Observation of switching related to bistability between twocross-coupled lateral modes in twin-stripe lasers

Switching between two cross-coupled lateral modes in gain-guided twin-stripe lasers has been experimentally observed with current injection of nominally identical pulses, which strongly indicates bistability. Near- and far-field patterns at both facets are presented, which clearly shows a skewed light field which couples from under one stripe to under the other. Cross-coupled mode operation was obtained only for relatively long cavity lasers, which is consistent with the theory for twin-stripe lasers with high interstripe gain     

Near-field control in multistripe geometry injection lasers

Control of the intensity and position of the near field is demonstrated in an analysis of twin-stripe and triple-stripe injection lasers. Calculations of file electrooptical properties of the structures are presented, taking into account the interaction between the carrier concentration profile and the optical field. For twin-stripe devices interstripe coupling is investigated as a function of stripe separation. For stripe separation comparable with stripewidth, the properties of triple-stripe lasers become of interest. Nonlinear light-current characteristics for the twin-stripe device are obtained and lead to an interpretation of such characteristics in conventional stripe geometry lasers.     

Compensation of line-broadening factor in twin-stripe semiconductor lasers and improved modulation potential

A concept for a twin-stripe semiconductor laser is presented in which the simultaneous gain and refractive index variation induced by carriers injected into one stripe can be converted into either a pure amplitude or a pure frequency variation in the lasing supermode. Applications include high-frequency chirp-free amplitude modulation, reduced line width and pure phase modulation.     

Analysis of the cross-coupled lateral mode in a twin-stripefour-contact laser with diagonal current injection

Cross-coupled resonant lateral modes in a twin-stripe four-contact laser are analyzed by coupled-mode theory for conditions in which the current injection into each diagonal pair of stripes is equal. The dependence of the optical power distribution on the laser length and on the carrier-density or the current-density distribution is investigated. The most interesting result is that the highest optical power interesting result is that the highest optical power appears in the waveguide with the lowest carrier density when the carrier-density difference between the adjacent waveguides is small and the laser is shorter than the coupling length. This makes it possible to show that a cross-coupled mode can be supported even in a two-contact twin-stripe laser and that bistable switching between the mode and its mirror image is possible     

Spatio-temporal dynamics of gain-guided semiconductor laser arrays

A continuous model based on the coupled field-matter Maxwell-Bloch equations for a two-level homogeneously broadened single mode laser is developed. The model includes a Langevin formulation to model thermal and spontaneous emission noises and accounts for carrier diffusion, optical field diffraction and current spreading. Our model is flexible enough to simulate any gain-guided longitudinally uniform laser geometry and is applied to both a single-stripe and a four-stripe gain-guided semiconductor lasers where the influence of the injection current, the interstripe distance and carrier diffusion is discussed within the context of the laser dynamics. We show that an array operating with quasi-independent stripes may be achieved at low pumps and larger interstripe distances. However, as injection current is increased or the interstripe distance is decreased, the device passes through a variety of dynamical instabilities which can be analyzed in the context of lateral cavity modes. Moreover, we also show that the array dynamics is strongly influenced by carrier diffusion which may also lead to different thresholds for each element of the array     

Two cross-coupled-mode operation of a twin-stripe laser:bistability for wide ranges of output power level and current ratio

A theoretical approach is reported which models cases where the twin-stripe laser generates either one resonant mode alone or two resonant modes simultaneously. The model determines the ratio of output powers of the light emitted from the two stripes as a function of the ratio of currents to the two stripes. The model simulates the laser operation in regions for which an earlier single-mode approach does not provide solutions. Bistability is predicted to occur over much wider ranges of output power level and current ratio than the previous single-mode case     

Influence of external mirror on modal behavior of twin-stripeindex-guided injection lasers

The coupled-mode theory of parallel waveguides is used to calculate the influence of an external mirror on the modal behavior of the AR-coated laser array. The case of twin-stripe index-guided injection lasers with separate contacts is treated in detail. It is shown that for asymmetrical current injection, the external cavity couples the laser's guided array modes and creates new laser-cavity modes with a better mode discrimination in favour of the one having a single far-field pattern. These results imply that multiple laser arrays might benefit from an additional external mirror     

Analysis of lateral-mode behavior of twin-stripe lasers related tothe negative slope in their current-light characteristics

