser sources of short wavelength (for example, VCSEL sources at 850nm, typically). In this way, heuristically g (r) can vary from being optimized at 1300nm in the center, to be optimized for 850nm for intermediate radios, and optimized at 1300nm for higher radii. In practice, it is suitable for g (r) to vary from a larger value (EQ mode delays closer to 780-850nm) near the center to a lower value (equalizing closer to 1300) on the outside. In practice g (r) never intentionally goes below the appropriate value for 1300nm. It is important for the OFL bandwidth that g (r) varies uniformly and consistently. Such an index profile with a g (r) variant may perhaps be visualized more easily with a third method for describing the index profiles. This method uses what is known to those skilled in the art as differential mode delay (DMD) measurements. The briefly described method involves scanning a pulse of an optical fiber simply radially through the multimodal fiber core. , and the measurement of the output pulse and mean delay time for the pulses launched in different starting positions with respect to the core of the multimodal fiber. The use delays are plotted as a function of the radial position, and the local inclination of DMD compared to (r / a) 2, where "r" is defined as the radial compensation of the fiber in a simple way in relation to the multimodal core center (ie, the distance between the axial center of the fiber in a simple way and the axial center of the multimodal core), and "a" is defined as the radius of the core of the multimodal fiber, approximates the parameter g (r) of index profile. The local inclination of DMD compared to the curve of (r / a) 2 is proportional to the local error g (r) in relation to g (or alpha) optimal for the determined wavelengths and Delta of the multimodal optical fiber. The relationships between the DMD, the index error, and the "alpha error" are known to those skilled in the art and are described in the following references.

