Showing papers in "IEEE Journal of Quantum Electronics in 2019"

A Review of High-Performance Quantum Dot Lasers on Silicon

Abstract: Laser gain regions using quantum dots have numerous improvements over quantum wells for photonic integration. Their atom-like density of states gives them unique gain properties that can be finely tuned by changing growth conditions. The gain bandwidth can be engineered to be broad or narrow and to emit at a wide range of wavelengths throughout the near infrared. The large energy level separation of the dot states from the surrounding material results in excellent high-temperature performance and gain recovery at sub-picosecond timescales. The fact that the quantum dots are isolated from each other and act independently at inhomogeneously broadened wavelengths results in ultralow linewidth enhancement factors, highly stable broadband mode-locked lasers, single-section mode locking, and the possibility of reduced crosstalk between amplified signals at low signal injection and enhanced four-wave mixing at high signal injection. The high carrier confinement and areal dot density provide reduced sensitivity to crystalline defects allowing for long device lifetimes even when epitaxially grown on silicon at high dislocation densities.

Fabrication and Characterization of Active-Matrix $960\times540$ Blue GaN-Based Micro-LED Display

Abstract: In this paper, we demonstrate a high-resolution $960\times 540$ blue-emitting active matrix micro-display. The blue micro-display have a diagonal length of 0.55 inch, a pixel size of $8~\mu \text{m}$ with a pixel pitch of $12.8~\mu \text{m}$ , and high pixel density of 2000 pixels per inch. The single pixel of micro-display exhibits excellent characteristics including an extremely low-leakage current of 0.1 pA at −5 V, a low forward voltage of 2.73 V, a narrow full width at half maximum of 15.7 nm of electroluminescence spectra, a high external quantum efficiency of 13.3%, and a deep-blue emission with CIE coordinates of (0.1589, 0.0542) at $11~\mu \text{A}$ . Besides, the single pixel of micro-LED also shows high brightness of $4.2 \times 10^{6}$ and $7.4 \times 10^{6}$ cd/m2 at $500~\mu \text{A}$ and 1 mA, respectively. The complete $960\times 540$ micro-display has a contrast ratio of 3600000:1, the power consumption with all on is 0.5 W, and the pixel yield rate of about 98.674% analyzed by the software ImageJ.

Designing Dual-Band Absorbers by Graphene/Metallic Metasurfaces

Abstract: This paper presents a novel approach for designing dual-band absorbers based on graphene and metallic metasurfaces for terahertz and mid-infrared regimes, respectively. The absorbers are composed of a 2D array of square patches deposited on a dielectric film terminated by a metal plate. Using an analytical circuit model, we obtain closed-form relations for different parameters of the structure to achieve the dual-band absorber. Two absorption bands with an obtained absorptivity of 98% at 0.53 and 1.53 THz for the graphene-based structure and 7 and 25 THz for the metallic-based case are achieved. We demonstrate that the graphene-based absorber remains as the dual band for a wide range of the Fermi level. Furthermore, the recommended dual-band absorbers are insensitive in terms of polarization and remain within various incident angles. The most important advantage of this device is its simplicity compared with the previously reported structures.

The Importance of p-Doping for Quantum Dot Laser on Silicon Performance

Abstract: $p$ -type modulation doping of the quantum dot active region is known to improve high temperature and dynamic performance of quantum dot lasers. These improvements are critical to realizing commercially relevant quantum dot devices on silicon and are shown to enable continuous wave operation over 100°C, nearly complete insensitivity to optical feedback, and orders of magnitude improvement in device reliability relative to unintentionally doped active regions. Also described is a spectrally resolved analysis of the effect of p-modulation doping on the optical gain revealing anomalous behavior that explains the high characteristic temperatures commonly observed in literature for similar devices on native substrate.

