Abstract:
The invention relates to a line for processing an optical fiber having first and second ends, the line comprising a support for receiving a reel with the fiber wounded thereon; a de-winder for unwinding the fiber without substantial rotation of the reel; and a processing station for receiving the optical fiber from said de-winder to perform a processing on a portion of the optical fiber. The invention also relates to a method for writing a grating on a fiber having first and second ends, the fiber being wounded on a first reel and being capable of being wounded on a second reel, the method comprising connecting the first end of the fiber to a circulator; connecting said circulator to a source of light and to a first measurement means; de-winding the fiber from the first reel without rotation of the reel; writing a grating on the fiber with a source of radiation; and measuring reflection spectra of the grating with said first measurement means. The method also comprises winding the fiber on the second reel without rotation of the reel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a reel to reel manufacturing line for processing an optical fiber. 
     SUMMARY OF THE INVENTION 
     The invention seeks to provide an automated manufacturing line to write successive optical devices, such as Bragg gratings, on an optical fiber. The line includes all the required functions to provide complete final products fully characterized, including quality control, requiring only to be cut in desired length segments and to be packaged. Alternatively, any optical waveguide which could be wound on a reel could be processed by the manufacturing line. 
     The manufacturing line comprises an apparatus for unwinding (de-winder) the optical fiber from a first reel without rotating the reel, the apparatus being located at one end of the manufacturing line. The de-winder can be placed in a cooled enclosure if the first reel has a hydrogen-loaded fiber wound thereon. At the other end of the line, the line comprises an apparatus for winding the fiber on a second reel also without rotating the reel. This enables the connection of both ends of the fiber, which can be a few kilometers long, to optical measurement instruments. Indeed, instead of using a rotating coupler, standard couplers and connectors are used. 
     A fabrication apparatus (e.g. a source of optical radiation) is placed between the first and second reels, and data acquisition and process control are possible since the fiber is connected at both ends. The fabrication apparatus can be a fiber grating-manufacturing device (e.g. a laser), a fiber grating measurement device, a fiber sectional measurement device or a fiber coating modification device. 
     For a reel to reel manufacturing line for writing Bragg gratings, the line comprises a source of optical radiation (e.g. a laser) delivering the high energy (e.g. a beam) to write the Bragg gratings and an apparatus for aligning the fiber with the source of optical radiation. The apparatus for aligning the fiber with the laser comprises a support for holding the fiber, wherein in use the support is oriented such that the beam emitted by the laser illuminates a first portion of the fiber thereby causing the fiber to emit photoluminescence and a sensor located in proximity to the fiber for detecting photoluminescence emitted radially by the fiber and generating an intensity signal indicative of a measure of the photoluminescence detected. The apparatus also comprises a controller module responsive to the intensity signal for causing the beam emitted by the laser to illuminate a second portion of the fiber. 
     The line may also be used to write arrays of different gratings, at the same wavelengths or not, and by using a synchronized encoder, evenly spacing them or not along the fiber. 
     The use of the connected reel to reel line increases throughput and measurement accuracy. By adding proper inspection stations, all of the quality control can be made in line. No other measurement is therefore required and the fiber only needs to unwound from the second reel, cut at desired locations and packed and identified for shipping purposes. 
     Guiding devices can be used to restrict the fiber path. Furthermore, the line comprises functional units, such as cleaning units, a stripping unit, an annealing unit, inspection units or a recoating unit, each unit possibly comprising clamping devices to position and tension the fiber. 
     Preferably, the section of the fiber to be treated is grabbed on each side by a clamping device as this section of the fiber leaves the first reel. The clamping device is mounted on a cart that is movable from one functional unit to the next one. The clamping device comprises a mechanism to adjust and monitor the tension in the grabbed section of the fiber that is used to optimize tension for each functional unit. In both cases, the different functional operations can be made one after the other or simultaneously. At each functional unit, either the fiber can be moved in place and/or the specific apparatus can be brought to the fiber by pneumatic piston and/or standard optical stage for example. 
     Accordingly, as embodied and broadly described herein, the invention seeks to provide a line for processing an optical fiber having first and second ends, the line comprising a support for receiving a reel with the fiber wound thereon; a de-winder for unwinding the fiber without substantial rotation of the reel; and a processing station for receiving the optical fiber from said de-winder to perform a processing on a portion of the optical fiber. Preferably, the line also comprises a second support for receiving a second reel and a winder for winding the fiber on the second reel without rotation of the second reel. The line also comprises a source of optical radiation (e.g. a laser) for writing a grating on the fiber. 
