Method for making an optical element having a textured surface and an optical element having a textured surface

There is provided a method for making an optical element having a textured surface. The method comprises the steps of: a) providing a plurality of primary optical fiber segments, each primary fiber segment comprising one or more cores; b) bundling the primary fiber segments into an assembly with the cores of said primary fiber segments extending parallely; c) transforming the assembly into a secondary structure comprising the parallely extending cores; and d) etching a surface of the secondary structure according to an etch profile of said secondary structure, the etch profile being defined by the parallely extending cores, thereby forming the textured surface of the optical element. An optical element having a textured surface is also provided.

FIELD OF THE INVENTION

The present invention relates to a method for making an optical element having a textured surface, such as, for example, a sub-wavelength microstructured surface providing antireflective properties, and its resulting product.

BACKGROUND

It is well known in the art to provide an antireflective layer on the surface of an optical element to minimize or eliminate losses through Fresnel reflections occurring when light is transmitted through an interface between two different media, for example glass and air. The end faces of optical fibers and the surface of lenses of any size are two examples of optical elements typically requiring an antireflective layer.

It is known in the art to apply an antireflective treatment involving the deposition of antireflective coatings on an interface of an optical element. This technique is based on the application of multilayer interference structures with alternating high and low refractive indices leading to a surface having a low reflectivity. Another technique known in the art involves patterning the interface of an optical element to provide sub-wavelength structures. This technique mimics to property of a moth's eye, which includes a natural nanostructured film preventing reflections. As known in the art, multiple structures of dimensions and periodicity smaller than half the wavelength of light crossing the interface can provide a refractive index gradient which essentially removes the reflection inducing transition at the interface.

Antireflective treatments on optical elements can be challenging to implement. For instance, the equipment needed to perform the deposition of antireflective coatings can be expensive and the deposition process itself can be time consuming. Furthermore, formation of fine sub-wavelength structures on an optical interface requires sophisticated manufacturing techniques such as interference lithography, which are typically costly to undertake and can be both energy and time consuming without achieving repeatedly the desired results.

Thus, there is a need for a more affordable and practical manufacturing method to form a textured surface on an interface of an optical element.

SUMMARY OF THE INVENTION

In accordance with various aspects, there are provided methods for making an optical element having a textured surface involving the use of a fiber or an assembly having multiple cores. The multiple cores define an etch profile which results, upon etching, in the formation of the desired textured surface.

In accordance with an aspect of the invention, there is provided a method for making an optical element having a textured surface. The method comprises the steps of:a) providing a plurality of primary optical fiber segments, each primary fiber segment comprising one or more cores;b) bundling the primary fiber segments into an assembly with the cores of the primary fiber segments extending parallely;c) transforming the assembly into a secondary structure comprising the parallely extending cores; andd) etching a surface of the secondary structure according to an etch profile of the secondary structure, the etch profile being defined by the parallely extending cores, thereby forming the textured surface of the optical element.

In accordance with another aspect, there is also provided an optical element having a textured surface made in accordance with an embodiment of the above method.

In accordance with a further aspect of the invention, there is provided an optical element comprising a secondary structure. The secondary structure includes a plurality of cores extending parallely and transversally to an optical axis of the optical element, the parallely extending cores defining a periodically varying etch profile. The secondary structure has an extremity etched according to the etch profile and forms a textured surface.

The optical element may for example be a lens, a reflector, an optical fiber or the like. In some implementations the texture provides an antireflecting effect on the optical element. In other implementations, the textured surface defines a diffraction grating on the optical element.

Other features and advantages of the invention will be better understood upon reading of embodiments thereof with reference to the appended figures.

DETAILED DESCRIPTION

In the following description, the same numerical references refer to similar elements. Furthermore, for the sake of simplicity and clarity, namely so as to not unduly burden the figures with several references numbers, not all figures contain references to all the components and features, and references to some components and features may be found in only one figure, and components and features of the present disclosure which are illustrated in other figures can be easily inferred therefrom. The embodiments, geometrical configurations, materials mentioned and/or dimensions shown in the figures are optional, and are given for exemplification purposes only. Of course, numerous modifications could be made to the above-described configurations without departing from the scope of the disclosure.

In accordance with an aspect of the invention, there is provided a method for making an optical element having a textured surface.

