1. Generation of Spurious Signals in Nonlinear Frequency Conversion Tyler Brewer, Russell Barbour, Zeb Barber

2. Introduction S2 Corp. investigating spatial-spectral holography Ultra-high bandwidth signal detection Their research requires: –Electro-Optic Modulators –Nonlinear frequency conversion

3. Spatial-Spectral Signal Analysis (a) S2 Crystal (c) EO Modulator CW Laser (1.5 µm) Fiber Optic Link KTP (b) Frequency Conversion ΔV = 1GHz Frequency conversion step required −Best components built for 1.5 μm −SSH requires visible light

4. Frequency Conversion X 2 = + = Second Harmon Generation Frequency, Energy χ 2 Processes Sum Frequency Generation Conversion efficiency: 50%+ AdvR developed high- power capable waveguides to produce 400 mW of Second Harmonic Generation

5. Questions Undesired signals (“spurs”) produced when undergoing nonlinear frequency conversion Where do they come from: the EOM, amplifier, or the waveguides? How do we reduce or eliminate them?

6. Approach Combine and focus 3 lasers into the KTP –Pump –Two-tone signal (Δv = 1GHz)  These tones interfere to create a 1 GHz RF “beat” Combine output with 4 th laser (the “local oscillator”) Measure signal interference with a precision RF detector

7. Frequency Conversion Nonlinear Optical χ (2) Process Potassium Titanyl Phosphate (KTP) 2 μm x 2 μm x 2 cm waveguides contain light to maximize χ 2 process Periodic poling for quasi-phase matching Waveguide technology developed by AdvR Inc. Applicable to many interest groups: Quantum Networks, Cold Atom Sensors, Ladar/Lidar applications, etc.

8. Frequency Conversion Focused Input Beam Frequency-Converted Output Waveguides 2 µm x 2 µm 2 cm Not to scale! 2 mm

9. Wavelength Spectra Optical Power (mW) Wavelength (nm) Optical Signal Analyzer displays: Scale and signal spacing exaggerated for clarity Experimental data taken with lasers spaced much closer together

10. Wavelength Spectra Optical Power (mW) Pump 2 Tone Signal Wavelength (nm) ΔV = 1GHz Interference of tones produces 1 GHz RF signal This RF signal emulates the behavior of a 1 GHz frequency modulation from an EOM

11. Wavelength Spectra Optical Power (mW) Pump Wavelength (nm) Pump + Signal 1Pump + Signal 2 2 Tone Signal

12. Wavelength Spectra Optical Power (mW) Pump Wavelength (nm) Pump + Signal 1Pump + Signal 2 2 nd Order Spurs 2 Tone Signal

13. Wavelength Spectra Optical Power (mW) Pump Wavelength (nm) Pump + Signal 1Pump + Signal 2 3 rd Order Spur 2 nd Order Spurs Intentionally Large Spurs 2 Tone Signal

14. Heterodyne Detection Interference between two optical waves produces a detectable RF frequency Closely-tuned lasers produce RF frequency equal to difference between laser frequencies RF detection has high dynamic range, allowing reduced noise and detection of weak spurs

15. Heterodyne Detection Relative Amplitude Local Oscillator Frequency (GHz) 10 515 Wavelength (nm) 793 ΔV = 1GHz Relative Power

16. Heterodyne Detection Relative Amplitude Local Oscillator Frequency (GHz) 10 515 Wavelength (nm) 793 ΔV = 1GHz Relative Power

17. Heterodyne Detection Relative Amplitude Local Oscillator Frequency (GHz) 10 515 Wavelength (nm) 793 ΔV = 1GHz Relative Power ΔV = 1GHz

18. Heterodyne Detection Relative Amplitude Local Oscillator Frequency (GHz) 10 515 Wavelength (nm) 793 ΔV = 1GHz Relative Power ΔV = 1GHz

19. Heterodyne Detection Relative Amplitude Local Oscillator Frequency (GHz) 10 515 Wavelength (nm) 793 ΔV = 1GHz Relative Power ΔV = 1GHz

20. Spur Free Dynamic Range Pump power fixed at 22 dBm in waveguide Varied the signal power Slope = -2 dB/dBm

21. Three-wave Mixing Model Black lines are various spurs

22. Why do these matter? Unfilterable Close proximity to main signal Still above noise floor (RF detectors have large dynamic range, >60dB)

23. Conclusions Nonlinear frequency conversion responsible for undesired spurs Spur Free Dynamic Range depends on pump power vs. signal power (More pump power allows better range) S2 uses nonlinear conversion in SSH systems

24. Questions Acknowledgements: MBRCT #15-14 AdvR Inc. S2 Corp.