Showing papers on "Laser linewidth published in 2009"
TL;DR: A nanoplasmonic analogue of EIT is experimentally demonstrated using a stacked optical metamaterial to achieve a very narrow transparency window with high modulation depth owing to nearly complete suppression of radiative losses.
Abstract: In atomic physics, the coherent coupling of a broad and a narrow resonance leads to quantum interference and provides the general recipe for electromagnetically induced transparency (EIT). A sharp resonance of nearly perfect transmission can arise within a broad absorption profile. These features show remarkable potential for slow light, novel sensors and low-loss metamaterials. In nanophotonics, plasmonic structures enable large field strengths within small mode volumes. Therefore, combining EIT with nanoplasmonics would pave the way towards ultracompact sensors with extremely high sensitivity. Here, we experimentally demonstrate a nanoplasmonic analogue of EIT using a stacked optical metamaterial. A dipole antenna with a large radiatively broadened linewidth is coupled to an underlying quadrupole antenna, of which the narrow linewidth is solely limited by the fundamental non-radiative Drude damping. In accordance with EIT theory, we achieve a very narrow transparency window with high modulation depth owing to nearly complete suppression of radiative losses. Plasmonic nanostructures enable the concentration of large electric fields into small spaces. The classical analogue of electromagnetically induced transparency has now been achieved in such devices, leading to a narrow resonance in their absorption spectrum. This combination of high electric-field concentration and sharp resonance offers a pathway to ultracompact sensors with extremely high sensitivity.
1,652 citations
TL;DR: In this paper, a general analytic approach to the theory of microwave generation in magnetic nano-structures driven by spin-polarized current was proposed. But the proposed approach is based on the universal model of an auto-oscillator with negative damping and nonlinear frequency shift.
Abstract: This paper formulates a general analytic approach to the theory of microwave generation in magnetic nano-structures driven by spin-polarized current and reviews analytic results obtained in this theory. The proposed approach is based on the universal model of an auto-oscillator with negative damping and nonlinear frequency shift. It is demonstrated that this universal model, when applied to the case of a spin-torque oscillator (STO) based on a current-driven magnetic nano-pillar or nano-contact, gives adequate description of most of the experimentally observed properties of STO. In particular, the model describes the power and frequency of the generated microwave signal as functions of the bias current and magnetic field, predicts the magnitude and properties of the generation linewidth, and explains the STO behavior under the influence of periodic and stochastic external signals: frequency modulation, phase-locking to external signals, mutual phase-locking in an array of STO, broadening of the generation linewidth near the generation threshold, etc. The proposed nonlinear auto-oscillator theory is rather general and can be used not only for the development of practical nano-sized STO, but, also, for the description of nonlinear auto-oscillating systems of any physical nature.
713 citations
TL;DR: A new light source based on having alkaline-earth atoms in an optical lattice collectively emit photons on an ultranarrow clock transition into the mode of a high Q resonator has the potential to improve the stability of the best clocks by 2 orders of magnitude.
Abstract: We propose a new light source based on having alkaline-earth atoms in an optical lattice collectively emit photons on an ultranarrow clock transition into the mode of a high Q resonator. The resultant optical radiation has an extremely narrow linewidth in the mHz range, even smaller than that of the clock transition itself due to collective effects. A power level of order 10;{-12} W is possible, sufficient for phase locking a slave optical local oscillator. Realizing this light source has the potential to improve the stability of the best clocks by 2 orders of magnitude.
325 citations
TL;DR: It is concluded that emission arises from a low concentration of aggregates which are more disordered than the dominant species responsible for absorption, and emissive aggregates are characterized by shorter average conjugation lengths and hence greater exciton bandwidths.
