Dual-probe near-field fiber head with gap servo control for data storage applications

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1 ual-pob a-fl fb ha wh gap svo cool fo aa soag applcaos J-Yu ag, hug-hao T, a Ha-Pg. Shh pam of Phoocs a Isu of Elco-Opcal Egg pam of Phoocs a splay Isu Naoal hao Tug Uvsy, Hschu 000, Tawa yfag.o9g@cu.u.w Absac: W ps a ovl fb-bas a-fl opcal ha cossg of a saw-shap wg pob a a fla gap ssg pob. Th sawshap pob wh a -apu o h fac xhbs hac asmsso by a faco of os of magu ov a covoal fb pob u o a hyb ffc ha xcs boh popagao mos a sufac plasmo wavs. I h gap ssg pob, h spacg bw h pob a h sk sufac fucos as a xal cavy. Th hgh ssvy of h oupu pow o h chag h gap wh s us as a fback cool sgal. W chaacz a sg h saw-shap wg pob a h fla gap ssg pob. Th ual-pob sysm s sall o a covoal baxal acuao o mosa h capably of flyg ov a sk sufac wh aom poso pcso. 007 Opcal Socy of Amca OIS cos: Opcal sysms sg; Apus; b sg a fabcao; Las ssos; 0.00 Opcal aa soag fcs a lks.. W. Pohl, W. k, a M. Laz, Opcal shoscopy: mag cog wh soluo λ/0, Appl. Phys. L. 44, E. Bzg a J. K. Tauma, Na-fl opcs: mcoscopy, spcoscopy, a sufac mofcao byo h ffaco lm, Scc 57, B.. Ts, H. J. Mam, a. uga, Na-fl opcal aa soag, Appl. Phys. L. 68, X. Luo a T. Ishhaa, Subwavlgh phoolhogaphy bas o sufac-plasmo polao soac, Op. Expss 4, B.. Ts, H. J. Mam,. uga, W.. Sumu, a G. S. Ko, Na-fl opcal aa soag usg a sol mmso ls, Appl. Phys. L. 65, W.-H. Yh a M. Masupu, Evasc couplg mago-opcal a phas-chag sk sysms bas o h sol mmso ls, Appl. Op. 9, Guo, T. E. Schlsg, a.. Sacl, Opcal fl suy of a-fl opcal cog wh a sol mmso ls, Appl. Op. 9, T. Ishmoo, K. Sao, M. Shoa, T. Koo, A. Nakaok, a M. Yamamoo, Gap svo sysm fo a baxal vc usg a opcal gap sgal a a fl aou sysm, Jp. J. Appl. Phys. 4, 79-74, J.I. L, M.A.H. va Aa,.A. Vschu,. Zjp, a M.B. va Mak, vlopm of a a gap svo sysm fo hgh aa asf a a fl opcal cog, Jp. J. Appl. Phys. 44, T. Yasu, M. Kouog, a M. Ohsu, Icasg houghpu of a a-fl opcal fb pob ov 000 ms by h us of a pl-ap sucu, Appl. Phys. L. 7, P. N. Mh, T. Oo, H. Waaab, S. S. L, Y. Haga, a M. Esash, Hyb opcal fb-apu calv a-fl pob, Appl. Phys. L. 79, G. M. Km, B. J. Km, E. S. T Hav,. Sgk, N.. Va Huls, a J. Bugg, Phooplasc a-fl opcal pob wh sub-00 m apu ma by plcao fom a aomoul, J. Mcosc. 09, P A. cha, S. K. w, S. E. Iv, a A. Y. Elzzab, Hgh-asmsso sol-mmso apu opcal pobs fo a-fl scag opcal mcoscopy, Appl. Phys. L. 86, H. T, Y.-. La, T.. Mls, a H.-P.. Shh, sg a fabcao of fblss fo opcal cog applcaos, Jp. J. Appl. Phys. 4,

