Nanostrutture con funzionalità avanzate

Transcription

1 Unità di Ricerca 4 Nanostrutture con funzionalità avanzate Progettazione, simulazione e test di componenti planari per optoelettronica, compatibili con la tecnologia CMOS (cristalli fotonici, guide d onda, sorgenti laser, risonatori, specchi dielettrici, filtri, amplificatori, ) Studio di fattibilità di prototipi e nuovi dispositivi (attivi o passivi) optoelettronici e fotonici (quali commutatori e transistor ottici) che possano essere integrati su moduli multi-chip o a singolo CMOS- chip.

2 Integrated Silicon Nanophotonics Futuristic Silicon chip with integrated photonic and electronic circuits IBM Research, (2007) The ultimate goal of Si nanophotonics is to develop a technology for on-chip integration of ultra-compact nanophotonic circuits for manipulating the light signals, similar to the way electrical signals are manipulated in a computer chip

3 Integrated Silicon Nanophotonics The interconnection bottleneck RC delay: speed Microwave Crosstalk Heat/power issue

4 Integrated Silicon Nanophotonics An electron/photon convergence Long haul telecommunications Microelectronics IC chip

5 Integrated Silicon Nanophotonics Application: on-chip optical clock distribution

6 Optical waveguides for Si nanophotonics Wires for electrons, waveguides for photons n 1 n 1 =1 n 2 > n 1, n 3 n 3 Substrate Planar dielectric waveguide Light is transported in-plane losslessly by total internal reflection at the wg interfaces Loss, dispersion Planar integration (CMOS) Waveguides for the silicon platform: - Silica, SiON, Si 3 N 4, poly-si, a-si, SOI

7 Progetto FIRB - WP5 Silicon-On-Insulator (SOI) waveguides SOI platform Si photonic wires air Si SiO 2 n 1 = n 1=1 n 2 = 3.5 n 3 =1.45 Si Fabricated by SOITEC, up to 12 inch wafers High dielectric contrast Fully CMOS compatibility Processable with standard CMOS technology (electron beam/optical lithography & reactive ion etching) Propagation losses < 3 db/cm Y. Vlasov et al. Optics Express 12, 1622 (2004)

8 Bends and Splits Routing the light on the chip Silicon photonic wires with µ bends Bend radius R = 5 µm Loss = db/bend Silicon photonic wires with µ splits 90 : loss = 2.7 db/split 15 : loss = 0.7 db/split Y. Vlasov et al. Optics Express 12, 1622 (2004)

9 Silicon Nanophotonics Si potonics scaling in 2 decades: Higher refractive index contrast = smaller bending radius = higher integration density IBM Research, (2007)

10 Photonic Crystal Waveguides

11 Progetto FIRB - WP5 Photonic crystals ω ω = k ε 1 Uniform medium ε 1 0 ω Add a small real periodicity ε 2 = ε 1 + ε k sin π a x a ε (x) = ε (x+a) ε 1 ε 2 ε 1 ε 2 ε 1 ε 2 ε 1 ε 2 ε 1 ε 2 ε 1 ε 2 band gap cos π a x 0 π/a

12 Progetto FIRB - WP5 Photonic Crystals Strong modification of the dispersion relation with scale invariance! frequency photonic band gap backwards slope: negative refraction dω/dk 0: slow light wavevector strong dispersion: super-prism effect + negative refraction

13 Progetto FIRB - WP5 SOI Photonic crystal slabs one-dimensional two-dimensional membrane W1 line defects with line-defects with point -defects Ridge Waveguides 6 µm membrane

14 SOI photonic crystal waveguides, bends & splits PhC straight wg Propagation Loss ~ 3 db/cm Y. Vlasov et al. Optics Express 11, 2927 (2003) PhC bends & splits Bend Loss ~ 0.05 db/bend Split Loss ~ 3 db/split Y. Vlasov et al. Optics Letters 31, 745 (2003)

15 Optical Spectroscopy tools for nanophotonics FT spectrometer + white light source spectral range for transmission/emission µm Tunable Laser source: µm (spectral resolution 2 pm)

16 Propagation Loss Spectra of Si 3 N 4 /SiO 2 waveguides nm 500 nm 200 nm 2000 nm Si 3 N 4 oxide (SiO 2 ) oxide (BPSG) Coll. with Univ. Trento IRST-ITC Cut-back Si TE polarization TM polarization db/cm db/cm Loss (db/cm) Transmission (db) db/cm 4.7 db/cm 1544 nm 780 nm 532 nm Transmission(dB) db/cm 5.7 db/cm 1200 nm 780 nm 532 nm Loss (db/cm) Length (cm) Length (cm) Wavelength (µm) Wavelength (µm)

17 Progetto FIRB - WP5 Waveguide Transmission on SOI 2D PhC structures 5 µm Energy (ev) triangular array of air holes GK a = 400 GM Γ Κ nm; r/a = 0.34 TE Polarization Γ Μ TE-like TM-like Energy (ev) Trasmittance Μ Γ Κ µm Energy (ev) W1.5 σ kz = Energy (ev) TE Polarization Transmittance σ kz = k x a/π

18 Attenuated Total Reflection spectroscopy on SOI wg ATR spectroscopy 2,0 2,0 Evanescent coupling to guided modes 1,5 TM exp. TE exp. TM calc. TE calc. 1,5 θ ZnSe, Si Energy (ev) 1,0 1,0 Si core Air layer SiO 2 cladding ω sin ( ), c n k = prism θ ω 0,5 0, βd SOI slab d S = 0 nm, d = 270 nm 0,5 1,5 2,0 2,5 3,0 0,0 n eff Direct measure of the guided mode dispersion M. Galli et al., Appl. Phys. Lett. 89, (2006)

