Abstract:
An optical device is disclosed that includes a chip containing a Vertical Cavity Surface Emitting Laser (VCSEL) active region that produces a laser beam on a first axis. The VCSEL can further include a post having a central axis offset a distance from the first axis. A lens can be mounted on the post such that it bends the laser beam away from the first axis. Alternately, the chip can include multiple VCSEL active regions each of which produces a laser beam on a different axis. The chip can include a post having a central axis offset from the laser beam axes. A lens can be mounted on the post such that the lens bends the laser beams away from the central axis.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. The Field of the Invention  
         [0002]     Exemplary embodiments of the present invention relate to the field of laser optics, and, more specifically, to designs of Lens-on-Chip (LOC) and Lens-on-Post-on-Chip (LOPOC) Vertical Cavity Surface Emitting Lasers.  
         [0003]     2. The Relevant Technology  
         [0004]     Lasers have a wide range of applications in today&#39;s technological world. For example, lasers are used in data communications applications, in entertainment devices, as sensors, as measuring devices, and in a host of other applications. One type of laser used in these devices is the vertical cavity surface emitting laser (VCSEL). Over the years, the various devices that use VCSELs have become smaller and smaller. This has resulted in a technical challenge to engineers, who must design these components to be smaller and smaller, yet still perform to the same or better technical specifications.  
         [0005]     One method used to miniaturize laser transmitters and laser transmission assemblies is to reduce the number of components. Another method is to make the various components themselves, smaller. For example, the beam of light that exits from a laser transmitter often needs to be focused or collimated. External lenses have been used for this purpose for many years. Recently, lens on chip (LOC) and lens on post on chip (LOPOC) technologies have been developed. LOC technology incorporates a polymer lens onto the laser chip during the wafer fabrication process. The fabrication process includes lithographically forming a region on the wafer to accept a polymer and subsequently placing the lens on the wafer using an inkjet or needle. LOPOC includes an additional polymer standoff to allow the lens to be raised from the surface of the laser chip, thus making it possible to achieve greater optical power. Previously, LOC and LOPOC were used to couple laser light from a VCSEL directly into a fiber, such as a fiber optic cable in a data communications network. This coupling was achieved on a single axis, the axis of the fiber optic cable and the axis of the light beam exiting from the VCSEL being co-linear.  
         [0006]     One example of a basic LOPOC apparatus is shown in  FIG. 1A  and designated generally as reference numeral  100 . Apparatus  100  includes a semiconductor emitter/detector  102 . Semiconductor emitter/detector  102  can be, for example, a VCSEL, a laser beam detector, or both. Apparatus  100  further includes a polymer standoff or post  104  that maintains a lens  106  at a desired offset distance from the surface of semiconductor emitter detector  102 . This allows a laser beam  108  to be focused on a desired point above apparatus  100 . Alternately, or in addition to focusing the beam to a desired point, laser beam  108  can be focused on the detector via a portion of beam  108  that is reflected from lens  106 .  
         [0007]     Currently LOPOC devices only allow the beam to be directed in a straight line upward or downward, along the optical axis of the standoff and/or lens, i.e. on a single axis. However, to make the overall package smaller, it is sometimes desirable to tilt the beam or direct the beam to a point that is “off” this optical axis.  FIG. 1B  illustrates one prior art system used to tilt the laser beam, designated generally as reference numeral  150 . System  150  includes a semiconductor emitter  152 , such as a VCSEL, and a laser detector  154 . An external lens  156  is used to focus a beam  158  towards a point  160  that is positioned off the optical axis of beam  158 , i.e. on a different axis. A portion  162  of beam  158  is reflected back from the surface of lens  156  to detector  154 .  
         [0008]     Unfortunately, the above design to tilt the beam suffers from some significant drawbacks. Most importantly, because of the large offset between lens  156  and emitter  152 , system  150  takes up an undesirable amount of space. This limits the size of the various devices that can use these VCSEL assemblies.  
