WO2004017111A1

WO2004017111A1 - Photosensitive polymer materials useful as photonic crystals

Info

Publication number: WO2004017111A1
Application number: PCT/AU2003/001051
Authority: WO
Inventors: Martin Straub
Original assignee: Univ Swinburne; Gu Min; Martin Straub; Ventura Michael
Priority date: 2002-08-19
Filing date: 2003-08-19
Publication date: 2004-02-26
Also published as: EP1535094A4; EP1535094A1; AU2003250602B2; AU2003250602A1; AU2002950855A0

Abstract

The invention relates to photosensitive polymer materials comprising one or more elongate voids and to photonic crystals comprising photosensitive polymer materials with an ordered array of elongate voids. The ordered array of elongate voids may include one or more optical waveguide forming defects such that the photonic crystal may comprise an optical signal conducting fibre or optical integrated circuit. The invention also provides methods of formation of elongate voids within a photosensitive polymer material which comprise placing the material and/or a source of focused coherent light under spatial control and subjecting the material to focused coherent light at wavelength and power suitable to initiate void formation while moving the material at desired rate so as to track coherent light focus through the material in axial direction of intended elongate void formation. Related methods can be used to form arrays of elongate voids within photonic crystals. The invention also relates to apparatus for forming elongate voids within photosensitive polymer materials.

Description

PHOTOSENSITIVE POLYMER MATERIALS USEFUL AS PHOTONIC

CRYSTALS

FIELD OF THE INVENTION

The present invention relates to photosensitive polymer materials comprising one or more elongate voids, and in particular, but not exclusively, to photonic crystals fabricated from such photosensitive polymer materials. The invention also relates to methods of formation of elongate voids within photosensitive polymer materials and to related methods of fabrication of photonic crystals as well as to the apparatus that may be utilised in these processes.

BACKGROUND OF THE INVENTION

With the ever increasing demands upon speed and efficiency of information transfer and switching in the information technology and telecommunications fields there is a continuing need to develop ever smaller and more efficient data transfer and switching materials. Although there has been a significant shift towards information transmission using optical fibre links over recent years there has to date been little practical development of switching technologies that rely upon means other than electronic signals. As a result, many current information technology and communications networks require conversion of optical pulses to electronic signals for processing, which are subsequently converted back to optical pulses for further transmission. Network performance could be significantly enhanced if these repeated conversions could be avoided. As such there is presently considerable effort being invested in the development of entirely optical networks and components.

One possibility that has received considerable attention in the quest to develop entirely optical networks and components is the possibility of controlling light flow utilising photonic crystals. Photonic crystals are dielectric structures with a periodic or regularly repeating structure and high refractive contrast over micron, or sub-micron scale operational volume. Photonic crystals, which are also referred to as photonic bandgap materials, exhibit the unique ability to incorporate wavelength-dependent functionality over a small operational volume by exhibiting the characteristic of forbidding propagation of light of particular frequency, which is known as the property of optical bandgap. In this way photonic crystals may be considered to operate as an optical analogue of semiconductor materials, and they may therefore have applications in a variety of important contexts; for example including as optical waveguides for optical signal transmission and in integrated circuits. Particularly in the context of optical waveguides photonic crystals may offer a solution to the problem of transmission of optical signals through sharp angles, without any substantial loss of intensity and with the possible additional benefit relative to known optical waveguides of single-mode operation at all wavelengths.

The great challenge in the development of practical photonic crystal materials is the need to develop such materials with repeating or periodic structures in the micron or sub-micron scale using low cost, repeatable and high fidelity fabrication approaches. Previous workers have attempted to produce photonic crystal materials utilising photopolymerisation of resin and subsequent solvent removal of non-polymerised material¹'², creation of voids inside both doped silica³ and polymethylmethacrylate (PMMA)⁴ as well as other methods utilising lithography and etching⁵. To date these approaches have not been particularly successful.

The present inventors have now determined that it is possible to produce elongate voids within photopoiymer materials. As well as having potential utilities in optical bit data storage, materials according to the invention which include ordered arrays of elongate voids may be utilised in applications where photonic crystal functionality is required, such as in optical signal switching and transmission. SUMMARY OF THE INVENTION

According to one embodiment of the present invention there is provided a photosensitive polymer material comprising one or more elongate voids. Preferably the elongate voids have a substantially elliptical cross sectional shape.

According to another embodiment of the present invention there is provided a photonic crystal comprising a photosensitive polymer material with an ordered array of elongate voids.

