| 摘要 |
A diffractive beam expander (50) comprises a substantially planar waveguiding substrate, an input grating (10) to provide an in-coupled beam (B1) propagating within said substrate, and an output grating (30) to provide an out-coupled beam. The expander (50) comprises also four or more further grating portions to expand the height of the in-coupled beam (B1). A part of the in-coupled light is diffracted by a first deflecting grating portion (21a) to provide a first deflected beam. A part of the in-coupled light is diffracted by a second deflecting grating portion (22a) to provide a second deflected beam. The first deflected beam propagates downwards and the second deflected beam propagates upwards with respect to the in-coupled beam (B1). The first deflected beam impinges on a first direction-restoring grating portion (21b) and the second deflected beam impinges on a second direction-restoring grating portion (22b). The first restoring grating portion (21b) provides a first restored beam (V1) and the second restoring grating portion (22b) provides a second restored beam (V2), which both have the same direction as the in-coupled beam (B1). Out-coupling provides an output beam which is parallel to the input beam, and has a greater vertical dimension than said input beam. |