       BRIEF SUMMARY OF THE EMBODIMENTS  
       [0009]     Embodiments of the present invention provide a Vertical Cavity Surface Emitting Laser (VCSEL) that can be configured to direct a beam of light emitted from the laser to a point offset from an optical axis of the laser. Additionally, embodiments of the present invention can also reduce the overall height of the VCSEL as configured to enable the apparatus to be used in low profile devices. In this manner, embodiments of the present invention can be used in low profile devices that cannot physically be built using prior art technology. Illustrative devices can include, by way of example and not limitation, optical mice, optical pens, paper sensors, and other devices that use small lasers to perform various functions.  
         [0010]     In one embodiment, a VCSEL is disclosed that includes a chip containing a VCSEL active region that produces a laser beam on a first axis. The VCSEL can further include a post having a central axis therethrough. The central axis of the post can be offset a distance from the first axis. The VCSEL can further include a lens mounted on the post such that it bends or directs the laser beam away from the first axis.  
         [0011]     In an alternate embodiment, a VCSEL is disclosed that includes a chip containing at least a first and a second VCSEL active region. The first VCSEL active if region produces a first laser beam on a first axis, while the second VCSEL active region produces a second laser beam on a second axis. The VCSEL can further include a post having a central axis therethrough. The central axis of the post can be offset from both of the first and second axes. The VCSEL can further include a lens mounted on the post such that the lens bends or directs the first and second laser beams away from the central axis. The lens can be designed to focus, collimate, or diverge the laser beam, as desired.  
         [0012]     In both of the above embodiments, the post can be made from a photoresist material, including, but not limited to, SU-8 and Benzocyclobutene. The lens can be made from an optical epoxy that is deposited via ink jet or other manners onto the post. In some of the embodiments, the lens can be used to focus a portion of the laser beam(s) onto a photodiode or other optical receptor. These embodiments can be used in low profile devices that cannot physically be built using prior art technology. Illustrative devices can include, by way of example and not limitation, optical mice, optical pens, paper sensors, and other devices that use small lasers to perform various functions.  
         [0013]     These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
         [0015]      FIG. 1A  illustrates a prior art example of a vertical cavity surface emitting laser (VCSEL) with a lens on the laser chip that directs the laser beam directly upward;  
         [0016]      FIG. 1B  illustrates one prior art apparatus for bending a light beam transmitted from a laser;  
         [0017]      FIGS. 2A and 2B  illustrate a side and top view, respectively, of one embodiment of a VCSEL according to the present invention;  
         [0018]      FIG. 3  illustrates a side view of an alternate construction of the embodiment of  FIGS. 2A and 2B ;  
         [0019]     FIGS.  4  illustrates a side view of an alternate embodiment of a VCSEL according to the present invention that includes a photodetector on the chip; and  
         [0020]      FIGS. 5A and 5B  illustrate additional alternate embodiments incorporating multiple VCSEL active regions on a single chip.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0021]     Embodiments of the present invention provide an apparatus that can direct a beam of light emitted from a laser to a point offset from an optical axis of the laser. Additionally, embodiments of the present invention can also reduce the overall height of the apparatus to enable the apparatus to be used in low profile devices. In this manner, embodiments of the present invention can be used in low profile devices that cannot physically be built using prior art technology. Illustrative devices can include, by way of example and not limitation, optical mice, optical pens, paper sensors, and other devices that use small lasers to perform various functions. Various embodiments of such an apparatus are discussed below.  
         [0022]      FIGS. 2A and 2B  illustrate a side view and a top view, respectively, of one embodiment of a VCSEL  200  that can direct a laser beam generated by VCSEL  200  at an angle relative to an axis of the laser beam emitted from a laser emitter of VCSEL  200 . This allows for a smaller overall package size than was available with the VCSEL shown in  FIG. 1 .  
         [0023]     With continued reference to  FIG. 2A , VCSEL  200  can include a chip  202  that contains a laser emitter  204 . Mounted to chip  202  and optically communicating with laser emitter  204  is a standoff or post  206  that supports a lens  208 . The standoff  206  facilitates propagation of a laser beam  210  emitted by laser emitter  204  to lens  208 , while lens  208  directs laser beam  210  toward a point  212  offset from an axis of laser beam  210  emitted by laser emitter  204 . In this manner, VCSEL  200  can direct laser beam  210  in a path “off axis” to a perpendicular to the surface of chip  202 , without using optical components external to VCSEL  200 . By so doing, VCSEL  200  provides a smaller overall package size than is currently available with the VCSEL shown in  FIG. 1B , and provides greater variability in laser beam path than is capable with the VCSEL shown in  FIG. 1A .  
