Ultrafast laser, with ultra-short duration, ultra-wide spectral bandwidth, and ultra-high peak power, have been widely used in many fields, such as precise distance measurements, micromachining, optical communication, quantum coherent control and so on. The emergence of pulse shaping technology has greatly broadened the application scenarios of ultrafast lasers. For many applications it would be desirable to achieve dynamic pulse shaping at high updating rate. However, conventional pulse shapers based on liquid crystal SLMs (LCSLMs) or digital micromirror devices (DMDs) respond only on a time scale of milliseconds.

In this letter, we demonstrate a one-dimension (1D) high-speed lithium niobate SLM (LNSLM) with 128 individual modulation channels and a modulation speed of 1 MHz. Based on the LNSLM, we experimentally establish a high-speed Fourier-transform pulse shaper, the experimental setup is shown in Fig. 1, and the width of the pulse is characterized by the second-harmonic signal generated in the nonlinear crystal KDP. Figure 2 shows the pulse width variation before and after optimization, achieving a pulse compression ratio of about 17 with little variation in spectral shape. Figure 3 shows the high-speed modulation performance of the pulse shaper. We perform fast switching between random and optimized voltage combinations obtained by the above experiment at 350 kHz. Figure 5(a) shows the temporal characteristic of the SH signal under high-speed pulse shaping at 350 kHz. The pulse shaping speed of 350 kHz is demonstrated, which is more than three orders of magnitude faster than the typical LCSLM-based shaper. The high-speed pulse shaping shows a great potential of real-time dynamic operation, which is extremely important in microscopy, material micromachining, optical communication, and so on.

Fig. 1. Experimental setup.

Fig. 2. Autocorrelation traces (a) and power spectrum (b) of the uncompressed pulses. Autocorrelation traces (c) and power spectrum (d) of the compressed pulses.

Fig. 3. (a) Temporal characteristic of the SH signal generated from the KDP crystal by high-speed switching of optimized and random voltage combinations at 350 kHz. (b) The zoom-in view of the SH pulse sequences in the marked regions in (a).

This research is published in “Fengchao Ni, Honggen Li, Haigang Liu, Yuanlin Zheng, and Xianfeng Chen, High-speed optical pulse shaping based on programmable lithium niobate spatial light modulator, Optics Letters, 48(4), 884-887 (2023)”.

Link: https://doi.org/10.1364/OL.477967