Reference is made to Marcuse, Principles of Optical Fiber Measurements. pages 255-310, (Academic Press, 1981), which is incorporated herein by reference in its entirety, and to Olshansky, R., "Propagation in Glass Optical Waveguides," Rev. Mod. Phvs., Vol. 51, No. 2 , April 1979, pages 341-367, which is incorporated herein by reference in its entirety, for a more detailed explanation of the DMD measurements and techniques. In accordance with a preferred embodiment of the present invention, the OFL and laser bandwidth of several fibers with different refractive index profiles (and therefore DMD) is measured, and fibers that achieve a high bandwidth with both sources, laser and LED, are identified. The DMD of these optimal fibers characterizes the desired or objective profile for duplication in additional multimodal optical fibers. This empirical procedure using the DMD does not characterize the Pm of the different sources. Instead, it works to characterize the fiber that works with the sources. A key aspect of the present invention is that the laser intensity distributions are generally much smaller than those of LEDs. For this reason, among others, it is possible to optimize the fiber index profile for both laser operation and LED operation. In accordance with one embodiment of the present invention, the outer portion of the index profile is optimized for 1300 nm LEDs, thereby ensuring good performance, i.e., an OFL bandwidth greater than 500 MHz.km, for legacy systems. The inner portion of the index profile is optimized to provide a more equal laser bandwidth at 1300 nm and 850 nm. By increasing this design with manufacturing techniques that ensure a uniform index change, a multimodal optical fiber having a high laser bandwidth and a low laser fluctuation of both wavelengths can be elaborated repeatedly. Detailed reference will now be made to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. When possible, the same reference numbers will be used in the drawings to name the same or similar parts. An exemplary embodiment of the multimodal optical fiber of the present invention is shown in Figure 1, and is generally designed with the reference number 10. The preferred multimodal optical fiber 10 is a 62.5 μm multimodal optical fiber optimized to obtain a first optical fiber. laser bandwidth greater than 220MHz.km at 850 nm, and a second laser bandwidth greater than 500MHz.km at 1300 nm. However, those skilled in the art will understand that multimodal fibers in accordance with the present invention have probably been made having similar large bandwidths in 850 and 1300 nm operating windows, ie, between about 810 nm and 890 nm , very preferably between 830 nm and 870 nm, and between about 1260 nm and 1340 nm, very much preferably between about 1280 nm and 1320 nm. In addition, the preferred multimodal optical fiber 10 includes a first OFL bandwidth of at least 160 MHz.km in the 850 nm window, and a second OFL bandwidth of at least 500 MHz.km in the 1300 window nm. However, most preferably the multimodal optical fiber 10 has a core of 62.5 μm 12 and is designed for a minimum laser bandwidth of 385 MHz.km at 850 nm, and a minimum laser bandwidth of 746 MHz.km to 1300 nm. It should be noted that the laser bandwidth at 1300 nm mentioned and described in the present specification, should preferably be measured with a 1300 nm laser created for use with standard single mode fibers. Currently, many skilled in the art believe that telecommunication systems capable of supplying data at equal speeds or exceeding one (1) gigabit / second will require a mode conditioning connection conductor to compensate for the laser launch at 1300 nm. However, for the multimodal optical fiber of the present invention, the laser launch at 1300 nm is measured with most of the power thrown along the central axis of the multimodal fiber. This avoids the need for such modal conditioning connection conductors, thus reducing the instrumentation of the system, its cost, as well as its complexity. For a multimodal optical fiber having a core of 50 μm (not shown), the minimum laser bandwidth is preferably 500 MHz.km in the short wavelength window and 1684 MHz.km in the longitude window long wave. When employed in a multimodal transmission system employing high-speed laser sources, such as a telecommunications system designed to transmit data at a rate of at least one (1) gigabit / second, the multimodal optical fiber 10 having a 12 core of 62.5 μm can carry at least one (1) gigabit / second of information on a laser length of at least 500 meters at short wavelength, and over a link length of 1000 meters at the long wavelength. These distances are increased to link lengths of more than 600 meters and 2000 meters, respectively, for a multimodal optical fiber with a core of 50 μm. However, those skilled in the art will recognize that the preferred multimodal optical fiber 10 is not limited to a transmission speed of one (1) gigabit second. Instead, the present invention is capable of transmitting data at a rate of more than ten (10) gigabits / second over important link lengths. The DMD measurement curves indicative of multimodal optical fibers with a core of 62.5 μm that have sufficient properties to cover the operating parameters described in the previous paragraphs are illustrated in figures from 2 to 5. Figure 2 shows a measurement curve of DMD 20 of a multimodal optical fiber 10 made in accordance with the present invention. The DMD measurements of the multimodal optical fiber 10 were taken at 1300 nm using a standard pulse-based measurement technique similar to that described in Marcuse, Principles of Optical Fiber Measurements. pages 255-310, (Academic Press, 1981), and Olshansky, R., "Propagation in Glass Optical Waveguides," Rev. Mod. Phvs. Vol. 51, No. 2, April 1979, pages 341-367 , which have been incorporated herein by reference. In a region where the DMD measurement curve at 1300 nm is inclined towards the index profile it is optimized essentially for a wavelength less than 1300 nm, and in a region where the DMD curve slopes down the profile of index is essentially optimized for a wavelength greater than 1300 nm, and in the region where the DMD curve is almost flat the index profile is essentially optimized for 1300 nm. A DMD measurement curve 30 of a multimodal optical fiber 10, measured at 850 nm using a commercially available photon-Kinetics model 2500 fiber optic measurement mark, is illustrated in Figure 3. Again, in the region in where the DMD curve rises slightly, the index profile is optimized for a wavelength slightly less than 850 nm, and in the region where the DMD curve slopes downward, it indicates an optimized index profile for a length of wave greater than 850 nm A DMD profile 40 measured at 1300 nm of a second preferred multimodal optical fiber (not shown) is illustrated in Figure 4. Although the DMD 40 profile differs slightly from the DMD 20 profile, it also describes multimodal optical fibers having sufficient properties to cover the desired operating parameters with a multimodal optical fiber having a core of 62.5 μm or 50 μm. Both DMD profiles, 20 and 40, are shown in the same graph in Figure 5 measured at 1300 nm. Each of the strokes has been rotated so that they agree on a common point where the inclinations are similar (instead of (r / a) 2 = 0), and this point is arbitrarily defined as a delay of zero (0). In general, when measured at a wavelength of 1300 nm, a target DMD profile includes a first region that has a measured average inclination of (r / a) 2 = 0.0 to 0.25, and a second region that has an inclination Average measure of (r / a) 2 = 0.25 to 0.50, the inclination of the first region being greater than the inclination of the second region. Otherwise, a target DMD profile is not linear. Preferably, the inclination of the first region is at least 1.5 times greater than the inclination of the second region. It is especially preferred that the target DMD profile includes a third region that has a measured average inclination of (r / a) 2 = 0.4 to 0.6, where the change in the DMD from (r / a) 2 = 0.4 to 0.6 is when much +0.20 nseg / km. The preferred method for forming a multimodal optical fiber according to the present invention and having the target DMD profile described above includes the steps of reacting thermochemically a precursor reagent containing silica and at least one doping reagent to form soot, supplying the soot in a target in a manner sufficient to produce a glass preform having specified characteristics, and extracting the glass preform in a multimodal optical fiber having a core region of 62.5 μm or 50 μm. The step of further reacting includes selecting the precursor reagent and at least one reagent reagent in accordance with a sufficient soot deposition formula to result in a multimodal optical fiber exhibiting the characteristics of the target DMD profile. In a preferred embodiment, the soot deposition formula includes the required proportions of SiCU and GeCI4 which results in a multimodal optical fiber meeting the requirements of the desired target profile. When measured at a wavelength of 1300 nm, such a multimodal optical fiber will have a first average inclination measured over a ppmera region of (r / a) 2 = 0.0 to 0.25, and a second average inclination measured over a second region of ( r / a) 2 = 0.25 to 0.50, with the first average inclination being greater than the second average inclination. However, it will be understood that the present invention is not limited to SiCU and GeCI. Figure 7 shows the profile curve of the parabolic refractive index substantially of the first preferred embodiment of the multimodal optical fiber of the present invention (the same fiber that exhibits the DMD profile curve of Figure 2 and 3). Figure 8 shows the substantially parabolic refractive index profile curve of the second preferred embodiment of the multimodal optical fiber of the present invention (the same fiber exhibited by the DMD profile of Figure 4). Although these figures are not needed to perform the present invention, as described above, they clearly demonstrate the benefit of the DMD measurement techniques used in accordance with the present invention. With the exception of the slight differences in the alterations of the refractive index profile in the peak regions of the refractive index profiles illustrated in figure 7 and 8, the other regions of the refractive index profiles are very similar, both for the first as for the second preferred embodiment of the multimodal optical fibers of the present invention. Although not specifically described herein, a multimodal optical fiber having a core of 50.0 μm can be formed in the same way. Those skilled in the art will understand that the target DMD profile for said multimodal optical fiber will differ from the target DMD profile of a multimodal optical fiber having a core of 62.5 μm as described above. In this way, the soot deposition formula will also differ. It will also be understood that a target DMD profile can be described by defining the regions of inclination as a first region of (r / a) 2 = 0.0 to 0.2, and a second region of (r / a) 2 = 0.2 to 0.4.

