GB2199960A - Flexible delivery system - Google Patents

Abstract

A flexible light-guide for infra-red light such as the output of a CO2 laser comprises many short sections of rigid tubing (44) in a material capable of guiding said light such as alumina, in a flexible plastic or rubber tube (45) such as to ensure both close lateral alignment and some overall flexure. Other light guides comprising rigid alumina tubes optionally with infra-red mirrors between tubes are disclosed. Such tubes may be of the same or different diameter and the mirrors may be rotatable. The light guides may be used in endoscopes or periscopes. <IMAGE>

Description

TITLE: METHOD AND APPARATUS FOR GUIDING INFRA-RED LIGHT BACKGROUND TO THE INVENTION The present invention relates to a method and apparatus for guiding infra-red light and in particular to guiding the output from a CO2 laser efficiently from one point to another.

Much effort has been put into developing convenient and efficient methods of transferring the output energy of a CO2 laser, which typically produces tens of watts of Continuous Wave (CW) power at 10.6cm, from the laser head to the point of application of this radiant energy. This is an important requirement in the field of medicine where the concentrated power of the 10.6 > CI beam can be used as an effective scalpel, particularly for internal surgery. The laser head itself is preferably held stationary, whilst the "laser scalpel" should be free to move under the control of the surgeon. In addition, for internal applications, the infra-red beam must pass through a distance typically in excess of 20cms down an endoscope which has a strictly limited cross section.This has proved to be a technically difficult problem to solve in practice primarily because of the unavailability of efficient optical materials at the 10.6p wavelength. These are also required to transmit visible light for alignment purposes. Nevertheless, prior art techniques still employ lenses and mirrors to direct a conventionally focussed beam to the required area, and it is found that in practice, these are both difficult to align and lose in the region of 50% of the initial beam's energy. A further problem is that certain materials which are optlcally suitable (such as ZnSe), are,in fact, toxic and thus of limited value in the medical environment.

OBJECT OF THE INVENTION An object of the invention is to provide a method and apparatus for guiding infra-red energy efficiently from a collimated source to a remote point of application without extensive use of special materials or the need for critical alignment.

Another object of the invention is to provide a flexible path for a directed beam of infra-red energy which, at least in certain forms, may be produced at relatively low cost.

SUMMARY OF THE INVENTION The invention provides in one embodiment apparatus comprising a cylindrical hollow ceramic guide and means for directing the output of a collimated source of infra-red energy to be substantially colinear with the axis and incident on the input aperture of the guide so that in use, energy is transmitted with substantially no loss through the guide to emerge from the output aperture of the guide in substantially collimated form.

The invention also provides in another embodiment apparatus comprising several sections of cylindrical guide arranged to move relative to one another so that in use collimated energy emerging from one section of guide enters another section with no substantial loss and providing a flexible guide or articulated arm.

In further embodiments of the invention the output of one guide may be switched to any one of several guide inputs or more than one guide output may be directed into a particular guide input.

Thus according to one embodiment of the invention, infra-red guiding apparatus comprises source of infra-red energy, imaging means in the path of rays from said source and arranged to form a collimated beam of said energy, said beam having a cross-section of width less than but comparable to a defined dimension; and hollow cylindrical means having an inner bore diameter of said dimension and arranged to be substantially aligned with and receive said collimated beam so that, in use, said beam is substantially guided by said cylindrical means and rays of said beam pass through said cylindrical means at angles of grazing incidence to the inner surface of said cylindrical means, thereby suffering minimal loss of energy and emerging from said cylindrical means in substantially collimated form.

Preferably the cylindrical means comprises at least one ceramic tube of alumina.

Advantageously the source of said energy is a carbon dioxide laser.

The cylindrical means may comprise a plurality of tube sections at least one of which is arranged to be substantially aligned with the collimated beam output from another section and positioned so that the input end of said at least one section is spaced less than five times the inner bore diameter of said another section from the output end of said another section.

The guiding apparatus may include reflecting means positioned in the path of rays travelling from one tube section to a neighbouring tube section said reflecting means being arranged to change the direction of said rays prior to their entry into said neighbouring tube section.

