Multi Frequency Laser Driver for Near Infrared Optical

Spectroscopy in Biomedical Application

Chenpeng Mu  

Department of Electrical and Computer Engineering, Drexel Univ, Philadelphia,PA, 19104

IntroductionWhat is tissue spectroscopy?Near infrared spectroscopy system introduction.Driver design

Gain, frequency response, linearity and noise

System evaluationOptical property extractionConclusion

SpectroscopyAbsorption and scattering parameters of tissue are different with different wavelength of light.

Frequency domain photon migration (FDPM) is used to extract optical properties of tissue(absorption and scattering).

Photon penetrates tissue and penetration depth depends on modulation frequency.

Tissue is multi-layer constructure, so multi-frequency should be used for better spatial resolution.

GHzFrequencies

MHzFrequencies

Detector-1 Detector-2Source-1

Fat

Muscle

760 850 980

Laser Diode System

Broad Bandwidth Frequency Domain Instrument

TURBID MEDIUM

Network Analyzer (HP 8753ES)Sample channelRF source

SP4TRF Switch

LD4980 nm

LD1680 nm

LD 2780nm

LD3830 nm

4 X N Optical Switch

Source Fibers …

N

Amplifier

Photodiode

M X 1 Optical Switch

…M Detector Fibers

Turbid medium(tissue)

Optical link driver

Designed Active Laser Driver : AC simulation

Frequency (MHz) Input current (mA) Output current (mA)

100 5.63 453.70

200 6.94 453.31

300 8.69 452.75

400 10.66 451.98

500 12.73 450.99

600 14.86 449.80

700 17.01 448.41

800 19.18 446.81

900 21.33 445.03

1000 23.47 443.06

•RF current is monitored•RF current = 450mA

P_ACPORT3

Freq=freqPac=polar(dbmtow(0),0)Z=50 OhmNum=3

CC11C=10 pF

RR21R=50 Ohm

I_ProbeI_Probe1 V_DC

SRC12Vdc=1.5 V

RR1R=6.5 Ohm

LL2

R=L=1000 nH

LL5

R=L=82 nH

LL3

R=L=82 nH

CC4C=100 pF

RR8R=3100 Ohm

RR18R=477 Ohm

RR2R=500 Ohm

CC7C=100 pF

LL4

R=L=82 nH

RR12R=130 Ohm

V_DCSRC9Vdc=12 V

I_ProbeI_Probe2

CC1C=100 pF

CC9C=100 pF

V_DCSRC1Vdc=12 V

BJ T_NPNBJ T1

Mode=nonlinearTemp=Region=Area=Model=BJ TM1

Designed Active Laser Driver : Amplitude Response and Phase Response

Simulation vs. Measurement

(A)

(B)

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1 1.0

3

6

9

12

15

18

0

20

Frequency(GHz)

S21(

dB)

SimulationMeasurementPhase distortion < 1 degreeMagnitude distortion < 1.5 dB

Noise measurement of Driver

Calculation

0

2

4

6

8

10

100 300 500 700 900

Frequency (MHz)

Noi

se F

igur

e (d

B)

+3.3V

Experimental Setup

Laser Diode Driver

outputI_NoiseRIN_Noise1

I_NoiseShot_Noise1

I_NoiseDark_Noise1

T ermT erm2

Z=50 OhmNum=2 S2P _Eqn

S2P 1

S[2,2]=0S[2,1]=1S[1,2]=1S[1,1]=0

I_NoiseT hermal_Noise

AmplifierAMP 4

S12=0S22=polar(0,180)S11=polar(0,0)S21=dbpolar(36,0)

CC9C=0.45 pF

P _ACP ORT 1

Freq=freqP ac=polar(dbmtow(-5),0)Z=50 OhmNum=1

CCCSSRC4G=Ita_L*Hp*L_F*Ita_D

CC4C=100 pF

I_P robeR_j_current1

CC1C=100 pF

I_P robeInput_current

RR2R=3100 Ohm

LL2

R=L=82 nH

RR3R=477 Ohm

LL1

R=L=82 nH

RR1R=50 Ohm

CC2C=1.0 pF

V_DCSRC1Vdc=12 V

CC3C=100 pF

LL3

R=L=82 nH

RR4R=500 Ohm

BJ T _NP NBJ T 1

Mode=nonlinearT emp=Region=Area=Model=BJ T M1

RR6R=1 Ohm

LL6

R=L=9 nH

CC7C=0.6 pF

CC6C=1.5 pF

LL5

R=L=0.7 nH

I_P robeDriving_current

V_DCSRC3Vdc=12 V

V_DCSRC2Vdc=12 V

RR5R=130 Ohm

LL4

R=L=82 nH

CC5C=390 pF

CC8C=1.5 pF

Laser Driver

Laser Diode Model

Photo Detector

Optical System Performance: Simulation

Hamamatsu Amplifier, G=34dB

LD APD (Photodetector)

Automated Network Analyzer (ANA)

Optical transmitter

(driver)

TISSUE

m1freq=300.0MHzmag(output)=0.116

m2freq=300.0MHzoutput.noise=2.215uV

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1 1.0

1E-4

1E-3

1E-2

1E-1

1E-5

3E-1

freq, GHz

mag(o

utp

ut)

m1

outp

ut.nois

e, V

m2

Total Noise 2.215uV

Thermal Noise 1.809uV

RIN Noise 1.183uV

Shot Noise 0.488uV

Dark Noise 0.011uV

Thermal Noise is dominant.

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1 1.0

45

55

65

35

70

freq, GHz

Vol

t age

S/ N

rat

i o (

dB)

Optical Link Performance: simulation results

A

B

Phase distortion < 5 degreesMagnitude distortion < 2 dB

Optical Link Performance: Experiment result

Phase

Magnitude

Extraction of Optical Properties: Transmission Model

For N number of dipoles one can get the analytical solution for transmittance as:

])(

)(exp(

)(

))exp([

4),( 0

1 mR

mikR

mR

mikR

D

Str

c

c

o

N

m

2))',(

,(2))',(

,(2

phantomP

satheoryPinP

phantomAsatheoryA

iinA

Calibration-corrected data are fitted with normalized theoretical transmittance to extract the optical absorption and scattering properties of the tissue.

Extraction of Optical Properties: Experiment Result

Phantom

ANA

APDLaser

Mount

d   Phantom Extracted

F (MHz) a (cm-1) s’ (cm-1) a (cm-1) s’ (cm-1)

118 0.05 10 0.052 10.1

226 0.05 10 0.054 10.5

316 0.05 10 0.048 9.8

838 0.05 10 0.058 11.0

910 0.05 10 0.051 11.2

964 0.05 10 0.057 10.6

ConclusionAn active laser driver is developed for a broadband operation of four-color sources in near IR.

A multi-frequency domain instrument is reported for near infrared light spectroscopy applications. High power (up to 1.2W) and high-speed (up to 1GHz) laser diode driver exhibited a flat frequency response.

Extracted optical parameters a and s for phantom

resembling breast tissue demonstrates the high accuracy of this measurement technique and extraction method.