EXAMPLE The invention will be understood more clearly by the following example which was created with the intention of exemplifying the invention.

EXAMPLE 1 One method to test the performance of the optimized multimodal laser fiber is to make a fiber that has the desired DMD characteristics and test it with a variety of laser sources. The results of said tests are shown in Figure 6. The "effective" bandwidth (MHz.Km) of the multimodal optical fiber characterized by the DMD profile illustrated in Figures 2-3 and 7 are shown in Figure 6. for a variety of Gigabit Ethernet systems lasers from 780 to 850 nm. The overfilled bandwidth (OFL) of the fiber, measured using the measurements and standard launching techniques already mentioned in this application, was 288 MHz.Km at 850 nm and 1054 MHz.KM at 1300nm. The bandwidth of the fiber laser, measured using the standard measurement and launching techniques named above in this application, was 930 MHz.Km at 850 nm (using the connecting conductor with a 23.5um diameter core, as well as a 850 nm laser source with a RMS spectral width less than 0.85 nm, as described above) and 2028 MHz.Km at 1300 nm (using a typical Fabry-Perot laser for fiber applications in a simple way and a connecting conductor ensuring a launch compensation of 4 um from the center of the nucleus). The "effective" bandwidths shown in Figure 6 for various Gigabit Ethernet system laser sources are measured with the same measurement technique as defined in the laser bandwidth at 850 nm with a connection conductor of 23.5 um, but with a launch condition that varies with each Gigabit Ethernet system laser because each laser has a different power distribution, both in the near field and in the far field. This demonstrates that the large bandwidths can be exhibited using the fibers of the present invention together with a wide variety of laser releases. The laser bandwidth measured with the defined launch (930 MHz.Km) is approximately the same as it was obtained with several Gigabit Ethernet system lasers. The laser bandwidths of the short wavelength Gigabit Ethernet system are all clearly superior to the 850 nm OFL bandwidth of 288 MHz.Km and in the required margin to significantly extend the Ethernet system link lengths Gigabit In addition, the laser bandwidth at 1300 nm measured using a Fabry-Perot laser at 1300 nm with a compensation of 4um was more than twice that of the OFL bandwidth at 1300 nm.

