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Single-mode diode lasers on an InP(001) substrate have been developed using InAs/In0.53Ga0.47As quantum dash (Qdash) active regions and etched lateral Bragg gratings. The lasers have been designed to operate at wavelengths near 2 lm and exhibit a threshold current of 65mA for a 600 lm long cavity, and a room temperature continuous wave output power per facet >5mW. Using our novel growth approach based on the low ternary In0.53Ga0.47As barriers, we also demonstrate ridge-waveguide lasers emitting up to 2.1 lm and underline the possibilities for further pushing the emission wavelength out towards longer wavelengths with this material system. By introducing experimentally the concept of high-duty-cycle lateral Bragg gratings, a side mode suppression ratio of >37 dB has been achieved, owing to an appreciably increased grating coupling coefficient of j~40 cm-1. These laterally coupled distributed feedback (LC-DFB) lasers combine the advantage of high and well-controlled coupling coefficients achieved in conventional DFB lasers, with the regrowth-free fabrication process of lateral gratings, and exhibit substantially lower optical losses compared to the conventional metal-based LC-DFB lasers. [ABSTRACT FROM AUTHOR]

We report on the design, growth, fabrication, and performance of InAs/InP quantum dash (QD) multi-wavelength lasers (MWLs) developed by the National Research Council (NRC) Canada. The key technical specifications investigated include optical and RF beating spectra, relative intensity noise (RIN), and optical phase noise of each individual wavelength channel. Data bandwidth transmission capacity of 5.376 Tbit/s and 10.8 Tbit/s respectively in the PAM-4 and 16-QAM modulation formats are demonstrated using only a single C-band QD 34.2-GHz MWL chip. We have also developed a monolithic InAs/InP QD dual-wavelength (DW) DFB laser as a compact optical beat source to generate millimeter-wave (MMW) signals. Due to the common cavity, highly coherent and correlated optical modes with optical linewidth as low as 15.83 kHz, spectrally pure MMW signals around 46.8 GHz with a linewidth down to 26.1 kHz were experimentally demonstrated. By using this QD DW-DFB laser, a one GBaud (2 Gbps) MMW over-fiber transmission link is demonstrated with PAM-4 signals. The results show that the demonstrated device is suitable for high speed high capacity MMW fiber-wireless integrated fronthaul of 5G networks. [ABSTRACT FROM AUTHOR]

The intermode beat frequency stability of a 1 mm long quantum dash self mode‐locked semiconductor laser emitting optical frequency combs centred at 1535 nm is improved by single‐cavity optical self‐injection. A novel all‐fibre based cavity employing a piezo‐stretchable fibre spool provides both macroscopic optical path cavity length of 76 m and microscopic fine‐delay fibre length control. The maximum achieved intermode beat frequency tuning is 2 MHz. The intermode beat frequency line width indicating the optical frequency comb stability is improved from 67 kHz to below 900 Hz constituting an improvement by a factor of 74. An independent free‐space stabilisation experiment and stochastic time‐domain modelling confirm the demonstrated intermode beat frequency tuning range. [ABSTRACT FROM AUTHOR]

An advanced low cost bidirectional wavelength-division-multiplexing hybrid fiber-wired/fiber-wireless/fiber-VLC/fiber-IVLC transmission system based on a self-seeded InP based quantum dash-laser diode (QD-LD) and reflective semiconductor amplifier (RSOA) is proposed and experimentally demonstrated. In this paper, 10 Gbps/50 GHz MMW and 10 Gbps/100 GHz MMW over 50-km SMF as well as 40-m optical and 10-m radio-frequency (RF) wireless link, and 10 Gbps baseband (BB) data stream over 50-km SMF are successfully transmitted by employing self-injection locking scheme on QD-LD in downlink. RSOA is utilized at the receiving site to broadcast 2.5 Gbps data signal over 50-km SMF plus 10-m free-space link in uplink by reusing the carrier, that makes the system cost-effective. High receiver sensitivity and signal-to-noise ratio (SNR), low bit-error-rate (BER) and low error vector magnitude (EVM), and excellent eye-diagrams in our proposed network build the system more reliable and stable with acceptable performance. Therefore, proposed hybrid transmission system could become prominent alternative not only for progressive fiber backbone network but also for RF/optical wireless feeder networks. [ABSTRACT FROM AUTHOR]

