Coupling elements for surface plasmon resonance sensors

A method of forming a first surface relief pattern adapted to be replicated onto a substantially plane surface of a substantially transparent member to form a first diffractive optical element, said substantially transparent member being adapted to form part of a surface plasmon resonance sensor, the method comprising the steps of

• providing a master substrate, said master substrate having a substantially plane surface,
• providing a photosensitive layer of material onto the substantially plane surface of the master substrate,
• exposing the photosensitive layer to a first and a second wave of electromagnetic radiation so as to expose the photosensitive layer to a first interference pattern generated by a spatial overlap at an intersection between the first and second waves of electromagnetic radiation, wherein
• the first wave of electromagnetic radiation, at the position of the photosensitive layer, has a first mean propagation vector, and wherein
• the second wave of electromagnetic radiation, at the position of the photosensitive layer, has a second mean propagation vector, the second mean propagation vector forming an angle to the first mean propagation vector at the intersection between the first and second wave of electromagnetic radiation,
• wherein the angle between the first and second mean propagation vectors is selected so as to change direction of propagation of an incoming wave of electromagnetic radiation having an incoming mean propagation vector in such a way that the smallest angle between the incoming mean propagation vector and a diffracted mean propagation vector is larger than 40 degrees when said incoming wave of electromagnetic radiation is incident upon the first diffractive optical element replicated in the substantially plane surface of the substantially transparent member.