Abstract: The photoluminescence (PL) spectral line shape of regioregular poly(3-hexylthiophene) thin films is analyzed using a model which treats the polymer pi-stacks as H-aggregates with exciton-vibrational coupling and spatially correlated site disorder The Stokes shift, linewidth, and relative vibronic peak intensities in the low-temperature PL spectrum (T=10 K) are accurately reproduced, allowing the coherence function corresponding to the lowest energy (emitting) exciton to be determined from the ratio of the 0-0 to 0-1 peak intensities The exciton migration length is determined from the N-dependent Stokes shift, where N is the number of segments comprising the stack Based on the temperature dependence of the PL spectrum it is concluded that emission arises from a low concentration of aggregates which are more disordered than the dominant species responsible for absorption The emissive aggregates are characterized by shorter average conjugation lengths and hence greater exciton bandwidths The coherence length of the emitting exciton is estimated to be only three lattice spacings ( approximately 11 nm) along the pi-stacking direction By contrast, the exciton migration length for incoherent hopping between coherent domains is estimated to be approximately 15 nm
265 citations
TL;DR: An electrically-pumped hybrid silicon microring laser fabricated by a self-aligned process with compact structure and small electrical and optical losses is demonstrated and application as on-chip optical interconnects is discussed.
Abstract: We demonstrate an electrically-pumped hybrid silicon microring laser fabricated by a self-aligned process. The compact structure (D = 50 μm) and small electrical and optical losses result in lasing threshold as low as 5.4 mA and up to 65 °C operation temperature in continuous-wave (cw) mode. The spectrum is single mode with large extinction ratio and small linewidth observed. Application as on-chip optical interconnects is discussed from a system perspective.
186 citations
TL;DR: In this paper, the quantum-confined Stark effect can be employed to quickly and reversibly switch the dot-cavity coupling simply by varying a gate voltage, with Purcell factors ≥ 7.
Abstract: We report the design, fabrication and optical investigation of electrically tunable single quantum dots—photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light–matter interaction. Unlike previous studies where the dot–cavity spectral detuning was varied by changing the lattice temperature, or by the adsorption of inert gases at low temperatures, we demonstrate that the quantum-confined Stark effect can be employed to quickly and reversibly switch the dot–cavity coupling simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by ~4 meV relative to the nanocavity mode before the emission quenches due to carrier tunneling escape. This range is much larger than the typical linewidth of the high-Q cavity modes (~100 μeV) allowing us to explore and contrast regimes where the dots couple to the cavity or decay by spontaneous emission into the two-dimensional photonic bandgap. In the weak-coupling regime, we show that the dot spontaneous emission rate can be tuned using a gate voltage, with Purcell factors ≥7. New information is obtained on the nature of the dot–cavity coupling in the weak coupling regime, and electrical control of zero-dimensional polaritons is demonstrated for the highest-Q cavities (Q≥12 000). Vacuum Rabi splittings up to ~120 μeV are observed, larger than the linewidths of either the decoupled exciton (γ≤40 μeV) or cavity mode. These observations represent a voltage switchable optical nonlinearity at the single photon level, paving the way towards on-chip dot-based nano-photonic devices that can be integrated with passive optical components.
175 citations
TL;DR: In this article, a broadband FMR setup has been used to investigate the origin of the enhanced linewidth in a material in which the PMA could be systematically reduced by irradiation with Helium ions.
Abstract: Transition-metal ferromagnetic films with perpendicular magnetic anisotropy (PMA) have ferromagnetic resonance (FMR) linewidths that are one order of magnitude larger than soft magnetic materials, such as pure iron (Fe) and Permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate the origin of the enhanced linewidth in a material in which the PMA could be systematically reduced by irradiation with Helium ions: $\text{Ni}\ensuremath{\mid}\text{Co}$ multilayers. The FMR linewidth depends linearly on frequency for perpendicular applied fields and increases significantly when the magnetization is rotated into the film plane. Irradiation of the film with Helium ions decreases the PMA and the distribution of PMA parameters, leading to a large reduction in the FMR linewidth for in-plane magnetization. These results suggest that fluctuations in PMA lead to a large two magnon scattering contribution to the linewidth for in-plane magnetization and establish that the Gilbert damping is enhanced in such materials ($\ensuremath{\alpha}\ensuremath{\approx}0.04$, compared to $\ensuremath{\alpha}\ensuremath{\approx}0.002$ for pure Fe).