The next generation of optical access communication networks that support 100 Gbps and beyond, require advances in modulation schemes, spectrum utilization, new transmission bands, and efficient devices, particularly laser diodes. In this paper, we investigated the viability of new-class of InAs/InP Quantum-dash laser diode (Qdash-LD) exhibiting multiple longitudinal light modes in the L-band to carry high-speed data rate for access network applications. We exploited external and self injection-locking techniques on Qdash-LD to generate large number of stable and tunable locked modes, and compared them. To stem the capability of each locked mode as a potential subcarrier, data transmission is carried out over two mediums; single mode fiber (SMF) and free space optics (FSO) to emulate real deployment scenarios of optical networks. The results showed that with external-injection locking (EIL), an error-free transmission of 100 Gbps dual polarization quadrature phase shift keying (DP-QPSK) signal is demonstrated over 10 km SMF and 4 m indoor FSO channels, with capability of reaching up to 128 Gbps, demonstrated under back-to-back (BTB) configuration. On the other hand, using self-injection locking (SIL) scheme, a successful data transmission of 64 Gbps and 128 Gbps DP-QPSK signal over 20 km SMF and 10 m indoor FSO links, respectively, is achieved. [ABSTRACT FROM AUTHOR]

We investigate the thermal characteristics of multi-stack chirped barrier thickness InAs/InGaAlAs/InP quantum-dash-in-a-well lasers of different ridge widths 2, 3, 4 and 15 µm. The effect of varying this geometrical parameter on the extracted thermal resistance and characteristic temperature, and their stability with temperature are examined. The results show an inverse relation of ridge-width with junction temperature with 2 µm device exhibiting the largest junction temperature buildup owing to an associated high thermal resistance of ∼45 °C/W. Under the light of this thermal analysis, lasing behavior of different ridge-width quantum-dash (Qdash) lasers with injection currents and operating temperatures, is investigated. Thermionic carrier escape and phonon-assisted tunneling are found to be the dominant carrier transport mechanisms resulting in wide thermal spread of carriers across the available transition states of the chirped active region. An emission coverage of ∼75 nm and 3 dB bandwidth of ∼55 nm is exhibited by the 2 µm device, thus possibly exploiting the inhomogeneous optical transitions to the fullest. Furthermore, successful external modulation of a single Qdash Fabry-Perot laser mode via injection locking is demonstrated with eye diagrams at bit rates of 2–12 Gbit/s incorporating various modulation schemes. These devices are being considered as potential light sources for future high-speed wavelength-division multiplexed optical communication systems. [ABSTRACT FROM AUTHOR]

The exciton and biexciton confinement regimes in strongly anisotropic epitaxial InAs nanostructures called quantum dashes (QDashes) embedded in an In0.53Ga0.23Al0.24 As matrix, which is lattice-matched to InP(001) substrate, have been investigated. For that purpose, we have performed low-temperature spatially and polarization-resolved photoluminescence and time-resolved photoluminescence measurements on a set of single QDashes. The main conclusions are drawn based on the experimentally obtained distribution of the ratio between the exciton and biexciton lifetimes. We have found that a majority of QDashes for which the abovementioned ratio falls into the range of 1.2 ± 0.1-1.6 ± 0.1 corresponds to the so called intermediate confinement regime, whereas for several cases, it is close to 1 or 2, suggesting reaching the conditions of weak and strong confinement, respectively. Eventually, we support this data with dependence of the lifetimes' ratio on the biexciton binding energy, implying importance of Coulomb correlations, which change significantly with the confinement regime. [ABSTRACT FROM AUTHOR]

