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Showing papers in "Electronics Letters in 2018"


Journal ArticleDOI
TL;DR: A long short-term memory based recurrent neural network is proposed and used for automatically identifying hardware-specific features and classifying transmitters and demonstrated the effectiveness of the proposed scheme.
Abstract: Author(s): Wu, Q; Feres, C; Kuzmenko, D; Zhi, D; Yu, Z; Liu, X; Liu, X | Abstract: RF fingerprinting is an emerging technology for identifying hardware-specific features of wireless transmitters and may find important applications in wireless security. In this study, the authors present a new RF fingerprinting scheme using deep neural networks. In particular, a long short-term memory based recurrent neural network is proposed and used for automatically identifying hardware-specific features and classifying transmitters. Experimental studies using identical RF transmitters showed very high detection accuracy in the presence of strong noise (signal-to-noise ratio as low as −12 dB) and demonstrated the effectiveness of the proposed scheme.

71 citations


Journal ArticleDOI
TL;DR: A new image encryption method based on permutation–diffusion architecture is proposed, which is more sensitive to input image since input parameters required for secure key generation depend upon the input image.
Abstract: A new image encryption method based on permutation–diffusion architecture is proposed. Permutation and diffusion operations are performed row-wise and column-wise on input image. To permute and diffuse the pixels, Lorenz-like chaotic system with varying bifurcation parameter is used to generate six random sequences. Initially, three sequences help in change the pixel’s position and next three used to diffuse the pixels. The main benefit of this method is that it is more sensitive to input image. Since input parameters required for secure key generation depend upon the input image.

67 citations


Journal ArticleDOI
TL;DR: In this paper, a novel Zeonex-based porous fiber is proposed for biomedical imaging and polarisation preserving applications of terahertz waves, which shows high numerical aperture of 0.48, high birefringence of 0,039 and a flattened dispersion of 1.07 ± 0.05 ps/THz/cm.
Abstract: A novel Zeonex based porous fibre is proposed for biomedical imaging and polarisation preserving applications of terahertz waves. The standard finite element method is used to simulate the propagation characteristics of the fibre that shows high numerical aperture of 0.48, high birefringence of 0.039 and a flattened dispersion of 1.07 ± 0.05 ps/THz/cm. In addition, the fibre also possesses low effective material loss and negligible confinement loss in the terahertz frequency band.

61 citations


Journal ArticleDOI
TL;DR: In this article, a four-port MIMO antenna design focused on the sub-6 GHz fifth generation wireless communication application is presented, which does not need any other decoupling structure for achieving isolation between multiple ports.
Abstract: A four-port MIMO antenna design focused on the sub-6 GHz fifth generation wireless communication application is presented. The design does not need any other decoupling structure for achieving isolation between multiple ports. A combination of four single wideband antenna units results in the formation of a circular-shaped metallic disc in the ground plane of the proposed antenna. This disc acts as a pool of current with 180° phase difference leading to isolation between various ports. Diversity performance of the antenna is shown with the help of an envelope correlation coefficient using both S-parameter and far-field data. The radiation pattern of the proposed antenna has four lobes in four quadrants for proper reception of signals from different directions. A prototype of the designed antenna is fabricated and measured successfully.

61 citations


Journal ArticleDOI
TL;DR: In this paper, two ground radiation antennas with polarisation diversity performance were proposed for MIMO WLAN applications in wearable devices, which can simultaneously excite the vertical mode and horizontal mode of the ground plane and the phase difference between the two modes can be controlled by utilising an inductor-loaded metal strip in the ground planes, generating circular polarisation.
Abstract: Two ground radiation antennas with polarisation diversity performance were proposed for MIMO WLAN applications in wearable devices. The antennas can simultaneously excite the vertical mode and horizontal mode of the ground plane and the phase difference between the two modes can be controlled by utilising an inductor-loaded metal strip in the ground plane, generating circular polarisation. A 3:1 VSWR bandwidth of 140 MHz with high isolation (above 17 dB) and a 3 dB axial ratio bandwidth of 100 MHz was obtained. The opposite rotations generated by the two antennas resulted in good diversity performance, which was verified by the measured envelope correlation coefficient.

