J. M. G. Tijero

Beam Properties of 980-nm Tapered Lasers With Separate Contacts: Experiments and Simulations

The beam properties of 980-nm tapered lasers with separate current drives for the ridge waveguide and tapered sections are analyzed by means of a comparison between simulations and experimental results. The simulations are performed with a new model for this type of tapered lasers, providing a good qualitative agreement with experiments. The observed improvement in the beam quality by a stronger pumping of the ridge waveguide section with respect to the tapered section is attributed to the reduction of the backward field intensity. The simulations show that this improvement, far from being a general rule, depends on the details of the device geometry.

High-peak-power pulse generation from a monolithic master oscillator power amplifier at 1.5 μm

We present an experimental study on the generation of high-peak-power short optical pulses from a fully integrated master-oscillator power-amplifier emitting at 1.5 μm. High-peak-power (2.7 W) optical pulses with short duration (100 ps) have been generated by gain switching the master oscillator under optimized driving conditions. The static and dynamic characteristics of the device have been studied as a function of the driving conditions. The ripples appearing in the power-current characteristics under cw conditions have been attributed to mode hopping between the master oscillator resonant mode and the Fabry-Perot modes of the entire device cavity. Although compound cavity effects have been evidenced to affect the static and dynamic performance of the device, we have demonstrated that trains of single-mode short optical pulses at gigahertz frequencies can be conveniently generated in these devices.

Enhanced Brightness of Tapered Laser Diodes Based on an Asymmetric Epitaxial Design

A significant enhancement of the brightness is predicted in tapered lasers with the active layer asymmetrically located in the optical cavity. The balance between the reduced tendency to beam filamentation, the increase of threshold current, and the decrease of secondary mode discrimination is analyzed using numerical simulations. An optimized design for a 975-nm tapered laser is proposed.

Effect of nitrogen on the band structure and material gain of In/sub y/Ga/sub 1-y/As/sub 1-x/N/sub x/-GaAs quantum wells

The conduction subband structure of InGaAsN-GaAs quantum wells (QWs) is calculated using the band anticrossing model, and its influence on the design of long-wavelength InGaAsN-GaAs QW lasers is analyzed. A good agreement with experimental values is found for the QW zone center transition energies. In particular, a different dependence of the effective bandgap with temperature when compared to the equivalent N-free structure is predicted by the model and experimentally observed. A detailed analysis of the conduction subband structure shows that nitrogen strongly decreases the electron energies and increases the effective masses. A very small N incorporation is also found to increase the nonparabolicity, but this effect saturates for higher nitrogen contents. Both the In content and well width decrease the effective masses and nonparabolicity of the conduction subbands. Material gain as a function of the injection level is calculated for InGaAsN-GaAs QWs for moderate carrier densities. The peak gain at a fixed carrier density is found to be reduced, compared to InGaAs, for a small N content, but this reduction tends to saturate when the N content is further increased. For the gain peak energy, a monotonous strong shift to lower energies is obtained for increasing N content, supporting the feasibility of 1.55-/spl mu/m emission from InGaAsN-GaAs QW laser diodes.

High Power Three-Section Integrated Master Oscillator Power Amplifier at 1.5 μm

We present the design and the performance of a monolithically integrated master oscillator power amplifier at 1.5 μm. The three-section device includes a distributed feedback laser, a modulation section, and a high power tapered amplifier. In order to mitigate the coupling effects of the light reflected at the facets, the device has been designed with a bent longitudinal axis and a tilted front facet. The device delivers >400 mW mode-hopping free output power. In static regime, the modulation section allows an extinction ratio of 35 dB.

