Losses in single-mode silicon-on-insulator strip waveguides and ...

2. IntroductionX dB/kmSilica fiberPlastic optical fiber (POF)XXX dB/kmSilicon-on-Insulator(SOI)X dB/cm……But… our Object :“Integration of discrete photoniccomponents <strong>in</strong>to a s<strong>in</strong>gle chipat λ=1.3-1.5μm”4

2. IntroductionIn current mature silica-on-<strong>silicon</strong> technology,Method 1. Silica + dop<strong>in</strong>g w/ P or Ge.but, it needs the large m<strong>in</strong>imal bend<strong>in</strong>g R of silica waveguides.Method 2. SiON + Silica cladd<strong>in</strong>g.it reduces bend<strong>in</strong>g R below 1mm.And, further aggressive,,,,,,,,,,,,!!Method 3. Si + Silica (Silicon-on-<strong>in</strong>sulator, SOI)• Extremely high refractive <strong>in</strong>dex contrast• M<strong>in</strong>imal bend<strong>in</strong>g radius can be reduced to the μm range.5

3. Experimental DesignThis 445 x 220 nm waveguideCan be support a s<strong>in</strong>gle <strong>mode</strong><strong>in</strong> 1350~1750 nm wavelength region.Exp.1 Propagation Loss4.7mm 7.74mm 21.1mm. Each waveguides have 8 bends w/ R=5umExp.2 Bend<strong>in</strong>g Loss10 bends and 20 bends would be averaged loss per bend.bend<strong>in</strong>g radius was selected 1um, 2um, 5um.6

4. Propagation <strong>Losses</strong>• Propagation losses measurementsThe losses (dB) are negativeproportional to wavelength.So, the power loss (W) isexponentially decay<strong>in</strong>g.TE <strong>mode</strong>TE <strong>mode</strong>7

4. Propagation <strong>Losses</strong>Strongerscatter<strong>in</strong>g• Propagation losses measurements2 2 2σ kh0Eα = ⋅ S∆n2β E dxTM <strong>mode</strong>∫2TM <strong>mode</strong><strong>Losses</strong> is proportional toSquare of Interface roughness(σ)and Normalized E.Near the cut-offfrequency∇ E( y) + ( k( y) − β ) E( y) = 0k2 2 2xyy2 2= ( nk ) − β1 0TE <strong>mode</strong>TE <strong>mode</strong>“Stronger scatter<strong>in</strong>g of the <strong>mode</strong> as the roughness amplitudeis <strong>in</strong>creased relative to the wavelength.”8

4. Propagation <strong>Losses</strong>• 1300nm wavelength Loss SpectrumTMTE• The TE <strong>mode</strong> profile is characterized by much higher E field <strong>in</strong>tensityat the sidewall and correspond<strong>in</strong>gly higher propagation losses.• The TM <strong>mode</strong> has a relatively small amplitude at the sidewalls, butmuch higher at the top and bottom <strong>in</strong>terfaces.But! This research did not optimizethe surface roughness(σ)!!9

4. Propagation <strong>Losses</strong>• Comparison with literature results10

5. Bend<strong>in</strong>g <strong>Losses</strong>• Spectra of Bend<strong>in</strong>g <strong>Losses</strong> for TE/TM polarization1325um-1525umNear the Cut-offNear the Cut-off11

5. Bend<strong>in</strong>g <strong>Losses</strong>α = K ⋅exp( − cR), where c = β(2 ∆n/ n )“But, Observed dependence on pre-page of bend<strong>in</strong>g loss onpolarization <strong>in</strong>dicates that the surface roughness is an importantfactor def<strong>in</strong><strong>in</strong>g the losses.Despite of it, measured bend<strong>in</strong>g losses are very low without anyoptimization!”effeff3/212

6. Conclusion• With 445x220nm process,I. Propagation losses as small as 3.6dB/cm were measured.II.Bend<strong>in</strong>g losses is to be below 0.005dB/turn for R=5um.• Further optimization of the process<strong>in</strong>g by for example 1) oxidationsmooth<strong>in</strong>g of the sidewalls and 2) optimization of the bend designmay allow losses to be reduced still further.• Useful as a benchmark for further development of <strong>silicon</strong>microphotonics components and circuit on SOI platform(photoniccrystals, arrayed waveguide grat<strong>in</strong>g, r<strong>in</strong>g resonators)13