145 citations
TL;DR: This Letter reports on the generation of photons with 3 MHz linewidth by cavity-enhanced parametric down-conversion and demonstrates direct proof of their single-photon character by detection of heralding idler photons.
Abstract: Narrow-band single photons represent an important resource for quantum memories due to their efficient interaction with atomic resonances. In this Letter, we report on the generation of photons with 3 MHz linewidth by cavity-enhanced parametric down-conversion and demonstrate direct proof of their single-photon character by detection of heralding idler photons. Compared to a Poissonian source, a suppression of higher-order photon numbers by nearly 2 orders of magnitude could be achieved. Moreover, the brightness of our source exceeds previous realizations by more than a factor of 100.
139 citations
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TL;DR: Active optical clock as mentioned in this paper is a special laser combining the laser physics of one-atom laser, bad-cavity gas laser, super cavity stabilized laser and optical atomic clock together.
Abstract: This article presents the principles and techniques of active optical clock, a special laser combining the laser physics of one-atom laser, bad-cavity gas laser, super-cavity stabilized laser and optical atomic clock together. As a simple example, an active optical clock based on thermal strontium atomic beam shows a quantum-limited linewidth of 0.51 Hz, which is insensitive to laser cavity-length noise, and may surpass the recorded narrowest 6.7 Hz of Hg ion optical clock and 1.5 Hz of very recent optical lattice clock. The estimated 0.1 Hz one-second instability and 0.27 Hz uncertainty are limited only by the relativistic Doppler effect, and can be improved by cold atoms.
132 citations
TL;DR: In this article, an erbium-doped fiber distributed-feedback laser using an all-fiber-based Michelson interferometer of large arm imbalance is reported.
Abstract: We report the frequency stabilization of an erbium-doped fiber distributed-feedback laser using an all-fiber-based Michelson interferometer of large arm imbalance. The interferometer uses a 1 km SMF-28 optical fiber spool and an acousto-optic modulator allowing heterodyne detection. The frequency-noise power spectral density is reduced by more than 40 dB for Fourier frequencies ranging from 1 Hz to 10 kHz, corresponding to a level well below 1 Hz2/Hz over the entire range; it reaches 10(-2) Hz2/Hz at 1 kHz. Between 40 Hz and 30 kHz, the frequency noise is shown to be comparable to the one obtained by Pound-Drever-Hall locking to a high-finesse Fabry-Perot cavity. Locking to a fiber delay line could consequently represent a reliable, simple, and compact alternative to cavity stabilization for short-term linewidth reduction.
130 citations
TL;DR: Using a single-mode Er-doped fiber laser at 1575 nm as a core-pump source, a 2-cm-long distributed Bragg reflector fiber laser delivers single-frequency output at 1950 nm with laser linewidth less than 3 kHz, which is, to the best of the authors' knowledge, the narrowest linewitzer demonstrated to date from any 2 microm single- frequency laser.
Abstract: Single-frequency laser operation near 2 μm has been demonstrated in an all-fiber short-cavity (2-6 cm) distributed feedback laser cavity using both cladding- and core-pump configurations in a newly developed heavily Tm-doped multicomponent silicate glass fiber. Using a single-mode Er-doped fiber laser at 1575 nm as a core-pump source, a 2-cm-long distributed Bragg reflector fiber laser delivers single-frequency output at 1950 nm with laser linewidth less than 3 kHz, which is, to the best of our knowledge, the narrowest linewidth demonstrated to date from any 2 μm single-frequency laser.
TL;DR: The results demonstrate the narrow linewidth Raman fiber amplifier technology as a promising solution for developing laser for sodium laser guide star adaptive optics.
Abstract: We report on a 25 W continuous wave narrow linewidth ( 95%) coherent beam combination of two narrow linewidth (< 1.5 MHz) Raman fiber amplifiers with a Mach-Zehnder interferometer scheme and frequency doubling in an external resonant cavity with an efficiency of 86%. The results demonstrate the narrow linewidth Raman fiber amplifier technology as a promising solution for developing laser for sodium laser guide star adaptive optics.