As will be readily understood by one skilled in the art, such a textured surface may result in different optical properties depending on the size of the structures defining the texture of the surface. In some implementations an antireflective effect may be desired, in which case the structures of the textured surface are preferably of sub-wavelength dimensions. As known in the art, a sub-wavelength structure typically has a periodicity in the range of or smaller than half the wavelength of the light which is intended to cross the interface without undergoing Fresnel reflections. This limit may therefore vary from one implementation to the next according to various factors such as the wavelength range in which the optical element is to be used, the materials on either sides of the interface, the shape and periodicity of the structures, etc.

In other implementations, the structures of the textured surface may have a periodicity greater than sub-wavelength and within the Bragg regime with respect to light interacting with the optical element, the textured surface therefore acting as a diffraction grating. As it is well known in the art, diffraction gratings have reflective and/or transmissive properties dependent on the wavelength of the light they interact with, and can therefore be used to separate different spectral components of a light beam or signal.

The optical element may be, for example, an optical fiber. The textured surface may therefore be provided on an end face of the fiber, interacting with light entering and/or exiting the fiber. In other embodiments, the optical element may be embodied by a lens, the textured surface covering one or more light interfaces of the lens, totally or in part. In yet another embodiment the optical element may be a reflector. For example, in some applications it may be advantageous to provide a diffraction grating on a reflective surface to provided spectrally selective properties.

In accordance with an aspect of the present invention, the method of making the optical element having a textured surface involves the use of an optical fiber or of an assembly having multiple cores. The multiple cores define an etch profile which results, upon etching, in the formation of the desired textured surface.

With reference toFIG. 1, in accordance with some implementations, the method100includes the following steps:a) providing110a plurality of primary optical fiber segments, each primary fiber segment comprising one or more cores;b) bundling120the primary fiber segments into an assembly with the cores of said primary fibers extending parallely;c) transforming130the assembly into a secondary structure comprising the parallely extending cores; andd) etching140a surface of the secondary structure according to an etch profile of said secondary structure, the etch profile being defined by the parallely extending cores, thereby forming the textured surface of the optical element.

Two examples of implementation of the method100are described below.

First Example

Referring toFIG. 2, there is provided a method200for making an optical element having a textured surface according to one exemplary implementation of the method100.

The first step of the method200involves providing a plurality of optical fiber segments, each primary optical fiber segment having one or more cores. In the illustrated implementation, this step involves the substeps of providing210a primary optical fiber, and sectioning220the primary optical fiber into the plurality of primary optical fiber segments. The primary optical fiber can be made of any material suited to make an optical element, such as silica based glass, ZBLAN glasses, chalcogenide glass, plastic materials or the like. Sectioning of the primary optical fiber may be performed using, for instance, suitable scissors or a cleaver.

In an embodiment, the primary optical fiber segments are free of cladding and their cores have an etching profile varying across a radius of the corresponding primary optical fiber segment. This may for example be achieved by providing a cladding-free primary optical fiber which has a core having a varying chemical composition profile and a varying index profile. It is understood that both chemical composition profile and index profile can vary along the optical fiber radius. In other words, the core can have a chemical composition profile that is a function of the radial distance from the center axis of the primary optical fiber. More details about the varying chemical composition profile and varying index profile will be provided further below.

In one variant, the cladding-free primary optical fiber may be obtained from the manufacturing of a fiber initially including one or more claddings surrounding the core and having a different chemical composition profile and index profile than that of the core. As illustrated inFIG. 2, the method200may further include an initial substep of removing202a cladding surrounding a primary preform comprising the one or more cores, the primary preform being then drawn into the primary optical fiber of the providing step. In another variant, the cladding or claddings can be removed from the primary optical fiber by mechanical or chemical techniques, or a combination thereof, in order to provide a cladding-free primary optical fiber core. In either case, the result is a cladding-free core assembly having a varying chemical composition profile and index profile, both being function of the radius of the assembly.

In other variants primary optical fiber segments without cladding or claddings may be obtained from one or more monolithic structures fabricated directly with the desired chemical composition profile, without having a cladding requiring removal. It will be readily understood by one skilled in the art that the term “core” includes such an embodiment, even though the core in such a case was never part of core-cladding guiding structure. As such, the expression “core” is understood to refer to an elongated structure apt to guide light if surrounded by a cladding, regardless of the manner in which it was fabricated.

