GB2123973A

GB2123973A - Combined condenser lens and optical fibre specimen holder for optical microscopic examination

Info

Publication number: GB2123973A
Application number: GB08220274A
Authority: GB
Inventors: Robert Gibson
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-07-13
Filing date: 1982-07-13
Publication date: 1984-02-08
Also published as: GB2123973B

Abstract

A combined condenser lens and optical fibre specimen holder for examination of the ends of optical fibres by optical microscopy. This replaces the condenser lens of a conventional microscope, which is unsuited for optical fibre examination due to the minimum length of optical fibre specimens being very much larger than the thickness of typical microscope specimens viewed by transmission. The fibre 4 is clamped in a groove and arranged to cooperate optically with a spherical condenser lens 2. <IMAGE>

Description

SPECIFICATION Combined condenser lens and optical fibre specimen holder for optical microscopic examination This invention relates to a combined condensor lens assembly and optical fibre specimen holder for end examination of specimens of optical fibre by optical microscopy.

In the production of optical fibre there is a requirement to make periodic optical microscopy examination of the ends of specimen samples of the optical fibre to determine its quality, particularly the size, roundness, and concentricity of its core. It may be sufficient for this quality assessment to be carried out, examination of the optical image by eye; more usually a photographic record is required, or another form of record produced by for instance projecting the image on to a TV camera interface with computerised analysis equipment.

A conventional biological optical microscope is not suited to providing a well illuminated image for optical examination of the end of an optical fibre sample because that sample is very much longer than the thickness of typical biological specimens for which the optics of such microscopes are designed.

It is probable that more detail would be resolved if the optical fibre specimens could be reduced in axial length to the thickness of biological specimens, but this believed unlikely to become a practical proposition at least for routine examination work because the relative hardness of the fibre make the preparation of such samples difficult to achieve.

One approach to this problem has been to dispense with the illumination system of the microscope and to use samples of fibre that are long enough for the fibre end remote from that under the microscope objective to be led away from the microscope and placed against a light bulb. This approach allows examinations to be made, but has the disadvantages of being cumbersome and of providing far from ideal conditions of illumination, and consequent impairment of resolution.

According to the present invention there is provided a condenser lens assembly and optical fibre specimen holder combination for an optical microscope, which combination includes a pair of mating clamp parts at least one of which is provided with a groove for axial location of an optical fibre specimen clamped between the parts, a base member provided with means for locating a spherical condenser lens, and means integral with or secured to the base member for receiving the pair of mating clamp parts in their mated condition and locating them with respect to the base member such that the point of emergence of the fibre location axis from the mating parts lies in the region of the focus of the condenser lens, with the axis itself passing through the lens centre.

There follows a description of a combined condenser lens assembly and optical fibre specimen holder embodying the invention in a preferred form.

The description refers to the accompanying drawings in which Figure 1 depicts a plan view of the combination and Figure2 depicts a sectional view on the line A-A'.

Referring to the drawings, a metal base plate 1 is provided with a central aperture to accommodate a spherical condenser lens 2 which may be provided for instance by a 6mm glass boiling bead. Coaxial with this aperture, the base plate is provided with an externally threaded hollow spigot 3.

A specimen length of optical fibre 4 is held between a pair of metal clamping parts 5 and 6 which fit together with dowels 7. Clamping part 5 is provided with a Vee groove to locate the fibre which is lightly pressed into this groove by a resilient pad 8 inset into clamping part 6. By this means the fibre is secured on the axis of the clamping parts which are held together in position by inserting them in a metal collar 9 which is internally threaded to engage the threads of the spigot 3. Optionally the collar may be provided with an annular finger grip 10 which can conveniently take the form of an O-ring stretched over the curved surface of the collar.

To use this device in a microscope, the condenser lens sub-stage may be removed or moved out of the way and the assembly mounted on the microscope specimen stage. Alternatively the assembly may be mounted on the sub-stage in place of the condenser lens mount. In this instance coarse focus of the specimen can be achieved by racking the sub-stage, while X and Y movements can be adjusted using the condenser lens centering screws of the sub-stage.

The assembly is dimensioned so that if the lower end of the fibre terminates approximately flush with the bottom of the clamping parts it will lie in the region of the focal point of the condenser lens 2. In a conventional microscope the condenser is positioned to receive a substantially collimated beam of light from the microscope light source, and hence the, lens 2 forms a concentrated beam of light for launching into the fibre. It is not essential to position the lower end of the fibre exactly at the point of focus ofthe light, and hence it is not essential for the collar to be adjustable in height with respect to the base plate.However, it is found that when an adjustable height collar is employed, changes in its height do produce small changes in the appearance of the image, and it is believed that these are attributable to alterations in the distribution of optical power between the modes launched into the fibre from lens 2.

For this reason a facility for height adjustment is preferred.

