POWER MONITORING ARRANGEMENT FOR BROKEN FIBER DETECTOR

Abstract: A method for monitoring power of laser-light delivered by an optical fiber from a laser to an optical system is disclosed. The optical fiber has a delivery-end from which the laser-light is delivered and the optical system has a lens axially spaced apart from the optical fiber. A detector is positioned facing the space between the delivery-end of the optical fiber and the lens such that it can not directly receive laser-light reflected or scattered by the lens but indirectly receives a portion of laser-light via multiple reflections from the lens the delivery end of the optical fiber or a housing in which the lens and the delivery end of the optical fiber are located. The received light provides a signal representative of the power of laser-light delivered by the optical fiber. This signal can be electronically compared with a reference level either predetermined or monitored at an input end of the fiber. A change in the comparison can be interpreted as an indication of a break in the optical fiber. The detector arrangement is small enough that it can be easily incorporated in a surgical laser handpiece.

Description: POWER MONITORING ARRANGEMENT FOR BROKEN FIBER DETECTOR Inventors: Nubar S. Manoukian and Edward D. Reed Jr. PRIORITY This application claims the benefit of U.S. Provisional Application No. 60/147,562, filed August 6, 1999, and entitled: POWER MONITORING ARRANGEMENT FOR BROKEN FIBER DETECTOR. TECHNICAL FIELD OF THE INVENTION The present invention relates in general to verifying integrity of an optical fiber delivering laser- light from a source thereof to apparatus or a site at which the laser- light is to be used. The invention relates in particular to an arrangement for determining the power of laser-light exiting an optical fiber at the delivery-end thereof. DISCUSSION OF BACKGROUND ART Optical fibers are used extensively in medical laser systems for delivering light from a laser to a site to be treated or to an optical system for shaping or focusing the laser- light for purposes of the treatment. In many such systems the delivery-end of an optical fiber is connected to a handpiece used by an operator of the system to direct the laser- light. The handpiece may incorporate at least a simple optical system for focusing, shaping or further directing laser-light exiting the optical fiber. One well-known principle which is used in prior-art arrangements for detecting fiber breakage or damage is to monitor the power of laser- light at the delivery-end of the optical fiber. The monitored power is compared electronically either with power monitored at the entrance-end of the optical fiber or with a predetermined reference level representative of power delivered by the optical fiber in an undamaged condition. One particular problem in measuring power at the delivery-end of an optical fiber incorporated in a handpiece, of course, is finding sufficient space for a sampling arrangement to divert a portion of the light exiting the optical fiber for measurement purposes. By way of example, prior-art arrangements have included a beamsplitter to divert a portion of the delivered light to a detector for monitoring. In another arrangement, what might be described as a scraping arrangement, an aperture stop in the path of the delivered light is used for selecting a portion of light to be measured. This latter arrangement is disclosed in U.S. Patent 4,556,875. Even where space is available in a handpiece for such arrangements, a problem in using such arrangements may result from variations in form or polarization of a beam of laser-light exiting the optical fiber. Such variations result from changes in the form and amount of bends in the fiber which occur as the handpiece is used by the operator. Such variations in form and polarization of an exiting beam could result in significant variations in detected power, even without damage or breakage of the fiber. This in turn, could result in false indication of damage or breakage. There is a need for an arrangement for monitoring power in a beam of light exiting an optical fiber which is small enough to be accommodated in a handpiece or the like and is insensitive to shape and polarization variations in the exiting beam. SUMMARY OF THE INVENTION The present invention is directed to a method and apparatus for monitoring power of laser-light delivered by an optical fiber from a laser to an optical system. The optical fiber has an output end from which the laser-light is delivered and the optical system has a lens axially spaced apart from the optical fiber. The power monitoring method comprises positioning a detector facing the space between the optical fiber and the optical element such that the detector can not directly receive laser-light reflected or scattered by the lens. Instead, the detector indirectly receives a portion of reflected or scattered laser-light