As shown inFIG. 5, the plurality of primary optical fiber segments30can be of even length. In another embodiment, the plurality of primary optical fiber segments may be sectioned at uneven lengths. It will be readily understood by one skilled in the art that in typical implementations, the surface quality of the cut ends of the plurality of optical fiber segment can be irrelevant to the final quality of the optical element, as the primary optical fiber segments are destined to be later subjected to further drawing and cutting. In other variations, it may be desirable to section the plurality of primary optical fiber segments at selected non-void angle and/or in several different orientations to form facets at an end thereof. Any suitable technique known in the art to section optical fibers may be used, such as for example using scissors or a cleaver suited to section optical fibers.

The length of the individual primary optical fiber segments may be selected to be within the range of a typical fiber preform. The length can vary for example from 10 cm to 1 m. As will be readily understood, the optical fiber drawing process routinely yields kilometers of fiber, and thousands of primary optical fiber segments in the range of 1 m can be obtained from a single primary optical fiber draw.

Referring back toFIG. 2, the next step of the method200involves bundling230the primary fiber segments into an assembly with the cores of the primary fibers extending parallely. The bundling230of the primary optical fiber segments can be performed with different bundling techniques or a combination thereof.

For example, as illustrated inFIG. 5, in one implementation the bundling of the primary optical fiber segments30can involve a substep of holding the primary optical fiber segments in close relation to one another by a ring40tightened around the bundle of primary optical fiber segments30. The bundle of primary optical fiber segments30thus forms the assembly32. Alternatively, the primary optical fiber segments can be placed into a tube, such as a silica tube, and packed to be in close relation to one another, hence making a bundle of primary optical fiber segments distributed into a given patterned configuration. In this example, the silica tube can have the same length as the primary optical fiber segments. In yet another embodiment, the primary optical fiber segments can be bundled and held in close relation to one another by a tube sheet having a patterned configuration. The patterned configuration can be a square pattern, a diamond pattern, a spiral, fold symmetry or a combination thereof. The tube sheet can be a plate through which the primary optical fiber segments of the bundle are placed for support and placed into the patterned configuration defined by the holes of the tube sheet. In another embodiment, the bundling of the primary optical fiber segments may involve holding the primary optical fiber segments in close relation to one another and at least partially fusing the segments together. For instance, the primary optical fiber segments can be fused on their longitudinal surface over a portion of their length, for example near an extremity thereof. The fusing of the primary optical fiber segments may be performed using a furnace, a flame, or any heating apparatus capable of fusing the cores, at least partially, together. It is to be understood that other bundling techniques can be used to perform this step of the method.

The next step of the method involves transforming the assembly into a secondary structure comprising the parallely extending cores.

In the embodiment of the method200illustrated inFIG. 2, the transforming step involves a substep of consolidating240the assembly so as to obtain a secondary preform comprising the parallely extending cores. In other words, after consolidation, the secondary preform comprises the cores which are contiguous to one another and fused together. The substep of consolidating240can be conducted using a furnace, a flame, or any heating apparatus capable of fusing the cores together so that the interstitial spaces between the cores shrink partially or completely disappear. In an embodiment, the substep of consolidating240is optional since the assembly, being a preform, can be drawn using a drawing tower during a substep of drawing. Partial or complete consolidation thus occurs during drawing. More detail about the substep of drawing is provided below.

Then, if required, the transforming step may further include a substep of removing250the bundling mean (the ring, the silica tube, etc.) from the secondary preform. In the case of the bundling mean being a ring, the ring can be removed by cutting away a portion of the secondary preform comprising the ring which can have been consolidated in part with the cores. Other techniques, such as mechanical or chemical techniques or a combination thereof, can be used to remove the bundling mean from the secondary preform.

Still referring toFIG. 2, it is then possible to opt to form different final products. For instance, and not limitative to only those products, a lens, a reflector or an optical fiber can be formed from the secondary preform.

