Gain In Semiconductor Lasers Research Articles

Optical-parametric oscillation in photonic-crystal ring resonators

By-design access to laser wavelength, especially with integrated photonics, is critical to advance quantum sensors, such as optical clocks and quantum-information systems, and open opportunities in optical communication. Semiconductor-laser gain provides exemplary efficiency and integration but merely in developed wavelength bands. Alternatively, nonlinear optics requires control of phase matching, but the principle of nonlinear conversion of a pump laser to a designed wavelength is extensible. We report on laser-wavelength access by versatile customization of optical-parametric oscillation (OPO) with a photonic-crystal ring resonator (PhCR). Leveraging the exquisite control of laser propagation provided by a photonic crystal in a traveling-wave ring resonator, we enable OPO generation across a wavelength range of 1234–2093 nm with a 1550-nm pump and 1016–1110 nm with a 1064-nm pump. Moreover, our platform offers pump-to-sideband conversion efficiency of > 10 % and negligible additive optical-frequency noise across the output range. From laser design to simulation of nonlinear dynamics, we use a Lugiato–Lefever framework that predicts the system characteristics, including bidirectional OPO generation in the PhCR and conversion efficiency in agreement with our observations. Our experiments introduce broadband lasers by design with PhCR OPOs, providing critical functionalities in integrated photonics.

Chip-scale high-peak-power semiconductor/solid-state vertically integrated laser

Compact lasers capable of producing kilowatt class peak power are highly desirable for applications in various fields, including laser remote sensing, laser micromachining, and biomedical photonics. In this paper, we propose a high-peak-power chip-scale semiconductor/solid-state vertically integrated laser in which two cavities are optically coupled at the solid-state laser gain medium. The first cavity is for the intra-pumping of ytterbium-doped yttrium aluminum garnet (Yb:YAG) with an electrically driven indium gallium arsenide (InGaAs) quantum well, and the second cavity consists of Yb:YAG and chromium-doped yttrium aluminum garnet (Cr:YAG) for passive Q-switching. The proposed laser produces pulses as short as 450 ps, and an estimated peak power of 57.0 kW with a laser chip dimension of 1 mm3. To the best of our knowledge, this is the first monolithic integration of semiconductor and solid-state laser gain mediums to realize a compact high-peak-power laser.

Improved optical confinement in ambipolar field-effect transistors toward electrical injection organic lasers

Increasing optical confinement is critical to lowering laser thresholds and increasing modal gain in semiconductor lasers. Here, mode-solver calculations are used to demonstrate that improvements to optical confinement are possible in organic field-effect transistor geometries by using high refractive index cladding layers. Optical experiments show that the proposed structure increases the efficiency of amplified spontaneous emission (ASE) and lowers ASE thresholds without incurring additional losses. The results suggest that the structure can be used to improve optical confinement for both optically pumped and electrical injection organic lasers where thin, low refractive index active materials are required.

A highly sensitive chemosensor for solution based on organic semiconductor laser gain media

Laser has been widely applied in the scientific and engineering areas including communications, medical treatment, industry, and military due to its extremely strict monochromaticity, high coherence and high energy density. Organic laser based on solution processable polymer gain media has attracted considerable attention in various applications due to its easy fabrication, compact system and flexibility. At present, the chemosensors based on organic semiconductor laser have been widely developed. It has been reported to achieve solution monitoring by organic DFB (distributed feedback) laser. Although the method has its own advantages, there are still many operability and craftsmanship problems to be resolved. In this paper we introduce a new type of the real-time monitoring for various solution. The monitor is realized by using amplified spontaneous emission (ASE) from optically pumped organic semiconductor gain media. The gain media comprising blends of poly(9, 9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(3-hexylthiophene) (P3HT) at a ratio of 15:85 wt.% is dissolved into toluene (25 mg/mL). Thin films (90 nm thickness) of P3HT/F8BT are obtained by spin coating (2000 rpm) from solution onto pre-cleaned quartz substrates. The P3HT/F8BT film demonstrates the absorption peak at 471 nm, the PL peak at 622 nm, and the ASE peak at 661 nm with FWHM (full-width-at-half-maximum) linewidth of ～ 10 nm under the stripe laser pumping. The thin films are, then, covered by droplet of solution to form planar waveguide structure with variable effective refractive index. Upon analyte binding, a change in refractive index at the P3HT/F8BT film surface results in a change in the effective refractive index of the planar waveguide and in turn induces shift of the ASE mode wavelength and variation of ASE threshold of the organic gain media. The changes in ASE wavelength and threshold can be monitored for sensing. The red shift of 4.5 nm in the ASE spectrum is from 661 to 665.5 nm and the threshold increases from 0.579 J/pulse to 1.447 J/pulse which can be detected with the concentration of sodium chloride increasing from 0 to 25 wt.% in pure water. Our experimental results show that this method is easy to detect the concentration grads of 1 wt.% sodium chloride solution. The measurement sensitivity of solution reaches 97.8 nm/RIU (refractive index unit), and accuracy reaches 141.9 nm/RIU. Furthermore, we demonstrate that the chemosensor could be used for detecting different kinds of solution in the same concentration. The ASE peak position and threshold display clearly different when the droplet 10 wt.% sodium, chloride solution and hydromel solution onto P3HT/F8BT film. Our study suggests that the organic gain media films have potentiality to be developed as a high sensitivity and high accuracy chemosensor to detect solution due to the high sensitivity of the ASE peak position and threshold to the refractive index of the solution.