In one aspect the ordered array of elongate voids may include one or more optical waveguide forming defects. Such a photonic crystal may comprise an optical signal conducting fibre.

In another aspect the photonic crystal comprises an integrated circuit. Integrated circuits of this kind may be used in a wide variety of electronic and communications equipment.

According to a further embodiment of the present invention there is provided a method of formation of an elongate void within a photosensitive polymer material which comprises placing said material and/or a source of focussed coherent light under spatial control and subjecting said material to focused coherent light at wavelength and power suitable to initiate void formation while moving said material relative to said light at desired constant rate so as to track coherent light focus through said material in axial direction of intended elongate void formation.

According to another embodiment of the present invention there is provided a metho4 of fabrication of a photonic crystal which comprises forming a plurality of elongate voids in an ordered array within a photosensitive polymer material by placing said material and/or a source of focussed coherent light under spatial control and subjecting said material to focused coherent light at wavelength and power sufficient to initiate void formation while moving said material relative to said light at desired constant rate so as to track coherent light focus through said material in axial direction of intended elongate void formation, then repeating process to form subsequent voids in intended locations; wherein said material is not subjected to said coherent light during periods when said material is moved to track coherent light focus from final locus of previously formed void to starting locus of subsequently formed void.

According to a still further embodiment of the present invention there is provided apparatus for forming one or more elongate voids within a photosensitive polymer material which comprises a source of coherent light of suitable wavelength and power to initiate void formation within said material, a spatially controlled mount adapted to retain said material and means for focusing said coherent light at desired locus within said material.

The apparatus according to the invention may further comprise a coherent light diverter which when active prevents said material being subjected to said coherent light; the diverter being controlled in concert with said spatially controlled mount. Preferably said coherent light diverter comprises a shutter.

According to the invention the elongate voids preferably have a micron or sub-micron scale cross-sectional diameter. Particularly preferably the elongate voids have a cross- sectional diameter of between about 0.0 lμm to about 100/ιm, more preferably between about 0.1 μm to about 10/ m.

It is also preferred according to the invention that surfaces of the elongate voids are substantially uniform.

The polymer material according to the invention may comprise a copolymer. In another aspect the polymer material may comprise a blend of polymers. The polymer material may further comprise one or more suitable additives. The additives may be selected from one or more of plasticisers, stabilisers, hardening agents, fillers, colouring agents, dyes, impact modifiers and flame retardants. In a preferred embodiment of the invention the photosensitive polymer material comprises one or more of polymethylmethacrylate, SU-8, SR-368, SR-9008 and NOA63. Preferably the photosensitive polymer material comprises NOA63.

Preferably the wavelength of the focused coherent light is between about 350 and about 750nm, more preferably between about 450 and 650nm, most preferably between about 500 and about 600nm. In a particularly preferred embodiment of the invention the coherent light wavelength is about 540nm. Preferably the coherent light has power between about 10 and about 80mW, preferably between about 20 and about 60m W, more preferably between about 30 and about 50mW. In a preferred embodiment of the invention the coherent light power is 30 to 40mW. The coherent light may have a pulse width between about 50fs to about 500fs, preferably between about lOOfs and 300fs, more preferably between about 150fs and about 250fs. In a preferred embodiment of the invention the coherent light pulse width is about 200fs.

In a preferred embodiment of the invention the coherent light is derived from a Ti:Sapphire laser preferably operated in conjunction with an optical frequency doubler, an optical parametric oscillator or a combination of both. It is also preferred that the coherent light is directed via a telescope to the rear of an objective lens from which it is focused to a desired locus within the material. The objective lens may have numerical aperture between about 0.6 to about 1.4 and the lens may comprise a 40-100X magnification oil immersion objective lens.

According to a preferred embodiment of the invention said desired constant rate moving of said material may range between about 1 to about 500/ m/s, preferably between about 10 to about 400μm/s, more preferably between about 40 to about 300μm/s, more preferably between about 80 to about 200μ,m/s. In a particularly preferred embodiment of the invention the desired constant rate of material movement is about 60μm/s and in another preferred embodiment it is about 300μm/s. BRIEF DESCRIPTION OF THE FIGURES

The present invention will be described further, and by way of example only, with reference to the figures, wherein:

Figure 1 is a schematic representation of the apparatus that may be utilised in forming elongate voids within photopolymer materials.

Figure 2 shows a plot of scanning stage movement speed (μm/s) against coherent light power (mW) which demonstrates the transition regions within the Norland Products Inc. NOA63 polymer material which has been subjected to coherent light at 540nm and 200fs.