Quantum dashes were synthesized in the molecular beam epitaxial growth of InAs on GaAs(2 2 1). By changing the arsenic pressure it was possible to obtain highly ordered one-dimensional InAs arrays as demonstrated by autocorrelation function analysis. Polarized Raman spectroscopy was utilized in order to characterize the samples and to estimate the stress at the InAs/GaAs interface as well as the surface anisotropy imposed by the quasi one-dimensional character of the quantum dashes. The most ordered surface, showed the lowest correlation length, and for this sample the Raman spectra exhibits small shift of the GaAs resonance modes indicating likewise small GaAs tensile strain. [ABSTRACT FROM AUTHOR]

In this work, InAs/InGaAlAs/InP quantum dashes have been investigated in terms of their optical, kinetic, and excitonic properties with respect to their application within the 1300± 40 nm spectral range, i.e. the O-band of the telecommunication technologies. We focused on the basic excitonic complexes such as neutral exciton, biexciton, and charged exciton, which have been identified by means of photoluminescence measurements. Emission and carriers' dynamics have been analyzed using rate equation model and fitting the experimental data obtained for both continuous-wave and pulsed excitation regimes. There has been found a significant impact of the charge carrier imbalance in the system and electron capturing rate on the dynamics of the optical and electronic transitions, which results in a high occupation of the negatively charged trion state. Autocorrelation measurements show clear antibunching of trion emission for non-resonant excitation which indicates a potential of such kind of emitters as single photon sources for short-range quantum communication schemes. [ABSTRACT FROM AUTHOR]

A single channel 100 Gb/s dual–polarization quadrature phase shift keying transmission based on injection-locked broadband quantum-dash Fabry–Pérot laser, and employing external modulation, has been demonstrated. By employing a far L–band ~1621-nm sub-carrier, −17.4-dBm sensitivity at the bit error rate 3.8\times 10^-3 has been obtained after 10 km standard single mode fiber transmission. Besides, an injection locked mode wavelength tunability of ~23 nm, which translates to ~50 sub-carriers, is accomplished. These results favor the viability of deploying broadband quantum-dash lasers as unified upstream and downstream transmitters in next generation wavelength division multiplexed-based passive optical networks. [ABSTRACT FROM PUBLISHER]

We investigate the amplitude and phase noise of an optical frequency comb based on InAs/InP quantum-dash mode-locked laser. The laser demonstrates low relative intensity noise (< −125 dB/Hz) and phase noise in the passive mode-locking regime. By actively mode-locking the laser, we observe a reduction in the flicker FM noise and timing jitter, as a result of which the optical linewidth decreases, and hence the effective bandwidth compatible with optical coherent systems increases by more than 50% to $\sim 1.1$ THz. [ABSTRACT FROM PUBLISHER]

We experimentally investigate the corner frequency in the 1/f frequency noise of the longitudinal modes of an InAs/InP quantum-dash based single-section passive mode-locked laser. The corner frequency features a strong asymmetry across the optical frequency comb with the values ranging from 10 MHz in the low-frequency side to 180 MHz in the high-frequency side. Actively modelocking the laser induces a reduction in the corner frequency as it changes from 3 MHz in the low-frequency side to 70 MHz in the high-frequency side and the asymmetry persists. [ABSTRACT FROM AUTHOR]

The dynamic properties of MOVPE grown InP/InAs quantum-dot and quantum-dash lasers, showing identical structural design, emitting in the C-band are investigated and compared to each other. Based on the small-signal measurements, we show the impact of the density of states function on the cut-off frequency, being larger for quantum dots at low currents, and reaching similar values for quantum dashes only at higher currents. The large-signal measurements show error-free data transmission at 22.5 and 17.5 Gbit/s for the quantum-dot and quantum-dash lasers. [ABSTRACT FROM AUTHOR]

We demonstrate a quantum dash quantum cascade photodetector (QDash-QCD) by incorporating self-assembled InAs quantum dashes into the active region of a long wave infrared QCD. Sensitive photoresponse to normal incident light at 10 μm was observed, which is attributed to the intersubband (ISB) transitions in the quantum well/quantum dash (QW/QDash) hybrid absorption region and the following transfer of excited electrons on the extraction stair-like quantum levels separated by LO-phonon energy. The high density InAs quantum dashes were formed in the Stranski-Krastanow mode and stair-like levels were formed by a lattice matched InGaAs/InAlAs superlattice. A stable responsivity from 5 mA/W at 77 K to 3 mA/W at as high as 190 K was observed, which makes the QDash-QCD promising in high temperature operation. [ABSTRACT FROM AUTHOR]

