Showing papers in "IEEE Journal of Quantum Electronics in 2016"
TL;DR: A review of recent developments in radio-over-fiber technologies that can support the distribution of broadband wireless signals in a converged optical/wireless network and the challenges for the successful application in future wireless systems, such as 5G and 60-GHz networks are presented.
Abstract: Radio-over-fiber transmission has extensively been studied as a means to realizing a fiber optic wireless distribution network that enables seamless integration of the optical and wireless network infrastructures. Emerging wireless communication networks that support new broadband services provide increased opportunities for photonics technologies to play a prominent role in the realization of the next generation integrated optical/wireless networks. In this paper, we present a review of recent developments in radio-over-fiber technologies that can support the distribution of broadband wireless signals in a converged optical/wireless network. We also describe some of the challenges for the successful application of radio-over-fiber technologies in future wireless systems, such as 5G and 60-GHz networks.
179 citations
TL;DR: Recent new methods in wideband microwave photonic processing are presented, including ultra-wideband phase shifters and true time delays for phased array beamforming, widely tunable single passband filters, switchable microwave Photonic filters, wideband photonic mixers, high-resolution multiple frequency microwave photonics measurement systems, and photonic RF memory structures.
Abstract: Microwave photonic techniques are attractive for processing high bandwidth signals, overcoming inherent electronic limitations. These processors provide new capabilities for realizing adaptive processing over extremely wide microwave frequency ranges, ultra-wideband operation, and electromagnetic interference immunity. In-fiber signal processors are inherently compatible with fiber-wireless systems, and can provide connectivity with in-built signal conditioning. Recent new methods in wideband microwave photonic processing are presented, including ultra-wideband phase shifters and true time delays for phased array beamforming, widely tunable single passband filters, switchable microwave photonic filters, wideband photonic mixers, high-resolution multiple frequency microwave photonic measurement systems, and photonic RF memory structures.
118 citations
TL;DR: The conceptual architecture and the analytical model of OEOs, a comprehensive review to advances in OEO-based sensing, measurement, and detection applications is presented, including length change and distance measurement, refractive index estimation, load and strain sensing, temperature and acoustic sensing, optical clock recovery, and low-power RF signal detection.
Abstract: Besides distinct features on RF/optical signal generation, optoelectronic oscillators (OEOs) have also been rapidly developed as emerging techniques towards sensing, measurement, and detection. In this paper, we start with the conceptual architecture and the analytical model of OEOs. Then, three operation principles behind sensing, measurement, and detection applications are categorized, including the variation on the time delay of loop, the passband reconfiguration of microwave photonic filter in loop, and the oscillation gain from injection locking, which clearly clarify the X-to-frequency mapping (X denotes target parameter or signal) for supporting practical solutions and approaches. Next, a comprehensive review to advances in OEO-based sensing, measurement, and detection applications is presented, including length change and distance measurement, refractive index estimation, load and strain sensing, temperature and acoustic sensing, optical clock recovery, and low-power RF signal detection. As a new application example, a novel approach for in-line position finding is proposed. When a long fiber Bragg grating inserted into OEO is locally heated to slightly broaden its reflection spectrum, the target position heated is mapped into the oscillating frequency shift, according to the first operation principle. A sensitivity of 254.66 kHz/cm is obtained for position finding in the experiment. Afterward, solutions for calibration and stabilization are briefly introduced, which enable us to improve the accuracy and reliability. Finally, features and future prospects on the sensing, measurement, and detection applications are discussed, such as compact and integrated OEOs.
110 citations
TL;DR: An overview about the recent work on silicon-based integrated microwave photonics is presented with an emphasis on Silicon-based on-chip photonic arbitrary microwave waveform generation and microwave signals processing.
Abstract: Integrated microwave photonics is an emerging field in which photonic integrated technologies are employed to realize on-chip integration of microwave photonic systems with the aim to enrich the functionalities and enhance the system performance. Silicon photonics, as one of the various photonic integrated technology platforms, has attracted worldwide attention to achieve microwave photonic system integration for its compatibility with the current CMOS technology and its potential of seamless integration with electronics. In this paper, an overview about our recent work on silicon-based integrated microwave photonics is presented with an emphasis on silicon-based on-chip photonic arbitrary microwave waveform generation and microwave signals processing.
