CN1242082A - Method for coupling light from single fiberoptic to a multi-fiber bundle with enhanced field uniformity and better coupling efficiency - Google Patents

Abstract

A device which adjusts the angle of illumination of light exiting a fiber optic light guide. A first light guide has a first numerical aperture for emitting light from a light source, and light exiting the first light guide has a first light intensity angular profile. A second light guide has a second numerical aperture for receiving the light from the first light guide, and light exiting the second light guide has a second light intensity angular profile. Light from the first light guide is dispersed by a device including at least a first surface interposed between the first light guide and the second light guide such that light from the first light guide having the first light intensity profile irradiates the first surface and the angular intensity profile of the light irradiating the second light guide is modified so as to cause the second light intensity angular profile to be modified. The first light guide preferably has a single fiber, and the second light guide preferably has a fiber bundle. The dispersion is preferably be effected with a GRIN lens and a fiber bundle having an angled endface, or with a GRIN lens, a fixed fiber bundle having an angled endface and a rotatable fiber bundle having an angled endface.

Description

Method for coupling light from a single fiber onto a multi-fiber bundle with enhanced field uniformity and better coupling efficiency

The present invention relates to methods and apparatus for coupling light from a first optical fiber to a second optical fiber, and more particularly to methods and apparatus for coupling light from a single optical fiber to a multi-fiber bundle, such as the multi-fibers of an endoscope.

The following background art description represents the inventor's knowledge of functions, uses, problems, etc. related to the background art, which are not necessarily known to those skilled in the art.

The coupling between the light source and the endoscope (both flexible and rigid types used in industrial and medical applications) is usually done with fiber optic bundle cables. Such cables contain thousands of small diameter optical fibers within a jacket. The weight is heavy and each individual fiber is fragile and prone to breaking in the cable during normal handling and cleaning. The transmission efficiency of the fiber optic cable is also relatively low, which depends on the length of the cable, the fiber packing factor and the number of broken fibers inside the cable.

For example, the output intensity distribution of an endoscope depends in part on two factors: the illumination distribution on the distal end of the endoscope and the coupling between the endoscope and the fiber optic bundle cable. The quality standard against which performance can be measured is the uniformity of illumination over the field of view of the endoscope. A perfectly uniform field has an optically flat intensity distribution from edge to edge across the field of view. Whether the field is optically flat depends in part on the observation method. Typically, endoscopes are used with television cameras where the gain at the center is greater than the gain at the sides. Thus, a uniform field observed by a television camera corresponds to an actual intensity distribution in the center of the field of view slightly lower than the sides (such as the "donut distribution" discussed below).

In reality, achieving this distribution is difficult because most fiber bundles, such as those inside endoscopes, have random fiber packaging. To the extent that the fibers are not random, it is only possible to establish a "donut distribution" (discussed below) if the light sent to the endoscope is similarly distributed. For endoscopes with random fiber bundles, an optically flat illumination field requires that the input to the endoscope is also uniform.

Many endoscopes contain on their input ends a light collecting cone designed to concentrate light from a large diameter to a smaller diameter focal point to match the diameter of the inner beam. In this approach, the numerical aperture (NA) of the light increases and light is lost unless the optical fiber inside the endoscope has a NA large enough to accept the increased NA of the focused light from the focusing cone. Creating a homogeneous field when there is a concentrating cone at the input end of the endoscope involves different requirements than sending a homogeneous illumination field at the distal end. In this case, the uniformity depends on both the characteristics of the cone and the randomness of the inner fiber.

To the extent that the diameter of the fiber optic bundle light sending cable matches the diameter of the beam, the intensity distribution of the illuminated field of view depends on the above characteristics. Additional considerations apply when the optical delivery system is a single optical fiber with a diameter of approximately 1mm or less. Often, it is necessary to expand the light from a single fiber to match the diameter of a beam or the like. Furthermore, the intensity distribution needs to be corrected so as not to cause thermal damage to the beam. If a light cone is included to concentrate light into a smaller fiber bundle, the output of the individual fibers should be adjusted to match the optical performance of the light cone.

According to the present invention, means are provided for modifying the light intensity distribution of an optical fiber prior to its coupling into, for example, an endoscope or the like. Two notable features of the present invention include: (a) the ability to expand the output end to match the diameter of the input beam of an endoscope or other fiber optic beam device; and (b) the ability to modify the intensity distribution of the expanded beam to match the focused The focusing properties of the light cones are consistently matched.