Numerical and experimental analysis of optical frequency comb generation in gain-switched semiconductor lasers

Abstract: This work was funded by the Ministerio de Economia y Competitividad of Spain (COMBINA, TEC201565212-C3-1-P and TEC201565212-C3-2-P). A. Rosado, A. Perez-Serrano, J. M. G. Tijero and I. Esquivias also acknowledge support from Comunidad de Madrid and European Structural Funds under program SINFOTON2-CM (P2018/NMT-4326). A. Perez-Serrano acknowledges support from the Programa Propio of the Universidad Politecnica de Madrid.

Self-Correction Limits in Dual-Comb Interferometry

Abstract: Self-sufficient correction algorithms have recently been developed to estimate and compensate the relative frequency noise between two free-running frequency combs using only their dual-comb interferograms (IGMs). However, such algorithms are limited by the relatively low observation rate of the frequency noise, equal to the IGM repetition rate. In this paper, we analyze the effectiveness of estimation methods based on the cross-correlation function and the ambiguity function. We derive estimators and obtain their theoretical variances as a function of the IGMs’ measurable parameters to later establish criteria that verify the success rate of each method for the correction and coherent averaging of successive IGMs. Finally, we present different cases of both real and simulated dual-comb systems and assess their compatibility with these estimation methods.

Optical Frequency Comb Generation Using CMOS Compatible Cascaded Mach–Zehnder Modulators

Abstract: Optical frequency combs (OFCs) play a key role in a variety of applications and have been implemented primarily using mode-locked lasers, Kerr resonators, and electro-optic (EO) modulation. EO modulation-based OFC generation may not yield as many comb lines nor span as broad a bandwidth as mode-locked lasers or Kerr resonators; however, it offers a high degree of tunability in central frequency and comb spacing. Integrated solutions are of interest as they significantly reduce device footprint and enable large scale system integration. In this paper, we demonstrate flexible on-chip OFC generation using two cascaded EO Mach-Zehnder modulators in silicon photonics. We demonstrate quasi-rectangular OFCs with 9 lines and a comb spacing of up to 10 GHz with an amplitude variation (comb flatness) within 6.5 dB. The corresponding time-domain waveforms have a good fit with sinc-shaped Nyquist pulses having a full-width at half maximum duration as short as 11.4 ps.

Mid-Wave Infrared InAs/GaSb Type-II Superlattice Photodetector With n-B-p Design Grown on GaAs Substrate

Abstract: In this paper, we report the direct growth and characterization of a mid-wave infrared InAs/GaSb type-II superlattice n-B-p photodetector on a GaAs substrate. The design consists of an n-doped contact, a wide bandgap unipolar barrier, and a p-doped absorber, which uses photogenerated electron as minority carriers to enjoy the longer electron diffusion length compared with hole diffusion length. At 77 K, the device exhibits a dark current density of $2.9\times 10^{-5}$ A/cm2 under −0.1 V and a zero-bias differential-resistance-area product (R0A) in excess of $8\times 10^{3}~ \Omega \cdot \text {cm}^{2}$ . Arrhenius analysis of dark current demonstrates that the dominant mechanism is diffusion at a temperature higher than 130 K. 50% cutoff wavelength of the detector is found at $6.4~\mu \text{m}$ at 77 K under zero bias, with a peak responsivity of 0.56 A/W. The corresponding specific detectivity is $7.6\times 10^{11}~\text {cm}\cdot \text {Hz}^{1/2}$ /W. The key device parameters which limit the further optimization of performance are discussed.

Design of InP-Based High-Speed Photodiode for 2- $\mu$ m Wavelength Application

Abstract: In this paper, we proposed and designed the high speed uni-traveling carrier photodiodes operating beyond $2~\mu \text{m}$ . InGaAs/GaAsSb type-II multiple quantum wells (MQWs) were used as the absorption region of uni-traveling carrier photodiode to have optical response beyond $2~\mu \text{m}$ . A rate equation model was developed to study the bandwidth characteristics of this photodiode. The carrier dynamics of the carrier sweeping out process was discussed, and the structure parameters of the quantum wells were optimized. Result shows a 3-dB bandwidth over 40 GHz can be achieved with the optimized design. We also studied the feasibility of dual depletion PIN (DD-PIN) photodiode with MQWs absorber. The optimized DD-PIN photodiode could achieve similar bandwidth under relatively high-bias condition.

