Phase customization and coding of self-assembled pulses


Recently, the research group of Professor Sun Qizhen and Professor Tang Xiahui of the School of Optics and Electronic Information of Huazhong University of Science and Technology, the research group of Professor Luo Yiyang of the School of Optoelectronic Engineering of Chongqing University and the research group of Professor Shen Ping of Southern University of Science and Technology reported the phase evolution of self-assembled pulse with programmable gain control, and defined four phase evolution intervals, thereby constructing a quaternary coding format customized based on the self-assembly pulse phase. The effectiveness of the phase customization method is verified by simulation and experiment.

Research background

In recent years, ultrashort pulses generated in ultrafast fiber lasers have inspired potential applications in the field of ultrafast science and information technology. This ultrashort pulse is transmitted inside the laser by a composite balance of gain and loss, dispersion and nonlinearity. Analogous to material particles, the entanglement of ultrashort pulses introduces a rich multi-pulse dynamic process. Parameters such as gain dynamics, nonlinear effects, dispersion, and photoacoustic effects enable different numbers of ultrashort pulses to be spontaneously assembled in different arrangements. The study of the time-domain arrangement and transient dynamics of these self-assembled pulses also guides the in-depth exploration of the artificial manipulation of self-assembled pulses.

At the same time, the cutting-edge research and diversified application requirements of ultrafast optics have also promoted the in-depth exploration of the control mechanism of ultrashort pulse, which in turn drives the continuous development of ultrafast laser precision control technology. Through active control or passive feedback control to change the parameters such as gain, energy, filter effect, polarization state and other parameters in the laser cavity, the amplitude, wavelength, pulse width, waveform, spectrum and other characteristics of the self-assembled pulse can be realized. The precise manual control of these pulse characteristics also provides new ideas for ultrafast laser measurement, optical storage, optical computing and other application scenarios. Therefore, how to achieve the precise switching of the phase characteristics of self-assembled pulses and on-demand reconstruction has become the key difficulty of intelligent control of ultrafast lasers.

Innovative research

In this work, the researchers manually manipulated and classified the internal phase evolution of self-assembled pulses by finely adjusting the intracavity gain of ultrafast fiber lasers, revealing the influence of gain on the transient evolution of self-assembled pulses. According to the phase evolution characteristics, four self-assembled pulse phase evolution intervals are defined, which are represented as “none” phase, “negative” phase, “stable” phase, and “positive” phase (Figure 1a). The corresponding phase evolution examples of the four self-assembled pulses are shown in Figure 1b, and the phases evolve in different directions with a high degree of recognition.

Figure 1 (a) Phase evolution of self-assembled pulses for gain control. (b) Example of phase evolution of the four intervals.

In addition, the researchers periodically electrically modulated the laser pump to make the gain in the cavity change rapidly, and then drive the self-assembly pulse for deterministic assembly or dissociation, and the corresponding real-time spectral evolution is shown in Figure 2a. Combined with real-time spectral interferometry, the phase evolution of self-assembled pulses is analyzed, and the specific process of pulse switching and its manipulation mechanism are revealed (Figure 2b). This precise modulation of the laser gain provides an efficient method for fast manual manipulation of self-assembled pulses.

Figure 2 All-optical switching between the four phase intervals. (a) Real-time spectral evolution map. (b) Self-assembling pulse phase evolution.

Because the phase symbols of these four intervals are highly recognizable, they are used to build a new phase-based customized quaternary encoding format. The length of one bit is set to 200 microseconds. By setting a suitable phase threshold, the phase evolution class of the self-assembled pulse is determined, and the phase information stored in each bit is identified. This fine electrical modulation of the laser gain enables phase custom coding with high fidelity. In addition, the solution of the phase evolution of the self-assembled pulse is relatively simple, which also ensures fast decoding of the phase information. To verify the usability of this phase custom coding, the researchers programmed the word “fiber” into the pulse stream and phased it out, as shown in Figure 3. On this basis, if the phase evolution speed or other self-assembling pulse transient evolution is added to the coding format, the multicoding and all-optical storage capacity can be further improved.

Figure 3 Example of phase custom quaternary encoding “fiber”. (a) Encoded data streams. (b) Quaternary representation of each letter. (c) Phase evolution trajectory of “r”.

Summary and outlook

This paper reports the phase evolution of self-assembled pulses for programmable gain control, from which a new phase-custom quaternary encoding format is constructed. This phase customization method based on gain control provides a new idea for the manual manipulation of self-assembled pulses, which is expected to further expand many emerging application scenarios such as optical measurement, optical storage, and optical computing, and open up a new way for the research of ultrafast optics.

The research results were recently published in the top international academic journal Light: Science & Applications, entitled “Phase-tailored assembly and encoding of dissipative soliton molecules”.

Huazhong University of Science and Technology and Chongqing University jointly trained doctoral student Liu Yusong as the first author of the paper, Associate Professor Luo Yiyang of Chongqing University and Professor Sun Qizhen of Huazhong University of Science and Technology are co-corresponding authors of the paper. (Source: LightScience Applications WeChat public account)

Related paper information:‍-023-0‍1170-x

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