Terahertz time-domain spectroscopy (THz-TDS) is a useful technology that has a wide range of applications. However, the conventional THz-TDS system is very time-consuming for taking time domain measurements due to the usage of the mechanical stepper. While the existing rapid scan method introduces greater complexity to the system. We developed a rapid scan system for real-time THz acquisition using a rapid shaker as the delay line and utilizing a Michelson interferometer to achieve high-accuracy position tracking of the delay line, which enables real-time time-domain measurement for high-frequency THz electrical fields.
Although advances in THz radiation sources have resulted in a wide variety of applications in communications, security scanning, medical imaging, spectroscopy, etc., an absence of viable sources has stalled the transition of THz technologies from the laboratory into the real world. This has in turn led to a resounding lack of commercially available THz components. Typical computer numerical control (CNC) machining tolerances are on the order of 100 µm, which is much higher than the submicron accuracy that would be ideal for the fabrication of THz components. Here, we present a twisted waveguide designed to rotate the electric field polarisation of free space THz radiation from 1 THz to 2.5 THz by 90° with near perfect efficiency, fabricated using two-photon lithography. We envision such methods being utilised for the quick prototyping of various passive THz components in both the laboratory and commercial settings.
Increases in data bandwidth requirements are constantly pushing wireless communications networks to frequencies. With operating frequencies starting to approach the Terahertz (THz) band, it is important to develop compact, chip-based THz radiation sources that are compatible with both the semiconductor industry and the Si photonics scene. In recent years, spintronic THz emitters, thin film heterostructures with a stack thickness of 5 nm capable of producing THz pulses via femtosecond laser pulse excitation have been the subject of much interest due to their efficiency, small footprint, and ease of integration with various platforms. Here, we present spintronic THz radiation emitters on Si and SiO2 substrates integrated with optical waveguides that allow for modulation of the generated THz radiation power by up to 87% via variation of the optical pump polarization. As a result of the gradual trend towards higher frequencies, we envision such structures as being utilised for various on-chip applications alongside electronic and photonic circuits.
We present an efficient and compact laser pulse-pumped terahertz (THz) source suitable for on-chip applications. The THz emitter itself consists of a W(1.8 nm)/Fe(2 nm)/Pt(1.8 nm) metallic trilayer deposited via DC magnetron sputtering. Waveguides and a horn antenna are 3D-printed via 3D lithography and integrated with the emitter, resulting in a 19.6 dB increase in the measured THz power emitted at the design frequency of 1.5 THz.
This conference presentation, “Multi-band photonic sources based on phase-matched second-order nonlinear interactions” was presented at the Ultrafast Phenomena and Nanophotonics XXVI conference at SPIE Photonics West 2022.
We investigate the effect of surface oxide contamination on the terahertz (THz) emission via the inverse spin Hall effect from spintronic Fe/Pt bilayers pumped using femtosecond laser pulses. The metallic films were grown on Si and quartz substrates, both with and without a 300 nm Al2O3 spacer layer. The presence of the Al2O3 layer between the substrate and the metallic films results in a 350% increase in the measured THz electric field in the case of Si substrates, while an increase of 10% is observed when using quartz substrates. X-ray photoelectron spectroscopy (XPS) is used to gain insight into the elemental composition of the emitters, and the presence and intensity of iron oxide peaks explains the difference in the emitted THz signals.
Most recently, electrochromic (EC) oxides, such as WO3, have transcended far beyond their traditional scope of transmission modulation in smart windows. The ionically facilitated EC effect, leads to an extraordinary increase in excess charge carriers in the host oxide, effectively doping WO3 up to 1022 cm-3 electrons. With the protonation doping, the dielectric properties of the given oxide can be altered dynamically and locally. Hence, WO3 changes its refractive index from n = 1.9 to 2.3, and its extinction by Δ𝑘 = 0.5 in the near infrared (NIR). Here, we introduce a plasmonic, EC (‘plasmochromic’) nanowaveguide modulator, for ultrahigh modulation depth. WO3 is integrated into a plasmonic metalinsulator- metal (MIM) waveguide structure with a dual-function waveguide core containing amorphous LiNbO3 (LN). In this novel architecture, LN provides sufficient ionic conduction for EC switching, while simultaneously supporting optical mode propagation. By decoupling the ionic pathway and the direction of plasmon propagation, the EC waveguide achieves unprecedented modulation speed and depth when compared to traditional EC devices. FDTD simulations predict a maximum modulation depth of 80 dB for 20 μm waveguide length, while measured values show up to 2.5 dB/μm modulation with switching times of a few seconds. The waveguide platform further provides great retention (> 20 h) of the switching state, while allowing very low operating voltages with a figure of merit of 8 dB/V. We envision EC oxide to provide pathways to dynamic photonic devices under low voltage settings, where high modulation is necessary.
As of late, research related to plasmonic-electrochromic (“plasmochromic”) devices and nanostructures has gained significant interest from a multidisciplinary field of researchers. The dynamic optical properties of electrochromic materials in combination with the enhanced light-matter interaction of plasmonic nanostructures and metal films, makes this new class of devices contenders in the fields of color printing, light, and resonance modulation. While conventionally used in electrochromic smart windows, plasmochromic devices use the individual parts of the refractive index. The most important electrochromic material is tungsten oxide (WO3), which exhibits a high change in the refractive index () and extinction (Delta k=0.5) during reversible ion intercalation. Here, plasmochromic resonance modulation is used to create a dynamic reflective display with a wavelength modulation of over 64 nm in the visible range. The results are verified via FDTD analysis, which projects a maximum wavelength shift of over 100 nm.
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