The guiding apparatus may include rotation means for rotating the reflecting means about an axis so that the direction of the beam output from said one tube section may be varied prior to entry into another tube section moveable with respect to said one section.

Alternatively, the output from said one section may be switched by said rotation means to enter one of a number of different tube sections or one of said different tube sections may be selected by said rotation means to pass its output to the input of a particular tube section.

The cylindrical means may comprise a substantial plurality of cylindrical tube sections held in lateral and longitudinal alignment.by a flexible outer sheath so as to provide, in use, a flexible guide for a collimated beam of infra-red energy in which the angle between the rotational axes of symmetry of two adjacent sections does not exceed a few degrees and energy is transferred between said adjacent sections with substantially no loss.

In a preferred embodiment guiding apparatus comprises an endoscope in, which a cylindrical hollow tube section transfers energy from one end to thee other end of said endoscope.

In another preferred embodiment guiding apparatus comprises a plurality of tube sections arranged to move with respect to each other and provided with reflecting means in the path of rays between neighbouring sections so as to provide an articulated arm for guiding infra-red energy.

In a further preferred embodiment guiding apparatus provides a path, coincident with that of the guided energy, for gas to pass through and to the end of the hollow cylindrical means so that, in use, the energy path of the guiding apparatus is maintained free of foreign matter.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 i 1 lu s t r a t e s s cb e m a t i c al ly and in section a cylindrical guide used in accordance with the invention.

Figures 2 and 3 show diagrammatically how two cylindrical guides may be arranged with respect to each other in accordance with the invention.

Figure 4 illustrates how the principles of the invention may be applied to an endoscope.

Figure 5 shows how a mirror may be rotated to transfer energy between a selected pair of cylindrical guides in accordance with the invention.

Figure 6 provides a sectional view of part of a flexible arm constructed in accordance with the invention.

Figure 7 shows in section a flexible guide in accordance with the invention.

Figure 9 illustrates how guides of different diameter may be matched.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The launching of a beam of infra-red energy at 10.6cm is illustrated in Figure 1. A CO2 laser 1 has a collimated output 2 of approximtely 5mms diameter. For a gauss ivan cross section this is assumed to be the width of the beam at its l/e2 energy points.

Lens 3 of focal length 150mRs and lens 4 of focal length 37.5mms transform the beam waist at the output of laser 1 into a narrower beam waste at the input of an alumina tube 5 shown in section with an inner diameter of 2mms. The l/e2 points of this new waist are ideally separated by 0.64 times this inner tube diameter, which gives the best guiding properties with minimal loss of the energy entering the tube. At a beam waist the curvature of the wavefront is zero and thus a gauss ivan coAlimated beam enters tube 5 which acts a a circular waveguide. In the prior art the waveguiding property of alumina tube has been utilised inside the cavity of a CO2 laser as a single straight integral element.The current invention allows an external source to be coupled into a guiding element and extends this to combining several elements in different configurations. In fact the utilisation of alumina cylindrical tube as an efficient transmission device for infra-red energy is only approximately

Small deviations of beam direction and some wave front curvature can be accommodated. The grazing incidence of rays as these are deflected by the inner walls of the tube still provide exceptional efficiency. In the pure guided mode, the energy profile across the section of the tube remains constant and approximately gauss ivan and the output beam 6 emerging from the tube 5 may be considered to have a waist at this point.

Near a beam waist the cross section of a beam changes very slowly according to the function

in which do is the beam diameter at the waist, X is the wavelength of the radiation and Z is the distance from the waist at which the beam's diameter d(Z) is to be derived.

In Figure 2, two cylindrical guides 7 and 8 are shown in the region around their neighbouring ends. In this example the guides have 2 mms inner bore diameter as the tube 5 in Figure 1.

The two parallel lines 9 represent the l/e2 width of the beam emerging from tube 7. At the point of emergence this is yiven by do = 1.28mm (0.64 x tube bore).