     As embodied and broadly described herein, the invention also seeks to provide a method for processing an optical fiber having first and second ends, the fiber being wound on a first reel and being capable of being wound on a second reel, the method comprising: connecting the first end of the fiber to a source of light and a measurement means; de-winding the fiber from the first reel without substantially turning the reel; processing a portion of the fiber with a source of optical radiation; and during the process, measuring reflection spectra of the portion of the fiber with said measurement means. Preferably, the method further comprises connecting the second end of the fiber to a second measurement means and measuring transmission spectra of the portion with said second measurement means. The method also comprises winding the fiber on the second reel without substantial rotation of the reel. 
     As embodied and broadly described herein, the invention also seeks to provide a method for performing a predetermined process on an optical fiber, comprising: providing a reel having a continuous optical fiber wound thereon, the optical fiber having a first end and a second end; unwinding the optical fiber from the reel without substantially turning the reel; introducing light via one of the first and second ends of the optical fiber such that the light propagates in the optical fiber; performing a predetermined process on a portion of the optical fiber unwound from the reel. 
     As embodied and broadly described herein, the invention also seeks to provide a method for performing a predetermined process on an optical fiber wound on a first reel, the optical fiber having first and second ends, the method comprising: unwinding the optical fiber from the first reel substantially without rotation of the first reel to create an unwound portion; performing a predetermined process on the unwound portion; winding the unwound portion after the predetermined process has been performed on a second reel substantially without rotation of the second reel; during the predetermined process introducing light via one of the first and second ends of the optical fiber such that the light propagates to the unwound portion through a portion of the optical fiber wound on either one of the first and second reels. 
     As embodied and broadly described herein, the invention also seeks to provide a line for measuring optical properties of gratings written on a fiber having first and second ends, the line comprising: first and second supports for receiving first and second reels, the first reel having the fiber wound thereon; a de-winder for unwinding the fiber without rotation of the reel; a winder for winding the fiber on the second reel without rotation of the second reel; a source of light connected at one of the first and second ends of the fiber; and a measurement means connected at one of the first and second ends of the fiber for measuring optical properties of the gratings. 
     Other objects and features of the invention will become apparent by reference to the following description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of specific embodiments of the present invention is provided herein below, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a process flow for a reel to reel manufacturing line for writing gratings on a fiber, the line being constructed in accordance with an embodiment of the invention; 
         FIG. 2  shows one end of the line having a dancer arm assembly, an electronic tensioner, an air bushing, a winder and a reel mounted on a support; 
         FIG. 3  is a side elevational view of the dancer arm assembly of  FIG. 2 ; 
         FIG. 4  is a side elevational view of the electronic tensioner of  FIG. 2 ; 
         FIG. 5  is a side elevational view of the air bushing of  FIG. 2 ; 
         FIG. 6  is a top plan view of the air bushing of  FIG. 5 ; 
         FIG. 7  is a front elevational view of the air bushing of  FIG. 5 ; 
         FIG. 8  is a front elevational view of the winder of  FIG. 2 ; 
         FIG. 9  is a perspective view of the winder of  FIG. 8 ; 
         FIG. 10  is a side elevational view of the winder of  FIG. 8 ; 
         FIG. 11  is a top plan view of the winder of  FIG. 8 ; 
         FIG. 12  is a cross-sectional view of the rotatable arm of the winder of  FIG. 8 ; and 
         FIG. 13  is a side elevational view of the reel and support of FIG.  2 . 
     
    
    
     In the drawings, specific embodiments of the invention are illustrated by way of examples. It is to be expressly understood that the description and drawings are only for the purpose of illustration and are an aid for understanding. They are not intended to be a definition of the limits of the invention. 
     DETAILED DESCRIPTION 
     A reel to reel manufacturing line for writing gratings on a fiber is illustrated in FIG.  1 . 
     With reference to  FIG. 1 , the line comprises an apparatus for unwinding the fiber from a first reel (de-winder  1 ). De-winder  1  is placed in a cooled container  2  to slow down out gazing from the fiber if necessary. 
     The line comprises first and second ends, the first end being connected via an optical circulator  3  to a source of light such as a broadband light source or a tunable laser  4  and a power meter  5  (or an optical spectrum analyzer) while the second end is connected to another power meter  5  (or an optical spectrum analyzer). 
     By placing an optical circulator between the source of light and the connection to the fiber, and connecting a light power detection device (power meter or optical spectrum analyzer) at the third branch of the circulator, the reflection spectrum of the created gratings can be measured. 
     It is thus possible to measure reflection spectra of the grating at the first end with power meter  5  (or optical spectrum analyzer) while measuring transmission spectra of the grating at the second end with the other power meter  5  (or optical spectrum analyzer). 
     It is to be understood that different commercially available optical measurement apparatus can be used to monitor different optical properties of the grating since both ends of the fiber are fixed, enabling any type of optical connections, even splices. 
