OPTICAL ENDOSCOPE

Abstract

The invention relates to an optical endoscope (1) comprising an optical fiber element (2) with a proximal end (3) and a distal end (4), wherein an optical waveguide block (6) is arranged at the distal end (4) of the optical fiber element (2), the optical waveguide block (6) comprising a rigid material with two or more optical waveguides (7) formed therein.

Claims

1. An optical endoscope (1) comprising an optical fiber element (2) with a proximal end (3) and a distal end (4), wherein an optical waveguide block (6) is arranged at the distal end (4) of the optical fiber element (2), the optical waveguide block (6) comprising a rigid material with two or more optical waveguides (7) formed therein.

2. The optical endoscope (1) of claim 1, wherein the two or more optical waveguides (7) are integrally formed with the rigid material of the optical waveguide block (6).

3. The optical endoscope (1) of claim 1 or 2, wherein the two or more optical waveguides (7) are formed by parts of the rigid material having a higher refractive index than the surrounding parts.

4. The optical endoscope (1) of any one of the preceding claims, wherein the two or more optical waveguides (7) are obtained by ultrafast laser inscription.

5. The optical endoscope (1) of any one of the preceding claims, wherein the rigid material is optically transparent at the operating wavelength of the optical endoscope (1).

6. The optical endoscope (1) of any one of the preceding claims, wherein the rigid material comprises a glass, a polymer and/or a semiconductor.

7. The optical endoscope (1) of any one of the preceding claims, wherein each of the two or more optical waveguides (7) comprise one end facing the optical fiber element (2) and arranged in a first surface of the optical waveguide block, the coupling end (8), and one end facing away from the optical fiber element (2) and arranged in a second surface of the optical waveguide block, the object end (9).

8. The optical endoscope (1) of claim 7, wherein the optical fiber element (2) comprises a multi-core optical fiber and wherein the two or more optical waveguides (7) are coupled to the optical fiber element (2) such that at the coupling end (8) the two or more optical waveguides (7) line up with cores (10) of the multi-core optical fiber.

9. The optical endoscope (1) of claim 8, wherein the cores (10) of the multi-core optical fiber are single mode cores at the operating wavelength.

10. The optical endoscope (1) of claim 7, wherein the optical fiber element (2) comprises a multi mode optical fiber (16) and wherein the two or more optical waveguides (7) are coupled to the multi-mode optical fiber (16) via a photonic lantern section (17) formed in the rigid material of the optical waveguide block (6).

11. The optical endoscope (1) of any one of claims 7-10, wherein the object end (9) is a flat surface perpendicular to or inclined with regard to the longitudinal axis of the optical fiber element (2).

12. The optical endoscope (1) of claim 11, wherein the two or more optical waveguides (7) fan out from the coupling end (8) to the object end (9) such that the inter-core spacing at the object end (9) is larger than at the coupling end (8).

13. The optical endoscope (1) of any one of claims 7-10, wherein the object end (9) is curved, particularly hemispherical.

14. The optical endoscope (1) of claim 13, wherein the mapping of the spatial distribution of the ends of the two or more optical waveguides (7) at the coupling end (8) to the spatial distribution of the ends of the two or more optical waveguides (7) at the object end (9) is mirror symmetrical with regard to a plane (13) extending parallel to the longitudinal axis of the optical fiber element (2).

15. The optical endoscope (1) of any one of the preceding claims, wherein additional optics (15), particularly one or more GRIN lenses and/or one or more micro lenses, are coupled with the optical waveguide block (6).

16. The optical endoscope (1) of any one of the preceding claims, wherein the optical waveguide block (6) is covered at least partially by an electrically conductive layer (24), in particular wherein the electrically conductive layer (24) is transparent or semi-transparent at the operating wavelength of the optical endoscope (1).

17. The optical endoscope (1) of any one of the preceding claims, wherein the optical waveguide block (6) comprises or consists of one or more planar chips (26, 27).

