- no emitters/amplifiers available. - complex process - no CMOS-compatible

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2 Advantages of photonic integrated circuits (PICs) in Microwave Photonics (MWP): compactness low-power consumption, stability flexibility possibility of aggregating optics and electronics functionalities Optical waveguide Advanced technological processes are required for the fabrication of reliable integrated microwave photonic circuits: high uniformity/reproducibility smooth waveguides fabrication (low loss) efficient packaging/assembly

3 Different technologies are available: Silicon On Insulator (SOI): Pros - compact - low-loss - CMOS-compatible Cons - no emitters/amplifiers available III-V semiconductors (InP, GaAs) Pros - available optical gain and sources Cons - complex process - no CMOS-compatible Others: Silica PLCs, Silicon Nitride

4 Devices: Filters (gratings, ring resonators, ) Dispersive elements (delay lines) Couplers/splitters Modulators Laser sources/optical amplifiers Photodetectors (opto-to-electrical conversion) Added degree of flexibility in circuit design Libraries available of consolidated designs Passive elements! Active Elements! Desired characteristics: Low propagation/insertion loss Tunability Reconfigurability Broadband operation

5 Designing photonic integrated circuits requires several steps: from idea to simulations process flow definition mask layout generation Choices at each step driven by the specific technological process We make use of various commercial software embedding physical simulators (i.e. based on Maxwell s equations) Height (µm) Waveguide modal analysis Field Intensity Width (µm) x D-FDTD for bend/straight waveguides coupling Mask file generation

6 Mode-locked Laser (MLL) ν ν Ν ν ν 0 ν 0 +N ν ν 0 ν 0 +N ν Radar pulse at δν CS-SSB modulator ν 0 δν Ν ν+δν ν 0 δν t 1 t 2 t N Phase-arrayed antenna (PAA) Optical filters to select different spectral regions Ν ν+δν Electro-optic modulator Optical True-time delay (TTD) lines for beam steering Opto-to-electrical converters All these functionalities can be integrated on single optical chip! (or module integration) addressed solution stems on micro-ring resonators

7 Cascaded ring resonators to provide box-like filtering response Input Drop Through 2-ring cascade 3-ring N-ring cascade Drop Trasmission (db) Calculated Spectral Response at Drop Port 0 single ring 2 rings 3 rings rings -40 Drop Wavelength (nm)

8 Filter synthesis allows to shape the response for desired operation device Example: modified Mach-Zehnder interferometer with only-phase elements Input L L+ L Output Transmission H a + a jζ N N 1 ( z) = e 1 1+ b1 z 1 z z b z N N N Wavelength (nm)

9 Large group-delay and group-delay dispersion, can be realized in compact micro-ring resonators all-pass filters Micro-ring resonator in allpass configuration Also in this case, several elements can be cascaded to shape the desired dispersion Group Delay [ps] Group delay of an all-pass ring resonator vs coupling Power coupling: 4% Power coupling: 6% Power coupling: 10% Power coupling: 12% f [GHz] 100 Group Group Delay Delay (ps) (ps) Group delay of cascaded ring resonators: five-stage T=0 design T=8 C Frequency (GHz)

10 Different mechanisms: Thermo-optic (large but slow) Carrier injection (weak but fast) Electro-optic (Pockels, Franz- Keldish ) Design of heater geometry for lowpower thermal tuning of Si-microrings Transmittivity (10 db/div.) db/div) Experimental measurement of frequency response of thermally-controlled ringresonator as a function of injected current 0mA 0 ma 1.5mA 2.5mA 3.5mA f (GHz) (Ghz) F. Bontempi, C.Porzi, G. Contestabile, F. Di Pasquale Technical Report ring resonance tuning with extremely low injected current!

11 thank you!