FIBER

FIELD OF THE INVENTION

The present invention relates, generally to the field of microstructured fiber technology. More particularly, the present invention relates to an apparatus and method for use in fabricating a microstructured fiber and to an article produced thereby.

BACKGROUND OF THE INVENTION

In the last 30 years, optical fibers have been used to replace copper cables in the modern telecommunications network. This is due to the numerous advantages of optical fibers (when compared to copper cables) such as having a large potential bandwidth, low transmission loss (less than 0.2 dB per km), a smaller size, electromagnetic interference immunity and low manufacturing cost.

An optical fiber has a circular cross-section, normally with a circular solid core and cladding. A single mode optical fiber typically has a diameter of 125 μηι and a solid core with the diameter of 9 μηι. Light is guided inside the optical fiber through a total internal reflection which requires the refractive index of the core to be higher than the cladding. The cladding is usually made of fused silica without any dopant and the core is normally doped with dopants such as Germanium to get a higher refractive index.

Flat fibers are different from other optical fibers due to their planar cross- sectional region. Having a wider cross-sectional area has opened the flat fiber to various functionalities which allows such modifications to be embedded on the fiber itself, which is not possible in the conventional optical fibers. The flat fiber can be described as a ribbon-like planar sample that has extended length and fully flexible substrate. Hence, the flat fiber comprises a combination of both structural advantages of the optical fibers as well as functional benefits of the planar devices. The planar devices are commonly built on rigid substrates, i.e. silicon wafers, which are not mechanically flexible. Photonic crystal fibers, a member of microstructure optical fibers, and a class of holey fibers, produce light guidance effect through a pattern of tiny holes which run along the entire length of the fiber. The photonic crystal fibers employ a microstructure arrangement of material in a background material of different refractive index. Typically, an undoped silica is chosen as the background material and a low index region is provided by air voids running along the fiber's axis. The core size of the fibers is varied as to make the fibers: first, to have either very low or very high optical non-linearity, and second, capable of light transmission in air through photonic band gap effect (Cregan et al, 1999).

One of the conventional methods to fabricate photonic crystal fibers is by a stack-and-draw process. Typically, the fabrication of the photonic crystal fibers involves two stages that are preform preparation and fiber drawing. In general, the preform preparation stage involves capillary fabrication, stacking the capillaries into glass tube, and drawing the tube to form a cane, while in the fiber drawing stage, the cane is jacketed by another glass tube and is placed in a drawing tower and drawn. U.S. Patent Application Publication No. 201 1 /01 21474 A1 describes a method of manufacturing a microstructure fiber which includes, providing a preform having a plurality of elongate holes, mating the holes with a connector and drawing the preform into the fiber at a controlled pressure such that the structure of the fiber is satisfactory. In addition, U.S. Patent Application Publication No. 2004/0105641 A1 describes the drawing of a preform that includes holes, into a fiber which require a differential pressure to certain holes in order to control changes in the fiber structure so that the fiber can be used as a polarization- preserving fiber. A flat microstructure fiber has a shape that is similar to the flat fiber but comprises air holes (in one row or more) running across its photosensitive core. The flat microstructure fiber provides a versatile platform which makes it capable of fabricating various optical components via UV writing on the photosensitive core of the flat microstructure fiber. The flat microstructure fiber also provides a large sensing surface area, which could increase sensing sensitivity of equipment. The present invention aims to improve the functionality of an optical fiber by introducing a new concept that is beyond the conventional functions of the optical fibers, such as fluid sensing. In addition to the above, a fully functional integrated optical chip which is fiber like and mechanically flexible, is highly in demand especially in the optoelectronic sensing field.

A need therefore exists for providing technology allowing for economically exploitation on the fabrication of a flat microstructured fiber. Thus, the present invention seeks to provide a relatively cost-efficient apparatus and method for fabricating such flat microstructured fiber that has a cross-section with minimal airhole deformations, precise and accurate size dimensions and allows a light to be guided either by total internal reflection or photonic bandgap effects using its functional planar shape. Although the teachings of the prior art disclose various apparatuses and methods for producing the optical fiber, none specifically relates to an improved apparatus and method for fabricating the flat microstructured fiber as claimed in the present invention. Therefore, a need for the aforementioned features is met. SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

Accordingly, the present invention provides an apparatus for use in fabricating a flat microstructured fiber. The apparatus comprises means for feeding a preform; a drawing chamber connected to the means for feeding and being configured for drawing the preform; and means for collecting the preform drawn by the drawing chamber. The apparatus comprises an assembly that is removably mounted to the means for feeding having a first body and a second body. The first body is configured for holding the preform. The second body is coupled to the first body and being configured to hold a portion of a capillary positioned in the preform. The second body has attachment means. The capillary may be a plurality of capillaries that are arranged in a predetermined arrangement. Preferably, the capillaries are sealed to each other at one point of their body. The apparatus further comprises a pressure system, a tractor unit, and a capstan. According to another embodiment, the preform has a diameter larger than that of the capillary. The preform may be a hollow preform. Preferably, the preform is made of fused silica.