According to one aspect of the present invention, there is provided an apparatus for adjusting the illumination angle of light exiting an optical fiber light guide, comprising: a first light guide having a first numerical aperture for emitting light from a light source, a first light guide exiting from the first light guide Light has a first angular distribution of light intensity; a second light guide having a second numerical aperture for receiving light from the first light guide, light exiting from the second light guide has a second angular distribution of light intensity; At least one first surface between the second light guide scatters light from the first light guide such that light from the first light guide having a first light guide intensity distribution impinges on the first surface and corrects on the second light guide The angular intensity distribution of the light so as to redistribute the light of the angular intensity distribution from the center of the second distribution to the periphery of the second distribution.

According to another aspect of the present invention, a method of adjusting the illumination angle of light exiting an optical fiber lightguide comprises the steps of: (a) sending light from a light source through a first lightguide having a first numerical aperture, exiting from said first lightguide light having a first angular distribution of light intensity; (b) receiving light exiting from the first light guide with a second light guide having a second numerical aperture, light exiting from the second light guide having a second angular distribution of light intensity; and (c ) scattering light from the first light guide with at least one first surface arranged between the first light guide and the second light guide such that light from the first light guide with a first light intensity distribution impinges on the first surface, and correcting The angular intensity distribution of light impinging the second light guide is such that the light of the angular intensity distribution is redistributed from the center of the second distribution to the periphery of the second distribution.

According to another aspect of the invention, the light scattering member includes a GRIN lens and a fiber optic bundle with beveled end faces.

According to yet another aspect of the present invention, the light scattering member includes a GRIN lens, a fixed fiber optic bundle with a beveled end face, and a rotatable fiber optic bundle with a beveled end face.

According to another aspect of the invention, the first light guide is preferably a single optical fiber; alternatively, the first light guide may be a bundle of optical fibers. Similarly, according to another aspect of the present invention, the second light guide preferably has a bundle of optical fibers.

Among other advantages, the present invention provides an improved method of coupling light, eg, from a single optical fiber into a multi-fiber bundle, with enhanced field uniformity and better coupling efficiency. The above and other advantages, features and aspects of the present invention will be more readily understood from the following description of its preferred embodiments taken together with the accompanying drawings and claims.

The invention is shown by way of example and not limitation in the accompanying drawings, wherein like reference numerals indicate like parts, in which:

Figure 1 is an illustrative and somewhat schematic side view of a first embodiment of the invention showing the arrangement of components and the intensity distribution of light transmitted through the components.

FIG. 2 is a diagram of an exit light intensity distribution such as that shown on the right side of FIG. 1;

Figure 3 is an illustrative side view of a second embodiment of the invention having a variable intensity distribution output;

Figure 4 is a somewhat schematic side view of an alternative third embodiment of the invention having a source fiber output end angled from the input end of an endoscope or the like.

Expansion of the light beam 11 from the first light guide 5 having eg an intensity profile 12 can be done eg with a lens matching the NA of the input 25 eg an endoscope. In a preferred embodiment, a collimating optic such as a gradient index rod lens (GRIN lens) 10 expands the light beam 11 . A properly chosen physical spacing between the GRIN lens 10 and the input end of the endoscope allows matching the diameter of the beam of light to the diameter of the beam. The GRIN lens 10 is sufficient by itself to couple light into the fiber bundle of almost any fiber configuration on the distal end of the endoscope, but is not optimized for uniform output. However, for an endoscope with a concentrating cone, the small NA (i.e., the low divergence angle of the light) does not match the desired input intensity distribution of the cone to generate a concentrating light large enough to fill the internal beam of the endoscope. beam. The consequence of this is an inhomogeneous intensity distribution on the distal end of the endoscope.

