Stratified volume holographic optical elements

Volume holographic optical elements are of considerable interest for applications in optical information processing and computing systems and in optical interconnect technology. Typical volume holographic optical elements are fabricated from bulk photosensitive materials, such that the holographic recording process occurs throughout the entire volume. We have investigated an alternative approach to the fabrication of such elements by employing a number of thin photosensitive layers interleaved among much thicker optically inactive buffer layers. As few as five thin but spatially separated active layers can exhibit essentially the same Bragg selectivity as a single distributed volume hologram. Performance characteristics of stratified volume holographic optical elements have been studied by the anisotropic optical beam propagation method, 1 including angular alignment sensitivity, buffer layer thickness sensitivity, crosstalk, and diffraction efficiency as a function of the number of active layers and relative layer thicknesses. Such a concept may allow highly photosensitive and very fast response time materials such as multiple quantum well (MQW) structures in III–V or II–VI compound semiconductors to be used in fabricating volume holographic optical elements, even though such materials are very difficult to grow in layer thicknesses sufficient to individually exhibit the requisite thick holographic characteristics. In addition, novel and intriguing device designs can be envisioned in MQW structures by utilizing applied electric fields to tune the device absorption and phase modulation resonances.