S. Kaunga-Nyirenda

Separate phase-locking and coherent combining of two laser diodes in a Michelson cavity

We describe a new coherent beam combining architecture based on passive phase-locking of two laser diodes in a Michelson external cavity on their rear facet, and their coherent combination on the front facet. As a proof-of-principle, two ridge lasers have been coherently combined with >90 % efficiency. The phase-locking range, and the resistance of the external cavity to perturbations have been thoroughly investigated. The combined power has been stabilized over more than 15 min with an optical feedback as well as with an automatic adjustment of the driving currents. Furthermore, two high-brightness high-power tapered laser diodes have been coherently combined in a similar arrangement; the combining efficiency is 70% and results in an output power of 4 W. We believe that this new configuration combines the simplicity of passive self-organizing architectures with the optical efficiency of master-oscillator power-amplifier ones.

Design Optimisation of High-Brightness Laser Diodes for External Cavity Operation in the BRIDLE Project

We report on the design aspects of high performance diode lasers for application in high-brightness spectral beam combining and coherent beam combining modules. Key performance trade-offs are identified and potential solutions are explored.

Theoretical investigation of the role of optically induced carrier pulsations in wave mixing in semiconductor optical amplifiers

A theoretical investigation of the role of interband effects in wave mixing in semiconductor optical amplifiers (SOA) is reported. Carrier density modulation (CDM) caused by optical wave beating in SOAs is examined along with its dependence on different operating parameters. Unlike most wave mixing theories, in which the existence and form of carrier pulsations are assumed a priori, we model the carrier dynamics and optical propagation in the time domain directly without invoking such an assumption. The dependence of CDM on the bias current, input power, and detuning between the pump and probe waves is investigated. Selected simulation results are verified experimentally. Good qualitative agreement is obtained between simulations and experiments for nearly degenerate wave mixing (restricted to 3 GHz by experimental limitations).

High-power operation of coherently coupled tapered laser diodes in an external cavity

We demonstrate a rear-side phase-locking architecture with two high-brightness diode lasers. This technique is based on the passive phase-locking of emitters in an external cavity on their rear facet, and their coherent combination on the front facet. Two high-brightness high-power tapered laser diodes are coherently combined using a Michelson-based cavity. The combining efficiency is above 80% and results in an output power of 6.7 W in a nearly diffraction-limited beam. The rear-side architecture is then used with a laser bar of 5 tapered emitters using an interferometric extended cavity, based on a diffractive optical element. We describe the experimental evaluation of the diffractive optical element, and the phase-locked operation of the laser bar.

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.

Self-consistent simulation of high-brightness diode lasers with external optical feedback

This paper presents a model for simulating the impact of external optical feedback on large-optical cavity high-brightness diode lasers. The simulations are performed with our 2.5D simulation tool for high-brightness laser diodes. The external cavity is modelled using commercial coherent ray tracing software. We consider the impact of the optical feedback on the excitation of amplified spontaneous emission in the parasitic vertical modes.

Design and simulation of high-speed nanophotonic electro-optic modulators

In this work, an ultracompact electro-optic modulator based on refractive index modulation by plasma dispersion effect in PhC all-optical gate (AOG) is proposed. The index modulation is achieved by applying a time-varying bias voltage across the electrical contacts of the AOG. The proposed modulator has potential for high-speed operation, with bandwidths in excess of 30GHz achievable.

Design and simulation of next generation high-brightness laser diodes and bars

We report on the design and simulation of high-power, high-brightness laser diodes and bars. Bar level simulations are demonstrated revealing important consequences of current competition and thermal crosstalk. We also demonstrate bidirectional coupling with external cavity optics, with the aim of evaluating the performance of full laser systems.

Design considerations for high-power external cavity laser diodes

Super large optical cavities can give the desired wide vertical near-field (and narrow vertical far-field), which simplify the optics and feedback in an external cavity laser. However, vertical structures support many higher order modes and may suffer from poor modal discrimination. We examine important additional considerations for the design of external cavity diode lasers. An optical trap can reduce the waveguide width and improve modal discrimination, but some higher order modes are still unavoidable. Thus, the laser materials and growth must be carefully optimised to ensure that light coupled back into the laser cannot propagate in these unwanted modes.

Factors influencing the brightness and beam quality of tapered laser diodes and bars

This paper examines some of the factors affecting the brightness of high-power tapered lasers, including bleaching of the ridge waveguide and mismatch between the taper and the beam diffraction angle, which excite high-order modes.