IE20000001A1 - Optical imaging systems - Google Patents

Abstract

A confocal microscope (1) includes an objective lens (2). An optical fibre bundle (3) is mounted behind the objective lens (2) and comprises a plurality of individual optical fibres (4). Each optical fibre (4) has an outer end (5) and an inner end (6). A lens array (7) is mounted spaced apart from the inner end (6) of the optical fibres (4). The lens array (7) comprises a number of microlenses (8), each optical fibre (4) having an associated microlens (8). Means is provided for applying a voltage to each microlens (8) for switching the microlens (8) into or out of focus with an inner end of its associated optical fibre (4). When in focus an image from an object being viewed is transmitted via a beam splitter (10) (11,12) to a photodetector (14). The photodetector (14) can be connected to any suitable means for displaying or recording the image. A controller is operable for sequentially applying focusing voltage to a number of sets of spaced-apart microlenses (8) to collect images of portions of an object (16) being viewed which images are then assembled to form a composite image of the object (16). <Figure 4>

Description

The invention relates generally to optical imaging systems, e.g. confocal microscope ···X. imaging systems and more particularly to direct-view confocal microscopes. o 'a* S'1 & L» Confocal microscopes used to obtain high lateral resolution and depth sectioning are now commercially significant. Confocal microscopy differs from conventional microscopy in that it uses a pinhole in the source and detector planes as illustrated in Fig. 1 which schematically illustrates a prior art confocal microscope. This means that it has a narrower depth of field giving images of thin slices of an object being examined. These images are obtained by scanning the object laterally relative to the light source. Successive slices of the object may be imaged to form a threedimensional image by scanning also in the axial direction. Direct-view or tandem scanning microscopes of which a prior art type is schematically illustrated in Fig. 2, which have become important commercially, exploit the basic confocal microscope by using a disc with an array of pinholes in the source and detector planes to effectively provide an array of confocal microscopes operating in parallel. The disc is scanned in is arrangement to ensure that all parts of the object are imaged. Scanning in the ial direction is necessary to obtain images of different slices of the object to build up three-dimensional image. The advantage of a direct-view microscope is that by paging in parallel, it can build up an image of an object faster than a single pinhole onfocal microscope. The spacing of the pinholes is critical to ensure that this crease in imaging speed is not compromised by any loss in resolution. However, hichever approach is used, single- or multiple-pinhole imaging approaches both require some kind of scanning in the lateral and axial directions. Optical fibre bundles are routinely used for remote imaging such as endoscopy in medicine. A fibre bundle may be used in conjunction with a direct-view microscope (DVM) for confocal imaging as shown in the schematic prior art illustration in Fig. 3. This pinhole disk in a DVM means that the fibres being illuminated at any given time are separated by large enough distances to avoid crosstalk. A number of different types of known confocal microscope devices are described in patent specification nos. US 5969846, US 5717519, US 5557452 and EP 0330008.

IE 000001 -2It is an object of the invention to overcome the above-mentioned problems.

It is a further object of the invention to permit two-dimensional and/or threedimensional confocal imaging without mechanical scanning. This would result in the removal of mechanical moving parts from a confocal microscope.

Summary of the Invention According to the invention, there is provided an optical imaging system 10 comprising:an optical fibre bundle having a plurality of optical fibres, eact) optical fibre having an outer end and an inner end, the outer end for reception of light from an object to be viewed, means for sequentially scanning the optical fibres in the optical fibre bundle , in groups of one or more selected optical fibres in a desired sequence, and means for building a composite image of the object from the scanned 20 optical fibre images, characterised in that the sequential scanning means includes a lens array having a lens associated with each optical fibre and means for selectively switching each lens into or out of focus with its associated optical fibre.

In a particularly preferred embodiment, each lens is a microlens of variable focal length.

Conveniently, means is provided for applying a switching voltage to each 30 microlens for adjustment of the focal length of the microlens to switch the microlens into and out of focus with its associated optical fibre.

In a further embodiment, a second lens array is mounted adjacent the outer end of the optical fibre bundle having a lens associated with each optical fibre, said IE 000001 -3second lens array having means for selectively focussing each lens at a portion of an object to be viewed.