19 ATR on single line-defect PhC waveguides W1 line-defect 0,92 0,90 0,92 0,90 3a Energy (ev) Energy (ev) W1.5 line-defect 1.5 3a 0,88 0,86 0,84 0,82 0,80 0,78 0,92 0,90 0,88 0,86 0,84 0,82 0,80 0,78 θ=55 θ=55 ATR W1.0 φ = 0 θ=39 W1.5 φ = 0 θ=40 θ=60 θ=60 ATR W1.0 W1.0 φ = 15 θ=43 W1.5 φ = 15 θ=38 0,88 0,86 0,84 σ kz = 1 0,82 σ kz = +1 0,80 0,78 0,92 0,90 W1.5 0,88 0,86 0,84 0,82 σ kz = 1 0,80 σ kz = +1 0, k x a/π M. Galli et al., Physical Review B 72, (2005)

20 Application: chip to chip? Clocking Chip to chip connections - Filters - Modulators - Light sources v

21 Planar Optical Microcavities Si ring resonators PhC cavities Q factor ~ 5 x 10 4 Q factor ~ 2 x 10 5

22 Ultra-small high-order optical filters Insertion loss: 1.8 db Y. Vlasov et al. Optics Express 15, (2007) 1dB band pass: 310 GHz Out of band rejection: 40 db

23 Photonic crystal add/drop filters The transmission frequency range of the output waveguide with bends is tuned by changing the size of the air holes at the apex of the corner. Noda et al. Appl. Phys. Lett. 84, 2226 (2004)

24 Encoding a channel: modulation Micrometer-scale Si electro-optic modulator Electrically driven by a p-i-n junction integrated with the ring resonator ~ 1 Gbit/s modulation speed with high modulation depth Only 12 µm footprint! Lipson et al., Nature 435, 325 (2005)

25 All-optical switching on a silicon chip optical bistability Notomi et al., Opt. Expr. 13, 2678 (2005)

26 Progetto FIRB - WP5 All-optical switching in silicon PhCs All-optical switching experiment at our Lab. (Pavia)

27 All-optical switching in silicon PhCs Tunable Laser source: µm (spectral resolution 2 pm)

28 Progetto FIRB - WP5 All-optical switching in silicon PhCs PhC cavity Signal Intensity (a.u.) 0,6 0,4 0,2 532 nm Pulsed Pump 0,0 Signal (V) E = 160 µev Q = Transmission (db) nm cw-probe Time (ns) λ = Energy (ev) Switching power ~ 140 nw

29 Active Si nanophotonics Light Sources & Waveguide Optical Amplifiers Challenge: CMOS integration Challenge: electrical injection Si Raman Laser Hybrid Si Laser InP wg Silicon Paniccia et al., Intel (2006) Paniccia et al., Intel (2006)

30 Active PhC based on III-V semiconductors Ultra low-threshold lasing in PhC nanocavities S. Strauf, L.C. Andreani et al., PRL 96, (2006)

31 Progetto FIRB - WP5 Optically active Silicon Doping with Si-nanocrystals and rare earth ions (Er 3+ ) Si-nanocrystals act as a very efficient Er-sensitizers for excitation by means of energy transfer process A. Polman, Nature Materials 1, 10 (2002)

32 Progetto FIRB - WP5 Active Silicon-On-Insulator waveguides Si core Active layer: Si-nc:Er:SiO 2 d S = nm Multilayer deposition by radiofrequency confocal magnetron sputtering (T=300K) Er-doped SiO x Si 37 at. % Er 3.8x nm

33 Progetto FIRB - WP5 High field-confining SOI waveguides Very efficient light emission from a 20 nm-thick only active layer PL Intensity (a.u.) TM/TE ratio Distance from edge (mm) L = 0.35 mm Microscope objective Pump beam WD >> L L L = 0.15 mm TM TE Energy (ev) M. Galli et al., Appl. Phys. Lett. 89, (2006)

34 Active silicon-on-insulator PhC slabs 0.85 Γ Κ Γ Μ 1070 nm Careful PhC deisgn Resonance of Er 3+ emission with a photonic mode 150-fold enhancement of emission 0.5 Er 3+ emission (a/λ) Μ Γ calc TM calc TE M. Galli et al., Appl. Phys. Lett. 88, (2006) Κ PL intensity (arb. units) PhC, a=1070 nm PhC, a=1210 nm 0.2 Unpatterned SOI 0.1 (x 5) Energy (ev) Reflectance (arb. units)

35 Progetto FIRB - WP5 Integrated light-emitting devices Electrical contacts n + poly Si n SiO + poly x :ErSi 3+ p + poly SiOSi x p + Si SiO µm A. Irrera et al., Nanotechnology 17, 1248 (2006)

36 Progetto FIRB - WP5 Task activities SOI Photonic crystal waveguides High-Q photonic crystal cavities All-optical switching in SOI PhC structures Active SOI waveguides and cavities Optical characterization and testing Waveguide transmission spectroscopy Angle-resolved reflectance and ATR spectroscopy Photoluminescence spectroscopy Theory and Design Photonic bands Propagation losses Cavity Q factors Emission properties Effect of disorder Device design