Frequently Asked Questions

Why do we need switchable holograms?
By combining SBG layers encoding different optical functionalities into a DigiLens™ and electrically switching the layers, it is possible to temporally multiltiplex a sequence of optical functions. For example, a DigiLens™ comprising red, green and blue diffracting SBGs provides a color sequential illumination source.

Can DigiLens™ Technology only be used with microdisplays?
The spectral bandwidth and fast switching capability of a DigiLens™ is ideally matched to the requirements of color sequential illumination for microdisplays.

How is a DigiLens™ fabricated
In its simplest form a SBG is a Bragg hologram recorded in a nanocomposite material called a Reactive Monomer Liquid Crystal Mix (RMLCM). During recording, the nanocomposite mixture undergoes phase separation, creating regions densely populated by liquid crystal micro-droplets, interspersed by regions of clear photopolymer resulting in a grating with very, high diffraction efficiency. Applying a voltage via ITO electrodes re-orientates the LC droplets, reducing the refractive index modulation. The resulting device called a DigiLens™ offers all of the usual benefits of a holographic optical element with the added benefit of fast switching. Applying a voltage effectively erases the optical properties. For more information, see Technology Backgrounder.

Does the material used in a DigiLens™ exhibit swelling/shrinkage?

During recording and post-processing, the DigiLens™ material, like most other holographic materials, shrinks slightly. DigiLens This shrinkage is taken into account in the design of the recording optics to ensure that the final product has its most efficient performance at the playback wavelengths and angles of interest.

What optical functions can be provided by a DigiLens™?

A DigiLens™ can encode one or more of the functions of beam deflection, focusing, beam and illumination shaping, spectral filtering, and distortion and aberration correction.

Can pictorial holograms be recorded into a DigiLens™?

Yes.

Does a DigiLens™ work at wavelengths other than that at which it was recorded?

Yes. While recording wavelengths are presently limited by sensitizing dye sensitivity characteristics, a DigiLens™ is effective from the UV to the near infrared.

What is the range of usable wavelengths?
From 0.4 to 1.6 um.

How is a DigiLens™ configured within an optical system?
A DigiLens™ will operate in axial and oblique incidence modes. Since it is desirable to have the output light on axis the oblique mode is favored for most applications. The oblique launch angle is provided by a passive diffractive element, ideally a HOE recorded in a photopolymer.

How are optical functions encoded within a DigiLens™ ?
Simple optical functions such as beam steering can be recorded by purely optical means. In the case of more complex optical functions such as diffusion, the process requires two steps. First a custom designed Computer Generated Hologram (CGH) with the desired characteristics is created. In the second step the CGH is recorded into the SBG.

What is the power consumption of DigiLens™ devices?
Typically, 5 mW/cm^2 for transmissive devices.

What losses are incurred by scatter?
Scatter represents less than 4% loss in the unswitched state, and less than 1% in the switched (off) state.

What optical design software can help me to design a DigiLens™ into my application?
There are several optical design programs which support holographic optical elements. For further information please refer to the Design Tools section.

Can SBG Labs Inc. help me to design a DigiLens™ for my application?
Do I have to know how to do all the construction optics?
We can provide all levels of support from design of the DigiLens™ and construction optics to the complete optical system design if required.

What are the environmental limits (storage and operating) for the devices?
DigiLens™ devices may be safely shipped and stored from 0 C to 70 C, and operated from 0 C to 40 C.

What happens when one overdrives the switching voltage of an DigiLens™?
The DigiLens™ may not switch to its fully transparent state, leading to crosstalk between colors. Beyond a certain voltage, irreversible damage will occur.

Should square or sinusoid waveforms be used?
Square-edged waveforms are preferred.

What is the maximum permissible DC voltage level that can be applied to a DigiLens™?
1 Volt maximum.

How big can you make a DigiLens™?
From as small as a few mm (0.25 inch) to component sizes commonly used in consumer visual displays.

Can you make an DigiLens™ on a curved substrate?
Yes, depending on the precise details of the application. Contact SBG Labs Inc. for further details.

Can a DigiLens™ be mass replicated?
In practice, DigiLens™ devices are mass replicated using standard holographic contact replication techniques from masters created in an authoring process. Contact SBG Labs Inc. for further details.

Can I get a sample DigiLens™ ?
Samples are being made available to select customers. Contact SBG Labs Inc. for further details.

Can you provide samples to my specifications?
SBG Labs Inc. provides samples to its customers throughout the authoring process for test and evaluation. Contact SBG Labs Inc. for further details.

Is the DigiLens™ material polarization sensitive?
Yes. A SBG has high diffraction efficiency for p-polarized light.

What are some good drive circuits for switching an DigiLens™?
The drive requirements of an DigiLens™ are very similar to those of electroluminescent panels, and drive IC's are available from a number of manufacturers.

Can SBG Labs, Inc. help me with electrical drive/video sync/system integration issues?
Yes. SBG Labs Inc. can provide support at any level of product integration.

Can the modulation index be treated as a design parameter?
To a limited degree. Contact SBG Labs Inc. for further details.

What is the range of substrate thicknesses?
To a minimum of 0.4 mm for glass.

Can a DigiLens™ handle light from a broad-band sources LED?
Yes. A DigiLens™ is ideally matched to LEDs and can also will most other broad-band sources used in projection displays.

Can a DigiLens™ be made with a non-rectangular (e.g. circular) form factor?
Yes.

Are AR coatings available?
Yes. The inner ITO electrode features an enhanced AR coating to maximize transmission, and AR coatings may also be applied to the outer glass surfaces.



Note
All specifications subject to change without notice. Please contact SBG Labs Inc. directly for latest specifications & data sheets prior to commencing system design.