Research experience PhD studies Trondheim 2010-2013 (Unfinished) Detecting ultasonic vibrations using Si-integrated opical sensor. Oleg Żero 

We have a Capacitive Ultrasonic Micromachined Transducer (CMUT) array. How do we make sonic-pixels for 30MHz detection? The pixels must be of surface area that is less than 10 x 10 µm2 . Si-integrated optical sensor Oleg Żero Problem outline. Why not using light? 

Si-integrated optical sensor Oleg Żero My initital idea was to use gratings. Use Silicon-on-Insulator (SOI) technology for high index contast. Low loss at λ = 1.55 μm. Silicon will be harmless for human body (intravascular applications in mind). 

Si-integrated optical sensor Oleg Żero My initital idea was to use gratings. Use Silicon-on-Insulator (SOI) technology for high index contast. Low loss at λ = 1.55 μm. Silicon will be harmless for human body (intravascular applications in mind). x y x y’ x y z x y x y’ Grating to couple the light out, which will reflect by a membrane, and interfere with the evanescently coupled beam. 

Si-integrated optical sensor Oleg Żero I started looking for more compact architectures. Use Silicon-on-Insulator (SOI) technology for high index contast. Low loss at λ = 1.55 μm. Silicon will be harmless for human body (intravascular applications in mind). Grating-based mechanism was hardly scalable... 

Si-integrated optical sensor Oleg Żero Then I realized plasmonics offers more confinement. COMSOL Multiphysics 4.2 a. Cantilever must be metal. Starting point is to model it as Perfect Electric Conductor (PEC) Sensitivity through effective index. Response through inter-modal interference. SiO 2 Si air continuity b. co. PEC PEC Model I started to search for optimal conditions for power transfer. 

Si-integrated optical sensor Oleg Żero Then I realized plasmonics offers more confinement. Assuming ideal MZI, slab waveguide The relative MZI sensitivity would be ~4%/nm change in light intensity with respect to change in cantilever’s position! TE fundamental mode sensitivity TM fundamental mode sensitivity 

Si-integrated optical sensor Oleg Żero That lead to MMI coupler as sensor. Again, breaking the symmetry turned out to promise high sensitivity. SiO 2 Si air continuity b. co. PEC PEC u 

Si-integrated optical sensor Oleg Żero That lead to MMI coupler as sensor. I began to construct a new model, in order to describe the new system. SiO 2 Si air continuity b. co. PEC PEC u xy xy symmetric or asymmetric PML 

Si-integrated optical sensor Oleg Żero That lead to MMI coupler as sensor. I began to construct a new model, in order to describe the new system. x y z xy xy xy That was it! It gave me the 2nd conference. 

Si-integrated optical sensor Oleg Żero That lead to MMI coupler as sensor. MMI’s length was 4.1 μm. The width was 1.5 μm and the waveguide’s height was 200nm. The asymmetric case showed steep response: 2.4%/nm around g = 50 nm. Simple and compact. We wanted to fabricate it too! O. Zero et al, ‘Investigation of parallel coupling mechanisms in silicon integrated chip sensors’, Proc. of SPIE, Vol. 8226 (2012). ISBN: 9780819489098. O. Zero et al., ‘Sensitivity limits of guided modes in silicon integrated waveguide-based sesnors’, Proc. SPIE 8561, Advanced Sensor Systems and Applications V, 85610P 

Si-integrated optical sensor Oleg Żero We wanted to fabricate it too. Jens Høvik, ‘’Photonic crystal waveguides’’, MSc thesis NTNU 2012 We wanted to • grow an a-Si:H based SOI • transfer waveguide patterns with EBL • transfer patterns with dry etch We lacked... • experience – no previous Si-photonics at NanoLab, • facility – no characterization equipment, • time... 

Si-integrated optical sensor Oleg Żero At this point I realized, I have... • Spent 2.5 years out of 4 in the programme. • Have 2 conferences. • Spent 9 months just teaching students. • Spent 6 months in the clean room just getting started. • None of my older colleagues has finished the programme (even now!)