Liquid crystals (LCs) have a widely tunable refractive index that can be exploited to counteract optical dispersion and thus extend the range over which light can be efficiently converted.
Generally, moderating the wavelength emanating from a crystal requires temperature management or angle-tuning to maintain phase-matching. These methods can be slow and require multiple crystals and complex mechanical tuning. Additionally, commonly used gratings result in inefficient wavelength conversions. Liquid crystals eliminate these issues and yield high-efficiency, fast, tunable, nonlinear wavelength conversion.
This innovation utilizes a nonlinear lithium niobate crystal clad in a liquid crystal. The LCs have a widely tunable refractive index that changes with voltage. Lithium niobate (LiNbO3) acts as a nonlinear planar waveguide and is transparent from the visible to the mid-infrared wavelength. The strong confinement in the waveguide allows for higher intensities and efficient nonlinear conversion, even at fairly low power levels.
This setup produces efficient nonlinear wavelength conversion that phase-matches the pump and signal wavelength as they travel through the crystal. Additionally, transition times are less than 100 microseconds, enabling wavelength switching at a rate of 10 KHz.