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Multi Frequency Laser Driver for Near Infrared Optical Spectroscopy in Biomedical Application

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. Introduction. What is tissue spectroscopy? Near infrared spectroscopy system introduction.

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Multi Frequency Laser Driver for Near Infrared Optical Spectroscopy in Biomedical Application

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  1. 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

  2. Introduction • What is tissue spectroscopy? • Near infrared spectroscopy system introduction. • Driver design Gain, frequency response, linearity and noise • System evaluation • Optical property extraction • Conclusion

  3. Source-1 Detector-1 Detector-2 Fat photon path Muscle GHz Frequencies MHz Frequencies 760 850 980 Spectroscopy • Absorption 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.

  4. Broad Bandwidth Frequency Domain Instrument RF source Sample channel Network Analyzer (HP 8753ES) SP4T RF Switch Amplifier Laser Diode System LD1 680 nm LD 2 780nm LD3 830 nm LD4 980 nm Photodiode M X 1 Optical Switch 4 X N Optical Switch … N … Detector Fibers Source Fibers M TURBID MEDIUM Turbid medium(tissue)

  5. Optical link driver

  6. 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 Designed Active Laser Driver : AC simulation • RF current is monitored • RF current = 450mA

  7. (A) (B) Designed Active Laser Driver : Amplitude Response and Phase ResponseSimulation vs. Measurement Measurement Phase distortion < 1 degree Magnitude distortion < 1.5 dB Simulation

  8. Experimental Setup Laser Diode Driver +3.3V Noise measurement of Driver Calculation

  9. Optical System Performance: Simulation Laser Driver Laser Diode Model Photo Detector Hamamatsu Amplifier, G=34dB Optical transmitter (driver) T I S S U E LD APD (Photodetector) Automated Network Analyzer (ANA)

  10. Optical Link Performance: simulation results 70 65 55 Voltage S/N ratio (dB) 45 35 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 freq, GHz Thermal Noise is dominant.

  11. Optical Link Performance: Experiment result A B Phase Magnitude Phase distortion < 5 degrees Magnitude distortion < 2 dB

  12. Extraction of Optical Properties: Transmission Model For N number of dipoles one can get the analytical solution for transmittance as: Calibration-corrected data are fitted with normalized theoretical transmittance to extract the optical absorption and scattering properties of the tissue.

  13. Phantom Extracted F (MHz) a (cm-1) s’ (cm-1) a (cm-1) s’ (cm-1) 118 0.05 10 0.052 10.1 ANA 226 0.05 10 0.054 10.5 Phantom Laser Mount APD 316 0.05 10 0.048 9.8 838 0.05 10 0.058 11.0 d 910 0.05 10 0.051 11.2 964 0.05 10 0.057 10.6 Extraction of Optical Properties: Experiment Result

  14. Conclusion • An 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 ma and ms for phantom resembling breast tissue demonstrates the high accuracy of this measurement technique and extraction method.

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