Abstract
We introduce a new device for group and phase delay steering of femtosecond pulse trains that makes use of cascaded, electrically driven, nematic liquid-crystal cells. Based on this approach we demonstrate a continuously tunable optical delay line. The simple collinear implementation with no moving parts enables to shape the achievable temporal range with sub-femtosecond accuracy. By appropriately choosing the bias voltages applied to the cascaded cells, the imparted group delay can be made either positive or negative and precisely adjusted. Moreover, independent control of the group delay and the phase of femtosecond pulses is demonstrated.
Highlights
Ultrafast optical waveforms propagating in any dispersive medium experience different group and phase velocities
Devices for temporal division are widely employed for measurement and characterization of ultrashort pulses [3], self-referenced spectral interferometry [4], ultrafast spectroscopy [5, 6, 7], nonlinear optics [8] and temporal multiplexing [9, 10]
The introduced group delay, response time and temporal resolution are adjustable depending on the desired application
Summary
Ultrafast optical waveforms propagating in any dispersive medium experience different group and phase velocities. We demonstrate an innovative and efficient device to control the group and phase delay of femtosecond pulses, which is realized by appropriately addressing one or two electricallydriven nematic liquid-crystal cells Based on this approach, we first focus on the group delay tuning with a single nematic cell and demonstrate a simple, collinear, continuously tunable optical delay line suitable for ultrafast pulse trains. Adequate electrical control of two cells with different thicknesses is shown to afford independent tuning of the phase and group delays These results demonstrate that nematic liquid-crystals cells enable the high-precision manipulation of optical pulses in the femtosecond regime. The setup is simple and offers many advantageous features, such as compactness, continuous tunability, collinearity and no moving parts
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