         [0024]     To aid with controlling the degree of bending or tilting of laser beam  210  relative to the perpendicular to the surface of chip  202 , the lens/standoff combination is not centered directly over laser emitter  204 , but is offset a distance from the center, the distance being identified as by reference “A”. For instance, a longitudinal axis of standoff  206  and the central axis of lens  208  can be offset from an axis of laser beam  210  emitted from laser emitter  204  before laser beam  210  enters lens  208 . This offset distance can be from 0 micrometers (μm) to about 200 μm, more preferably from about 50 μm to about 75 μm, or other distances outside the identified ranges. This offset allows a laser beam  210  transmitted from laser emitter  204  to be bent or directed at an angle from the perpendicular by lens  208 , and focused to a point  212 . The exact angle of the bend or tilt can depend on the height and shape of lens  208 . In exemplary embodiments, this angle can be from about 10° to about 45° from the perpendicular, although other angles are possible. Further, although reference is made to lens  208  focusing the beam, it can be understood that in other configurations the lens can be designed to focus, collimate, or diverge the laser beam, as desired.  
         [0025]     The specific direction of beam  210  shown in  FIGS. 2A and 2B  is arbitrary. As long as beam  210  is bent or tilted at an angle from the perpendicular, beam  210  can be directed to any point around a circumference of laser emitter  204  by placing standoff  206  and lens  208  in an appropriate position.  
         [0026]     To reduce reflections and other undesirable optical effects, standoff  206  can be in physical contact with chip  202 . In one exemplary embodiment, standoff  206  can be attached to chip  202  using, for example, an optically clear adhesive. Similarly, lens  208  can be in physical contact with polymer standoff  206 . In one embodiment, lens  208  can be attached to polymer standoff  206  using, for example, an optically clear adhesive. In alternate embodiments, chip  202 , polymer standoff  206 , and lens  208  can be held in physical contact with each other using a frame or housing (not shown). In yet other alternate embodiments, chip  202 , polymer standoff  206  and lens  208  can be optically aligned without being in physical contact with each other.  
         [0027]     The standoff  206  and lens  208  can be fabricated from similar or dissimilar polymers. In one embodiment, standoff  206  can be fabricated from a photoresist material. A photoresist material can be defined as a light sensitive liquid or film, which, when selectively exposed to light and then developed, masks off an area based upon the configuration of a photomask positioned above the photoresist material. In one process, by way of example and not limitation, the photoresist material can be uniformly deposited on the surface of chip  202 . A photomask can then be applied, and undesired portions of the photoresist material can be removed by exposing the photoresist material uncovered by the photomask to selected light or radiation, thus forming standoff  206  in a desired location on chip  202 . In some embodiments, larger than normal chips can be fabricated to allow for an additional standoff distance. In some embodiments, the photoresist material can be SU-8, Benzocyclobutene (BCB), or other photoresist materials known to those of skill in the art.  
         [0028]     The lens  208  can be fabricated from, by way of example and not limitation, an optical epoxy. Once standoff  206  is formed on the surface of chip  202 , a lithographic process, or other processes known to those of skill in the art, can be used to deposit the optical epoxy onto the top surface of standoff  206 . In one embodiment, lens  208  can be formed by using an ink jet process to deposit the polymer on top of standoff  206 . The specific shape of lens  208  can be determined by, among other things, operational considerations. For example, lens  208  can be designed to produce a converging beam  210 , as shown in  FIGS. 2A and 2B . Alternately, lens  208  can be designed to provide a collimating or diverging beam. In these cases, other external lenses or optical waveguides can be used to further direct beam  210 .  FIG. 3  illustrates one embodiment of the present invention in which a lens  208   a  collimates beam  210 . Although reference is made to lens  208   a  collimating the beam, it can be understood that in other configurations the lens can be designed to focus, collimate, or diverge the laser beam, as desired.  
