The effects of anisotropic dielectric properties of ferroelectric Ba 1Ϫx Sr x TiO 3 ͑BST͒ films on the characteristics of the interdigital ͑IDT͒ capacitors have been studied in microwave regions at room temperature. Ferroelectric BST films with ͑001͒, ͑011͒, and ͑111͒ orientation were epitaxially grown on ͑001͒, ͑011͒, and ͑111͒ MgO substrates, respectively, by the pulsed laser deposition method. The microwave properties of orientation engineered BST films were investigated using interdigital capacitors. The calculated dielectric constant tunability with 40 V dc bias variation and the calculated dielectric quality factor values for IDT capacitors based on ͑001͒, ͑011͒, and ͑111͒ oriented BST films at 9 GHz with no dc bias were about 47%, 55%, 43%, and 12, 14, 21, respectively.
A simple thickness measurement method based on the coherent homodyne CW THz system was demonstrated; it does not require precise control of the frequencies of the beat source, and only accurate scanning of the optical delay line is needed. Three beat frequencies are sufficient for measuring the thickness of a sample without considering the modulo 2π ambiguity. A novel compact 1.55 μm λ/4 phase-shifted dual-mode laser (DML) was developed as an optical beat source for the CW THz system. The thickness of a sample was accurately estimated from the measurements using the proposed method. Our results clearly show the possibility of a compact, simple, and cost-effective CW THz system for practical applications.
We report a high-speed (∼2 kHz) dynamic multiplexed fiber Bragg grating (FBG) sensor interrogation using a wavelength-swept laser (WSL) with a polygon-scanner-based wavelength filter. The scanning frequency of the WSL is 18 kHz, and the 10 dB scanning bandwidth is more than 90 nm around a center wavelength of 1,540 nm. The output from the WSL is coupled into the multiplexed FBG array, which consists of five FBGs. The reflected Bragg wavelengths of the FBGs are 1,532.02 nm, 1,537.84 nm, 1,543.48 nm, 1,547.98 nm, and 1,553.06 nm, respectively. A dynamic periodic strain ranging from 500 Hz to 2 kHz is applied to one of the multiplexed FBGs, which is fixed on the stage of the piezoelectric transducer stack. Good dynamic performance of the FBGs and recording of their fast Fourier transform spectra have been successfully achieved with a measuring speed of 18 kHz. The signal-to-noise ratio and the bandwidth over the whole frequency span are determined to be more than 30 dB and around 10 Hz, respectively. We successfully obtained a real-time measurement of the abrupt change of the periodic strain. The dynamic FBG sensor interrogation system can be read out with a WSL for high-speed and high-sensitivity real-time measurement.
We demonstrate a tunable continuous-wave (CW) terahertz (THz) homodyne system with a novel detuned dual-mode laser diode (DML) and low-temperature-grown (LTG) InGaAs photomixers. The optical beat source with the detuned DML showed a beat frequency tuning range of 0.26 to over 1.07 THz. Log-spiral antenna integrated LTG InGaAs photomixers are used as THz wave generators and detectors. The CW THz radiation frequency was continuously tuned to over 1 THz. Our results clearly show the feasibility of a compact and fast scanning CW THz spectrometer consisting of a fiber-coupled detuned DML and photomixers operating in the 1.55-μm range.
In this paper, we propose an asymmetric split-loop resonator with an outer square loop (ASLR-OSL) based on vanadium dioxide (VO) which can actively control the transmission characteristics of a terahertz wave while maintaining a high quality factor of the asymmetric split-loop resonator (ASLR) by adding an outer square loop. The proposed ASLR-OSL demonstrated transmission characteristics similar to those of ASLR, and the transmission characteristics of ASLR-OSL were successfully controlled by directly applying a bias voltage. These results show a simple method for imposing active properties on a common metamaterial having a high quality factor by adding a loop structure.
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