Material research on the InGaAs-emitting-layer VECSEL grown on GaAs substrate

Wafers of InGaAs-emitting-layer vertical external cavity surface emitting semiconductor laser (VECSEL) gain chip and separate active region were grown on semi-insulator GaAs substrates by low pressure metal–organic vapor phase epitaxy (MOVPE). Photoluminescence (PL) wavelength of the active region could be adjusted linearly about 1nm for increasing 1sccm H2 flow rate through TMIn under AsH3 flow rates of 150sccm. The complicated surface-emitted PL signal of the VECSEL gain chip was strongly modulated by interferences within the multilayer and was interpreted by the aberrance of the quantum wells emission with a profile filtered by a micro-cavity resonance in the longitudinal confinement factor. Material tests of the VECSEL wafer showed the reflectivity of the DBR mirrors was in good agreement with the active region photoluminescence, and the wafer was obtained with high crystal quality.

Generalized optical gain analysis in nonparabolic semiconductor laser

SUMMARY A simple generalized theory is developed for optical gain of nonparabolic semiconductor lasers based on the three-band model of Kane, by taking into account the wave-vector () dependence of the optical matrix element. The gain in laser of nonparabolic semiconductors is demonstrated, by taking InAs, InSb, Hg1−xCdxTe and In1−xGaxAsyP1−y lattice matched to InP as examples, and it has been found that the peak of the gain spectra for a given carrier density is higher in the three-band model of Kane than those with parabolic energy band approximations in all the cases. The difference between the peak of gain spectra for three-band model and the parabolic band model is greater for laser of narrow band gap materials in comparisons with that of laser of wide band gap materials, thereby reveals the necessity for inclusion of the nonparabolicity in modeling lasers of small band gap materials. The well-known results for wide band gap materials having parabolic energy bands has also been obtained from our generalized formulation under certain limiting condition. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental characterization of polarization gain properties of 808nm semiconductor laser and analysis of energy band based on amplified spontaneous emissions from double facets

The information of optical gain of semiconductor lasers can be obtained through the amplified spontaneous emission from double facets. By utilizing this new approach, an experimental research about polarization (TE and TM) gain characteristics of continuously-operated 808 nm GaAs/AlGaAs quantum well laser is introduced in this paper. Through the measured gain spectra which are compared with the theoretical gain curves, we analyze the variations of hole subband corresponding to the polarizations along with the change of injection current, meanwhile the actual status of gain spectra and influential factors of the continuously-operated laser are discussed as well.

Quantum modeling of semiconductor gain materials and vertical‐external‐cavity surface‐emitting laser systems

AbstractThis article gives an overview of the microscopic theory used to quantitatively model a wide range of semiconductor laser gain materials. As a snapshot of the current state of research, applications to a variety of actual quantum‐well systems are presented. Detailed theory–experiment comparisons are shown and it is analyzed how the theory can be used to extract poorly known material parameters. The intrinsic laser loss processes due to radiative and nonradiative Auger recombination are evaluated microscopically. The results are used for realistic simulations of vertical‐external‐cavity surface‐emitting laser systems. To account for nonequilibrium effects, a simplified model is presented using pre‐computed microscopic scattering and dephasing rates. Prominent deviations from quasi‐equilibrium carrier distributions are obtained under strong in‐well pumping conditions.