In some implementations, the transforming step further includes a substep of forming260a standalone optical element out of the secondary preform, the standalone optical element thus defining the secondary structure. In the present description, the expression “standalone optical element” is understood to be directed to an optical element which is designed to be used as a standalone product without attachment to another component. In some implementations, the standalone optical element can be a lens or a reflector. During the substep of forming260, the standalone optical element can be formed by cross-sectionally cutting the secondary preform into a shape suitable for making the desired end product. Thus, in some implementations, the lens or the reflector can be shaped and further modified to the desired final design at this stage. A subsequent step of etching300of the method200will be described further below.

Still referring toFIG. 2, the transforming step may involve, in some implementations, a substep of drawing270the assembly so as to obtain a secondary optical fiber. Thus, in such implementations, the secondary optical fiber defines the secondary structure. Hence, the secondary optical fiber comprises the plurality of parallely extending cores. As mentioned above, the substep of drawing270can be conducted using a drawing tower and related apparatus suited for manufacturing optical fiber. In contrast to the standalone optical element described above, the secondary optical fiber may be destined to be operatively connected to another optical element, such as another optical fiber. More detail in this regard is provided further below.

Referring toFIGS. 1 and 2, in some implementations, the transforming step130may further include additional substeps of:sectioning220the secondary optical fiber into a plurality of secondary optical fiber segments;bundling230the secondary fiber segments into a new assembly; anddrawing270the new assembly into a new secondary optical fiber.

In this case, the new secondary optical fiber defines the secondary structure.

Thus, as illustrated inFIG. 2, the additional substeps of sectioning, bundling, and drawing220,230,270(and optionally the additional substeps of consolidating240and removing250) can be repeated280for a plurality of iterations before obtaining the secondary structure. As will be understood by one skilled in the art, each iteration will increase the number of cores within the resulting secondary optical fiber and reduce the size of those cores. The repeating280of iterations can be performed until a targeted number of cores is obtained in the secondary structure or until the cores have reached a targeted size as several iterations of these substeps shrink the existing cores smaller and smaller.

For example, a secondary optical fiber obtained after a first iteration of the substep of drawing270can be sectioned into a plurality of secondary optical fiber segments; the plurality of secondary optical fiber segments can be bundled into a new assembly; the new assembly can optionally be consolidated into a new preform; the bundling mean can optionally be removed from the new preform, and the new preform can in turn be drawn into a new secondary optical fiber comprising yet more cores parallely extending to one another when compared to the secondary optical fiber obtained after the first iteration, this new secondary optical fiber thus defining the secondary structure. In another variant, the last drawing step may be omitted, and the new preform would therefore define the secondary structure, for example to manufacture a standalone optical element in which the cores are of smaller dimensions.

Still referring toFIGS. 1 and 2, in some implementations, the method200further includes an additional step of operatively connecting290at least a portion of the secondary optical fiber to another optical fiber after the transforming130of step c). For instance, a portion of the secondary optical fiber can be fused to an end surface of another optical fiber which is to be provided with an antireflecting surface or a diffraction grating. It is to be noted that the diameter of the secondary optical fiber that is to be provided with an antireflecting surface or a diffraction grating may be different from the diameter of the optical secondary optical fiber defining the secondary structure.

Referring toFIG. 2, the next step of the method200involves a step of etching300a surface of the secondary structure according to an etch profile of said secondary structure, the etch profile being defined by the parallely extending cores, thereby forming the textured surface of the optical element. The step of etching300is understood to include exposing a surface of the secondary structure to at least one etchant. The etchant may be embodied, for example, by a corrosive liquid such as hydrogen fluoride, potassium hydroxide, ammonia or nitric acid. The etchant can also be a chemically active ionized gas. In some implementations, a transversal surface of the secondary structure is etched. In other implementations, a surface of the secondary structure which is parallel or oblique to an optical axis of the optical element made therefrom is etched. It will be readily understood by one skilled in the art that the etchant may be selected in view of the materials present in the secondary structure and their corresponding etching rates for a given etchant.

As will be readily understood by one skilled in the art, the etching rate at any point of a surface of the secondary structure depends on the chemical composition at that particular point. The chemical composition of the plurality of cores of the secondary structure can therefore be used to define an etching profile which is suited to form the textured surface upon etching.

