Article

Terahertz wire-grid polarizers with micrometer-pitch Al gratings

National Institute of Advanced Industrial Science and Technology, Osaka, Japan.
Optics Letters (Impact Factor: 3.29). 03/2009; 34(3):274-6. DOI: 10.1364/OL.34.000274
Source: PubMed

ABSTRACT

We fabricated a terahertz wire-grid polarizer consisting of a micrometer-pitch Al grating on a Si substrate by photolithography and wet etching. The ratio of TM and TE transmittances (extinction ratio) was over 35 dB at 0.5 THz. At the Brewster angle of the Si substrate, the polarization transmittance of a TM wave through the fabricated polarizer exceeded 95% and the extinction ratio was over 45 dB at approximately 1 THz. The fabricated polarizer has a higher extinction ratio than conventional free-standing terahertz wire-grid polarizers.

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    • "To increase the PER, one common method is to decrease the period of the metallic sub-wavelength grating and change the shape of grating, which will bring difficulties in the structure fabrication. At present, the reported PER of THz polarizers with singlelayer metallic grating is about 10 to 50 dB [8] [9] [10] [11] [12]. To improve it, recently, a terahertz polarizer is presented consisting of a laminated metal-slit array on a polymer film [13]. "
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    ABSTRACT: Terahertz (THz) polarizers with low reflection and absorption loss and high polarization extinction ratio (PER) based on multilayer metallic gratings filled in polyimide (PI) film were studied theoretically and experimentally. In theory, THz polarization transmittance and PER of single-layer and multilayer polarizers at different THz frequencies were simulated and their variations with the layer number of the metallic grating structure were discussed. With the increase of the layer number, PER increases prominently due to the evanescent wave coupling between different layers. In experiment, a double-layer polarizer with an effective diameter of 42.3 mm was fabricated via layered imidization processes and evaluated by the THz time-domain spectroscopy (THz-TDS) measurements. Results showed that an average transmittance of 80.5% and a maximal PER of 70dB were achieved, which were in good agreement with the simulated results and were compared to or outperformed most reported single-layer or double-layer polarizers.
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    • "However, this model works well only for microwaves and millimeter waves with -polarization. Today, MGs on dielectric substrate [7], [17] demonstrate higher values of extinction ratio (the ratio of -and -transmittances ) than MGs, made by the technology of double-side jet etching. However, such mesh polarizers cannot be used in aerospace radio electronic systems because of the strong influence of environmental conditions (temperature, vibration, and others.). "
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    ABSTRACT: In this paper, the results of theoretical and experimental studies of 1-D metallic gratings for mesh polarizers used in radar and communication engineering are presented. To calculate the transmission characteristics of gratings with rectangular lamels, fabricated by the technology of double-side jet etching, a 2-D finite-element model with Floquet periodicity conditions is developed with the parameters of the signal at the grating input taken into account. Simple design equations are obtained by using regression analysis and the results of numerical modeling. Both numerical and analytical models are tested experimentally. The influence of three basic dimensions of the grating on the level of transmitted power is established for the s-polarized electromagnetic waves.
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    • "Thus, the effective manipulation of EM wave polarization is highly desirable, which has become an important research topic for long time. Conventionally, optical gratings and dichroic crystals can be used to manipulate polarization, which require a system much thicker than wavelength and is also inconvenient for low-frequency applications .[2] [3] Over the past decade, metamaterials (MMs) concept have been proposed and investigated widely due to exotic properties, and have opened a new way to manipulate polarizations.[4] "
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    ABSTRACT: In this paper, a chiral metamaterial (CMM) with triple-layer twisted split-ring resonators structure was proposed, which could exhibit a linear polarization conversion as well as asymmetric transmission only for forward and backward propagating linearly polarized waves in a broadband frequency range. The polariza- tion of broadband linearly polarized electromagnetic waves can be rotated in a specific direction by passing it through such a CMM slab with a thickness of about one-twelfth the operational center wavelength. Experiment and simulation calcula- tions are in good agreement, and the polarization conversion rate is above 90% in the frequency range of 5.5–11.1GHz. The physical mechanism of the broadband linear polarization conversion effect could be further illustrated by simulated electrical field and surface current distributions.
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