Abstract:
Embodiments of the invention provide methods and apparatuses to process optical subsystems. In one aspect, the optical subsystems are polished using an orbital polishing apparatus adapted to polish and clean an optical subsystem interconnect surface. The orbital polishing apparatus is adapted to incrementally advance a movable web of polishing material to provide polishing uniformity and consistent polishing performance device to device.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    Embodiments of the invention relate to methods and apparatuses for processing optical subsystems.  
           [0003]    2. Background of the Related Art  
           [0004]    In the fabrication of fiber optic communication systems, optical interconnects, fiber optics, and other components are assembled to form various interconnected optical subsystems. Typically, optical components are integrated into an optical subsystem that is collectively used to create, for example an optical switch. As the communication industry&#39;s need for optical communication bandwidth has increased, the ability for interconnect surfaces to provide a precise connection between optical subsystems is becoming critical, especially with regard to optical transmission modes that use multiple wavelengths of light to transmit information such as Dense Wavelength Division Multiplexing (DWDM). DWDM is a fiber-optic transmission technique that employs multiple light wavelengths to transmit data parallel-by-bit or serial-by-character. DWDM is a major component of optical networks that allows the transmission of e-mail, video, multimedia, data, and voice—carried in Internet protocol (IP), asynchronous transfer mode (ATM), and synchronous optical network/synchronous digital hierarchy (SONET/SDH), respectively, over fiber optic communication systems.  
           [0005]    Generally, fiber optic interconnections include two optical connections mated together to provide a continuous optical path. Conventionally, to form an optical interconnect interface, a fiber optic cable is generally terminated into an optical interconnection called a ferrule that is adapted to connect to optical systems or mating optical interconnects. Ideally, optical interconnects such as ferrules are manufactured with precisely polished and dimensionally optimized interconnect surfaces to provide low insertion loss and to prevent cross talk. Typically, ferrules are polished in batch mode where several ferrules are polished simultaneously with one polishing surface, and often are polished by hand. Unfortunately, as polishing pressure, type of polishing material, and direction of polishing between the surface of the optical components being polished and the polishing surface vary, the conventional batch process often leads to manufacturing issues such as specification repeatability, and undesirable interface aberrations affecting insertion loss, light polarization, extinction ratio, return loss performance, etc. Moreover, as polishing is done in a generally rotating fashion, particles embedded within the polishing material provided can form other aberrations such as scratches, nicks, undercuts, abrasions, etc., that can adversely affect the optical clarity of the interconnect surface and, thus, the optical transmission efficiency.  
           [0006]    Typically, interconnection inefficiencies are overcome by additional equipment such as repeaters. Repeaters amplify the optical signal to overcome insertion loss and signal attenuation, thereby extending the optical signal broadcast range. Additionally, testing equipment such as an interferometer is used to precisely test for example, the radius of curvature and apex offset. The radius of curvature is the radius of the interconnect surface and is critical for the proper mating of interconnect surfaces. The apex offset is the measure of the interconnect optical path alignment and is critical for the proper alignment of the optical paths between two optical interconnect surfaces. Unfortunately, testing each interconnection for parameters such as radius of curvature and apex offset increases the manufacturing time and, thus, the cost of the optical subassemblies. Further, for large fiber optic communication systems employing thousands of interconnections, using equipment such as repeaters designed to overcome the interconnect inefficiencies may lead to an overall increase in the cost of the fiber optic communication system. Thus, having optical interface aberrations that affect the transmission of light can adversely affect information flow, reduce the bandwidth, reduce the efficiency of fiber optic communication systems, increase equipment costs, and generally increase the cost of the communication system.  
           [0007]    Therefore, there is a need for a method and apparatus to provide a system for polishing optical component interfaces in a simple, repeatable, efficient, and cost effective manner.  
         SUMMARY OF THE INVENTION  
         [0008]    Aspects of the invention generally provide a method and apparatus for polishing optical component interfaces used in interconnecting optical subassemblies. In one embodiment, the invention provides an apparatus for processing optical components, including a polishing apparatus having a polishing table and a polishing material supply apparatus adapted to supply polishing material proximate the polishing table, an orbital actuator rotatably coupled to the polishing apparatus and adapted to rotate the polishing apparatus in an orbital motion, and a component support adapted to position an optical component in contact with polishing material adjacent the polishing table.  