99 citations
TL;DR: The potential photonic integration platforms are reviewed and discussed how a monolithic integration based on photonic membranes fits the photonic mm-wave beam steering application, especially for the ease of EIC and PIC integration on a single chip.
Abstract: Recently, the desired very high throughput of 5G wireless networks drives millimeter-wave (mm-wave) communication into practical applications. A phased array technique is required to increase the effective antenna aperture at mm-wave frequency. Integrated solutions of beamforming/beam steering are extremely attractive for practical implementations. After a discussion on the basic principles of radio beam steering, we review and explore the recent advanced integration techniques of silicon-based electronic integrated circuits (EICs), photonic integrated circuits (PICs), and antenna-on-chip (AoC). For EIC, the latest advanced designs of on-chip true time delay (TTD) are explored. Even with such advances, the fundamental loss of a silicon-based EIC still exists, which can be solved by advanced PIC solutions with ultra-broad bandwidth and low loss. Advanced PIC designs for mm-wave beam steering are then reviewed with emphasis on an optical TTD. Different from the mature silicon-based EIC, the photonic integration technology for PIC is still under development. In this paper, we review and explore the potential photonic integration platforms and discuss how a monolithic integration based on photonic membranes fits the photonic mm-wave beam steering application, especially for the ease of EIC and PIC integration on a single chip. To combine EIC, for its accurate and mature fabrication techniques, with PIC, for its ultra-broad bandwidth and low loss, a hierarchical mm-wave beam steering chip with large-array delays realized in PIC and sub-array delays realized in EIC can be a future-proof solution. Moreover, the antenna units can be further integrated on such a chip using AoC techniques. Among the mentioned techniques, the integration trends on device and system levels are discussed extensively.
96 citations
TL;DR: This paper presents a concrete example of ID Quantique's random-detector-efficiency countermeasure against detector blinding attacks and finds that it is still vulnerable against the modified blinding attack, because an assumption about hardware characteristics on which the proof relies fails in practice.
Abstract: In the last decade, efforts have been made to reconcile theoretical security with realistic imperfect implementations of quantum key distribution. Implementable countermeasures are proposed to patch the discovered loopholes. However, certain countermeasures are not as robust as would be expected. In this paper, we present a concrete example of ID Quantique’s random-detector-efficiency countermeasure against detector blinding attacks. As a third-party tester, we have found that the first industrial implementation of this countermeasure is effective against the original blinding attack, but not immune to a modified blinding attack. Then, we implement and test a later full version of this countermeasure containing a security proof. We find that it is still vulnerable against the modified blinding attack, because an assumption about hardware characteristics on which the proof relies fails in practice.
82 citations
TL;DR: It is shown that for the majority of radio access scenarios where front-haul optical links are less than 10-km long, the impact of inter-core crosstalk on the electrical carrier-to-noise ratio can be neglected, and thus, link design can be carried independently core by core.
Abstract: We propose the use of spatial division multiplexing supported by multicore fibers to implement a new generation of flexible and capacity reconfigurable cloud radio access network front-haul architectures capable of addressing their main present and future challenges. We show that for the majority of radio access scenarios where front-haul optical links are less than 10-km long, the impact of inter-core crosstalk on the electrical carrier-to-noise ratio can be neglected, and thus, link design can be carried independently core by core. In addition, this MCF-based approach, which is compatible with software defined networking and network function virtualization, can also support the integration of a passive optical network overlay.
65 citations
TL;DR: In this paper, the authors investigated the carrier transport characteristics of AlGaN-based deep-ultraviolet light-emitting diodes (LEDs) and showed that hole transport/injection may be severely obstructed by the large potential barrier at the p- electron-blocking layer/p-GaN interface.
Abstract: Carrier transport characteristics of AlGaN-based deep-ultraviolet light-emitting diodes (LEDs) are theoretically investigated. Simulation results reveal that hole transport/injection may be severely obstructed by the large potential barrier at the p- electron-blocking layer/p-GaN interface. Under this circumstance, the slope efficiency degrades and electron leakage increases accordingly. By inserting the AlGaN interlayers to form band-engineered staircase p-region, both the transport/injection of holes and $I$ – $V$ characteristic are improved. Moreover, the LED characteristics become less sensitive to the polarization field, which is beneficial for obtaining high LED performance with the LED of high crystalline quality.