TL;DR: The effect of chromatic dispersion on coherence length and noise of Fourier Domain Mode Locked (FDML) lasers and a simple model is developed providing a connection between timing, photon cavity lifetime and characteristic time constant of the filter.
Abstract: We report on the effect of chromatic dispersion on coherence length and noise of Fourier Domain Mode Locked (FDML) lasers. An FDML laser with a sweep range of 100nm around 1550nm has been investigated. Cavity configurations with and without dispersion compensation have been analyzed using different widths of the intra-cavity optical band-pass filter. The measurements are compared to non-FDML wavelength swept laser sources. Based on these observations, a simple model is developed providing a connection between timing, photon cavity lifetime and characteristic time constant of the filter. In an optimized configuration, an instantaneous laser linewidth of 20pm is observed, corresponding to a 10× narrowing compared to the intra-cavity optical band-pass filter. A relative intensity noise of -133dBc/Hz or 0.2% at 100MHz detection bandwidth during sweep operation is observed. For optimum operation, the filter drive frequency has to be set within 2ppm or 120mHz at 51kHz.
TL;DR: This paper makes use of the back-reflected signal, arising from a conical lens-tip fiber, as a reference signal for in-fiber CPOCT technique, and uses a Fourier-domain OCT system to demonstrate the feasibility of this technique upon biological tissue.
Abstract: Common-path optical coherence tomography (CPOCT) is known to reduce group velocity dispersion and polarization mismatch between the reference and the sample arm as both arms share the same physical path. Existing implementations of CPOCT typically require one to incorporate an additional cover glass within the beam path of the sample arm to provide a reference signal. In this paper, we aim to further reduce this step by directly making use of the back-reflected signal, arising from a conical lens-tip fiber, as a reference signal. The conical lens, which is directly manufactured onto the optical fiber tip via a simple selective-chemical etching process, fulfils two functions acting as both the imaging lens and the self-aligning reference plane. We use a Fourier-domain OCT system to demonstrate the feasibility of this technique upon biological tissue. An in-fiber CPOCT technique may prove potentially useful in endoscopic OCT imaging.
TL;DR: In this article, the authors used strain stiffening in fixed-fixed beam actuators to extend the tuning range of microelectromechanical-systems-based Fabry-Perot filters.
Abstract: This paper describes the use of strain stiffening in fixed-fixed beam actuators to extend the tuning range of microelectromechanical-systems-based Fabry-Perot filters. The measured wavelength tuning range of 1.615-2.425 mum is the largest reported for such a filter. Curvature in the movable mirror was corrected using a low-power oxygen plasma to controllably alter the stress gradient in the mirror. After curvature correction, the linewidth of a filter was 52 nm, close to the theoretical minimum for our mirror design. As a proof of concept, a filter was bonded to a broadband infrared detector, realizing a wavelength-tunable infrared detector. All measured data have been compared to theoretical models of the optics and mechanics of the filters, with excellent agreement between theory and measurement demonstrated in all cases. Finally, the Young's modulus and stress of the actuator materials were extracted directly from the measured voltage-displacement curves, demonstrating a novel technique for material property measurement.
TL;DR: In this paper, the authors demonstrate laser frequency stabilization to excited state transitions using cascade electromagnetically induced transparency, using a room temperature Rb vapor cell as a reference, and demonstrate a first diode laser to the D2 transition and a second laser to a transition from the intermediate 5P3/2 state to a highly excited state.
Abstract: We demonstrate laser frequency stabilization to excited state transitions using cascade electromagnetically induced transparency. Using a room temperature Rb vapor cell as a reference, we stabilize a first diode laser to the D2 transition and a second laser to a transition from the intermediate 5P3/2 state to a highly excited state with principal quantum number n=19–70. A combined laser linewidth of 280±50 kHz over a 100 μs time period is achieved. This method may be applied generally to any cascade system and allows laser stabilization to an atomic reference in the absence of a direct absorption signal.
TL;DR: In this article, a method for providing images using a multimodal nonlinear optical microscope is presented, which includes providing a foundation femtosecond laser beam, generating a first femto-cond laser beacon and a second femtocond beam corresponding to the foundation beam.