In accordance with another aspect, a method of fabricating a flat microstructured fiber is disclosed. The method comprises the steps of providing a preform; and drawing the preform. Preferably, the method comprises the steps of providing a capillary; deforming a portion of the capillary for mounting the capillary within an inner periphery of the preform; providing a vacuum; drawing the capillary and the preform to form a flat cane; and drawing the flat cane to form the flat microstructured fiber.

In yet another aspect, the present invention describes a planar or flat shaped article having air holes manufactured by the above method. It is an advantage of the present invention to provide an apparatus for fabricating a flat microstructured fiber that is relatively simple to manufacture, easy to install and use, and comparatively cost efficient.

It is another advantage of the present invention to provide a method of fabricating a flat microstructured fiber which is capable to minimize air hole deformations of the fiber and to provide a precise and accurate size dimension of the fiber.

It is yet another advantage of the present invention to provide a low cost flat microstructured fiber with high purity. Furthermore, the flat microstructured fiber of the present invention is configured for higher doping potential and exhibits an extended size dimension in length.

The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Figure 1 is a flowchart comprises steps for fabricating a flat microstructured fiber;

Figure 2 shows an apparatus used to fabricate the flat microstructured fiber; Figure 3(a) shows a cross-sectional area of the flat microstructured fiber;

Figure 3(b) shows microscopic view of the flat microstructured fiber;

Figures 4(a) to 4(c) depict examples of arrangements for the capillaries in the flat microstructured fiber;

Figures 5(a) to 5(c) envisage samples of the flat microstructured fiber with deformed air holes; and Figures 6(a) to 6(b) envisage samples of the flat microstructured fiber with no air holes deformation.

It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numberings represent like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The fabrication of the microstructured fiber or particularly, a flat or planar microstructured fiber, like in conventional fiber fabrication, starts with a preform. The preform is constructed by way of stacking a number of capillaries to form the desired arrangement in which as a result, allows flexibility and control of a core size and shape as well as an index profile throughout a cladding region. Subsequently, the preform is drawn to a fiber in a drawing tower. For example, in the fabrication of a flat fiber, a single stage drawing process is adequate. However, in fabricating the flat microstructured fiber, a dual-stage drawing with capillaries in the preform is preferred and as claimed in the present invention.

It is an object of the present disclosure to provide an apparatus and method for use in fabrication of a flat microstructured fiber that prevents air holes deformation. The flat microstructured fiber allows the light to be guided either through the total internal reflection or photonic band gap effects, while having a versatile flat or planar shape. The present disclosure also aims to encourage more development in fabrication of the optical components that is based on the planar shape which able to reduce connection and coupling losses. The present disclosure is capable to overcome some problems in the prior art that include deformation of air holes such as total collapse of holes, changes in hole size dimension, shape and position, and missing holes.

Figure 1 describes the steps that are employed in the fabrication of the flat microstructured fiber. In step 100, a capillary 202 which may include a plurality of the capillaries is prepared and provided. The capillary 202 can be made of fused silica and is cut into a desired length. The capillary 202 has a distal end and proximal end. The distal end of the capillary 202 is deformed to a shape such as a curved or angular piece. The proximal end is subject to be drawn in a drawing chamber 203. An example of the arrangement of the capillary 202 is schematically shown in Figure 2. The capillaries 202 can be arranged in a single array, multiple arrays, lattice or the like. To hold the capillaries 202 in the particular arrangement, a portion of the distal end of the capillaries 202 may be sealed.

The arrangement of the capillaries 202 as shown in Figure 4(a), for example, depicts that the flat microstructured fiber has one row of air holes. Figure 4(b), on the other hand, shows the flat microstructured fiber which has three rows of air holes and three solid cores within the air holes. Figure 4(c) shows the flat microstructured fiber has three rows of air holes and two solid cores. A preform 201 , preferably, a hollow preform is provided. The preform 201 has a diameter larger than the diameter of the capillary 202. The preform 201 can be made of the same material as the capillary 202. For example, the preform 201 can be made of material such as fused silica. The preform 201 , upon drawing, forms a cladding for the flat microstructured fiber which surrounds the air holes made by the capillaries 202. An example of a cross-sectional area 300 of the flat microstructured fiber is described schematically in Figure 3(a). The cross- sectional area 300 envisages the fiber cladding 301 , a fiber core 302 and the air holes 303. Alternatively, Figure 3(b) provides a microscopic image of the flat microstructured fiber.

