New kind of op­ti­cal nanosen­sor uses torque for sig­nal pro­cess­ing

Iran Daily - - Science & Technology -

The world of nanosen­sors may be phys­i­cally small, but the de­mand is large and grow­ing, with lit­tle sign of slow­ing.

As elec­tronic de­vices get smaller, their abil­ity to pro­vide pre­cise, chip-based sens­ing of dy­namic phys­i­cal prop­er­ties such as mo­tion become chal­leng­ing to de­velop, re­ported.

An in­ter­na­tional group of re­searchers have put a lit­eral twist on this chal­lenge, demon­strat­ing a new nanoscale op­tome­chan­i­cal res­onator that can de­tect tor­sional mo­tion at near state-of-the-art sen­si­tiv­ity.

Their res­onator, into which they cou­ple light, also demon­strates tor­sional fre­quency mix­ing, a novel abil­ity to im­pact op­ti­cal en­er­gies us­ing me­chan­i­cal mo­tions. They re­ported their work in the jour­nal Ap­plied Physics Let­ters.

Jian­guo Huang from Xi’an Jiao­tong Univer­sity in China, one of the work’s au­thors, said, “With devel­op­ments of nan­otech­nol­ogy, the abil­ity to mea­sure and con­trol tor­sional mo­tion at the nanoscale can pro­vide a pow­er­ful tool to ex­plore na­ture.

“We present a novel ‘beam-in-cav­ity’ de­sign in which a tor­sional me­chan­i­cal res­onator is em­bed­ded into a race­track op­ti­cal cav­ity, to demon­strate nanoscale tor­sional mo­tion sens­ing.”

Light has al­ready been used in some­what sim­i­lar ways to de­tect the me­chan­i­cal flex­ing or ‘breath­ing’ of nano­ma­te­ri­als, typ­i­cally re­quir­ing com­plex and sen­si­tive cou­pling to the light source.

This new ap­proach is novel not only in its de­tec­tion of nanoscale torques, but also in its in­te­grated light-cou­pling de­sign.

Us­ing a sil­i­con-based nanofab­ri­ca­tion method, Huang and his team de­signed the de­vice to al­low light to cou­ple di­rectly via an etched grat­ing to a wave­guide con­fig­u­ra­tion, called a race­track cav­ity, in which the nanores­onator sits.

Huang said, “As light is cou­pled into the race­track cav­ity through a grat­ing cou­pler, me­chan­i­cal tor­sional mo­tion in the cav­ity al­ters the prop­a­ga­tion of light and changes [the] power of out­put light.

“By de­tect­ing the small vari­a­tion of out­put light, the tor­sional mo­tions can be mea­sured.”

Be­yond just de­tect­ing torques on their mi­cron-length lever arms, the res­onators can also af­fect the re­sult­ing op­ti­cal prop­er­ties of the in­ci­dent sig­nal.

The tor­sional fre­quency of the me­chan­i­cal sys­tem mixes with the mod­u­lated op­ti­cal sig­nals.

Huang added, “The most sur­pris­ing part is that when we mod­u­late the in­put light, we can ob­serve the fre­quency mix­ing.

“It is ex­cit­ing for fre­quency mix­ing since it has only been demon­strated by flex­u­ral or breath­ing modes be­fore.

“This is the first demon­stra­tion of tor­sional fre­quency mix­ing, which may have im­pli­ca­tions for on-chip RF sig­nal mod­u­la­tion, such as su­per-het­ero­dyne re­ceivers us­ing op­ti­cal me­chan­i­cal res­onators.”

This is just the start for po­ten­tial uses of torque-based nanosen­sors.

The­o­ret­i­cally, there are a num­ber of fre­quency tricks these de­vices could play for sig­nal pro­cess­ing and sens­ing ap­pli­ca­tions.

Huang noted, “We will con­tinue to ex­plore unique char­ac­ters of this tor­sional op­tome­chan­i­cal sen­sor and try to demon­strate novel phe­nom­ena, such as in­fer­ence of dis­per­sive and dis­si­pa­tive op­tome­chan­i­cal cou­pling hid­den be­hind the sens­ing.

“For en­gi­neer­ing, mag­netic or elec­tri­cally-sen­si­tive ma­te­ri­als can be coated on the sur­face of tor­sional beams to sense small vari­a­tions of phys­i­cal fields, such as mag­netic or elec­tric fields to serve as mul­ti­func­tional sen­sors.” Schematic (animated) of tor­sional op­tome­chan­i­cal res­onator for sens­ing and fre­quency mix­ing

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