The chemical composition profile and the varying index profile of a core according to one embodiment will now be described in greater detail. The varying chemical composition may result, for example, from a gradient of dopant concentration inside the core of the primary optical fiber. For silica-based fibers, the dopant may for example be germanium, phosphorous, aluminum, fluorine, boron or combinations thereof. Thus, in an embodiment, each of said cores is doped with at least one dopant selected from the group comprising germanium, phosphorous, aluminum, fluorine and boron. In some implementations, the dopant has a low diffusion rate, to preserve the desired gradient profile during the substeps of consolidating and/or drawing. For instance, aluminum is a dopant having a low diffusion rate.

Referring toFIG. 6, there is shown a plot of a dopant concentration and refractive index of a primary optical fiber50as a function of the radial distance from the center axis A of the primary optical fiber50.FIG. 6illustrates a dopant concentration increasing gradually from the center axis A of the primary optical fiber50towards an outer surface54of the core52of the primary optical fiber50, where R is the radius of the core52. For instance, the concentration of dopant may vary between the outer surfaces54of the primary optical fiber50and the center axis A thereof. In some implementations, the etching rate is proportional to the dopant concentration. Therefore, the structure obtained after a given etching period can have a pattern determined by the difference in dopant concentration across the transversal surface of the primary optical fiber.

In the optical elements obtained from the above-described method200, either a lens, a reflector or a secondary optical fiber, each one of the parallely extending cores exposed to the etchant on a surface of the product is etched according to an etch profile which is a function of the chemical composition profile of the core. Thus, the etched cores form a textured surface upon the etching step300. In other words, the optical element comprises a secondary structure, the secondary structure including the plurality of cores extending parallely and transversally to an optical axis of the optical element, wherein the parallely extending cores define a periodically varying etch profile. Upon etching of an extremity of the optical element, the secondary structure is etched according to said etch profile and forms a textured surface on the optical element.

Referring toFIG. 7A, there is shown schematically an optical fiber60having at one end an optical element62operatively connected thereto. It will be readily understood that the size and relative dimensions of the components shown onFIG. 7Aare greatly exaggerated for clarity. The optical element62is made in accordance with the method described above. The optical element62has a textured surface64including substantially conical structures66. It is understood that in this example, the optical element62is a secondary optical fiber operatively connected to the optical fiber60and that the size of the substantially conical structures66has been exaggerated in this Figure since the substantially conical structures66form sub-wavelength structures. The substantially conical structures66have been obtained as a surface68of the secondary optical fiber62, which is transversal to an optical axis thereof, has been etched according to said etch profile. The above described etching step, involving the etch profile of the secondary optical fiber62and a carefully selected etchant and etching time, has led to the formation of the substantially conical structure66on each one of the cores. Given that the cores are transversally distributed over the transversal surface68of the secondary optical fiber62according to the optical axis thereof, the transversal surface68of the secondary optical fiber62has an etch profile suited to form the substantially conical structures66making the textured surface64after etching. Depending on their size, the parallely extending cores of the secondary structure may define sub-wavelength structures on the surface of the secondary structure after etching, the surface of the secondary structure thereby providing an antireflecting effect on the optical element, or may be sized according to a Bragg regime, the surface of the secondary structure thereby defining a diffraction grating.

Referring toFIG. 7B, there is shown an optical element70being a lens, the optical element70having been made in accordance with the method described above. The lens70has a textured surface72including substantially conical structures76, similar to the substantially conical structures66described above. In this example, the substantially conical structures76forming the textured surface72have been obtained as a transversal surface78of the lens has been etched according to said etch profile. Again, it will be readily understood that dimensions of the substantially conical structures76have been exaggerated for clarity purposes. As in the example shown inFIG. 7A, the substantially conical structures76are periodically distributed on the transversal surface78of the lens70and may provide either an antireflective effect or a Bragg grating to the transversal surface78of the lens70, depending on their size. In another example, a reflective layer can be deposited onto the textured surface to form a reflective grating.

In a variant where a surface of the secondary structure is etched and where said surface is parallel or oblique to an optical axis of the optical element made therefrom, the resulting profile formed by the cores at the etched surface may define lines instead of the peaks shown inFIGS. 7A and 7B. Such an embodiment may be of particular interest in embodiments where the secondary structure is destined to form a diffraction grating.

