Optical Waveguide Introduction Existing technology Much - - PowerPoint PPT Presentation

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Optical Waveguide Introduction Existing technology Much - - PowerPoint PPT Presentation

Apr 07, 2024 140 likes •336 views

Optical Waveguide Introduction Existing technology Much existing research has been done on silicon waveguides Optical fibre is an example of silicon waveguide technology Problem Transparency of silicon lies below 8m

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SLIDE 1

Optical Waveguide

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SLIDE 2

Introduction

  • Existing technology

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Much existing research has been done on silicon waveguides

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Optical fibre is an example of silicon waveguide technology

  • Problem

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Transparency of silicon lies below 8µm

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Germanium with a transparency range of 1.6µm to 18µm is more suitable

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SLIDE 3

Objective

Determine the cut

  • ff

dimensions

  • f

Single-mode Germanium on Silicon optical planar waveguide in mid-IR region

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SLIDE 4

Total Internal Reflection

  • For total internal reflection to occur, the propagating wave must be travelling

in a medium of higher refractive index and hit a boundary with a lower refractive index.

  • If angle of incidence > critical angle, total internal reflection will occur

The critical angle can be derived by equating the angle of refraction to be 90. 𝑜1𝑡𝑗𝑜𝜄𝑗 = 𝑜2𝑡𝑗𝑜𝜄𝑠 𝑡𝑗𝑜𝜄𝑗 = 𝑜2 𝑜1 𝑡𝑗𝑜𝜄𝑠

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SLIDE 5

Methodology

  • Ran simulations with the software MODE Solutions by Lumerical
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SLIDE 6

Parameters

  • Wavelength of source: 3.8 µm

Apart from the wavelength falling in the Mid-IR region, the actual laser source that is used in the lab now is a 3.8 µm laser.

  • Germanium core

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Transparency: 1.6 µm to 18 µm, suitable in the mid-IR region (2-20 µm).

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Refractive index of 4.03, higher than the silicon cladding with refractive index of 3.42.

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Higher electron mobility at 3900cm2V−1s−1 compared to silicon’s 1400cm2V−1s−1

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SLIDE 7

Parameters

  • Initial dimensions of germanium core:

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x span = 50 µm, y span = 2 µm, z span = 1.5 µm

  • Dimensions of substrate:

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x span = 50 µm, y span = 50 µm, z span = 10 µm

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SLIDE 8

Methodology

  • Obtain the modal analysis for the first four modes.

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Modes 1&2 (TE0, TM0) – Single Mode propagation

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Modes 3&4 (TE1, TM1) – Dual Mode propagation

  • Sweep the y and z span

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Obtain graph with y axis as effective refractive index and x axis as the y span and z span in two separate graphs

  • Determine the dimensions with the sweep results
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SLIDE 9

Results

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SLIDE 10

Results

  • Modal analysis
  • Ensure that first 2 modes are single mode, next 2 are dual

Mode 1 Mode 2

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SLIDE 11

Results

Mode 3 Mode 4

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SLIDE 12

Results

  • Vary the y- and z-spans
  • Obtain effective refractive index, neff, from the simulation
  • Calculate cutoff dimension where neff > nSi
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SLIDE 13

Results

Y-span Z-span

3.42

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SLIDE 14

Results

3.42 3.42

Z-span

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SLIDE 15

Results

  • Cut-off dimensions obtained: 50µm by 2µm by 0.6µm
  • Zhang.H. previously obtained values of 2 μm and 1.38μm (y and z)
  • Our results differ by 0.78μm in the z-span
  • Accounts for Zhang’s high transmission loss
  • Reduced loss
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SLIDE 16

Conclusion

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SLIDE 17

Conclusion

  • Germanium has many applications in chemical sensing and environment

monitoring

  • We found out the cutoff dimensions for a single-mode Ge waveguide
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SLIDE 18

Further Applications

  • Detection of specific chemicals
  • Optimising the waveguide dimensions to reduce loss