Inserting a value of Smms for the end seperation Z and a wavelength of 0.0106 mms ( = 10.6cm) in formula (1) d(Z) = 1.0008 do (2) To all intents and purposes there is no increase in beam width and providing the tube 8 is aligned with beam 9 ( small and aperture in correct path) substantially all the energy will be coupled into tube 8. In practice some angular misalignment can be accommodated. For a lmm bore tube a value for of 20 is found to introduce an energy loss of approximately 0.2%.

The possibility of physical separation between two cylindrical guide sections without any significant loss of energy transfer between them is put to good use in a principle of the invention illustrated in Figure 3 in which a significant change in beam direction is obtained. Infra-red reflecting mirror 10 is introduced in the optical path between guide section 11 and section 12. The three components may be brought sufficiently close together to avoid any significant losses and a nominal 900 bend is introduced in the beam path.

The principle illustrated ip Figure 3 is described in three seperate embodiments of the invention. The first of these is illustrated in Figure 4 which shows in diagrammatic section an endoscope. The basic endoscope consists of an eyepiece 13 comprising a lens assembly 14 which magnifies the end 15 of a coherent optical fibre bundle 16. The other end 17 of the bundle receives an image of the region of interest through a lens 18.

Normally, separate fibres gre used to pipe light down the endoscope to illuminate this region. For clarity these are not shown. An infra-red guiding alumina tube 19 runs alongside the fibre bundle and receives its energy from tube 20 via mirror 21.

require the use of a ZnSe lens focussing the beam of 1U.6 > down a tube of relatively large cross section. Apart from the alignment problems of such an optical arrangement, the sheer bulk makes the instrument unattractive. With a guiding tube of bore lmm an extremely compact instrument may be constructed in accordance with the invention. For instance, a 2mm pediatric cystoscope becomes a practical possibility whilst utilising a CO2 source of energy. A further advantage of the current invention over both the prior art and alternative methods involving the use of solid infra-red light guides based on chalcogenide glasses such as ZnSe, is that the materials used are non-toxic and completely sterilisable.The fact that no transmitting optical components are employed in the infra-red path also means that gas may be passed down this path to provide a simple and hygienic method of keeping the path clear of foreign matter. This can be particularly important when operating in close proximity to tissue and body fluids.

The second embodiment employing an infra-red reflecting mirror in the beam path is illustrated in Figure 5. This shows a four way turret assembly in sectioned plan and side elevation.

A mirror 22 of elliptical outline and set at 450 to an axel 23 which may rotate in a bearing 24 presents a circular cross section to five guides. One of these is in line with axel 23 and is shown as 25 in the elevation. Its end 25A is also partly shown below the cut away mirror section 22A. The bearing 24, guide 25 and the four guides 26, 27, 28 and 29 are all supported by a housing 30. A continuous path for a guided infra-red beam may be completed simply by turning the mirror 22 into the correct orientation to select the combination of guide 25 and anyone of the other four. It will be clear that this may be accomplished by a manual locating mechanism or a motorised control.The turret as illustrated may be used both as a means of switching a single source via guide 25 to a number of alternative destinations or as a means for selecting any one of four sources connected to guides 26 through 29 respectively for onward transmission via a particular path.

A third embodiment of the invention, using plane infra-red reflecting mirrors in the path of the beam between guide elements, is shown in Figure 6 and forms part of an articulated arm allowing the transfer of CO2 laser radiation. The assembly illustrated is the so called "wrist" and provides a high degree of mobility.

Energy is piped through guide section 31 into swivel subassembly 32. Sub-assembly 32 may be rotated around guide 31 which is provided 'with a miniature bearing 33 (shown in section) for this purpose. Mirror 34 is set at 450 to the beam emerging from guide 31 and deflects this energy into a short guide section 35 which forms part of sub assembly 32. Bearing 36 allows subassembly 37, similar to sub-assembly 32, to rotate about guide 35 and mirror 38 deflects the beam into guide section 39. Subassembly 40 which can rotate about bearing 41 introduces a final 900 bend in the beam via mirror 42 and completes the "wrist" assembly, so that the output guide 43 has the ability to point in any direction.