With the help of photoluminescence Spectroscopy (PLS), we have investigated the optoelectronic properties of two different families of InAs quantum dashes (QDashes) grown on misoriented InP(001) substrate with 2off miscut angle toward the [110] direction (2F type). The lowest full width at half maximum (FWHM) of the PL spectrum measured at 12 K indicates the good self organization of InAs QDashes. The weak ratio of the integrated PL measured in 12-300 K temperature range denotes the good spatial confinement of the photogenerated carriers in InAs QDashes. The fast redshift of the PL peaks energy and the anomalous decrease of the FWHM with the increase of the temperature are attributed to an efficient thermal relaxation process of photogenerated carriers in the vicinal sample. This result is highlighted with the help of theoretical modeling of the PL peak energy as a function of the temperature, using three models (Varshni, 'Vina, Logothetidis and Cardona' and Pässler). From experimental and theoretical results, we have evidenced the contribution of longitudinal acoustic-phonons (LA-phonons) in the PL of InAs/InP QDashes, via the deformation potential, especially in high temperatures range. We have attributed this behavior to the strained InAs/InP QDashes and/or to the topography of the vicinal InP(001) substrate which favors the presence of stepped phonons polarized along the steps. These vibrational modes can further interact with the excitons at high temperatures. The measured thermal activation energies of each family of InAs QDashes demonstrate that the InAs wetting layer act as a barrier for the thermoionic emission of photogenerated carriers. This result confirms the good spatial confinement of excitons in this sample. [ABSTRACT FROM AUTHOR]

The ultrafast carrier dynamics in a p-doped dash-in-a-well structure at 1.5 µm is experimentally investigated. An analysis of the timescales related to carrier relaxation and escape processes as well as the "dynamical" linewidth enhancement factor is presented and compared with results obtained from similar un-doped materials. Intentional p-doping of the active region results in an enhancement of the intermediate timescale of the gain dynamics associated with phonon-assisted electron capture and a reduction of the α-factor due to increased differential gain. [ABSTRACT FROM AUTHOR]

MBE (Molecular Beam Epitaxy) grown p-i-n laser heterostructure, based on InAs/InP Quantum Dashes with quaternary InGaAsP Quantum Well, were investigated through electroluminescence (EL) measurements. Bipolar injection set on just of forward bias,VF, 1.3 V, resulting an emission of long wavelength laser light, peaking of 1550 nm. This value was consistent with thermal energy band gap, deduced from current-voltage measurement in space charge limited regime where mobility of injected carriers followed Poole-Frenkel type conduction. [ABSTRACT FROM AUTHOR]

We report on single photon emission from a self-assembled InAs/InGaAlAs/InP quantum dash emitting at 1.55 µm at the elevated temperatures. The photon auto-correlation histograms of the emission from a charged exciton indicate clear antibunching dips with as-measured g(2)(0) values significantly below 0.5 recorded at temperatures up to 80 K. It proves that the charged exciton complex in a single quantum dash of the mature InP-based material system can act as a true single photon source up to at least liquid nitrogen temperature. This demonstrates the huge potential of InAs on InP nanostructures as the non-classical light emitters for long-distance fiber-based secure communication technologies. [ABSTRACT FROM AUTHOR]

