The development of new medical tools for minimal-invasive surgery is essential for the reduction of pain, side-effects and hospitalisation costs. The benefits of using optical methods in some procedures are now well recognised. In this context semiconductor optical sources offer the advantages of high efficiency, compactness, low cost, long lifetime, low power consumption and high reliability. The optical source presented in this paper comprises a phase-locked, high-power laser diode array and beam shaping optics designed to optimise the coupling to small-diameter optical fibres. The high-power, index-guided laser array used in this work was developed to achieve high-brightness by adopting a specially designed optical cavity based on the parabolic taper for each individual array element. With this design the individual elements are phase-coherent and the fundamental mode of the array is dominant, thus achieving quasi-diffraction-limited operation without the use of external lenses. Compared to other high-brightness laser arrays, the parabolic bow-tie laser array used here offers the advantages of simple device fabrication, reduced costs and compactness. In this work, specially designed lenses are used to circularise the beam and, therefore, to focus the beam to a small spot-size to improve coupling to single mode fibres. Details of the device characteristics, with emphasis on beam quality and phase front, and of the design of anamorphic optics for beam shaping and focusing will be presented in the context of the integration of the high-brightness laser array with the specially design optics to achieve optical power delivery exclusively where necessary via small-diameter optical fibres.
With the widespread use of laser diodes in modern industry there has been an increasing demand for high optical output power devices with good beam quality and, ideally, low production and packaging costs. Reliability and long lifetime are essential requirements since they determine the extent to which such sources will be utilised. The devices of interest here are arrays of parabolic bow-tie lasers which have been specially designed to achieve high power with high brightness without the need for re-growth or sophisticated device fabrication. This paper presents a comparative study on laser diode arrays to investigate the effects of scaling and device geometry on device operation, including degradation and ageing. Temperature profiles at the array facets have been obtained using a thermal imaging system. The HgCdTe-based detector operates in the 1-5.5μm wavelength range. The results obtained indicate a smaller increase in temperature (2-5°C) in uncoupled arrays with respect to phase-coherent arrays and a considerable increase in temperature with increasing number of elements in the array. Such considerations are essential to properly manage thermal dissipation and improve the operational characteristics of such devices.