Figure 3 shows a light microscope transmission image of two parallel elongate voids created in the void region (as referred to in figure 2) when the NOA63 polymer material was exposed to coherent light at 540nm, 200fs and 30mW, and where the scanning stage was moved at a rate of 60/m /s. The elongate voids are 100μ.m in length and are spaced apart by lOμm.

Figure 4 shows an optical transmission image of parallel elongate voids fabricated in the damage region (as referred to in Figure 2) under the same conditions adopted in figure 3, but with scanning stage movement at a rate of lOμm/s. The elongate voids are lOOμm in length and are spaced apart by 5μm.

Figure 5 shows the elliptical cross-sectional shape of three elongated voids that have been sliced tlirough and imaged using a scanning electron microscope (JEOL JSM-840). The elongate voids were formed under the same conditions adopted in relation to figure 3.

Figure 6 shows a plot of cross-sectional elongate void diameter (μm) against scanning stage scan speed (μm/s) for elongate voids formed using coherent light at 540nm, 200fs and powers of 13mW (depicted as filled circles), 19mW (depicted as filled triangles) and 34mW (depicted as filled squares). A 40X numerical aperture 1.3 objective was used; Figure 7 shows a scanning electron microscope (JEOL JSM-840) image of ends of elongate voids where each void is located 5μm from adjacent voids in both axial and transverse directions. The elongate voids were formed in NOA63 polymer material using coherent light at 540nm, 200fs and 20mW, with scanning stage movement rate of 95μm/s in the void region;

Figure 8 shows transmission and reflection spectra of a photonic crystal which was produced in NOA63 polymer material using coherent light at 540nm, 200fs and 34mW and where scanning stage movement in the void region is at a rate of lOOμm/s. The photonic crystal structure was fabricated by stacking of 20 layers where each layer consisted of 40 parallel elongate voids spaced at 1.8μm and alternate layers were rotated by 90°, with subsequent parallel void layers offset by half in-plane spacing. The layers were separated by 1.7μm;

Figure 9 shows a schematic representation of the photonic crystal array of elongate voids produced as described in figure 8.

DETAILED DESCRIPTION OF THE INVENTION

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

In a broad aspect the present invention relates to a photosensitive polymer material which comprises one or more elongate voids. Without wishing to exhaustively detail possible utilities of these types of materials, it will be understood such materials may be useful as optical waveguides, and in particular to be formulated into optical fibre or optical fibre components such as fibre core, connections, junctions and the like. Such materials may additionally have utility as optical bit data storage devices where the pattern of elongated void or voids formed within the material can be read, for example by confocal microscopy and which will encode for stored data or information. A particularly important utility of materials according to the invention is that they may be formed into photonic crystals which, as discussed above, may be utilised in optical data switching and information processing in the form of an optical integrated circuit. No matter what the intended function of the materials according to the invention an appropriate geometry of elongated voids can be designed, and may be formed within the material by adopting the methods outlined herein.

In the sense adopted within this specification the term "photosensitive" is intended to convey that the polymer material is subject to an alteration of its physical characteristics upon exposure to radiation, and particularly to radiation in the ultraviolet or visible regions of the electromagnetic spectrum. For example, as would be well understood by persons skilled in the art, a wide variety of polymer materials undergo a form of polymerisation, possibly involving crosslinking, which results in a change in physical structure and properties following exposure to radiation at a defined wavelength and power. For example in the commercially available polymer material NOA63 a polyurethane oligomer having unsaturated carbon-carbon bonds is polymerised and crosslinked to a mercapto- ester oligomer to form sulphide linkages upon exposure to ultraviolet light in the wavelength range 200-400nm, resulting in transformation from liquid to solid phase. There are many other examples of photosensitive polymers of this type, just a few of which include polymethyl methacrylate (PMMA), SU-8 (available from MicroChem,

Corp.) and SR-368 and SR-9008 (available from Sartomer).

By reference to the phrase "photosensitive polymer material" it is to be understood that the polymer material may constitute a single photosensitive polymer, a blend of two or more polymers, at least one of which has photosensitive characteristics, a copolymer having photosensitive characteristics or a polymer formulation including at least one polymer with photosensitive characteristics and one or more suitable additives. Suitable additives may, for example, be selected from the classes of fillers, plasticisers, stabilisers (for example antioxidant or UN stabilisers), hardening agents, colouring agents, dyes, impact modifiers and flame retardants, although it should be recognised that in order to qualify as being suitable in the context of the present invention such additives should not adversely affect light transmission qualities of the polymer material and should not be sensitive to the radiation wavelengths adopted in formation of elongated voids therewithin. Polymer materials which exhibit a high refractive index contrast between the polymer itself and voids contained therein are particularly preferred. Acceptable polymer materials may be those having refractive index contrast ranges exceeding about 1.4, more preferably exceeding about 3.0. The polymer materials are preferably substantially fully transparent to light of wavelength of about 2μm or less, although substantial transparency also at higher wavelengths is preferred.