We report on low-temperature cross-sectionalscanning tunneling microscopy and spectroscopy on InAs(P)/InGaAsP/InP(001)quantum dashes, embedded in a diode-laser structure. The laser activeregion consists of nine InAs(P) quantum dash layers separated by theInGaAsP quaternary alloy barriers. The effect of the p-i-n junctionbuilt-in potential on the band structure has been evidenced and quantifiedon large-scale tunneling spectroscopic measurements across the wholeactive region. By comparing the tunneling current onset channels,a consistent energy shift has been measured in successive quantumdash or barrier layers, either for the ground state energy of similar-sizedquantum dashes or for the conduction band edge of the barriers, correspondingto the band-bending slope. The extracted values are in good quantitativeagreement with the theoretical band structure calculations, demonstratingthe high sensitivity of this spectroscopic measurement to probe theelectronic structure of individual nanostructures, relative to localpotential variations. Furthermore, by taking advantage of the potentialgradient, we compared the local density of states over successivequantum dash layers. We observed that it does not vanish while increasingenergy, for any of the investigated quantum dashes, in contrast towhat would be expected for discrete level zero-dimensional (0D) structures.In order to acquire further proof and fully address the open questionconcerning the quantum dash dimensionality nature, we focused on individualquantum dashes obtaining high-energy-resolution measurements. Thestudy of the local density of states clearly indicates a 1D quantum-wirelikenature for these nanostructures whose electronic squared wave functionswere subsequently imaged by differential conductivity mapping. [ABSTRACT FROM AUTHOR]

We investigated the neutral and charged exciton fine structure in single InAs/InGaAlAs/InP quantum dashes emitting at 1.55 μm using polarization-resolved microphotoluminescence in a magnetic field. Inverted spin configuration of horizontally [1-10] and vertically [110] polarized transitions has been observed. An in-plane magnetic field of up to 5 Tesla has been applied to tailor the fine structure, and eventually to reduce the splitting of the bright exciton states down to zero. This inverted structure has been observed for all the investigated excitons, making it a characteristic feature for this class of nanostructures with the largest splitting reduction of 170 μeV. [ABSTRACT FROM AUTHOR]

We have investigated the dynamics of a quantum dash semiconductor,QDSC, laser under the effect of a number of control parameters that appear in the adopted theoretical modelviz carrier to photon decay rates(ƞ), injection current(J), gain value(g) and carrier escape rate(R). Relaxation oscillation in the output intensity of the QDSC laser is reduced and the dc part of the output can be increased as a result of choosing the set (ƞ,J,g,R) . [ABSTRACT FROM AUTHOR]

Strain-based band engineering in quantum dots and dashes has been predominantly limited to compressively strained systems. However, tensile strain strongly reduces the bandgaps of nanostructures, enabling nanostructures to emit light at lower energies than they could under compressive strain. We demonstrate the self-assembled growth of dislocation-free GaAs quantum dashes on an InP(111)B substrate, using a 3.8% tensile lattice-mismatch. Due to the high tensile strain, the GaAs quantum dashes luminesce at 110-240 meV below the bandgap of bulk GaAs. The emission energy is readily tuned by adjusting the size of the quantum dashes via deposition thickness. Tensile self-assembly creates new opportunities for engineering the band alignment, band structure, and optical properties of epitaxial nanostructures. [ABSTRACT FROM AUTHOR]

We report on the high-performance characteristics from superluminescent diodes (SLDs) based on four-stack InAs/InGaAlAs chirped-barrier thickness quantum dash (Qdash) in a well structure. The active region exhibits a measured broad gain spectrum of 140 nm, with a peak modal gain of ~41 cm-1. The noncoated two-section gainabsorber broad-area and ridge-waveguide device configuration exhibits an output power of > 20 mW and > 12 mW, respectively. The corresponding -3-dB bandwidths span ~82 nm and ~72 nm, with a small spectral ripple of <; 0.2 dB, related largely to the contribution from dispersive height dash ensembles of the highly inhomogeneous active region. These C-L communication band devices will find applications in various cross-disciplinary fields of optical metrology, optical coherent tomography, etc. [ABSTRACT FROM PUBLISHER]

We report on a direct observation of coherent light-matter interactions imprinted on a short pulse propagating along a room-temperature, electrically biased, quantum dash semiconductor optical amplifier. The principle of the observation is that we characterize the complex field (phase and amplitude) of the short optical pulse after the interaction. By comparing the measurements to a numerical simulation, we are able to decipher the time evolution of effective two-state Schrodinger wave functions representing the ensembles of electronic states along the propagation path. The imprinted signatures on the pulse phase and amplitude stem from the accumulated propagation and reveal systematically clear Rabi oscillations and self-induced transparency. The high sensitivity to the effective ensemble states is shown to result from the response of the refractive index. [ABSTRACT FROM AUTHOR]