60 citations
TL;DR: In this paper, the authors describe continuous millimeter-wave and terahertz (THz)-wave applications, where telecom-based photonics technologies are efficiently employed to enhance their performance.
Abstract: This paper describes continuous millimeter-wave and terahertz (THz)-wave applications, where telecom-based photonics technologies are efficiently employed to enhance their performance. First, 300-GHz-band wireless communications are described toward real-time error-free transmissions at 50 Gbit/s and beyond. Next, a novel approach to increase a phase measurement sensitivity in THz frequency-domain spectroscopy systems is explained, and a similar technique is successfully applied to the visualization of electric-field radiation and propagation. Finally, as a futuristic study, the manipulation of THz waves with a concept of photonic crystals and its possible applications to platforms in THz integrated systems are presented.
58 citations
TL;DR: A review of photonic-assisted radio-frequency arbitrary waveform generation (RF-AWG) with emphasis on programmable ultrabroadband microwave and millimeter-wave waveforms is presented in this paper.
Abstract: This paper reviews recent advances in photonic-assisted radio-frequency arbitrary waveform generation (RF-AWG), with emphasis on programmable ultrabroadband microwave and millimeter-wave waveforms. The key enabling components in these techniques are programmable optical pulse shaping, frequency-to-time mapping via dispersive propagation, and high-speed photodetection. The main advantages and challenges of several different photonic RF-AWG schemes are discussed. We further review some proof-of-concept demonstrations of ultrabroadband RF-AWG applications, including high-resolution ranging and ultrabroadband non-line-of-sight channel compensation. Finally, we present recent progress toward RF-AWG with increased time aperture and time-bandwidth product.
57 citations
TL;DR: In this paper, the authors investigated the extraordinary behavior of periodic photonic structures within radiation continuum from the perspective of interfering resonance and reformulated the coupled-channel equations of both TE-like and TM-like polarizations into the similar forms of the quantum-defect theory that describes the interference of resonances belonging to different Coulombic quantum channels.
Abstract: We investigate the extraordinary behavior of periodic photonic structures within radiation continuum from the perspective of interfering resonance. The coupled-channel equations of both TE-like and TM-like polarizations are reformulated into the similar forms of the quantum-defect theory that describes the interference of resonances belonging to different Coulombic quantum channels. The concepts of closed-channel, open-channel, coupling potential, and eigenvalues are well interpreted. Some iteration techniques, i.e., field-iteration and k-iteration, are proposed to obtain self-consistent solution of the coupled-channel equations. The iterations are important to guarantee quantitative accuracy for high-index-contrast structure, in which the strength of wave interactions is significantly enhanced compared with its low-index-contrast counterpart. The semianalytical results of resonance wavelength, transmissivity/reflectivity spectrum, and band structure agree well with the rigorous coupled-wave analysis (RCWA) and finite-difference time-domain (FDTD) simulation, confirming the accuracy of the iterations. The interfering resonance provides a clear and consistent picture to understand the periodic photonic structure within radiation continuum, and also reveals the intrinsic similarities between the photonic and quantum systems.
TL;DR: In this article, a modified Fowler equation is used to describe the internal photoemission effect (IPE) in Schottky junctions, and the existing Vickers model has been commented and enriched.
Abstract: The theory of an internal photoemission effect (IPE) in Schottky junctions has been reviewed, and the existing Vickers model has been commented and enriched. Indeed, since the modified Fowler equation is very often used to describe the IPE even when approximations on which it is based are not met, we have derived precise conditions that allow the use of the modified Fowler equation and, possibly, as it may change in the case where these conditions were not verified. Our theory shows how the performance of the surface-illuminated Schottky devices can be optimized, and we propose an analytical formulation able to calculate the metal thickness maximizing the efficiency of the devices. In addition, we prove how the minimum detectable optical power is closely linked to the area of the metal-semiconductor junction. The model has been applied to describe the theoretical limitations on the performance of surface-illuminated silicon Schottky photodetectors at both near-infrared wavelengths and room temperature. Our insights are of great importance to understand if IPE-based Si devices have the potentialities to compare favorably with photodetectors realized with materials based on III-V elements (e.g., GaAs and GaAsIn) and to play a key role in the telecommunications.