Abstract: A method for providing images using a multimodal nonlinear optical microscope is disclosed. The method includes providing a foundation femtosecond laser beam, generating a first femtosecond laser beam and a second femtosecond laser beam corresponding to the foundation femtosecond laser beam, combining the first femtosecond laser beam and the foundation femtosecond laser beam to generate a first combination femtosecond laser beam, and generating a coherent anti-Stokes Raman scattering (CARS) signal based on the first combination femtosecond laser beam. A multimodal nonlinear optical microscopy platform is also disclosed.
TL;DR: In this article, the homogeneous linewidth of plasmon resonances in nanoscale gold bipyramids at temperatures from 293 to 6 K was investigated and shown to drop linearly with temperature and approaches a constant value at approximately 50 K.
Abstract: We investigated the effectiveness of low temperatures in reducing plasmon damping by measuring the homogeneous linewidth of plasmon resonances $(\ensuremath{\sim}1.5\text{ }\text{eV})$ in nanoscale gold bipyramids at temperatures from 293 to 6 K. The linewidth drops linearly with temperature and approaches a constant value at approximately 50 K. Measurements were performed on monodisperse ensembles as well as on single particles. The 30% decrease in the homogeneous linewidth with decreasing temperature is well accounted for by the reduced electron-phonon scattering. The other relaxation mechanisms---electron-electron scattering, electron-surface scattering, and radiative relaxation---do not change significantly with temperature.
01 Dec 2009
TL;DR: In this paper, the effect of coherent coupling between the lasing levels with other levels on the transport properties and gain spectra was investigated and an expression for the slope discontinuity in the currentvoltage characteristics at lasing threshold was derived.
Abstract: We develop simple density-matrix models to describe the role of coherence in resonant-tunneling (RT) transport of quantum-cascade lasers (QCLs). Specifically, we investigate the effects of coherent coupling between the lasing levels with other levels on the transport properties and gain spectra. In the first part of the paper, we use a three-level density-matrix model to obtain useful analytical expressions for current transport through the injector barrier in a QCL. An expression for the slope discontinuity in the current-voltage characteristics at the lasing threshold is derived. This value is shown to be a direct measure of the population inversion at threshold and contradicts the previously held belief of it being indicative of ratio of the laser level lifetimes. In the second part of the paper, we use density matrices to compute the gain spectrum for a resonant-phonon terahertz QCL design. The large anticrossing of the doublet of lower radiative levels is reflected in a broad gain linewidth due to a coherent RT assisted depopulation process. At certain bias conditions, the gain spectrum exhibits double peaks which is supported by experimental observations.
TL;DR: In this paper, the frequency resolved magneto-optic Kerr effect was used to probe the spin dynamics and mode structure in 50-200-nm-diameter nanomagnets ranging from 3 to 10 nm in thickness.
Abstract: We use frequency resolved magneto-optic Kerr effect to probe the spin dynamics and mode structure in 50--200-nm-diameter ${\text{Ni}}_{80}{\text{Fe}}_{20}$ nanomagnets ranging from 3 to 10 nm in thickness. We find that the intrinsic Gilbert damping parameter is largely unaffected by the nanopatterning process despite a large linewidth dependence on the size of the nanomagnets. In the larger nanomagnets, both end and center modes are observed. The linewidth of these two modes differ considerably, which is most likely the result of the sensitivity of the end mode to small variations and imperfection of the shape and edge materials. We show that this effect can be exploited as a means to separately characterize the magnetic properties of the nanomagnets as well as the size and shape variations within the array.
TL;DR: In this article, a single-layer 1-D high-index-contrast subwavelength grating structure is proposed for a vertical-cavity surface-emitting laser (VCSEL) structure.
Abstract: Recent advances in a single-layer 1-D high-index-contrast subwavelength grating structure are reviewed. Its incorporation into a vertical-cavity surface-emitting laser (VCSEL) structure enabled simple fabrication, lithographically defined polarization control and large aperture, single-transverse-mode control. Extraordinarily large fabrication tolerance is demonstrated with plusmn20% variation of the high-contrast grating (HCG) critical dimension. Emission wavelength of HCG-VCSEL varied 0.2% with a 40% change in lithography linewidth. Tunable VCSELs are fabricated using HCG, which led to a 8000 times reduction in the tunable mirror size and 160 times improved tuning speed of 63 ns. This configuration will open the door for a wide spectrum of optoelectronic devices in large wavelength regimes.