50 citations


Journal ArticleDOI
TL;DR: In this paper, the design and development of a low profile and compact single probe-fed metamaterial (MTM)-based circularly polarised (CP) antenna using the modified rectangular patch with two pairs of spiral strips and vias for 5.2/5.8 GHz WLAN applications is described.
Abstract: This work explains the design and development of a low profile and compact single probe-fed metamaterial (MTM)-based circularly polarised (CP) antenna using the modified rectangular patch with two pairs of spiral strips and vias for 5.2/5.8 GHz WLAN applications. The intended CP antenna mainly consists of two pairs of radiators and each radiator is realised by using epsilon negative (ENG) transmission line (TL) to generate zeroth-order resonance. CP characteristics are achieved by placing two radiators for x -polarised wave are orthogonally aligned to the other two radiators for y -polarised wave. The antenna radiating element offers a compact size of 0.24λ 0 × 0.22λ 0 with a low profile of 0.04λ 0 at 5.5 GHz. To confirm the characteristics of the intended MTM CP antenna design, the designed antenna is fabricated and measured. Measurement results show that the antenna obtains -10 dB impedance bandwidth of 610 MHz (10.86%) which is 2.3 times larger than the standard microstrip patch antenna and axial ratio bandwidth of 140 MHz (2.54%) is obtained.

50 citations


Journal ArticleDOI
TL;DR: In this article, a dielectric resonator (DR)-based multiple-input-multiple-output (MIMO) antenna with bi-directional pattern diversity is presented. But the back-to-back arrangement of cylindrical DR antennas DRAs (cDRAs) is not considered.
Abstract: This Letter presents a dielectric resonator (DR)-based multiple-input-multiple-output (MIMO) antenna with bi-directional pattern diversity. The back-to-back arrangement of cylindrical DR antennas DRAs (cDRAs) is one of the unique features of the proposed design. The cDRAs are placed on an FR4 substrate with a common ground plane. Each cDRA element is excited by two ports to establish a four-port MIMO antenna system. At ports 1 and 2, the top cDRA is excited via co-planar waveguide (CPW) fed conformal strip lines. In case of ports 3 and 4, the bottom cDRA is excited by microstrip line fed conformal strip lines. Isolation between all ports is improved (better than 18 dB) by generating orthogonal modes in the cDRAs and use of opposite excitations. Measured results confirm that the proposed four-port MIMO antenna system is useful for the frequency ranges between 5.4 and 6.0 GHz for WLAN applications.

48 citations


Journal ArticleDOI
TL;DR: In this article, a single section passively mode-locked InAs/InGaAs quantum dot laser directly grown on on an on-axis (001) GaP/Si substrate was demonstrated.
Abstract: We demonstrate, for the first time, a single section passively mode-locked InAs/InGaAs quantum dot laser directly grown on on-axis (001) GaP/Si substrate. The laser has a continuous-wave threshold current of 34 mA at 20°C. By forward biasing the laser gain section current at 470 mA, 490 fs pulse generation with 31 GHz repetition rate can be obtained. This simple femtosecond pulse generation structure with CMOS fabrication compatibility makes the laser a promising light source candidate in future large-scale silicon photonic applications.

47 citations


Journal ArticleDOI
TL;DR: In this article, the authors achieved single-channel 100 Gbit/s transmission using linear unit-ravelling carrier photodiodes and QAM-16 modulation format in the indoor case.
Abstract: The achievement of single-channel 100 Gbit/s transmission, using linear unitravelling carrier photodiodes and QAM-16 modulation format is reported. The wireless link has been done in the indoor case, considering the recent frequency standardised 300 GHz bands.

47 citations


Journal ArticleDOI
TL;DR: The authors propose a deep architecture based on LSTM recurrent neural networks (RNNs) to model the spatio-temporal features of network traffic and then propose a novel TM prediction approach based on deep L STM RNNs and a linear regression model that can achieve state-of-the-art TM prediction performance.
Abstract: This Letter investigates traffic matrix (TM) prediction that is widely used in various network management tasks. To fastly and accurately attain timely TM estimation in large-scale networks, the authors propose a deep architecture based on LSTM recurrent neural networks (RNNs) to model the spatio-temporal features of network traffic and then propose a novel TM prediction approach based on deep LSTM RNNs and a linear regression model. By training and validating it on real-world data from Abilene network, the authors show that the proposed TM prediction approach can achieve state-of-the-art TM prediction performance.