TL;DR: In this paper, three types of perovskite solar cells are simulated with the program 1-D device simulation program for the analysis of microelectronic and photonic structure, and the hole transport material-free MAPbI3 solar cells attain the simulated PCE of 24.1%.
Abstract: The organic-metal halide perovskite solar cells have recently shown the high power conversion efficiency (PCE) exceeding 20%. A better understanding of the relationships between material parameters, device architectures, and performance is still required for the continued development of the perovskite solar cells. Three types of architectures are simulated with the program 1-D device simulation program for the analysis of microelectronic and photonic structure. The hole transport material-free MAPbI3 solar cells attain the simulated PCE of 24.1%. A maximum PCE of 26.60% and a maximum $V_{\mathrm {OC}}$ (open-circuit voltage) of 1.83 V for FTO/ZnO/MAPbX3 ( $X = I$ and Br)/CuSCN/Au-based solar cells are predicted, respectively. The FTO/ZnO/MAPbI3/MAPbBr3/CuSCN/Au-based solar cells first designed possesses a characteristic of tunable PCE and $V_{\mathrm {OC}}$ by changing the thicknesses of MAPbI3 and MAPbBr3, and the PCE of 27.50% ( $J_{\mathrm {SC}} = 26.17$ mA/cm2, $V_{\mathrm {OC}} = 1.19$ V, and $\textrm {FF} = 0.88$ ) was obtained. These simulation results can help researchers to reasonably choose materials and optimally design high-performance perovskite solar cells.
TL;DR: In this article, the authors evaluate the constriction resistance and current crowding in nanolasers using the finite-element method based calculations and identify the location where most current crowdings and most Joule heating occur.
Abstract: We evaluate the constriction resistance and current crowding in nanolasers using the finite-element method based calculations. We examine both the vertical contact and horizontal contact structures, representing the typical top contact and bottom contact of nanolasers, respectively. We find that, in general, constriction resistance and the degree of current crowding in the bottom horizontal contact in nanolasers are much larger than those in the top vertical contact. For both contacts, constriction resistance and, therefore, the degree of current crowding increase as the nanolaser radius decreases, the amount of undercut increases, or the angle (either positive or negative) of the sidewall tilt increases. The location where most current crowding and most Joule heating occur is identified. The results may provide insights into the design optimization of nanolasers.
TL;DR: This paper demonstrates ultra-fast millimeter wave beam steering with settling times below 50 ps, and shows the successful symbol-by-symbol steering for data streams as fast as 10 GBd, and suggests a scheme to enable novel high bit-rate multiple access schemes.
Abstract: In this paper, we demonstrate ultra-fast millimeter wave beam steering with settling times below 50 ps. A phased array antenna with two elements is employed to realize beam steering. The phased array feeder is implemented with a recently introduced time delay line that provides, at the same time, an ultra-fast tunability, broadband operation, and continuous tuning. Our implementation is used to perform symbol-by-symbol steering. In our demonstration, the beam direction is switched between two sequentially transmitted symbols toward two receivers placed 30° apart. We show the successful symbol-by-symbol steering for data streams as fast as 10 GBd. The suggested scheme shows that the ultra-fast beam steering is becoming practical and might ultimately enable novel high bit-rate multiple access schemes.
TL;DR: In this article, the amplitude and phase noise of an optical frequency comb based on InAs/InP quantum-dash mode-locked laser was investigated, and it was shown that by actively mode-locking the laser, 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 ~1.1 THz.
Abstract: 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 modelocking 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 ~1.1 THz.
TL;DR: In this paper, the authors present a numerical model that provides valuable insight into the dynamics of a dual-wavelength pumped fiber laser that can operate on the 3.5-and 2.8-MHz bands.
Abstract: The performance of mid-infrared Er3+-doped fiber lasers has dramatically improved in the last few years. In this paper, we present a numerical model that provides valuable insight into the dynamics of a dual-wavelength pumped fiber laser that can operate on the 3.5- and 2.8- $ {\mu }\text{m}$ bands. This model is a much needed tool for optimizing and understanding the performance of these laser systems. Comparisons between simulation and experimental results for three different systems are presented.
TL;DR: In this paper, the authors reported the observation of narrow tilted lobes in the far-field emission pattern of leaky oxide-confined vertical-cavity surface-emitting lasers (VCSELs).
