High speed optical coherence manipulation based on lithium niobate film modulator

Structured light fields have many outstanding properties. Further control of their optical coherence not only mitigates the potential negative effects of high coherence but also reveals new advantages, offering novel insights into light-matter interactions. Customizing the optical coherence of structured light fields to meet specific application requirements has become a crucial research focus. However, traditional optical modulation techniques are limited by low modulation rates, which is a major obstacle to advancing optical coherence manipulation from laboratory research to practical applications. Achieving high-speed optical coherence modulation is therefore a core challenge in this field.

Lithium niobate (LN) material has always been the first choice for high-speed electro-optic modulation materials due to its excellent linear electro-optic effect (Pockels effect). In recent years, with the maturity of lithium niobate films (LNF) preparation technology and the maturing advancement of microfabrication technique, a plethora of integrated photonic devices on the LNF on insulator platform have been investigated. Most electric beam deflectors and optical modulators are proposed based on the LN platform. Furthermore, by applying voltage to the LN waveguide, the phase distribution of the light field can be precisely and quickly controlled, which opens the possibility of tailoring optical coherence using LNF modulator.

Now the research introduce a novel application of LNF modulators for optical coherence manipulation. By designing specific modulation voltages, we achieve precise, high-speed control of the light field’s phase distribution and tailor optical coherence through the superposition of multiple coherence modes. Our experimental results are consistent with theoretical predictions, and the proposed strategy can also be easily extended to tailor the optical coherence of different special light fields. This strategy paves the way for practical applications of optical coherence tailoring.

Starting from the principle of coherence modulation, the coherence of random light fields is determined by phase distributions. Controlling phases via high-speed modulators enables optical coherence manipulation. The second-order field moment can be decomposed into incoherent superpositions of coherent modes, and the spectral degree of coherence correlates with phase difference statistics, forming the theoretical basis for modulation.

The designed LNF modulator is equipped with 64 independent channels, featuring a binary modulation rate of 2 MHz. Its structure comprises a gold electrode array, a Z-cut LN film, and a ground electrode. By applying voltage, it controls the refractive index differences to achieve precise phase modulation.

In order to verify the high-speed optical coherence manipulation capability of the LNF modulator, a one-dimensional Gaussian Schell-model source is selected as an experimental case. Young’s double-slit interference experiments measure far-field fringe visibility, verifying the partial coherence of generated fields. Experimental results align well with simulations, confirming coherent control.The LNF modulator achieves a 350 kHz modulation rate in the 0–2π phase range, far outperforming digital micro-mirror devices .

The research uses LNF modulator voltage distributions to load prescribed wavefront phases, synthesizing random fields with predefined coherence. Compared to traditional methods, this approach significantly improves the modulation rate while minimizing energy loss, paving the way for practical applications in optical imaging, encryption, and information transmission through random media. The strategy also offers flexibility for tailoring the optical coherence of different special light fields, though current limitations to one-dimensional modulation may be addressed by developing two-dimensional LNF modulators in the future.