TL;DR: In this article, the frequency stabilization of an erbium-doped fiber distributed-feedback laser using an all-fiber based Michelson interferometer of large arm imbalance was reported.
Abstract: We report the frequency stabilization of an erbium-doped fiber distributed-feedback laser using an all-fiber based Michelson interferometer of large arm imbalance. The interferometer uses a 1 km SMF-28 optical fiber spool and an acousto optic modulator allowing heterodyne detection. The frequency noise power spectral density is reduced by more than 40 dB for Fourier frequencies ranging from 1 Hz to 10 kHz, corresponding to a level well below 1 Hz^2/Hz over the whole range. It reaches 10^{-2} Hz^2/Hz at 1 kHz. Between 40 Hz and 30 kHz, the frequency noise is shown to be comparable to the one obtained by Pound-Drever-Hall locking to a high finesse Fabry-Perot cavity. Locking to a fiber delay line could consequently represent a reliable, simple and compact alternative to cavity stabilization for short term linewidth reduction.
TL;DR: In this paper, the effects of ubiquitous laser noise on cooling and the coherent dynamics in optomechanical systems were discussed and conditions for optical ground-state cooling and coherent operations were experimentally feasible.
Abstract: We present a detailed theoretical discussion of the effects of ubiquitous laser noise on cooling and the coherent dynamics in optomechanical systems. Phase fluctuations of the driving laser induce modulations of the linearized optomechanical coupling as well as a fluctuating force on the mirror due to variations of the mean cavity intensity. We first evaluate the influence of both effects on cavity cooling and find that for a small laser linewidth, the dominant heating mechanism arises from intensity fluctuations. The resulting limit on the final occupation number scales linearly with the cavity intensity both under weak- and strong-coupling conditions. For the strong-coupling regime, we also determine the effect of phase noise on the coherent transfer of single excitations between the cavity and the mechanical resonator and obtain a similar conclusion. Our results show that conditions for optical ground-state cooling and coherent operations are experimentally feasible and thus laser phase noise does pose a challenge but not a stringent limitation for optomechanical systems.
TL;DR: In this paper, the effect of coherent coupling between the lasing levels with other levels on the transport properties and gain spectra was investigated and an expression for the slope discontinuity in the currentvoltage characteristics at lasing threshold was derived.
Abstract: We develop simple density-matrix models to describe the role of coherence in resonant-tunneling (RT) transport of quantum-cascade lasers (QCLs). Specifically, we investigate the effects of coherent coupling between the lasing levels with other levels on the transport properties and gain spectra. In the first part of the paper, we use a three-level density-matrix model to obtain useful analytical expressions for current transport through the injector barrier in a QCL. An expression for the slope discontinuity in the current-voltage characteristics at the lasing threshold is derived. This value is shown to be a direct measure of the population inversion at threshold and contradicts the previously held belief of it being indicative of ratio of the laser level lifetimes. In the second part of the paper, we use density matrices to compute the gain spectrum for a resonant-phonon terahertz QCL design. The large anticrossing of the doublet of lower radiative levels is reflected in a broad gain linewidth due to a coherent RT assisted depopulation process. At certain bias conditions, the gain spectrum exhibits double peaks which is supported by experimental observations.
TL;DR: In this article, the epitaxial Fe-deficient yttrium iron garnet (YIG) films with ferromagnetic resonance (FMR) linewidth as narrow as 0.9 Oe were sintered by pulsed laser deposition (PLD) technique.
Abstract: Recently we sintered by pulsed laser deposition (PLD) technique the epitaxial Fe-deficient yttrium iron garnet (YIG) films with ferromagnetic resonance (FMR) linewidth as narrow as 0.9 Oe, the unia ...
