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ABSTRACT Lithium Ni

photonic resonatoncluding high e

and nonlinear echnology to esonators on a

niobate disk resofactor (Q) of 4Exploiting the hidisks, we weremechanical vibra

INTRODUCT

The lack ocrystal exhibits effect, linear photoelastic effeapplications in community, whmanufacturing phaking advantage

Thin film Land chip-scale phesonators have mpedance, high

coupling factor, tfilters. [1,2]. Cutilizing thin-filmmodulators, isolphotonics have achieving high smoothing at cldeposited high ioptical loss micmicro-machiningesonators on a

process, originalused to define lstrong cross-dompotentially be optomechanics.

MEMS FABR

There are twLN micro-photovertical side-waesidue, 2. Achie

substrate to enab MEMS nio

silicon dioxide 2,5]. However, nteract with cir

scattering, whichdevice. Acoustiwavelength of feare reflected by

HIGH OPT

iobate (LN or ors have promisfficiency electrooptics. This pachieve thin-

silicon platformonator that exhi

44,000, with 50gh optical Q in te able to optoation modes of a

TION of inversion sy

itself via its celectro-optic ect. The piezoele

surface acoushile the fiber hotonic modulate of its electro-opLN is a promisinhotonics applicarecently been

h mechanical towards the goa

Chip-scale photom SOI for implelators and opticbeen attemptedquality aniso

lose to meltingndex guiding mro-photonic stru

g technology tosilicon platformlly developed flow optical lossmain-coupling eused to realiz

RICATION TEwo distinct fabr

onic resonator oall and smootheving clearance ble efficient mod

obate resonators as a hard-maskany residue of

rculating photonh will significaic waves in Rew microns to tethe anisotropic

TICAL Q, P

C

just “niobate”)ing prospects in

o-optic modulatopaper presents film lithium

m. We fabricatedibits high intrin

0 GHz free-spethe released freeomechanically 150um radius d

mmetry in the characteristic steffect, pyroeleectric effect of bstic wave dev

optics industrtors and optical fptic effect.

ng platform for Mations. LN thin-fdemonstrated wQ and high e

al of achieving laonics has primementing monolical delay elemed [3,4]. Due totropic etching

g point or slabmaterial were usuctures. In conto realize thin f

m. An ion mill afor RF MEMS s photonic diskseffects in LN, ze novel devic

ECHNOLOGYrication challengon silicon substrh surface profilbetween the LNe confinement. to date have us

k to pattern thef metal or oxidns causing opticantly reduce theRF MEMS rens of microns. Tetching defined

GHZ FSRPHOTONI

R. WangCornell Unive

) thin-film micmany applicatio

ors, optomechanmicro-fabricati

niobate photond a 400 m radnsic optical qualctral-range (FSR

e-standing photondetect the rad

disk resonator.

Lithium Niobtrong piezoelectectric effect abulk LN has fouvices in the ry uses LN frequency doubl

MEMS applicatiofilm contour mo

with low motionelectro-mechaniarge bandwidth

marily focused ithic yet inefficients. LN thin-fio the difficulty

of LN, surfab waveguide wsed to achieve ltrast, we presenfilm LN photonanisotropic etchi

applications, ws. Leveraging this platform c

ces in chip-sc

Y ges to fabricate rate: 1. Achieviles without madevice and silic

sed either metale thin-film niobde left behind ccal absorption ae optical Q of esonators haveThe acoustic wav

device boundar

R LITHIUMC RESONA

g* and S. A. Bhersity, Ithaca,

cro-ons nics ion nic

dius lity R). nic

dial

bate tric and und RF for

lers

ons ode nal ical RF on ent ilm of

ace with

ow nt a nic ing

was the can cale

the ing ask con

or bate can and the

a ves ries

formingof the sidevices,contraryseveral propagathe surfThe angmode prthe scatprevious4 m thresist canecessarleft behself-balaadjustinact as anprocess,surface vertical coupling

Figure (a) Prepactivatiowafer; (ion millbetweenmask to

M-NIOBATATORS have NY, USA

g high Q acoustiidewall profile h, while the sidewy, optical wavel

hundred nanoates along the etcface roughness sgled sidewall is srofile to lie deepttering loss fromsly demonstratedhick photo-resisan then be easilry, an additional

hind. The Argonancing between

ng the ion beam an extra sidewall, we achieved sroughness, thusidewall that is

g of photons.