External cavity tunable type-I diode laser with continuous-wave singlemode operation at 3.24 [micro sign

A tunable external cavity laser (ECL) near 3.24 μm was developed using semiconductor laser gain chips based on GaSb. The type-1 interband laser diodes were grown by molecular beam epitaxy using 17 nm InGaAsSb compressively-strained quantum wells with 30 nm AlInGaAsSb quinary barriers for improved hole confinement. In continuous-wave operation with a diode temperature of 10°C, the ECLs produce up to 1.8 mW of singlemode output power with a tuning range of 60 nm. The devices are tunable through the fundamental ν 3 vibrational absorption features of methane gas, providing a platform for highly-sensitive detection of trace hydrocarbons.

Measurement of gain and losses of a midinfrared quantum cascade laser by wavelength chirping spectroscopy

We present an optimized technique for the measurement of gain and losses of semiconductor lasers. We optically inject the beam of a distributed feedback laser (DFB) inside the cavity of the lasers under study. The DFB laser operates in a pulsed mode and shifts its emission wavelength as a function of time. This frequency chirp creates the Fabry–Pérot fringes of the transmitted intensity that contains all the information on the cavity losses. The setup has been validated by a quantitative study of the losses as a function of the injected current, for a quantum cascade laser emitting at 7.6 μm.

Nonlinear Gain in Semiconductor Ring Lasers

Nonlinear gain in semiconductor ring lasers has been investigated theoretically based on density-matrix equations, including the effects of carrier density pulsations, carrier heating, spectral hole burning, and carrier diffusion. Expressions for nonlinear susceptibilities are derived analytically and compared with previous theoretical results. It is found that carrier diffusion have strong effects on both the amplitude and beat frequency dependency of the nonlinear susceptibilities. Various nonlinear parameters are also calculated based on the expressions obtained, and are consistent with published experimental results by other groups.

Measurement of Semiconductor Laser Gain by the Segmented Contact Method Under Strong Current Spreading Conditions

A segmented contact method for the measurement of optical gain is developed for the case of strong current spreading. A simple model of current spreading in a ridge laser with a segmented contact is proposed and analyzed. We show that current spreading effects should be taken into account in lasers with low threshold current densities and high ldquoopeningrdquo voltages. When applied to interband cascade lasers, the method gives an internal optical loss of ~ 10-17 cm-1 and a differential gain of ~ 2.9 cm/A at 80 K, which agrees well with previously reported Hakki-Paoli data. The limitations of the technique are discussed.

Thermal management in disc lasers: doped-dielectric and semiconductor laser gain media in thin-disc and microchip formats

Finite element and analytical modelling of thermal effects in doped-dielectric and semiconductor disc lasers is used to assess advanced approaches to thermal management. The prospective utility of high thermal conductivity materials such as diamond—particularly to improve the spectral coverage in semiconductor disc lasers and to scale the output power of quasi-monolithic microchip lasers—is illustrated. The potential of materials with strong pump absorption to improve the practicality of doped-dielectric thin-disc lasers, particularly for mobile applications, is also outlined.

Tunable External Cavity Laser With a Liquid-Crystal Subwavelength Resonant Grating Filter as Wavelength-Selective Mirror

We demonstrate a tunable external cavity laser consisting of a voltage-tuned liquid-crystal cladded subwavelength resonant grating filter placed directly in front of a semiconductor laser gain chip. The filter acts as a tunable wavelength-selective mirror. As the applied voltage to the filter changes from 0 to 22 V, the laser wavelength demonstrates a tuning range of 7 nm, which may be further increased. As the laser has simple cavity design and no moving parts, it can be low cost and easy to fabricate and assemble.

Simulations of Differential Gain and Linewidth Enhancement Factor of Quantum Dot Semiconductor Lasers

We present a multi-population rate equation model for the analysis of the static and dynamic characteristics of a quantum dot (QD) semiconductor laser. The model is applied to the extraction of the differential gain and linewidth enhancement factor of the QD laser simulating the same kind of experiments usually done in the laboratory. Coherently with the experimental results, we show the difference between the values of the differential parameters extracted in below and above threshold characterizations. We demonstrate that such discrepancy is due the complex dynamics of the carriers in those energy states, whose carrier concentration is not clamped by the stimulated emission process above threshold.

