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The grant aims to develop optimum single- and multi-tapered laser structures for high power operation, and is particularly concerned with a novel form of double-tapered laser, known as the bow-tie laser. Both CW operation and picosecond pulse generation by techniques such as Q-switching and mode-locking are being investigated. In addition to the experimental investigations, the work also involves advanced theoretical modelling of both the modal properties of tapered lasers and the dynamics of picosecond pulse generation in such devices.Progress:A theoretical model has been developed to simulate the effect of tapered waveguide structures on the modal profile at the output [1]. The model takes into account refractive index changes with carrier injection. It is therefore more accurate than previous models, and can be used for weakly index-guided structures, as well as ridge devices. To date, this model has been used to simulate tapered passive waveguide and amplifier structures, and has been found to agree closely with experimental observations. Experimentally, quasi-CW powers of about 0.7W per facet have been achieved from a bow-tie laser, with a narrow far-field distribution of about 2.5. This is very encouraging, and it is anticipated that higher injection current sources and improved heat-sinking will lead to still higher powers in a well-controlled mode. Experimental progress in Q-switching has also been extremely exciting [2, 3, 4], with pulse energies of 120 pJ being achieved from a bow-tie laser. The use of tapered lasers has also been shown to lead to significant improvements in the quality of mode-locked pulses.In summary, progress has been made on all of the above objectives. In addition, new forms of tapered lasers, not anticipated at the time of writing the grant, have been devised, and preliminary investigations on these devices have proved very promising. References:1. J. Sarma, G. Azpiroz, I. Middlemast, I.H. White, F.R. Laughton, K.A. Shore, K.A. Williams and R.V. Penty, SIOE 94, Cardiff, 1994.2. K.A. Williams, J. Sarma, I.H. White, R.V. Penty, I. Middlemast, T. Ryan, F.R. Laughton and J.S. Roberts, LEOS post deadline, Boston, 1993.3. K.A. Williams, J. Sarma, I.H. White, R.V. Penty, I. Middlemast, T. Ryan, F.R. Laughton and J.S. Roberts, Electron. Lett. 30, p. 320, 1994.4. K.A. Williams, J. Sarma, I.H. White, R.V. Penty, I. Middlemast, F.R. Laughton and J.S. Roberts, CLEO 94, Anaheim, 1994.
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