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We exploit the modal confinement properties of metal-metal ridge waveguides to reduce the thickness of the active laser cores in both terahertz and mid-infrared quantum cascade lasers. Devices with active regions over 60 times thinner than the free-space emission wavelength are demonstrated. The devices surprisingly show only a modest increase in threshold current density compared with conventional-thickness...
Electro-optic sampling in ZnTe is used to phase-lock the line of a 2.5 THz quantum cascade laser to the repetition rate of a femtosecond fibre laser and to perform an absolute measurement of the laser emission frequency.
We report here a compact and efficient sensing technique that utilises the self-mixing effect in terahertz Quantum Cascade Lasers (QCLs). A terahertz QCL is used both for the emission and the detection of light. Sensors based on this technique promise high sensitivity, simplicity of optical design and the potential for implementation in monolithic arrays.
This paper presents an algorithm to extract the region of interest (ROI) from the palm print image of the Hong Kong PolyU large-scale palm print database (version 2). Competitive coding method is used for feature extraction. Coding based methods are among the most promising palm print recognition methods because of their small feature size, fast matching speed, and high verification accuracy. Competitive...
We demonstrate that the cavity resonance frequency - the round-trip frequency - of terahertz quantum cascade lasers can be injection-locked by direct modulation of the bias current using an RF source. Metal-metal and single-plasmon waveguide devices with roundtrip frequencies up to 35GHz have been studied, and show locking ranges above 200MHz. Inside this locking range the laser round-trip frequency...
Gain and losses in a LO-phonon THz QCL are studied using TDS. At threshold the gain clamps at 25cm-1 and the gain FWHM is 0.6THz. At low biases, absorption features are observed below and above the laser frequency. They are shown to originate from the population of a parasitic electronic channel.
We describe a multiple-frequency imaging system based on an electrically-tunable terahertz (THz) frequency quantum cascade laser (QCL). The transverse resolution of the system was measured using gold-on-quartz resolution targets, and shown to remain unchanged as the radiation wavelength increased. This was explained through measurement of the far-field emission profile of the QCL. Using this imaging...
We report the performance of 3.5 THz quantum cascade lasers in which the laser cavities are formed by wet chemical etching and show that laser ridges can be obtained using angled facets. This opens up the possibility of monolithic integration of quantum cascade lasers into terahertz circuits.
The population inversion of a terahertz quantum cascade laser is placed out of equilibrium using an integrated Auston switch. As a result, the dynamic gain of the laser is no longer clamped at threshold by the mirror losses, and large amplification of input terahertz probe pulses is observed.
We demonstrate the phase-locking of Quantum Cascade Lasers emitting at 2.4 and 2.7Terahertz, to the repetition rate of a commercial Er-doped fiber-fs-laser. We observe a linewidth of the beat-note signal with a signal-to-noise of 80dB in 1Hz bandwidth.
In this paper a new approach is proposed to recognize gender from the face image. This approach will detect the face from the given image. Radon and Wavelet Transforms are combined to extract key facial features for each face images of male and female. These features will be used to classify the face images of each pattern. We have compared the DCT extracted face feature with our face feature extracted...
We have used the Pockels effect in ZnTe to demonstrate that the frequency and the phase of Quantum Cascade Lasers emitting at 2.4 and 2.7 Terahertz can be actively stabilized to the n-th harmonic of the 90 MHz repetition rate of a commercial, mode-locked Er-doped fiber-laser. The beating between the stabilized QCL frequency and the harmonic of the repetition rate yielded a signal-to-noise ratio >;...
A 3.1THz phonon depopulation-based quantum-cascade-laser is investigated using terahertz time domain spectroscopy. A gain of 25cm−1 and absorption features due to the lower laser level being populated from a parasitic electronic channel are highlighted.
A terahertz quantum cascade laser and an integrated Auston-switch are coupled to perform ultrafast gain switching. The resulting non-equilibrium gain is not clamped above laser threshold and large amplification of input terahertz pulses is demonstrated.
We report collimation of THz quantum-cascade lasers by patterning plasmonic structures on laser facets. A beam divergence angle of ∼10 degrees and an increase of the collected power by a factor of ∼5 are demonstrated.
Semiconductor microstructures can be used to tailor the dispersion properties of surface plasmon polaritons in the terahertz (THz) frequency range, and therefore can be used as important building blocks for terahertz optical devices. The physical principles of three structures are discussed: plasmonic second-order gratings, designer (spoof) surface plasmon polariton structures, and channel polariton...
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