46 citations


Journal ArticleDOI
TL;DR: In this article, a dual-band substrate integrated waveguide (SIW) bandpass filter (BPF) based on complementary split-ring resonators (CSRRs) is proposed.
Abstract: A novel dual-band substrate integrated waveguide (SIW) bandpass filter (BPF) based on complementary split-ring resonators (CSRRs) is proposed. It consists of an SIW dual-mode cavity loaded by two additional CSRRs on its top layer. Both TE 102 and TE 201 modes in the cavity can be excited by the proper positions of the feeding lines. Two additional CSRRs are etched on the top layer coupled with the TE 102 and TE 201 modes, respectively, to achieve the dual-frequency operation. Four transmission zeros are generated in the vicinity of the passbands to improve the selectivity. To validate the design concept, a dual-band SIW BPF operating at 7.89 and 8.89 GHz is designed, simulated and measured. The measured results are in good agreement with the simulations.

Journal ArticleDOI
TL;DR: The effective capacity of a communications system using unified models is analysed and a comparison between the simulated and numerical results using both distributions over composite α − η − μ /gamma fading channels have been provided.
Abstract: The effective capacity of a communications system using unified models is analysed. To obtain a simple closed-form mathematically tractable expression, two different unified approximate models have been used. The mixture gamma distribution which is a highly accurate approximation approach has been first employed to represent the signal-to-noise ratio of fading channel. In the second approach, the mixture of Gaussian distribution which is another unified representation approach has been utilised. A comparison between the simulated and numerical results using both distributions over composite α − η − μ /gamma fading channels have been provided.

Journal ArticleDOI
TL;DR: The experimental results on real radar data demonstrate that the proposed method is capable of dealing with multiple drones with satisfactory classification accuracy.
Abstract: Many studies have demonstrated the capability of radar micro-Doppler signature for classifying micro-drones. However, most existing works on radar classification of drones are based on the assumption that the received signal is only reflected from a single drone. When multiple drones are present simultaneously, the existing methods of drone classification fail due to the superimposition of the micro-Doppler features of multiple drones. In this Letter, a method for detection of multiple drones is proposed. First the time–frequency spectrogram is converted into the cadence-velocity diagram (CVD), which expresses how the curves in the time-frequency-domain repeat. Then the cadence frequency spectrum (CFS), as the basis vector of the training data from each class, of the CVD is extracted. Finally, the K-means classifier is used to recognise the component of multiple micro-drones based on the CFS. The experimental results on real radar data demonstrate that the proposed method is capable of dealing with multiple drones with satisfactory classification accuracy.

Journal ArticleDOI
TL;DR: In this article, the performance of the effective capacity metric under Fisher-Snedecor F fading channels is investigated, and a novel exact closed-form expression for effective capacity is derived.
Abstract: The performance of the effective capacity metric under Fisher–Snedecor F fading channels is investigated. To this end, a novel exact closed-form expression for the effective capacity is derived. Furthermore, in order to gain more insight, a simple asymptotic expression at the high signal-to-noise ratio regime is also provided. Additionally, expressions for the effective capacity of the Nakagami-m and Rayleigh distributions are deduced from the proposed results as special cases. The analytical results are compared to Monte-Carlo simulations to prove the correctness of the analysis. The results show that fading has a more positive influence on effective capacity performance than shadowing.

Journal ArticleDOI
TL;DR: A new convolutional neural networks architecture for fingerprint liveness detection problem that can provide a more robust framework for network training and detection than previous methods is introduced and is shown to provide higher accuracy when evaluated against the state-of-the-art method.
Abstract: With increasing markets for fingerprint authentication, there are also increasing concerns about spoofs or synthetically produced fingerprint identifications that can bypass the authentication process. In this Letter, the authors introduce a new convolutional neural networks (CNNs) architecture for fingerprint liveness detection problem that can provide a more robust framework for network training and detection than previous methods. The proposed method employs squared regression error for each receptive field without the usage of the fully connected layer. Such structure provides following advantages from the previous liveness fingerprint CNN. First, unlike the previous techniques which rely on the pre-trained features, the proposed CNN can be trained directly from fingerprints as the loss is minimised for each receptive field. Second, in contrast to the cross-entropy layer, the squared error layer allows them to set up a threshold value that can control the acceptable level of false positives or false negatives. Third, the absence of a fully connected layer allows them to crop the input fingerprints such that a trade-off between accuracy and computation time can be made without the negative effects of re-scaling. The proposed CNN is shown to provide higher accuracy for three out of four datasets when evaluated against the state-of-the-art method.

