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.