2 5..-H. T, H.-L. hou, Y. hu, W. Hsu, T.. Mls, Y.-. La, a H.-P.. Shh, b-ls-bas moul fo opcal cog applcaos, Jp. J. Appl. Phys. 4, Y.-J Km, K. Suzuk, a K. Goo, Paalll cog aay ha of ao-apu fla-p pobs fo hghsy a-fl opcal aa soag, Jp. J. Appl. Phys. 40, M. Haa, M. Oum, K. Nakajma, a T. Ohkubo, Na-l Opcal lyg Ha wh Poug Apu a Is abcao, Jp. J. Appl. Phys. 44, A. V. Iag,.. Sacl, J. A. Ba, a T. E. Schlsg, g wavgu as a a-fl opcal souc, Appl. Phys. L. 8, X. Sh,. L. Thoo, L. Hsslk, Ulahgh lgh asmsso hough a -shap aoapu, Op. L. 8, X. Sh a L. Hsslk, sg of a apu o achv λ/0 soluo a soa asmsso, J. Op. Soc. Am. B, L. Su a L. Hsslk, Low-loss subwavlgh mal -apu wavgu, Op. L., K. Su, W. hall, a. Pg, g wavgu as a a fl apu fo hgh sy aa soag, J. Appl. Phys. 96, Y.-. h, J.-Y. ag,.-h. T, a H.-P.. Shh, Hgh-asmsso hyb-ffc-asss aoapu, Op. L., Y.-. h, J.-Y. ag,.-h. T, a H.-P.. Shh, oubl-couga c-shap apu fo a-fl cog, Jp. J. Appl. Phys. 45, Y. X, A.. Zakhaa, J. V. Moloy a M. Masupu, Opcal asmsso a oblqu cc hough a poc aay of sub-wavlgh sls a mallc hos, Op. Expss 4, P.-K W, Y.-. Huag,.-. hg,.-g. Tsg a W. a, Off-agl llumao uc sufac plasmo couplg subwavlgh mallc sls, Op. Expss, H. ah: Sufac Plasmos o Smooh a ough Sufacs a o Gags Spg, Nw Yok, G. Gula, M. Noga, S. oa, a T. Bosch, Las o slf-mxg chqu fo ssg applcaos, J. Op. A: Pu Appl. Op. 4, S8 S O. Mls, A. ag, A. B. Tv, a T. G. Galloz, A xal cavy o las sso, J. Lghwav Tchol. LT-, J.-Y. Km, a H.. Hsh, A op-soao mol fo h aalyss of a sho xal-cavy las o a s applcao o h opcal sk ha, J. Lghwav Tchol. 0, J.-Y. Km, a H.. Hsh, Asymmy h opcal oupu pow chaacscs of a sho-xalcavy las o, IEEE Phoo. Tchol. L. 4, Iouco Achvg spaal soluo byo h ffaco lm s of ccal mpoac may fls, such as aa soag, opcal masum, a lhogaphy. Na-fl opcs ops a avu o bak hough h ffaco lm [-4]. Howv, low pow asmsso accompas a cas spo sz a ao-scal gap svo cool s also cssay o maa objcv lss o lgh soucs clos poxmy o ag sufacs. Sol mmso ls SIL was mosa o b abl o uc spo sz by a faco of h facv x of h SIL maal aa soag [5-7]. A xal opcal sysm ha o b mplm o lv a al wh opcal sgals [8, 9]. Th cofguao was also bulky a ffcul o ga wh oh sysms. Aoh appoach was o mploy a fb pob collcg lgh fom h ag [0-5]. Th spacg bw h pob a h ag sufac was kp cosa by moog h chag h oscllao of h pob sul fom sha foc o h pob as a fuco of h spacg. Bcaus h asmsso of covoal fb pobs wh a 00-m apu was aou 0-5, a sgal pocssg sysm was cssay o fl ou backgou os. I ao, o mauz h opcal sysm o mpov yamc spos a gao capably, ga wavgus w also ps [6-8]. Howv, fabcao pocsss w complx a o asly mass pouc coomcally. To achv hgh soluo a ffccy, mauzao, a acv gap svo cool, w popos a ual-pob a-fl fb ha sysm cossg of a saw-shap wg pob ha lvs opcal pow o h sk a a gap ssg pob ha cs h spacg a ss a fback sgal o h cooll. Th cofguao of h sysm wh wo p opcal pahs s schmacally llusa g.. I h wg pob, a 0/90 fb coupl s s o h opcal pah o spl h lgh o wo. 90% of h lgh gos o h saw-shap pob, wh h fac s coa wh a mallc flm a