Abstract: We report the observation of narrow tilted lobes in the far-field emission pattern of leaky oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The VCSEL cavity is surrounded by two selectively oxidized aperture layers, which are intentionally designed to produce a high lateral leakage of the high-order transverse modes of the vertical cavity. The device operates in the fundamental transverse mode at oxide aperture diameters below $5~\mu \text{m}$ and currents up to 4 and 5 mA. At higher currents or larger aperture diameters, an additional high-order transverse optical mode evolves. This mode is revealed by the appearance of a shorter wavelength emission line in the electroluminescence spectra of the device, resulting in multi-mode lasing and in the related changes in the near- and far-field patterns. In the far-field pattern, the evolution of the high-order mode is revealed by the evolution of the two overlapping emission lobes at moderate (~5°) tilt angles with respect to the normal to the surface and by the appearance of a multi-spot or a ring pattern in the CCD camera images. Most importantly, the appearance of this high-order transverse mode is accompanied by an observation of much narrower lobes in the far-field pattern observed at significantly larger tilt angles (~35°). The tilt angle and the narrow angular width of these emission lobes in the far-field spectrum are in agreement with those calculated in the 3-D cold cavity modeling of the optical modes of the device. These narrow tilted lobes revealed in this paper are the fingerprints of the leakage effect in specially designed oxide-confined VCSELs with their intensity being proportional to the optical power leaving the aperture region in the direction parallel to the surface and propagating into the oxidized region. The effect can be applied for engineering of single-mode VCSELs, coherently-coupled 2-D VCSEL arrays, laterally integrated VCSEL-photodetector chips, and VCSELs integrated to slow light waveguides, for coupled optical gates for optical computers and other types of photonic integrated circuits.
TL;DR: In this article, the authors designed modified OFDM signals with adaptive power and bit allocation to improve the bandwidth utilization and maximize the data rate in a 20-km standard single mode fiber link with a 10GHz commercial Mach-Zehnder (MZ) intensity modulator and direct detection.
Abstract: In current metro and access optical networks, the frequency band beyond the bandwidth of the electro-optical components is always deprecated due to the fading frequency response. On the other hand, an orthogonal frequency division multiplexing (OFDM) system is managed on individual subcarrier and can adapt to the varied channel frequency response by optimally allocating different modulation formats and powers across different subcarriers. Therefore, to reuse the commercial low bandwidth components in high speed networks, we design modified OFDM signals, which are with adaptive power and bit allocation, to improve the bandwidth utilization and maximize the data rate. We successfully transmit 16-GHz optical OFDM signals over a 20-km standard single mode fiber link with a 10-GHz commercial Mach–Zehnder (MZ) intensity modulator and direct detection. Eleven modulation formats are used for bit loading and the maximum data rate can reach 88.8 Gb/s. The modulation bandwidth utilization of the MZ modulator is increased by 60%.
TL;DR: In this paper, the authors derived an easy-to-apply fitting function, which allows the extraction of consistently expanded figures of merit for all VCSELs, particularly for devices with carrier reservoir splitting.
Abstract: In this paper, we show that the dynamic performance of multi-mode vertical-cavity surface-emitting lasers (VCSELs) can be modeled by single-mode rate equations developed for edge emitters as long as the lasing modes share a common carrier reservoir. However, this assumption does not hold for ultra-high performing VCSEL devices. Due to the high photon densities inside these optimized VCSELs, the common carrier reservoir splits up as a result of the spatial hole burning effect. This is caused by the high intensity of the multiple transverse modes. In this case, a small-signal modulation response with a different shape is expected. We derive an easy-to-apply fitting function, which allows the extraction of consistently expanded figures of merit. This novel function works for all VCSELs, particularly, including devices with carrier reservoir splitting. Furthermore, we use this new model to perform a detailed analysis of our latest VCSEL generation with a modulation bandwidth of up to 32.7 GHz.
TL;DR: A fast active-quenching circuit (FAQC) based on SiGe Hetero-junction Bipolar Transistor (HBT) and InGaP/GaAs HBT integrated circuits is designed for use with free-running single-photon avalanche diodes (SPADs) as discussed by the authors.
