Bello Leon, Strinati Marcello Calvanese, Ben-Ami Shai, Pe'er Avi
Department of Physics and BINA Center of Nanotechnology, Bar-Ilan University, 52900 Ramat-Gan, Israel.
Department of Physics, Bar-Ilan University, 52900 Ramat-Gan, Israel.
Phys Rev Lett. 2021 Feb 26;126(8):083601. doi: 10.1103/PhysRevLett.126.083601.
Mode locking in lasers is a collective effect, where due to a weak coupling a large number of frequency modes lock their phases to oscillate in unison, forming an ultrashort pulse in time. We demonstrate an analogous collective effect in coupled parametric oscillators, which we term "pairwise mode locking," where many pairs of modes with twin frequencies (symmetric around the center carrier) oscillate simultaneously with a locked phase sum, while the phases of individual modes remain undefined. Thus, despite being broadband and multimode, the emission is not pulsed and lacks first-order coherence, while possessing a very high degree of second-order coherence. Our configuration comprises two coupled parametric oscillators within identical multimode cavities, where the coupling between the oscillators is modulated in time at the repetition rate of the cavity modes, with some analogy to active mode locking in lasers. We demonstrate pairwise mode locking in a radio-frequency experiment, covering over an octave of bandwidth with approximately 20 resonant mode-locked pairs, filling most of the available bandwidth between dc and the pump frequency. We accompany our experiment with an analytic model that accounts for the properties of the coupled parametric oscillators near threshold.
激光中的锁模是一种集体效应，由于弱耦合，大量频率模式锁定其相位以同步振荡，从而在时间上形成超短脉冲。我们在耦合参量振荡器中展示了一种类似的集体效应，我们将其称为“成对锁模”，其中许多具有双频（围绕中心载波对称）的模式对以锁定的相位和同时振荡，而各个模式的相位仍然不确定。因此，尽管发射是宽带和多模的，但它不是脉冲式的，缺乏一阶相干性，同时具有非常高的二阶相干性。我们的配置包括两个位于相同多模腔内的耦合参量振荡器，其中振荡器之间的耦合以腔模的重复率进行时间调制，这与激光中的主动锁模有一些相似之处。我们在射频实验中展示了成对锁模，覆盖超过一个倍频程的带宽，有大约20个共振锁模对，占据了直流和泵浦频率之间的大部分可用带宽。我们用一个解析模型来伴随我们的实验，该模型解释了接近阈值的耦合参量振荡器的特性。
