Losses in single-mode silicon-on-insulator

strip waveguides and bends

Min Hyeong KIMHigh-Speed Circuits and Systems Laboratory

E.E. Engineering at YONSEI UNIVERITY2011. 3. 21.

Y. A. Vlasov and S. J. McNab

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[ Contents ]

1.Abstract

2.Introduction _ SOI

3.Experimental Design

4.Propagation Losses

5.Bending Losses

6.Conclusion

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1. Abstract

“Measurement a Propagation Losses / Bending Lossesin 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??

Bend radius R 3/2

exp( ),

(2 / )eff eff

K cR

where c n n

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Silica fiber

2. Introduction

Plastic optical fiber (POF)

Silicon-on-Insulator(SOI)

X dB/km

XXX dB/km

But… our Object :

“Integration of discrete

photonic components into a

single chip

at λ=1.3-1.5μm”

X dB/cm……

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2. Introduction

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.

In current mature silica-on-silicon technology,

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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

TE mode

Propagation losses measurements

The losses (dB) are negative proportional to wavelength.So, the power loss (W) is exponentially decaying.

TE mode

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4. Propagation Losses

Losses is proportional toSquare of Interface roughness(σ)and Normalized E.

2 2 220

2

Sk h En

E dx

TE mode

Near the cut-offfrequency

Stronger scattering

TE mode

TM mode

TM mode

Propagation losses measurements

2 2 2

2 21 0

( ) ( ( ) ) ( ) 0

( )

xy

y

E y k y E y

k n k

“Stronger scattering of the mode as the roughness amplitude is increased relative to the wavelength.”

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1300nm wavelength Loss Spectrum

• 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.

TE

TM

But! This research did not optimize the surface roughness(σ)!!

4. Propagation Losses

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4. Propagation Losses Comparison with literature results

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5. Bending Losses

1325um-1525um Near the Cut-off

Near the Cut-off

Spectra of Bending Losses for TE/TM polarization

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5. Bending Losses

“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!”

3/2exp( ), (2 / )eff effK cR where c n n

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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)