Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1999-08-16
2002-02-26
Healy, Brian (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000, C385S127000, C385S100000, C385S102000
Reexamination Certificate
active
06351589
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a removably coated optical waveguide and in particular to a removably coated optical fibre for laser transmission which may be incorporated into an optical device or telecommunication system.
Since their inception in the mid-1960's, the growth of the use of optical fibres, generally manufactured from silica or other glasses, in optical devices and telecommunication systems has been substantial. This growth has been due largely to the remarkable data carrying capacity displayed by fibres.
Generally speaking the optical fibre comprises an optical fibre core, of a certain refractive index, which may be clad by an optical cladding of slightly lower refractive index. Alternatively, a graded index fibre, which comprises layers of optical material with decreasing refractive indices, may be employed.
However, optical fibres do have a significant draw back, in that they are relatively brittle and fragile. Therefore, optical fibres are commonly provided with a protective coating of a plastics material, commonly a UV curable material such as an acrylate or a UV curable polymide. Desolite
950
-
106
,
950
-
108
,
950
-
131
and
3471
-
3
-
14
are routinely used for coating optical fibres for general purpose uses. Thermally cured silicon coatings, such as Sylgard
180
and
184
are also available. However, these materials provide a relatively soft and tacky coating which is used in either high temperatures or chemical environments in which acrylate coatings are not suitable.
For practical use in telecommunication systems such coated fibres may be combined into multi-fibre cables formed, for example, from a polyurethane outer jacket. If additional strengthening is required the jacket may be provided with strengthening members formed, for example, from Kevlar. However, as this application relates to the coating of individual fibres, such multi-fibre cables will not be discussed further herein.
In use optical fibres tend to be end coupled and end pumped, at least in part because of the requirement to coat the fibres. That is, any useful radiation within the optical fibre is injected through the end face of the fibre, travels the full length of the fibre through internal reflection, in the normal manner, and is transmitted from the remote end of the fibre.
However, in some situations there are significant advantages to be gained from direct access to uncoated portion of the optical fibre. By far the most important of these is the use of a light source to produce permanent light sensitive changes within the optical fibres. In other words advantages are gained from the use of a light source to produce a periodic refractive index modulation within the fibre in the form of a grating. The most common light source used is a UV laser such as an Eximer or Argon ion laser. Such gratings can be used in a host of devices from sensors and band pass filters to fibre laser mirrors.
Applications which require the removal of the coating over lengths exceeding 50 mm include, for example: fibre grating dispersion equalisers and long period gratings, which may be written into the optical fibre (either the core or the cladding), for applications which include gain flattening, polarisation rocking and or loss filters; wave length selective polarisers; and cladding mode pumped amplifiers. For example, a dispersion equaliser requires up to eight meters in length of coating to be removed from the fibre, which leaves a substantial length of optical fibre which is open to contamination or physical damage.
In this device a long chirped grating is written into a stripped fibre spanning the 32 nm gain window of an erbium amplifier. Such a device, when connected to the first output port of a three port circulator provides equalisation of dispersed signals transmitted down the fibre. The chirped grating simply removes the wavelength dependent time delay spreading arising from the dispersion in the transmission fibre.
Long period grating applications operate on the basis that a refractive index variation along the length of a fibre has a period that matches the difference in propagation constants for the lowest order mode in the fibre core and some higher order mode in the cladding. This causes power to be transferred from one mode to the other, which can be used to provide wavelength selective loss and polarisation rocking in two moded fibres, ie alternate coupling between the two polarisation modes that exist in so called single mode fibres. In cladding mode pumped amplifiers by writing the index changes in the cladding power can be transferred from the cladding to the core more efficiently than would otherwise be possible.
The invention would be useful for fused couplers where two or more optical fibres are melted together to enable light to be transferred between the respective cores. This process requires the absence of any polymer coating or residue on the fibres.
A further area in which the invention may be useful is in the area of non-intrusive taps wherein a loss mechanism such as micro-bending can be used to eject light from the length of the fibre. If the coating is removed this light can more easily and efficiently be accessed. Therefore, there is a conflict between the need for access to the fibre and the need for protective coatings.
At present, access to lengths of optical fibre is obtained either by dissolving the fibre coating in a suitable organic solvent or the removal of a length of coating using a blade, to scrape away the coating. The problem with the latter approach is that it can damage the fibre or its cladding. Also, the process of dipping the fibre in solvent and washing an drying the fibre thereafter can also result in fibre damage.
Neither of these processes are of real practical value when substantial lengths of fibre greater than a few centimeters need to be stripped. Particularly, the use of a blade to scrape away the protective coating causes significant stress on the fibre which can cause an unacceptable degree of damage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a coating for a fibre through which access to the fibre can be obtained, easily and conveniently, with minimal probability of damaging the fibre during the stripping process.
According to a first aspect of the present invention there is provided a removably coated optical fibre comprising:
(i) an optical fibre; and
(ii) a removable coating formed from an elongate tape having two edges, the tape being affixed adjacent to said edges along a substantial length of the tape to form a releasable seam, access to the fibre being obtainable by peeling apart said seam.
According to a second aspect of the present invention there is provided a removably coated optical fibre comprising:
(i) an optical fibre; and
(ii) a removable coating formed from first and second elongate tapes which are affixed on either side of said optical fibrealong a substantial length of said tapes to form a releasable seam, access to the optical fibre being obtainable by peeling apart said tapes.
The coating may thus be readily and easily removed from the optical fibre by peeling apart along the releasable seam. The seam is manufactured in such a way as to provide a relative weak point in the coating, as compared with the strength of the tapes or other material used to make the coating once access to the fibre has been initiated, relatively large sections of the fibre may be exposed, without damage to the fibre, simply by peeling, pulling or tearing the seam.
Preferably, the coated optical fibre comprises a lubricant provided between said coating and said fibre.
Most preferably, the lubricant is a fluid, for example, ethylene glycol.
Alternatively, the lubricant is a solid, for example, a layer of polytetraflurethene (PTFE) applied to the inner.
Preferably, the tape is formed from low density polyethelene.
Preferably, the tape is sealed adjacent said edges using an adhesive such as a latex based pressure sensitive adhesive.
Preferably, the first elongate tape is planar, sa
Healy Brian
Lee, Mann, Smith McWilliams, Sweeney and Ohlson
Nortel Networks Limited
LandOfFree
Removably coated optical fibre does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Removably coated optical fibre, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Removably coated optical fibre will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2947787