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Effect of phase noise in linear modulator systems.
Applied Optics
|August 25, 2010
Summary
Noise in linear modulator systems using semiconductor lasers and polarization-preserving fiber is ~10 dB above thermal noise due to phase-to-intensity conversion. Reducing this noise requires single-frequency lasers or standard single-mode fiber.
Area of Science:
- Optics and Photonics
- Semiconductor Laser Technology
Background:
- Linear modulator systems often utilize semiconductor lasers and polarization-preserving fiber.
- Laser phase-to-intensity noise conversion is a known phenomenon that can degrade signal quality.
Purpose of the Study:
- To quantify noise levels in linear modulator systems employing semiconductor lasers and polarization-preserving fiber.
- To investigate the impact of launching angles and fiber types on noise levels.
- To compare experimental results with theoretical predictions.
Main Methods:
- Measurements of noise levels were conducted using semiconductor lasers coupled to long lengths of polarization-preserving fiber.
- Data were collected for various launching angles into both polarization-preserving and polarizing fiber.
- Noise variations were analyzed with respect to output analyzer angles.
Main Results:
- Noise levels were found to be approximately 10 dB above thermal noise.
- This excess noise is attributed to laser phase-to-intensity noise conversion.
- Experimental data showed good agreement with theoretical models for noise variation.
Conclusions:
- Polarization-preserving fiber in linear modulator systems contributes significantly to noise above thermal levels.
- To mitigate this noise, employing a single-frequency laser source or replacing polarization-preserving fiber with conventional single-mode fiber is recommended.
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