TL;DR: A fiber-optic interferometer optimized for best performance in the frequency range from dc to 1 kHz, with displacement linearity of 1% over a range of +/- 25 nm, and noise-limited resolution of 2 pm, is developed.
Abstract: We have developed a fiber-optic interferometer optimized for best performance in the frequency range from dc to 1 kHz, with displacement linearity of 1% over a range of +/- 25 nm, and noise-limited resolution of 2 pm. The interferometer uses a tunable infrared laser source (nominal 1550 nm wavelength) with high amplitude and wavelength stability, low spontaneous self-emission noise, high sideband suppression, and a coherence control feature that broadens the laser linewidth and dramatically lowers the low-frequency noise in the system. The amplitude stability of the source, combined with the use of specially manufactured "bend-insensitive" fiber and all-spliced fiber construction, results in a robust homodyne interferometer system, which achieves resolution of 40 fm Hz(-1/2) above 20 Hz and approaches the shot-noise-limit of 20 fm Hz(-1/2) at 1 kHz for an optical power of 10 microW, without the need for differential detection. Here we describe the design and construction of the interferometer, as well as modes of operation, and demonstrate its performance.
TL;DR: In this article, the coupling of individual InAs quantum dots (QDs) to an external-mirror microcavity was reported. But this was done with a single InAs layer on top of a distributed Bragg reflector, and the external mirror was bonded to a fiber and positioned above a semiconductor sample.
Abstract: We report the coupling of individual InAs quantum dots (QDs) to an external-mirror microcavity. The external mirror is bonded to a fiber and positioned above a semiconductor sample consisting of a QD-containing GaAs layer on top of a distributed Bragg reflector. This open cavity can be rapidly tuned with a piezo-electric actuator without negatively affecting the QD linewidth. A mirror radius of curvature of 42 μm and a cavity length of 10 μm enable good mode matching and thus high collection efficiency directly into the fiber. With an improved finesse, this system may enter the strong coupling regime.
TL;DR: The authors report on the achievement of lasing in rolled-up semiconductor microtubes at room temperature, wherein self-organized InGaAs/GaAs quantum dots are incorporated as the gain medium.
Abstract: The authors report on the achievement of lasing in rolled-up semiconductor microtubes at room temperature, wherein self-organized InGaAs/GaAs quantum dots are incorporated as the gain medium. The free-standing quantum dot microtubes, with a diameter of ~ 5-6 μm and wall thickness of ~ 100 nm, are formed when the coherently strained InGaAs/GaAs quantum dot heterostructure is selectively released from the GaAs substrate. The devices are characterized by an ultralow threshold (~ 4 μW) and a minimum intrinsic linewidth of ~ 0.2 – 0.3 nm at room temperature. The multiple lasing modes are analyzed using both the finite-difference time domain method and also a planar dielectric waveguide model.
TL;DR: In this paper, a density-matrix based theory of transport and lasing in quantum-cascade lasers is proposed, which reveals that large disparity between luminescent linewidth and broadening of the tunneling transition changes the design guidelines to favor strong coupling between injector and upper laser level.
Abstract: A density-matrix based theory of transport and lasing in quantum-cascade lasers reveals that large disparity between luminescent linewidth and broadening of the tunneling transition changes the design guidelines to favor strong coupling between injector and upper laser level. This conclusion is supported by the experimental evidence.
TL;DR: In this paper, an L-band tunable distributed feedback laser array (TLA) with a new design was developed to reduce the spectral linewidth, achieving a wide wavelength tuning range of ~ 40 nm with a high fiber output power of 20 mW and a high side-mode suppression ratio of >50 dB in the TLA module.
Abstract: We have developed an L-band tunable distributed feedback laser array (TLA) with a new design to reduce the spectral linewidth. A wide wavelength tuning range of ~ 40 nm is obtained with a high fiber output power of 20 mW and a high side-mode suppression ratio of >50 dB in the TLA module. A narrow linewidth of less than 580 kHz is achieved over the entire tuning range. Furthermore, we investigated the causes of linewidth variation. We found that a TLA with a longer cavity is more tolerant to external feedback, which reduces the variation in linewidth.