Real-time observation of frequency Bloch oscillations with fibre loop modulation

Balloch oscillations (BOs) were initially predicted for electrons in a solid lattice as a static electric field is applied. Scientists in China constructed a synthetic functional lattice in a fiber loop, which was in a fiber loop under phased modulation and directly observed the frequency BO in real time.

The frequency spectrum in the telecommunications band can be as large as hundreds of GHz. The study can find applications in frequency manipulations in optical fiber communication systems.

BOs describe the periodic movement of electrons in a solid to which an external static electric field is applied. However, measuring BO directly in natural solids is challenging because the relaxation time of electrons is usually much shorter than the oscillation period.

To date, analogs of electron BO have been extended to synthetic dimensions of time, frequency and angular momentum.

In previous studies, the frequency BO has been experimentally demonstrated in a nonlinear fiber with cross-phase modulation. However, the frequency spectrum has only been obtained at the output of the fiber, and thus the BO’s growth process has only been measured indirectly.

In addition, frequency BOS has been theoretically demonstrated in a micro-resonator under temporal modulation. Considering the compact structure of the ring resonator, direct observation of BO still has difficulties in compensating for power cuts when assembling the signals.

In a new paper published in Optics and Applications, a team of scientists, led by Professor Bing Wang of the School of Physics and Wuhan National Laboratory for Optoelectronics, Huzhong University of Science and Technology, Wuhan, China and co-workers directly saw. Frequency BOS in a modified fiber loop over time.

The spectrum of the incident optical spectrum experienced a periodic movement in the frequency lattice formed by phase modulation. Time dating generated an effective electric-field force in the lattice, which was associated with differential effective vector potential with spectrum evolution.

Additionally, the transient evolution of the spectrum was measured in real time using the dispersive Fourier transform (DFT) technique. Based on frequency-domain BOs, a maximum frequency shift of up to 82 GHz was achieved. The bandwidth of the input pulse was also increased to 312 GHz.

The study provides a promising approach for realizing BO in synthetic dimensions and can find applications in frequency manipulations in optical fiber communication systems.

These summarize the principle of scientific work: “Phase modulation induces coupling between adjacent frequency modes that form a lattice in frequency amplitude. As the optical pulse propagates in the fiber loop, using an optical delay The roundtrip time can be adjusted. Line.

A short time can be initiated between the pulse circulation time and the modulation period, which acts as an effective electric-field force in the frequency lattice and thus the ground frequency gives rise to the BO. We show that the vector potential can also contribute to the formation of the effective force, which varies with the diffusion distance. “

To realize real-time measurements of the loop spectrum coupled to a loop, a spectroscope based on DFT is connected at the end of a fiber-loop circuit.

A long dispersion-compensating fiber performs the Fourier transform, which maps the spectrum envelope of the optical pulse into a time-domain waveform. Thanks to dispersion in the fiber, real-time measurements of the frequency spectrum can be achieved with a resolution of ~ 9.8 GHz. “

“We apply the incidence of both short and wide pulses and directly observe the oscillations and breathing modes of the frequency BO. As the short pulse propagates in the fiber loop, one sees that the spectrum of the incident pulse is a cochinoidal tracer. Evolves with, referring to. Frequency BOS. For a broad pulse, the spectrum reveals a breathing pattern with a self-focusing effect during development, “he said.

“Based on the current method, spectrum manipulations cross the microelectronics bandwidth limit. This study can find many applications in high efficiency frequency conversion and signal processing.

Additionally, in aid of BOS, we verified that vector gauge capability can be employed to manipulate the optical properties of photons in a synthetic frequency lattice, providing a unique way of controlling light, in particular In the field of topological photonics, ‚ÄĚScientific Prediction.

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