Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2002-08-12
2004-04-20
Kim, Ellen E. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Reexamination Certificate
active
06724965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a multimode optical fiber and method for use with telecommunication systems employing low data rates, as well as systems employing high data rates, and more particularly, to a multimode optical fiber and method optimized for applications designed for state of the art laser sources, as well as common light emitting diode sources.
While the present invention is subject to a wide range of applications, it is particularly well suited for use in telecommunications systems designed to transmit data at rates equal to and exceeding one gigabit/sec.
2. Technical Background
The goal of the telecommunication industry is generally to transmit greater amounts of information, over longer distances, in shorter periods of time. Over time, it has been shown that this objective is a moving target with no apparent end in sight. As the number of systems users and frequency of system use increase, demand for system resources increases as well.
Until recently, data networks have typically been served by Local Area Networks (LANs) that employ relatively low date rates. For this reason, Light Emitting Diodes (LEDs) have and continue to be the most common light source in these applications. However, as data rates begin to increase beyond the modulation capability of LEDs, system protocols are migrating away from LEDs, and instead, to laser sources. This migration is evidenced by the recent shift toward systems capable of delivering information at rates equal to and exceeding one (1) gigabit/sec.
While such transmission rates will greatly enhance the capabilities of LANs, it does create an immediate concern for system owners. Multimode optical fiber currently employed in telecommunication systems is designed primarily for use with LED sources and is generally not optimized for use with the lasers envisioned to operate in systems designed to transmit information at rates equal to or greater than one (1) gigabit/sec. Laser sources place different demands on multimode fiber quality and design, compared to LED sources.
Historically, the index profile at the core of multimode fibers has been tuned to produce high bandwidth with LED sources, which tend to overfill the core. The combination of the light intensity distribution from the LED source input pulse and the index profile of the fiber produces an overfilled modal weighting that results in an output pulse that has a relatively smooth rise and fall. Although peaks or plateaus resulting from small deviations from the ideal near-parabolic index profile do occur, their magnitude does not impact system performance at low data rates. In laser based systems, however, the intensity distribution of the source concentrates its power near the center of the multimode fiber. Consequently, small deviations in the fiber profile can produce significant perturbations in the impulse rise and fall, which can have a large effect on system performance. This effect can manifest itself in the form of excessively low bandwidth, as excessively high temporal jitter, or both. Although it is possible to correct these deficiencies to some degree by changing the launch condition of the source, such as the offset launch mode conditioning patch cord or the laser beam expander, this is typically not a practical solution for system owners.
A typical campus layout for a LAN system is designed to meet certain specified link lengths. The standard for the campus backbone (which travels between buildings) typically has a link length of up to about 2 km. The building backbone or riser (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. Older and current LAN technology, such as 10 Megabit Ethernet, can achieve a 2 km link length transmission with standard grade multimode optical fiber. However, next generation systems capable of gigabit/sec. and higher transmission rates cannot achieve all of these link lengths with standard multimode fiber presently available. In the 850 nm window, standard multimode fiber is limited to a link length of approximately 220 meters. In the 1300 nm window, standard grade fiber is limited to a link length of only about 550 meters. Accordingly, present technology only enables, at most, coverage for about two of the three campus link lengths. To fully enable a LAN for gigabit/sec. transmission rates, a multimode fiber capable of transmitting information over each of the three link lengths is necessary.
As used herein, overfilled (OFL) bandwidth is defined as the bandwidth using 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 FOTP-54 “Mode Scrambler Requirements for Overfilled Launching Conditions to Multimode Fibers”.
As used herein, laser bandwidth is defined as and measured using the standard measurement technique described in EIA/TIA 455-51 and either 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. Method (a), which is used to determine the 3 dB laser bandwidth at 1300 nm, utilizes a 4 nm RMS spectral width 1300 nm laser with a category 5 coupled power ratio launch modified by connection of a 2 meter, standard step index, single-mode fiber, patch-cord wrapped twice around a 50 mm diameter mandrel. The launch condition is further modified by mechanically offsetting the central axis of the singlemode fiber from that of the multimode fiber in such a manner that a 4 um lateral offset between the central axis of the core of the single mode fiber patch-cord and the multimode fiber under test is created. Note: category 5 coupled power ratio is described in and measured using procedures in TIA/EIA 526-14A OFSTP 14 appendix A “Optical Power Loss Measurements of Installed Multimode Fiber Cable Plant. Method (b), which is used to determine the 3 dB laser bandwidth at 850 nm, utilizes a 0.85 nm RMS spectral width 850 nm OFL launch condition, as described in EIA/TIA 455-54A FOTP 54, connected to a 1 meter length of a specially designed multimode fiber having a 0.208 numerical aperture and a graded index profile with and alpha of 2. Such a fiber can be created by drawing down a standard 50 &mgr;m diameter core multimode fiber having a 1.3 index of refraction delta (delta=n
o
2
−n
c
2
/2n
o
n
c
=where n
o
=the index of refraction of the core and n
c
=the index of refraction of the cladding) to a 23.5 &mgr;m diameter core.
Today, in order to increase distance, manufacturers typically shift bandwidth between two wavelength windows by changing the shape of the refractive index profile. Depending upon the changes made, the result is either high OFL bandwidth at the 850 nm window with low OFL bandwidth at the 1300 nm window, or low OFL bandwidth at the 850 nm with high OFL bandwidth at the 1300 nm window. For example, for a standard 2% Delta 62.5 um FDDI-type fiber, the refractive index profile can be adjusted to result in OFL bandwidth of 1000 MHz.km at 850 nm and 300 MHz.km at 1300 nm, or it can be adjusted to result in OFL bandwidth of 25 MHz.km at 850 nm and 400 MHz.km at 1300 nm. With such multimode 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. More typically, manufacturing tolerances would allow 850 nm/1300 nm OFL bandwidths of 600 MHz.km/300 MHz.km or 200 MHz.km/1000 MHz.km but not 600 MHz.km/1000 MHz.km.
There is a disconnect, however, between these historical bandwidth shifts, and what is necessary for gigabit/sec. transmission rates. Because high speed lasers are the standard light source for LANs designed to deliver information at rates exceeding
Abbott, III John S.
Harshbarger Douglas E.
Carlson Robert L.
Corning Incorporated
Kim Ellen E.
LandOfFree
Laser optimized multimode fiber and method for use with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laser optimized multimode fiber and method for use with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser optimized multimode fiber and method for use with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3202990