In an alternative embodiment, the secondary optical fiber features a varying radial concentration of dopant(s) thus providing a variable etching rate of the surface when exposed to an etchant, but at the same time, the secondary optical fiber features a constant refractive index. This combination of features can be achieved for instance by adding a lowering and increasing refractive index dopant in the core simultaneously. For example, known lowering index dopants comprise fluorine and boron while increasing index dopants comprise phosphorous, aluminum, and germanium. For example, a radial gradual increase of phosphorous and fluorine in the secondary optical fiber can yield a constant refractive index while providing a variable etching rate throughout a surface of the secondary optical fiber. The variable etching rate can allow for the formation of a textured surface upon etching. A constant refractive index may be desirable to provide a uniform transmission of light through the material.

In yet another embodiment, the secondary optical fiber can be formed by assembling a combination of different optical fibers. For instance, during the bundling step120described above, some optical fibers with a higher or lower overall refractive index can be inserted at various location within the bundle. Thus, a region of the secondary structure formed by the method can act as a core and another region can act as a cladding to enable light transmission in a waveguide region. All regions can be etched in order to provide a textured surface on the resulting product.

Second Example

Referring toFIG. 3, there is provided a second method400for making an optical element having a textured surface according to another example of implementation of the method100.

The first step of the method400involves providing a plurality of primary optical fiber segments, each primary optical fiber segment comprising one or more cores. In the illustrated implementation, this step involves substeps of providing410a primary optical fiber, and sectioning420the primary optical fiber into the plurality of primary optical fiber segments. The primary optical fiber can be made of any material suited to form an optical element, such as silica based glass, ZBLAN glasses, chalcogenide glass, plastic materials or the like.

In an embodiment, the primary optical fiber segments have one or more cores having a first chemical composition and a first index profile. Each one of the primary optical fiber segments further includes at least one cladding surrounding the one or more cores. The at least one cladding has a second chemical composition profile and a second index profile. In contrast to the method200described above, the cladding is preserved on the primary optical fiber segments that are provided.

Referring to the embodiment illustrated inFIG. 3, the sectioning420of the primary optical fiber segments is performed using, for instance, suitable scissors or a cleaver. Again, the plurality of primary optical fiber segments can be of even length or of uneven lengths. The plurality of primary optical fiber segments can also be sectioned at any non-void angle and can even be sectioned, in another embodiment, in several different orientations to form facets at an end thereof.

Still referring toFIG. 3, and as explained in the description of the method200according to the previous example, the next step of the method400involves bundling430the primary optical fiber segments into an assembly, the assembly comprising the parallely extending cores, surrounded by their corresponding cladding. It is understood that, in some implementations, the assembly defines a preform. The bundling430of the primary optical fiber segments can be performed using different bundling techniques or a combination thereof, as described above.

The next step of the method400involves transforming the assembly into a secondary structure comprising the parallely extending cores. Referring to the embodiment of the method illustrated inFIG. 4, this step involves a substep of consolidating440the assembly so as to obtain a secondary preform comprising the parallely extending cores. Again, the substep of consolidating440can be conducted in a furnace, with a flame or using any heating apparatus capable of fusing the primary optical fiber segments together so that the interstitial spaces between the cladding of each one of the primary optical fiber segments partially shrinks or disappear, leaving the cores surrounded by a consolidated cladding matrix. In some implementations, the substep of consolidating440is optional since the assembly can be drawn directly after bundling using a drawing tower during a substep of drawing. Partial or complete consolidation then occurs during drawing. In some applications, a partial consolidation may be desired during the substep of consolidating or for the resulting optical element having a textured surface.

Then, if required, the transforming step further includes a substep of removing450the bundling mean (the ring, the silica tube, etc.) from the secondary preform. The substep of removing can be conducted using the techniques described in the method200.

Still referring toFIG. 3, it is then possible to opt to form different final products. For instance, and not limitative to only those products, a standalone optical element such as a lens or a reflector, comprising the plurality of parallely extending cores surrounded by the matrix of cladding, can be formed. Accordingly, in an embodiment, the standalone optical element can be formed by cross-sectionally cutting the secondary preform into a shape suitable for making the desired end product. The standalone optical element can be shaped and further modified to the desired final design at this stage. A subsequent step of etching500of the method400will be described further below.