The present invention avoids the above problems by adding a second optical element that spreads the light over a wider angle. Preferably, in order to reproduce the far-end field intensity profile of the fiber optic bundle, the second optic should redistribute the Gaussian profile to create a uniform or "donut intensity profile". This is accomplished in the preferred embodiment with a short length of melting fiber bundle 20, actually a melting rod. The melting rod 20 is planar polished on the output end 21 , eg, with a vertical surface, and bevelled on the input end 22 , as shown in FIG. 1 . The molten fiber rod 20 contains thousands of small diameter optical fibers 23, each of which samples only a fraction of the incoming beam. The angle θ of the beveled polished end 22 causes the collimated light from the GRIN lens to have an effective angle of incidence greater than the angle emitted from the GRIN lens, causing more of the light 30 output therefrom to spread over the periphery of the output beam creating a "circle Pie Intensity Distribution" 40. Thus, on the output end face 21 of the rod, the light from the individual fibers of the melted rod is recombined to generate a donut-shaped distribution 43 . As shown in FIGS. 1 and 2 , distribution 43 is substantially symmetrical about central axis X such that concave center 41 lies within peak intensity ring or donut 42 . The size of the concave center depends on the beam incidence angle θ on the input end face 22 of the light rod. Thus, by adjusting the incident angle of the melting rod, the output intensity distribution can be modified from a typical Gaussian distribution to a relatively flat or donut-shaped distribution. By varying the angle, the invention can produce a wide variety of intensity distributions at the output of the second light guide. In an alternative embodiment, the melted fiber bundle may be replaced with a flat polished on the output end and a bevel polished on the input end such as a clad rod. It is also possible to arrange the light-collecting cone, shown schematically at 35 in FIG. 1 , between the second light guide 25 and the light-scattering element.

As shown in FIGS. 1 and 2, the angle θ of the end face 22 of the fused fiber bundle will determine the degree of modification of the intensity profile 43 . In the embodiments discussed below, this angle is set at approximately 24°; however, this is only an exemplary embodiment and the concepts of the present invention can be used to use a wide range of angles. While it is possible to find an angle θ that is close to optimal for most bundle configurations inside the endoscope, it is also possible to create adjustable profiles to optimize the intensity distribution for each particular bundle.

In this regard, a second embodiment of the invention is shown in FIG. 3 , in which the device 2 is configured to create a variable intensity distribution. A preferred configuration of the second embodiment replaces a single bevel polished fused fiber rod with two similar rods 50 and 60 . By rotating one rod relative to the other, the beam incidence angle can be adjusted to match that of the second melted fiber rod at will. In this way, the degree of center reduction of the intensity distribution can be varied accordingly. This yields an intensity distribution ranging from a Gaussian distribution to a donut distribution with severe suppression of central intensity.

According to a third embodiment of the present invention, as shown in FIG. 4 , the GRIN lens 10 on the output end of the source fiber 70 is set in relation to the input end 85 of an endoscope 80 etc. (e.g., with or without a transition cone). The fiber bundle) forms an angle θ. By varying the angle θ, the device can produce an intensity profile output 90 similar to profile 43 . A support connector 75 may be included to maintain the angle Θ as desired. The support connector can also contain means for adjusting the angle Θ. The bearing connector may be selected from any known bearing as long as the angle is maintained correctly according to the invention.

According to a preferred configuration, the GRIN lens is a cylindrical lens with a parabolic refractive index profile. By pressing the fiber optic source end against the input surface of the GRIN lens, the output beam is thereby substantially collimated. The bevel polished fiber bundle (which is fused) is then positioned at an appropriate distance such that it matches the size (eg diameter) of the output beam from the GRIN lens.

An exemplary embodiment includes: a) a GRIN lens having a diameter of 1.8 mm and a length of 3.6 mm (0.25 pitch) and a numerical aperture of 0.6, and b) a lens of 4.2 mm diameter, length of 7 mm, and a numerical aperture of 0.66, approximately at an angle to the normal n A polishing angle θ of 24°, and a fused fiber bundle with a diameter of 10 μm for each fiber in the bundle. As an example, the GRIN lens may be a SELFOC lens from NSG America, Somerset, N.J. As should be understood, the above dimensions, numerical apertures etc. are for exemplary purposes only and can be changed at will according to specific requirements.

The light transmission efficiency mainly depends on the numerical aperture (NA) mismatch of the components and the fiber packing factor of the fused fiber rod. By selecting matching components and high packing factor rods, a high light transmission efficiency of at least 80% can be achieved.

While the invention has been shown and described with reference to the preferred embodiment presently contemplated as the best mode of carrying out the invention, it should be understood that it may be made without departing from the broad inventive concepts disclosed herein and contained in the following claims. Various changes are made in adapting the invention to different embodiments.