In a preferred embodiment the second array of lenses comprises a plurality of microlenses of variable focal length with means for applying a voltage to each microlens for adjustment of the focal lens of the microlens.

In another embodiment, a pair of lens arrays are mounted back-to-back adjacent the outer end of the optical fibre bundle for collection of light from an outer end of the optical fibre bundle and focussing light on the object to be viewed, a complementary pair of lenses being associated with each optical fibre.

Preferably each lens array comprises a plurality of micro lenses of variable focal length with means for applying a voltage to each microlens for adjustment of the focal length of the microlens.

In another aspect the invention provides a confocal microscope incorporating the optical system comprising; an objective lens, an optical fibre bundle mounted behind the objective lens, said optical fibre bundle comprising a plurality of individual optical fibres, each optical fibre having an inner end and an outer end, a lens array associated with the optical fibre bundle mounted spaced out and apart from an inner end of the optical fibre bundle, said lens array having a plurality of variable focal lengths microlenses, a microlens being associated with each optical fibre in an optical fibre bundle, means for selectively applying a voltage to each microlens to vary the focal length to switch the microlens into or out of focus with the inner IE 000001 -4end of its associated optical fibre, a photo detector, means for directing an image from each to the photo detector, a light source and means for directing light from the light source through the optical fibre bundle and an object placed in front of the objective lens, control means possible for sequentially applying focusing voltages to a number of sets of spaced-apart micro lenses to collect images of portions of an object, and assembling said images to form a composite image of an object being viewed.

Brief Description of the Drawings The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which:—s.

Fig. 1 is a schematic diagram of a conventional prior art single-pinhole confocal microscope: Fig. 2 is a schematic diagram of a prior art direct-view or tandem-scanning microscope: Fig. 3 is a schematic diagram of a prior art direct-view confocal microscope using a coherent optical fibre bundle; Fig. 4 is a schematic diagram of an optical imaging system according to the invention comprising a variable focus microlens array used in conjunction with a coherent optical fibre bundle to achieve a non-scanning confocal microscope; IE 000001 -5Fig. 5 is a schematic detail view showing portion of the confocal microscope of Fig. 4; Fig. 6 is a schematic diagram of a second embodiment of the invention comprising a variable focus microlens array, with a coherent optical fibre bundle, standard lens and having additional variable focus microlens array, used to focus on a sample; Fig. 7 is a schematic diagram of a third embodiment of the invention comprising a variable focus microlens array, with a coherent optical fibre bundle, standard lens and two additional variable focus microlens arrays, used to collect light from the fibre bundle and focus on the sample; and Fig. 8 is a view similar to Fig 4 showing another optical imaging system.

Detailed Description of the Preferred Embodiments Referring to the drawings, and initially to Figs. 4 and 5 thereof, there is illustrated a confocal microscope according to the invention indicated generally by the reference numeral 1. The confocal microscope 1 includes an objective lens 2. An optical fibre bundle 3 is mounted behind the objective lens 2 and comprises a plurality of individual optical fibres 4. Each optical fibre 4 has an outer end 5 and an inner end 6. A lens array 7 is associated with the fibre bundle 3 and is mounted adjacent but spaced-apart from the inner ends 6 of the optical fibres 4. This lens array 7 has a number of microlenses 8, a microlens 8 being associated with each optical fibre 4 in the optical fibre bundle 3. Each microlens 8 can be selectively individually focussed on an inner end 6 of its associated optical fibre 4 for transmission of an image from the inner end 6 of the optical fibre 4 via a beam splitter 10 and lenses 11, 12 to a photodetector 14. The photodetector 14 is connected to any suitable means for displaying and/or recording the image (not shown).

A light source 15, which may be for example a laser or bright white light source, is IE 000001 -6provided for directing light through the beam splitter 10 and optical fibre bundle 3 at an object 16 placed in front of the objective lens 2 for viewing the object 16.

