Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
2001-06-12
2003-12-30
Juba, John (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S572000, C359S576000
Reexamination Certificate
active
06671095
ABSTRACT:
This invention relates to a micro relief element (MRE) and a method of preparing same.
An MRE, as referred to herein, is a 3-dimensional structure which is formed on the surface of a desired substrate and which structure is able to perform a specific function. Typically, the structure is a repetitive pattern which protrudes above the substrate to a defined height of the order of 0.1 to 1000 microns. Such an MRE can be used as an active component in micro-optic, micro-fluidic, micro-electrical and micro-mechanical devices. In particular, such an MRE can be used as a micro-optical element (MOE) and in which case the structure may be of a height in the range 0.1 to 1000 microns, more commonly in the range 0.1 to 10 microns. Where the MRE is a component in a micro-fluidic or micro-mechanical device then the structures are usually of heights in the range 10 to 1000 microns.
An MOE comprises a surface relief structure whose purpose is to induce phase changes on a light beam which is incident upon the structure such that a predetermined spatial distribution of the light results when the incident light is viewed either in reflection or transmission. MOEs also include structures in which the relief structure is embedded within a light transmissive material, hereinafter an immersed MOE, such as for example an immersed microlens.
MOEs may be used for a variety of applications, such as diffraction gratings, lenses, beam array generators, laser harmonic separators, focusing mirrors and microlens arrays.
Microlens arrays can be used for optical readers, interfaces between laser diodes and optical fibres, diffuser screens, integral photography, 3-d camera and display systems, integrated optical devices and imagebars.
Usually, an MOE is formed by exposing and developing the desired surface relief structure into a photosensitive material coated onto the supporting substrate and then transfering the surface relief structure into the substrate by plasma or chemical etching. The conventional design and fabrication of MOEs is discussed in “Synthetic diffractive elements for optical interconnects”, M R Taghizadeh et al, Optical Computing and Processing, Vol 2(4), pp 221-242, 1992; “Two-dimensional array of diffractive microlenses fabricated by thin film deposition”, J Jahns et al, Appl Opt, Vol 29(7), 931, 1990; “Continuous-relief diffractive optical elements for two-dimensional array generation”, M T Gale et al, Appl Opt, Vol 32(14), 2526, 1993; “Multilevel-grating array generators: fabrication error analysis and experiments”, J M Miller et al, Appl Opt, Vol 32(14), 2519, 1993; and “Fabricating binary optics in infrared and visible materials” M B Stem et al, SPIE, Vol 1751, Miniature and micro-optics, pp 85-95, 1992.
Microlens arrays have in the past been produced by different methods as described in “Polymer microlens arrays”, P Pantelis and D J McCartney, Pure Appl. Opt., Vol 3, 103 (1994); “The manufacture of microlenses by melting photoresist”, D Daley, R F Stevens, M C Hutley and N Davies, Meas. Sci. Technol., Vol 1, 759 (1990); and “Microlens array fabricated in surface relief with high numerical aperture”, H W Lau, N Davies, M McCormick, SPIE Vol 1544 Miniature and Micro-optics: Fabrication and System Applications, p178 (1991). Glass microlenses have been made by chemically etching glass, moulding glass, plasma etching glass to produce a surface relief structure. Polymer microlenses have been produced by melting islands of photoresist or by direct writing photosensitive materials with a laser beam or by directly writing a suitable material with an electron beam or by plasma etching or by moulding.
Unfortunately, conventional methods of fabrication for MREs are limited in the range of substrates that can be used and in the complexity and accuracy of the relief structures that can be formed.
It is an object of the present invention to provide a facile method for producing MREs, in particular MOEs, in a variety of substrates and complexity of designs. An advantage of the present method is that a wide range of heights of surface relief can be produced using the same process. Another advantage is that small lateral features can be successfully reproduced. Additionally, the process may be used to produce large area MREs.
Accordingly in a first aspect the present invention provides a micro relief element which comprises
a) a first layer of a first substrate, the first layer having a receptive surface capable of retaining a relief forming polymer;
(b) an overlay of a desired thickness of the relief forming polymer over the receptive surface; and
(c) at least one relief feature formed from the relief forming polymer and which protrudes above the overlay.
In a second aspect the present invention provides a structure for use as at least part of a micro-optical element, which structure comprises
(a) a first layer of an optically transmissive first substrate having a first refractive index, the first layer having a receptive surface capable of retaining an optically transmissive relief forming polymer;
(b) an overlay having an optically insignificant effect, preferably having a maximum thickness of less than 1.5 &mgr;m, of the relief forming polymer over the receptive surface, the relief forming polymer having a second refractive index which is the same as or different from the first refractive index; and
(c) at least one optically active relief feature formed from the relief forming polymer and which protrudes above the overlay.
In a third aspect of the present invention there is provided an immersed MOE comprising
3(a) a first layer of an optically transmissive first substrate having a first refractive index, the first layer having a receptive surface capable of retaining an optically transmissive relief forming polymer;
(b) an overlay having an optically insignificant effect, preferably having a maximum thickness of less than 1.5 &mgr;m, of the relief forming polymer over the receptive surface, the relief forming optically transmissive polymer having a second refractive index which is the same as or different from the first refractive index;
(c) at least one optically active relief feature formed from the relief forming polymer and which protrudes above the overlay; and
(d) a second layer of an optically transmissive second substrate having a third refractive index which is superimposed upon the at least one optically active relief feature and wherein not all of the first, second and third refractive indices are the same.
In a fourth aspect of the present invention there is provided a method of preparing a micro relief element which comprises
a) a first layer of a first substrate, the first layer having a receptive surface capable of retaining a relief forming polymer;
(b) an overlay of a desired thickness of the relief forming polymer over the receptive surface; and
(c) at least one relief feature formed from the relief forming polymer and which protrudes above the overlay
which method comprises
(a) forming a line of contact between the receptive surface and at least one mould feature formed in a flexible dispensing layer;
(b) applying sufficient of a resin, capable of being cured to form the relief forming polymer, to substantially fill the at least one mould feature, along the line of contact;
(c) progressively contacting the receptive surface with the flexible dispensing layer such that
(1) the line of contact moves across the receptive surface;
(2) sufficient of the resin is captured by the mould feature so as to substantially fill the mould feature; and
(3) no more than a quantity of resin capable of forming the overlay passes the line of contact;
(d) curing the resin filling the at least one mould feature so as to form the at least one relief feature; and, optionally, thereafter
(e) releasing the flexible dispensing layer from the at least one relief feature.
In a fifth aspect of the present invention there is provided a method of preparing a structure for use as at least part of a micro-optical element, which structure comprises
(a) a first layer of an optically transmissive first substrate
Carter Neil
Harvey Thomas Grierson
Ryan George Timothy
Summersgill Philip
Assaf Fayez
Epigem Limited
Jacobson & Holman PLLC
Juba John
LandOfFree
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