| 摘要 |
An optical system comprising a diffraction element ( 2 ) formed of a substantially rigid first material having a first refractive index. The diffraction element has a first plurality of grooves ( 4 ) at a first interface of the diffraction element with a second material ( 8 ) having a second refractive index; and a second, different, plurality of grooves ( 6 ) at a second, different, interface of the diffraction element with a third material ( 10 ) having a third refractive index. The first and second pluralities of grooves ( 4 ), ( 6 ) are aligned with respect to each other such that a combined diffractive effect is achieved. Moreover, the third material ( 10 ) is a liquid. The diffractive element may be manufactured using an injection moulding technique, following which the second and/or third materials may be applied in fluid form. By use of the invention, the two pluralities of grooves may be aligned with respect to each other with a high degree of efficiency and reliability
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