研究目的
To develop and demonstrate an absolute distance measurement method using spectral interferometry with a femtosecond optical frequency comb, focusing on improving accuracy and robustness by addressing phase noise issues and extending the non-ambiguity range for long-distance measurements.
研究成果
The PDSEH method provides a robust and high-precision approach for absolute distance measurement, achieving a standard deviation of 75 nm and a resolution better than 30 μm over 70 m, with a relative precision of 3.1e-7. It outperforms the traditional FT method in handling phase noise, making it suitable for arbitrary distance measurements in applications like metrology and manufacturing.
研究不足
The method is sensitive to environmental factors like temperature, pressure, and humidity, which affect the air refractive index. Phase noise in long-distance measurements can impact accuracy if not mitigated. The setup requires precise control and calibration, and the maximum distance is limited by the coherence length of the source.
1：Experimental Design and Method Selection:
The study uses spectral interferometry with a femtosecond optical frequency comb. A Michelson interferometer setup is employed to measure distance delays. The proposed PDSEH method (phase demodulation of signal envelops in a Hilbert way) is compared with the traditional FT method (band-pass filter and Fourier Transform) for phase unwrapping.
2：Sample Selection and Data Sources:
Measurements are conducted on an 80-m long optical tunnel at the National Institute of Metrology (NIM), China, with controlled environmental conditions (temperature, pressure, humidity). Data is collected using an optical spectrum analyzer.
3：List of Experimental Equipment and Materials:
Femtosecond source (Onefive Origami-15), rubidium clock (SRS FS725), photodetector (Menlo Systems FPD510-F), frequency counter (Agilent 53220A), optical spectrum analyzer (YOKOGAWA AQ6370D-20), He-Ne interferometers (Agilent 5519B), fiber splitters, circulators, collimators, coupler, corner-cube prisms.
4：Experimental Procedures and Operational Workflow:
The femtosecond laser is split into reference and measurement arms in a fiber Michelson interferometer. Interference signals are detected by the optical spectrum analyzer. Small distance measurements are performed near and far from the source, and long distance measurements up to 70 m are conducted with steps of 5 m. Each measurement is repeated 10 times for stability.
5：Data Analysis Methods:
Phase unwrapping is done using FT and PDSEH methods. Least square method (LSM) is used for fitting phase data. Uncertainty evaluation includes contributions from refractive index, repetition frequency, and phase demodulation.
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rubidium clock
FS725
SRS
Stabilizes the repetition frequency of the femtosecond source.
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photodetector
FPD510-F
Menlo Systems
Detects the repetition frequency of the source for monitoring.
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frequency counter
53220A
Agilent
Records the repetition frequency monitored by the photodetector.
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optical spectrum analyzer
AQ6370D-20
YOKOGAWA
Detects and samples interference signals from the interferometer.
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He-Ne interferometer
5519B
Agilent
Provides reference distance measurements for verification.
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femtosecond source
Origami-15
Onefive
Provides femtosecond optical frequency comb for spectral interferometry in distance measurement.
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