—\ Means is provided for applying a voltage to each microlens 8 for adjusting the focal length of the microlens 8. Thus, by varying the applied voltage each microlens 8 can be switched between an out of focus mode and an in focus mode in which the microlens 8 is focussed on an inner end 6 of its associated optical fibre 4 (as shown in Fig 5) to pick up the image for transmission to the photodetector 14. Control means (not shown) is operable for sequentially applying focussing voltages to a number of sets of spaced-apart microlenses 8 to collect images of portions of the object 16, which images are then assembled to form a composite image of the object 16 being viewed.

It will be appreciated that this invention simplifies the imaging system of the type shown in Fig. 3 prior art device by discarding the rotating disk in the DVM. However, discarding the pinhole disk would normally mean that all of the many fibres in the fibre bundle would be illuminated simultaneously. In particular, adjacent fibres would be illuminated. This would result in crosstalk in the image. The present invention manages to. avoid illuminating adjacent fibres by illuminating fibres which are typically 10 or 20 fibres apart. The variable focus microlens array is used to do this without mechanical scanning. Each microlens in the array is individually addressable. So it can be arranged at some time t1, for say, lenses nos. 1, 11, 21 etc. to have focal lengths so that they are focused on associated optical fibres 1, 11, 21. All other lenses 8 would be out of focus on all other optical fibres 4. In this way, crosstalk is eliminated. At time t2, lenses 2, 12, 22 etc. would be in focus on optical fibres 2, 12, 22 and a second confocal image would be obtained. This addressing system offers a simple way of obtaining remote confocal images, potentially over large areas.

Using this technique, a controlled sub-array of microlenses will be focused on the object sample to be imaged at any time. At the next instant anotherxontrolled subarray of the same microlens array will be used to image new points on the sample. The presence of the optical fibre bundle 3 means that these images are confocal. By superimposing each of these array images, a confocal image of the whole specimen may be built up.

IE 000001 -7Effectively the individual addressing of microlenses replaces the mask effect of a Nipkow disk of the type shown in the prior art device of Fig. 3. The fibres replace the point source/detector effect of a Nipkow disk. Use of the fibre offers remote imaging capabilities. In effect, mechanical scanning of the disk is replaced by electronic scanning.

••X The system couples light from appropriate microlenses 8 into corresponding optical fibres 4, while avoiding mechanical scanning to do so. The inventive optical system includes an array of microlenses 8 whose focal length may be varied. That is, the system includes an optical source 15, e.g. a laser or a bright white light source, a system component impinged upon by light emitted by the source 15 and transmitted by the coherent optical fibre bundle 3 to a photodetector 14. The system component includes a variable focus microlens array 7 with a coherent optical fibre bundle 3 which replaces the scanned Nipkow disk shown the prior art device of Fig. 3.

The system involves an optical/electronic system, e.g. an array of variable-focus microlenses on liquid crystal. The system functions so that voltages applied to an array of liquid crystal elements control the focal lengths of an array of optical microlenses. This electronic control provides variable focussing in the axial direction •-•X and purely electronic lateral scanning.

Standard microlenses have been used for fibre-to-fibre coupling in a switching network for telecommunications or as an optical interconnect for parallel processing. Refractive microlenses may be fabricated simply by melting photoresist islands on a substrate. This limits the focal length of microlenses. This limitation may be overcome by immersing the microlens array in fluids having different refractive indices and using a cover glass to enclose the hybrid lens. This gives much greater flexibility in the design of focal lengths. In particular, a microlens may be immersed in a nematic liquid crystal cell. By applying an analogue voltage to the nematic liquid crystal, a variable focal length microlens array may be formed. The microlenses to be used in this inventive step are designed to have a working distance and numerical aperture giving the correct acceptance angle for the optical fibres in the coherent optical fibre bundle. In this way, when the appropriate focal position of the selected microlens sub-array is IE 000001 -8chosen, only light from these array elements is transmitted through the fibre bundle. The microlenses are formed using standard techniques on top of transparent planar electrodes.

