Distributed photomixers

Duerr, E.K.; McIntosh, K. A.; Verghese, S.

doi:10.1109/cleo.2000.907150

Cited by 3 publications

(2 citation statements)

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“…We can relate the photon density m to the emitted light power L via the expression: 16) where τ m is the mirror photon escape time, defined by τ −1 m = α m v g . Given that the pumping rate is defined by The quantity in brackets is a dimensionless quantity that takes the role of an internal efficiency η i .…”

Section: C1 Above Thresholdmentioning

confidence: 99%

Terahertz quantum-cascade lasers

2007

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The development of the terahertz frequency range (1-10 THz, λ ≈ 30-300 µm) has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) that operate in the terahertz with photon energies below the semiconductor Reststrahlen band. Photons are emitted via electronic intersubband transitions that take place entirely within the conduction band, where the wavelength is chosen by engineering the well and barrier widths in multiple-quantum-well heterostructures. Fabrication of such long wavelength lasers has traditionally been challenging, since it is difficult to obtain a population inversion between such closely spaced energy levels (hω ≈ 4-40 meV), and because traditional dielectric waveguides become extremely lossy due to free carrier absorption.This thesis reports the development of terahertz QCLs in which the lower radiative state is depopulated via resonant longitudinal-optical phonon scattering. This mechanism is efficient and temperature insensitive, and provides protection from thermal backfilling due to the large energy separation (∼36 meV) between the lower radiative state and the injector. Both properties are important in allowing higher temperature operation at longer wavelengths. Lasers using a surface plasmon based waveguide grown on a semi-insulating (SI) GaAs substrate were demonstrated at 3.4 THz (λ ≈ 88 µm) in pulsed mode up to 87 K, with peak collected powers of 14 mW at 5 K, and 4 mW at 77 K.Additionally, the first terahertz QCLs have been demonstrated that use metalmetal waveguides, where the mode is confined between metal layers placed immediately above and below the active region. These devices have confinement factors close to unity, and are expected to be advantageous over SI-surface-plasmon waveguides, especially at long wavelengths. Such a waveguide was used to obtain lasing at 3.8 THz (λ ≈ 79 µm) in pulsed mode up to a record high temperature of 137 K, whereas similar devices fabricated in SI-surface-plasmon waveguides had lower maximum lasing temperatures (∼92 K) due to the higher losses and lower confinement factors.This thesis describes the theory, design, fabrication, and testing of terahertz quantum cascade laser devices. A summary of theory relevant to design is presented, 3 including intersubband radiative transitions and gain, intersubband scattering, and coherent resonant tunneling transport using a tight-binding density matrix model. Analysis of the effects of the complex heterostructure phonon spectra on terahertz QCL design are considered. Calculations of the properties of various terahertz waveguides are presented and compared with experimental results. Various fabrication methods have been developed, including a robust metallic wafer bonding technique used to fabricate metal-metal waveguides. A wide variety of quantum cascade structures, both lasing and non-lasing, have been experimentally characterized, which yield valuable information about the transport ...

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Section: C1 Above Thresholdmentioning

confidence: 99%

Terahertz quantum-cascade lasers

2007

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“…Duerr et al. 7 In this paper, we will propose and analyze a combination of an ultrafast photoconductive optical waveguide with HTS CPW electrodes in a traveling-wave photodetector. 8 Our theoretical investigation comprises of optical waveguide analysis, optical-to-THz conversion calculation and THz CPW analysis in an integrated photoconductive/superconductive CPW-loaded rib waveguide photodetector.…”

Section: Introductionmentioning

confidence: 99%

THz signal generation/propagation in an integrated traveling-wave superconductive/photoconductive heterodyne photodetector

Majedi

Ghamsari

2006

SPIE Proceedings

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The ultrafast and sensitive detection of an optical beat signal generated from an optical heterodyne system in an integrated traveling-wave photoconductive detector with high-temperature superconducting (HTS) coplanar electrode lines has been introduced for generating THz signals.While the optical beat signal has been absorbed by photoconductive substrate and an HTS center strip, the THz signal is gradually bulit up on the HTS coplanar waveguide (CPW). The kinetic inductive photoresponse of the HTS strip contributes excessively in the generation of multi-THz signal while the response of the photoconductor substrate decreases with increasing THz frequency. A rigorous optical analysis of a multilayer waveguide in conjunction of optical-to-THz signal conversion analysis have been carried out to find the external conversion efficiency of such a photodetector. Our simulation shows that the GaAs-based structure with YBCO electrode at1.5 µm exhibits more output THz power than its Si counterpart in 850 nm wavelength.

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All–optoelectronic continuous–wave terahertz systems

Löffler

Siebert

Quast

et al. 2003

Philosophical Transactions of the Royal Society of London. Seri

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We discuss the optoelectronic generation and detection of continuous-wave terahertz (THz) radiation by the mixing of visible/near-infrared laser radiation in photoconductive antennas. We review attempts to reach higher THz output-power levels by reverting from mobility-lifetime-limited photomixers to transit-time-limited p-i-n photodiodes. We then describe our implementation of a THz spectroscopy and imaging-measurement system and demonstrate its imaging performance with several examples. Possible application areas of THz imaging in the biomedical field and in surface characterization for industrial purposes are explored.

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Distributed photomixers

Cited by 3 publications

References 50 publications

Terahertz quantum-cascade lasers

Terahertz quantum-cascade lasers

THz signal generation/propagation in an integrated traveling-wave superconductive/photoconductive heterodyne photodetector

All–optoelectronic continuous–wave terahertz systems

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