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The single-mode stability for DFB lasers with various e-beam-written grating configurations has been investigated theoretically and experimentally, both for as-cleaved and ARcoated lasers. Other laser properties interesting for coherent and multichannel communications systems such as linewidth and tunability have also briefly been investigated. Lasers with more sophisticated grating structures, such as an optimized multiple phase-shifted or a corrugation-pitch-modulated grating, did not exhibit any performance significantly superior to X/4-shifted DFB lasers with an appropriate coupling coefficient. AR-coating of the end facets proved indispensable to obtain a high yield of lasers with single-mode operation at high output power and to reduce the large chip-to-chip variation seen for the as-cleaved lasers. A theoretical investigation dealing with the effect of end reflections on the stop-band and the problem to determine the coupling coefficient was also made.

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The dependence of output coupling efficiency on the periodicity of a surface grating outcoupler was investigated. Horizontal cavity InGaAs/AlGaAs laser oscillators with two first-order surface gratings as feedback elements were integrated with detuned rectangular second-order gratings as surface output couplers by the use of electron-beam lithography and chemically assisted ion-beam etching. A high surface emission efficiency of more than 60% was achieved for grating periodicities detuned -2.5 nm to -15 nm and +2.5 nm from the resonance periodicity of 295 nm. For larger positive detuning, the surface emission efficiency is reduced because of the onset of secondorder diffraction into the substrate.

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