The lateral oscillation mode in twin-stripe lasers is analysed with the diffusion constant D in the active layer as a parameter. Characteristics of modal gain and optical intensity distribution vs. current are shown to be strongly dependent on the diffusion constant because the diffusion constant determines the depth of the dip in the carrier distribution. For certain values of D, results which are in good agreement with experimentally observed results were obtained. A negative slope appears in the curves of modal gain vs. current, and the optical field is in the weakly pumped side in the negative slope region. The condition for which the negative slope appears is determined     

A coupled-mode analysis of twin-stripe index-guided lasers

An approximated coupled-mode solution to the problem of lateral mode behavior in twin-stripe index-guided injection lasers near threshold is presented. The optical properties are determined by the coupling coefficients between the two waveguides, taking into account the external current-dependent perturbation to the dielectric constant. In the calculations of the external perturbation, a simple model of current spreading under the contacts and carrier diffusion in the active layer is given for a multistripe structure. Emphasis is on the influence of the current ratio on the lateral field shape and modal gain. It is shown that for symmetrical current injection, the fundamental supermode has a slight advantage (higher gain) over the second 180° phase-shifted mode. As the injected current ratio is driven away from the symmetrical point, the second supermode is favored with increasing modal gain difference. The coupled-mode approach is relatively simple and can describe rather accurately this already-known behavior     

Numerical solution of lateral current spreading and diffusion in near-threshold DH twin-stripe lasers

A numerical solution is presented to the problem of lateral current spreading in double heterostructure twin-stripe lasers when lateral diffusion of carriers and bimolecular recombination effects are present. The current components flowing into both the p-type confining layer and the active layer are solved simultaneously, subject to the boundary conditions imposed at the heterojunction. This yields the two-dimensional potential and the current density distributions in the p-type confining layer and the lateral carder density distribution in the active region. Diffusion and bimolecular radiative recombination effects are included in the solution of the current distribution in the active layer. The lateral current and carrier density distributions along the active layer are presented for single- and twin-stripe devices for a variety of electrode injection currents. The paper highlights the influence of device geometry and diffusion on the carrier distributions found beneath the stripes of twin-stripe lasers.     

Brillouin/erbium fiber lasers

Brillouin/erbium fiber lasers (BEFLs) have been recently demonstrated as a novel mode of operation of a fiber laser. In a hybrid Brillouin/erbium fiber laser, the combination of two gain media, the gain from the erbium-doped fiber (EDF) and Brillouin gain in single-mode optical fibers allows a resonator to be constructed which supports a laser comb with ~10 GHz or ~0.1 nm line spacing at room temperature. In this paper, we present a detailed discussion of the operation of BEFLs. Single and multiple wavelength generation is discussed, and modeling of single wavelength operation is described     

Nonlinear analysis of a dielectric distributed feedback laser withcomplex coupling coefficient

An approximate analysis of the nonlinear operation of DFB a dielectric laser with complex coupling coefficient is presented, An expression relating the small signal gain to the output power and the system parameters, including the spatial hole burning effect, is obtained. It is shown that the gain grating, the loss grating, and the higher order Bragg grating all contribute to laser operation above the threshold in a different manner. Moreover, it is possible to achieve a “negative” gain effect in the partly gain-coupled structure operating above the threshold, which depends on the output power level, the distributed loss level and the spatial hole burning effect     

Theoretical and experimental investigations of small-signal gainfor a diode-pumped Q-switched Cr:LiSAF laser

We present a theoretical model proving that up-conversion and thermal quenching of fluorescence strongly limit small-signal gain in a CW pumped Cr:LiSAF laser. We have a good agreement with experimental measurements of small-signal gain obtained with a new simple method. We have then optimized the gain in a Cr:LiSAF laser pumped by two 400-mW red diodes. The highest gain, 1.11 at 600 mW of absorbed pump power, is obtained if the pump spot is circularized inside the crystal and if the Cr:LiSAF is pumped on both sides. In Q-switched operation, this laser produces tunable pulses (up to 6.5 μJ at 10 kHz) between 800 and 900 nm     

InP-based optically pumped VECSEL operating CW at 1550 nm

We present a vertical external-cavity surface-emitting laser operating at 1550 nm. The laser comprises an InGaAsP-based gain element, with a resonant periodic gain structure on top of a distributed Bragg reflector, and a high reflectivity spherical mirror as the external reflector. Optical pumping is achieved using a 1250-nm fiber Raman laser. A maximum continuous output power of 70 mW was obtained under multitransverse mode operation at 233 K. Under single-mode operation, we obtained a maximum power of 60 mW with a beam quality factor M/sup 2/ less than 1.1.     