Claims (24)

1, a kind ofly be used to redistribute, comprise from the equipment of the illumination angle of the light of fibre-optic light guide outlet:

Be used for first photoconduction with first numerical aperture from source emissioning light, the light that exports from described first photoconduction has the distribution of the first light intensity angle;

Be used to receive second photoconduction with second value aperture from first photoconduction, the light that exports from described second photoconduction has the distribution of the second light intensity angle; And

The light scattering part, be used for to be arranged at least one first surface scattering between described first photoconduction and described second photoconduction from the light of described first photoconduction, make rayed from described first intensity distributions of having of described first photoconduction on described first surface, and revise the angle intensity distributions that is radiated at the light on described second photoconduction so that redistribute the light that this intensity angle distributes to described second periphery that distributes from described second center of distribution.

2, the equipment of claim 1, wherein said second distribution is smooth haply.

3, the equipment of claim 1, wherein said second distributes has recessed center.

4, the equipment of claim 1, wherein said light scattering part comprises the fibre bundle with at least one angled end-face.

5, the equipment of claim 4, wherein said fibre bundle melts.

6, the equipment of claim 1, wherein said first photoconduction is a simple optical fiber.

7, the equipment of claim 1, wherein said first photoconduction is a fibre bundle.

8, the equipment of claim 1, wherein said light scattering part comprise grin lens and have the fibre bundle of at least one angled end-face.

9, the equipment of claim 8, the described fibre bundle that wherein has at least one angled end-face melts.

10, the equipment of claim 1, wherein said light scattering part comprises grin lens, have the fixed fiber bundle of angled end-face and have the rotating fibre bundle of the angled end-face on the described angled end-face that is adjusted to described fixed fiber bundle.

11, the equipment of claim 10, wherein said fixing with rotating fibre bundle melted.

12, the equipment of claim 1, wherein said second photoconduction is a fibre bundle.

13, the equipment of claim 12 wherein is arranged in optically focused awl between described second photoconduction and the described light scattering part.

14, the equipment of claim 12, wherein said fibre bundle are the parts of endoscope.

15, a kind of adjusting comprises the steps: from the method for the illumination angle of the light of fibre-optic light guide outlet

A) send light by first photoconduction with first numerical aperture from light source, the light that exports from described first photoconduction has the distribution of the first light intensity angle;

B) receive from the light of first photoconduction outlet with second photoconduction with second value aperture, the light that exports from described second photoconduction has the distribution of the second light intensity angle; And

C) with being arranged at least one first surface scattering between first photoconduction and second photoconduction from the light of first photoconduction, make rayed from first photoconduction on first surface, and revise the angle intensity distributions that is radiated at the light on second photoconduction so that redistribute the light that this intensity angle distributes to second periphery that distributes from second center of distribution with first light intensity distributions.

16, the method for claim 15 wherein comprises by simple optical fiber transmission light from the described step that light source sends light by first photoconduction.

17, the method for claim 15 wherein comprises by fibre bundle transmission light from the described step that light source sends light by first photoconduction.

18, the method for claim 15, wherein said scattering step are to carry out with grin lens and the fibre bundle with angled end-face.

19, the method for claim 15, wherein said scattering step are to carry out with grin lens and the rotating fibre bundle that has the fixed fiber bundle of angled end-face and have an angled end-face.

20, the process of claim 1 wherein to receive and comprise with fibre bundle from the described step of the light of first photoconduction outlet second photoconduction is set with second photoconduction.

21, the process of claim 1 wherein to receive and comprise with single light beam from the described step of the light of first photoconduction outlet second photoconduction is set with second photoconduction.

22, the method for claim 20, wherein said fibre bundle are to be provided with as the part of endoscope.

23, a kind ofly be used to redistribute, comprise from the equipment of the illumination angle of the light of fibre-optic light guide outlet:

Be used for first photoconduction with first numerical aperture from source emissioning light, the light that exports from described first photoconduction has the distribution of the first light intensity angle;

Be used to receive second photoconduction with second value aperture from the light of first photoconduction, the light that exports from described second photoconduction has the distribution of the second light intensity angle;

Axially align the grin lens on the output terminal of described first photoconduction; And

The supporting connector, it remains on predetermined angle to described second photoconduction towards last with described first photoconduction and described gradient-index lens, thereby revise light, so that redistribute the light that this intensity angle distributes to described second periphery that distributes from described second center of distribution from described first light intensity distributions of having of described first photoconduction.

24, the equipment of claim 23, wherein said supporting connector comprise be used to regulate described angle towards in case can change this angle towards device.

Images