OPTICAL APPARATUS

Abstract: Apparatus for the projection of a light beam onto a target comprises a light source (10) such as a laser or an arc lamp, a light guide such as an optical fibre (12) and focusing means (20). The focusing means (20) is at the output end of the light guide (12) and includes a diffractive optical element (24). The apparatus is particularly useful in the activation of tissue adhesive.

Description: Title - Optical Apparatus This invention relates to an optical apparatus, in particular to apparatus for use in the projection of a light beam onto a target. An important application of such apparatus is for directing light from an intense light source onto a photo-activatable tissue adhesive with sufficient intensity to bring about polymerization of the adhesive. Sealants and adhesives for the in vivo bonding of living tissues are known. Typically such adhesives comprise protein solutions which are cross-linked by heating. Heat energy can be transferred to the proteins by incorporating into the adhesive a photon-absorbing material and exposing the adhesive to light of sufficiently high intensity. The amount of energy required to reach temperatures high enough for curing of the adhesive to occur necessitates the supply of a large number of photons of radiation within the absorption spectrum of the photon- absorbing material. It is also generally the case that the light beam which is used in such application be of very small dimensions. In a typical set up for the curing of a tissue adhesive, an intense light source such as a laser is used to generate a beam of light which is carried along a flexible optical fibre. The end of the optical fibre is fitted with a handpiece which is used to focus the output light beam onto the target tissue. In use, the handpiece is held by the surgeon and manipulated such that the light beam is directed at the tissue to which adhesive has been applied, operation of the apparatus typically being controlled by means of a foot pedal or the like. The light beam is typically focused by lenses in the handpiece at a point a few centimetres from the end of the handpiece. A disadvantage of known arrangements of the type described above is that it may be difficult for the surgeon to maintain the handpiece in such a position that the target tissue is precisely at the focal point of the output beam. As a result the intensity of the irradiation at the target may be less than desired. In addition, the light beam will normally be focused into a circular spot, which may not be the most appropriate form of illumination for the target. There has now been devised apparatus for the projection of a light beam onto a target which overcomes or substantially mitigates the above-mentioned disadvantages. According to the invention, apparatus for the projection of a light beam onto a target comprises a light source, light guide means adapted to conduct light from the light source to the vicinity of the target, and focusing means at an output end of said light guide means, said focusing means including a diffractive optical element. The apparatus according to the invention is advantageous primarily in that the use of a diffractive optical element allows the output light beam to be focused into a spot (or, indeed, two or more spots) of any desired shape and size. In addition, by appropriate design of the diffractive optical element, it may be possible to focus the light beam over a range of distances, allowing greater tolerance in the positioning of the light beam with respect to a target. For many applications, the focusing means is preferably housed within a hand-piece which is of such a size and shape that it can be readily manipulated by a user. Such a handpiece may typically be cylindrical, with a length of, say, 15cm and a diameter of the order of 2cm. In some cases, however such a handpiece may not be necessary, the focusing means including the diffractive optical element being applied directly to the end of the light guide means. Preferably, the diffractive optical element is used in conjunction with a refractive optical element, ie a lens. In such an arrangement the diffractive optical element is preferably provided on one face of the lens. In a particularly preferred arrangement, the diffractive optical element is applied to the planar face of a plano-convex lens. The diffractive optical element may be fabricated by methods known per se for the manufacture of such components. Most preferably, the diffractive optical element is made of silica, though other materials may be used, including plastics materials. The diffractive optical element most preferably comprises an array of discrete cells, eg a square array, the properties of the element being determined by the relative thicknesses of the cells. Where the light source is monochromatic the diffractive optical element may have a relatively simple structure comprising cells each with one of a small number of discrete thicknesses. Where the light beam is polychromatic the structure may be more complex, the thicknesses of the individual cells being quantised into a larger number of discrete values, eg sixteen discrete thicknesses, for instance in order to correct chromatic aberrations. Any suitable light source may be used, provided that light of sufficient intensity is generated for the application for which the apparatus is to be used. The light source may be a laser light source, or may be a polychromatic light source, eg an arc lamp. The light guide means most preferably comprises an optical fibre, which may in general be of conventional form. For many applications, the optical fibre will have a length of from about one to three metres. In order to maximise energy input into the optical fibre it preferably has a relatively high numerical aperture NA=sinΘ, where Θ is the semi-angle of the acceptance cone at the end plate of the optical fibre. Preferably, the numerical aperture is greater than 0.49. Such a numerical aperture can be attained with a glass fibre. A single fibre may be used, or a bundle of fibres. The optical fibre, or bundle of fibres, is most preferably contained within a protective sheath, which is most commonly of plastics material. For many applications, it is desirable that the light guide means be flexible. Although described herein principally in connection with the curing of tissue adhesive, the apparatus according to the invention may be used in a variety of other applications. Other medical applications include endoscopy and other applications in which lasers or other intense light sources are conventionally used, such as biostimulation, photodynamic therapy, curing of dental materials, cosmetic methods of tattoo or hair removal, and minimally invasive surgery. Other applications include curing of materials such as semiconductor photoresists and industrial adhesives, and research applications in photochemistry, spectroscopy and microscopy. The invention will now be described in greater detail, by way of example only, with reference to the drawings, in which Figure 1 is a schematic view of apparatus in accordance with the invention, for the curing of photo-activatable tissue adhesive; Figure 2 is a sectional view on a larger scale of a handpiece forming part of the apparatus of Figure 1; Figure 3 is a schematic representation of the face of a diffractive optical element used in the handpiece of Figure 2; Figure 4 is a schematic cross-sectional view (not to scale) of the diffractive optical element of Figure 3; Figure 5 is a simulated view of the face of the diffractive optical element, the depths of the individual cells making up the element being represented on a grey scale, the darker colours representing greater thicknesses. Referring first to Figure 1, apparatus for delivering an intense light beam to a site at which two living tissues are to be bonded together comprises generally a light source unit 10, an optical fibre tube 12 and a hand-piece 14. The apparatus is used to direct light of sufficient intensity onto tissue adhesive applied to the junction of two living tissues. The light source unit 10 includes an intense light source, which may be a laser light source or a polychromatic light source. In the latter case, appropriate filtering means will generally be provided to limit the light which is transmitted by the optical fibre tube 12 to a parti cular bandwidth. Appropriate optical components will also be provided to direct the light beam onto the end plate of an optical fibre which is housed within the optical fibre tube 12. The light beam is transmitted along the optical fibre to the handpiece 14 by which it is focused in the manner described below. In use, a surgeon applies adhesive to tissues which are to be bonded, and brings those tissues into contact. Holding the handpiece 14, the surgeon then uses it to apply light to the adhesive. For ease of use, a foot pedal may be provided by which the surgeon can increase the light output to full power. Application of high intensity light is continued for sufficient time to effect curing of the adhesive. Figure 2 is a schematic sectional view of the handpiece 14. The optical fibre tube 12 terminates within the handpiece 14, 15mm from a hybrid optical element 20. The optical element 20 consists of a refractive plano-convex lens 22, the plane face of which is bonded to a diffractive optical element 24. The lens 22 has a focal length of 15mm, a thickness of 3.8mm, and an effective aperture of 10mm. The diffractive optical element 24 (shown schematically in more detail in Figures 3 and 4) has an effective aperture of approximately 7.5mm and comprises an array of square cells (see Figure 3) which are built up on a silica substrate approximately 1mm in thickness. In reality, the array comprises 1024x1024 cells, for clarity a much smaller number being depicted in Figure 3. Each cell is 7.5 μm square and has a thickness chosen such that the overall diffractive optical element 24 focuses the light beam in the desired manner. Figure 4 shows a typical cross-section (in arbitrary units and not to scale) of one vertical row of cells (the actual number of discrete thicknesses shown corresponding to the number of cells shown in Figure 3 and not to the actual number of 1024). Figure 5 is a pictorial representation of the face of the diffractive optical element 24, in which each cell is shown with one of sixteen thickness levels, the greater thicknesses being represented by the darker tones on the grey scale shown at the right of the Figure. The form of the diffractive optical element 24 may be such as simply to focus the light beam to a spot at a fixed distance from the diffractive optical element 24. Such a distance may be typically 100mm. Other forms of diffractive optical element may confer on the spot a particular shape, eg the spot may be rectangular. Still other forms of diffractive optical element may be used to provide a focal range, rather than a single focal length, thereby providing greater tolerance in the positioning of the handpiece 14 relative to the target tissues.

