A THz transverse electromagnetic mode two-dimensional interconnect layer incorporating quasi-optics

Abstract

We report the demonstration of a planar THz interconnect layer capable of transmitting subpicosecond pulses in the transverse electromagnetic ͑TEM͒ mode over arbitrarily long paths with low absorption and no observable group velocity dispersion. Quasioptical elements are incorporated within the interconnect layer forming a configurable THz bandwidth TEM-mode planar interconnect with negligible group velocity dispersion and low loss. For a 146 mm guided path length, including four reflections, the pulses are broadened by the frequency dependent absorption of the interconnect layer from 0.28 to 0.32 ps, and attenuated by the factor 0. Terahertz ͑THz͒ waveguides have recently been demonstrated to be an alternative to high-speed coplanar transmission lines. [1][2][3][4] For frequencies up to 3.5 THz, the attenuation coefficient of metal waveguides has been shown to be less than 1/10 that of lithographically defined transmission lines on dielectric substrates. Within the passband of the waveguide, the measured power coupling into the waveguide was typically 40% of the incoming THz power. For the single conductor circular and rectangular metal waveguides the observed excessive THz pulse broadening was caused by the extreme group velocity dispersion ͑GVD͒ near the cutoff frequency. Such pulse broadening does not occur for the transverse electromagnetic ͑TEM͒ mode of a parallel-plate metal waveguide, since it has no cutoff frequency. The group and phase velocities of the TEM mode are determined solely by the dielectric. Recent experiments have shown efficient quasioptic coupling of freely propagating subpicosecond ͑subps͒ pulses of THz radiation into parallel-plate metal waveguides and the subsequent low-loss, single TEM mode propagation exhibiting negligible GVD. 3,4 Consequently, a THz interconnect, 5 capable of propagating subps pulses with minimal loss and no distortion, has been realized.However, all of these demonstrations involved quasioptical input and output coupling of freely propagating THz beams into and out of the THz waveguides. The remaining challenge is to efficiently connect the THz TEM waveguide with integrated circuitry. To address this problem we have begun to study a macroscopic planar interconnect approach using two-dimensional ͑2D͒ quasioptics. The interconnect consists of two relatively large ͑many centimeters͒ metal plates separated from each other by approximately 100 m. Within this 100 m thick, free-space interconnect layer, planar quasioptical components are placed to guide, collimate, or focus the propagating THz TEM waves. This 2D planar quasioptics approach has the potential to realize a spatially localized point-to-point interconnect with the low-loss, broad bandwidth, and negligible GVD of the single-mode THz TEM planar metal waveguides. This 2D interconnect is related to previous works by Mink, in which he proposed and demonstrated the hybrid dielectric slab-beam waveguide ͑HDSBW͒. 6,7 The HDSBW uses two distinct waveguiding principles to guide electromagnetic waves in a dielectric slab...

THz Sommerfeld wave propagation on a single metal wire

“…1͑b͒ average power of 10 mW, enabling the measurement of the propagated THz pulses, by changing the relative time delay between the excitation and detection pulses. [1][2][3][4][5] As shown in Fig. 1͑c͒, the wire is supported by two tightly fitting Teflon disks of 3 mm thickness.…”

“…[1][2][3][4] Among various types of THz waveguides, parallelplate metal waveguides have attracted considerable attention due to the low loss and low group velocity dispersion in the transverse-electromagnetic ͑TEM͒ mode propagation. [2][3][4] For a parallel-plate copper waveguide with 100 m plate separation, the typical frequency-dependent amplitude absorption coefficient caused by the finite conductivity of copper is approximately 0.06 cm −1 at 0.5 THz, [2][3][4] and is proportional to the square root of frequency and inversely proportional to the plate separation. Quasioptic coupling has been the primary coupling mechanism in these studies, where the THz pulses are coupled into and out of the waveguides by hyperspherical or plano-cylindrical silicon lenses.…”

Parallel plate THz transmitter

“…1,2 Very recently, quasioptical components have been demonstrated within these guides and have demonstrated a viable means of confocally coupling the TEM guided mode with minimal loss and dispersion for arbitrarily long path lengths. 3 The so-called two-dimensional interconnect layer confines the beam to a plane and guides both dimensions orthogonal to the direction of propagation. 3 The remaining challenge to the realization of integrated guided wave TEM-mode THz bandwidth structures is the ability to generate and detect THz within the waveguide.…”

“…3 The so-called two-dimensional interconnect layer confines the beam to a plane and guides both dimensions orthogonal to the direction of propagation. 3 The remaining challenge to the realization of integrated guided wave TEM-mode THz bandwidth structures is the ability to generate and detect THz within the waveguide.…”

Guided-wave THz time-domain spectroscopy of highly doped silicon using parallel-plate waveguides

“…These parallel-plate structures have been used to demonstrate two-dimensional interconnect layers [3], sense nanometre water layers [4], study photonic crystals [5], and for building biosensing systems [6]. This Letter describes another novel use of these structures for the characterisation of highly conductive, optically dense materials resolving some of the fundamental problems associated with standard THz time-domain spectroscopy (THz-TDS) [7,8].…”