WO2004038466A2 - Photonic crystal fibers and methods for the production thereof - Google Patents

Abstract

The invention relates to photonic fibers and methods for the production thereof. A photonic fiber consists of a central area and ducts surrounding said central area and is characterized by the fact that at least two metallic conductors (2) are disposed near and along a central fiber (1). A photonic crystal fiber consists of a central fiber core and air ducts surrounding said central fiber core and is characterized in that at least six inner ducts are arranged so as to border the central fiber core while outer ducts are disposed so as to border the inner ducts. According to the inventive method for producing said photonic fibers, capillary elements and/or rods made of glass are combined into geometrical structures comprising at least one central fiber and an outer coating, said geometrical structures are heated and are subjected to a drawing process, and molten liquid metal is filled into hollow spaces of the capillary elements near the central fiber once the drawing process has been completed.

Description

 Photonic fibers and processes for their manufacture

description

The invention relates to a photonic fiber and a photonic crystal fiber and methods for their production and is applicable in particular for the production of new materials, components and devices. These are used, for example, to form short light pulses for nonlinear frequency conversion, as optical switches and to control the dispersion of other nonlinear optical effects ^, and to generate a super continuum in a wide spectral range.

New devices that can be implemented by the invention are, for example, broadband fiber lasers, magnetoresistors and oscillators.

The invention allows the solution of a ^'series of problems of modern physics, including spectroscopic applications. The use of broadband sources for coherent radiation in linear and non-linear spectroscopy allows the spectra to be recorded with a single laser pulse, which is extremely important for the investigation of non-stationary media and superfast phenomena. In the past, photonic crystals were considered an exotic idea for basic research. Currently, however, a variety of methods for realizing such structures are developing, the basis for the known methods being the planar technology for the synthesis of thin layers and heterostructures and the lithography technology which ensure the nano-dimension of the structure.

However, the use of lithographic technology has a number of disadvantages. In this way, no elements with a high aspect ratio can be produced. Also, no micro-conductors, no electrical capacitors and no windings can be produced within the micro-product with a predetermined shape of the cross section. Finally, with the help of this technology, products with a complicated outer surface such as e.g. a helical surface design.

A metal-dielectric photonic crystal is known from US Pat. No. 5,990,850, which has a three-dimensional structure which consists of metallic balls which are surrounded by dielectric material.

EP 1 015 917 describes a transparent metal dielectric structure which allows the transmission of light in a large wavelength interval.

Furthermore, WO 99/00685 AI describes a single-mode fiber, this fiber consisting of a central area and air channels surrounding this area. A manufacturing method for a perforated fiber is described in US Pat. No. 6,444,133.

Also known is a structure described in the article by K. Saitoh, M. Koshiba et all (April 21, 2003, vol. 11, No. 8 ^' OpticsExpress, p 843). In this article a theoretical model of a photonic crystal fiber Structure with variable step size of the annular layers surrounding the central defect core is presented.

The invention has for its object to provide a photonic fiber and a photonic crystal fiber and processes for their production, the processes should enable series production with reproducible parameters and a simple and inexpensive production of the photonic crystal fibers and the photonic crystal fibers in the generation of a super continuum in enable a wide spectral range.

This object is achieved according to the invention by the features in the characterizing part of claims 1, 5, 8 and 13 in conjunction with the features in the respective preamble. Appropriate embodiments of the invention are contained in the subclaims.

A particular advantage of the ^' invention is that the photonic fiber is completely new optical and electrical

Has properties. This is achieved in that at least two metallic conductors are arranged in spatial proximity and along a central fiber. The new structure contains a central fiber and a periodic sheathing, two diametrically arranged metal fibers, which can act as metallic nano conductors, for example, are located in close proximity to the central fiber.

Another advantage of the invention is that it is effective

Manufacture of photonic fibers based on traditional fiber and drawing technologies. ^'The procedure is realized such that the capillaries and / or bars to geometric shapes are combined with at least one central fiber and a _jacket. the geometrical see structures are heated and subjected to a drawing process and molten liquid metal is filled into cavities of the capillaries in close proximity to the central fiber. The metal can be filled into the capillaries after the drawing process has ended or, preferably, as an intermediate step such that the metal fibers or metal rods are then further drawn together with the glass capillaries and the glass rods in the further drawing process. In addition, it is possible for elements made of soluble glass to be introduced into the geometric structures before the drawing process. After the drawing process, these elements can be completely or partially dissolved, which creates voids in the structure of the photonic fiber.

The use of metals in microstructured light guides allows more effective control of dispersion and non-linearity as well as the production of nanomaterial, which in principle has new optical and electrical or magnetic properties.

A next advantage of the invention is that the photonic crystal fiber enables the production of compact and stable, highly brilliant broadband light sources, in that the photonic crystal fiber is designed in such a way that at least six inner channels adjoin a central fiber core and a large number of them adjoin the inner channels Outer channels, the diameter of which increases with the distance to the central defect or to the central fiber core, are arranged.

