Optical Beam Steering

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Optical Beam Steering

• Christina Carlsson, Chris Reardon,
• and Thomas Krauss
• St. Andrews University
• cc90_at_st-andrews.ac.uk

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Liquid Crystal VCSEL approach

• Steering angle 5 - 40
• Steering power µW (few V)

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Liquid Crystals

• Characteristics
• A rod-like molecular structure
• Tendency of the molecules to point along a common
  axis
• Strong dipole

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E0
Emax
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Liquid Crystals

• Liquid crystals are found to be birefringent, due
  to their anisotropic nature.Which is due to the
  alignment and the shape of the molecules.

Maximum angle is dependent on the Index
difference (Dn) Thickness of the cell (d) Width
of the pixel (w)
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Liquid Crystal Cell
ITO
E 0
Glass
SiO (alignment layer)
ITO Indium Tin Oxide (transparent and
conducting)
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Liquid Crystal Cell
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Liquid Crystal Cell
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Preliminary result
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Summary LC cells

• Next step a proper test of the cells
• Efficiency
• Angle
• Future optimisation
• Pixel dimensions
• Cell thickness

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Next integration step
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The VCSEL array approach

• Array of 9 VCSELs with integrated diffractive
  optics

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The light source The VCSEL

• Properties
• Surface emitting
• On wafer testing
• Array integration (1D and 2D)
• Device size 10x10 ?m
• Threshold current lt 0.5 mA
• Output power few mWs
• Power efficiency 50
• Modulation bandwidth 10 GHz
• Low divergence circular beam
• (simplifies coupling to optical fibers)

VCSEL Vertical Cavity Surface Emitting Laser
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VCSEL Photolithography
UV-Light
After developing the sample
Mask
Photo- resist
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VCSEL Lift-Off
After developing the sample in Acetone
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VCSEL Mesa etch
Chemically Assisted Ion Beam Etching with Argon
and Chlorine gas
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VCSEL Resist removal
Reactive Ion Etching with Oxygen
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VCSEL Oxidation
Oxidation in the mirror
Oxidation with water vapour
Oxide aperture
Mesa
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Insulation and Gold Contacts
Si3N4
Gold
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Summary - VCSEL

• Continue testing insulation layers
• Optimising the dimensions
• Etch depth
• Oxidation aperture
• Gold thickness