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Optical modulation techniques for length sensing and control of optical cavities
B W Barr1, S H Huttner, J R Taylor
1Department of Physics and Astronomy, University of Glasgow, University Avenue, Glasgow G12 8QQ, Scotland. b.barr@physics.gla.ac.uk
Applied Optics
|November 2, 2007
Summary
Amplitude modulation for gravitational-wave detector optical cavities can introduce unwanted phase modulation. Adjusting modulator systems can compensate for these effects, improving signal accuracy and control flexibility.
Area of Science:
- Physics
- Optical Engineering
- Astrophysics
Background:
- Laser interferometric gravitational-wave detectors rely on precise optical cavity control.
- Amplitude modulation is a common technique for length sensing and control in these cavities.
- Traditional amplitude modulation methods can inadvertently introduce phase modulation, complicating signal demodulation.
Purpose of the Study:
- To analyze the impact of inherent phase modulation in amplitude modulation techniques on optical cavity length sensing.
- To investigate signal offsets caused by quadrature demodulation of amplitude-modulated signals.
- To propose adjustments for compensating extra modulation components and enhancing control flexibility.
Main Methods:
- Theoretical discussion of amplitude and phase modulation coupling in optical cavities.
- Experimental demonstration using a simplified optical cavity setup.
- Analysis of signal demodulation in quadrature.
Main Results:
- Amplitude modulation inherently produces phase modulation, contaminating the desired signal.
- Quadrature demodulation of these signals leads to systematic offsets.
- Minor modifications to the modulator system can effectively compensate for these unwanted phase components.
Conclusions:
- The presence of phase modulation in amplitude modulation techniques poses a challenge for precise optical cavity control in gravitational-wave detectors.
- Demonstrated that simple adjustments to the modulator system can mitigate these issues.
- Proposed a method to improve signal fidelity and control flexibility for these sensitive instruments.
