JRA1: Lithography limits for Nanophotonic Devices

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JRA1 Lithography limits for Nanophotonic Devices

• Coordinator Thomas F Krauss tfk_at_st-and.ac.uk
• Deputy Coordinator William Whelan-Curtin (Liam
  OFaolain) jww1_at_st-and.ac.uk

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Research Integration Targets

• Machine comparison
• Agreement on Interaction
• Comparison of Proximity correction
• Examination of effects of processing (e.g
  sidewall roughness and long vs short range
  disorder
• Submission of at least 2 papers

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Agreement/Papers

• Agreement on data dissemination that satisfied
  the concerned partners
• 1 paper submitted
• 1 about to be submitted
• 2 in preparation

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Proximity Correction

• dR/R measured off SEM images
• Proxecco (Glasgow) 2.2
• Nanopecs (ETHZ) 1.7
• Termination affects coupling into slow light
  regime (adjacent to mode edge)

Good
Poor
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Processing/Disorder

• Etching quality is the primary factor influencing
  loss
• Small errors dramatically increase the loss
• High freq. disorder important

• Low frequency (over 100s periods) disorder
  (writefield distortion, beam drift) has little
  effect on loss
• Causes chirping rather than scattering

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Photonic Wires

• Delay due to long original process development
• Repeatability problems due to post
  lithography/etch processing
• Effects of stitching very critical

• Glasgow 6db/cm (600um Writefield)
• St Andrews 15.5db/cm (100um Writefield)- Light
  often seen to scatter at WF boundaries

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Machine Comparison
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JRE- Shot shifting

• Politecnico di Torino to St Andrews
• Giuseppe Pagnotta- 6 months
• Project- minimise stitch errors by exposing each
  point from multiple stage positions
• Loss- from 15.5db/cm down to 8.5db/cm (700nm
  wires)

2 exposures
4 exposures
Normal
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Research Highlights Low Loss Photonic Crystals
Blue Loss Red- 0.1 mm W1 Green 1.89mm W1

• 4.1 db/cm W1 waveguide patterned on the LEICA
  EBPG 5 at Glasgow
• Worlds 2nd best Silicon photonic crystal (to our
  knowledge)
• At the sub 10db/cm level, the bigger writefield
  becomes important

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Research Highlights Disorder Induced Loss in
Photonic Crystals

• Deliberately positionally disordered W1s
• Initial Quadratic dependence than sharp drop
  (mode edge shifts causing reflection)
• In absence of reflection
• TA-B(xC)2
• T- transmission, x- deliberate disorder A-
  Coupling, B- loss dependence on disorder, C-
  intrinsic positional disorder

Scattering loss
Reflection loss

• Plot B against vg
• 1/vg1/2 best fit
• Previous reports (Hughes et al.)- 1/vg2
• Zero intrinsic positional disorder within error
  (0.5nm)

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Most valuable outcome of this activity

• Photonic crystals of the highest standard
• High performance photonic crystals can be
  patterned using relatively low specification beam
  writers
• Understanding of Disorder Induced loss in
  photonic crystals

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Continuation / New activity

• Nanostructuring Platform
• See earlier talk