1. A condenser lens assembly and optical fibre specimen holder combination for an optical microscope, which combination includes a pair of mating clamp parts at least one of which is provided with a groove for axial location of an optical fibre specimen clamped between the parts, a base member provided with means for locating a spherical condenser lens, and means integral with or secured to the base member for receiving the pair of mating clamp parts in their mated condition and locating them with respect to the base member such that the point of emergence of the fibre location axis from the mating

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Combined condenser lens and optical fibre specimen holder for optical microscopic examination This invention relates to a combined condensor lens assembly and optical fibre specimen holder for end examination of specimens of optical fibre by optical microscopy. In the production of optical fibre there is a requirement to make periodic optical microscopy examination of the ends of specimen samples of the optical fibre to determine its quality, particularly the size, roundness, and concentricity of its core. It may be sufficient for this quality assessment to be carried out, examination of the optical image by eye; more usually a photographic record is required, or another form of record produced by for instance projecting the image on to a TV camera interface with computerised analysis equipment. A conventional biological optical microscope is not suited to providing a well illuminated image for optical examination of the end of an optical fibre sample because that sample is very much longer than the thickness of typical biological specimens for which the optics of such microscopes are designed. It is probable that more detail would be resolved if the optical fibre specimens could be reduced in axial length to the thickness of biological specimens, but this believed unlikely to become a practical proposition at least for routine examination work because the relative hardness of the fibre make the preparation of such samples difficult to achieve. One approach to this problem has been to dispense with the illumination system of the microscope and to use samples of fibre that are long enough for the fibre end remote from that under the microscope objective to be led away from the microscope and placed against a light bulb. This approach allows examinations to be made, but has the disadvantages of being cumbersome and of providing far from ideal conditions of illumination, and consequent impairment of resolution. According to the present invention there is provided a condenser lens assembly and optical fibre specimen holder combination for an optical microscope, which combination includes a pair of mating clamp parts at least one of which is provided with a groove for axial location of an optical fibre specimen clamped between the parts, a base member provided with means for locating a spherical condenser lens, and means integral with or secured to the base member for receiving the pair of mating clamp parts in their mated condition and locating them with respect to the base member such that the point of emergence of the fibre location axis from the mating parts lies in the region of the focus of the condenser lens, with the axis itself passing through the lens centre. There follows a description of a combined condenser lens assembly and optical fibre specimen holder embodying the invention in a preferred form. The description refers to the accompanying drawings in which Figure 1 depicts a plan view of the combination and Figure2 depicts a sectional view on the line A-A'. Referring to the drawings, a metal base plate 1 is provided with a central aperture to accommodate a spherical condenser lens 2 which may be provided for instance by a 6mm glass boiling bead. Coaxial with this aperture, the base plate is provided with an externally threaded hollow spigot 3. A specimen length of optical fibre 4 is held between a pair of metal clamping parts 5 and 6 which fit together with dowels 7. Clamping part 5 is provided with a Vee groove to locate the fibre which is lightly pressed into this groove by a resilient pad 8 inset into clamping part 6. By this means the fibre is secured on the axis of the clamping parts which are held together in position by inserting them in a metal collar 9 which is internally threaded to engage the threads of the spigot 3. Optionally the collar may be provided with an annular finger grip 10 which can conveniently take the form of an O-ring stretched over the curved surface of the collar. To use this device in a microscope, the condenser lens sub-stage may be removed or moved out of the way and the assembly mounted on the microscope specimen stage. Alternatively the assembly may be mounted on the sub-stage in place of the condenser lens mount. In this instance coarse focus of the specimen can be achieved by racking the sub-stage, while X and Y movements can be adjusted using the condenser lens centering screws of the sub-stage. The assembly is dimensioned so that if the lower end of the fibre terminates approximately flush with the bottom of the clamping parts it will lie in the region of the focal point of the condenser lens 2. In a conventional microscope the condenser is positioned to receive a substantially collimated beam of light from the microscope light source, and hence the, lens 2 forms a concentrated beam of light for launching into the fibre. It is not essential to position the lower end of the fibre exactly at the point of focus ofthe light, and hence it is not essential for the collar to be adjustable in height with respect to the base plate.However, it is found that when an adjustable height collar is employed, changes in its height do produce small changes in the appearance of the image, and it is believed that these are attributable to alterations in the distribution of optical power between the modes launched into the fibre from lens 2. For this reason a facility for height adjustment is preferred. CLAIMS

1. A condenser lens assembly and optical fibre specimen holder combination for an optical microscope, which combination includes a pair of mating clamp parts at least one of which is provided with a groove for axial location of an optical fibre specimen clamped between the parts, a base member provided with means for locating a spherical condenser lens, and means integral with or secured to the base member for receiving the pair of mating clamp parts in their mated condition and locating them with respect to the base member such that the point of emergence of the fibre location axis from the mating parts lies in the region of the focus of the condenser lens, with the axis itself passing through the lens centre.

2. A combination as claimed in claim 1, wherein the clamp parts are located in a collar screwthreadedly engaged with the base member, whereby the height of the located clamp parts with respect to the base member is adjustable.

3. A combined condenser lens assembly and optical fibre specimen holder substantially as hereinbefore described with reference to the accompanying drawings.