EXAMPLE 2 As a second example, the fiber whose measured DMD is shown in FIG. 4 and whose measured index profile is shown in FIG. 8 was tested for an OFL bandwidth, for a "defined" laser bandwidth using a laser conductor. 23.5um connection at 850 nm and 4um compensation at 1300 nm and for an "effective" bandwidth with a Gigabit Ethernet system laser set. The standard OFL bandwidth was measured at 564 MHz.Km at 850 nm and 560 MHz.Km at 1300 nm. The laser bandwidth "defined" at 850 nm using the connecting conductor with a core with a diameter of 23.5um was 826 MHz.Km, while at 1300 nm the laser bandwidth defined using a Fabry-Perot laser with a 4um compensation had a value of 5279 MHz.Km. The "effective" bandwidths measured with 13 Gigabit Ethernet system lasers at 850 nm or 780 nm were as follows: 1214, 886, 880, 876, 792, 786, 754, 726, 614, 394, 376, 434 and 472 MHz.Km. Again, the laser launch defined for 850 nm with a connecting conductor with a core diameter of 23.5 um produced a bandwidth that approximates the "effective" bandwidth seen with several current Gigabit Ethernet laser sources. It will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention, as long as they fall within the scope of the appended claims and their equivalents.

Claims (17)

NOVELTY OF THE INVENTION CLAIMS

1. - A multimodal optical fiber for use in a telecommunications system, said multimodal fiber comprises: a first laser bandwidth greater than 385 MHz.km in the 850 nm window; a second laser bandwidth greater than 746 MHz.km in the 1300 nm window; a first OFL bandwidth of at least 160 MHz.km in the 850 nm window, and a second OFL bandwidth of at least 500 MHz.km in the 1300 nm window in the 1300 nm window.

2. The multimodal optical fiber according to claim 1, further characterized in that said laser bandwidth comprises at least 385 MHz.km in the 850 nm window.

3. The multimodal optical fiber according to claim 1, further characterized in that said second laser bandwidth comprises at least 746 MHz.km in the 1300 nm window.

4. The multimodal optical fiber according to claim 1, further characterized in that said first laser bandwidth comprises at least 500 MHz.km in the 850 nm window, and wherein said second laser bandwidth comprises at least minus 1684 MHz.km in the 1300 nm window.

5. - The multimodal optical fiber according to claim 4, further characterized in that it comprises a core having a diameter of 62.5 μm.

6. The multimodal optical fiber according to claim 4, further characterized in that it comprises a core having a diameter of 50 μm.

7. The multimodal optical fiber according to claim 4, further characterized in that said first laser bandwidth is capable of transporting at least one (1) gigabit / second of information over a length of at least 500 m.

8. The multimodal optical fiber according to claim 4, further characterized in that said second laser bandwidth is capable of transporting at least one (1) gigabit / second of information over a length of at least 1000 m.

9. The multimodal optical fiber according to claim 5, further characterized in that said first laser bandwidth is capable of transporting at least one (1) gigabit / second of information over a length of at least 600 m.

10. The multimodal optical fiber according to claim 5, further characterized in that said second laser bandwidth is capable of transporting at least one (1) gigabit / second of information over a length of at least 2000 m.

11. - The multimodal optical fiber according to claim 3, further characterized in that the bandwidth of 1300 nm is measured with a launch in the center from a laser for use with a fiber in a simple way.

12. The multimodal optical fiber according to claim 4, further characterized in that it comprises a transmission system capable of transmitting data at equal speeds and exceeding one (1) gigabit second, said system comprises: a laser source that transmits through at least one (1) gigabit / second of information, and wherein said multimodal optical fiber communicates with said laser source to carry the information at least 500 m in the 850 nm window, and at least 1000 m in the 1300 nm window.

13. The multimodal transmission system according to claim 12, further characterized in that the first laser bandwidth comprises at least 600 MHz.km in the 850 nm window, and wherein the second laser bandwidth comprises at least 1684 MHz.km in the 1300 nm window, and where the first and second laser bandwidths are capable of transporting the information by at least 600 m and 2000 m, respectively.

14. The multimodal transmission system according to claim 12, further characterized in that said multimodal optical fiber includes a core having a diameter of approximately 62.5 μm.

15. - The multimodal transmission system according to claim 13, further characterized in that said multimodal optical fiber includes a core having a diameter of approximately 50.0 μm.

16. The multimodal transmission system according to claim 12, further characterized in that said laser source comprises a VCSEL of 850 nm.

17. The multimodal transmission system according to claim 12, further characterized in that said laser source comprises a Fabry-Perot laser of 1300 nm.