Physical Origin of the Optical Degradation of InAs Quantum Dot Lasers

Abstract: We present an extensive analysis of the physical mechanisms responsible for the degradation of 1.3-μm InAs quantum dot lasers epitaxially grown on Si, for application in silicon photonics. For the first time, we characterize the degradation of the devices by combined electro-optical measurements, electroluminescence spectra, and current-voltage analysis. We demonstrate the following original results: when submitted to a current step-stress experiment: 1) QD lasers show a measurable increase in threshold current, which is correlated to a decrease in slope efficiency; 2) the degradation process is stronger, when devices are stressed at current higher than 200 mA, i.e., in the stress regime, where both ground-state and excited-state emission are present; and 3) in the same range of stress currents, an increase in the defect-related current components is also detected, along with a slight decrease in the series resistance. Based on the experimental evidence collected within this paper, the degradation of QD lasers is ascribed to a recombination-enhanced defect reaction (REDR) process, activated by the escape of electrons out of the quantum dots.

Efficient Tm:LiYF 4 Lasers at ${\sim}2.3~\mu$ m: Effect of Energy-Transfer Upconversion

Abstract: The 3H4 $ \to $ 3H5 transition of Thulium ions (Tm3+), which features laser emission at $\sim 2.3~\mu \text{m}$ is studied in details. We revise the conditions for efficient laser operation using a rate-equation model accounting for the ground-state bleaching, cross-relaxation and energy-transfer upconversion (ETU). We show that ETU has a crucial role in reaching more than unity pump quantum efficiency (QE) for $\sim 2.3~\mu \text{m}$ Tm lasers based on highly-doped crystals. A Ti:Sapphire pumped quasi-continuous-wave 3.5 at.% Tm:LiYF4 laser generated 0.73 W at 2306 nm with a record-high slope efficiency of 47.3% (versus the absorbed pump power, for double-pass pumping) featuring a QE of 1.27. Diode-pumping of this crystal yielded a peak output power of >2 W. The first $2.3~\mu \text{m}$ Tm waveguide laser is also reported based on Tm:LiYF4 epitaxial layers with even higher doping of 6.2 at.% generating 0.23 W with a slope efficiency of 19.8%. The spectroscopic properties of Tm:LiYF4 relevant for the $\sim 2.3~\mu \text{m}$ laser operation are revised as well.

SiGe Photo-Transistor for Low-Cost SSMF-Based Radio-Over-Fiber Applications at 850nm

Abstract: This paper investigates the possibility of implementing SiGe Hetero-junction bipolar Photo-Transistor (HPT) within low cost and low power consumption Radio-over-Fiber (RoF) systems based on standard single mode fiber (SSMF) operating in the first optical window for wireless communication networks scenarios. The SiGe HPT under study has potential lower cost compared to standard PIN photo-detectors as it is fabricated through the consolidated SiGe bipolar transistor process technologies, allowing the possible integration with Si-based circuits. Various operation modes of the photo-transistor (such as three-terminals and two-terminals) are investigated, analyzing their impact on the SSMF-based RoF link in terms of gain and noise (including modal noise fluctuations) for a frequency range up to 2.5 GHz. A 20 MHz LTE transmission is finally demonstrated as example of possible applications of the studied RoF link.