           [0009]    In another embodiment the invention provides an apparatus for processing optical components, including an orbital actuator rotatably and flexibly coupled to a polishing apparatus having a polishing table, and a polishing material supply apparatus and a polishing material receiver coupled to the polishing apparatus wherein the polishing material supply apparatus is adapted to provide a web of polishing material to the polishing material receiver to define a renewable polishing surface adjacent the polishing table.  
           [0010]    In another embodiment the invention provides a method of processing optical components, including rotating a polishing apparatus comprising a polishing table thereon and a polishing material supply apparatus in an orbital direction, providing from the polishing material apparatus a renewable web of polishing material positioned adjacent the polishing table, maintaining a polishing pressure of a surface of an optical component against the web of polishing material and against the polishing table, and polishing the surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    A more particular description of aspects of the invention, briefly summarized above, may be had by reference to the embodiments thereof, which are illustrated in the appended drawings.  
         [0012]    It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0013]    [0013]FIG. 1 is a perspective view of an optical-subsystem polishing tool.  
         [0014]    [0014]FIG. 2 is a substantially front perspective view of the optical-subsystem polishing tool of FIG. 1.  
         [0015]    [0015]FIG. 3 is a substantially side perspective view of an optical-subsystem polishing tool of FIG. 1.  
         [0016]    [0016]FIG. 4 is a substantially back view of the optical-subsystem polishing tool of FIG. 1.  
         [0017]    [0017]FIG. 5 is an exploded view of the optical-subsystem polishing tool of FIG. 1 illustrating the eccentric shaft and polishing orbital assembly.  
         [0018]    [0018]FIG. 6 is a front view of an optical component support.  
         [0019]    [0019]FIG. 7 is a partial-section al view of an optical component support.  
         [0020]    [0020]FIG. 8 is a side view of an optical component support.  
         [0021]    [0021]FIG. 9 is a flow diagram illustrating a polishing process using the polishing tool of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    [0022]FIG. 1 is a perspective view of one embodiment of a staged optical component polishing system  100 . The staged optical component polishing system  100  is a self-contained system having the necessary processing utilities supported on a mainframe structure  101  which can be easily installed and which provides a quick start up for operation. The optical component processing system  100  shown generally includes three polishing apparatuses  108  that provide three optical component polishing stages, namely, a coarse polishing stage  102  where optical components are given an initial coarse polish, a fine polishing stage  104  where optical components are given a finer polish than the initial coarse polish, and a finish polishing stage  106  where optical components are given a final finish polish. The optical components are polished at each stage using a web of polishing material having a polishing surface thereon including materials such as silicon-carbide, diamonds, silicon-dioxide, and the like. In one aspect, after the coarse and fine polishing stages, the component is cleaned with de-ionized water. Subsequently, an inert pressurized gas such as CO 2  is used as a cleaning agent to remove the fine residue adhering to the optical surfaces produced during the polishing process. The substrate processing system  100  also includes a back end (not shown) which houses the support utilities needed for operation of the system  100 , such as compressed air used to power portions of the system  100 , de-ionized water used for cleaning, vacuum, and electrical power distribution. While the processing system illustrates three polishing stages, the arrangement and combination of the individual polishing stages may be altered for purposes of performing specific polishing steps. For example, the coarse polishing stage may be configured to provide a finish polish step.  
         [0023]    In one aspect, the polishing processes are controlled by a process controller  105  such as programmable logic controller (PLC) or other suitable device coupled to the three optical polishing apparatuses  108  via input/output (I/O) cable  90 . In general, the processing system controller  105  includes, or is coupled to, a central processing unit (CPU), and a memory. The memory contains a polishing control program that, when executed on the CPU, instructs the polishing apparatuses  108  to perform a polishing process. The polishing control program conforms to any one of a number of different programming languages. For example, the program code can be written in programmable logic controller (PLC) code (e.g., ladder logic), C, C++, BASIC, Pascal, or a number of other languages.  
