1. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-1 ECEG287 Optical Detection Course Notes Part 11: Coherent Detection Profs. Charles A. DiMarzio and Stephen W. McKnight Northeastern University, Spring 2004

2. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-2 Overview Coherent Detection Fundamentals Signals and Noise Balanced Detection Resolving Ambiguities –Heterodyne –Offset Homodyne –Optical Quadrature

3. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-3 Coherent Laser Radar Laser /4 /2 Optional Pulsed Amplifier

4. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-4 Mixing Equations

5. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-5 Coherent Detection Advantages SNR Enhancement wrt Detector Noise Dynamic Range Reduction Phase Information (at least partial) fW mWnW

6. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-6 Coherent Detection Model Detector Noise Signal Local Oscillator Noise: h B

7. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-7 Coherent Detection Noise Issues 020406080100 0 2000 4000 6000 8000 10000 P sig Signal 4kTB Quantum Noise 020406080100 0 1 2 3 4 5 6 x 10 4 P sig Dotted Lines: Higher LO

8. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-8 Balanced Mixing sig ref sig+ref sig-ref Subtract |sig-ref| 2 |sig+ref| 2 =|sig| 2 +|ref| 2 - 2Re(sig*ref * ) =|sig| 2 +|ref| 2 + 2Re(sig*ref * ) 4Re(sig*ref * ) Stopped Mon 23 Feb 04

9. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-9 Balanced Mixing Implementation sig ref sig+ref sig-ref

10. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-10 Another Implementation sig ref sig+ref sig-ref

11. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-11 Direction (Phase) Ambiguity 0 f Transmitter LO Signal (Postive Doppler) Transmitter LO Signal (Postive Doppler) (Negative Doppler) (Negative Doppler)

12. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-12 Offset Local Oscillator 0 f Transmitter LO Signal (Postive Doppler) Transmitter LO Signal (Postive Doppler)

13. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-13 Offset LO Implementation (1) Laser /4 /2 Optional Pulsed Amplifier Laser

14. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-14 Offset LO Implementation (2) Laser /4 /2 Optional Pulsed Amplifier Bragg Cell

15. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-15 A Very Simple Laser Radar Laser Current Monitor i t

16. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-16 Quadrature Demodulation Signal LO (Ref) I 90 Deg Q z=I+iQ

17. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-17 Optical Quadrature Demodulation (End View of Polarization) Reference (Circular Polarization) Signal (Linear Polarization)

18. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-18 Optical Quadrature and Balanced Mixing Based on Mach-Zehdner interferometer. Signal Arm: 45-Degree Linear Polarization (E x =E y ) Local Oscillator: Circular Polarization (E x =iE y ) Both Interferometer Outputs used for balanced detection (common mode rejection) Light source is low power HeNe or diode laser. LO SIG From Laser To Cameras /4 Objective Condenser

19. February 2004 Charles A. DiMarzio, Northeastern University 10464-11-19 Optical Quadrature Microscope. -10 0 10 20 30 40 50 60 Unwraped Phase from Experiment, Radians -60 -40 -20 0 20 40 60 n=1.6 d=53  m