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A High Speed MEMS Scannerfor 140-kHz SS-OCT

A High Speed MEMS ScannerA High Speed MEMS Scannerfor 140for 140--kHz SSkHz SS--OCTOCT

IEEE Int. Conf. on Optical MEMS and Nanophotonics,Istanbul, Turkey, Aug. 8-10, 2011

Keiji Isamoto, Kohki Totsuka, Toru Sakai, Takuya Suzuki, Atsushi Morosawa, Changho Chong

(Santec Corporation)Hiroyuki Fujita, Hiroshi Toshiyoshi

(The University of Tokyo)

This research is supported by Optoelectronic Industry and Technology Development Association (OITDA), subsidized by JKA through its Promotion funds from KEIRIN RACE.

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Power Supply(λ 1.5 µm)

Optical Fiber

Collimator

Photovoltaic Cell

Beam Splitter

Focal Lens

MEMS Scanner

OCT Probe(λ 1.3 µm)

10 mW, λ 1.5 µm, max 10 V

OCT Probe(λ 1.3 µm)

Tissue under Test

Electrical Interconnection

MEMS in OCT EndoscopeMEMS in OCT Endoscope

■ Powering at 1.5 µm■ OCT measurement at 1.3 µm

Optical MEMS 2008 Freiburg

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PC

AttenuatorOptical

Delay Line PolarizationController

BalancedDetector

Pre-Amplifier

DAQI/O InterfaceSynchronizer

WDM Coupler

Powering Light 1.5 um

Optical Circulator

Endoscope

OCT Probe 1.3 um

Delay Line Equalizer

Another MEMS in OCT TodayAnother MEMS in OCT TodayFast Scanner Slow Scanner

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High Coherence Source

Wavelength Scan(A Scan)

B Scan

A S

can

FFT

A S

can

!"#$%&'#(")*+$",,*-",().$*/0!

Advantage of SSAdvantage of SS--OCTOCT

Reference Arm

Sample Arm

!1",*2'34

Time-Domain OCT (TD-OCT) Swept-Source OCT (SS-OCT)

TD-OCT SS-OCTSensitivity dB ~ 90 dB ~ 110

Frame Rate fps 1 54Resolution µm 10~15 5~10

Fast and High-Resolution

cornea

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MEMS Scanner

Scanner

BeamExpander

DiffractionGrating

Gain ChipOutput

External Cavity Laser

SweptSwept--Source with MEMSSource with MEMS

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0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120 140 160Scan Speed kHz

Fine

sse

(= B

andw

idth

/ FW

HM

)

OphthalmologyAxial Length

λ = 1 um∆λ = 20~40 nm

δλ = 0.02~0.03 nmf = 1~5 kHz

Dental λ = 1.3 um

∆λ = 100 nm δλ = 0.15 nm f = 30~100 kHz

IndustrialEndoscope

Vascular Inspection∆λ = 80~100 nm

δλ = 0.12 nmf = 40~100 kHz

Anterior Segmentλ = 1 um, ∆λ = 100 nm

δλ = 0.1 nm, f = 20~100 kHz

Retina Inspectionλ = 1 um, ∆λ = 100 nm

δλ = 0.1 nm, f = 50~140 kHz

2nd Gen. 3rd Gen.

MEMSScanner

R&D of OCT Light SourcesR&D of OCT Light SourcesHigher Resolution, Faster Imaging

PolygonScanner

Target : Over 100 kHz

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2DoF MEMS Scanner2DoF MEMS Scanner

Mirror

CombElectrodes

CombElectrodes

(a)

(b)

(c)

See (b)See (c)

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Mirror Mirror

Actuator ActuatorActuator Actuator

Hinge Hinge OuterHinge

OuterHinge

Inner Hinge

Frequency Frequency

Am

plitu

de

ActuatorPlate

MirrorLeverage

5 ~ 10 x

2DoF MEMS Scanner2DoF MEMS ScannerWith Angle Magnifying Mechanism

Co-developed by Epson and Santec in 2005M. Yoda, K. Isamoto, C. Chong, H. Ito, A. Murata, and H. Toshiyoshi, "Design and Fabrication of A MEMS 1-D Optical Scanner using Self-Assembled Vertical Combs and Scan-Angle Magnifying Mechanism," IEEE/LEOS Int. Conf. on Optical MEMS and Their Applications, August 1-4, 2005, Oulu, Finland. (oral B2)

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SOI (60 um)

Photoresist

BOX (4 um)

Substrate (400 um)

Aluminum (100 nm)

Photoresist

DRIE

DRIE

MirrorComb

ElectrodesComb

Electrodes

Stiction Assembly

(1)

(2)

(3)

Fabrication ProcessFabrication ProcessOnly Two Photolithography Steps

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2 ms / frame

3 mm

OCT with Conventional 35 kHzOCT with Conventional 35 kHz

100 µm

Poor Resolution ~ 50 µm

A-scan35 kHz

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100 µm

3 mm

2 ms / frameHigh Resolution ~ 10 µm

OCT of This Work 140 kHzOCT of This Work 140 kHz

A-scan140 kHz

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Experimental Results NoteScan Speed 140 kHz Round-Trip ScanBand Width 100 nm

1310 nm(in Air)

OCT Resolution 9 µmSpectrum Width 0.25 nm

Coherence Length 3 mmMaximum Power 20 mWDynamic Range 60 dB

Summary: High Speed OCTSummary: High Speed OCT

114 mm174 mm

75 mm

6.5 deg70 kHz70Vdc +/- 70Vac

MEMS Scanners for Both Endoscope Head and Light Source