Soliton dual comb in crystalline microresonators
  We present a novel compact dual-comb source based on a monolithic optical crystalline MgF$_2$ multi-resonator stack. The coherent soliton combs generated in two microresonators of the stack with the repetition rate of 12.1 GHz and difference of 1.62 MHz provided after heterodyning a 300 MHz wide radio-frequency comb. Analogous system can be used for dual-comb spectroscopy, coherent LIDAR applications and massively parallel optical communications. 
N. G. Pavlov, G. Lihachev, S. Koptyaev, E. Lucas, M. Karpov, N. M.   Kondratiev, I. A. Bilenko, T. J. Kippenberg, and M. L. ...
nlin.PS physics.optics