J. J. Lim

Narrow-line coherently combined tapered laser diodes in a Talbot external cavity with a volume Bragg grating

We present the phase locking of an array of index-guided tapered laser diodes. An external cavity based on the self-imaging Talbot effect has been built. A volume Bragg grating is used as the output coupler to stabilize and narrow the spectrum at 976nm. A power of 1.7W is achieved in the in-phase single main lobe mode with a high visibility. We have checked that each emitter is locked to the Bragg wavelength with a 100pm spectrum linewidth. The experimental results compare well with numerical simulations performed with two-dimensional wide-angle finite difference beam propagation method.

The impact of hot-phonons on the performance of 1.3µm dilute nitride edge-emitting quantum well lasers

A robust opto-electronic device simulation tool is extended to model the phonon bottleneck in edge-emitting 1.3µm InGaAsN double quantum well (QW) laser diodes. Both the steady state operation and the transient response of the phonon bottleneck are examined as a function of injection current and heatsink temperature. It is found that the hot phonon population can raise the electron and hole temperatures in the QW active region by up to 7K above the equilibrium lattice temperature at moderate injection currents. At high injection currents, it is found that the phonon bottleneck can significantly decrease the optical power.

10 Gb/s uncooled dilute-nitride optical transmitters operating at 1.3 µm

Dilute-nitride lasers with record performances have been used to build uncooled transceivers and failure free 10 Gb/s optical transmission was achieved over 815 m of multimode Corning InfiniCor fiber under the LRM standard.

Emulation of the operation and degradation of high-power laser bars using simulation tools

We report on the simulation of high-power laser bars and the emulation of their ageing behaviour, using simulation tools originally developed for single emitter laser diodes. Simulations of a simplified bar indicated that the hotter emitters located at the centre of the bar emit more power than their cooler neighbours, while degradation emulations showed that the centre emitters degrade faster. Although the degraded emitters produced less light, they drew an increasingly large fraction of the total current. These insights into the operation and degradation of the bar motivated new experimental investigations, which confirmed the predicted behaviour.

External-cavity designs for phase-coupled laser diode arrays

Both configurations have been extensively studied theoretically as well as experimentally. We have obtained a stable coherent operation of the laser arrays, on a single transverse array mode. The main advantage of the angular filtering cavity is here that it is perfectly adapted to the high filling-factor laser bar, and then provides directly a nearly diffraction-limited output beam; nevertheless these bars have limited output powers because of the strong heating of the array. On the other hand, Talbot external cavities may be used with very different kind of bars, in simple extended-cavity designs. Finally, the use of the filtering properties of VBG has been demonstrated to efficiently control the laser emission.

Thermal performance investigation of DQW GaInNAs laser diodes

Inthis work,weoptimize thethermal performance ofadouble quantumwellGaInNAsridge waveguide laser using anaccurate in-house 2D electro-opto-thermal laser simulator. Thesimulator hasshowngoodagreement withexperiments after a detailed calibration procedure. Usingcalibrated material parameters, we investigate theinfluence ofthep-cladding doping concentration ontheheatgeneration within thelaser. It isfoundthatduetothecompetition betweenJouleandfree carrier absorption heating, an optimump-cladding doping concentration/profile exists.

Static and dynamic performance optimisation of a 1.3 μm GaInNAs ridge waveguide laser

In this work, we optimise the structure of an uncooled directly modulated 1.3 mum GaInNAs ridge waveguide laser for high temperature operation. The static and dynamic performance of the optimised design is analyzed using an accurate in-house 2D electro-opto-thermal laser simulator. The optimised structure is shown to have a lower threshold current, higher efficiency, higher modulation bandwidth and lower vertical beam divergence compared to a reference structure with a conventional design. Large-signal 10 Gbit/s digital modulation simulations were performed and demonstrate the improved performance of the optimised structure especially under high temperature operation.

Simulation of high-brightness diode lasers with optical feedback from modules and systems

The performance of high-brightness laser diode emitters and bars is often affected by external optical feedback from the modules and systems in which they are deployed. We report on the coupling of an advanced simulation tool for high-brightness laser diodes with commercial optical design software. The aim of this work is to create a software tool which can be applied to the design and optimisation of high-brightness diode laser modules and systems intended for use in industrial applications requiring the cutting and welding of sheet metal.

Reliability assessment and degradation analysis of 1.3 μm GaInNAs lasers

The degradation of 1.3 mu m GaInNAs lasers was investigated using accelerated aging tests. This was followed by comprehensive characterization, including standard light-current-voltage (L-I-V) characterization, capacitance measurements, photoluminescence microscopy (PLM), on-axis amplified spontaneous emission (ASE) spectra measurements, and photocurrent (PC) and electroluminescence (EL) spectroscopies. The slope efficiency of the device dropped by 50% with a 300% increase in the threshold current after the accelerated aging test. The ideality factors of the aged devices are higher than those of the unaged devices. PLM images showed no evidence of catastrophic optical mirror damage. The measured capacitances of the aged devices are all similar to those of the unaged devices, indicating that there was no significant dopant diffusion in the junction region. Fourier transforms of the ASE spectra showed that no intracavity defects were present in the aged lasers, suggesting that intracavity defects are not responsible for the rapid degradation of the aged devices. Although the PC measurements showed defects at 0.88-0.95 eV and at similar to 0.76 eV, these defect signatures did not increase with aging. On the other hand, EL measurements revealed that radiative deep level defects were generated during the aging tests. which may be related to the degradation of the devices. Based on the above measurement results, we identify, the generation Of radiative deep level defects as the main causes of degradation of these devices.

Numerical emulation of the degradation of 975nm high power tapered laser bars

We have demonstrated the simulation tool for both single and multiple emitters. Investigations of a model bar with a non-uniform temperature distribution showed that the hotter emitters at the centre of the bar drew more current and emitted higher powers, but also degraded faster than the cooler edge emitters. Similar behaviour has been observed experimentally. However, the simulation results for a real bar showed poor agreement with the observed power distribution. This was attributed to thermal crosstalk between the emitters and is being addressed by the introduction of a global thermal model to Barlase.