Slow-Nonlinearity Assisted Supercontinuum Generation in a CS2-Core Photonic Crystal Fiber

Abstract: In this paper, we theoretically investigate the supercontinuum generations (SCGs) in a carbon disulfide (CS 2 )-core photonic crystal fiber (PCF). We show that the intrinsic slow nonlinearity of CS 2 plays a significant role to control the soliton fission process. The initiation of the soliton fission process can be distinctly delayed. More importantly, the transition between the smooth soliton fission and the sub-solitons' chaotic-like interference is sufficiently extended so that the optical spectrum can keep broadening continuously while still maintaining a smooth spectral profile. When pumping a designed CS 2 -core PCF at wavelength 1.55 μm in the anomalous dispersion region, we obtain temperature-controllable and highly coherent SCs spanning over one octave at the -30-dB spectral intensity. The unique feature of large slow nonlinearity and the controllable dispersion and nonlinearity of CS 2 -core PCF confirm that as a versatile platform for highly coherent and octave-spanning SCGs.

Traveling Wave Analysis of Non-Thermal Far-Field Blooming in High-Power Broad-Area Lasers

Abstract: With rising current, the lateral far-field angle of high-power broad-area lasers widens (far-field blooming), which can be partly attributed to non-thermal effects due to carrier-induced refractive index and gain changes that become the dominant mechanism under pulsed operation. To analyze the non-thermal contribution to far-field blooming, we use a traveling wave-based model that properly describes the injection of the current into and the diffusion of the carriers within the active region. Although no pre-assumptions regarding the modal composition of the field is made and filamentation is automatically accounted for, the highly dynamic time-dependent optical field distribution can be very well represented by only a few modes of the corresponding stationary waveguide equation obtained by a temporal average of the carrier density and field intensity. The reduction of current spreading and spatial holeburning by selecting proper design parameters can substantially improve the beam quality of the laser.

Suppressing Spectral Crosstalk in Dual-Band Long- Wavelength Infrared Photodetectors With Monolithically Integrated Air-Gapped Distributed Bragg Reflectors

Abstract: Antimonide-based type-II superlattices (T2SLs) have made possible the development of high-performance infrared cameras for use in a wide variety of thermal imaging applications, many of which could benefit from dual-band imaging. The performance of this material system has not reached its limits. One of the key issues in dual-band infrared photodetection is spectral crosstalk. In this paper, air-gapped distributed Bragg reflectors (DBRs) have been monolithically integrated between the two channels in long-/very long-wavelength dual-band InAs/InAs1– x Sb x /AlAs1– x Sb x -based T2SLs photodetectors to suppress the spectral crosstalk. This air-gapped DBR has achieved a significant spectral suppression in the 4.5–7.5 $\mu \text{m}$ photonic stopband while transmitting the optical wavelengths beyond $7.5~\mu \text{m}$ , which is confirmed by theoretical calculations, numerical simulation, and experimental results.

Concealment of Time Delay Signature of Chaotic Semiconductor Nanolasers With Double Chaotic Optical Injections

Abstract: The time delay signature (TDS) concealment properties of a novel semiconductor nanolaser subject to double chaotic optical injections are investigated numerically. The TDS concealment is evaluated by the peak size of the autocorrelation function (ACF). The effects of feedback rate, injection rate, frequency detuning, Purcell cavity-enhanced spontaneous emission factor, and spontaneous emission coupling factor on the TDS concealment are carefully examined. It is found that, with the double chaotic optical injections, the TDS can be concealed in wide ranges of feedback rate, injection rate, and frequency detuning. Moreover, better TDS concealment can be achieved for a smaller frequency detuning and a larger injection rate. The 2-D maps of peak size of ACF further show that the range of parameter space contributing to better TDS concealment is wider for a moderate Purcell cavity-enhanced spontaneous emission factor and a smaller spontaneous emission coupling factor. These results may be interesting for the enhanced chaotic sources on-a-chip based on novel semiconductor nanolasers.

Modified Shockley Equation for GaInN-Based Light-Emitting Diodes: Origin of the Power- Efficiency Degradation Under High Current Injection

Abstract: As an attempt to elucidate the origin of the power-efficiency (PE) degradation at high current injection for GaInN-based light-emitting diodes, the injection current is quantitatively separated to radiative and nonradiative current components as a function of applied voltage. It is found that the conventional Shockley equation for the current-voltage curve of a Si pn diode is not adequate for the LED since the carrier transport and recombination processes are quite different from those of the Si pn diode. Hence, we propose a diode equation for an LED where the radiative and nonradiative currents are separately expressed as a function of applied voltage. By analyzing the proposed diode equation, it is concluded that the PE degradation at high injection currents is due to the increase of the junction voltage and the decrease of the internal quantum efficiency at the same time. The phenomena can be understood by the insufficient recombination rate in the active quantum wells.