An apparatus for fabricating the flat microstructured fiber is disclosed as shown in Figure 2. The apparatus comprises an assembly 200 that is mounted to means for feeding the preform 201. The assembly 200 has a first body and a second body. The first body is configured to hold the preform 201 in position where the preform 201 is drawn. The second body is configured to hold the capillaries 202 by attachment means coupled to the body in position where the side wall of the capillaries 202 is parallel to the side wall of the preform 201 . The attachment means of the capillary 202 coupled to the second body may be, but not limited to, by hanging, clipping and the like, or a fastener. The second body is also configured to hold the capillaries 202 consistently at any arrangement throughout the drawing process such that the thusly produced fiber forms air holes without deformation or distortion as in Figures 6(a) and 6(b). On the contrary, a flat microstructured fiber with the deformed air holes is shown in Figure 5. Figure 5(a) envisages total collapse of the air holes that is occurred in the flat microstructured fiber. Figure 5(b) shows that shape and size of the air holes is deformed or changed due to the failure to control the parameters during the drawing process. Figure 5(c), on the other hand, depicts the flat microstructured fiber with some of the air holes which are missing or being totally deformed. The apparatus comprises a drawing chamber 203 which is coupled to the means for feeding and means for collecting the preform 201 which has been drawn. The capillaries 202 and the preform 201 are being drawn at desired parameters and conditions in the drawing chamber 203. A pressure system is employed to the apparatus so as to provide a vacuum for the drawing process. The pressure system may comprise a vacuum valve and a vacuum hose. The resulting product, which is the flat microstructured fiber, is collected by using a tractor unit 204 and a capstan 205.

In step 101 , the capillaries 202 which have been arranged according to the desired arrangement are positioned in the preform 201 . The capillaries 202, preferably, are placed within an inner periphery of the preform 201 by engaging the distal end of the capillaries 202 to the second body of the assembly 200.

The flat microstructured fiber, according to one embodiment, is fabricated using a dual-stage drawing method. At the first stage of the method, in step 102, the preform 201 and the capillaries 202, in the position, are drawn to form a flat cane. The flat cane, at the second stage, is drawn to form a flat microstructured fiber having a desired size dimension as in step 103. The flat cane has a size dimension larger than the flat microstructured fiber. It is found that by using the method, the flat microstructured fiber exhibits no air holes deformation and has a precise and accurate resulting fiber. The flat microstructured fiber is discharged for further processing or storage as in step 104.

The following specific embodiments are to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. The present invention will now be described in further detail by way of experimental example. EXPERIMENTAL EXAMPLE

Seven capillaries having about 1 m in length and 3 mm in diameter are provided. The distal end for each of the capillaries is deformed. A portion of the capillaries, before the distal end, is sealed to hold the capillaries together in an arrangement or stack.

The capillaries are placed in a preform having an outer diameter of about 25 mm and an inner diameter of about 19 mm. The drawing process which occurs in a drawing chamber starts at temperature around 2100 degree Celsius. A vacuum pressure about 2.5 kPa is applied.

At the first stage, the proximal end of the capillaries and the preform is drawn together in the drawing chamber at a feed rate of 5 mm per minute, and draw feed of 0.34 m per minute. A flat cane which is set to a diameter of 3 mm is formed.

At the second stage, the flat cane is drawn in the drawing chamber to form a flat microstructured fiber (end product) which has a size dimension of 300 x 125 μηι. While this invention has been particularly shown and described with reference to the exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.

INDUSTRIAL APPLICATION

The present invention which is the flat microstructured fiber, method and apparatus can be made or used in the industries of the following fields:

Waveguide devices

It would be advantageous that present invention can be fabricated as a low-loss fiber, broadband optical fiber, saturation absorber for high power fiber laser, nonlinear optical fiber and/or the like. Grating-based devices

It would be advantageous that present invention can be fabricated as point and distributed laser sensors (strain, chemical), narrowband filters, optical couplers, lab-on-chip devices, microfluidic based devices, and/or the like.

Optically active devices

It would be advantageous that present invention can be fabricated as rare earth doped lasers, rare earth doped amplifiers and/or the like.