         [0024]    [0024]FIGS. 2, 3, and  4 , are a substantially front, side, and back perspective views, respectively, illustrating one embodiment of a polishing apparatus  108 . The polishing apparatus  108  may be used to polish the interconnect surfaces of optical components such as ferrules. The term ferrule is used herein to denote a fiber-optic cable connector. Ferrules generally have three parts, a flange portion usually made of a rigid material such as stainless steel to allow the ferrule to be mechanically coupled to an optical subassembly, a body, and an optical transmission portion having a small center opening used to receive a fiber optic cable therein. The body of the ferrule is typically made of materials such as zirconia, alumina, and the like, adapted to support the fiber optic cable. Ferrule connectors are available in several different light transmission modes such as single mode used to transmit one signal per fiber, or multimode used to transmit many signals per fiber, depending on the number of wavelengths contained within the transmission.  
         [0025]    The polishing apparatus  108  includes a body  112 , a support  118 , and a mounting plate  115 . In one aspect, the body  112 , support  118 , frame  101 , and mounting plate  115  are mounted to each other using conventional fasteners such as screws, bolts, nuts, and the like, and in another aspect may be a single component. While in one aspect, the support  118  is vertically mounted on the mounting plate  115  to define a vertical polishing position for an orbital assembly  120  to help in the removal of polishing debris, it is contemplated that the orbital assembly  120  may mounted in any position to perform the same polishing function. In one aspect, a collection tray  160  is disposed under the orbital assembly  120  to collect debris and fluids during processing. The tray  160  is coupled to a drain  161  that is fluidly coupled to a waste collection system or container (not shown).  
         [0026]    The orbital assembly  120  includes a polishing assembly  130  and a spacer  132  flexibly coupled to the polishing assembly  130  and rigidly mounted to the support  118 . The polishing assembly  130  is positioned to allow the optical component to be polished at generally an orthogonal direction relative the support  118 . The polishing assembly  130  includes a right and left side plate  134 ,  136 , respectively, adapted to support a polishing table  138 , a polishing material supply apparatus  140 , and a polishing material receiver  142 . In one aspect, the polishing table  138  is formed from a rigid material having a low coefficient of friction such as Teflon® impregnated aluminum, stainless steel, or other materials having a low friction surface thereon. In another aspect, the low friction surface may be applied to the polishing table  138  as a coating thereon. The polishing table  138  also includes a polishing surface recess  139  formed therein. In operation, a web of polishing material  165  is disposed over the polishing table  138  proximate the recess  139  and between the polishing material supplier  140  and polishing material receiver  142 .  
         [0027]    In one aspect, a sub-pad  156  typically composed of a flexible material such as rubber, vinyl, resin, plastic, and the like, that provides a flexible but firm polishing surface, is disposed in the recess  139 . The sub-pad  156  is also adapted to provide a desired amount of flexure and resistance under the polishing material  165  against the component to form a desired radius of curvature for the optical surface being polished. In one aspect, the sub-pad  156  is adapted to form a radius of curvature dependant upon the pressure developed between the surfaces being polished, polishing material  165 , and the sub-pad  156 . For example, a lighter pressure between an optical component being polished, polishing material  165 , and the sub-pad  156  provides for a flatter (i.e., smaller) radius of curvature whereas a greater pressure provides for a rounder (i.e., larger) radius of curvature. In another aspect, to provide for a greater polishing pressure to form a desired radius of curvature while decreasing the polishing time required, the sub-pad  156  includes a firmer surface having more flexure resistance thereon. It is contemplated that the compliance and resilience of the sub-pad  156  may be selected to provide any desired radius of curvature, flexure, and processing time.  
         [0028]    In one aspect, the polishing material supply apparatus  140  is adapted to support a roll of polishing material  165  thereon and includes a brake  152 . The brake  152  applies a frictional force to the polishing material supply apparatus  140  which keeps the roll of polishing material  165  taught. The polishing material supply apparatus  140  further includes a supply clutch  154  to control the dispensing of the polishing material  165  from the polishing material supply apparatus  140 . The polishing material receiver  142  is coupled to a receiver clutch  164  mounted to the left side plate  136 . The receiver clutch  164  constrains the web of polishing material movement to only one direction from the polishing material supply apparatus  140  to the polishing material receiver  142 . The polishing material receiver  142  is rotated by a drive linkage  166  coupled to a drive apparatus  143  to take up and thereby advance the polishing material  165  across the polishing table  138  and sub-pad  156 . In one aspect, the supply clutch  154 , the receiver clutch  164 , and brake  152  are operated together to control the advancement of the web of polishing material  165  while maintaining a taught web of polishing material  165  across the polishing table and sub-pad  156 .  