Method for Generating High Purity Laguerre–Gaussian Vortex Modes

Abstract: Generation of a donut-shaped first-order Laguerre–Gaussian (LG01) vortex mode via a method designed to yield high mode purity is reported. Our approach utilizes a novel twin-spot end-pumping scheme to directly excite the first order Hermite–Gaussian (HG01) mode in a solid-state laser, followed by a novel astigmatic mode converter based on spherical (concave) mirrors aligned at oblique incidence. A simple theoretical model for the mode converter is derived and from this the design approach is explained along with the potential benefits compared with conventional schemes-based cylindrical-lens astigmatic mode converters, particularly for power scaling. As a proof-of-principle and to confirm the benefits of this scheme in terms of high mode purity we have applied it to an end-pumped Nd:YVO4 laser to generate a (LG01) beam with a controllable sense of azimuthal phase and hence orbital angular momentum. A method for characterizing the resulting beam-based on analysis of the spiral interference pattern derived with the aid of a Mach–Zehnder interferometer is described and yields a value for the LG01 mode purity of 94%. Common sources of mode impurity are identified and the prospects for scaling to higher power whilst maintaining high mode purity are considered.

Comment on “A Broadband Terahertz Metamaterial Absorber Based on Two Circular Split Rings”

Abstract: In a published report, Pan et al. presented a broadband terahertz metamaterial absorber to obtain a broadband absorption with a stability at the wide angle of incidence. In this paper, we discover that the absorption rate of the proposed absorber is wrongly calculated because of the negligence of the cross-polarization reflection component. In fact, the absorption peaks are only 30.12% and 50.72% at 0.85 and 1.93 THz, respectively. The researchers proposed an absorber with poor performance.

Optical Gain and Lasing Properties of InP/AlGaInP Quantum-Dot Laser Diode Emitting at 660 nm

Abstract: We investigated the optical gain properties and lasing characteristics of a pulsed electrically pumped laser structure, which consists of a single layer of self-assembled InP quantum dots (QDs) assembled in (Al 0.10 Ga 0.90 ) 0.52 In 0.48 P barriers. The optical gain and absorption spectra were obtained by analyzing the amplified spontaneous emission as a function of the excitation length. At a current density of 1.2 kA/cm 2 , an internal optical loss value of 5 ± 2 cm -1 and a peak modal gain of 39.3 cm -1 corresponding to a material gain of approximately 2675 cm -1 per QD layer were determined at room temperature. For a 2.24-mm-long laser with uncoated facets emitting at 660 nm, a low threshold current density of 281 A/cm 2 and an external differential quantum efficiency of 34.2% were determined. The internal quantum efficiency of 66% and the transparent current density of 65.8 A/cm 2 for a single layer of QDs were also demonstrated.

Highly Reliable Frequency-Resolved Optical Gating Pulse-Retrieval Algorithmic Approach

Abstract: Frequency-resolved optical gating (FROG) is widely used to measure ultrashort laser pulses, also providing an excellent indication of pulse-shape instabilities by disagreement between measured and retrieved FROG traces. However, FROG requires—but currently lacks—an extremely reliable pulse-retrieval algorithm; therefore, this work provides one. It uses a simple procedure for directly retrieving the precise pulse spectrum from the measured trace. In addition, it implements a multi-grid scheme, also quickly yielding a vastly improved guess for the spectral phase before implementing the entire measured trace. As a result, it achieves 100% convergence for the three most common variants of FROG for pulses with time-bandwidth products as large as 100, even with traces contaminated with noise. Here, in this paper, we consider the polarization-gate (PG) and transient-grating (TG) variants of FROG, which measure amplified, UV, and broadly tunable pulses. Convergence occurs for all of the >20 000 simulated noisy PG/TG FROG traces considered and is also faster.