In a preferred aspect the invention relates to a photonic crystal fabricated from the photosensitive polymer material by virtue of introducing into the material an ordered array of elongate voids. Using mathematical analysis of wave characteristics it is possible to design appropriate ordered array geometries which will impart upon the polymer material the desired light transmission and bandgap qualities. The voids introduced into the polymer materials may preferably have a substantially elliptical cross-sectional profile and will preferably have a diameter in the micron or sub-micron scale range. By this it is intended to mean for example that cross-sectional diameters of the voids may be between about O.Olμm to about lOOμm, preferably between about O.lμm to about lOμm depending upon the function in which the material is to be employed. The present inventors have recognised that cross-sectional diameter of the elongated voids can be varied as a function of both the power of coherent light used to generate void formation and the rate of movement of the coherent light focus relative to the polymer material. In practice, this movement may conveniently be adopted by way of positioning the polymer material on a spatially controllable mount or scanning stage, the direction and rate of movement of which can be finely controlled in at least two and preferably three dimensions. Other aspects of the invention may involve movement of the coherent light focus, or indeed movement of both the focus and the material.

In one embodiment of the invention, where for example the photonic crystal is intended to be used as an optical waveguide the ordered array of elongate voids fabricated within the polymer material may include one or more optical waveguide forming defects. By this what is meant is that the regular pattern of voids introduced into the material may be interrupted by the absence of one or more voids in locations predicted according to the pattern, which may confer upon the material optical waveguide capabilities. Photonic crystals including such materials may conveniently be utilised in production of optical signal conducting fibre or components thereof such as core as well as junctions or connectors.

In general terms, elongated voids may be formed within photosensitive polymer materials according to the invention by placing the material under spatial control and subjecting the material to focused coherent light at a wavelength and power suitable to initiate void formation, while moving the material at a desired (preferably, but not necessarily constant) rate so as to track the focus of the coherent light through the material in the axial direction of intended elongate void formation. By conducting the same process, photonic crystals, which include a plurality of elongate voids in an ordered array, may also be fabricated. Clearly, given the microscopic geometry of these products it is important to ensure accuracy in the spatial relationship between the polymer material and the focus of the void forming coherent light during the production process. One way in which this can be achieved is by carefully fixing in position the optical apparatus through which the light is transmitted and then carefully controlling movement of the polymer material, which is removably mounted on a scanning stage, the movement of which is under computer control. In the case of fabrication of a photopolymer crystal where a plurality of elongate voids must be formed it is required to provide some means of preventing coherent light exposure of the polymer material during the period when the material is moved to track the focus of the coherent light from the final locus of the previously produced void to the starting locus of the next void to be fabricated. This may be achieved utilising some form of coherent light diverter, which is controlled in concert with the spatially controlled mount upon which the material is retained. For example the coherent light diverter may switch off, reflect, absorb or deflect the coherent light away from the material during movement of the material in preparation for placing the light focus in position for formation of the next void to be produced. Preferably, the diverter will constitute a shutter that is operated under the same computer control as the spatially controlled mount.

In forming the elongated voids within the polymer material it is important for a finely focused point or locus within the material to be subjected to coherent light which is at a wavelength and power suitable to initiate void formation. By this it is intended to mean that the wavelength and power of focused light to which the locus is subjected is selected such that based upon absorption characteristics of the material sufficient heat and pressure will be generated within the material to soften or melt the material at the locus and redistribute softened/melted polymer material to edges of the focal spot. As the focal spot or locus is tracked through the polymer material by virtue of movement relative to the focal point of the spatially controlled mount or scanning stage the softening/melting of polymer material and its deposition at edges of the focal spot will continue to form an axial or elongated void.

The result of softening/melting and deposition of polymer material about the edges of the focal spot is that edges or surfaces of the void are generally smooth or substantially uniform and that the walls of the void have higher density and different refractive index compared to the polymer material generally. Further, as the inventors have determined that cross-sectional diameter of the elongate voids is a function of both the speed of tracking of the focal spot and the power of the coherent light a desired (preferably, but not necessarily constant) rate of movement of the spatially controlled mount (and consequently the polymer material) should be selected, which at the coherent light power adopted will result in voids of desired diameter.

