This paper gives an experimental result on the measurement of the maximum coupling coefficient and the coupling length between the active waveguide and the passive output waveguide in GaAs/AlGaAs integrated twin-guide (ITG) injection lasers prepared by LPE. Very high coupling efficiency between the active and the passive waveguides was experimentally confirmed. The maximum coupling coefficient and the coupling length were measured to be about 90% and 250 µm, respectively. These values were in agreement with theory. At properly chosen parameters, the threshold current density on an ITG-type" laser was as low as 3 kA/cm2 at room temperature.

The corrugated waveguide parameters and the threshold current densities of the TE and TM modes in InGaAsP/InP λ/4-shifted DFB lasers with non-reflective ends were calculated and the TE/TM ratio over 30 dB was expected. The experimental TE/TM ratios of about 35 dB in a directly modulated condition were shown.

The threshold current Ith of a 1.5 µm range InGaAsP/InP λ/4-shifted DFB laser with low-reflectivity ends was theoretically expected to be 10 mA or less. Experimentally, Ith of 14-16 mA at 20 and the sub-mode suppression ratio of about 35 dB or more in the temperature range of 10-70 were obtained.

In this paper we analyze the characteristics of tapered multimode interference (MMI)-based coherent lightwave combiners, and theoretically confirm that the stable and clear multimode interference images exist in the tapered MMI combiners. We present the output characteristics of 21 tapered MMI-based coherent lightwave combiners under various structures, which are useful to optimally design the combiners. In order to extend the combiner to a multi-port (N1, N > 2) configuration, a new structure with the border shapes of two tangent arcs is proposed, by which we show an output power imbalance of about 0.5 dB between different input ports of an 81 tapered coherent lightwave combiner. Due to the advantages of no end-facet reflection, easy extension to a multi-port configuration, high tolerance for fabrication errors and a compact size, the tapered MMI structure is a good candidate as a coherent lightwave combiner used in large-scale photonic integrated circuits.