Optical waveguides – With splice – Alignment of fiber ends prior to splicing
Reexamination Certificate
2000-08-30
2002-10-15
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With splice
Alignment of fiber ends prior to splicing
C385S096000, C385S097000
Reexamination Certificate
active
06464410
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention generally relates to fiber optics and, more particularly, to fiber splices, fiber splicing machines and methods therefore.
2. Description of Related Art
Conventional splicing operations and equipment are designed to minimize or eliminate optical signal attenuation. To that end, conventional splicing machines are designed to bring the two fibers into as perfect an alignment as possible. This goal of achieving optimum alignment between the fibers is met by utilizing various detectors and fine alignment control functions so that the fibers are aligned. Typically, the respective optical axes are aligned first and then the fibers are brought together so that their ends are in direct contact.
Conventional splicing machines utilize an electric arc to fuse the fibers. Such machines permit an operator to set fusing current, fusing time and fine tune fiber alignment to achieve the best alignment possible between the fibers. Such conventional splicing machines are designed to minimize the insertion loss or attenuation of the resulting splice by, for example, accurately aligning the fibers. These conventional splicing machines may be programmed according to various recipes that specify optimum fusing currents and fusing times for a variety of fiber types, core diameters and other fiber properties.
Such conventional splicing machines also permit an operator to intentionally misalign the fibers in a crude effort to perform an attenuating splice. Using various recipes similar to those mentioned above, an operator can construct an attenuating splice. This conventional attenuating splice operation requires a high degree of operator experience to choose the proper parameters such as fusion time and current. Furthermore, these operations are labor intensive and include typing in the large number of parameters at each step. The success rate also varies with the skill of the operator, machine condition, and environmental conditions. Even with an experienced operator and ideal conditions, these conventional techniques cannot provide an accurate attenuation value.
Various other conventional techniques exist for constructing attenuating splices. Gleason et al. (U.S. Pat. No. 4,557,557), for example, heats aligned optical fiber ends until they are in a plastic state. Then, the fiber ends are physically distorted by axial movement of one of the fiber ends. The amount of movement is controlled according to a measured optical loss across the splice. The fusion splice formed by this technique imposes a lumped optical loss value between the fiber ends. Yamamoto, et al. (U.S. Pat. No. 4,884,859) also heats aligned optical fiber ends to a temperature sufficient to soften the materials and then applies a tension and/or twist to the fiber to thereby form an optical attenuation area having fine cracks that scatter light. A major shortcoming of such techniques is the amount of attenuation is very difficult to control.
Forrester (U.S. Pat. No. 5,142,603) is another example of constructing a fusion splice with a controlled attenuation. Forrester fuses the ends of aligned fiber ends with heat. Once fused, the heat is continued for a time period sufficient to cause dopant to migrate out of the core and result in a desired attenuation.
Lin, et al. (U.S. Pat. No. 5,398,296) constructs a mode filter overlapping the fiber ends such that the fiber ends are parallel and overlapping. These overlapping fiber ends are then welded. Lin slightly separates the fibers to pull and narrow the welded portion. As the fibers are being separated, a power meter is monitored. When the readout reaches an object value, e.g. 3 dB, the process is stopped and the fibers are cooled. A material having a high index of refraction is then applied to the welded portion to form a mode filter.
Emmons, et al. (U.S. Pat. No. 5,588,087) constructs an overlapping fusion attenuator by overlapping two fiber ends to define an overlapped portion of the fibers. Heat is then applied to the overlapped portion by energizing an electric arc for about one second. The transmission loss is then measured and, if greater than a desired loss, the electric arc is turned on again for the same time period. As a result, the cores move closer together in the overlapped portion which results in a reduced transmission loss. This technique has serious shortcomings and can only produce at attenuation of greater than 10 dB. Alternative embodiments produce lower attenuation values by moving the fibers relative to one another in much the same way as described above to change the attenuation value.
SUMMARY OF THE INVENTION
The invention adds or otherwise produces a highly-controlled amount of attenuation in a fiber splice during the fiber splicing process. This process includes intentionally misaligning fiber cores during the splicing operation. Such intentional misalignment increases the insertion loss of the resulting splice.
In addition, the method disclosed here accurately controls the amount of attenuation introduced in the fiber splice. The degree of control is quite excellent and allows the manufacture of attenuating splices having an insertion loss that is controlled within +/−0.25 dB and, preferably, within +/−0.1 dB or less.
To this end, the inventive methods control the total amount power applied to the fibers during the fusing process. When utilizing an electric arc as the energy source, the invention may control the amount of power by controlling the driving current applied to the arc.
The inventive methods may exercise this control in a so-called power control mode or shut-down mode wherein the driving current (or other parameter for controlling power applied by a splicing machine) is applied until the measured insertion loss is within a margin of the desired insertion loss value. As the hot splice cools, the insertion loss decreases and will settle at a value close to the desired insertion loss value. The shut-down mode operates while the fiber is energized and connected to a power meter. By monitoring the power meter, the method can determine when the insertion loss is within the desired margin and then shut down the energy source fusing the fibers.
The inventive method may also utilize an energy control mode or repeat mode either alone or in conjunction with the shut-down mode. The repeat mode changes the energy applied to the fibers during the splicing operation. When utilizing an electric arc as the energy source, the invention may control the driving current as well as the time the driving current is applied to fuse the fibers. The fused fibers are preferably allowed to cool and then a reading is taken of the insertion loss. If the insertion loss is not acceptable, then the process is repeated until the insertion loss is within the desired range.
The above inventions may be further improved by utilizing an estimation algorithm to estimate optimal splicing parameters and intelligent control schemes to maximize the yield of the process while, simultaneously, reducing dependence upon operators. Instead of utilizing a margin such as in the power mode where power is applied until the measured insertion loss is within a margin of the desired insertion loss value, the invention estimates the final attenuation jump that occurs when the power is shut off. By accurately estimating this final jump, the splicing power may be shut down at the precise moment to produce a splice having the desired attenuation value. If the estimation turns out to be incorrect, then the repeat or energy control mode can be utilized to produce a splice with the desired attenuation value.
Intelligent control algorithms utilize a knowledge base to adjust the estimation parameters so that the system can learn and more accurately estimate the final jump. Intelligent control algorithms may also be used to determine the optimal amount of energy (e.g. time and driving current) for the repeat or energy control mode based on information from the shut-down or power control mode and, if any, previous repeat mode splici
Csipkes Andrei
Mahmood Waqar
Sahinci Erin
Cammarata Michael R.
CIENA Corporation
Rojas, Jr. Omar
Sanghavi Hemang
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