Claims: Claims 1. Apparatus for the projection of a light beam onto a target, said apparatus comprising a light source, light guide means adapted to conduct light from the light source to the vicinity of the target, and focusing means at an output end of said light guide means, said focusing means including a diffractive optical element. 2. Apparatus as claimed in Claim 1, wherein the focusing means is housed within a hand-piece which is of such a size and shape that it can be readily manipulated by a user. 3. Apparatus as claimed in Claim 2, wherein the handpiece is cylindrical. 4. Apparatus as claimed in any preceding claim, wherein the focusing means including the diffractive optical element is applied directly to the end of the light guide means. 5. Apparatus as claimed in any preceding claim, wherein the diffractive optical element is used in conjunction with a lens. 6. Apparatus as claimed in Claim 5, wherein the diffractive optical element is provided on one face of the lens. 7. Apparatus as claimed in Claim 6, wherein the diffractive optical element is applied to the planar face of a plano-convex lens. 8. Apparatus as claimed in any preceding claim, wherein the diffractive optical element comprises an array of discrete cells, the properties of the element being determined by the relative thicknesses of the cells. 9. Apparatus as claimed in any preceding claim, wherein the light guide means comprises an optical fibre. 10. Apparatus as claimed in Claim 9, wherein the optical fibre has a length of from about one to three metres. 11. Apparatus as claimed in Claim 9 or Claim 10, wherein the optical fibre has a numerical aperture greater than 0.49. 12. A method for the bonding together of living tissues, which method comprises applying a photo-activatable tissue adhesive to at least one of the tissues to be bonded, bringing said tissues into contact, and projecting light onto the adhesive using apparatus according to any preceding claim.

Inventors: MOLLOY JAMES OSCAR, STEWART DOUGLAS ALASTAIR, MOLLOY, JAMES, OSCAR, STEWART, DOUGLAS, ALASTAIR
Applicants: MOLLOY JAMES OSCAR, STEWART DOUGLAS ALASTAIR, TISSUEMED LTD, MOLLOY, JAMES, OSCAR, STEWART, DOUGLAS, ALASTAIR, TISSUEMED LIMITED
Application year: 2000
Main classification: A61B18
IPC codes: A61B17, A61B18, A61C5, A61C13, B23K26, G02B5, G02B6, G02B13