Journal ArticleDOI
TL;DR: A closed-form upper bound on the probability density function of the respective system capacity in a random field of moving blockers is obtained, which indicates that user connectivity to several base stations simultaneously while switching between them whenever the currently active connection becomes blocked.
Abstract: Outage events caused by dynamic blockage of a radio signal propagation path are one of the key challenges in 5G millimetre-wave (mmWave) cellular networks. To mitigate them, Third Generation Partnership Project standardisation has recently ratified multi-connectivity techniques aiming to enable user connectivity to several base stations simultaneously, while switching between them whenever the currently active connection becomes blocked. A closed-form upper bound on the probability density function of the respective system capacity in a random field of moving blockers is obtained.

Journal ArticleDOI
TL;DR: In this paper, a record output power of 16.1 W with a direct-bonded dual-SiC-heatspreader distributed Bragg reflector (DBR)-free active region at 10.5°C coolant temperature is reported.
Abstract: A record output power of 16.1 W with a direct-bonded dual-SiC-heatspreader distributed Bragg reflector (DBR)-free active region at 10.5°C coolant temperature is reported. A comparison in laser performance confirms the dual-heatspreader DBR-free configuration dissipates heat more effectively than the single-heatspreader geometry.

Journal ArticleDOI
TL;DR: In this paper, a Fermi-level managed barrier (FMB) diode was used for the first time for the heterodyne detection of terahertz waves.
Abstract: A Fermi-level managed barrier (FMB) diode was used for the heterodyne detection of terahertz waves for the first time. A quasi-optical module integrating an FMB diode and a broadband trans-impedance amplifier exhibited an intermediate frequency bandwidth of 11 GHz. A very low noise-equivalent-power of 1.1 × 10−18 W/Hz was achieved at ∼300 GHz with a very low local oscillator power of 6 × 10−6 W.

Journal ArticleDOI
TL;DR: In this article, a compact dual-band filtering power divider (FPD) is presented based on substrate-integrated waveguide (SIW) triangular cavities (TCs), by exploiting the first two modes in SIW TCs, the FPD is synthesized and designed with center frequencies of 5.5 and 8.3 GHz and identical absolute bandwidths of 0.8 GHz.
Abstract: A compact dual-band filtering power divider (FPD) is presented based on substrate-integrated waveguide (SIW) triangular cavities (TCs). By exploiting the first two modes in SIW TCs, the FPD is synthesised and designed with centre frequencies of 5.5 and 8.3 GHz and identical absolute bandwidths of 0.8 GHz. Two-section 50-Ω transmission lines loaded with two resistors are explored to achieve good isolation at two arbitrary frequency bands of the dual-band PFD. Good agreements can be observed between the measured and simulated results and better than 20-dB isolation within the two passbands has been successfully achieved.

Journal ArticleDOI
TL;DR: In this paper, a compact seventh-order wideband bandpass filter (BPF) with sharp roll-off skirts using coupled lines and open stubs (OSs)/shorted stubs(SSs) is proposed.
Abstract: A compact seventh-order wideband bandpass filter (BPF) with sharp roll-off skirts using coupled lines and open stubs (OSs)/shorted stubs (SSs) is proposed. Seven transmission poles in the passband and four deep transmission zeros from 0 to 2f 0 (f 0 denotes centre frequency of the passband) can be realised with the help of half-wavelength OSs and quarter-wavelength SSs. For demonstration, a wideband BPF prototype is designed, fabricated with a measured 3-dB fractional bandwidth of 78% (1.22–2.77 GHz) and transition band roll-off rates of over 175 dB/GHz. Good agreement between the simulations and measurements validates the design method.

Journal ArticleDOI
TL;DR: In this article, the complementary cumulative distribution function of peak-to-average power ratio (PAPR) of the so-called GreenOFDM is derived and computer simulations show that the proposed method outperforms any other SLM-OFDM proposed method so far.
Abstract: A new selected mapping orthogonal frequency division multiplexing modulation (SLM-OFDM) that generates urn:x-wiley:00135194:media:ell2bf05566:ell2bf05566-math-0001 symbol candidates using U inverse fast Fourier transform is presented. The complementary cumulative distribution function of peak-to-average power ratio (PAPR) of the so-called GreenOFDM is derived and computer simulations show that the proposed method outperforms any other SLM-OFDM proposed method so far. Also, GreenOFDM is compared with localised single carrier frequency division multiple access as it is a well-known PAPR reduction technique standardised for long-term evolution advanced.