         [0029]    An air inlet/outlet  147  is disposed on the right side plate  134 , in communication with the polishing table  138 , and coupled to air conduction channels (not shown) that extend through the polishing table  138 . The air conduction channels are coupled to holes  151  disposed around the recess  139  within a groove  158 . A vacuum pressure may be provided to the groove  158  via the air inlet/outlet  147  through the holes  151  to hold the web of polishing material  165  to the sub-pad  156  and polishing table  138  during a polish process. In one aspect, the holes  151  may be distributed throughout the recess  139  and/or the groove  158  to allow the recess  139  under vacuum to hold the web of polishing material  165  to the sub-pad  156  and polishing table  138 . In another aspect, air pressure may be provided from the air inlet/outlet  147  to the holes  151  during a polish material cleaning/renewing process to force the polishing material  165  away from the polishing table  138  releasing debris and/or allowing the polishing material  165  to be dispensed from the polishing material supply apparatus  140  to the polishing material receiver  142 .  
         [0030]    A component support  182 , used to support optical components during processing, is mounted by a support  175  to a polishing force apparatus  144 . The polishing force apparatus  144  is used to position and force optical components held by the component support  182  against the polishing material  165  and sub-pad  156 . The polishing force apparatus  144  may be any apparatus such as a motor driven actuator adapted to move the component support  182  generally perpendicular toward and away from the polishing table  138 , and as needed, during a polishing operation, maintains pressure of the optical component against the polishing material  165  and sub-pad  156 . The polishing force apparatus  144  may be slidably mounted to a polishing position apparatus  146  which is mounted to an upper end  122  of the support  118 . The polishing position apparatus  146  may be any apparatus such as a motor driven actuator adapted to laterally move the component support  182  generally parallel to the polishing table  138  and across the surface of the polishing material  165 . In one aspect, the component support  182  is independently mounted to the frame  101  to provide vibration isolation from the polishing assembly  130 . In another aspect, the polishing force apparatus  144  and polishing position apparatus  146  are mounted to the support  118  via flexible mounting fasteners such as rubber, vinyl, plastic, nylon, and the like, adapted to provide vibration damping therebetween.  
         [0031]    In one aspect, the component support  182  includes a fluid nozzle  185  that is mounted to the support  175 . The fluid nozzle  185  receives fluids such as polishing slurries, de-ionized water, and the like, from a fluid supply (not shown) and delivers the fluids through a nozzle extension  186 . The nozzle extension  186  is aligned to spray a stream of fluids upon the surface of the polishing material  165 .  
         [0032]    In one aspect, the component support  182  further includes a sensor assembly  188 , adapted to measure the polishing pressure of the optical component against the polishing material  165  during a polishing process and provide a signal to the process controller  105  indicative of the polishing pressure. In operation, the polishing force apparatus  144 , sensor assembly  188 , and process controller  105  form a polishing pressure feedback system to maintain a generally constant pressure between the optical component, polishing material  165 , and the polishing table  138  throughout the polishing process.  
         [0033]    [0033]FIG. 5 is an exploded view of the polishing apparatus  108  of FIG. 2 illustrating the eccentric shaft  176  and polishing assembly  130 . FIGS.  1 - 4  are referenced as needed in the discussion of FIG. 5.  
         [0034]    The polishing assembly  130  is coupled to an orbital actuator  170  to move the polishing assembly  130  in an orbital motion about a polishing plane that is generally orthogonal to the surface of the optical component being polished. The orbital actuator  170  includes a drive frame  180  supporting a motor  174  coupled to an eccentric shaft  176  extending generally perpendicular through the support  118 . The support  118  includes a central opening  205  therein for receiving the eccentric shaft  176  therethrough. The central opening  205  is sized to allow the eccentric shaft  176  to move in an orbital motion within the central opening  205  without touching the support  118 . One end of the eccentric shaft  176  is rotatably coupled to the polishing assembly  130  via a bearing  172 . An opposite end of the eccentric shaft  176  is coupled to the shaft of the motor  174  via a flexible coupling  198 . One or more counter balances  178  are disposed on the eccentric shaft  176  to offset the centrifugal and centripetal forces developed by the non-uniform mass distribution of the polishing assembly  130  during operation, thereby minimizing vibration.  