     Moreover, by using a device to rotate the orientation of the polarization states of the light source in synchronization with the power readings, the polarization dependence loss (PDL) of the created gratings can be measured. 
     Once the fiber is un-winded without rotation of the first reel, it passes through a cleaning unit  6  and then trough an inspection unit  7  that marks defective segments by an ink jet marker  8 . If the source of optical radiation (e.g. a laser) used to write the gratings can damage the removable coating or jacket of the fiber, or if the radiation is distorted by such coating or jacket, the line includes stripping apparatus (e.g. a mechanical stripper)  9  to remove the coating or jacket before the gratings is written. It is to be understood that different types of stripping apparatus can be used, such as blades based equipment, hot or cold blades; thermal/energy, such as electric elements, laser or hot gas based equipment; or chemical/solvent based equipment. 
     The bare glass fiber section is then cleaned by a cleaning unit  10 , inspected and marked if defective. Several type of cleaning units such as fiber surface sweeping by soft wet tissue and/or brush, inert gas flow and electrostatic discharge can be used. 
     The fiber is then guided by guiding devices  11  designed to avoid contacts with the stripped region of the fiber until the latter leaves a recoating unit  14 . 
     Once the stripped region of the fiber reaches a processing station such as a source of optical radiation (e.g. a laser or holoscope)  12 , it is grabbed on each coated side by tensioning clamps (e.g. tensioners)  13 . 
     By putting the stripped region of the fiber under desired longitudinal tension while it is under the source of optical radiation  12 , the spectra of the gratings can be separated from the spectra of those previously written, enabling real time monitoring for fabrication process control. Moderated longitudinal tension on the fiber does not deform the spectra, but translates it along the wavelength axis. So, an array of even similar gratings can be made and individual spectra can be measured by tensioning longitudinally the fiber while writing and annealing, and relieving the tension for re-winding. As the longitudinal tension on the fiber is relieved, another optical measurement can be made to track the spectra&#39;s peaks translation along the wavelength axis for exact center wavelength measurement. 
     Alternatively, the stripped region of the fiber can be put under minimal tension and the previously formed gratings can be re-wound under tension to translate same to other wavelengths. 
     If Fabri-Perot effects are negligible, it is understood that final optical measurements of the previous grating can be used as a base reference, and it is then possible to monitor the changes in the spectra as a new grating is created to isolate the optical properties of that particular grating from the others. Since, each grating can be written and annealed successively, its final optical properties can be measured directly in line with more precision since all the other optical elements between the light source and the detector are stable during the full fabrication process, and so these other elements can be characterized in an initial reference measurement. 
     Once the grating is written, stabilized and measured, the stripped and written region of the fiber moves into the recoating unit  14 . If, in addition, the process includes an in-line fiber gratings annealing step, instead of an off-line batch annealing, the written region would not require further optical measurements since both ends of the fiber are connected and all the quality control can therefore be made in line. 
     The recoated fiber passes through another inspection unit  7  that marks defective segments by an ink jet marker. The inspection may be performed by visual inspection stations having for example cameras or analyzer systems. With this type of inspection, the protective coating integrity is monitored all along the fiber and in-line proof testing is possible after the recoating station to insure the fiber&#39;s mechanical (microcracks) integrity and mechanical lifetime. 
     An ink jet encoder  15  identifies the cutting lines and the sub-section for the automated packing line. Finally, the fiber is re-wound on a second reel by an apparatus for winding (winder  16 ), without rotation of the second reel. 
     Since both ends of the fiber are fixed and stable all along the delivering of the fiber from the first reel to the second reel, it is possible to have a line that is compatible to any optical measurement system, regardless of the type and sensitivity of connections required. It is to be understood that multiple types of optical measurements, such as chromatic dispersion, can be used in conjunction with the line. 
     All the components of the line are controlled by a central computer that synchronizes the motions, analyzes the acquired data and controls the process, and stores all pertinent data for process monitoring and optimization in a central database. Synchronization of motions is achieved by pre-mapping, calibration and position sensors combined to a software program, running in a constant feedback loop mode, that sends parameter settings to the different functional units and movable devices. 
     The in-line optical measurements are in a constant feedback loop mode to control the parameters and the duration of the expositions in the source of optical radiation  12  during the fiber grating writing, as well as, during the fiber grating annealing. 
     Results of the fiber inspection units are acquired by the computer and a software program analyze them to re-adjust specific functional apparatus parameters settings. 
     The central computer also controls the ink jet markers that are located all along the line. A bar code protocol can be used to mark the fiber with specific messages at specific locations. These messages may include the serial number of the device, the cutting lines where the fiber should be cut later on, as well as different quality control codes for various ranges of defects. The bar code marks can be read in other automated lines, such as an un-winding/packing/triage automated line to obtain ready to ship products. 