Optical investigation of the relaxation process in InGaAs/GaAs single strained quantum wells grown on (001) and (111)B GaAs substrates

Molecular Beam Epitaxy (MBE) growth of a series of Single Strained Quantum Wells (SSQWs) of InGaAs/GaAs with indium content ranging from 10% to 35% and 100 A well thickness was performed on (001) and (111)B GaAs substrates under optimized growth conditions for simultaneous growth. The Critical Layer Thickness (CLT) of the heterostructures grown on both substrates was comparatively studied by low temperature Photoluminescence (PL). Relaxation is readily observed in the structures grown on (001) GaAs for 24% In-content. This value is in close agreement with both a calculation of the excess strain associated with the two Matthews and Blakeslee strain relieving dislocation mechanisms and the onset of three-dimensional growth. By contrast, heterostructures grown on (111)B GaAs remain pseudomorphic for In-contents above 25%. A maximum PL peak wavelength of 1.1 microns at room temperature has been reached under the growth conditions used. This would correspond to an In-content around 31%. The study shows that (111)B is a preferable choice of substrate orientation for the growth of InGaAs/GaAs heterostructures for optoelectronic applications at wavelengths beyond 1 μm.

High-brightness tapered lasers with an Al-free active region at 1060 nm

High-brightness diode lasers at 1060 nm are useful in display applications (to provide green light by frequency doubling) and in free-space optical communications. On Al-free active region laser structures, we have obtained low optical losses of 0.9 cm-1, a high internal quantum efficiency of 98% and a low transparency current density of 64 A/cm2. On uncoated broad-area lasers (2 mm x 100 μm) at 20°C CW, we have obtained a high maximum wall-plug efficiency of 66%, and an optical power higher than 3W per facet. Based on these good results, we have realized 3.7 mm long gain-guided tapered lasers, delivering a high power of 3W at 10°C CW, together with a low M2 of 3 at 1/e2 and a high maximum wall-plug efficiency of 57%. We have also realized separate electrode lasers, in which the ridge and tapered sections are biased separately. In this configuration, the current through the ridge section is only a few tens mA while the current on the tapered section is several Amps. This allows to control a large output power with only a small change of the ridge current. By moving the ridge current from 0 to 50 mA, keeping a constant 4A current through the tapered section, we have obtained a large change of the output power from 0.09 W to 2.6 W, which corresponds to a high modulation efficiency of 50 W/A under static operation. In dynamic regime, the separate electrode laser can be operated at 700 Mbps, showing a high modulation efficiency of 19 W/A, optical modulation amplitude of 1.6 W and extinction ratio of 19dB [1]. These modulation efficiencies are, to our knowledge, record values.

A Self-Consistent CW Model of Unstable Cavity Semiconductor Lasers including Symmetrical and Antisymmetrical Solutions

We present a quasi-three dimensional (3D) CW simulation model for unstable cavity semiconductor lasers which propagates simultaneously a symmetrical and an antisymmetrical optical field along the cavity until a stable solution is found.

Wavelength Jumps and Multimode Instabilities in Integrated Master Oscillator Power Amplifiers at 1.5

We analyze the large (>10 nm) and abrupt jumps in emission wavelength, together with the multimode instabilities associated with them, which are observed in monolithically integrated master oscillator power amplifiers emitting at 1.5 μm. The physical origin of such phenomena is investigated in the framework of a travelling-wave model which phenomenologically incorporates thermal effects via self and cross-heating of the different sections of the device. The occurrence of the wavelength jumps and the instabilities as a function of the injected currents in the two sections is interpreted in terms of a thermally tuned competition between the modes of the master oscillator and the compound cavity modes.

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We propose an integrated path differential absorption (IPDA) lidar system based on a hybrid master oscillator power amplifier (MOPA) and single photon counting detection for column-averaged measurements of atmospheric CO2. The random modulated continuous wave (RM-CW) approach has been selected as the best suited to the average output power obtained from hybrid and monolithically integrated MOPAs. A compact RM-CW IPDA lidar instrument has been designed and fabricated. High-sensitivity and low-noise single photon counting has been used for the receiver. Colocated 2-km horizontal trial path experiments with a pulsed system and in situ measurements were performed for comparison. The RM-CW IPDA lidar instrument shows a relative accuracy of the order of about ±10% or ±40 parts per million CO2 concentration in absolute terms. The measurements qualitatively demonstrate the feasibility of CO2 IPDA measurements with an RM-CW system.