3 pfoa by a -apu a h c; whl h mag lgh gos o h ba fla fc pob wh w masu h m pow o v h oupu fom h sawshap pob. I h gap ssg pob, h spacg bw h pob a h ag sufac fucos as a xal cavy fo h las o. Th fc bw h flc lgh a h fl s h las cavy maks h oupu pow p o h gap wh. Th oupu pow moula by h gap wh s c by h phooo a s o h cooll as a fback sgal. Th ual-pob fb ha s sall o a covoal baxal acuao v by h cooll o maa h gap wh aom poso pcso. g. ofguao of a ual-pob a-fl fb-bas lgh lvy sysm I hs pap, w calcula h asmsso of a -shap ao-apu wh oblqu cc o chaacz a sg h saw-shap fb pob. I ao, a slf-mxg fomc sgal as a fuco of h gap wh s mol a masu fo cooll sg. osquly, a saw-shap fb pob wh a 45-g agl a a gap ssg pob a fabca a sall o a covoal baxal acuao. Th xpmal suls mosa h pfomac of h sysm o a movg sk sufac.. Sysm haaczao a sg. Saw-shap Wg Pob A -shap ao-apu whch fucos as a g wavgu suppos popagao mos a hus suffcly cass h asmsso hough h apu [8-]. To fuh hac h asmsso hough a -apu a a-fl lgh souc sysm, w mosa a ao-apu suou by a poc cougao ca uc a hyb ffc cossg of popagao mos a sufac plasmo xcao [, 4]. Bcaus h sufac plasmo s abl o b xc wh oblqu cc [5, 6], w popos ha a -apu wh oblqu c llumao ca also uc h hyb ffc. Th opcal mol s schmacally plo g. a. A asvs-magc TM pla wav llumas h apu a 00-m slv flm wh a complx facv x of N= fom a lcc subsa wh N=.475 a a f-spac c wavlgh λ=6 m. Th msos of h -apu a show g. b. Th pow houghpu PT s f as h ao of h asm opcal pow ou of a apu o h c pow ov h apu aa o ps h phoo capug capably. A apu wh h PT ga ha mpls som phoos obsuc bh h flm ca b capu by h apu a go hough h apu. Thfo, o vsga h aco bw h apu a h

4 c lgh, h PT of h -shap ao-apu wh oblqu cc s calcula as a opmz paam by mployg h -ffc Tm oma mho T. Y 0 m 40 m 55 m X a b 60 m g. a Schmac llusao of h opcal mol a b h msos of h -apu Z Y 4.00 X PT 0 PT p flco coffc p λ sp a-m ~0.6 Z X λ sp -m ~ a Ic Agl g b g. a Th pow houghpu PT a a sac of 50 m fom h apu a flco coffc p as a fuco of h c agl a b alcula E z fl pofl XZ pla wh h c agl was 44 g. Th ash l shows h coou of h mal flm a h -apu. Th pow houghpu as a fuco of h c agl s show g. a. Th calcula pow houghpu xhbs a pak of.5 a a 44-g cc whch cocs wh h poso of a p h fco coffc wh aua oal flco AT occus. I coas o h pow houghpu of.4 wh omal cc, h maxmum pow houghpu yls a hacm as hgh as.5. Accog o sufac plasmo hoy, h cocc cas ha h xcao of sufac plasmo h lcc-mal fac cobus o h pow houghpu hacm wh oblqu cc. Th calcula Ez fl pofl XZ pla a 44-g cc, as show g. b, fuh vals h sufac plasmo xcao h lcc-mal fac uc by h c lcc fl compo ppcula o h sufac. Th wavlgh of h sufac plasmo wav alog x co ca b oba by [7] 4