Journal ArticleDOI
Linbin Zhang1, Huanpei Lv1, Dapeng Tan1, Fang Xu1, Jiaoliao Chen1, Guanjun Bao1, Cai Shibo1 
TL;DR: An adaptive quantum genetic algorithm based on artificial potential field and gradient of object function is proposed to optimise the solving process, and to obtain the optimal TSP scheme.
Abstract: Task sequence planning (TSP) is the key factor to the efficiency, stableness, and cost of a complex assembly system. To address the issue, an adaptive quantum genetic algorithm based on artificial potential field and gradient of object function is proposed to optimise the solving process, and to obtain the optimal TSP scheme. The simulation results indicate that the proposed algorithm can perform higher efficiency and stableness than the previously reported methods.

Journal ArticleDOI
TL;DR: In this article, the authors present a new analytical method for determining the parameter values for the single-diode model of photovoltaic (PV) panels and propose explicit equations for all the parameters of the model so that their values can be directly extracted from the data provided in the PV panel datasheet.
Abstract: In this Letter, the authors present a new analytical method for determining the parameter values for the single-diode model of photovoltaic (PV) panels. More specifically, the authors propose explicit equations for all the parameters of the model so that their values can be directly extracted from the data provided in the PV panel datasheet. The results show that the proposed method provides smaller errors between the calculated and experimental I-V curves than other analytical approaches.

Journal ArticleDOI
TL;DR: In this paper, a coplanar waveguide-fed multiple notched monopole antenna for ultra wide bandwidth (UWB) application is presented by introducing multiple inverted L-shaped stubs embedded within a polygonal shaped monopole antennas.
Abstract: A miniaturised coplanar waveguide-fed multiple notched monopole antenna for ultra-wide bandwidth (UWB) application is presented. By introducing multiple inverted L-shaped stubs embedded within a polygonal shaped monopole antenna, multiple notches can be achieved. A prototype antenna with triple band-notched at WiMAX, WLAN, and X-band is designed and fabricated. The proposed antenna has an impedance bandwidth of 3–12 GHz with a voltage standing wave ratio of <2 except for the selected notched bands. The main advantage of the antenna is its miniaturised size (21 × 14 mm2), as well as the straightforward design. The antenna has a unipolar configuration and good omnidirectional radiation pattern with negligible distortion which is suitable for UWB applications.

Journal ArticleDOI
TL;DR: Taking the advantages of symmetry of planar UWB antennas, asymmetric feeding scheme miniaturising technique is utilised to improve the inter-element isolation of a reference MIMO antenna made up of four previously designed slot antenna elements, closely-disposed orthogonally.
Abstract: With the increasingly multiple-input multiple-output (MIMO) applications in ultra-wideband (UWB) communication systems, antenna researchers face big challenges in designing compact operational geometries that meet the essential demand of achieving high isolation among antenna elements over the ultra-wide operating bandwidth. Disposed antenna elements orthogonally are seen to be the most common methodology to reduce mutual coupling of MIMO antenna by exploiting polarisation diversity performance. In such configuration, the mutual coupling mainly depends on the inter-element spacing, which it may not be in line with the compact structure. In this Letter, taking the advantages of symmetry of planar UWB antennas, asymmetric feeding scheme miniaturising technique is utilised to improve the inter-element isolation of a reference MIMO antenna made up of four previously designed slot antenna elements, closely-disposed orthogonally. Analytical results have validated the design concept and the improved MIMO antenna using the halved-chopped elements, showing good performance in terms of impedance matching, isolation, radiation features, signal correlation, and system fidelity factor.

Journal ArticleDOI
TL;DR: This Letter proposes a low-cost, single event double-upset tolerant latch which utilises interlocked nodes to keep data, clock gating in Muller C-element (MCE) to turn off the storage cell, a three-input MCE to block the soft error from the Storage cell and a weak keeper to prevent high impedance state.
Abstract: This Letter proposes a low-cost, single event double-upset tolerant latch which utilises interlocked nodes to keep data, clock gating (CG) in Muller C-element (MCE) to turn off the storage cell, a three-input MCE to block the soft error from the storage cell and a weak keeper to prevent high impedance state. The storage cell in the proposed latch has better reliability than the conventional triple path dual-interlocked storage cell (TPDICE). Most up-to-date single event double-upset (SEDU) tolerant latches are carried out with too large cost penalties. The proposed one saves up to 93.32% area-power-delay product (APDP) compared with one up-to-date SEDU tolerant latch and even saves 36.36% APDP compared with only single event upset (SEU) tolerant latch in the referential. Simulation results have verified SEU and SEDU tolerance of the proposed latch.