Basic components of the apparatus that may be utilised in forming voids within the polymer material are a source of coherent light, which is at the wavelength and power desired according to the polymer material adopted. For example, a laser light source may be utilised and if it is necessary to modify the wavelength of the coherent light produced by this laser the light may appropriately pass through a coherent optical frequency doubler. It is also important that the coherent light is sharply focused onto a focal spot within the polymer material. This may be achieved by utilising an objective lens in conjunction with means such as a telescope or lenses, which serve to collimate the coherent light at the rear of the objective lens. For example, the laser light source may be a Ti:Sapphire laser such as the Mira 900-F which could be used in conjunction with the Mira-OPO containing an intracavity frequency doubler to thereby produce a coherent light source of wavelength 540nm and pulse width of 200fs. Generally however, and of course depending upon the nature of the polymer material selected, the wavelength of the focused coherent light is between about 300 and about 750nm, preferably between about 450 and 650nm, and particularly preferably between about 500 and about 600nm. Again depending upon the nature of the polymer material and the desired void diameter the coherent light power may be between about 10 and about 80mW, preferably between about 20 and about 60mW and more preferably between 30 and about 50mW. The pulse width adopted in relation to the coherent light may for example range between about 50fs to about 500fs, preferably between about lOOfs and about 300fs and most preferably between about 150fs and about 250fs.

Once again depending upon the nature of the polymer material and the desired void diameter the rate of movement of the spatially controlled mount adapted to retain the polymer material can be selected. Generally, however, the rate of movement of the spatially controlled mount will be between about 1 to about 500μm/s, preferably between about 10 to about 400μm/s, more preferably between about 40 to about 300μm/s, more preferably between about 80 to about 200μm/s. In a particularly preferred embodiment of the invention the desired constant rate of material movement is about 60μm/s and in another preferred embodiment it is about 300μm/s, during void formation within the polymer material. For optimal results the movement rate of the coherent light focus within the material should remain substantially constant during void formation. The present invention will be further described by way of example only with reference to the following non-limiting examples.

EXAMPLES

Example 1 - Elongate Void Formation

Photopolymer Material

A commercially available photopolymer, NOA63 from Norland Products Inc., was used. The material is a clear, colourless liquid photopolymer that can be cured when exposed to ultraviolet light.

Methods and Apparatus

A small drop of NOA63 photopolymer was placed on a cover slip and irradiated for two hours by a focused wide band ultraviolet light source (200-400nm at 30W). This exposure time expended much of the photo-initiator leaving a transparent solid sample.

Coherent light derived from a Coherent Mira-OPO Tusapphire mode-locked laser operating at 710nm, 800mW was passed through a Coherent Mina OPO with optical frequency doubler (540nm, 40mW). A telescope arrangement was used to uniformly illuminate the back of a 40X magnification oil immersion objective lens with numerical aperture (NA) 1.3. In situ observations of light reflected from the material via a dichoric mirror (DC) were made via a CCD camera and monitor arrangement.

A three dimensional (3D) array of elongate voids was produced within the material by translation of the sample in both axial and transverse directions through the focus of the objective using a 3D scanning stage. Motion of the stage was controlled via a National Instruments PCI-6177 data acquisition (DAQ) card installed in a computer. The four channel analogue outputs of the DAQ card control x,y and z stage movements, as well as a shutter. The DAQ was controlled by a Labview program, which takes a design file and translates that to a swing in the DAQ output voltage. This software allows for many variables in scan performance to be changed.

Example 2 - Void Analysis

Void Rod Fabrication

Four transition states have been observed for the NOA63 resin under different writing conditions. Figure 2 shows the four regions and how they are dependent on both scan speed and power. The region of interest in relation to this invention is the void region. In this region an elongate void (also referred to as a void channel or void rod) is generated at the focus of the objective. Material in the focus is placed under high temperature and pressure causing the material to soften or melt and be re-distributed to the edge of the focal spot. The resulting structure is that of a continuous, smooth edged void channel, with the surrounding walls having a higher density than the polymer material generally due to the ejection of material from the centre of the void (Figure 3). In the damage region, channels are not smooth and adjacent channels are merged together (Figure 4).