Periodic resonators for average-power scaling of stable-resonatorsolid-state lasers

Thermal lensing of solid-state laser gain media causes the resonator-mode parameters to vary with pump power. For a single-rod laser system, this effect limits the output-power range for stable laser operation. For multirod laser systems, the power range for stable operation can be increased beyond the limit of single-rod resonators by placing the rods in a periodic resonator structure     

Dual-purpose VCSELs for short-haul bidirectional communicationlinks

The operation of a new dual-purpose vertical-cavity surface-emitting laser (VCSEL), which functions either as a laser or as an avalanche detector, is presented. The original laser structure is modified by focused ion beam etching, enabling photodetection operation, with avalanche gain in excess of 10 available under reverse bias. Successful operation of a 2-Gb/s link employing two dual-purpose VCSELs as “ping-pong” transceivers is described. The noise performance is also examined     

Nonlinear operation of a planar circular-grating DBR laser

An approximate method for the analysis of the nonlinear operation of a planar circular-grating distributed Bragg reflector laser is presented. The analysis is based upon vector-wave self-consistent coupled-mode equations modified to take into account gain saturation effects. With the help of an energy theorem and threshold field approximation, an approximate formula relating small-signal gain to the output power and laser parameters is derived. The laser characteristics obtained reveal behavior of the optimal coupling strength of the Bragg reflector, which provides maximal power efficiency as a function of the laser parameters. It is also shown that the gain saturation effect provides mode selectivity in the laser structure     

Resonance transition radiation X-ray lasers

A free electron laser is proposed using a periodic dielectric and helical magnetic field. Periodic synchronism between the electrons and the optical wave is obtained at the period of the dielectric and not at the period of the helical magnetic field. The synchronism condition and the gain of the new device are derived. The effects on the gain of the new device are derived. The effects on the gain from dephasing and beam expansion due to elastic scattering of the electrons in the periodic medium are included in the gain calculation. Examples of the resonance transition radiation laser and klystron are given. Operation at photon energies between 2.5 and 3.5 keV with net gain up to 12% is feasible using high electron-beam energies of 3 and 5 GeV. Moderate (300-MeV) beam energy allows operation between 80 to 110 eV with up to 57% net gain using a klystron design. In both cases, rapid foil heating may limit operation to a single electron-beam pulse     

Stability of single-mode optically pumped lasers

We study mode competition in optically pumped lasers with one active laser line. The stability of single-mode operation under one mode pumping (both fields arbitrarily intense) is determined by calculating the saturated laser gain using either a mono- or bichromatic probe. The probe spectra differ dramatically from the single-mode, intense field gain curves occasionally exploited in this context in earlier works. Some features in the spectra are interpreted with the dressed atom picture. The mathematically simpler single probe gain is shown to be a good approximation for large mode spacings. When the strong field induced Rabi flipping is comparable to the mode spacing, however, a bichromatic probe containing two frequencies which are symmetric with respect to the intense mode is usually needed. Typical mono- and bichromatic probe spectra are discussed and parameter regions are explored which give stable single-mode operation. The results are also relevant in general laser instability studies: some aspects due to the strong field induced coherences will be pointed out.     

一种新型的高功率双波长自相似抛物线脉冲激光器

基于正色散单模光纤、掺Yb3+增益光纤和多模光纤光栅,提出了一种可调高功率双波长自相似抛物线脉冲激光器。采用非线性薛定谔方程描述双波长自相似抛物线脉冲的传输和演化过程,并利用分步傅里叶方法进行数值模拟。输入脉冲在正色散单模光纤与掺镱增益光纤中产生自相似抛物线脉冲,多模光纤布拉格光栅对激光器进行双波长选择,通过调节偏振控制器实现双波长稳定运行。数值模拟分析结果表明该激光器的运行是可行且有效的。