In figure 2, two sections of guide are illustrated to have both physical separation and some directional misalignment without incurring any substantial transmission losses. This property of the cylindrical guide section is utilised by an embodiment of the invention illustrated in Figure 7. A flexible guide is provided by abutting end-to-end a large number of short sections of alumina cylindrical guide 44. These are held in longitudinal and lateral position with respect to each other by a flexible outer sheath 45 made of a plastic or rubber material.

Each section transfers the guided energy efficiently to its neighbour and, given less than fifty short sections of lmm bore alumina, a 900 bend may be introduced whilst transmitting in excess of 90% of the energy launched into the flexible guide assembly, each section being misaligned with its neighbour by no more than two degrees.

In practical systems it is frequently a requirement that guides of different internal bore sizes be used together. An embodiment of the invention which allows transfer of guided energy from a guide section to one of half its internal bore size in a compact assembly is illustrated in Figure 8.

2 A 2mm inner bore guide 46 provides a beam (1/e2 rays shown as lines 47) of 1.28 mms, approximate diameter. A concave mirror 48 positioned Smms away from guide 46 and having a focal length of about 15mms is positioned in the beam at an angle of incidence of approximately 140. The beam converges onto a second convex mirror 49 having a focal length of about 8 mms and placed at approximately this distance from mirror 48 and at the same angle of incidence to the beam. A new beam waist is formed at about Smms from the second mirror 49 having half the diameter of the waist which is found at the end of guide 46. A lmm inner bore guide 50 is aligned with the reduced beam and its end positioned at the new waist for maximum efficiency.Enclosure 51 maintains all components in their respective positions and provides a sealed environment.

Figures 1 to 8 illustrate only some of the many possible embodiments of this invention. For instance, in Figure 1 a straight guide section 5 is illustrated. In practice a small bend may be introduced in a single long section of tubular guide, without discernable loss of power transmitted. In the Figure 2 description the loss introduced by separating guide sections 7 and 8 by 5 mms is -calculated. In practice a separation of 2cms between guide sections with a 2mm inner bore has been found to be acceptable.

The beam launch mechanism of Figure 1 utilises two positive lens components in'the form of a Keplerian telescope. It will be clear that alternative combinations of positive and negative lens or reflecting components are equally possible. Although a waist in the guided beam is ideally formed at the input of the guide to have dimensions which match the ideal for the particular guide, it is found in practice that changes in convergence of the beam prior to entry into the guide section can result in a modified beam profile on emergence from the guide, and may, in fact, provide a more concentrated output than the normal l/e2 points,at 0.64 of the guide diameter, would suggest.

The endoscope illustrated in Figure 3 has the optical viewing axis displaced from the CO2 guide section axis. It is possible to combine infra-red reflecting mirrors in the form of a periscope, one mirror of which would be transparent to the visible light viewed through the fibre optic system. This would allow the CO2 beam to be made colinear with the viewiny axis.

Secondly, whilst magnifying reflecting components are illustrated in Figure 8 such optics may be used in a periscope near the point of application to further concentrate the applied energy.

The turret assembly of Figure 5 may be used in combination with further multiport assemblies to select one of a number of sources and direct this selection to one of several destinations.

A complete articulated arm assembly would require further straight guide sections and swivel joints to provide "shoulder" and "elbow" joints in addition to the wrist illustrated in Figure 6.

In summary, the current invention provides a highly flexible means of transferring an infra-red collimated beam from a source to a remote point of application. It can provide this facility whilst using throughout non-toxic and completely sterilisable materials. Transmitting optical components are not required in the guided beam path and this provides the opportunity to pass gas down the entire length of this path keeping it clear of unwanted foreign matter.

Although certain embodiments described have related to medical applications, other application areas such as robot welders, engraving or other machining applications will benefit by applying the principles of this invention.

Claims (3)

1. An apparatus for providing the flexible delivery of infra red light from a suitable optical source to a distance point utilising a multiplicity of short sections of rigid tubing, the latter being held closely together through bonding to or containment in an outer sleeve of semi flexible rubber or plastic thus providing modest flexure between each rigid section whilst maintaining lateral alignment of the end aperture of any one tube section with the entrance aperture of the next section.

2. An apparatus as claimed in claim 1 utilising ceramic tubing, for example alumina.

3. An apparatus as substantially described herein with reference to figure 1.