via multiple reflection events. The received light provides a signal representative of the power of laser-light delivered by the optical fiber. In one example of the inventive method, the multiple reflection events occur, inter alia, via reflection or scattering from an end face of the optical fiber, a wall of a housing in which the lens and the delivery-end of the optical fiber are located, and the lens itself. The detector is in optical communication with the space between the lens and the optical fiber via an aperture in the wall of the housing. The detector is arranged with respect to the aperture such that laser-light reflected or scattered from the lens can not reach the detector directly. The lens and the optical fiber are sufficiently closely spaced that the lens collects all laser-light delivered by the optical fiber under any variations of beam-shape of the delivered laser- light resulting from changes in the path or form of the optical fiber to the optical system. This, together with preventing the detector from receiving direct reflection or scatter from the lens, minimizes the effects of such variations in beam shape. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, schematically illustrate a preferred embodiment of the present invention, and together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention. FIG. 1 schematically illustrates a diode-laser system for treating age-related macular degeneration, the system including a optical assembly attachable to a slit lamp microscope and an optical fiber for delivering laser-light from a diode-laser array to an optical system contained in the optical assembly, the optical assembly including one embodiment of a power monitoring arrangement in accordance with the present invention. FIG. 2 is a side-elevation view, partly in cross-section, of an optical fiber connected to a lens-cell incorporated in the optical assembly of FIG. 1, schematically illustrating details of the power monitoring arrangement of FIG. 1. FIG. 3 is an end-elevation view schematically illustrating details of the lens-cell of FIG. 2. FIG. 4 is a three-dimensional view schematically illustrating further details of the lens-cell of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION Turning now to the drawings, wherein like components are designated by like reference numerals, FIG. 1 schematically illustrates a diode- laser system 10 for treating age-related macular degeneration. System 10 includes a diode-laser array package 12 providing laser-light at having a wavelength of 689 nanometers (nm) . This laser-light is the light used for treatment . Laser-light from a diode-laser array package 12 is transmitted by an optical fiber 16 to a beam- conditioning and control unit 20. Control unit 20 includes means for attenuating the treatment laser- light, and means for monitoring power in the treatment laser-light. A diode-laser (not shown) located in control unit 20 provides laser-light at a wavelength of about 635 nm. This 635 nm laser-light is used for beam-aiming purposes. Control unit 20 includes means for combining aiming and treatment laser-light along a common optical path, and means for focusing the combined aiming and treatment light into an optical fiber 22. Control unit 20 also includes monitoring and control circuitry necessary for operating the system. Optical fiber 22 transports the aiming and treatment laser-light to an assembly 24 having an enclosure 26. Assembly 24 includes a lens-cell 28 located in enclosure 26. Lens-cell 28 includes an optical system 30 including one or more lenses or lens-elements. Only first and last lenses 32 and 34 respectively, are illustrated in FIG. 2. Lens 32 immediately follows optical fiber 22 in the direction of light transmitted thereby (illustrated schematically by dotted line 36) . Light passing through lens 34 is directed by a 45 degree mirror 38 to an eye 40 being treated. Mirror 38 is selectively-reflective for treatment and laser-light wavelengths and transmissive for other visible light wavelengths . Aiming and treatment are observed by operator 42 through mirror 38 as indicated by dotted line 44. A monitoring arrangement 50 in accordance with the present invention is located in assembly 24. The monitoring arrangement includes a detector 52 situated generally between the exit-end (delivery- end) of optical fiber 22 and lens 32, but entirely out of the path of light exiting optical fiber 22. Detector 52 is electrically connected by leads 54 (only one thereof shown for clarity) to control unit 20. Optical fiber 22 and leads 54 are gathered within an umbilical sheath indicated in FIG. 1 by lines 56. Turning now to FIGS 2, 3, and 4, with particular reference to FIG. 2, details of monitoring arrangement 50 are illustrated. Here, lens-cell 28 includes a body portion 28A. Extending from body portion 28A is a connector portion 28B. A bore 29 extends axially through connector portion 