Journal ArticleDOI
TL;DR: Zhang et al. as discussed by the authors used scene segmentation to identify the horizon, regardless of whether the boundary between the sea and sky is smooth or blurry, or whether the image contains many line elements like the horizon.
Abstract: A method for horizon detection in maritime scenes using a scene parsing network is proposed. First, each pixel from an input image is segmented into corresponding semantic categories using a scene parsing network, which relies on a deep neural network. Then, the boundary information related to the horizon and the sea is extracted. Scene segmentation allows the proposed method to identify the horizon, regardless of whether the boundary between the sea and sky is smooth or blurry, or whether the image contains many line elements like the horizon. Moreover, least squares and median filtering are iteratively used to retrieve an accurate estimation of the horizon line. Experimental results demonstrate the superior accuracy of the proposed method to identify the horizon when compared to state-of-the-art methods.

Journal ArticleDOI
TL;DR: A wearable EEG device for in-ear SSVEP detection and monitoring is proposed, and the experiments demonstrated that the system can be utilised for unobtrusive monitoring ofSSVEP in BCI applications.
Abstract: Steady-state visual evoked potential (SSVEP) has been widely used in electroencephalogram (EEG)-based brain-computer interfaces (BCIs) due to its high information transfer rate (ITR) and short training time. Current methods usually measure SSVEP from electrodes on the scalp, which is an uncomfortable and time-consuming method. Furthermore, most research relies on expensive and non-portable EEG devices. To utilise BCIs in daily life, however, these are critical issues to address. Hence, a wearable EEG device for in-ear SSVEP detection is proposed. The system is 40 × 21 × 10.5 mm 3 and weighs 14.2 g, thus being light weight and wearable. Moreover, the system has a noise level of 0.11 μVrms, which is comparable with commercial EEG systems. Six subjects participated in an offline BCI experiment that consisted of six visual targets using the developed in-the-ear EEG system. The results showed a highest ITR of 11.03±4.18bits/min with an accuracy of 79.9 ± 13.1%, and the experiments demonstrated that the system can be utilised for unobtrusive monitoring of SSVEP in BCI applications.

Journal ArticleDOI
TL;DR: In this paper, a low profile single-fed circularly polarised single-layer metasurface antenna for wideband operation is proposed, which consists of nine unit cells arranged in a 3 × 3 layout and four slits are incorporated into four of them, respectively, to form two orthogonal currents with 90° phase difference.
Abstract: A novel low-profile single-fed circularly polarised single-layer metasurface antenna for wideband operation is proposed in this Letter. The metasurface antenna consists of nine unit cells arranged in a 3 × 3 layout. Four slits are incorporated into four of them, respectively, to form two orthogonal currents with 90° phase difference; hence, circularly polarised fields are excited. Moreover, a modified L-type slot is etched on the middle lattice to improve impedance bandwidth and axial ratio performance. The proposed dielectric-filled (ɛ r = 3.5, tan δ = 0.001) antenna with a low profile of 0.038λ 0 (λ 0 is the working wavelength at 5.7 GHz in free space) achieves about 18.0% measured −10 dB impedance bandwidth. The measured 3-dB axial ratio bandwidth of the proposed antenna is about 12.8% (5.35–6.08 GHz) with a broadside gain of more than 6.9 dBi.

Journal ArticleDOI
TL;DR: In this paper, a broadband, heterogeneous terahertz frequency quantum cascade laser was demonstrated by exploiting an active region design based on longitudinal optical-phonon-assisted interminiband transitions.
Abstract: The authors demonstrate a broadband, heterogeneous terahertz frequency quantum cascade laser by exploiting an active region design based on longitudinal optical-phonon-assisted interminiband transitions. They obtain continuous wave laser emission with a threshold current density of ~120 A/cm 2 , a dynamic range of ~3.1, and an emission spectrum spanning from 2.4 to 3.4 THz at 15 K.