GB2107069A - Optical fibre test grips - Google Patents

Abstract

Each one of a pair of optical fibre test grips has a fixed elastomeric capstan 1 around which several turns of fibre are wrapped. The final turn is accommodated in a groove 4 and clamped in position by means of a clamping plate 7 which urges the side walls of the groove together. <IMAGE>

Description

SPECIFICATION Optical fibre test grips This invention relates to the design of test grips for performing tensile tests on lengths of on-line coated optical fibres.

For many applications of optical fibre an important parameter is the change of optical performance brought about by the imposition of tensile stress. In order to be able to make measurements of such changes it is necessary to grip the fibre in two spaced apart regions and apply tension over the intervening region. Clearly the gripping must be sufficiently tight to prevent slippage at the values of tension required to be investigated. Normally this gripping will involve applying lateral compressive forces to the fibre.

These forces are themselves liable to damage the optical performance of the fibre, and hence it is necessary to use test grips which can support without slippage a relatively large tensile force with a relatively low compressive force.

Since the strength of a freshly drawn glass optical fibre deteriorates relatively rapidily if its surface is left exposed to atmospheric attack, it is general practice to arrange for the fibre to be provided with a protective coating on-line with the fibre drawing operation. For some applications, it is desirable to use such an on-line coated fibre where it is subject to tension without first having received any other coating. For such applications it may be necessary to measure the tensile strength of the on-line coated fibre over a wide temperature range, typically20 C to +600C, for example.

According to the present invention there is provided a pair of tensile test grips for gripping a plastics coated optical fibre in two spaced apart regions for subjecting the intervening region of fibre to tensile stress, each of which test grips includes a non-rotating elastomeric cylindrical capstan provided, adjacent the edge of one of the capstan end faces, with a circumferential groove to a depth greater than a fibre diameter, wherein the capstan is provided with a substantially rigid capping plate and means for clamping said plate against said one end face to urge together the side walls of the groove so as to trap an optical fibre inserted therebetween.

A feature of this design is that it is relatively compact, and it is particularly useful when testing is required in special environments of controlled temperature and humidity within a confined space. The grips are useable over a wide temperature range of-600C to +1200C, without incurring degradation to capstans or to the on-line coated fibre, and in addition obviating the slippage of fibre over such a large temperature range. Such grips are also suitable for conducting specialised static fatigue tests on on-line coated fibres.

There follows a description of one of a pair of test grips embodying the invention in a preferred form. The description refers to the accompanying drawing which depicts an exploded perspective view of one test grip.

Referring to the drawing, a substantially cylindrical natural rubber capstan 1 is rigidly attached to a metal bracket member 2 by means of a length of studding 3. This particular capstan is designed for performing tests on optical fibre having a diameter in the range 1 000 microns encased in a primary coating, and the capstan has a diameter of about 6 cm and a length between its end faces of about 4.5 cm.

The choice of a suitable diameter depends not only upon mechanical considerations but also upon optical ones. A typical silica optical fibre can be bent to a significantly tighter radius having regard to its mechanical properties, but in the case of low numerical aperture fibre a significantly tighter radius will be undesirable if it is tight enough to introduce radiative losses.

Typically with the 6 cm diameter capstan enough fibre is held in contact with the capstan by somewhere in the region of five whole turns of fibre wrapped around the smooth curved capstan surface, after which a final, nearly complete turn is accommodated in the fine groove 4 formed in the curved surface of the capstan near its outer end face 5.

Secured to this outer end face 5 by means of the studding 3 and the wing nut 6 is a metal capping disc 7 having the same diameter as the main portion of the capstan 1, and the groove 4 is preferablyshaped in cross-section and dimensioned so that the on-line coated fibre is pinched between the walls of the U. Typically the groove is about 0.1 mm wide, and about 1 to 2 mm in depth. The fibre is actually clamped by the action of the capping disc compressing the rubber end face, thereby pressing the two walls of the groove onto the fibre and holding the fibre in position.

Claims

1. A pair of tensile test grips for gripping a plastics coated optical fibre in two spaced apart regions for subjecting the intervening region of fibre to tensile stress, each of which test grips includes a non-rotating elastomeric cylindrical capstan provided, adjacent the edge of one of the capstan end face, with a circumferential groove to a depth greater than a fibre diameter, wherein the capstan is provided with a substantially rigid capping plate and means for clamping said plate against said one end face to urge together the side walls of the groove so as to trap an optical fibre inserted therebetween.