28B into body portion 28A. A further bore 31 extends from bore 29 through body portion 28A. Lens 32 is located in bore 31. Exit (distal) end 22A of optical fiber 22 is surrounded by a sheath 23. Exit face 22B of optical fiber 22 is flush with end face 23A of sheath 23. Distal end 22A of optical fiber 22 and its surrounding sheath 23 are inserted into bore 29 such that end face 23A of the sheath is separated from surface 32A of lens 32 by a distance equal to about the diameter of bore 29. A space 60 between end face 23A of the fiber sheath is enclosed by the end fiber sheath and the walls of bore 29. As such, space 60 may be designated as a chamber or enclosure. Another bore 62 extends transversely through body portion 28A of lens-cell 28 into enclosure 60. Detector 52, preferably a silicon photodiode, is aligned with bore 62 and has optical access to enclosure 60. Detector 52 is electrically isolated from lens-cell 28 by an insulator 53. In one example of dimensions of the optical fiber/lens-cell arrangement of FIG. 2, lens 32, and sheath 23 have a diameter of about 3.0 millimeters (mm) and bores 29 and 31 are correspondingly sized. Optical fiber 22 has a diameter of about 200 micrometers (μm) . The cone of divergence of laser- light exiting optical fiber 22 has a half-angle of about 8 degrees, i . e . , a numerical aperture of about 0.14. The relatively close spacing of exit-face 22B of optical fiber 22 and lens 32 combined with a relatively large ratio of lens diameter to fiber diameter provides that lens 32 can collect all laser- light exiting optical fiber 22 under all anticipated variations of beam-shape resulting from changes in the path or bending of optical fiber 22 between assembly 24 and control unit 20. Although, here, arranged as an assembly attachable to a slit-lamp microscope, assembly 24 has general dimensions of a laser-delivery handpiece. Some proportion of laser-light exiting optical fiber 22 and passing directly through lens 32 is reflected or scattered from faces 32A and 32B of the lens or from sides of the lens, back into enclosure 60, for example, as indicated schematically in FIG. 2 by dotted line 37. In enclosure 60 laser-light reflected or scattered from the lens is in turn reflected or scattered from walls of bore 29 and/or end face 23A of sheath 23. Reflections from the walls of the bore and from the sheath may be specular or diffuse reflections. For purposes of this description and the appended claims these multiple scattering diffuse and specular reflections events are referred to collectively hereinafter simply as reflections. It has been found that a sufficient amount of this multiply-reflected light reaches detector 52 via bore 62 that the detector provides a signal of sufficient strength to be used for determining the power of laser-light exiting the fiber. Further, it has been found that the strength of the signal is insensitive to changes in the path or bending of optical fiber 22 between control unit 20 and assembly 24. It is believed that the insensitivity of the monitored signal to changes in the path or bending of optical fiber results from the particular arrangement of the detector with respect to exit face (end face) 22B of the optical fiber and lens 32. Those skilled in the art will recognize from the description provided herein that this arrangement prevents detector 52 from receiving, directly, any light specularly reflected, diffusely reflected, or scattered from lens 32, as the detector is positioned out of any direct line of sight with the lens. By directly, here, of course, is meant proceeding from the lens to the detector without intermediate spectral reflection, diffuse reflection or scattering. Light proceeding indirectly from the lens to the detector via above-discussed multiple reflections is believed not to be significantly affected by changes in the path or bending of optical fiber. This results from the above-discussed close spacing of the delivery-end of the fiber which ensures that all light emitted by the fiber is incident on lens 32 under all anticipated variations of beam-shape resulting from changes in the path or bending of optical fiber 22 between assembly 24 and control unit 20. In exemplary system 10, power to be monitored may range from a lowest value of 1.5 mW for the aiming laser-light to a highest value of about 400 mW for the treatment laser-light. It is desirable to be able to monitor power of the aiming laser-light, as this provides a means of determining the integrity of optical fiber 22 before treatment is initiated. Monitoring power of treatment laser-light, of course, enables damage to optical fiber 22 to be determined in the course of treatment . The amount of multiply reflected or scattered light can be increased by omitting an antireflection coating from one or more of faces 32A and 32B of lens 32. This can be effective in providing a greater signal for monitoring lower power levels. It