Widely tunable comb-locked frequency-swept synthesizer

Advantages Optical synthesizer

• the scanning cw laser is permanently phase-locked to the frequency comb and inherits its low phase noise and precision
• the comb’s intrinsic constant mode spacing allows a strictly linear scan
• locking the comb allows absolute measurement that is traceable to the frequency standard
• the scan can be on the fly adopted for various measurement conditions

Features Optical synthesizer

• central wavelength ~ 1570 nm
• frequency range ~ 10 THz : mode hop free
• frequency resolution   < 0.1 Hz
• scanning speed 100 kHz/s … 1 THz/s
• scanning form : saw tooth, triangle
• slew rate modulation for dispersion correction

Optical synthesizer : proved applications

R. Gotti, et al, “Comb-locked frequency-swept synthesizer for high precision broadband spectroscopy,” Sci. Rep. 10(1), 2523 (2020).

T. A. Puppe, Y. Mayzlin, J. Robinson-Tait and R. Wilk, "Comb-locked Frequency-domain terahertz spectrometer," 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Paris, France, 2019, pp. 1-1, doi: 10.1109/IRMMW-THz.2019.8874007.

Conclusion and outlook

• The optical synthesizer is suitable for OFDR resolution of 10 mm at 20 km distance in fiber to our knowledge, it is 14 times better as the best reported up-to-date.
• In current experiment only 0.1 % of available synthesizer scan range is utilized.
• At the given oscillator noise, the large possible scan range is advantageous for shorter distances.
• Locking the comb to a frequency standard allows for traceable absolute distance measurement.
• Wide scan could allow for atmosphere dispersion correction as in dual band systems.
• The main challenge for product development is to identify features for certain application.