18. A method for manufacturing an optical endoscope comprising the steps of: providing an optical fiber element with a proximal end and a distal end, providing an optical waveguide block comprising a rigid material, forming two or more optical waveguides in the rigid material, and connecting the optical waveguide block to the distal end of the optical fiber element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG. 1 illustrates the basic setup of an optical endoscope according to the invention in a schematic illustration;

[0059] FIG. 2 shows parts of an optical endoscope according to a first embodiment of the invention;

[0060] FIG. 3 shows parts of an optical endoscope according to a second embodiment of the invention;

[0061] FIG. 4 shows an exemplary optical waveguide block for an optical endoscope according to the invention;

[0062] FIG. 5 shows another exemplary optical waveguide block for an optical endoscope according to the invention;

[0063] FIG. 6 shows parts of an optical endoscope according to a third embodiment of the invention;

[0064] FIG. 7 shows another exemplary optical waveguide block for an optical endoscope according to the invention;

[0065] FIG. 8 shows parts of an optical endoscope according to a fourth embodiment of the invention;

[0066] FIGS. 9a and 9b illustrate a photonic lantern usable in the context of an optical endoscope according to the invention;

[0067] FIG. 10 shows parts of an optical endoscope according to a fifth embodiment of the invention;

[0068] FIG. 11 shows parts of an optical endoscope according to a sixth embodiment of the invention;

[0069] FIG. 12 shows another exemplary optical waveguide block for an optical endoscope according to the invention; and

[0070] FIG. 13 shows another exemplary optical waveguide block for an optical endoscope according to the invention.

DETAILED DESCRIPTION

[0071] FIG. 1 illustrates in a schematic way the basic setup of an optical endoscope according to the invention. The optical endoscope 1 comprises an optical fiber element 2, typically including one or more optical fibers arranged within a flexible sheath material. The optical fiber element 2 has a proximal end 3 and a distal end 4. At the proximal end 3 imaging optics element 5 is arranged. The imaging optics element 5 may comprise optics for imaging the light transmitted via the optical fiber element 2 onto, for instance, a digital image sensor. The imaging optics element 5 may also comprise an LCD display to display the image obtained from the digital image sensor. The elements provided at the proximal end 3 of the optical fiber element 2 are standard elements known per se.

[0072] At the distal end 4 of the optical fiber element 2, an optical waveguide block 6 is arranged. As further detailed below, the optical waveguide block 6 comprises a rigid material in which two or more optical waveguides are formed. This optical waveguide block 6 allows providing an improved optical endoscope 1 as will also become apparent from the specific embodiments described herein below.

[0073] The optical fiber element 2 extends along a longitudinal direction, which defines the longitudinal axis of the optical endoscope 1. Since the optical fiber element 2 is usually flexible, the longitudinal direction/axis will normally be curved. The optical fiber element 2 is usually cylindrical with the central axis defining the symmetry axis of the cylinder. The longitudinal axis of the optical fiber element 2 can be considered as extending beyond its proximal and distal ends, in particular as straight lines perpendicular to the proximal/distal end surface. The longitudinal axis of the optical fiber element 2, thus is used herein as a reference axis with regard to which indications such as lateral or radial should be understood, particularly with respect to the optical waveguide block 6.

[0074] FIG. 2 illustrates a first embodiment of the invention. The optical fiber element 2 comprises a multi-core fiber with a plurality of cores 10 coated in a common, flexible polymer jacket 11. Many different types of multi-core fibers are known. The invention is not particularly limited to any specific embodiment for the multi-core fiber nor to any specific arrangement of the fibers in the optical fiber element 2.

[0075] The optical waveguide block 6 has the form of a cuboid in this specific embodiment and is made of glass. The optical waveguide block 6 may also be cylindrical or may have any other desired shape. A cylindrical optical waveguide block 6 would have the same appearance in the cross-sectional view of FIG. 2 as a cuboid one. The invention is not limited to glass as a rigid material for the optical waveguide block 6. The optical waveguide block 6 could also be formed of a rigid polymer or a rigid semiconductor, which are particularly optically transparent at the operating wavelength of the optical endoscope.

[0076] The optical waveguide block 6 comprises a plurality of 3-D ultrafast laser inscribed optical waveguides 7 leading from a coupling end 8 of the optical waveguide block 6 to an object end 9. The coupling end 8 faces the optical fiber element 2 while the object end 9 faces the object when the optical endoscope is in use, for instance, the interior of an organ of the human body.

