A Fast Method for Analysis of Guided Waves and Radiation From a Nano-Scale Slit Loaded Waveguide for a THz Photoconductive Source (original) (raw)

Introduction to THz Wave Photonics

2010

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Terahertz waveguides

Journal of the Optical Society of America B, 2000

Quasi-optical techniques are used to efficiently couple freely propagating pulses of terahertz (THz) electromagnetic radiation into circular and rectangular metal waveguides. We have observed very dispersive, low-loss propagation over the frequency band from 0.65 to 3.5 THz with typical waveguide cross-section dimensions on the order of 300 m and lengths of 25 mm. Classical waveguide theory is utilized to calculate the coupling coefficients into the modes of the waveguide for the incoming focused THz beam. It is shown that the linearly polarized incoming THz pulses significantly couple only into the TE 11 , TE 12 , and TM 11 modes of the circular waveguide and the TE 10 and TM 12 modes of the rectangular guide. The propagation of the pulse through the guide is described as a linear superposition of the coupled propagating modes, each with a unique complex propagation vector. This picture explains in detail all the observed features of the THz pulse emerging from the waveguide. We demonstrate both theoretically and experimentally that it is possible to achieve TE 10 single-mode coupling and propagation in a suitably sized rectangular waveguide for an incoming focused, linearly polarized THz pulse with a bandwidth covering many octaves in frequency and that overlaps more than 35 waveguide modes. Finally, to facilitate the application of these THz waveguides to THz time-domain spectroscopy of various configurations of dielectrics in the waveguide including surface layers, we present analytic results for the absorption and the dispersion of such layers.

Optimization design of optical waveguide control by nanoslit-enhanced THz field

Photonics and Nanostructures - Fundamentals and Applications, 2013

We discuss design issues of devices which were proposed recently [Opt. Lett. 37 (2012) 3903] for terahertz (THz) control of the propagation of an optical waveguide mode. The mode propagates through a nonlinear dielectric material placed in a metallic nanoslit illuminated by THz radiation. The THz field in the slit is strongly localized and thus significantly enhanced, facilitating nonlinear interactions with the dielectric waveguide material. This enhancement can lead to notable changes in the refractive index of the waveguide. The closer the waveguide is to the slit walls, the higher the nonlinear effects are, but with the cost of increasing propagation losses due to parasitic coupling to surface plasmon polaritons at the metal interfaces. We analyze several optical waveguide configurations and define a figure of merit that allows us to design the optimal configuration. We find that designs with less overlap of the THz and optical fields but also with lower losses are better than designs where both these parameters are higher. The estimated terahertz field incident onto the metallic nanoslit required to manipulate the waveguide mode has reasonable values which can be achieved in practice.

THz generation using 800 to 1550 nm excitation of photoconductors

2009

We demonstrate the efficient generation of terahertz (THz) radiation from Fe-doped InGaAs-based photoconductive antennas. We present time-domain data showing generation of pulsed THz radiation from antennas fabricated on two different wafers, optimized to maximize the near-infrared-to-THz conversion efficiency. Detection was performed using both (110) ZnTe and GaP crystals, with pump and probe wavelengths being adjusted from 800 nm to 1550 nm using a cavity-tuned OPO pumped by a pulsed near-infrared Ti:Sapphire laser.

Design and characterization of optical-THz phase-matched traveling-wave photomixers

Terahertz and Gigahertz Photonics, 1999

Design and characterization of optical-THz phase-matched traveling-wave photomixers for difference-frequency generation of THz waves are presented. A dc-biased coplanar stripline fabricated on low-temperature-grown GaAs is illuminated by two non-collinear laser beams which generate moving interference fringes that are accompanied by THz waves. By tuning the offset angle between the two laser beams, the velocity of the interference fringe can be matched to the phase velocity of the THz wave in the coplanar stripline. The generated THz waves are radiated into free space by the antenna at the termination of the stripline. Enhancement of the output power was clearly observed when the phase-matching condition was satisfied. The output power spectrum has a 3-dB bandwidth of 2 THz and rolls off as-9 dB/Oct which is determined by the frequency dependent attenuation in the stripline, while the bandwidth of conventional photomixer design has the limitation by the RC time constant due to the electrode capacitance. The device can handle the laser power of over 380 mW, which is 5times higher than the maximum power handring capability of conventional small area devices. The results show that the traveling-wave photomixers have the potential to surpass small area designs, especially at higher frequencies over 1 THz, owing to their great thermal dissipation capability and capacitance-free wide bandwidth.

Emergence of THz technologies and design and optimisation low-loss waveguides and devices

8th International Conference on Electrical and Computer Engineering, 2014

THz is an emerging technology with many important applications in imaging and sensing, but due to lack of suitable low-loss waveguides future progress can be limited. A rigorous full-vectorial modal solution approach based on the computationally efficient finite element method is used to find the propagation properties of THz waveguides. Design approaches are presented to reduce the modal loss of such waveguides. Designs of several THz devices, including quantum cascade lasers, power splitters and narrow-band filters are also presented.