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Magnetically tunable room-temperature 2π liquid crystal terahertz phase shifter

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Tunable phase shift up to 360° at 1 THz is achieved with a liquid crystal (LC) device. The key to this design is (1) the use of a nematic LC, E7, which exhibits a birefringence of ~0.17 (0.2–1.2 THz); (2) a LC cell (3-mm in thickness) with sandwiched structure to increase the interaction length while minimizing interface Fresnel losses; and (3) the use of magnetic field to align the thick LC cell and achieve continuous tuning of phase from 0 to 360°. This device can be operated over a broad range near room temperature.

©2004 Optical Society of America

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Figures (4)

Fig. 1.
Fig. 1. The schematic diagram of the LC THz phase shifter. The inset shows the sandwiched structures of the LC cells used.
Fig. 2.
Fig. 2. The room-temperature (a) extraordinary (red circles) and ordinary (blue circles) refractive indices, (b) birefringence, and (c) imaginary extraordinary (blue circles) and ordinary (red circles) refractive indices of E7 are shown as a function of frequency between 0.2 to 1.2 THz.
Fig. 3.
Fig. 3. . The measured THz waveforms transmitted through the LC phase shifter at various magnetic inclination angles. The inset shows the spectrum of the THz signal.
Fig. 4.
Fig. 4. The phase shift of the THz waves versus the magnetic inclination angle. The solid curves are theoretical predictions. The red and blue circles are experimentally measured phase shift at 0.49 and 1.025 THz.

Equations (2)

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δ ( θ ) = 0 L 2 π f c Δ n eff ( θ , z ) dz ,
δ ( θ ) = 2 π L f c { [ cos 2 ( θ ) n o 2 + sin 2 ( θ ) n e 2 ] 1 2 n o } ,


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