         [0029]     VCSEL  200  can have various configurations to generate laser beam  210  by way of stimulated photonic emission. For instance, and not by way of limitation, VCSEL  200  can be an air post VCSEL, a buried re-growth VCSEL, or other types of VCSELs that incorporate a plurality of Distributed Bragg Reflectors (DBRs). Specific construction/manufacturing techniques for VCSELs are known to those of skill in the art. The VCSEL  200  can be operated at a wavelength of between about 650 nm and about 1500 nm. However, other wavelengths, both below and above this range, are also possible.  
         [0030]     Similarly, the configuration of chip  202  can vary based upon the general functionality of VCSEL  200 . VCSEL chips can, in general, be manufactured as a wafer of many chips that can then be cleaved into individual chips. As noted above, the specific dimensions of chip  202  can vary depending on the specific application, wavelength, and degree of offset of standoff  206 . It is therefore understood that the specific illustrated embodiments provide examples only, and should not be construed to limit the invention in any way.  
         [0031]      FIG. 3  illustrates an alternate exemplary embodiment of the VCSEL of  FIG. 2 . As with  FIG. 2 ,  FIG. 3  shows a VCSEL  200  that can include a chip  202  that contains a laser emitter  204 . Mounted to chip  202  and optically communicating with laser emitter  204  is a standoff or post  206  that supports a lens  208   a . The standoff  206  facilitates propagation of a laser beam  210  emitted by laser emitter  204  to lens  208   a , while lens  208   a  collimates laser beam  210  and directs it towards an optional external lens  214 . External lens  214  directs beam  210  to a point  212  offset from an axis of laser beam  210  emitted by laser emitter  204 . In this manner, VCSEL  200  can direct laser beam  210  in a path “off axis” to a perpendicular to the surface of chip  202 . By so doing, VCSEL  200  provides greater variability in laser beam path than is capable with the VCSEL shown in  FIG. 1A .  
         [0032]     To aid with controlling the degree of bending or tilting of laser beam  210  relative to the perpendicular to the surface of chip  202 , the lens/standoff combination is not centered directly over laser emitter  204 , but is offset a distance from the center, the distance being identified as by reference “A”. For instance, a longitudinal axis of standoff  206  and the central axis of lens  208   a  are offset from an axis of laser beam  210  emitted from laser emitter  204  before laser beam  210  enters lens  208   a . This offset distance can be from 0 micrometers (μm) to about 200 μm and more preferably from about 50 μm to about 75 μm. This offset allows a laser beam  210  transmitted from laser emitter  204  to be bent or directed at an angle from the perpendicular by lens  208   a , and further directed at an angle by external lens  214 . Lens  208   a  has a slightly different shape, and correspondingly different optical properties, than lens  208  of  FIG. 2 .  
         [0033]     The specific direction of beam  210  shown in  FIG. 3  is arbitrary. As long as beam  210  is directed or tilted at an angle from the perpendicular, beam  210  can be directed to any point around a circumference of laser emitter  204  by placing standoff  206 , lens  208   a , and external lens  214  in appropriate positions. The specific configuration of standoff  206 , chip  202 , and lens  208   a  is similar to the previous discussion with respect to  FIGS. 2A and 2B .  
         [0034]      FIG. 4  illustrates an alternate embodiment of the present invention. In  FIG. 4 , a VCSEL  400  can include a chip  402  that contains a laser emitter  404 . A photodiode  406  or other laser detector can also be located on chip  402 . Mounted to chip  402  and optically communicating with laser emitter  404  is a standoff or post  408  that supports a lens  410 . The standoff  408  facilitates propagation of a laser beam  412  emitted by laser emitter  404  to lens  410 , while lens  410  directs laser beam  412  toward a point  414  offset from an axis of laser beam  412  emitted by laser emitter  404 . In this manner, VCSEL  400  can direct laser beam  412  in a path “off axis” to a perpendicular to the surface of chip  402 . By so doing, VCSEL  400  provides greater variability in laser beam path than is capable with the VCSEL shown in  FIG. 1A . The ranges of offset distances of lens  410  and the angles of beam  412  as it exits lens  410  can be the same as those discussed above with respect to  FIGS. 2A and 2B . Further, although reference is made to lens  410  focusing the beam to a particular point, it can be understood that in other configurations the lens can be designed to focus, collimate, or diverge the laser beam, as desired.  