5 π λsp = k x Th wav vco compo alog x co k x s ε m ε / k x = k0 ε m + ε wh ε m s h lcc cosa of h mal flm, ε s ha of h lcc maal, a k 0 s h wav vco of c lgh. Th calcula wavlgh a h lcc-mal fac λ sp -m s 0.9 μm a a h a-mal fac λ sp a-m s 0.6 μm, whch ag wh h T smulao suls. Thfo, accog o ou smulao, a 45-g saw-shap fb pob s popos. Th oblqu c llumao o a -shap apu ucs h xcao of h sufac plasmo wav h lcc-mal fac a fuh hacs h asmsso hough h apu. ompa o h calcula pow houghpu of a squa apu of 0 - mployg T, h saw-shap fb pob povs a hacm by a faco of x0.. Gap Ssg Pob a b g. 4a ofguao of a xal-cavy las o wh a lgh of fb a b a quval las o By mas of h slf-mxg fomc ffc, las os ca fuco as poso ssos [8]. Howv, o fuh mpov gao capably a yamc spos chaacscs, a lgh of fb s aach o h las o sso as a gap ssg pob. To chaacz h fback sgal fom h gap ssg pob, w cos a las o of lgh L coc o a sgl-mo fb SM of lgh L a a ag sufac bg gap fo of h fb, as show g. 4a. Bcaus h splacm of h ag sufac a h spacg a assum o b a fw wavlghs,.. Δ<< L a << L, h chag h cavy mos caus by h psc a movm of h ag sufac s go [9]. To chaacz h moulao oupu pow as a fuco of h gap bw h ag sufac a h fb, a quval las o wh ffcv flcvy ms of flco coffcs a complx couplg coffc s mploy [0, ]. Th couplg coffc pss h ao of flc lgh couplg o h las o a h h flco a s a complx fuco of h xal cavy lgh psg boh phas shf a amplu uco. Th quavl gap ssg sysm s show g. 4b. Th ffcv flcvy s w as = [ + = + ], 5

6 6 wh,,,, a o h amplu flco coffcs of h las facs, fb facs, a h xal flco,,, a o h pow flcvy of h las o fac a fb facs, a Φ, Φ, a Φ, o h phas shf sul fom h opcal pah ffc bw h las cavy a h flcg sufacs,, a, spcvly. =, wh =,,, a. 4 Th phas shf Φ sul fom h spacg λ π = 4. 5 If w assum h flcvy of h fb facs s much lss ha, h o ca b appoxma by. Th ffcv flcvy ca b oba as follows [ + = = ] +. 6 Bcaus h flcvy coffc m cass mo aply ha h couplg coffc as h flco cass, h flcvy coffc m fom h ag sufac omas h amplu. Th couplg coffc s ga as a fuco of h spacg a p o h flco. Th h ffcv flcvy ca b v as blow: = = = = + + = +. 7 If w assum h flcvy of h ag sufac s much hgh ha ha of h fb facs,.. = >>, h sco a h m of Eq. 7 ca b go. Th a smplf fomula ca b oba + =. 8 If w assum a cosa cu appl o h las o, h oupu pow ca b ps ms of h appl cu I a h hshol cu I h whch s a fuco of h ffcv flcvy ] l [ h P I I P, 9 wh P s a cosa. I h cas of = 0.99, = 0.9, = 0.8, a λ = 0.65 μm, w calcula h pow oupu as a fuco of h spacg bw h las a h ag sufac accog o h quaos v abov, as show g. 5. Bcaus h absolu valu of oupu sgals s hghly p o ga of h cool sysm, w omalz boh masu a calcula sgals o uy by bg v by h maxmum valu a cov hm o a

7 fuco of lav poso ms of wavlgh. Th compaso shows ha h popos mol ags wll wh h masum. Th sul also claly xhbs a asymmy h oupu pow. Ths phomo suls fom a phas shf ha h flc fl xpcs as s coupl o h las cavy. Th phas shf s p o h opcal pah ffc as a sul of chag h gap wh. Thfo, h couplg coffc s a complx fuco of h gap wh cossg of a amplu uco m a a phas shf m. Th g of asymmy ss wh a cas of h flcvy of h ag sufac. I coas, h absc of h phas shf, h pak of h sgal wll loca a h lav poso of 0.5λ,.. h oupu pow s a symmc cuv. osquly, h asymmy h sgal also fs h movg co of h ag sufac. Moov, h slop of h sgal, h ssvy of h sgal o h poso vaao a also h mmum splacm soluo ha h ssg pob ca achv, s oba by fg h vav of h sgal fuco. Ths chaacsc mpls ha h p h slop of h sgal s, h f h splacm soluo s. alcula poso accuacy ca hocally b as low as m, whch s compv wh oh cool mhos. Nomalz Pow Oupu Masum 0. Smulao lav Poso λ g. 5 ompaso of a masu fback sgal a a calcula slf-mxg fomc sgal Th a-fl gap cool sysm cosss of a las o, a fb ssg pob, a acuao, v ccus, a a cooll. Th m lgh fom h las o s coupl o h fb a lv o h fb whch fucos as a poso sso. Th vaao h gap wh bw h fb a h ag sufac als h moog oupu pow c by h phooo s h las o. Th moulao o oupu pow s cov o a volag sgal a s o h cooll. A popooal gal PI cooll s sg o acua h al-m movm of h pckup a a la compsao s ga o h cooll o mpov phas a ga mags. A pckup v a a sgal amplf a also sg accogly o v h acuao a suppss os. Th cofguao of h sysm s show g. 6. 7