Abstract: A fast active-quenching circuit (FAQC) based on SiGe Hetero-junction Bipolar Transistor (HBT) and InGaP/GaAs HBT integrated circuits is designed for use with free-running single-photon avalanche diodes (SPADs). The performances of both InGaAsP/InP SPAD and InGaAs/InP SPAD are tested. Results show that the typical avalanche duration using the FAQC is 1.6 ns, and the total afterpulse probability is lower than 10% when the hold-off time is above 1 μs at 1.5 V excess bias or 10 μs at 3.0 V excess bias. This result is comparable to recently developed negative-feedback avalanche diodes. The FAQC is based on commercially available integrated circuits and can be used with typical SPADs, providing a low-cost approach to build a free-running single-photon detector.
TL;DR: In this article, the influence of traditional AlGaN bulk electron blocking layer (EBL) and AlGaNs/GaN superlattice (SL EBL) with various thicknesses of GaN layers on NUV LEDs is explored.
Abstract: The optical performance and relevant physical properties of near-ultraviolet (NUV) GaN-based light-emitting diodes (LEDs) are investigated. Specifically, the influence of traditional AlGaN bulk electron blocking layer (EBL) and AlGaN/GaN superlattice (SL) EBL with various thicknesses of AlGaN layers on NUV LEDs is explored. It is indicated from the band diagrams, electrostatic field profile, electron reflecting and hole transmitting spectra, and carrier concentrations profile that the use of a thin AlGaN layer of AlGaN/GaN SL EBL is beneficial to the electron confinement and hole injection in the active region, which results in the high internal quantum efficiency and low efficiency droop at high injection current. Moreover, the experimental results show that replacing the traditional AlGaN bulk EBL with the AlGaN/GaN SL EBL can markedly improve the optical performance. When compared with the NUV LED with traditional AlGaN bulk EBL, the output power of the NUV LED with the proposed AlGaN/GaN SL EBL increases from 13.5 to 48.7 mW at 100 mA.
TL;DR: Based on the nonlinear effect of high order sideband generation in the nonperturbative regime, the optical high-order sideband combs consisting of equally spaced spectral lines in frequency space can be generated in both cavities of the molecule.
Abstract: An optical high-order sideband comb generation scheme is theoretically and numerically studied in a photonic molecule optomechanical system. The photonic molecule optomechanical system consists of two directly coupled optical microcavities with one cavity of the molecule supports a mechanical mode. The system is coherently driven by an input two-tone laser, which consists of a continuous-wave coupling field and an intense continuous-wave pump field. Based on the nonlinear effect of high-order sideband generation in the nonperturbative regime, the optical high-order sideband combs consisting of equally spaced spectral lines in frequency space can be generated in both cavities of the molecule. This paper reveals that the comb generation is associated with the cavity-cavity coupling strength, and the comb generation and manipulation in a controlled way might be achieved using the proposed setup.
TL;DR: In this article, the authors presented explicit expressions of the bimodal interferometer response, proving phenomena such as 100% reflection peaks and predicting their positions, and provided a completely new perspective on high contrast gratings.
Abstract: The operation of several optical components, such as high-contrast gratings, is based on the interference between two oscillation modes Therefore, this paper is devoted to the complete characterization of bimodal Fabry–Perot interferometers, which can effectively model such two-mode interactions Thanks to a novel parameterization of the mirror scattering matrices, this paper presents for the first time explicit expressions of the bimodal interferometer response, proving phenomena such as 100% reflection peaks, and predicting their positions For this reason, this paper, which complements—rather than replaces—the existing numerical techniques, provides a completely new perspective on high-contrast gratings
TL;DR: In this article, a peak value of autocorrelation coefficient at the feedback round trip time and the ratio between this peak value and its background are used to quantitatively identify the time-delay (TD) signature of chaos.
Abstract: The time-delay signature and the chaos bandwidth in three-cascaded vertical-cavity surface-emitting lasers have been investigated experimentally. A peak value of autocorrelation coefficient at the feedback round trip time and the ratio between this peak value and its background are used to quantitatively identify the time-delay (TD) signature of chaos. A new concept—peak to side-peak ratio is introduced for better quantification of the TD signature concealment. The peak to side-peak ratio is defined as the ratio between the peak value of autocorrelation coefficient at the TD and the peak value at a delay time other than the TD and zero delay time. Three injection cases, namely, small bandwidth, intermediate bandwidth, and wide bandwidth of the injecting chaos signals, have been used to study the effect of the bandwidth of the injecting chaos on the TD concealment. The experimental results show that the time-delay signature can be totally concealed in the slave laser subject to the intermediate bandwidth of chaotic optical injection over a wide frequency detuning range.