Another advantage of the invention is the effective production of the photonic crystal fibers based on traditional fiber and drawing technologies, the Process flow is characterized by the process steps listed below.

Arrangement of at least six capillaries with a first inner diameter around a central fiber core,

Arranging a large number of further capillaries with a second inner diameter around the at least six capillaries with the first inner diameter,

Heating of the entire bundle to the softening temperature,

- Pull the entire bundle until the geometric final dimensions are reached.

The capillary used and the central fiber core are made of glass, the first inner diameter of the capillary being smaller than the second inner diameter and the second inner diameter of the capillary being smaller than the third inner diameter, etc.

It is advisable to apply a coating during the drawing process, which is preferably made of plastic. The final structure of the photonic crystal fiber can be realized by a single or a repeated drawing process, depending on the geometry to be achieved.

The invention is to be described in more detail below with reference to exemplary embodiments shown at least in part in the figures. Show it:

1 shows the cross section of a metal-dielectric photonic fiber; 2 shows an embodiment variant, in which the channels 3 also have a hexagonal structure;

3 shows a greatly enlarged illustration of the central region of the photonic crystal fiber in cross section and

Fig. 4 is a cross-sectional view of the entire photonic crystal fiber.

FIG. 1 shows the cross section of a metal-dielectric photonic fiber. In the present exemplary embodiment, the cross section is a hexagonal structure, with a multiplicity of air-filled channels 3, which surround a central fiber 1 arranged in the center of the hexagonal structure. Two diametrically opposed metallic nanoconductors 2 are arranged in the immediate vicinity of the central fiber 1. The metallic nano conductors 2 are metal fibers which extend along the central fiber 1 and have been formed by pouring liquid molten metal into channels 3 lying on both sides next to the central fiber 1.

As can be seen from FIG. 1, the air-filled channels 3 form a sheath in relation to the central fiber 1. In addition to the air-filled channels 3, this sheathing can also contain rods and dielectric. It is also possible to arrange elements made of soluble glass in the casing, which can be completely or partially removed after the drawing process and thus the formation of

Cavities and the creation of specific geometric structures.

FIG. 2 shows a variant in which the channels 3 also have a hexagonal structure. In the present exemplary embodiment, the metal which is filled into the channels 3 according to FIGS. 1 and 2 is a slightly melting solder, which consists of lead or tin or a lead-tin alloy or silver.

The process for producing the metal-dielectric photonic fibers is to be described in detail below.

The essence of manufacturing technology is the drawing of capillaries and rods, their arrangement in, for example, hexagonal packages, the heating and multiple drawing until the required geometry and the required dimensions of the individual structural elements are achieved. It is essential in this manufacturing technology that the channels 3 formed by the capillaries are filled with molten metal, e.g. low melting solder. In the present exemplary embodiment, the metal is introduced into the channels 3 in an intermediate step and the drawing process is then continued.

In a preliminary stage of the method according to the invention, tubes and rods are drawn from the glass melt, for which glass blocks with a weight of thirty to fifty kilograms are used. The tubes or capillaries and rods are drawn with a certain geometry. For example, they can be circular or hexagonal depending on the nozzle used for drawing. Basic elements and soluble elements are produced using different types of glass. From these preforms with macro dimensions, elements with smaller dimensions are drawn according to the principle of similarity. In the following, these elements are sorted, cut, calibrated and prepared for arrangement in packages. The topological image of the package corresponds in shape and geometric dimensions against the required product, the necessary cavities, gaps and the like being generated by the arrangement of elements made of soluble glass.

The formed package is reduced in size by a factor of 10 by drawing at defined temperatures, while the geometric relationships are maintained according to the principle of similarity. The drawn elements are then cut into pieces of a certain length, ground and polished. This mechanical processing is followed by a washing process with which the soluble glass is removed. In the present exemplary embodiment, the glass is easily soluble and is removed in a weak hydrochloric acid solution at a temperature of 60-80 ° C. within 20 to 40 minutes *.

The elements created up to this point now go through a process of metallization for the application of contact coatings if this is necessary for the specific areas of application.