We investigate charged and neutral exciton complexes confined in a single self-assembled InAs/InGaAlAs/InP quantum dash emitting at 1.55 μm. The emission characteristics have been probed by measuring high-spatial-resolution polarization-resolved photoluminescence and cross-correlations of photon emission statistics at T=5K. The photon auto-correlation histogram of the emission from both the neutral and charged exciton indicates a clear antibunching dip with as-measured g(2)(0) values of 0.18 and 0.31, respectively. It proves that these exciton complexes confined in single quantum dashes of InP-based material system can act as true single photon emitters being compatible with standard long-distance fiber communication technology. [ABSTRACT FROM AUTHOR]

Room-temperature electroluminescence is observed for the first time in type-II heterostructures based on InSb quantum dashes embedded in a narrow-gap n-InAs matrix. The heterostructures exhibit positive luminescence at wavelengths in the range 3-4 μm. This is due to the interfacial radiative transitions of electrons from self-consistent quantum wells on the side of InAs matrix layers across the broken-gap type-II InSb/InAs heterointerface to quantum-well hole levels in the InSb quantum dashes, situated in the energy gap of the matrix near the InAs conduction-band bottom. [ABSTRACT FROM AUTHOR]

A numerical study of the effect of injection current modulation on the dynamics of a quantum dash semiconductor laser is presented. The control parameters chosen to affect the temporal intensity variation are the gain, the dc and ac parts of the injection current, the modulation frequency, carrier escape rate and ratio of carrier to photon decay rates . Various output ranging from single pulses to chaotic one produced. [ABSTRACT FROM AUTHOR]

In this paper, we present a systematic investigation of passive mode-locked InAs/InP quantum-dash lasers in terms of frequency and timing stability. Mode-locking features are analyzed using the frequency domain approach based on the concept of supermodes. It is shown that the phase of adjacent longitudinal modes is correlated over 1.3-THz frequency span. The observed strong coherence between modes enables low timing jitter and a long-term stability of the repetition rate frequency within 5×10-8 over 100 s. [ABSTRACT FROM PUBLISHER]

In this paper, we assessed the effect of additionally broadened quantum dash (Qdash) optical transitions in the multi-stack dash-in-a-well laser structure at both, material and device level. A broad photoluminescence linewidth of ~ 150 nm demonstrates the formation of highly inhomogeneous InAs-dashes across the stacks. The transmission electron microscopy revealed small (large) average dash height from the Qdash stack with thick (thin) over grown barrier layer. The Fabry-Perot laser diodes fabricated from this chirped structure exhibits unique device physics under the short pulsewidth (SPW) and quasi-continuous wave (QCW) operation. Varying the ridge-width (W) from 2 to 4 μm showed quenching of ultrabroad lasing signature in the SPW operation, and consistent even for a wide 15 μm oxide strip laser diode. A lasing spectral split with reduced intensity gap in the center is observed in the QCW operation with the gap decreasing with increasing ridge-width. Such atypical lasing operation, influenced by the waveguiding mechanism is qualitatively realized by associating to the reduced vertical coupling effect of the Qdash stacks in the operation of small ridge-width lasers compared with large ridge-width and oxide stripe lasers, and leading to varying non-uniform distribution of carriers among the inhomogeneously broadened Qdash stacks in each case. Our chirped 2 × 830 μm ridge laser demonstrated marked improvement in the internal quantum efficiency (~ 80%) and -3 dB lasing bandwidth, centered at ~1.61 μm. [ABSTRACT FROM PUBLISHER]

Highlights: [•] We give an original results about the optical properties of InAs/InP(001) quantum dashes used in optoelectronic devices. [•] The optoelectronic properties of InAs/InP(001) QDas are investigated with photoluminescence spectroscopy. [•] The lateral coupling behavior observed for the nominal sample is completely eliminated in the case of the vicinal sample. [•] The vicinal sample has an excellent thermal stability and a broad emission range. [•] The optical properties of the vicinal sample give the opportunity to use it in solar cells and in infrared photodetectors. [ABSTRACT FROM AUTHOR]