has been found, for example, that omitting a coating from surface 32B is particularly effective in this regard. It has also been found that omitting an antireflection coating from surface 32B of lens 32 can be done without noticeably compromising optical performance of system 10. Those skilled in the art may devise other optical coating schemes, such as using "partially effective" reflection-reducing coatings which reduce reflection less than is usual in the art, or even by using coatings which slightly increase the reflection of a lens surface, without departing from the spirit and scope of the present invention. Regarding electronically processing the signal from detector 52 for the purpose of using monitored power to indicate optical fiber damage, this may be done by comparing monitored power with power monitored at the entrance (proximal) end of optical fiber 22, or by comparing the monitored power with predetermined reference levels. In one preferred arrangement of system 10, for example, damage is determined by comparing power monitored by detector 52 with a electronic gain value which can be calibrated or adjusted to provide that a standard reference level is established which is independent of optical fiber and optical system variations which may be encountered in assembly or operation of the system. Control unit 20 also includes an automatic range-switching arrangement for accommodating the relatively very large power difference between the aiming laser-light and the treatment laser-light. This enables essentially continuous monitoring of the integrity of optical fiber 22 before, during, and after treatment without operator intervention. It should be noted here that in the description provided above, details of other elements of an optical system in handpiece 24 have been omitted as such details are not necessary for understanding principles of the present invention. In the example of system 10, the lens system is a zoom-lens system having a total of four elements, including movable elements. Lens-element 32 is a fixed element of that zoom-lens system. other fixed and movable elements (not shown) are mounted in arms 28D and 28E extending from body portion 28A of lens-cell 28. It is believed that none of these other elements provides a significant contribution to light which reaches detector 52. Accordingly, the inventive power-monitoring method is applicable to any optical- system which has at least one lens or lens-element arranged relative to a delivery fiber and detector as exemplified in the arrangement of FIG. 2. It is also emphasized that while the present invention is described above in terms of monitoring laser-light at wavelengths of 635 and 689 nm, the monitoring arrangement of the present invention is not limited to these wavelengths. The present invention is described above with reference to a preferred and other embodiments. The invention, however, is not limited to the embodiments described and depicted herein. Rather, the invention is limited only by the claims appended hereto.

Claims: WHAT IS CLAIMED IS: 1. A power monitoring arrangement for monitoring laser- light delivered by an optical fiber from a laser to an optical system, the optical fiber having an delivery-end from which the laser-light is delivered and the optical system having a lens axially spaced apart from the delivery-end of optical fiber, the laser-light following a path from the delivery-end of the optical fiber to the lens, the invention comprising: a detector located out of the path of laser-light proceeding from the delivery-end of optical fiber to the lens and facing the space between the optical fiber and lens, the delivery-end of the optical fiber, the lens- element and said detector being arranged such that a portion of laser-light being reflected from the lens element is indirectly received by said detector, thereby providing a signal representative of the power of laser-light exiting the optical fiber. 2. The power monitoring arrangement of claim 1, wherein said detector faces said space in a direction transverse to the path of laser-light proceeding from the delivery-end the of optical fiber to the lens . 3. The power monitoring arrangement of claim 1, wherein said detector is arranged such that it can not receive said reflected light directly from said lens. 4. The power monitoring arrangement of claim 1, wherein said lens has an uncoated surface facing the delivery-end of the optical fiber. 5. The power monitoring arrangement of claim 1, wherein said lens, on a surface thereof facing the delivery-end of the optical fiber, has a coating for increasing the reflectivity of said surface . 6. The power monitoring arrangement of claim 1, wherein said lens, on a surface thereof facing the delivery-end of the optical fiber, has a coating for reducing the reflectivity of said surface. 