As discussed above, in the void region, smooth, continuous void channels are generated. The void channels generated in this region are also elongated in the axial direction (z-axis) as can be seen in Figure 5. Figure 6 shows the dependence of the transverse (x-axis) void channel diameter on writing power and scan speed.

From Figure 6 it can be seen that there is a linear dependence on the diameter of the void channels for a specific power and scan speed. At low power (2 to lOmW) small variations in scan speed dramatically affect the cross-sectional diameter of the void channels generated. Channels having diameter from 1.25μm to 0.65μm can be created over a small deviation in scan speed (l-8μm/sec).

For higher powers (lOmW to 35mW) void rod diameters are still affected by scan speed, however, a greater change in speed variation is required to cause a change in void channel diameters. At a power of 19mW void channel diameters vary by 0.3μm over a 20μm/s range of scanning stage speeds, and at 34mW the same variation in diameter requires a 40μm/s range of scan speeds.

This dependence on scan speed and power allows for void channels to be created with any specific diameter in the range 0.65 to 1.26μm, using the particular material and fabrication apparatus adopted.

Also using the present material and fabrication approach the proximity within which adjacent void channels can be fabricated successfully has been measured to be 1.3μm in both transverse dimensions (x, y-axis) and 1.5μm in the axial direction (z-axis). The proximity within which adjacent void channels can be brought together and the size of channels is yet to be optimized but there are a number of techniques that can be used to reduce channel diameter and increase the number of void channels in the x, y and z directions.

Example 3 - Application Of Elongate Voids

Elongate voids (void channels) can be arranged in an organized fashion in all axes (Figure 7). Such structures have been fabricated with varying layer spacing (z-axis). Figure 8 shows the bandgap of one such structure, exhibiting an 80% bandgap with a gap/midgap ratio of 0.11 at a wavelength of 4.75μm. The structure (Figure 9) was fabricated by stacking up 20 layers. Each layer consisting of 40 parallel void channels spaced at 1.8μm. Each layer was rotated by 90 degrees with respect to the previous layer, and subsequent layers were offset by half in-plane spacing. Layers were separated by 1.7μm.

The fabrication method of the present invention has been demonstrated to allow for micro- scale elongate voids to be fabricated inside a photopolymer material. This method enables any arbitrary shaped void channel to be generated in three dimensions. Straight void channels have been shown to have smooth edges. An ability to use highly ordered individual void channels in the construction of a photonic crystal has also been shown. It is to be recognised that the present invention has been described by way of example only and that modifications and/or alterations thereto which would be apparent to persons skilled in the art, based upon the disclosure herein, are also considered to fall within the' spirit and scope of the invention as defined in the appended claims.

REFERENCES

1. H-Bo. Sun and V. Mizeikis, App. Phys. Lett. 79, 1 (2001) Microcavities in polymeric photonic crystals.

2. H-Bo. Sun, S. Matsuo and H. Misawa, App. Phys. Lett. 74, 6 (1999) Three- dimensional photonic crystal structures achieved with two-photon-absorption photopolymerization of resin.

3. H-Bo. Sun, Y. Xu, S. Juodkazis, Opt. Lett. 26, 6 (2001) Arbitrary-lattice photonic crystals created by multiphoton microfabrication.

4. D. Day and M. Gu, Appl. Phys. Lett. 80, 13 (2002) Formation of voids in doped polymethylmethacrylate polymer.

5. P. Ni, B. Cheng and D. Zhang, App. Phys. Lett. 80, 11 (2002) Inverse opal with an ultraviolet gap.

Claims

CLAIMS:

1. A photosensitive polymer material comprising one or more elongate voids.

2. The photosensitive polymer material according to claim 1 wherein the elongate voids have a substantially elliptical cross sectional shape.

3. The photosensitive polymer material according to either claim 1 or claim 2 wherein the elongate voids have a micron or sub-micron scale cross-sectional diameter.

4. The photosensitive polymer material according to any one of claims 1 to 3 wherein the elongate voids have a cross-sectional diameter of between about O.Olμm to about lOOμm.

5. The photosensitive polymer material according to any one of claims 1 to 3 wherein the elongate voids have a cross-sectional diameter of between about 0.1 μm to about lOμm.

6. The photosensitive polymer material according to any one of claims 1 to 5 wherein the surfaces of the elongate voids are substantially uniform.

7. The photosensitive polymer material according to any one of claims 1 to 6 comprising a copolymer.

8. The photosensitive polymer material according to any one of claims 1 to 6 comprising a blend of polymers.

9. The photosensitive polymer material according to any one of claims 1 to 6 comprising one or more suitable additives.

10. The photosensitive polymer material according to claim 9 wherein the additives are selected from one or more of plasticisers, stabilisers, hardening agents, fillers, colouring agents, dyes, impact modifiers and flame retardants.