Referring now to Fig. 6, there is shown another confocal microscope according to a second embodiment of the invention indicated generally by the reference numeral 20, Parts similar to those described previously are assigned the same reference numerals. In this case, the confocal microscope 20 includes a second variable focus microlens array 21 spaced-apart from the outer ends 5 of the optical fibres 4 in the optical fibre bundle 3. The second microlens array 21 is similar to the primary microlens array 7 and in this case the ability to vary the focal length of the microlenses 8 may be used to image different height levels in the object 16 being viewed.

Referring now to Fig. 7, there is illustrated another confocal microscope according to a third , embodiment of the invention indicated generally by the reference numeral 30. Parts similar to those described previously are assigned the same reference numerals. In this case, a second microlens array 21 and a third microlens array.61 are provided back to back spaced-apart from the outer end 5 of the optical fibres 4 in the optical fibre bundle 3. This allows the collection of light from the optical fibre bundle 3 and the focussing of light on the object 16 allowing large objects to be imaged consistent with the size chosen for the microlens arrays 7, 21, 31 and the coherent optical fibre bundle 3.

It is envisaged that the beam splitter may be mounted elsewhere if convenient. For example, referring to Fig 8, there is shown another confocal microscope 40 which is largely similar to the confocal microscope 1 described with reference to Figs 4 and 5, and like parts are assigned the same reference numerals. In this case the beam splitter 10 is mounted in an alternative location intermediate the lens array 7 and the inner end 6 of the optical fibre bundle 3.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the appended claims.

Claims (10)

1. An optical system comprising: an optical fibre bundle having a plurality of optical fibres, each optical fibre having an outer end and an inner end, the outer end for reception of light from an object to be viewed, means for sequentially scanning the optical fibres in the optical fibre bundle in groups of one or more selected optical fibres in a desired sequence, and means for building a composite image of the object from the scanned optical fibre images, characterised in that the sequential scanning means includes a lens array having a lens associated with each optical fibre and means for selectively switching each lens into or out of focus with its associated optical fibre.

2. An optical system as claimed in claim 1 herein each lens is a microlens of variable focal length.

3. An optical system as claimed in claim 2 wherein means is provided for applying a switching voltage to each microlens for adjustment of the focal length of the microlens to switch the microlens into or out of focus with its associated optical fibre.

4. An optical system as claimed in any preceding claim wherein a second array of lenses is mounted adjacent the outer end of the optical fibre bundle, having a lens associated with each optical fibre, said second lens array having means for selectively focusing each lens at portion of an object to be viewed.

5. An optical system as claimed in claim 4 wherein the second array of lenses comprises a plurality of microlenses of variable focal length, with means for IE 000001 -10applying a voltage to each microlens for adjustment of the focal length of the microlens.

6. An optical system as claimed in any preceding claim wherein a pair of lens arrays are mounted back to back adjacent an outer end of the optical fibre bundle for collection of light from an outer end of the optical fibre bundle and focussing light on the object to be viewed, having a complementary pair of lenses associated with each optical fibre.

7. An optical system as claimed in claim 6 wherein each lens array comprises a plurality of microlenses of variable focal lengths with means for applying a voltage to each microlens for adjustment of the focal length of the microlens.

8. A confocal microscope incorporating the optical system as claimed in any proceeding claim, comprising: an objective lens, an optical fibre bundle mounted behind the objective lens, -x said optical fibre bundle comprising a plurality of individual optical fibres, each optical fibre having an inner end and an outer end, a lens array associated with the optical fibre bundle mounted spaced-apart from an inner end of the optical fibre bundle, said lens array having a plurality of variable focal length microlenses, a microlens being associated with each optical fibre in the optical fibre bundle, means for selectively applying a voltage to each microlens to vary the focal length to switch the microlens into or out of focus with the inner end of its associated optical fibre, ' IE 000001 -11a photodetector, means for directing an image from each microlens to the 5 photodetector, a light source and means for directing light from the light source though the optical fibre bundle at an object placed in front of the objective lens, control means operable for sequentially applying focusing voltages to a number of sets of spaced-apart microlenses to collect images of portions of an object, and assembling said images to form a composite image of an object being viewed.

9. An optical system substantially as hereinbefore described with reference to the accompanying drawings.

10. A confocal microscope substantially as hereinbefore described with reference 20 to the accompanying drawings.