SUSPENDING DEVICE FOR OPTICAL FIBRE PREFORMS

Abstract

An optical fibre preform suspending device for vertically holding an optical fibre preform by a preform handle comprising a handle enlarged-width portion is provided. The preform suspending device having a substantially cylindrical shape and comprising a housing portion having a receiving space with a front top opening and a front bottom opening and a supporting surface between the front top opening and the front bottom opening. The preform suspending device also comprises a supporting member placed on the supporting surface, for holding the handle enlarged-width portion. The supporting member is radially independent from the housing portion.

Claims

1. An optical fibre preform suspending device for vertically holding an optical fibre preform by a preform handle comprising a handle enlarged-width portion, the preform suspending device having a substantially cylindrical shape and comprising: a housing portion having: a receiving space with a front top opening and a front bottom opening, and a supporting surface between the front top opening and the front bottom opening, a supporting member placed on the supporting surface, for holding the handle enlarged-width portion, wherein the supporting member is radially independent from the housing portion.

2. The suspending device of claim 1, wherein the housing portion is made of quartz.

3. (canceled)

4. The suspending device of claim 1, wherein the supporting member is made of a ceramic material.

5. The suspending device of claim 4, wherein the supporting member is made of a non-oxygen-combustible material.

6. The suspending device of claim 4, wherein the supporting member is made of graphite.

7. The suspending device of claim 4, wherein the supporting member is made of alumina.

8. The suspending device of claim 1, wherein the supporting member covers at least 80% of the supporting surface width.

9. The suspending device of claim 1, wherein the supporting member is U-shaped.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will now be described in more detail hereinafter with reference to the accompanying drawings, in which some embodiments of the invention are shown. Drawings illustrating the embodiments are not-to-scale schematic representations.

[0039] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term about. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

[0040] FIG. 1a and FIG. 1b are vertical front views of part of a suspending device for hanging a preform (not shown) by a handle, in original condition and in the presence of a deformation, respectively.

[0041] FIG. 2 is a schematic vertical front view of a suspending device according to the invention, showing also the positional relationship of a handle joined to a partially porous preform to the supporting portion of the device.

[0042] FIG. 3 is a partial section perspective view of suspending device of FIG. 2 (optical fibre preform with handle not shown).

[0043] FIG. 4 is cross section of the suspending device of FIG. 2, along the plane IV-IV.

[0044] FIG. 5 is an enlarged vertical front view of part of a suspending device for hanging a preform (not shown) by a handle, according to the invention, in rest condition.

DETAILED DESCRIPTION

[0045] FIG. 2 is a schematic vertical front view of a suspending device for holding a preform by a handle. The figure shows also the positional relationship of a handle joined to a partially porous preform and the supporting portion of the device. FIGS. 3 and 4 are, respectively, a partial section perspective view and a cross-section view of the suspending device of FIG. 2, in which the handle and the preform are not shown.

[0046] An optical fibre preform 16 is suspended, at its upper end, in a vertical orientation to a suspending and holding device 10 by a handle 2, which is joined to the preform. In the embodiment shown in FIG. 2, the preform 16 is partially porous and comprises a glass core rod 17 surrounded by a silica soot overcladding layer 18 deposited on the core rod.

[0047] The handle 2 is attached at one end of the core rod 17, e.g. by fusing the handle to the rod 17 at the position schematically indicated with referral number 21. Preferably, the handle is made of fused quartz, with a composition similar to the one of the silica glass of the core rod. Within the context of the present disclosure, with handle it is indicated an element by which the preform is manipulated and/or supported. It is possible, for example, for the handle to be integral with the core rod or separately attached to the core rod.

[0048] The handle 2 is generally cylindrical in shape and comprises an enlarged-width longitudinal portion 3, which is shaped as a spherical ball of diameter larger than that of remaining upper and lower portions 2a and 2b of the handle. It is to be understood that the enlarged-width portion may have a different shape from a spherical ball and/or it may be located at the upper end of the handle, instead of at an intermediate portion of the same.

[0049] Commonly employed methods of manufacturing the glass core rod are for example an inside tube deposition process, such as plasma chemical vapour deposition (PCVD), or an outside deposition process, such as outside vapour deposition (OVD) or vapour axial deposition (VAD).

[0050] The suspending device 10 comprises a housing portion 19 having a receiving space 11, configured to house the preform handle 2.

[0051] The receiving space 11 comprises an upper cavity 11c, forming a front top opening 11a on the front surface of the suspending device 10, and a lower cavity 11d, forming a front bottom opening 11b on the front surface of the suspending device. The lower cavity 11d is open on the bottom face of the suspending device 10.

[0052] The lower cavity 11d has a smaller width than the upper cavity 11c.