Abstract: This paper treats the impact of post growth tuned InAs/InP quantum dashes' (QDas) size/composition distribution on carriers' localization and thermal redistribution. The spread of this distribution depends on the experimental conditions used for the phosphorus ion implantation enhanced intermixing process. Atypical temperature-dependent luminescence properties have been observed and found to be strongly dependent on the amount of QDas size/composition dispersion. The experimental results have been reproduced by a model that takes into account the width of the QDas localized states distribution and consequent thermally induced carriers' redistribution. This model gives critical temperature values marking the beginning and the end of carriers delocalization and thermal transfer processes via an intermixing induced carrier's transfer channel located below the wetting layer states. [Copyright &y& Elsevier]

Exciton and biexciton dynamics in a single self-assembled InAs/In0.53Ga0.23Al0.24As/InP(001) quantum dash emitting near 1.55 μm has been investigated by micro-photoluminescence and time-resolved micro-photoluminescence at T = 4.2 K. The exciton and biexciton fine structure splitting of ∼60 μeV, the biexciton binding energy of ∼3.5 meV, and the characteristic exciton and biexciton decay times of 2.0 ± 0.1 ns and 1.1 ± 0.1 ns, respectively, have been determined. The measurement of the biexciton and exciton cross-correlation statistics of the photon emission confirmed the cascaded relaxation process. The exciton-to-biexciton decay time ratio and a small fine structure splitting suggest carrier localization within the investigated quantum dash. [ABSTRACT FROM AUTHOR]

The linear optical gain of gain-clamped quantum dash semiconductor optical amplifiers (GCSOAs) has been investigated using the rate equation model. The gain spectrum of GCSOA for different wavelength detuning and different doping has been studied. Our analysis shows that the linear gain can be increased as the laser wavelength is detuned to high wavelength where the peak of the optical gain, which is found at wavelengths below the ground state wavelength, is shifted to lower wavelength as the laser wavelength is increased. We find that doping the dashes by either N-type or P-type enhances the linear optical gain and shifts the gain peak to lower wavelength. Moreover, we found that GCSOA with lightly N-type doping demonstrates large separation between the laser and the amplifier wavelength. Also we find that small inhomogeneous line broadening enhances the linear gain peak, shifts the gain peak to wavelength lower than the GS wavelength and widens the gain spectrum. [ABSTRACT FROM AUTHOR]

In this report we have investigated theoretically the phonon-assisted recombination process of excitons con- fined in strongly elongated semiconductor nanostructures, called quantum dashes. Interaction with phonon bath leads to the occurrence of phonon-assisted recombination, which in the case of acoustic phonons is manifested in the optical spectra as a deviation of the homogeneously broadened emission line shape from expected Lorentzian profile via occurrence of the so-called phonon sidebands. Hereby, we have modeled the influence of the quantum dash geometry on this spectral feature proving pronounced suppression of phonon-induced decoherence for strongly elongated nanostructures. Furthermore, the importance of different phonon coupling mechanisms has been evaluated and the spectral diffusion effects, unavoidable in the time-integrated photoluminescence experiments, have been accounted for. [ABSTRACT FROM AUTHOR]

The influence of confinement potential anisotropy on emission properties of strongly elongated single InAs/ InGaAlAs/InP quantum dashes has been investigated by polarization-resolved microphotoluminescence spectroscopy at around 1.5 μm. There have been determined the exciton fine structure splitting, degree of linear polarization of surface emission and biexciton binding energy. The investigated dashes exhibited usually: the exciton anisotropy splitting larger than 100 μeV, the corresponding biexciton binding energy of about 3 meV, and the degree of linear polarization values in the range from 24% to 55%. Here, we presented a correlation of these parameters for several quantum dashes, which can be attributed either to a change in lateral aspect ratio within the ensemble, or the carrier localization on random fluctuations of the dash confinement potential. [ABSTRACT FROM AUTHOR]