[0077] Ultrafast laser inscription is known as such and works as follows: a high-intensity, focused femtosecond laser beam is applied to the rigid material in order to induce a permanent positive refractive index change through a multi-photon absorption mechanism. By 3-D translating the laser focus through the block of rigid material, the path traced out by the focus therefore becomes a light guiding core due to its resultant higher refractive index, with effective cladding provided by the unmodified remainder of the rigid material block. Doing multiple scanning runs enables writing an arbitrary number of waveguides with arbitrary 3-D shapes in a single block of rigid material. Various approaches are possible to account for the fact that the shape of the focused laser is not the ideal shape of a waveguide core, for instance, using multiple scanning runs with a slight offset from each other and annealing the rigid material block after ultrafast laser inscription by heating.

[0078] Further details of writing waveguides in glass with a femtosecond laser may be found in K. M. Davis, K. Miura, N. Sugimoto, and K. Hirao, Writing waveguides in glass with a femtosecond laser, Optics Letters, vol. 21, no. 21, p. 1729, 1996.

[0079] In the optical waveguide block 6 of FIG. 2, the object end 9 is a polished flat surface, perpendicular to the longitudinal axis of the optical fiber element 2. In view of the coupling between the optical waveguide block 6 and the optical fiber element 2, the longitudinal axis of the optical fiber element 2 may be considered as extending into the optical waveguide block 6, with the object end 9 being perpendicular thereto. It is also possible to arrange the object end 9 at a slight angle with regard to the longitudinal axis to remove or minimize back reflections. The angle depends on the refractive indices of the block and the surrounding medium. Typically it varies between a few degrees and ten degrees. The angle, thus, may be more than 1 and less than 10.

[0080] In general, the coupling end 8 is defined by the surface of the optical waveguide block 6 where the ends of the optical waveguides 7 are arranged facing the optical fiber element 2, while the object end 9 is defined as the surface area of the optical waveguide block 6 in which the ends of the optical waveguides 7 are arranged facing the object when the optical endoscope is in use or in other words, facing away from the optical fiber element 2.

[0081] In the embodiment of FIG. 2, the optical waveguides 7 in the optical waveguide block 6 fan out from the coupling end 8 towards the object end 9, effectively replicating the distribution of the waveguide ends at the coupling end 8, just with a larger inter-core spacing. The field of view is thus increased. The field of view is increased at the expense of spatial resolution; however, the acceptance angle remains the same as in a regular multi-core fiber endoscope.

[0082] Every core 10 of the multi-core fiber of the optical fiber element 2 butt-couples in this example to an end of an optical waveguide 7 at the coupling end 8 (not illustrated in the Figure). In this way, transmission of light from the object end 9 to the proximal end of the optical endoscope is possible.

[0083] Optionally, at least one additional optical element 12, such as a GRIN rod lens or micro lens or multiple such lenses, may be attached at the object end 9. If only using single mode waveguides, this embodiment is also compatible with coherent imaging techniques such as optical coherence tomography.

[0084] The object end pattern of the optical waveguides 7 is not particularly limited. The distribution could also be mono-dimensional, i.e. a linear array of waveguides or otherwise different from the distribution of the ends of the waveguide 7 at the coupling end 8. Similarly, the coupling end pattern may be one-dimensional or two-dimensional.

[0085] The fully rigid construction of the optical waveguide block 6 ensures long-term stability and no degradation in optical signal.

[0086] FIG. 3 illustrates another embodiment of the invention. In contrast to the embodiment of FIG. 2, the optical waveguide block 6 has an object end 9 that is hemispherical. Optical waveguides 7 in the optical waveguide block 6, thus, map the flat 2-D distribution of the coupling end 8 to the 3-D hemisphere, thereby increasing the solid angle. In other words, optical waveguides 7 also lead to a side surface of the optical waveguide block 6 with respect to the longitudinal axis of the optical fiber element 2 as reference axis. In this way, the solid angle may be increased to 2. The maximum solid angle can be even larger in the case of the optical waveguides 7 bending backwards. This may introduce, however, optical loss, since waveguide losses increase as the waveguide radius decreases.

[0087] FIGS. 4 and 5 illustrate possible alternatives to the optical waveguide block 6 illustrated in FIG. 3. In FIGS. 4 and 5, a theoretical plane 13 extending parallel to the longitudinal axis of the optical fiber element 2 and including the symmetry axis of the optical fiber element 2 is illustrated. In some embodiments, instead of plane 13, the rotational axis of symmetry of the optical waveguide block 6 may be used as reference. Waveguides 7 lead from one lateral side of the plane or axis 13 at the coupling end 8 to the other lateral side of the plane or axis 13 on the object end 9. In this way, it is possible to maintain the radius of curvature large enough to keep curvature losses acceptably low. The optical waveguides 7 may be designed with angles and distances from each other in such a manner to minimize crosstalk (see FIG. 5). In both alternatives (FIG. 4 and FIG. 5) the optical waveguides 7 are not intersecting in three-dimension, but only in projection.