7. The power monitoring arrangement of claim 1, wherein said spacing between the delivery- end of the optical fiber and said lens is sufficiently close that said lens collects all laser- light delivered by said optical fiber under all anticipated variations of beam-shape of the delivered laser-light resulting from changes in the path of said optical fiber to said optical system. 8. An optical system including one or more lenses and arranged to receive laser-light from a laser via an optical fiber, comprising: a housing in which at least a first of said lenses is mounted, said housing arranged to receive an end of said optical fiber from which said laser-light is delivered, said first lens being axially spaced apart from said delivery- end of the optical fiber in the path of light delivered therefrom, said delivery-end of the optical fiber, said lens-element and said wall being arranged such that laser-light being reflected from said first lens element is further reflected from at least one of said delivery-end of the optical fiber, said first lens and said housing; and a detector facing said space between said delivery-end of the optical fiber and said first lens and arranged to receive a portion of said further reflected laser-light thereby providing a signal representative of the power of laser- light exiting the optical fiber. 9. The optical system of claim 8, wherein said housing includes a wall partially surrounding said space between said end face and said first lens, said wall having a aperture therein, said detector being in optical communication with said space via said aperture for receiving said portion of said further reflected laser-light. 10. The optical system of claim 9, wherein said wall and said aperture therein are arranged such that said detector can not receive reflected laser-light directly from said first lens. 11. The optical system of claim 8, wherein said lens has an uncoated surface facing said end face of said delivery-end of the optical fiber. 12. The optical system of claim 8, wherein said lens, on a surface thereof facing said delivery-end of the optical fiber, has a coating for increasing the reflectivity of said surface. 13. The optical system of claim 8, wherein said lens, on a surface thereof facing said delivery-end of the optical fiber, has a coating for reducing the reflectivity of said surface. 14. The optical system of claim 8 wherein said spacing between said delivery-end of the optical fiber and said lens is sufficiently close that said lens collects all laser-light delivered by said optical fiber under all anticipated variations of beam-shape of the delivered laser- light resulting from changes in the path of said optical fiber to said optical system. 15. In an arrangement for delivering laser- light from a laser to an optical system via an optical fiber, the optical fiber having an input end into which laser-light from the laser is directed and an delivery-end from which the laser-light is delivered to the optical system, the optical system being located in a housing having a lens axially spaced apart from the delivery-end of the optical fiber, the laser- light following a path from the delivery-end of the optical fiber to the lens, a method of detecting a break in the optical fiber, comprising the steps of: (a) positioning a detector facing the space between the delivery-end of the optical fiber and the lens such that said detector can not directly receive laser-light reflected by the lens but indirectly receives a portion of laser- light via multiple reflection events, the received light providing a first signal representative of the power of laser- light exiting the optical fiber; and (b) interpreting a change in said first signal relative to a reference level as indicative of a break in the optical fiber. 16. The method of claim 15, wherein said reference level is provided by a second signal derived from monitoring a portion of the laser-light directed into the optical fiber at the delivery-end thereof . 17. The method of claim 15, wherein said reference level is a fixed predetermined reference level . 18. A method for monitoring power of laser- light delivered by an optical fiber from a laser to an optical system, the optical fiber having a delivery-end from which the laser-light is delivered and the optical system having a lens axially spaced apart from the optical fiber, the method comprising: (a) positioning a detector facing the space between the delivery-end of the optical fiber and the lens such that said detector can not directly receive laser-light reflected by the lens but indirectly receives a portion of laser- light via multiple reflection events, the received light providing a first signal representative of the power of laser- light delivered by the optical fiber.

Inventors: MANOUKIAN NUBAR S, REED EDWARD A, MANOUKIAN, NUBAR, S., REED, EDWARD, A.
Applicants: COHERENT INC, COHERENT, INC.
Application year: 2000
Main classification: G01M11
IPC codes: A61B17, A61B18, A61F9, A61N5, G01J1, G01M11