Nanocavities for measuring torque-actuated motion

Marcelo Wu A. Hryciw, B. Khanaliloo, M. Freeman, J. Davis

Supervisor: Paul Barclay

University of Calgary/NRC-NINT

CLEO 2012 – CW1M.7 - May 9, 12:15pm

Optomechanical coupling

Yale: M. Bagheri et al., Nature Nanotechnology (2011)

Parameters:gom: optomechanical coupling rate [Hz/nm]

Mechanical properties: Qm, fm, meff

Optical properties: Qo, fo, Vo

Optomechanical coupling

1) Lausanne/Max-Plack-Institut: E. Gavartin et al., arXiv:1112.0797v1(2011)

2) Max-Plack-Institut/CeNS/Lausanne: G. Anetsberger et al., Nature Physics (2009) 

3) NIST/Maryland: K. Srinivasan et al., Nano Letters (2011)

4) Yale/Columbia: Z. Sun et al., Nano Letters (2012)

5) Caltech: M. Eichenfield et al., Nature Letters 462 (2009)

6) Caltech: M. Eichenfield et al., Nature Letters 459 (2009)

7) Caltech: A. Safavi-Naeini et al., APL (2010)

8) Columbia: Y. Li et al., Optics Express (2010)

9) Tokyo: M. Nomura, Optics Express (2012)

meff = fg~pg

gom → 1THz/nm

Torsional actuation

Interaction between magnetic moments and fields at the nanoscale:

constant magnetic field: no force, only torque!

Torsional actuation

UofA: J. Davis et al., APL (2010) Yale: A. C. Bleszynski-Jayich et al., Science (2009)

Example systems: Nanomagnetic fluctuationsPersistent current measurements

Torsional actuation

Queensland: S. Forstner et al., PRL (2012)

Optical readout

Torsional actuation

Our proposal

Sensitive readout of torqueMonolithic integration

Photonic crystal nanobeam cavity

1D photonic crystal cavity

See also:Harvard: M.W. McCutcheon and M. Lončar , Optics Express (2008)Caltech: J. Chan et al., Optics Express (2009)Caltech: M. Eichenfield et al., Optics Express (2009)

Caltech: A. H. Safavi-Naeini et al., PRL (2012)

Harvard: P. Deotare et al., APL (2009)

HP Labs: P.E. Barlcay, Optics Express (2009)

Small Vo

Small massOverlaps mechanical and optical modes

Photonic crystal nanobeam cavity

Small form factor

Acceptor mode optical cavity

High Q-factor ~ 106

Small mode volume < (λ/nSi)3

Near-field mechanical resonator

Trade-off: gom vs Qo

Floating paddle cavity

Overlap mechanical and optical modes

Floating paddle cavity

See also: Yale and LMU: J.C. Sankey et al., Nature Physics (2010)

Vienna: Vanner, Physical Review X (2011)

No optomechanical coupling in linear regime

Membrane in the middle:Second order coupling

Odd mechanical modes

Optomechanical design

• Still want large linear gom

• Want large Qo and maintain small meff

• Natural mechanical modes are odd

Caltech: M. Eichenfield et al., Optics Express (2009)

Linear gom Quadratic gom Quadratic gom Linear gom

Split-beam cavity

Donor mode cavity with gap at the centre

Eo1

Eo2

For a gap size, find the dimensions of first ellipse

Split-beam cavity

Optimization of ellipses: maximizing mirror strength1 γ by varying (Rx,Ry)

1Q. Quan and M. Lončar Opt. Express (2011)A. Yariv and P. Yeh, Oxford University Press (2006)

w at Eo1 band edge

w at Eo2 band edge

Mid-gap w

w at Eo1 band edge

at cavity centre

Split-beam cavity

Optical properties Qtotal: 1.1 x 106

Qx : 2.3 x 108

Qy : 5.9 x 106

Qz : 1.3 x 106

Split-beam cavity

Mechanical modes

meff = 0.5~1.1 pg

gom = 5~17 GHz/nm

Flexible design

Summary

• Optimized optical cavity• High Q ~ 106

• Mechanical modes suitable for torsional actuation

• Low meff (0.5~1.1 pg)

• Flexible designs• Large linear gom (5~17 GHz/nm)

Future work

• Optomechanical design• Analysis of torsional actuation• Actuation to readout: sensitivity and noise

analysis• Fabrication and measurement