         [0035]    As the eccentric shaft  176  axially spins, it orbitally rotates about a motor shaft center  215 . As the bearing  172  generally provides some rotational friction, the polishing assembly  130  is rotationally urged about the shaft  176  in the direction of the shaft rotation. To rotationally constrain the polishing assembly  130 , while allowing the polishing assembly  130  to simultaneously move with the orbital rotation of the eccentric shaft  176 , four flexible supports  210 A-D are rotatably mounted on one end to the spacer  132  and on an opposite end to the polishing assembly  130 . The spacer  132  and support  118  form a counterbalance cavity  230  to hold the one or more counterbalances  178  therein. Thus, in operation, the polishing assembly  130  moves in an orbital fashion about the shaft  176  while maintaining a generally parallel position with respect to the support  118 .  
         [0036]    [0036]FIGS. 6 and 7 are front views illustrating one embodiment of the component support  182  comprising a pair of grippers  184  (e.g., jaws) adapted to hold the optical component  227  to be polished in a desired position generally orthogonal to the polishing table  138 . In one aspect, the grippers  184  include two blades  220 A and  220 B adapted to hold an optical component  227  therebetween. The two blades  220 A,  220 B include a component notch  179 A and  179 B that when brought together form a component groove  225  sized to hold various types of optical components therein and is adapted to hold the central axis of the optical component in a polishing position. In another aspect, the grippers  184  are operated pneumatically. In another aspect, the blades  220 A and  220 B include an air nozzle  177  to provide air pressure to clean the optical component and polishing material  165  of residue. FIG. 8 is a side view of the grippers  184  illustrating the grippers  184  holding an optical component  227  proximate the polishing table  138  and sub-pad  156 .  
         [0037]    Operation  
         [0038]    [0038]FIG. 9 is a flow diagram illustrating one embodiment of a method  900  of a polishing sequence. FIGS.  1 - 8  are referenced as needed in the following discussion of FIG. 9.  
         [0039]    The method  900  begins when, for example, a polishing process is initiated at step  902 . At step  904 , the method  900  initializes the polishing apparatus  108 . At step  906 , the method  900  checks to see if the polishing material  165  is available, sets the polishing table vacuum on to hold the polishing material  165  securely to the polishing table  138  using the groove  156 , and starts the optical component pick up sequence by retrieving the settings for the polishing force apparatus  144  and the polishing position apparatus  146  from, for example, the process controller  105  via data line  90 . Subsequently, at step  908 , method  900  determines if the polishing table vacuum (not shown) is working to supply a vacuum to grove  158 . If the polishing table vacuum is not working then the method  900  aborts the operation at step  914 . If the polishing table vacuum is working properly, then the method  900  proceeds to step  910 . At step  910 , the grippers  184  are opened. At step  912 , the method  900  determines if the grippers  184  are opened sufficiently to hold the optical component. If the grippers  184  are not open sufficiently then method  900  aborts at step  914 . If the grippers  184  are open sufficiently then method  900  proceeds to step  916 . At step  916 , the method  900  sets the polishing force apparatus  144  and the polishing position apparatus  146  to an optical component pickup position and closes the grippers  184  around the optical component. At step  920 , the method  900  determines if the grippers  184  are closed sufficiently to allow picking up the optical component. If the grippers  184  are not closed sufficiently, then method  900  aborts the process at step  914 . If the grippers  184  are closed sufficiently to pickup and hold the optical component, the optical component is picked up. In one aspect, the gripper tension is determined by the amount of air-pressure used to close the grippers  184  around the component. At step  922 , the method  900  retrieves the polishing sequence from the process controller  105  and sets the polishing time, polishing force for the polishing force apparatus  144 , orbital rotation speed of the orbital actuator  170 , de-ionized water fluid flow rate, and the stroke speed of the polishing position apparatus  146 . At step  924 , the motor  174  and liquid dispensers (not shown) are started. In one aspect, the motor  174  spins the eccentric shaft  176  at about 2000 rpm to about 4000 rpm. At step  726 , the method  700  moves the grippers  184  holding the optical component to the position generally orthogonal the polishing table  138  and using the polishing force apparatus  144  forces the component surface being polished against the polishing