8 g. 6 Block agam of h gap cool sysm. Expm a suls. Saw-shap Wg Pob Accog o h sg, a 45-g saw-shap fb pob was fabca by a amo sawg pocss, as show g. 7a. A 00-m slv flm was pos o h fac of h fb pob by usg a spug pocss a pfoa wh a -apu, of whch h msos a show g. 7b, by focus o bam mllg IB. Lm by h soluo of IB, h ou mso of h fabca -apu s 00 m H 00 m W whl h l wh s 00 m. A 6-m las bam was coupl o h fb pob a h h a-fl sy sbuo of h fb pob h pla paalll o h fac was masu by a a-fl scag opcal mcoscop NSOM. Bcaus h spaal soluo s wos ha 50 m, h masu spo sz a a sac of 50 m fom h apu s ov 400 m, whch s lag ha h smula o. Moov, sc h masum was ca ou u h sam s-up, h lav opcal sy m fom h wavgu was ps by h sgal amplu. ompa o h sgal amplu of 0.0 V h cas of a ccula apu wh a am of 00 m, h saw-shap fb pob wh h amplu of V yls h pak sy hacm by a faco of 0 hgh ha covoal pobs. Y μm 5μm a b X μm g. 7 a Opcal mcoscopc phoo of a 45-g saw-shap fb pob, b SEM phoo of h -apu o h fac of h fb pob, a c a-fl sy sbuo masu by NSOM. Gap Ssg Pob To mol h gap svo cool sysm, h op-loop fqucy spos of compos, clug h baxal acuao a h v ccus, was masu a chaacz by asf fucos. Th cooll was sg a fabca cosquly accog o h c 8

9 sysm qums. Th op-loop fqucy spos of h sysm was h masu a compa wh h sg ag whch was umcally v fom cool hoy a h asf fucos. om h masum suls, w fou ha wh h cas of fqucy, h splacm of h acuao v by h cool sysm was aua. Wh h vg fqucy was ov 0 Hz, h splacm bcam small ha h soluo of h las fom. osquly, h masum o cas a sul a black spo h cuv. Alhough h masum pcso ga hgh-fqucy go, h suls plo g. 8 sll xhb agm bw h masum a smulao. ompacss of h fb ssg pob ma possbl o sall h fb pob o a covoal baxal acuao whou gag h yamc spos. Th phas a ga mag of hs sysm was as hgh as 5 a -4 B, spcvly. Th sysm was s by movg h gap ssg pob owa h ag sufac wh a sac of coupls of wavlgh u a acua sufac wh splacm of 5 μm. If h amplu ga fom h phoo-o o h sgal amplf s G V/V, h ssvy of h las sso s S V/m, a h amplu of h o sgal s A V, h sual poso o ca b oba by A/S G. Accog o hs smply calculao, h xpmal sul show g. 9 claly xhbs ha h sual poso o s maa wh ±.5 m h cas of A=6 mv/m a S= V/V, whch s clos o h sg ag of ± m. 00 Magu B Phas g masu sg qucy Hz g. 8 qucy spos of h cool sysm 9

10 back Sgal back Sgal af amplf ±.5 m b Eo Sgal v Sgal g. 9 Expmal sul wh h axal uou was 5 μm 4. oclusos W mosa a a-fl fb ha sysm comps of a saw-shap wg pob whch pov hgh pow houghpu mployg h hyb ffc a a gap ssg pob whch fuco as a poso sso a moula h oupu pow of h las o usg slf-mxg fomc ffc. W sg a mosa h saw-shap wg pob a h gap ssg pob o a covoal baxal acuao. Th avaags of hgh asmsso, compacss, achvably, a gao mak hs sysm compv a pov a ovl appoach o a-fl applcaos, clug aa soag, opcal masum, a lhogaphy. Ackowlgms Ths sach s paally suppo by h Naoal Scc oucl, Tawa, fo Pomog Acamc Excllc of h Uvsy Phoocs Scc a Tchology fo Ta Ea, u ga NS E PAE. 0