Optical projectors for head-up displays

Claim 1

A head-up display head, comprising: a combiner arrangement through which an observer can view a scene; and an optical projector arranged to project light representing a display onto the combiner arrangement for reflection to the observer, thereby to provide the observer with a view of the display superimposed on his view of said scene through the combiner arrangement; said projector comprising: a first luminous data source; a first lens arrangement having an optical axis and arranged to receive light from said first source; a second lens arrangement having an optical axis at an angle to the optical axis of the first lens arrangement; between said first and second lens arrangements a first body of light refractive material having alight input face via which light enters said first body from said first source via said first lens arrangement, and two further faces which define a wedge-shaped portion of said first body extending across a light input surface of said second lens arrangement; a second luminous data source which produces light in a waveband different from that of said first source; a third lens arrangement arranged to receive light from said second source; a second body of light refractive material having a light input face via which light enters said second body from said second source via said third lens arrangement and two further faces which define a wedge-shaped portion of said second body; and a dichroic coating between an interface between one of said further faces of said first body and one of said further faces of said second body, said coating being reflective to light from said first source and transmissive to light from said second source; light from said first source following a first light path such that on entering said first body via said first lens arrangement it undergoes critical angle reflection at the other further face of said first body to said one further face of said first body from whence, after reflection at said coating, it is transmitted without substantial reflection, by said other further face of said first body to said second lens arrangement for transmission thereby onto said combiner arrangement; and light from said second source following a second light path such that on entering said second body via said third lens arrangement it is first reflected at the other further face of said second body from whence it is transmitted, via said coating, to said second lens arrangement for transmission thereby onto said combiner arrangement; the lengths of said first and second light paths being substantially the same.