[0088] FIG. 5 further shows the alternative of composing the object end 9 of a plurality of flat facets 14, which together join in a prismatic manner to cover the hemispherical object end 9. This discontinuous design of the hemispherical object end 9 may be used independently of the optical waveguide pattern inside the optical waveguide block 6.

[0089] FIG. 6 illustrates a further embodiment of the invention, which basically corresponds to the embodiment described with reference to FIG. 3. In this case, however, micro lenses 15 are affixed to the optical waveguide ends at the object end 9 of the optical waveguide block 6. In particular, microscopic plano-convex lenses 15 made from fused silica or silicon are used in this example. In this embodiment, a hemispherical object space is imaged and transmitted through the optical fiber element 2 towards the proximal end. In the case of all waveguides being single mode, optical coherence tomography may be used, as mentioned above, with the number of pixels equal to the number of waveguides in the optical waveguide block 6.

[0090] FIG. 7 illustrates an alternative optical waveguide block 6, which may be used to reduce curvature loss. In this example, optical waveguides 7a closer to the plane or axis 13 are mapped to the lateral surface areas of the object end, while the optical waveguides 7b closer to the edge of the optical waveguide block 6 map to a forward facing surface area of the object end. The side facing surface area can either be a cylindrical surface, or through the use of micro lenses with different focal lengths can be modified to more closely match a hemispherical surface. Likewise, the forward facing surface area can be flat as illustrated in FIG. 2 or curved as illustrated, for instance, in FIG. 3.

[0091] Optional micro lenses or GRIN optics are illustrated as additional optical elements 15 in FIG. 7.

[0092] FIG. 8 illustrates another embodiment of the invention, which uses instead of a multi-core fiber for the optical fiber element 2 a multi-mode fiber 16. All the previous embodiments discussed herein can also be used with a multi-mode fiber. Coherent imaging techniques, such as optical coherence tomography, however, cannot be implemented with a multi-mode fiber. In order to couple the two or more optical waveguides in the optical waveguide block 6 to the multi-mode fiber 16 a photonic lantern section 17 is provided, which is also obtained by ultrafast laser inscription.

[0093] FIGS. 9a and 9b illustrate so-called photonic lanterns. Photonic lanterns are optical devices connecting a multi-mode waveguide to a plurality of waveguides with fewer, possibly only single, modes. FIG. 9a shows the alternative of mapping one multi-mode waveguide 19 to a number of single mode waveguides 18. FIG. 9b illustrates spreading out of a multi-mode waveguide 19 to a plurality of single mode waveguides 18 and then recombining to a single multi-mode waveguide 20 again. This alternative is particularly useful, since FBG (Fiber Bragg Grating) filters can be inscribed in the region of the single mode waveguides 18. From the alternative shown in FIG. 9b, the photonic lantern takes its name. Both embodiments of the photonic lanterns shown in FIGS. 9a and 9b may be used in the context of the present invention. FBG (Fiber Bragg Grating) filters may be inscribed in the optical waveguide block 6, particularly in the single mode waveguides 18 of a photonic lantern section 17.

[0094] Referring again to FIG. 8, the modes of the multi-mode fiber 16 first couple to the individual waveguides in the photonic lantern section 17 and then spread out according to the needs of the specific embodiment. In this case, the object end 8 is made consistent with the example shown in FIG. 6.

[0095] Since endoscopes using a multi-mode fiber are sensitive to bending during use, it is necessary to obtain a transfer function for effective operation, as known per se in the art.

[0096] FIG. 10 shows another embodiment of an optical endoscope according to the invention. For the optical fiber element 2, a single mode or multi-mode fiber 21 may be used. Again a photonic lantern section 17 is written into the optical waveguide block 6. The optical lantern section 17 is implemented in a branched manner, that is, with a spread out from a multi-mode waveguide to fewer-moded waveguides occurring over multiple fan out steps.

[0097] If a multi-mode fiber is used for the optical fiber element 2, at every splitting level, the number of modes from the larger input waveguide is divided up amongst its branches. Functionally, this alternative is identical to the embodiment described with reference to FIG. 8 with the only difference being that the photonic lantern section 17 does not fan out at once.