11. The photosensitive polymer material according to any one of claims 1 to 10 comprising one or more of polymethylmethacrylate, SU-8, SR-368, SR-9008 and NOA63.

12. The photosensitive polymer material according to claim 11 comprising NOA63.

13. A photonic crystal comprising a photosensitive polymer material with an ordered array of elongate voids.

14. The photonic crystal according to claim 13 wherein the ordered array of elongate voids includes one or more optical waveguide forming defects.

15. The photonic crystal according to claim 14 which comprises an optical signal conducting fibre.

16. The photonic crystal according to claim 14 which comprises an integrated circuit.

17. The photonic crystal according to any one of claims 13 to 16 wherein the elongate voids have a substantially elliptical cross sectional shape.

18. The photonic crystal according to any one of claims 13 to 17 wherein the elongate voids have a micron or sub-micron scale cross-sectional diameter.

19. The photonic crystal according to any one of claims 13 to 18 wherein the elongate voids have a cross-sectional diameter of between about O.Olμm to about lOOμm.

20. The photonic crystal according to any one of claims 13 to 18 wherein the elongate voids have a cross-sectional diameter of between about 0.1 μm to about lOμm.

21. The photonic crystal according to any one of claims 13 to 20 wherein the surfaces of the elongate voids are substantially uniform.

22. The photonic crystal according to any one of claims 13 to 21 comprising a copolymer.

23. The photonic crystal according to any one of claims 13 to 21 comprising a blend of polymers.

24. The photonic crystal according to any one of claims 13 to 21 comprising one or more suitable additives.

25. The photonic crystal according to claim 24 wherein the additives are selected from one or more of plasticisers, stabilisers, hardening agents, fillers, colouring agents, dyes, impact modifiers and flame retardants.

26. The photonic crystal according to any one of claims 13 to 25 comprising one or more of polymethylmethacrylate, SU-8, SR-368, SR-9008 and NOA63.

27. The photonic crystal according to claim 26 comprising NOA63.

28. A method of formation of an elongate void within a photosensitive polymer material which comprises placing said material and/or a source of focussed coherent light under spatial control and subjecting said material to focused coherent light at wavelength and power suitable to initiate void formation while moving said material relative to said light at desired rate so as to track coherent light focus through said material in axial direction of intended elongate void formation.

29. A method of fabrication of a photonic crystal which comprises forming a plurality of elongate voids in an ordered array within a photosensitive polymer material by placing said material and/or a source of focussed coherent light under spatial control and subjecting said material to focused coherent light at wavelength and power sufficient to initiate void formation while moving said material relative to said light at desired rate so as to track coherent light focus through said material in axial direction of intended elongate void formation, then repeating process to form subsequent voids in intended locations; wherein said material is not subjected to said coherent light during periods when said material is moved to track coherent light focus from final locus of previously formed void to starting locus of subsequently formed void.

30. The method according to either claim 28 or claim 29 wherein the elongate voids have a substantially elliptical cross sectional shape.

31. The method according to either claim 28 or claim 29 wherein the elongate voids have a micron or sub-micron scale cross-sectional diameter.

32. The method according to either claim 28 or claim 29 wherein the elongate voids have a cross-sectional diameter of between about O.Olμm to about lOOμm.

33. The method according to either claim 28 or claim 29 wherein the elongate voids have a cross-sectional diameter of between about 0.1 μm to about lOμm.

34. The method according to either claim 28 or claim 29 wherein the surfaces of the elongate voids are substantially uniform.

35. The method according to either claim 28 or claim 29 wherein the photosensitive polymer material comprises a copolymer.

36. The method according to either claim 28 or claim 29 wherein the photosensitive polymer material comprises a blend of polymers.

37. The method according to either claim 28 or claim 29 wherein the photosensitive polymer material comprises one or more suitable additives.

38. The method according to claim 37 wherein the additives are selected from one or more of plasticisers, stabilisers, hardening agents, fillers, colouring agents, dyes, impact modifiers and flame retardants.

39. The method according to either claim 28 or claim 29 wherein the photosensitive polymer material comprises one or more of polymethylmethacrylate, SU-8, SR-368, SR- 9008 and NO A63.

40. The method according to claim 39 wherein the photosensitive polymer material comprises NOA63.

41. The method according to either claim 28 or claim 29 wherein the wavelength of the focused coherent light is between about 350 and about 750nm.