         [0035]     The photodiode  406  measures a portion of beam  412  that is reflected from lens  410 . Photodiode  406  allows an operator to monitor the laser power from laser  404 . In some embodiments, this power can then be adjusted according to operational requirements to more effectively control operation of laser  404 .  
         [0036]     While the exemplary embodiments shown in  FIGS. 2-4  illustrate a chip with only one active VCSEL region, multiple active VCSEL regions are also possible. One exemplary embodiment of a laser chip having multiple active VCSEL regions is shown in  FIG. 5A , and designated generally as reference numeral  500 . As with the previous embodiments, laser  500  can include a chip  502 . However, in this exemplary embodiment, chip  502  can now include two laser emitters  504   a  and  504   b . Emitters  504   a ,  504   b  correspond to two active VCSEL regions on the single chip  502 . Emitters  504   a ,  504   b  can be operated on the same or different frequencies.  
         [0037]     Mounted to chip  502  and optically communicating with laser emitters  504   a  and  504   b  is a standoff or post (not shown in this view) that supports a lens  508 . The standoff facilitates propagation of a laser beam  510   a  emitted by laser emitter  504   a  and a laser beam  510   b  emitted by laser  504   b , to lens  508 . Lens  508  directs both laser beams  510   a ,  510   b  toward a point  512   a ,  512   b  respectively, offset from an axis of laser beams  510   a ,  510   b  emitted by laser emitters  504   a ,  504   b.    
         [0038]     In this manner, VCSEL  500  can direct both laser beams  510   a ,  510   b  in a path “off axis” to a perpendicular to the surface of chip  502 , without using optical components external to VCSEL  500 . By so doing, VCSEL  500  provides a smaller overall package size than is currently available with the VCSEL shown in  FIG. 1B , and provides greater variability in laser beam path than is capable with the VCSEL shown in  FIG. 1A . Additionally, since two laser beams  510   a ,  510   b  are used, this exemplary embodiment allows laser  500  to be used in a device that can discriminate between motion in a first direction and motion in a second direction. Such devices can include, by way of example and not limitation, optical mice, optical pens, paper sensors, etc.  
         [0039]     To aid with controlling the degree of bending or tilting of laser beams  510   a ,  510   b  relative to the perpendicular to the surface of chip  502 , the lens/standoff combination is not centered directly over laser emitters  504   a ,  504   b , but is offset a distance from the center, the distance being identified as by reference “A”. In one exemplary embodiment, the lasers  504   a ,  504   b  and lens  508  can be spaced such that the offset distance “A” between lasers  504   a ,  504   b  and the center of lens  508  are the same. In alternate embodiments, the offset distance can be different for each laser emitter  504   a ,  504   b.    
         [0040]     This offset allows a laser beam  510   a  transmitted from laser emitter  504   a , and a laser beam  510   b  transmitted from laser emitter  504   b , to be bent at an angle from the perpendicular by lens  508 . In exemplary embodiments, this angle can be from about 10° to about 45° from the perpendicular, although other angles above or below those identified are possible. In one exemplary embodiment, the angle is about 45° from the perpendicular for each beam. The specific direction of the beams shown in  FIG. 5A  is arbitrary. As long as each beam  510   a ,  510   b  is bent at an angle from the perpendicular, the beam can be directed to any point around a circumference of chip  502  by placing the polymer standoff and lens  508  in an appropriate position. However, there is an advantage in having the beams  510   a ,  510   b  perpendicular to each other. When the beams are perpendicular to each other, laser  500  can be used to decode movement in both an x and a y direction. This is very useful in, by way of example and not limitation, an optical mouse application.  
         [0041]     In some embodiments, it is possible to direct both beams  510   a ,  510   b  to a single point, such as, by way of example and not limitation, an optical fiber. In this case, beams  510   a and  510   b  would be operated on different frequencies so that they could be coupled into the same fiber.  