Still referring toFIG. 3, the transforming step may involve, in some implementations, a substep of drawing470the assembly so as to obtain a secondary optical fiber. Thus, in such implementations, the secondary optical fiber defines the secondary structure. Hence, the secondary optical fiber comprises the plurality of parallely extending cores surrounded by the matrix of cladding. As mentioned above, the substep of drawing470can be conducted using a drawing tower and related apparatus suited for manufacturing optical fiber. In contrast to the standalone optical element described above, the secondary optical fiber may be directed to be operatively connected to another optical element, such as another optical fiber.

Referring toFIGS. 1 and 3, in some implementations, the transforming step130of c) further includes additional substeps of:sectioning420the secondary optical fiber into a plurality of secondary optical fiber segments;bundling430the secondary fiber segments into a new assembly; anddrawing470the new assembly into a new secondary optical fiber;
such that the new secondary optical fiber defines the secondary structure.

Thus, as illustrated inFIG. 3, the additional substeps of sectioning, bundling, and drawing420,430,470(and optionally the additional substeps of consolidating440and removing450) can be repeated480for a plurality of iterations before obtaining the secondary structure. The repeating480of iterations can be performed until a targeted number of cores is obtained in the secondary optical fiber or until the cores and the surrounding cladding matrix have reached a targeted size, as several iterations of these substeps shrink the existing cores and the surrounding cladding matrix smaller and smaller. Thus, in an embodiment, the secondary optical fiber can have a plurality of cores parallely extending to one another, each core being surrounded by a matrix of cladding.

Still referring toFIGS. 1 and 3, in some implementations, the method400further includes an additional step of operatively connecting490at least a portion of the secondary optical fiber to another optical fiber after the transforming130of step c), as described above.

Referring toFIG. 3, the next step of the method400involves a step of etching500a surface of the secondary structure according to an etch profile of this secondary structure, the etch profile being defined by the parallely extending cores and the surrounding cladding, thereby forming the textured surface of the optical element upon etching. Similar etchants as the ones described above can be used during the step of etching500. Thus, the optical element comprises a secondary structure, the secondary structure including the plurality of cores extending parallely and transversally to an optical axis of the optical element, wherein the parallely extending cores, each surrounded by a matrix of cladding, define a periodically varying etch profile. Upon etching of an extremity of the optical element, the secondary structure is etched according to said etch profile and forms a textured surface.

Referring toFIG. 8, there is schematically illustrated the variation in chemical composition in the primary optical fiber80comprising a core82and a surrounding cladding84. Thus, in the secondary optical fiber, the first chemical composition of the one or more cores and the second chemical composition of the surrounding matrix of cladding can lead to a differential etching response. With a carefully selected etchant and etching time, the one or more cores82and the surrounding cladding84exposed to the etchant can be etched at a different rate leading to the formation of a textured surface over a surface of the secondary structure. Referring toFIG. 9, in accordance with an embodiment, there is shown an extremity of a secondary optical fiber that has been etched according to said etch profile, and forming a textured surface86. The textured surface86is formed of substantially rounded cylindrical sub-wavelength structures88formed upon etching of the cores82and the matrix of cladding84. In the illustrated embodiment ofFIG. 9, the sub-wavelength structures88form a textured surface86wherein the sub-wavelength structures88are periodically distributed on the transversal surface of the secondary optical fiber, according to an optical axis thereof. The textured surface86formed on the secondary optical fiber provides an antireflective effect to the transversal surface of the secondary optical fiber.

In another embodiment, substantially rounded cylindrical holes can be etched into the surface of the secondary optical fiber, lens or optical element using an etchant suited to etch more rapidly the cores compared to the surrounding matrix of cladding. In this embodiment, the operation wavelength of the antireflective surface can depend on the depth of the substantially rounded cylindrical holes provided upon etching.

In a variant, the parallely extending cores and the surrounding matrix of cladding of the secondary structure are sized according to a Bragg regime. Thus, the surface of the secondary structure thereby defines a diffraction grating.

It will be readily understood that the examples above are not limitative to the scope of protection and that other embodiments could involve a different succession of steps than those described herein. In one variant, cores having a varying dopant concentration, such as in example 1 described above, may be used in combination with a secondary optical fiber having a matrix of cladding, such as in example 2 described above.

Of course, numerous modifications could be made to the embodiments above without departing from the scope of the present invention.