Sub-millimeter resolution and high-precision φ-OFDR using a complex-domain denoising method.

Phase noise is one of the main obstacles to achieve high spatial resolution, high precision, and large measurement range in φ-OFDR. Here, we proposed a complex-domain denoising method to achieve unwrapping of phase signals. In this method, the wrapped phase was used to construct a complex signal, and then both real and imaginary parts are denoised by using a wavelet packet. The two sets of denoised signals are reconstructed into a complex form, allowing to obtain an unwrapped phase. Additionally, the spatial position correction algorithm addresses the phase decoherence from strain accumulation. Finally, a high numerical aperture optical fiber is used to enhance the Rayleigh scattering intensity by 15 dB. The comprehensive approach yields remarkable results: a sensing resolution of 0.89 mm, a root mean square error of 1.5 µÎµ, and a maximum strain sensing capability of 2050 µÎµ.

Ultra-high harmonic mode-locking with a micro-fiber knot resonator and Lyot filter.

We report on ultra-high harmonic mode-locking with a repetition rate of up to ∼1 THz by combining a microfiber knot resonator (MKR) and a Lyot filter. The harmonic mode-locked pulses are tunable by changing the diameter of MKR, which agrees well with the theoretical calculation. Our results indicate that the ultrafast pulse generation mechanism is due to the dissipative four-wave mixing mode-locking technique. This work provides a simple and efficient scheme to generate tunable ultrafast pulses with a high repetition rate for various applications, such as THz generation and ultrafast data communication.

All-optical Ti3C2Tx modulator based on a sandwich structure.

All-optical modulators based on a MXene-Ti3C2Tx have recently garnered much attention due to their broadband light-matter interactions and ultrafast carrier dynamics. To investigate the modulation characteristics of pump intensity and pump light modulation frequency, we establish an all-optical modulator with a sandwich structure based on MXene-Ti3C2Tx/PVA (polyvinyl alcohol) film. The result shows that this modulator can achieve a high modulation depth of 12.55 dB and a modulation frequency of 50 kHz corresponding to a response time at the microsecond scale. The successful preparation of the modulator is attributed to the saturable absorption characteristics of the MXene-Ti3C2Tx. This modulator has great potential in all-optical communications and ultrafast optical signal processing.