Outdoor atmospheric optical two-way time transfer with serial time code

Area of Science:

• Optical physics
• Metrology
• Telecommunications

Background:

• Accurate time transfer is crucial for various scientific and technological applications.
• Existing methods like GPS-based time transfer have limitations in certain environments.
• Free-space optical links offer potential for high-bandwidth, secure data transmission.

Purpose of the Study:

• To demonstrate an optical two-way time transfer scheme in an outdoor free-space link.
• To evaluate the performance and precision of this novel time transfer method.
• To compare the proposed method with existing Global Positioning System (GPS)-based time transfer.

Main Methods:

• Implementation of a complex programmable logic device-based serial time coder/decoder.
• Transmission of a 100 Hz signal with time information over a 120-m outdoor atmospheric link.
• Measurement of time drift, time deviation, and frequency instability to assess signal quality.

Main Results:

• Achieved a root-mean-square time drift of approximately 81 ps over 11 hours.
• Measured time deviation of 70 ps at 1-s averaging time, improving to 10 ps at 100-s averaging time.
• Demonstrated fractional frequency instability on the order of 1.4 × 10⁻¹⁰ at 1 s and 3.0 × 10⁻¹⁵ at 10,000 s.

Conclusions:

• The optical two-way time transfer scheme is effective for outdoor free-space links.
• The method exhibits superior time deviation and frequency instability compared to GPS-based methods.
• This technique is suitable for high-precision, short-distance time transfer applications in atmospheric conditions.