Optical modal gain in multiple quantum-well semiconductor lasers based on InP

An approach to determine the optical modal gain spectra in multiple quantum-well semiconductor lasers based on InP in terms of the current at electrodes is presented. The link between the current at the electrodes and the density of carriers inside each quantum well was provided by rate equations with the inclusion of carrier transport effects. Description of hole dispersion is based on a 4 × 4 Luttinger–Kohn Hamiltonian and was done with the electrostatic effects of the carrier charges. Electrostatic effects were included via a self-consistent solution of electron and hole wave equations and the Poisson equation. The optical gain for the TE (transverse electric) mode has been determined with the inclusion of non-Markovian effects, Coulombic enhancement, and band-gap renormalization. The theoretical approach was compared with experimental measurements of the optical gain on a laser structure consisting of four quantum wells using the Hakki–Paoli method. The important role played by the leakage current was revealed when the results were compared. PACS No.: 73.63.Hs, 78.20.Bh, 78.20.Ci

Novel laser based on magnetic tunneling

A new principle for a compact spin-based solid-state laser is proposed. It operates in the 1–100 THz regime, which is difficult to reach with small size lasers. Spin-flip processes in ferromagnetic conductors form a basis—the mechanism is due to a coupling of light to the exchange interaction in magnetically ordered conductors via the dependence of the exchange constant on the conduction electron momenta. The interaction strength is proportional to the large exchange energy and exceeds the Zeeman interaction by orders of magnitude. A giant lasing effect is predicted in a system where a population inversion has been created by injection of spin-polarized electrons from one ferromagnetic conductor into another through an intermediate tunnel region or weak link; the magnetizations of the two ferromagnets have different orientations. We show that the laser frequency will be in the range 1–100 THz if the experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization are used. The optical gain is estimated to be gopt∼107 cm−1. This exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. An experimental configuration is proposed in order to solve heating problems at a relatively high threshold current density.

The impact of energy band diagram and inhomogeneous broadening on the optical differential gain in nanostructure lasers

We present a general theoretical model for the optical differential gain in semiconductor lasers. The model describes self assembly quantum dots (QDs), self assembly quantum wires (QWRs) and single quantum-well lasers. We have introduced the inhomogeneous broadening due to size fluctuations in the assembly cases. At each dimensionality, we have considered the carrier populations in the excited states and in the reservoirs, where conduction and valence bands are treated separately. We show that for room temperature operation the differential gain reduction due to increased size inhomogeneity is more pronounced in QDs than in QWRs. We show this reduction to be smaller than the one-order reduction attributed to state filling in conventional dot and wire assemblies operating at room temperature. The integration prefactor coefficient of the differential gain in zero-dimensional cases exceed one- and two-dimensional coefficients only for low temperatures where the homogenous broadening is considerably smaller than the thermal energy. The differential gain of QDs, QWRs, and compressively strained single quantum-well lasers operating at room temperature and close to equilibrium is nearly the same.

Characterization of semiconductor laser gain media by the segmented contact method

In this paper, we describe methods for analysis of edge-emitted amplified spontaneous emission spectra measured as a function of the pumped stripe length. We show that both the modal gain and the unamplified spontaneous emission spectra can be extracted from the data, and we describe a means of calibrating the spontaneous emission in real units, without requiring the carrier populations to be described by Fermi functions. The gain and emission spectra can be determined for transverse electric and transverse magnetic polarizations and by summing the recombination currents for each polarization the total radiative current can be measured. This enables the overall internal radiative quantum efficiency to be calculated. Once the calibration factor is known the internal stimulated recombination rate at the facet can also be estimated. The experiment can be configured to give a measurement of the passive modal absorption of the gain medium. The internal optical mode loss can be determined from the long-wavelength region of the gain spectrum or the modal absorption spectrum. In summary, we show that measurements of amplified spontaneous emission spectra provide a full characterization of the gain medium.

Side-mode gain in grating-tuned extended-cavity semiconductor lasers: investigation of stable single-mode operation conditions

In semiconductor lasers, nonlinear phenomena inside the active medium change the side-mode gain with respect to the static threshold-gain. For a given side mode, the sign and the magnitude of the change depend on the lasing-mode optical power and on the wavelength detuning from the lasing mode. If the side-mode gain is enhanced, mode-hopping can occur toward a side mode whose loss is higher than the lasing-mode one. Conversely, in the case of side-mode-gain suppression, the side-mode loss can be smaller with no mode-hop. In this paper, effects of carrier-density pulsation, carrier heating, and spectral-hole burning on the conditions of stable single-mode operation in grating-tuned single-mode extended-cavity semiconductor lasers are investigated. Taking into account the external cavity spectral selectivity and mode coupling, we present a theoretical analysis of experimental results. We perform calculations that compare well with the experimental data obtained with a 1.55-/spl mu/m extended-cavity laser.