The ultimate goal of any augmented reality is to have a low-power, monolithic, high resolution display. Though this target is still some ways in the future, we at the BYU Electroholography Lab have made another adavncement towards this goal.
We recently published about this advancement in Optics Express (this is the article "Backside emission leaky-mode modulators"). With the technology offered by our backside emitting leaky-mode modulators, the dangling carrot of wearable, transparent, monolithic, displays are enticingly closer to fruition.
This section will be a high level overview of leaky-mode modulators and the modifications which make our approach more feasible as a method for near eye displays. For a more in depth look at the basis of the leaky-mode modulator, we refer you to
"Anisotropic leaky-mode modulator for holographic video displays."
by Dr. Daniel Smalley.
Leaky-mode modulators work on the premise of waveguided light interacting with surface acoustic waves(SAW). The waveguided light propagates at a given angle, but the SAW causes a variable shift in this angle, which allows the light to escape the waveguided over a range of angles. This range of angles corresponds directly to the frequency of the SAW used to couple the light out of the waveguide. This can be visualized in a k-map (below). The angle of the guided light is changed into the range where it can escape into air, this range is shown as leaky-mode output.
By controlling this leaky-mode output, it is possible to create addressable points and angles. However, using this output requires several stages of control and filtering to be useful as a display device. For a closer look at this approach, please refer to
"Progress on waveguide-based holographic video,"
McLaughlin, et al.
To exit from the backside of the device, the glancing angle of output must be overcome. The addition of a high frequency grating on the backside of the device helps to offset this angular issue. This phenomena is shown in the figure below.
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