In this work we investigate the electronic structure of coupled quantum dashes. The respective confined state energy levels are calculated for various cross-sectional shapes and sizes of the dashes and in function of the lateral distance between them. The results are confronted with the existing experimental data on the optical transitions in such structures. It has been concluded that for realistic system parameters (geometry and spatial in-plane separation) the obtained direct coupling is weak and in most of the applications the dashes can be considered individually, as long as the ensemble is strongly inhomegeneous. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) quantum efficiency (QE) is experimentally investigated, using an integrating sphere, as a function of excitation power on both InAs/InP quantum rod nanowires (QRod‐NWs) and radial quantum well nanowires (QWell‐NWs) grown on silicon substrates. The measured values of the QE are compared with those of the planar analogues such as quantum dash and quantum well samples, and found to be comparable for the quantum well structures at relatively low power density. Further studies reveal that the values of QE of the QRod‐NWs and QWell‐NWs are limited by the low quality of the InP NW structure and the quality of radial quantum well, respectively. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) Part of Focus Issue on “Semiconductor Nanowires” (Eds.: Chennupati Jagadish, Lutz Geelhaar, Silvija Gradecak) The quantum efficiency of InAs/InP nanowire heterostructures grown on silicon, such as quantum rod and quantum well nanowires, is studied as a function of excitation power. The experimental results are compared to that measured on analogues InAs(P)/InP planar heterostructures (quantum dashes and quantum well). From the obtained results we conclude about possible ways to improve the quantum efficiency of the nanowire heterostructures which can serve for the fabrication of high‐efficiency light emitting devices working in telecommunication window. [ABSTRACT FROM AUTHOR]

We have investigated the fabrication and optical performance of free-standing rolled-up InGaAsP tube optical cavities, wherein self-organized InAs quantum dots or dashes are incorporated as the gain media. Such tubular optical cavities are formed when the coherently strained InAs/InGaAsP quantum dot/dash nanomembrane is selectively released from the host substrate. We have achieved lasing from rolled-up InAs/InGaAsP quantum dash microtubes at room temperature under continuous wave optical pumping. The measured threshold is ~6 μW, and the Purcell factor and the spontaneous emission coupling factor are estimated to be ~6.54 and ~0.87, respectively. [ABSTRACT FROM AUTHOR]

We study the enhanced inhomogeneity across the InAs quantum-dash (Qdash) layers by incorporating a chirped AlGaInAs barrier thickness in the InAs/InP laser structure. The lasing operation is investigated via Fabry-Pérot ridge-waveguide laser characterization, which shows a peculiar behavior under quasi-continuous-wave (QCW) operation. Continuous energy transfer between different dash ensembles initiated quenching of lasing action among certain dash groups, causing a reduced intensity gap in the lasing spectra. We discuss these characteristics in terms of the quasi-zero-dimensional density of states (DOS) of dashes and the active region inhomogeneity.

P-doped quantum dash based lasers have shown superior dynamic performance as compared to their un-doped counterparts. This improvement in performance is strongly observed in line-width enhancement factor. These devices show a dramatic reduction in the αH parameter, resulting in very low chirp. This letter discusses the nature line-width enhancement factor of p-doped quantum dash lasers as opposed to un-doped counterparts. Owing to the p-doping a low and bias-stable alpha parameter is demonstrated. [ABSTRACT FROM AUTHOR]

An innovative 10 Gbit/s single mode optical transmitter with the capacity of error‐free transmission is demonstrated in the range of 0–100 km with constant biasing conditions by using a quantum dash directly modulated laser. A commercially available etalon filter is used as a passive optical filter to achieve penalty‐free transmission with a dynamic extinction ratio >6 dB over a large range of fibre spans. [ABSTRACT FROM AUTHOR]

We report an InP based vertical cavity surface emitting laser (VCSEL) achieving a lasing operation between 1529 and 1646 nm. This optically-pumped VCSEL includes a wide-gain bandwidth active region based on InAs quantum dashes and wideband dielectric Bragg mirrors. Based on a wedge microcavity design, we obtain a spatial dependence of the resonant wavelength along the wafer, enabling thus to monitor the gain material bandwidth. We demonstrate a 117 nm continuous wavelength variation of the VCSEL emission, a consequence of the important and wide gain afforded by the use of optimized quantum dashes. [ABSTRACT FROM PUBLISHER]