     Using the methods, tests and criteria known by the person skilled in the art, the following quality control parameters are measured on the line: surface and coating defects and contamination all along the process, mechanical integrity through the in-line proof test functional unit, final and intermediary optical properties (transmission and reflection spectra, polarization dependence loss (PDL), polarization mode dispersion (PMD) and optical life expectancy through index profile decay during annealing. 
     In a particular embodiment, a commercially available self-synchronized multi-ports sweep system is used for the optical measurements. This system includes a rotational device of the polarization states that enables in line measurements of polarization dependence loss (PDL) and polarization mode dispersion (PMD) in addition to the transmission and reflection spectra. These measurements are in compliance with the telecommunication industrial standards, such as the Fiber Optic Test Procedure of the Electronic Industry Association and Telecommunication Industry Association. 
     Computerized data acquisition from the different elements of the line can be used to identify the spectra, location, quality/integrity of the different gratings and parts of the array. In a second step, the second reel can feed an automated packing line. The completed manufacturing reel to reel line can be located in an atmosphere-controlled chamber. 
     With reference to  FIGS. 2  to  13 , the second end of the reel to reel manufacturing line is illustrated in more details. 
     The fiber passes through a dancer arm assembly  100 , an electronic tensioner  200 , an air bushing  300 , a winder  400  having a rotatable arm  402  that turns around a reel  500  mounted on a support  600 . 
     More specifically, the fiber enters dancer arm assembly  100  under a first roller  102 , then passes over a second roller  104  and under a third roller  106 . Dancer arm assembly  100  also comprises an arm  108  having second roller  104  mounted at its distal end and third roller  106  mounted adjacent its proximal end. Proximal end of arm  108  is attached to an adjustment mechanism  110  through a spring  1   12 . Spring  1   12  counter balances the force exerted by the fiber on second roller  104 . The tension of spring  112  can be adjusted by adjustment mechanism  110 . Third roller  106  is mounted adjacent to a potentiometer  114  that reads the angular position of arm  108 . In this matter, the tension in the fiber is also read. In fact, tension sensors such as potentiometer  114 , provide feedback to the software program for sudden acceleration and fine tuning of the synchronization and speed of the fiber. If the feedback loop frequency is to low, due to specific hardware limitations in combination with specific fast accelerations of the fiber, direct logical circuitry can be used to increase the feedback loop frequency. 
     The fiber then passes between first and second wheels  202 ,  204  mounted on electronic tensioner  200 , up and around (a full turn) a wire brake wheel also mounted on electronic tensioner  200 , then up (half a turn) and around a wire tension take-up wheel  206 . 
     The fiber then passes through air bushing  300  that serves to guide and push the fiber through winder  400 . The air enters by a fitting  302 , its flow being adjusted by a valve  304 , and leaves through orifice  306 . 
     The optical fiber then passes under a first roller  404  of winder  400  and then over a second roller  406 , rollers  404 ,  406  being mounted at each end of rotatable arm  402 . Winder  400  also comprises a counter weight  408 . Winder  400  further comprises a winder servomotor  410  that actuates rotatable arm  402  via a belt  412 . Winder servomotor  410  is placed beside the fiber path and its speed is controlled by the position of arm position  108 , via potentiometer  114 . Winder  400  further comprises a position servomotor  414  and a pair of rails  416  on which position servomotor  414  is movable. Winder servomotor  410  is mounted on position servomotor  414 . The translation speed of position servomotor  414  and the rotational speed of winder servomotor  410  are controlled and synchronized in order to properly wind the fiber on reel  500 . 
     It is understood that the present invention can be used on any existing grating writing process to enhance its throughput, for re-measurements of fiber grating arrays, or for many kind of measurement of properties of the fiber along its length since the de-winder and winder of the reels that de-winds and winds the fiber without its rotation enables the permanent connections of both ends of the fiber to measurement devices. 
     Indeed, the present invention also covers a line for measuring optical properties of gratings written on a fiber having first and second ends. More particularly, the line also comprises first and second supports for receiving first and second reels, the first reel having the fiber wound thereon. The line further comprises a de-winder for unwinding the fiber without rotation of the first reel and a winder for winding the fiber on the second reel without rotation of the second reel. Finally, the line comprises a source of light connected at one of the first and second ends of the fiber and a measurement means connected at one of the first and second ends of the fiber for measuring optical properties of the gratings. 
     The above description of specific embodiments should not be interpreted in a limiting manner since other variations, modifications and refinements are possible within the spirit and scope of the present invention. The scope of the invention is defined in the appended claims and their equivalents.