Towards Surface Leakage Free High Fill-Factor Extended Wavelength InGaAs Focal-Plane Arrays

Abstract: By incorporating of a combined mesa cleaning of SF 6 plasma bombarding and HCl rinsing prior to the SiN x passivation, an ultra-low dark current density of 9.1 nA/cm 2 at 180 K under a reverse bias of -10 mV for 30 μm pitch In 0.83 Ga 0.17 As focal plane arrays (FPAs) with an extended cutoff wavelength of 2.6 μm has been achieved. Six times higher dynamic differential resistance-area product of 35 Ω · cm at 300 K and increased activation energies for dark current were also attained in comparison to reference FPAs. Shockley-Read-Hall lifetimes of ~40 and ~200 ns at 300 and 180 K were determined from theoretical simulation analyses, respectively. These results suggest such methods effectively remove the low resistance leakage pathways on the micro-mesa sidewall surfaces, and are essential for large format and high fill-factor FPAs with negligible surface leakage current.

Dynamics of Wideband Time-Delayed Optoelectronic Oscillators With Nonlinear Filters

Abstract: We present a theoretical and experimental study of an optoelectronic oscillator featuring a cubic-nonlinear filter in the feedback loop. In this architecture, the nonlinearity introduces an additional timescale that leads to the emergence of complex behavior and multiscale dynamics, ultimately leading to chaos as the gain is increased. A complete bifurcation analysis is performed and successfully compared to experimental measurements. We expect this class of systems to emulate novel functionalities for analog signal processing based on time-delayed optoelectronic oscillators.

Nonlinear Distortions Compensation Based on Artificial Neural Networks in Wideband and Multi-Carrier Systems

Abstract: Three-order inter-modulation distortions (IMD3) is a tough problem which appears in analog photonics links (APL). In multi-carrier systems, out-band signals will also lead to nonlinear distortion which is referred as cross-modulation distortion (XMD). The two kinds of distortion will jointly limit dynamic range. In this paper, we propose to adopt an artificial neural network (ANN) as the processing approach which could mitigate IMD3 and XMD simultaneously. The IMD3 and XMD are suppressed by 29.76 dB and 22.18 dB respectively in the experiment. Compared with traditional approaches, the proposed method shows better performance and generalization ability.

Polarization Responses of a Solitary and Optically Injected Vertical Cavity Spin Laser

Abstract: The polarisation properties of a quantum well spin – vertical cavity surface emitting laser (spin – VCSEL), both without injection and with variable polarisation optical injection, are investigated experimentally and compared with the spin flip model (SFM). Without injection, we demonstrate two distinct types of VCSEL-pump response depending on the signs of the linewidth enhancement factor, birefringence and dichroism: firstly where the pump and VCSEL have the same sign of the ellipticity, and secondly where the VCSEL ellipticity, accompanied by the linear polarisation, switches sign. We show that by controlling the injected power, ellipticity or linear angle, near circular polarisation can be obtained. These responses both give insight into the electro-optical injected spin-VCSEL system, and have practical implications for the use of spin VCSELs in unique applications exploiting the ellipticity degree of freedom.

Magneto-Optical and Thermo-Optical Properties of Ce, Pr, and Ho Doped TAG Ceramics

Abstract: Samples of TAG ceramics doped with Ce and Pr ions (0, 0.5, 1, 1.5, 2 at.% concentrations) and with Ho ions (0.5 at.%) were studied. The wavelength dependence of the Verdet constant of each sample in the 405 nm – 1064 nm range was measured, and analytical approximation was found. The obtained value of the Verdet constant of the studied TAG ceramics did not depend on the dopant concentration and type in the studied range of concentrations. The dependence of thermally induced depolarization on laser radiation power was investigated, and the magneto - optical figure of merit was estimated for each studied sample. It was demonstrated that doping of ceramics can provide a substantial reduction of the magneto-optical figure of merit. The obtained results will be useful for creating Faraday isolators and rotators based on TAG ceramics.

