Y. A. Vlasov and S. J. McNab
Min Hyeong KIM
High-Speed Circuits and Systems Laboratory
E.E. Engineering at YONSEI UNIVERITY
2011. 3. 21.
[ Contents ]
1. Abstract
2. Introduction _ SOI
3. Experimental Design
4. Propagation Losses
5. Bending Losses
6. Conclusion
2
1. Abstract
“Measurement a Propagation Losses / Bending Losses
in single-mode SOI waveguide”
On a 200mm CMOS Fab. Line process,
Propagation Losses (TE mode,1.5um) : 3.6±0.1dB/cm
Bending Losses (per 90˚, R=1μm)
: 0.086±0.005dB/cm
Bending Losses (per 90˚, R=2μm)
: 0.013±0.005dB/cm
** Bending Loss??
  K  exp(  cR ),
Bend radius R
w here c   (2  n eff / n eff )
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2. Introduction
X dB/km
Silica fiber
Silicon-on-Insulator(SOI)
X dB/cm……
But… our Object :
XXX dB/km
Plastic optical fiber (POF)
“Integration of discrete photonic
components into a single chip
at λ=1.3-1.5μm”
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2. Introduction
In current mature silica-on-silicon technology,
Method 1. Silica + doping w/ P or Ge.
but, it needs the large minimal bending R of silica waveguides.
Method 2. SiON + Silica cladding.
it reduces bending R below 1mm.
And, further aggressive,,,,,,,,,,,,!!
Method 3. Si + Silica (Silicon-on-insulator, SOI)
• Extremely high refractive index contrast
• Minimal bending radius can be reduced to the μm range.
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3. Experimental Design
This 445 x 220 nm waveguide
Can be support a single mode
in 1350~1750 nm wavelength region.
Exp.1 Propagation Loss
4.7mm 7.74mm 21.1mm. Each waveguides have 8 bends w/ R=5um
Exp.2 Bending Loss
10 bends and 20 bends would be averaged loss per bend.
bending radius was selected 1um, 2um, 5um.
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4. Propagation Losses
 Propagation losses measurements
The losses (dB) are negative
proportional to wavelength.
So, the power loss (W) is
exponentially decaying.
TE mode
TE mode
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4. Propagation Losses
 Propagation losses measurements
 k0 h
2
 
2

2

ES
E
TM mode
2
n
2
dx
Losses is proportional to
Square of Interface roughness(σ)
and Normalized E.
Near the cut-off
frequency
TM mode
 xy E ( y )  ( k ( y )   ) E ( y )  0
2
Stronger
scattering
ky 
TE mode
2
( n1 k 0 )  
2
TE mode
“Stronger scattering of the mode as the roughness amplitude
is increased relative to the wavelength.”
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2
2
4. Propagation Losses
TM
 1300nm wavelength Loss Spectrum
TE
• The TE mode profile is characterized by much higher E field intensity
at the sidewall and correspondingly higher propagation losses.
• The TM mode has a relatively small amplitude at the sidewalls, but
much higher at the top and bottom interfaces.
But! This research did not optimize
the surface roughness(σ)!!
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4. Propagation Losses
 Comparison with literature results
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5. Bending Losses
 Spectra of Bending Losses for TE/TM polarization
1325um-1525um
Near the Cut-off
Near the Cut-off
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5. Bending Losses
  K  exp(  cR ), w here c   (2  n eff / n eff )
3/2
“But, Observed dependence on pre-page of bending loss on
polarization indicates that the surface roughness is an important
factor defining the losses.
Despite of it, measured bending losses are very low without any
optimization!”
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6. Conclusion

With 445x220nm process,
I.
Propagation losses as small as 3.6dB/cm were measured.
II. Bending losses is to be below 0.005dB/turn for R=5um.

Further optimization of the processing by for example 1) oxidation
smoothing of the sidewalls and 2) optimization of the bend design
may allow losses to be reduced still further.

Useful as a benchmark for further development of silicon
microphotonics components and circuit on SOI platform(photonic
crystals, arrayed waveguide grating, ring resonators)
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