1: Fabricationepare the devicon; (b) Direct b(c) Grounding thl to reduce the Ln LN and Silica

define device ge

TE-ON-SIL

ic cavity. Therehas less impact owall angle has a length in LN o

ometers to 2umching defined destrongly affects sometimes benep within the guidm the surface d LN contour-mst as the mask ly rinsed off by l O2 plasma clean ion mill etchin etching and incident angle,

l “protection” dusidewall angle ous meeting the s necessary for f

process of the ce wafer for boonding of the LNhe device wafer LN film to 400nm

optical fiber; (eeometry; (f) XeF

LICON

efore, the surfacon the mechanicamore important

optical devices rm, and the opevice boundary. the optical sca

ficial as it forceding material, throughness. Our

mode RF resonatowith ion mill eacetone with so

an ensures that nng can be contrre-sputtering bwhere the re-spuring the etchinof 87 degrees w

requirement ofuture integrated

LN disk opticaonding by plasN device wafer tto 1um thicknesm for better inde(e) Ion mill withF2 timed-etch rel

e roughness al Q of these role. On the

ranges from ptical wave As a result,

attering loss. s the optical

hus reducing r group has ors [1] using etching. The onication. If no residue is rolled to be

by carefully puttering can ng. With this with <10nm f a smooth

d waveguide

l resonator: sma surface to Si carrier ss; (d) Blank ex matching

h photoresist lease.

9781940470016/HH2014/$25©2014TRF 411 Solid-State Sensors, Actuators and Microsystems WorkshopHilton Head Island, South Carolina, June 8-12, 2014

lisrnoaom

Frwr

thTTddtadLinthb4rLdath

Silicon has hight that couple

substrate. Usingesonator enable

niobate disk andoptical mode conaddition, the optomechanical imodes.

Figure 2: SEM resonator; Inset:wall, which is cresonator.

Fig. 1 showhese key MEMS

The bonding surThen, the devicedevice wafer isdiscussed later, wapered fiber, an

disk resonators iLN disk and the nfrared light is ihe core for the

blanket ion mill 400nm to reduceesonator. Ideally

LN device thickdisk geometry is and the devices he SEMs of LN

higher refractivees into the niobag XeF2 dry-etces us to achieved silicon substrnfinement in ni

free-standing interactions betw

(

(

of the LN reson: Zoom-in view

crucial for high

ws the completS processes. We rface is activate

e wafer is flip-bos ground downwe perform opti

nd one of the chs the large refrasilica fiber, wh

in the range of 2SMF-28 singleetching is used

e the effective iny a photonics d

kness to avoid thdefined by Arg

are released by disks with diffe

e index (3.4) thaate disk will leah to undercut e >10 m clearate, thereby enaobate and thus

disk structuween the mecha

(a)

(b)

nators. (a) 40umof the rim shooptical Q; (b)

te fabrication pstart with a Z-cu

ed by plasma (onded to the Si

n to 1um thickical tests on thehallenges for coactive index mismhere the refractiv. 2~2.3, and the

e mode fiber is to further thin t

dex of the opticadesigner could shis ion mill etchgon ion mill with

timed XeF2 etcherent radii. As th

an LN (2.3). So aak into the silicthe niobate d

rance between tabling outstandihigh optical Q.

ure will enabanical and photon

m radius LN optiowing smooth s500um radius L

process leveragiut white LN wafsimilar as in [6handle wafer. T

kness. As will e LN disks usingoupling light to Lmatch between ve index of LN refractive index1.45. Thereforethe device layeral mode in the dtart with a thinnh step. Finally, h photoresist mahing. Fig. 2 shohe bonding proc

any con disk the ing In

ble nic

cal ide LN

ing fer. 6]). The

be g a LN the for

x of e, a r to disk ner the

ask, ows ess

was perobservedion millhigh opt OPTIC

Figure coupling

Figure 150um r

Wenear-IR 3 showsbetweenindex ofcontact A polaripolarizaresonatophotodio

rformed at roomd in the releasedl produced a smtical quality fact

CAL CHARAC

3: Optical chag to the LN disks

4: Microscope radius LN disk.

e use a tapered olaser (Santec T

s the experimenn the resonatorf light in the tapwith the LN disization controlle

ation in fiber sucor. The transmitode (Newport

m temperature, d disks. The insemooth clean sidtor.

CTERIZATIO

aracterization ses.

image of the ta

optical fiber [7] tTSL-510) to the ntal setup. Due t

optical mode apered fiber, the sk rim to achieveer is introduced ch that it couplestted optical sign1544A) and m

no buckling oret of Fig. 2(a) shdewall, which is

ON

etup using a ta

apered fiber co

to couple light fniobate disk res

to the large indeand the effectivtaper is broughte efficient couplto carefully adjs strongly with tnal is sent to amonitored on

r bending is hows that the s crucial for

apered fiber

oupling to a

from tunable sonator. Fig. ex mismatch ve refractive t to physical ling (Fig. 4). ust the light the photonic

a high-speed an Agilent

412

(inep[

Fo

lermfrFem4Tr

FcL

DSO9404A) osnput light, we

extract the opticapropagation loss7].

