<title>The reality of holographic optical head</title>

Abstract

The performance of an Optical head can be improved by using HOE's (Holographic Optical Element). The HOE is compact, light and can perform multiple functions. We have demonstrated the feasibility of a holographic optical head (HOH) design which employs two spherical lenses and two HOE's. The two HOE's correct the spherical aberrations of the lenses, change the elliptical to circular beam. The tolerance of wavelength variation is ±5nm. The observed reconstruction spot size from an experimental setup was 1.6 μm as compared with the designed theoretical value of 1.0 μm . We believe the discrepancy is largely due to the misalignment of the components and inaccuracy of the HOE's. The HOE's used in the experimental HOH were actually made optically using an intermediate CGH. We have also done computer simulations for the HOH using aspherical lenses. The wavelength variation tolerance can be extended to ±15nm. In the aspherical HOH design, the correction of the residual spherical and chromatic aberration of the aspherical lenses were also included. Though possible, we did not include astigmatism correction of the laser source because the current computer program cannot handle the calculation. We believe the inclusion of astigmatism will not affect the performance. In view of the good performance, design and fabrication tools now becoming available and the potential of great cost advantages, the holographic optical head can become a reality in the near future.