Terahertz attenuation and dispersion characteristics of coplanar transmission lines

Frankel, M.Y.; Gupta, Sandeep; Valdmanis, J. A.; Mourou, G.

doi:10.1109/22.81658

Cited by 292 publications

(164 citation statements)

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“…The effect of diffusion of quasiparticles from the central strip at the antenna feed is therefore negligible. Furthermore we checked that for this geometry radiation losses are a factor 10 lower than absorption in the superconductor 39 . The measured energy gap in the FTS response occurs at 324 GHz, corresponding to a T c of 4.4 K, assuming 2∆ = 3.52k B T c .…”

mentioning

confidence: 99%

The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band

Visser

Yates

Guruswamy

et al. 2015

Applied Physics Letters

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We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on the response drops to half the maximum response at twice the pairbreaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice this is the first measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different nonequilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.In a superconductor at low temperature, most of the electrons are bound in Cooper pairs. These pairs can be broken into quasiparticles by absorbing photons with an energy larger than the binding energy. This mechanism is frequently used to detect submillimetre and terahertz radiation using conventional superconductors such as aluminium. Pair-breaking detectors are usually assumed to measure the number of quasiparticles created by the absorbed radiation. The observable that measures the number of quasiparticles varies from the complex conductivity for microwave kinetic inductance detectors 1 (MKIDs), the current through a tunnel junction 2 to the capacitance of a small superconducting island 3 . These observables are mainly sensitive to quasiparticles with an energy close to the gap energy of the superconductor, ∆. The working principle of these detectors is usually explained in terms of an effective number of quasiparticles which is maintained by a balance between the radiation power and electron-phonon interaction (recombination) 4 . To convert the power (P ) into a number of quasiparticles (N qp ), the quasiparticle creation efficiency η pb is introduced, which compares the actual N qp with the maximum possible N qp when all created quasiparticles would have an energy ∆. Since Cooper pairs have a binding a) Electronic mail: p.j.devisser@tudelft.nl; Current address: Department of Quantum Matter Physics, University of Geneva, Geneva 1211, Switzerland energy of 2∆, a photon with an energy in between 2∆ and 4∆ can still only create two quasiparticles. The rest of the energy is lost through electron-phonon scattering, hence η pb < 1. For higher energies η pb depends on the phonon trapping factor, which determines whether high energy phonons are directly lost or can break an additional pair. η pb is therefore not an efficiency in the sense that photons are lost, but it reduces the detector responsivity. MKIDs are superconducting microwave resonators which sense the number of quasiparticles through the complex conductivity of the superconductor. The phase response (θ) of such a resonator can be approximated bywhere σ 2 is the imaginary part of the complex conductivity. For the last propo...

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mentioning

confidence: 99%

The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band

Visser

Yates

Guruswamy

et al. 2015

Applied Physics Letters

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“…From 500 GHz, α R increases in these two transmission lines. In CPW, α R reaches 0.43 dB/mm at 1 THz following a cubic relation with the frequency as in [10], and in microstrip, α R equals 1.48 dB/mm at 1 THz. This originates from the shock wave radiation when a V p mismatch exists between the main propagating mode and the substrate wave.…”

Section: Radiation Losses α Rmentioning

confidence: 85%

“…These limitations can be overcome by planar waveguides such as: microstrip [7][8][9], coplanar waveguide (CPW) [10][11][12], coplanar stripline (CPS) [10,13,14], slotline [15,16] or the planar Goubau line [17]. But all these waveguides have much more losses than metallic and dielectric waveguides.…”

Section: Introductionmentioning

confidence: 99%

Comparison and Optimization of Dispersion, and Losses of Planar Waveguides on Benzocyclobutene (Bcb) at THZ Frequencies: Coplanar Waveguide (Cpw), Microstrip, Stripline and Slotline

Cao¹,

Grimault-Jacquin

Aniel³

2013

PIER B

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Abstract-This paper proposes an investigation in the terahertz (THz) frequency range of the dispersion and an individual quantitative treatment of the losses of the most classical microwave waveguides (coplanar, slotline, microstrip and stripline) numerically led in three dimensions (3D). An original strategy has been used to quantify radiation losses associated with leaky modes. A very low THz permittivity polymer (benzocyclobutene (BCB)) was used as a very convenient substrate to be easily grafted as a THz environment of integrated passive or/and active devices. Direct comparisons of the losses and the dispersion have been performed following two criteria: a constant characteristic impedance Z c fixed at 100 Ω and a constant effective width W eff fixed at 30 µm. The best waveguides are microstrip (α T = 2.52 dB/mm for Z c = 100 Ω and for W/H = 35/50 µm (with W the strip width and H the substrate height) and α T = 2.29 dB/mm for W eff = 30 µm at 1 THz with H = 30 µm) and stripline (with quasi-null radiation losses and the best quality factor Q T = 63 for Z c = 100 Ω). The large dispersion and radiation losses of the slotline (SL) can be reduced with a thick BCB encapsulation to enhance the THz signal. The coplanar waveguide (CPW) remains in a medium position. Besides the parasitic mode (SL) and low Q T problems due to mainly ohmic losses, its major advantage is its planar geometry allowing to an easy circuit integration with THz sources, amplifiers and detectors based on semiconductor. Consequently, these THz studies on BCB microwave standard waveguides open to various perspectives to carry out a broad panel of integrated THz circuits.

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“…The antenna presented here has some distinct advantages over thin membrane antennas: the metallic-slit based antenna has lower conductor loss due to increased conductor surface area, it is less delicate due to the material and thickness, and the manufacturing process doesn't require harsh etchants (EDP, HF, etc). Other substrate-based antennas [2][3][4] which closely model coplanar strip/slotline configurations can have a total loss of ≈17dB/mm at 1 THz [24], whereas the free-space metallic-slit geometry has a loss of <1dB/mm at 1 THz [16]. To note, these numbers are not representative of all designs, but they illustrate the possible large difference between the expected losses.…”

Section: Designmentioning

confidence: 94%

THz-TDS using a photoconductive free-space linear tapered slot antenna transmitter

Smith¹,

Jooshesh²,

Zhang³

et al. 2017

Opt. Express

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A near-field edge-coupled photoconductive free-space linear tapered slot antenna has been constructed as a planar alternative to the standard photoconductive switch coupled to a silicon substrate lens. The temporal response along the optical axis is investigated to ensure the structure itself does not introduce pulse distortion which would fundamentally limit the usefulness of the structure. Experimental results show that a 1.6 THz bandwidth with a ≈50dB dynamic range is achievable with the new structure which is comparable to our reference experiment with a standard silicon substrate lens. The investigated structure has the added benefit of a potential substantial physical size reduction and can also be used to excite waveguides in the near-field.

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Terahertz attenuation and dispersion characteristics of coplanar transmission lines

Cited by 292 publications

References 10 publications

The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band

The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band

Comparison and Optimization of Dispersion, and Losses of Planar Waveguides on Benzocyclobutene (Bcb) at THZ Frequencies: Coplanar Waveguide (Cpw), Microstrip, Stripline and Slotline

THz-TDS using a photoconductive free-space linear tapered slot antenna transmitter

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