The actual production of the photonic fibers takes place in such a way that capillaries are arranged around a rod which later forms the central fiber and these then form a geometric structure or a package. The capillaries are arranged according to specific specifications

Achievement of a desired final shape (in the present exemplary embodiment to achieve a hexagonal cross-sectional structure). In addition to the capillaries, other rods or elements made of soluble glass can be arranged. The central fiber and the capillaries as well as the rods can consist of glass of the same type or of different glass. After heating and carrying out the drawing process, molten liquid metal is poured into the cavities of the capillaries 3 in close proximity to the central fiber 1. It is also possible to fill further capillaries with metal or other substances. The targeted dissolution of the soluble glass can create voids or specific geometric structures. 5

The use of the technology described above allows complex topological / morphological images to be formed in a uniform technological cycle by bundling individual elements. The fiber

10 technology guarantees the geometric dimensions with an accuracy of ± 1%, which is ensured by pulling the glass products according to the principle of similarity. The accuracy of the dimensions and shapes of the cavities provided is assured as they are made from

15 high-precision preforms can be formed from soluble glass (e.g. with a diameter of 30 mm, the accuracy is + 0.02 mm). The fiber technology allows the use of preforms of complex shapes and a high degree of automation of the drawing process. In addition, the

20. Fiber technology the manufacture of micro products of a completely new quality. It becomes practically any geometric shape of the details and individual elements

(actually a three-dimensional one). The geometric shapes can be, for example, cylindrical, flat, conical, twisted, barrel-shaped or as any polygons

structures (even and uneven). With these structures, the construction of complicated micromechanisms with a large selection of functional possibilities is given.

30 The surface roughness of the individual elements in the present exemplary embodiment is 0.01 to 0.003 μm, which enables the design and manufacture of movement elements with extremely low frictional forces. In the micromechanics, in addition to the electrical conductors, microchannels with a predetermined one can be used directly during their manufacture Cross-section ^' (including with a thin membrane), which can perform various functions. Such functions are, for example, lines for working fluid, waveguides for electromagnetic radiation and thermal neutrons, molecular and biological filters, electrostatic electric lenses and pressure sensors.

As shown in FIG. 3, the photonic crystal fiber consists of a central fiber core la and air channels surrounding this central fiber core la, a large number of outer channels 3a being arranged on the central fiber core la six-inner channels 2a and adjacent to these inner channels 2a. The inner diameter of the outer channels 3a can be designed differently. It is thus possible to make the inside diameter of the outer channels 3a smaller, for example 1 μm, in the area around the central fiber core la than the inside diameter in the direction of the periphery 7. The inside diameter can increase continuously or discontinuously in the direction of the periphery 7.

As can be seen in FIG. 4, inner cavities 4 are arranged between the central fiber core 1a and the inner channels 2a. There are outer cavities 5a between the inner channels 2a and the outer channels 3a and outer cavities 5b are arranged between the outer channels 3a. The inner channels 2a and / or the outer channels 3a have a sheathing 6, which in the present exemplary embodiment is hexagonal. In contrast, the inner cavities 4 and / or the outer cavities 5 have a triangular cross-sectional shape in the present exemplary embodiment. The casing 6 consists of glass of the glass type K-8 (crown glass), which corresponds to the glass type Schott BK7. The production of a photonic crystal fiber will be described in more detail below using a specific exemplary embodiment.

In this exemplary embodiment, the photonic crystal fiber is a photonic fiber with different periodicity, ie de facto a quasi-periodic photonic fiber. To produce the photonic crystal fiber, a total of six capillaries with an inner diameter are arranged around the central fiber core la in a first process step. In the present exemplary embodiment, this first inner diameter is 0.6 mm, the wall thickness of the capillary is 0.035 mm and thus the outer diameter of the capillary is 0.67 mm.

A large number of further capillaries, in the present exemplary embodiment 1261 capillaries, with a second inner diameter are arranged around these six capillaries with the first inner diameter surrounding the central fiber core 1 a. This second inner diameter is significantly larger than the first inner diameter and is 1.8 mm in the present exemplary embodiment, the wall thickness of the capillary 0.1 mm and thus the outer diameter of this capillary 2 mm.

Now that these capillaries are arranged around the central fiber core la, the entire bundle is heated to the softening temperature. The softening temperature in the present exemplary embodiment is approximately 590 ° C. Now the entire bundle is pulled through to

Reaching the final geometrical dimensions. In the present exemplary embodiment, the final dimensions are an outer diameter of the overall structure of 73.3 μm (without coating). The drawing process is based on the similarity principle and can be carried out in one or more stages. It is moderate to coat the fiber structure during the drawing process. The layer created with the coating consists of plastic, for example acrylate, and serves to increase the mechanical stability, elasticity and flexibility of the structure.

In the following exemplary embodiment, the drawn photonic crystal fiber has the following geometrical final dimensions:

- outer diameter (without coating) 73.3 μm, diameter of the outer channels 3a 1.8 μm,

Hole spacing of the outer channels 3a in the casing 6 2.2 μm,

Outside diameter of the centrally arranged quasi structure, that is to say of the central fiber core la, with the inner channels 2a 2.2 μm surrounding it, diameter of the inner channels 2a 0.6 μm, hole spacing between the inner channels 2a 0.7 μm, diameter of the central fiber core la 0 , 7 µm.

A preferred use of the photonic crystal fiber is the generation of a super continuum by coupling in laser radiation.