surface of the polishing material  165  and the sub-pad  156 , to establish the appropriate polishing force. In one aspect, the polishing force includes a minimum and maximum value whereby if the minimum or maximum values are exceeded the process controller alarms the system to abort the polish process. The polishing position apparatus  146  is set to a beginning position. In one aspect, the optical component is then polished for a predetermined time between about zero and two minutes while the polishing position apparatus  146  is advanced generally parallel to and proximate the polishing material  165 , exposing the surface of the optical component being polished to a new portion of the orbiting polishing surface. At step  728 , the polishing sequence is ended. The method  700  retracts the grippers  184  from the polishing position, sets the liquid dispensing to off, stops the motor  174 , turns on an air blow through holes  151  to clean the surface of the polishing table  138  and release the polishing material  165 . The method  700  then places the grippers  184  into a unload component position to unload the optical component. Once the optical component has reached an appropriate delivery location, the grippers  184  are opened to deliver the optical component to a receiving tray (not shown). Subsequently, the polishing apparatus  108  is prepared for the next component at step  930 . At step  930 , the method  900  advances the polishing material  165  via the polishing material receiver  142  to provide a clean polishing surface for the next optical component. Once the polishing material  165  is advanced, the polishing table vacuum is initiated to hold the material to the polishing table  138  and air jets  177  are activated to clean the polishing material surface of contaminates. Thus, the polishing apparatus  108  is set to polish the next optical component.  
         [0040]    Staged Polish Process  
         [0041]    The process regime from FIG. 9 can be used for one or more stages of polishing. In one aspect, as illustrated in FIG. 1, three stages of polishing are established by mounting three polishing apparatuses  108  in series to provide three stages of polishing. The first stage of polishing may be a coarse stage whereby the polishing material  165  used includes a more abrasive polishing surface relative to the subsequent polishing stages. The second stage of polishing receives the optical component polished by the first stage and polishes the optical component surface use a markedly less abrasive polishing surface than the first stage. The final stage of polishing accepts the optical component from the second stage and polishes the component with a markedly less abrasive surface than the second stage. Thus, each stage represents one polishing process that when combined provides a precisely polished optical component surface. In one aspect, a transfer carrier and transfer system (not shown) are used to shuttle the optical components between stages.  
         [0042]    Although various embodiments which incorporate the teachings of the invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments within the scope of the invention. For example, it is contemplated that the polishing apparatus  108  may be configured with polishing material  165  that has different polishing surfaces thereon. Therefore, by adjusting the polishing material  165 , a single polishing apparatus  108  may be adapted to perform more than one type of polishing process. For example, a coarse polish surface may be on a first section of polish material, a fine on a second section of polish material, and a finish polish surface on a third section of the polish material. In addition, the various polish surfaces may be set side-by-side so that as the optical component is incrementally moved by the polishing position apparatus  146 , the optical component  165  moves through each polishing process in a single stroke. In another aspect, the sub-pad  156  can be adapted to have several areas of differing radius of curvature for the same pressure. For example, the sub-pad  156  may have four quadrants whereby each quadrant provides for a different radius of curvature with the same pressure applied between the optical surface being polished, the polishing material  165 , and sub-pad  156 . Thus, by matching optical components to a quadrant having the desired radius of curvature for a given pressure and process time, the same polishing apparatus may be used to maintain an optimal throughput while polishing any number of different optical surfaces requiring different radiuses of curvature. In another aspect, the sub-pad  156  and the polishing material  165  are adapted to polish a multi-connector cable where the body of the ferrule includes a plurality of individual optical surfaces, each having their own radius of curvature requirements. The sub-pad  156  is adapted to receive the individual optical surfaces thereon.  
         [0043]    While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.