[0053] The lower cavity 11d and the upper cavity 11c are sized for the insertion, respectively, of the preform handle 2 and of the enlarged-width portion 3 of the preform handle 2.

[0054] Preferably, at least the housing portion 19 of the suspending device 10 is made of quartz, more preferably, the whole suspending device is made of quartz.

[0055] Between the upper cavity 11c and the lower cavity 11d a supporting surface 12 is defined. Preferably, the supporting surface 12 is horizontal, and perpendicular to the vertical lay of suspension of the preform, indicated by the longitudinal axis 20, which corresponds to the main longitudinal extension of the suspending device 10.

[0056] Preferably, there is a clearance in the longitudinal direction between the handle and the sidewalls of the lower cavity.

[0057] Preferably, the upper cavity 11c and the lower cavity 11d have a U-shaped cross-section.

[0058] The supporting surface 12 defines a bottom surface of the cavity 11c for the engagement of the enlarged-width portion of the handle.

[0059] A supporting member 13 is placed on the supporting surface 12 for supporting the handle enlarged-width portion 3, wherein the supporting member 13 is configured to lay over the supporting surface 12 and to leave sufficient room in the receiving space clear for the insertion of the handle. In this way, when the preform handle is inserted in the receiving space, the enlarged-width portion 3 of the handle lays on the supporting member 13.

[0060] Preferably, the supporting member 13 substantially extends substantially over the whole supporting surface 12. Covering substantially the whole supporting surface 12 is preferred in order to reduce the precision required for the insertion of the handle in the receiving space of the suspending device.

[0061] With substantial covering of the whole (supporting) surface it is meant that the horizontal width of the supporting member 13 is equal to or smaller by less than about 20% than the width of the supporting surface 12, to allow for normal manufacturing tolerances.

[0062] The supporting surface 12 is preferably a continuous surface between two ends at the front opening of the suspending device.

[0063] The supporting member 13 is preferably removably disposed on the supporting surface 12, as indicated in FIG. 3. The supporting member 13 can be inserted in the receiving cavity 11 and laid down on the supporting surface 12. This enables an easy substitution of the supporting member 13 in case of its accidental damage, wear or rupture during handling of the piece.

[0064] Preferably, the supporting surface 12 is U-shaped and the supporting member 13 is U-shaped and extends over at least a portion of the supporting surface 12.

[0065] Preferably, the U-shaped supporting member 13 extends over at least a portion of the width of the supporting surface 12, which is not less than 80% of the surface width of the supporting surface 12.

[0066] Preferably, the supporting member 13 comprises two parallel arms 13a, 13b extending from a connection curved portion 13c. The distance between the arms 13a, 13b is selected to allow an easy insertion of the preform handle 2.

[0067] For example, the supporting surface 12 has width d1 of 5 mm and the U-shaped supporting member 13 has width d2 of 4 mm, as shown in FIG. 4.

[0068] It is to be understood that numerical examples are purely indicative since dimensions of the supporting surface 12 and thus of the supporting member 13 may depend on the size of the enlarged-width portion of the handle.

[0069] Preferably, the supporting member 13 is made of a material having a melting point of at least 2000 C., preferably a ceramic material.

[0070] Given that temperatures used for dehydration and consolidation of porous soot preforms typically range from 1300 C. to 1650 C., a relatively high melting point prevents thermal deformation of the supporting member 13 during dehydration and sintering of the preform.

[0071] Preferably, the melting point of the material of the supporting member 13 is of at least about 1750 C.

[0072] Preferably, the supporting member 13 is made of a non-oxygen-combustible material, such as graphite or a graphite-based material.

[0073] Alternatively, the supporting member 13 is made of alumina or an alumina based material.

[0074] Preferably, the supporting member 13 has a thickness t of from 2 mm to 15 mm, preferably of from 4 mm to 12 mm.

[0075] The suspending device 10 further comprises an upper connecting portion 15 connected with or integral to the housing portion 19 and arranged above the same. The upper connecting portion 15 is configured to be operatively connected to a vertical driving device (not shown in the figures), for vertically moving the suspended preform. Preferably, the upper connecting portion is integral to the housing portion so as to form a whole body, the body being preferably made of quartz.

[0076] The vertical driving device for lowering the preform into the furnace can be of conventional type. Typically, the furnace body of a furnace for dehydration and consolidation of optical fibre preforms is elongated, for example of a generally cylindrical shape and a conventional vertical driving device imparts to the suspending device a translational movement (up and down in the downfeed direction 20) along the furnace body, for example by means of a guide and a translational transfer mechanism. A rotation around the downfeed direction may be also imparted to the preform from a motor mounted on the vertical driving device.