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. 2014 Mar 11:4:4346.
doi: 10.1038/srep04346.

Ultrafast optical control of group delay of narrow-band terahertz waves

Fumiaki Miyamaru  1 , Hiroki Morita  1 , Yohei Nishiyama  1 , Tsubasa Nishida  1 , Toshihiro Nakanishi  2 , Masao Kitano  2 , Mitsuo W Takeda  1
Affiliations

Ultrafast optical control of group delay of narrow-band terahertz waves

Fumiaki Miyamaru et al. Sci Rep. .

Abstract

We experimentally demonstrate control over the group delay of narrow-band (quasi continuous wave) terahertz (THz) pulses with constant amplitude based on optical switching of a metasurface characteristic. The near-field coupling between resonant modes of a complementary split ring resonator pair and a rectangular slit show an electromagnetically induced transparency-like (EIT-like) spectral shape in the reflection spectrum of a metasurface. This coupling induces group delay of a narrow-band THz pulse around the resonant frequency of the EIT-like spectrum. By irradiating the metasurface with an optical excitation pulse, the metasurface becomes mirror-like and thus the incident narrow-band THz pulse is reflected without a delay. Remarkably, if we select the appropriate excitation power, only the group delay of the narrow-band THz pulse can be switched while the amplitude is maintained before and after optical excitation.

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Figures

Figure 1
Figure 1. Photograph and schematic of metasurface on GaAs substrate.
(a) A photograph of our metasurface, with a unit cell consisting of rectangular slits sandwiched between two complementary split ring resonators. Geometrical parameters are also shown in the figure. (b) Schematic of the optical configuration of the incident terahertz wave and the metasurface.
Figure 2
Figure 2. Terahertz wave reflection measurement.
Schematic of the optical configuration of our experiment.
Figure 3
Figure 3. Reflection spectra of metasurface.
Reflection spectra are shown for various levels of photoexcitation power. The excitation pulse timing with respect to the incident terahertz wave was −40 ps.
Figure 4
Figure 4. Phase shift and group delay spectra.
(a) Phase shift and (b) group delay spectra for various levels of photoexcitation power.
Figure 5
Figure 5. Group delay switching of a narrow-band THz pulse.
Schematic of optical switching of the group delay for a narrow-band THz pulse.
See this image and copyright information in PMC

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