2. A pair of tensile test grips substantially as hereinbefore described with reference to the accompanying drawings.

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

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical fibre test grips This invention relates to the design of test grips for performing tensile tests on lengths of on-line coated optical fibres. For many applications of optical fibre an important parameter is the change of optical performance brought about by the imposition of tensile stress. In order to be able to make measurements of such changes it is necessary to grip the fibre in two spaced apart regions and apply tension over the intervening region. Clearly the gripping must be sufficiently tight to prevent slippage at the values of tension required to be investigated. Normally this gripping will involve applying lateral compressive forces to the fibre. These forces are themselves liable to damage the optical performance of the fibre, and hence it is necessary to use test grips which can support without slippage a relatively large tensile force with a relatively low compressive force. Since the strength of a freshly drawn glass optical fibre deteriorates relatively rapidily if its surface is left exposed to atmospheric attack, it is general practice to arrange for the fibre to be provided with a protective coating on-line with the fibre drawing operation. For some applications, it is desirable to use such an on-line coated fibre where it is subject to tension without first having received any other coating. For such applications it may be necessary to measure the tensile strength of the on-line coated fibre over a wide temperature range, typically20 C to +600C, for example. According to the present invention there is provided a pair of tensile test grips for gripping a plastics coated optical fibre in two spaced apart regions for subjecting the intervening region of fibre to tensile stress, each of which test grips includes a non-rotating elastomeric cylindrical capstan provided, adjacent the edge of one of the capstan end faces, with a circumferential groove to a depth greater than a fibre diameter, wherein the capstan is provided with a substantially rigid capping plate and means for clamping said plate against said one end face to urge together the side walls of the groove so as to trap an optical fibre inserted therebetween. A feature of this design is that it is relatively compact, and it is particularly useful when testing is required in special environments of controlled temperature and humidity within a confined space. The grips are useable over a wide temperature range of-600C to +1200C, without incurring degradation to capstans or to the on-line coated fibre, and in addition obviating the slippage of fibre over such a large temperature range. Such grips are also suitable for conducting specialised static fatigue tests on on-line coated fibres. There follows a description of one of a pair of test grips embodying the invention in a preferred form. The description refers to the accompanying drawing which depicts an exploded perspective view of one test grip. Referring to the drawing, a substantially cylindrical natural rubber capstan 1 is rigidly attached to a metal bracket member 2 by means of a length of studding 3. This particular capstan is designed for performing tests on optical fibre having a diameter in the range 1 000 microns encased in a primary coating, and the capstan has a diameter of about 6 cm and a length between its end faces of about 4.5 cm. The choice of a suitable diameter depends not only upon mechanical considerations but also upon optical ones. A typical silica optical fibre can be bent to a significantly tighter radius having regard to its mechanical properties, but in the case of low numerical aperture fibre a significantly tighter radius will be undesirable if it is tight enough to introduce radiative losses. Typically with the 6 cm diameter capstan enough fibre is held in contact with the capstan by somewhere in the region of five whole turns of fibre wrapped around the smooth curved capstan surface, after which a final, nearly complete turn is accommodated in the fine groove 4 formed in the curved surface of the capstan near its outer end face 5. Secured to this outer end face 5 by means of the studding 3 and the wing nut 6 is a metal capping disc 7 having the same diameter as the main portion of the capstan 1, and the groove 4 is preferablyshaped in cross-section and dimensioned so that the on-line coated fibre is pinched between the walls of the U. Typically the groove is about 0.1 mm wide, and about 1 to 2 mm in depth. The fibre is actually clamped by the action of the capping disc compressing the rubber end face, thereby pressing the two walls of the groove onto the fibre and holding the fibre in position. Claims

1. A pair of tensile test grips for gripping a plastics coated optical fibre in two spaced apart regions for subjecting the intervening region of fibre to tensile stress, each of which test grips includes a non-rotating elastomeric cylindrical capstan provided, adjacent the edge of one of the capstan end face, with a circumferential groove to a depth greater than a fibre diameter, wherein the capstan is provided with a substantially rigid capping plate and means for clamping said plate against said one end face to urge together the side walls of the groove so as to trap an optical fibre inserted therebetween.

2. A pair of tensile test grips substantially as hereinbefore described with reference to the accompanying drawings.