         [0042]     Another alternate exemplary embodiment of a laser with multiple active regions is shown in  FIG. 5B , and designated generally as reference numeral  550 . As with the previous embodiments, laser  550  can include a chip  552 . However, chip  552  can now include three laser emitters  554   a ,  554   b  and  554   c . Emitters  554   a ,  554   b , and  554   c  correspond to three active VCSEL regions on the single chip  552 . Mounted to chip  552  and optically communicating with laser emitters  554   a ,  554   b  and  554   c  is a standoff (not shown in this view) that supports a lens  558 . The standoff facilitates propagation of a laser beam  560   a  emitted by laser emitter  554   a , a laser beam  560   b  emitted by laser  554   b , and a laser beam  560   c  emitted by laser  554   c , to lens  558 . Lens  558  directs all three laser beams  560   a ,  560   b , and  560   c  toward a point  562   a ,  562   b ,  562   c  respectively, offset from an axis of laser beams  560   a ,  560   b  and  560   c  emitted by laser emitters  554   a ,  554   b and  554   c , respectively. As with the previous embodiments, lens  558  can be used to focus, collimate or diverge beams  560   a ,  560   b  and  560   c.    
         [0043]     In this manner, VCSEL  550  can direct all three laser beams  560   a ,  560   b ,  560   c  in a path “off axis” to a perpendicular to the surface of chip  552 , without using optical components external to VCSEL  550 . By so doing, VCSEL  550  provides a smaller overall package size than is currently available with the VCSEL shown in  FIG. 1B , and provides greater variability in laser beam path than is capable with the VCSEL shown in  FIG. 1A . Additionally, since three laser beams  560   a ,  560   b , and  560   c  are now used, this exemplary embodiment allows laser  550  to be used in a device that can discriminate between motions in three different directions. Such devices can include, by way of example and not limitation, optical mice, optical pens, laser scanners used in CD drives, DVD drives, etc. Likewise, as with the embodiment illustrated in  FIG. 5A , all three of the beams can be operated on different frequencies and/or directed to a single point, such as an optical fiber.  
         [0044]     To aid with controlling the degree of bending or tilting of laser beams  560   a ,  560   b ,  560   c  relative to the perpendicular to the surface of chip  552 , the lens/standoff combination is not centered directly over laser emitters  554   a ,  554   b ,  554   c  but is offset a distance from the center, the distance being identified by reference “A”. In one exemplary embodiment, the lasers  554   a ,  554   b ,  554   c  and lens  558  can be spaced such that the offset distance “A” between lasers  554   a ,  554   b ,  554   c  and the center of lens  558  are the same. In alternate embodiments, the offset distance can be different for each laser emitter  554   a ,  554   b ,  554   c . In yet other alternate embodiments, the offset distance can be the same for two of the emitters, and different for the third.  
         [0045]     This offset allows a laser beam  560   a transmitted from laser emitter  554   a , a laser beam  560   b  transmitted from laser emitter  554   b , and a laser beam  560   c  transmitted from laser emitter  554   c , to be bent at an angle from the perpendicular by lens  558 . In exemplary embodiments, this angle can be from about 10° to about 45° from the perpendicular, although other angles above or below those identified are possible. In one embodiment, the angle is about 45° from the perpendicular for each beam. However, different angles for each beam are also possible. The specific direction of the beams shown in  FIG. 5B  is arbitrary. As long as each beam  560   a ,  560   b  and  560   c  is bent at an angle from the perpendicular, the beam can be directed to any point around a circumference of chip  552  by placing the polymer standoff and lens  558  in an appropriate position.  
         [0046]     The embodiments of  FIGS. 2A, 2B ,  4 ,  5 A and  5 B provide the advantage that shorter distances are required to focus the laser beam onto a desired surface. By way of example and not limitation, the overall package height for a package that can use the exemplary embodiments can be less than about 2 mm. In alternate exemplary embodiments, the package height can be 1.5 mm or less. This facilitates the use of these embodiments in low profile devices that cannot physically be built using prior art technology. Such devices can include, by way of example and not limitation, an optical mouse, an optical pen, paper sensors, and other devices that use small lasers to perform various functions.  
         [0047]     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.