1. ECEG287 Optical Detection Course Notes Part 12: More on Coherent Detection
Profs. Charles A. DiMarzio
and
Stephen W. McKnight
Northeastern University, Spring 2004
February 2004
Charles A. DiMarzio, Northeastern University

2. Charles A. DiMarzio, Northeastern University
Overview
Circuit Components
Splitters
Mixers
Filtering
Wavefront Matching
Mixing Efficiency
Mixing in a Photo-Refractive Crystal
February 2004
Charles A. DiMarzio, Northeastern University

3. Charles A. DiMarzio, Northeastern University
Splitter
R=?
R=? R0 A R0
R=?
Input R0 B
February 2004
Charles A. DiMarzio, Northeastern University

4. Mixer Signal In Large LO Out
from
February 2004
Charles A. DiMarzio, Northeastern University

5. Charles A. DiMarzio, Northeastern University
Filters
Signal
Filter
LO (Ref) f f
February 2004
Charles A. DiMarzio, Northeastern University

6. Charles A. DiMarzio, Northeastern University
Wavefront Matching
Mismatched
in Position
Mismatched
in Angle
February 2004
Charles A. DiMarzio, Northeastern University

7. Mixing Efficiency
Calculate the integrals at any position, provided that the limits are infinite.
Even calculate at the target!
February 2004
Charles A. DiMarzio, Northeastern University

8. Charles A. DiMarzio, Northeastern University
Back-Propagation
Laser
Laser
February 2004
Charles A. DiMarzio, Northeastern University

9. SNR for Coherent Detection
Incoherent Target
Integrate at Target
Perfect Mixing:
February 2004
Charles A. DiMarzio, Northeastern University

10. Charles A. DiMarzio, Northeastern University
Speckle Issues
Random Speckle Pattern
Random Phase
Random Amplitude
Laser
February 2004
Charles A. DiMarzio, Northeastern University

11. Speckle Matching with a Photorefractive Crystal
Reference
Signal
February 2004
Charles A. DiMarzio, Northeastern University

12. Charles A. DiMarzio, Northeastern University
Hologram Generation
Reference
Signal
February 2004
Charles A. DiMarzio, Northeastern University

13. Charles A. DiMarzio, Northeastern University
Hologram Playback
Reference
Signal
February 2004
Charles A. DiMarzio, Northeastern University

14. Charles A. DiMarzio, Northeastern University
PRC Playback
Wrong
Direction
Reference
Signal
February 2004
Charles A. DiMarzio, Northeastern University

15. Temporal Issues Reference Signal For Small A
The PRC response is slow compared to f(t),
so G applies only to the first term.
Signal
February 2004
Charles A. DiMarzio, Northeastern University

16. Speckle Matching with a Photorefractive Crystal
Reference
i.e. mix the signal with a wave that has the signal shape and the reference time dependence
Signal
February 2004
Charles A. DiMarzio, Northeastern University

17. Coherent Detection Summary
Approach
Strong Reference Beam with Stable Phase
Good News:
Enhanced Signals
Enhanced Photon Noise
Phase Information
Improved Dynamic Range
Bad News
More Complicated Optics
More Complicated Electronics
Higher Frequencies?
Need for Wavefront Matching
Other Issues
Polarization
Beamsplitting Losses
February 2004
Charles A. DiMarzio, Northeastern University