Figure 5: Broadboptical resonator

Fig. 5 showm radius LN dess than 150uWesponse from th

making it an frequency spacedFrom the FSR, wextinction for themode is critical44,000 corresponThis is the higheesonators to date

Figure 6: Zoomcritically coupledLorentzian yields

scilloscope. By measure the op

al parameters (qs) by fitting the

band transmissior, showing 50GH

ws the broad-bandisk resonator. I of input opticalhe device. The exciting candi

d optical frequewe estimate the e optical resonanly coupled. Thending to an opticest optical Q dee (Figure 6).

m-in view of thd dip (at 1536.19s an extracted in

sweeping the wptical transmiss

quality factor, grtransmission d

on spectrum of aHz FSR.

nd transmission In the transmissl power was usedresonator has andate for gener

ency combs in agroup index to b

nce at 1536.19nme extracted intrcal propagation lemonstrated in c

he transmission93nm). Curve fit

ntrinsic optical Q

wavelength of sion spectrum aroup index, optiip to a Lorentz

a 400um radius L

spectrum of a 4sion measuremed to ensure a linn FSR of 50 Grating microwaa sub-1 mm2 arbe 2.09. The hi

m indicates that rinsic optical Qloss of 1.94dB/cchip-scale LN d

n spectrum of tting of the dip to

Q of 44,000.

the and ical ian

LN

400 ent, ear

GHz ave rea. igh the

Q is cm. disk

the o a

OPTO

Figure 7sensing

Figure transmisto the LN

Figoptomecradius) ian AC analyzerof the noscilloscwavelenresonanport 1 oof the L

OMECHANICA

7: Schematic of of disk vibration

8: Backgrounssion measuremN disk resonator

g. 7 shows the chanical transdis mounted on avoltage from p

r. The RF outpunetwork analyzecope to track thngth is blue-dence. When the aof the network aLN resonator, th

AL INTERAC

f the experimentan.

nd noise floorment, where the t

r.

schematic of tduction. The LNa PZT shaker, whport 1 of an A

ut of the photodeer, and the DC he transmitted Detuned to a higactuation frequenanalyzer corresphe acoustic energ

CTION

al setup for opto

r of the opto-tapered fiber is

the experimentaN disk resonathich is excited bAgilent (N5230Aetector is connectoutput is monit

DC optical powegh optical Q, 1ncy of the PZTonds to a mechagy couples from

omechanical

-mechanical not coupled

al setup for tor (150um

by supplying A) network ted to port 2 tored on the er. The laser 1500.597nm

T excited by anical mode

m the PZT to

413

thmpmocr

Ftasthpw

la8mffrvcoamm C

wmthmnsoth

he LN disk. Themodulation of propagating in mechanical vibraoptical signal. characterize the esonator.

Figure 9: Opto-apered fiber is c

showing a 13MHhe radial breath

peaks (below 5Mwhich are also ob

To improve

aunched into the8dBm. The detumaximize the oufloor when the tfrequency peaksvibration modes.coupled to the doptimized for maat 13MHz, whichmode of the diskmodes of the lase

CONCLUSIOThe MEMS

work opens upmodulators, frequhe multi-domain

monolithic LN-oniobate enables smaller than silioptomechanical he LN disk.

e resulting mechthe effective othe optical res

ation of the disBy measuringmechanical res

-mechanical trancoupled to the L

Hz peak corresphing mode of th

MHz) correspondbserved in Fig. 8

the output signae taper, and the nuning of the lautput signal. Figtaper is far away

(below 5MHz). Fig. 9 shows thdisk and the detaximum transduh corresponds tok. The peaks neer cavity.

N S-based fabricatp new avenuesuency doublers an {RF, photonicon-Silicon platfous to achieve 5ica resonators [guided-light det

hanical vibrationoptical path lensonator cavity. k is imprinted g the S21 parsonance of the

nsmission measLN disk resonatoonding to mechahe micro-disk. Td to tapered fibe8.

al strength, 10mWnetwork analyzeaser wavelengthg. 8 shows the y from the LN ) corresponds tohe S21 parametertuning of the la

uction. The specto the fundamentear 18MHz are

tion technology s to realize oand frequency cc, optomechanicorm. The high r50 GHz FSR, w[8]. In addition,tection of mech

n of the disk caungth of the ligAs a result, t

on the transmittrameter, we cLN photonic d

surement when or (150um radiuanical vibrationThe low frequener vibration mod

W optical powerer stimulus is seth is fine tuned

background noresonator, the l

o the tapered fibr when the taperaser wavelengthtrum shows a petal radial breathifrom the vibrati

presented in toptical resonatoombs that leveracal} coupling inrefractive index

with a footprint , we demonstratanical vibration

ses ght the ted can

disk

the us), n of ncy des,

r is t to

to oise ow ber r is

h is eak ing ion

this ors, age n a

of 4 ted of

ACKNTh

SridaranResearcThe desLaboratfacility, Network(Grant E

REFER[1] R.

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[8] J. Llowrep(20

CONT*R. Wan

NOWLEDGEMe authors wish ton for proof-readch Foundation foscribed work watory, and was pe

a member of thk, which is suppECCS-0335765)

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