Optimization of under-sampling phase detection accuracy in phase laser ranging.

Under-sampling is an advantageous way for lowering sampling circuit complexity in phase laser ranging while maintaining high modulated frequency operation. Improving the accuracy of the ranging system is the aim of the proposed selection criteria with involved under-sampling parameters. These parameters include signal frequency, sampling frequency, and calculation points. Setting the number of one periodic sampling points to be an integer power of 2 (p o w e r=2-6) optimizes the accuracy in integral periodic sampling. Levering up calculated periods with limited calculated points and averaging the calculated phase by employing the corresponding average parameter can both enhance accuracy in non-integral periodic sampling. These criteria are verified through derivation and simulation and are applied to the ranging system. The experimental results demonstrate that, by applying these selection criteria, the phase detection accuracy in the under-sampling ranging system can be potently improved without any pre-processing or algorithmic refinement.

Asynchronous and synchronous dual-wavelength pulse generation in a passively mode-locked fiber laser with a mode-locker.

The evolution from asynchronous to synchronous dual-wavelength pulse generation in a passively mode-locked fiber laser is experimentally investigated by tailoring the intracavity dispersion. Through tuning the intracavity-loss-dependent gain profile and the birefringence-induced filter effect, asynchronous dual-wavelength soliton pulses can be generated until the intracavity anomalous dispersion is reduced to ∼8 fs/nm. The transition from asynchronous to synchronous pulse generation is then observed at an elevated pump power in the presence of residual anomalous dispersion, and it is shown that pulses are temporally synchronized at the mode-locker in the cavity. Spectral sidelobes are observed and could be attributed to the four-wave-mixing effect between dual-wavelength pulses at the carbon nanotube mode-locker. These results could provide further insight into the design and realization of such dual-wavelength ultrafast lasers for different applications such as dual-comb metrology as well as better understanding of the inter-pulse interactions in such dual-comb lasers.

Picometer-resolution dual-comb spectroscopy with a free-running fiber laser.

Dual-comb spectroscopy holds the promise as real-time, high-resolution spectroscopy tools. However, in its conventional schemes, the stringent requirement on the coherence between two lasers requires sophisticated control systems. By replacing control electronics with an all-optical dual-comb lasing scheme, a simplified dual-comb spectroscopy scheme is demonstrated using one dual-wavelength, passively mode-locked fiber laser. Pulses with a intracavity-dispersion-determined repetition-frequency difference are shown to have good mutual coherence and stability. Capability to resolve the comb teeth and a picometer-wide optical spectral resolution are demonstrated using a simple data acquisition system. Energy-efficient, free-running fiber lasers with a small comb-tooth-spacing could enable low-cost dual-comb systems.