Limits...
Switchable Ultrathin Quarter-wave Plate in Terahertz Using Active Phase-change Metasurface.

Wang D, Zhang L, Gu Y, Mehmood MQ, Gong Y, Srivastava A, Jian L, Venkatesan T, Qiu CW, Hong M - Sci Rep (2015)

Bottom Line: In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO2), with a metasurface.After the transition to metal phase, the quarter-wave plate operates at 0.502 THz.At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.

ABSTRACT
Metamaterials open up various exotic means to control electromagnetic waves and among them polarization manipulations with metamaterials have attracted intense attention. As of today, static responses of resonators in metamaterials lead to a narrow-band and single-function operation. Extension of the working frequency relies on multilayer metamaterials or different unit cells, which hinder the development of ultra-compact optical systems. In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO2), with a metasurface. Before the phase transition, VO2 behaves as a semiconductor and the metasurface operates as a quarter-wave plate at 0.468 THz. After the transition to metal phase, the quarter-wave plate operates at 0.502 THz. At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light. This work reveals the feasibility to realize tunable/active and extremely low-profile polarization manipulation devices in the terahertz regime through the incorporation of such phase-change metasurfaces, enabling novel applications of ultrathin terahertz meta-devices.

No MeSH data available.


Performance of the THz QWP at different temperatures.(a) Calculated Stokes parameter S0 with respect to different temperatures based on THz-TDS measured results, indicating that the output power decreases when the temperature increases. (b) Measured ellipticities of the output THz wave at different temperatures, indicating the operation frequencies switching of the output circularly polarized THz wave. (c) Numerically simulated Stokes parameter S0 with respect to different conductivities of VO2 and (d) the corresponding ellipticities of the output THz wave.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4595731&req=5

f3: Performance of the THz QWP at different temperatures.(a) Calculated Stokes parameter S0 with respect to different temperatures based on THz-TDS measured results, indicating that the output power decreases when the temperature increases. (b) Measured ellipticities of the output THz wave at different temperatures, indicating the operation frequencies switching of the output circularly polarized THz wave. (c) Numerically simulated Stokes parameter S0 with respect to different conductivities of VO2 and (d) the corresponding ellipticities of the output THz wave.

Mentions: Figure 3a shows the measured S0 parameters at different temperatures, which indicate the power of the output THz wave. It is observed that when the temperature increases from 300 to 400 K, the output power decreases. This is attributed to loss in the VO2 pads. At 300 K, the VO2 pads behave as a semiconductor and the corresponding loss is low. When the temperature increases, free carries in the VO2 pads increase, leading to a high damping loss and small output power. From Fig. 2a and 3a, we can observe asymmetric transmitted peak amplitudes of and . When the conductivity of VO2 increases, the resonance frequency of shifts to a higher frequency, which is closer to the wood’s anomaly at 0.59 THz. The peak amplitude of becomes smaller, which is shown in Fig. 2a. Another contribution to this asymmetric peak transmission is the different sizes of VO2 pads. As shown in Fig. 1a, the size of VO2 pads along the x-axis is much larger than that along y-axis. This leads to different VO2 damping losses for and . The polarization state of the output THz wave can be described by ellipticity, which is defined as χ = S3/S0. When χ equals to either 1 or −1, the output THz wave is circularly polarized. Figure 3b shows the ellipticity of the output THz wave at different temperatures. At 300 K, the ellipticity of the output THz wave is around 0.98 at 0.468 THz. At 400 K, the ellipticity is around 0.97 at 0.502 THz. Between 300 and 400 K, the ellipticity is close to 1 with the operating frequency switching from 0.468 to 0.502 THz. This indicates that the output THz wave is circularly polarized at different temperatures. The numerical simulation results are shown in Fig. 3c,d, which will be discussed in the following section.


Switchable Ultrathin Quarter-wave Plate in Terahertz Using Active Phase-change Metasurface.

Wang D, Zhang L, Gu Y, Mehmood MQ, Gong Y, Srivastava A, Jian L, Venkatesan T, Qiu CW, Hong M - Sci Rep (2015)

Performance of the THz QWP at different temperatures.(a) Calculated Stokes parameter S0 with respect to different temperatures based on THz-TDS measured results, indicating that the output power decreases when the temperature increases. (b) Measured ellipticities of the output THz wave at different temperatures, indicating the operation frequencies switching of the output circularly polarized THz wave. (c) Numerically simulated Stokes parameter S0 with respect to different conductivities of VO2 and (d) the corresponding ellipticities of the output THz wave.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595731&req=5

f3: Performance of the THz QWP at different temperatures.(a) Calculated Stokes parameter S0 with respect to different temperatures based on THz-TDS measured results, indicating that the output power decreases when the temperature increases. (b) Measured ellipticities of the output THz wave at different temperatures, indicating the operation frequencies switching of the output circularly polarized THz wave. (c) Numerically simulated Stokes parameter S0 with respect to different conductivities of VO2 and (d) the corresponding ellipticities of the output THz wave.
Mentions: Figure 3a shows the measured S0 parameters at different temperatures, which indicate the power of the output THz wave. It is observed that when the temperature increases from 300 to 400 K, the output power decreases. This is attributed to loss in the VO2 pads. At 300 K, the VO2 pads behave as a semiconductor and the corresponding loss is low. When the temperature increases, free carries in the VO2 pads increase, leading to a high damping loss and small output power. From Fig. 2a and 3a, we can observe asymmetric transmitted peak amplitudes of and . When the conductivity of VO2 increases, the resonance frequency of shifts to a higher frequency, which is closer to the wood’s anomaly at 0.59 THz. The peak amplitude of becomes smaller, which is shown in Fig. 2a. Another contribution to this asymmetric peak transmission is the different sizes of VO2 pads. As shown in Fig. 1a, the size of VO2 pads along the x-axis is much larger than that along y-axis. This leads to different VO2 damping losses for and . The polarization state of the output THz wave can be described by ellipticity, which is defined as χ = S3/S0. When χ equals to either 1 or −1, the output THz wave is circularly polarized. Figure 3b shows the ellipticity of the output THz wave at different temperatures. At 300 K, the ellipticity of the output THz wave is around 0.98 at 0.468 THz. At 400 K, the ellipticity is around 0.97 at 0.502 THz. Between 300 and 400 K, the ellipticity is close to 1 with the operating frequency switching from 0.468 to 0.502 THz. This indicates that the output THz wave is circularly polarized at different temperatures. The numerical simulation results are shown in Fig. 3c,d, which will be discussed in the following section.

Bottom Line: In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO2), with a metasurface.After the transition to metal phase, the quarter-wave plate operates at 0.502 THz.At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.

ABSTRACT
Metamaterials open up various exotic means to control electromagnetic waves and among them polarization manipulations with metamaterials have attracted intense attention. As of today, static responses of resonators in metamaterials lead to a narrow-band and single-function operation. Extension of the working frequency relies on multilayer metamaterials or different unit cells, which hinder the development of ultra-compact optical systems. In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO2), with a metasurface. Before the phase transition, VO2 behaves as a semiconductor and the metasurface operates as a quarter-wave plate at 0.468 THz. After the transition to metal phase, the quarter-wave plate operates at 0.502 THz. At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light. This work reveals the feasibility to realize tunable/active and extremely low-profile polarization manipulation devices in the terahertz regime through the incorporation of such phase-change metasurfaces, enabling novel applications of ultrathin terahertz meta-devices.

No MeSH data available.