Efficiency and Threshold Characteristics of Spectrally Beam Combined High-Power Diode Lasers

Abstract: The efficiency, threshold characteristics, and the stability of spectral beam combining (SBC) of diode laser array had been studied based on different output couplers (OC). It was found that the lower OC reflectivity, lower internal loss, and shorter cavity-length of emitter were helpful for the realization of high efficiency SBC in an external cavity. However, too low OC reflectivity would also result in an unstable combining with the characteristic of side lobes appeared in far-field and the degraded efficiency. The influence of OC reflectivity on threshold current, lasing spectra, and the beam quality of SBC was investigated and analyzed.

Improved Performance of Near UV GaN-Based Light Emitting Diodes With Asymmetric Triangular Multiple Quantum Wells

Abstract: Near-ultraviolet (NUV) light-emitting diodes (LEDs) have been used in several potential applications such as UV curing and biochemical sensors. However, the internal quantum efficiency (IQE) of NUV-LEDs is still a crucial issue. To improve the IQE, in this paper, an asymmetric triangular multiple quantum well (MQW) structure was used, which exhibited a higher emission efficiency and lower efficiency droop with nitrogen face-oriented inclination. This is in contrast to the trend observed in blue LEDs. Furthermore, we demonstrated that holes are more confined in MQWs with nitrogen face-oriented inclination than in MQWs with gallium face-oriented inclination. Moreover, simulations revealed that the IQE improved by approximately 32% compared with that of symmetric square MQW NUV-LEDs; this trend was also confirmed through experimental results. The external quantum efficiency of thin-film flip-chip LEDs with nitrogen face-oriented inclination MQWs was 52%.

Incoherent Gain-Assisted Ring Enhanced Gas Absorption Spectroscopy

Abstract: A novel incoherent gain-assisted ring enhanced spectroscopy technique is presented in overcoming the need for precise optical alignment and high-reflectivity dielectric mirrors. A gain medium pumped below the lasing threshold is used to improve the ring finesse and, thus the interaction length. Two configurations are considered and compared. The first configuration is dual coupler ring with the source outside the ring and the gain medium inside the ring, while the second configuration is single coupler resonator with the gain medium acting as the source. The configurations are studied analytically and experimentally for different system parameters. The experimental results are obtained for a coupling ratio of 90/10. The broadband source is the amplified spontaneous emission of a semiconductor optical amplifier (SOA), while another SOA is used as the gain medium. Acetylene (C2H2) gas absorption is measured around 1540-nm wavelength. The output spectrum of the ring is measured using a 70-pm resolution. The interaction length is found to be enhanced by a factor of 9.35 and 44 in case of the dual coupler and a single coupler resonator, respectively, compared with the direct absorption of the gas cell.

Chaos Bandwidth Enhancement of Fabry-Perot Laser Diode With Dual-Mode Continuous-Wave Optical Injection

Abstract: We show numerically that dual-mode continues wave optical injection into a Fabry-Perot laser diode subject to optical feedback generates a chaos bandwidth, which is four to six times that without optical injection. As a comparison, it is shown that single-mode optical injection can increase the chaos bandwidth threefold with careful choice of detuning. Furthermore, any combination of dual-mode injection will enhance the chaos bandwidth and especially for strong injection and over relatively large positive detuning ranges. Even, when the bias current of the Fabry-Perot laser diode is relatively low, the bandwidth of chaos can reach 35 GHz after dual-mode optical injection, which is six times than that of without optical injection. The enhanced bandwidth with dual-beam optical injection is in accordance with our previous experiments [25]. The present simulations provide detailed guidance on the choice of experimentally accessible parameters to generate chaotic signals with enhanced bandwidth by using single or dual-beam optical injection into a Fabry-Perot laser diode with optical feedback.