Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With measuring – controlling – sensing – programming – timing,...
Reexamination Certificate
2000-01-21
2002-06-25
Hoffmann, John (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With measuring, controlling, sensing, programming, timing,...
C065S384000, C065S488000
Reexamination Certificate
active
06408651
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus and method of manufacturing optical waveguides which comprises non-optically measuring the average temperature of a moving optical waveguide as it exits a heated draw furnace that is heated to a draw temperature. In particular, the apparatus comprises a chamber having a plurality of differential thermopiles to generate an output signal that is representative of a maximum amount of radiant energy radiated by the optical waveguide fiber within the chamber. While the invention may be used in manufacturing other types of optical waveguides, it is especially suited for use in manufacturing silica optical waveguides, and will be particularly described in that connection.
BACKGROUND OF THE INVENTION
An optical waveguide fiber is manufactured by drawing the optical waveguide fiber vertically from a heated optical waveguide preform located within a draw furnace. Because the moving optical waveguide fiber being drawn is at a high temperature of about 1500° C. to 1800° C., and due to the small diameter (about 125 microns) of the optical waveguide fiber, non-contact temperature measurement is a preferred choice with such a small, moving or inaccessible optical waveguide. One non-contact way of measuring the temperature of an optical waveguide fiber is the use of radiation thermometers.
Temperature measurement with a radiation thermometer is based on the fact that all objects emit radiant energy. Radiant energy is emitted in the form of electromagnetic waves, considered to be a stream of photons traveling at the speed of light. The wavelengths of radiant energy emitted by a hot object range from the ultraviolet, 0.1 micron to the far infrared, 100 microns. However, the majority of the energy radiated by an object between 1500° C. and 1800° C. is in the near infrared region, 1.0 to 2.0 microns. Radiation thermometers measure the temperature of an object, such as an optical waveguide, by measuring the amount of thermal electromagnetic radiation received from a spot on the object whose temperature is being measured. The intensity and wavelengths of the radiation emitted by an object depends on the emissivity and the temperature of the object. Emissivity is a measure of an object's ability to emit radiant energy. The emissivity of an object is the ratio of energy emitted while at a particular temperature to that of a perfect emitter or “blackbody” at the same temperature. Since emittance will differ from one object to another, a standard, called a blackbody, is used as a reference for calibrating radiation thermometers and serves as the basis for the laws that define the relationship of the intensity of radiation and wavelength with temperature. A blackbody is an object having a surface that does not reflect or pass radiation. It is considered a perfect emitter because it absorbs all electromagnetic radiation to which it is exposed and re-emits the maximum spectral radiation allowed by Plank's law. The intensity of radiant energy increases as temperature increases. Thus, such devices are capable of measuring the temperature by measuring the intensity of the radiation that the object emits.
A radiation thermometer consists of optical lenses that collect and focus the radiant energy emitted by an object, and a radiation detector/sensor converts the focused radiant energy into an electrical signal and an indicator provides a readout of the measurement. A disadvantage of radiation thermometers is that they require a prior knowledge of the optical properties of the object being measured and, more specifically, the emissivity, ∈ of the object. Thermal radiation by an object always contains stray radiation emitted by the environment surrounding the object area and reflected by the object's surface. Hence, to maintain high measurement accuracy of a radiation thermometer precise compensation/adjustment is necessary. For example, a radiation thermometer that is sensitive to energy in the wavelength range from 4.9 &mgr;m to 5.5 &mgr;m with a spot size or field of view of 1.1 mm does not yield accurate temperature data when attempting to measure the temperature of a 0.125 mm diameter optical fiber for several reasons. First, the accuracy of a radiation thermometer is a function of the emissivity of the fiber within the sensitive wavelength range of the radiation thermometer, namely, 4.9 &mgr;m to 5.5 &mgr;m. Emissivity is the ratio of the emitted radiation by an object at specific wavelengths and temperature to the emitted radiation from a blackbody at the same wavelengths and temperature and unfortunately emissivity can be temperature and geometry dependent. The object, in this case is an optical waveguide fiber, which is made primarily of silica. Silica is partially transparent to radiation at wavelengths shorter than approximately 8 microns for certain thicknesses. Also, the effect of the cylindrical geometry of the fiber on its emissivity is not well understood. The above mentioned emissivity uncertainties along with the fact that the fiber occupies approximately only 15% of the thermometer's field of view as well as vibrating in and out of the field of view make any attempt to measure it's temperature using a radiation thermometer unreliable. One version of a radiation thermometer attempts to overcome the vibrating fiber issue by using a panning mirror that pans an area looking for the optical waveguide fiber and recording the peak temperatures over time. Thus, when the temperature peaks, it is assumed that the optical waveguide fiber is occupying the maximum 15% of the field of view however the effective emissivity of the fiber is not known and therefore cannot be entered into the thermometer. Another disadvantage of radiation thermometers is that they are quite expensive.
In light of the foregoing, it is desirable to provide an apparatus and method of accurately measuring the temperature of a moving optical waveguide. In addition, it is desirable to provide an apparatus and method that minimizes any stray radiation and/or ambient temperature changes from effecting the temperature measurement of the optical waveguide. Further, it is desirable to provide an apparatus that is rugged and capable of withstanding high temperatures, as well as an apparatus that can consistently provide an accurate average temperature measurement and has a fast response time. A further object of the invention is to provide a reliable method of manufacturing silica glass optical waveguides, while reliably monitoring and controlling the temperature of the waveguide during the manufacturing process. Finally, it is desirable to provide an apparatus that is relatively inexpensive to manufacture.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an apparatus and method of manufacturing optical waveguides that comprises non-optically measuring the average temperature of a moving optical waveguide fiber as it exits a heated draw furnace using a temperature device or monitor. In particular, the invention provides an apparatus and method of measuring an average temperature of a moving optical waveguide, where the radiant energy emitted by the moving optical waveguide is non-optically processed by the temperature device. The invention provides an optical waveguide temperature monitor and a method of measuring the average temperature of a moving optical waveguide by non-optically detecting the radiant energy emitted by the moving optical waveguide and non-optically measuring the heat flux radiated by the moving optical waveguide within a chamber that is adapted to receive the moving optical waveguide through a central channel. The principal advantage of the present invention is the provision of an arrangement that overcomes the limitations and disadvantages of the described prior arrangements. Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other adv
Corning Incorporated
Murphy Silvy A.
Wayland Randall S.
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