42. The method according to either claim 28 or claim 29 wherein the wavelength of the focussed coherent light is between about 450 and 650nm.

43. The method according to either claim 28 or claim 29 wherein the wavelength of the focussed coherent light is between about 500 and about 600nm.

44. The method according to either claim 28 or claim 29 wherein the wavelength of the focussed coherent light is about 540nm.

45. The method according to either claim 28 or claim 29 wherein the coherent light has power between about 10 and about 80mW.

46. The method according to either claim 28 or claim 29 wherein the coherent light has power between about 20 and about 60mW.

47. The method according to either claim 28 or claim 29 wherein the coherent light has power between about 30 and about 50mW.

48. The method according to either claim 28 or claim 29 wherein the coherent light has power between about 30 to 40mW.

49. The method according to either claim 28 or claim 29 wherein the coherent light has a pulse width between about 50fs to about 500fs.

50. The method according to either claim 28 or claim 29 wherein the coherent light has a pulse width between about lOOfs and 300fs.

51. The method according to either claim 28 or claim 29 wherein the coherent light has a pulse width between about 150fs and about 250fs.

52. The method according to either claim 28 or claim 29 wherein the coherent light has a pulse width of about 200fs.

53. The method according to either claim 28 or claim 29 wherein the coherent light source is a TύSapphire laser operated in conjunction with an optical frequency doubler, an optical parametric oscillator or a combination of both.

54. The method according to either claim 28 or claim 29 wherein the coherent light is directed via a telescope to the rear of an objective lens from which it is focused to a desired locus within the material.

55. The method according to claim 54 wherein the objective lens has a numerical aperture between about 0.6 to about 1.4.

56. . The method according to either claim 28 or claim 29 wherein the lens comprises a 40X magnification oil immersion objective lens.

57. The method according to either claim 28 or claim 29 wherein said desired rate moving of said material ranges between about 1 to about 500μm/s.

58. The method according to either claim 28 or claim 29 wherein said desired rate moving of said material ranges between about 10 to about 400μm/s.

59. The method according to either claim 28 or claim 29 wherein said desired rate moving of said material is about 60μm/s or about 300μm/s.

60. Apparatus for forming one or more elongate voids within a photosensitive polymer material which comprises a source of coherent light of suitable wavelength and power to initiate void formation within said material, a spatially controlled mount adapted to retain said material and means for focusing said coherent light at desired locus within said material.

61. The apparatus according claim 60 further comprising a coherent light diverter which when active prevents said material being subjected to said coherent light; the diverter being controlled in concert with said spatially controlled mount.

62. The apparatus according to claim 61 wherein said coherent light diverter comprises a shutter.

63. The apparatus according to claim 60 wherein the wavelength of the focused coherent light is between about 350 and about 750nm.

64. The apparatus according to claim 60 wherein the wavelength of the focussed coherent light is between about 450 and 650nm.

65. The apparatus according to claim 60 wherein the wavelength of the focussed coherent light is between about 500 and about 600nm.

66. The apparatus according to claim 60 wherein the wavelength of the focussed coherent light is about 540nm.

67. The apparatus according to claim 60 wherein the coherent light has power between about 10 and about 80mW.

68. The apparatus according to claim 60 wherein the coherent light has power between about 20 and about 60mW.

69. The apparatus according to claim 60 wherein the coherent light has power between about 30 and about 50mW.

70. The apparatus according to claim 60 wherein the coherent light has power between about 30 to 40mW.

71. The apparatus according to claim 60 wherein the coherent light has a pulse width between about 50fs to about 500fs.

72. The apparatus according to claim 60 wherein the coherent light has a pulse width between about lOOfs and 300fs.

73. The apparatus according to claim 60 wherein the coherent light has a pulse width between about 150fs and about 250fs.

74. The apparatus according to claim 60 wherein the coherent light has a pulse width of about 200fs.

75. The apparatus according to claim 60 wherein the coherent light source is a Ti:Sapphire laser operated in conjunction with an optical frequency doubler, an optical parametric oscillator or a combination of both.

76. The apparatus according to claim 60 wherein the coherent light is directed via a telescope to the rear of an objective lens from which it is focused to a desired locus within the material.

77. The apparatus according to claim 60 wherein the objective lens has a numerical aperture between about 0.6 to about 1.4.

78. The apparatus according to claim 60 wherein the lens comprises a 40-100X magnification oil immersion objective lens.