Speaker
Description
Within both science and industry, volume holograms have found countless applications; examples include data storage, signal processing and structured light generation. In practice, a hologram is produced by the interference of two light waves (reference and object) on a photosensitive medium. The resulting interference pattern is imprinted onto the medium as a modulation in its refractive index or transmission. With holography, it is possible to create holographic optical elements (HOE) that apply transformations to the input field using principles of diffractions. Volume Bragg gratings (VBG) are among the simplest HOEs. A VBG is a device whose periodic refractive index causes it to diffract light within a narrow angular range (called the Bragg condition) while leaving any other light unaffected. They can be created holographically if both writing waves are plane waves and the recording material is thick relative to the wavelength of light used. While the production of single VBGs is a straightforward task, there has been a growing interest in manufacturing VBGs that are multiplexed, namely, several VBGs overlapping with different Bragg angles and orientations at the same position in the medium. Recent work on multiplexed VBGs has been based on writing holograms sequentially by making manual adjustments. These schemes lack flexibility in the kinds of holograms that can be written and do not lend themselves well to automating the task.
We present a configuration for holographically writing multiplexed VBGs using a spatial light modulator (SLM) that requires no moving parts. A beam is sent to a single SLM, where it is split into two beams separated by a programmable angle. These pair beams are recombined on a holographic plate in a Mach-Zehnder-like configuration, with lenses ensuring they strike the same area regardless of their separation at the SLM. Rapid switching of the SLM pattern allows for several VBGs to be written in a cyclical fashion. The approach promises great flexibility in the breadth of holograms that can be multiplexed with little effort on the part of the user.
| Keyword-1 | Volume Holography |
|---|---|
| Keyword-2 | Hologram Multiplexing |
| Keyword-3 | Diffractive Optics |