TL;DR: In this article, the response of nanolasers subject to optical injection has been analyzed using rate equations, which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor I².
Abstract: The response of nanolasers subject to optical injection has been analyzed. Calculations have been performed using rate equations, which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor I². In the analysis, the influence of F and I² is evaluated for varying the injection strength and frequency detuning between the master and slave laser. It is observed that, in general, increased F and I² increases the stable locking region and have only a few regions of dynamic instability as compared with conventional semiconductor lasers over a large frequency detuning. It is also found that for larger F, the modulation bandwidths of 90 GHz can be achieved.
TL;DR: In this article, it was shown that the spectrum of an optical pulse splits into multiple, widely separated, spectral bands when it arrives at a temporal boundary across which the refractive index suddenly changes.
Abstract: We show numerically that the spectrum of an optical pulse splits into multiple, widely separated, spectral bands when it arrives at a temporal boundary across which the refractive index suddenly changes. At the same time, the pulse breaks into several temporally separated pulses traveling at different speeds. The number of such pulses depends on the dispersive properties of the medium. We study the effect of second- and third-order dispersion in detail but also briefly consider the impact of other higher order terms. A temporal waveguide formed with two temporal boundaries can reflect the temporally separated pulses again and again, increasing the number of pulses trapped within the temporal waveguide.
TL;DR: In this article, the effects of gain nonlinearity on the time delay signature (TDS) of both intensity and phase chaos in semiconductor lasers (SLs) with optical feedback are investigated numerically.
Abstract: The effects of gain nonlinearity on the time delay signature (TDS) of both intensity and phase chaos in semiconductor lasers (SLs) with optical feedback are investigated numerically. The SLs subject to single-path feedback are mainly considered, and SLs with dual-path feedback are also discussed for the sake of generality. The TDS is evaluated via both auto-correlation function (ACF) and permutation entropy function. It is found that the TDS is more sensitive to nonlinear gain factor (NGF) for large injection current and low feedback strength. For given feedback strength, the peak heights of ACF for both intensity and phase chaos around TDS can be decreased by using SL with low NGF, especially when the injection current is relative high. Furthermore, with low NGF, successful TDS concealment can be achieved in wider region in the parameter planes of feedback strength and injection current. Hence, careful selection of an internal parameter is an effective candidate for TDS concealment in wider parameter region, which is complementary to the existing techniques by controlling the external parameters, and thus is highly desirable for expanding the key space for chaos-based secure communication.
TL;DR: In this paper, a model including pump absorption saturation effect and overlap efficiency along the beam propagation direction, as well as non-radiative decays due to high doping concentration was developed.
Abstract: In this paper, factors influencing the performance of high-gain Nd:YVO4 amplifiers are analyzed and a schematic map of the relationships between different factors is given. A model, including the pump absorption saturation effect and overlap efficiency along the beam propagation direction, as well as non-radiative decays due to high doping concentration, is developed. The performance of laser amplifier is studied by changing doping concentration, pump beam quality, and focal size of pump laser. To get high gain, samples with low doping concentration should cooperate with long crystals and laser diodes with good beam quality. Based on the model, the focal radius of pump laser could be optimized for different doping concentrations and beam qualities of pump laser. Experiments were conducted and the results agreed well with the simulated ones. Moreover, a single-stage and single-pass amplifier was realized, achieving a small-signal gain of 51 dB.
TL;DR: In this article, the dynamics of mutually coupled nano-laser has been explored theoretically using rate equations which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor β.
Abstract: The dynamics of mutually coupled nano-lasers has been explored theoretically. Calculations have been performed using rate equations which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor β. In the analysis, the influence of F and β has been evaluated for varying optical injection strength and distance between the two lasers. It is observed that, in general, for increased bias current, the system can maintain stable output for a larger mutual coupling strength. It is also found that for short inter-laser distances and larger F, the stability of mutually coupled nano-lasers is enhanced.