By coupling pulsed laser radiation, for example from a Ti-sapphire laser at a wavelength of 0.79 μm, into the central fiber core la, a broad super continuum is generated that extends over a wavelength of 180 nm to 1800 nm. In this exemplary embodiment, the average power of the laser is 900 mW at a wavelength of 800 nm. The pulse duration is 100 fs at a pulse rate of 80 MHz. With these parameters it is possible to create a super continuum from the UV range to the near infrared range. This results in the possibility of realizing compact, stable and highly brilliant broadband light sources by means of the photonic crystal fibers according to the invention. The photonic crystal structures according to the invention make it possible to significantly broaden the spectrum of laser pulses in the femtosecond range, a significant proportion being in the far and near UV range. These options for controlling the spectrum of ultrashort light pulses can be used to solve problems in medical optics, in particular for the implementation of arrangements for optical coherent tomography and the production of broadband radiation sources. The use of broadband coherent radiation sources in linear and nonlinear spectroscopy allows the registration of the spectra during a laser pulse, which is extremely important for the investigation of non-stationary media and superfast biological reactions.

The invention is not limited to the exemplary embodiments shown here, rather it is possible to implement further embodiment variants by combining the means and features shown without leaving the scope of the invention.

Claims

claims 1. Photonic fiber, consisting of a central area and channels surrounding this central area, characterized in that at least two metallic conductors (2) are arranged in spatial proximity and along a central fiber (1). 2. Photonic fiber according to claim 1, characterized in that the metallic conductors (2) are designed as nano conductors, and are arranged diametrically opposite one another next to the central fiber (1) and the metallic conductors (2) are metal-filled channels (3) The central fiber (1) and the metallic conductors (2) are surrounded by a sheath consisting of air-filled channels (3) and / or rods and / or dielectric. 3. Photonic fiber, according to claim 1 or 2, characterized in that the metal is a low-melting solder and the solder consists of lead and / or tin and / or silver. 4. Photonic fiber according to claim 2, characterized in that elements made of soluble glass can be arranged in the sheathing and can be completely or partially removed to form cavities. 5. A process for the production of photonic fibers, characterized in that Capillaries and / or rods made of glass are joined to geometric structures with at least one central fiber and a sheathing, the geometric structures are heated and subjected to a drawing process and molten liquid metal in spatial proximity to the central fiber before or after the end of the drawing process in cavities of the capillary is filled. 6. The method according to claim 5, characterized in that the metal fibers or metal rods formed by filling liquid metal into the capillaries are subjected together with the capillaries and / or glass rods to the further drawing process. 7. The method according to claim 5, characterized in that before the drawing process, elements made of soluble glass are introduced into the geometric structures, which form cavities after their total or partial dissolution and or serve to create specific geometric structures and the geometric structures after the drawing process Pieces of a defined length can be cut, sanded and polished. 8. Photonic crystal fiber, consisting of a central fiber core (1) and the central fiber core (1) surrounding air channels, characterized in that At least six inner channels (2) are arranged adjacent to the central fiber core (1) and outer channels (3) are arranged adjacent to the inner channels (2). 9. Photonic crystal fiber according to claim 8, characterized in that between the central fiber core (1) and the inner channels (2) inner cavities (4) and between the inner channels (2) and the outer channels (3) outer cavities (5a) and between the outer channels (3) outer cavities (5b) are arranged. 10. Photonic crystal fiber according to claims 8 or 9, characterized in that the outer channels (4) 'have different inner diameters and the inner diameter of the outer channels (3) from the area around the central fiber core (1) in the direction of the periphery (4) increasingly are trained. 11. Photonic crystal fiber according to one of the preceding claims 8 to 10, characterized in that the inner channels (2) and / or the outer channels (3) have a sheath (6) which is hexagonal and the inner cavities (4) and / or the outer cavities (5) have a triangular cross-sectional shape. 12. Photonic crystal fiber according to claim 5, characterized in that the casing (6) consists of glass of the glass type K-8 (crown glass) or Schott BK7. 13. Process for the production of photonic crystal fibers, consisting of a central fiber core and surrounding air channels, characterized by the following process steps: Arrangement of at least six capillaries with a first inner diameter around a central fiber core, arrangement of a large number of further capillaries with a second inner diameter around the six capillaries with the first inner diameter, Heating of the entire bundle to the softening temperature, Pulling the entire bundle until the geometrical final dimensions are reached, wherein the first inner diameter of the capillary is smaller than the second inner diameter and the second Inner diameter is smaller than the third inner diameter. 14. The method according to claim 13, characterized in that during the drawing process the fiber structure is coated and the coating consists of plastic and the entire bundle is drawn several times. 15. Use of a photonic crystal fiber according to ^' Claim 8 for generating a super continuum by coupling in laser radiation.