Nonlinear properties of high-Q optical microresonators in normal dispersion range

Artem Shitikov, Valery Lobanov, Nikolay Pavlov, Andrey Voloshin, Igor Bilenko, Michael Gorodetsky, V.V. Samartsev, A.A. Kalachev, A.V. Naumov, M.G. Gladush, K.R. Karimullin
2017 EPJ Web of Conferences  
We demonstrate the generation of Kerr frequency combs and platicons in whispering gallery mode crystalline microresonators in normal group velocity regime at 780 nm and 1064 nm wavelengths. Whispering gallery mode (WGM) microresonators can have extremely high values of quality-factor (exceeding 10 9 ) in the optical range, that allows low threshold of many interesting nonlinear effects, in particular, the generation of Kerr frequency combs [1] . Kerr combs in optical microresonators may become
more » ... onators may become a basis for a new class of compact devices for spectroscopy, precision measurements, and generation of femtosecond pulses. Coherent low-noise frequency combs are of particular interest. These combs may be generated in the form of dissipative Kerr solitons in the region of anomalous group velocity dispersion (GVD) [2] and to date have been already demonstrated on different platforms. However, most materials suitable for the manufacturing of WGM microresonators (for example, widely used fluorides MgF2 and CaF2) have a normal GVD in the visible and near IR ranges, which prevents soft generation of coherent frequency combs and bright dissipative Kerr solitons. Therefore, the development of new methods for coherent frequency comb excitation in microresonators with normal GVD and studying the properties of such combs is an actual and practically significant task. It was shown recently that in the normal GVD regime coherent frequency combs could be achieved in the form of soliton-like pulses of a particular form, so-called platicons [3] . It was also demonstrated that the efficiency of the transformation of pump power into the power of the frequency comb lines is significantly better for platicons compared to the generation of bright solitons in anomalous GVD regime. This properties of platicons are important for many practical applications. In the recent years, several methods for the generation of platicons were proposed: the use of a local dispersion perturbations caused by mode interactions [3, 4] , pump modulation at a frequency equal to the free spectral range (FSR) of a microresonator and biharmonic pump [5], self-injection locking of a laser source to a mode of the WGM microresonator [6]. In our work MgF 2 microresonators and prism coupling were used. For 3 mm in diameter MgF2 microresonators the GVD is mostly determined by material dispersion which is normal at given wavelengths. The microresonator's loaded quality-factor exceeded 5x10 8 . For the pump at 1064 nm, the experimental setup was adapted both for biharmonic and for the amplitude-modulated pump (see Fig. 1 ). For the pump at 780 nm, a setup with an
doi:10.1051/epjconf/201716102025 fatcat:75wzqnqipneyng2lyasfveobyu