[0098] According to the alternative of a single mode fiber being used for the optical fiber element 2, each branch functions as a splitter rather than a fan out device. In this manner, it is possible for the single mode input light propagating toward the object end 9 to split and coherently reach the entire field of view. The photonic lantern section 17, thus, functions as the multiplexing element.

[0099] Another embodiment of the invention is illustrated with reference to FIG. 11. Sometimes, optical endoscopes are intended to be used for radiofrequency ablation of internal tissues. The embodiment of FIG. 11 is suitable for such purposes. Particularly, a conductive tube 22 of a conductive material, such as a metal, is provided around optical fiber element 2 with an optional insulating sheath 23. The optical waveguide block 6 is embedded in a conductive layer 24, which has proper openings 25 for optical access to the optical waveguides of the optical waveguide block 6. Current may be transmitted to the distal end by means of the conductive tube 22 surrounding the optical fiber element 2. Optionally, several layers of conductive and insulating tubes may surround the optical fiber element 2 to enable ring electrodes for monitoring purposes. The conductive tube 22 is in electrical contact with the conductive layer 24 of the optical waveguide block 6, so that the current may be transmitted to the conductive layer 24 of the optical waveguide block 6. In this way, ablation treatments can be performed. This radiofrequency ablation functionality can be used with any one of the previous embodiments. If a multi-mode fiber should be used for the optical fiber element 2, a photonic lantern section as illustrated in FIG. 8 or 10 can be inscribed in the optical waveguide block.

[0100] In an alternative embodiment, the conductive layer 24 may be semi-transparent or transparent at the operating wavelength of the optical endoscope. In this case, the openings 25 may be omitted. The conductive layer 24 may particularly be formed of a transparent or semi-transparent material and/or may be made sufficiently thin to allow light at the operating wavelength of the optical endoscope to pass at least partially through the layer.

[0101] FIGS. 12 and 13 illustrate further alternatives for the optical waveguide block 6, as it may be used for optical endoscopes according to the invention.

[0102] In FIG. 12, the optical waveguide block 6 is formed as a planar chip 26 with a 2-D distribution of five exemplary optical waveguides 7 formed therein. The central optical waveguide extends straight or uncurved from the coupling end to the object end, while the other optical waveguides are curved towards a side surface of the planar chip 26. The thickness of the planar chip 26 is significantly less than its length and width.

[0103] In FIG. 13, the optical waveguide block 6 is formed by two orthogonally intersecting planar chips 26, 27 each with a 2-D distribution of optical waveguides 7 formed therein. The planar chips 26, 27 are arranged such that each of planar chips 26, 27 is divided in half by the respective other chip. In this way, a 3-D distribution of the optical waveguides 7 may be achieved while reducing the amount of rigid material. Each of the planar chips 26, 27 may comprise two or more elements. For instance, the planar chip 26 may comprise two halves, each connected to the planar chip 27.

[0104] In the described embodiments, the optical waveguides formed in the rigid material of the optical waveguide block 6 may be single-mode or multi-mode waveguides.

[0105] Although the previously discussed embodiments and examples of the present invention have been described separately, it is to be understood that some or all of the above-described features can also be combined in different ways. For instance, the described optical waveguide blocks may be used in combination with different kinds of optical fiber elements.

[0106] In the figures, several features are only illustrated in a schematic way. For instance, the optical waveguide block is often shown as spaced from the distal end of the optical fiber element, This is only for illustrational purposes. The optical waveguide block is actually coupled with the distal end of the optical fiber element such that light may be transmitted via the two or more optical waveguides and the optical fiber element to the proximal end of the endoscope. For instance, a butt coupling may be realized.

[0107] The discussed embodiments are not intended as limitations, but serve as examples illustrating features and advantages of the invention. Particularly, the pattern of the optical waveguides in the optical waveguide block is determined by the desired application. Similarly, while glass is used for the optical waveguide block according to the embodiments, the optical waveguide block may consist of any transparent, rigid material of appropriate index of refraction that offers the possibility of hosting 3-D optical waveguides as described. With the described embodiments, it is possible to increase the field of view or the solid angle over known optical endoscopes. This is possible while at the same time providing a mechanically reliable, inexpensive solution that can be used with any type of fiber.