Lossless operation of 4×4 laser diode optical gate switches using Y reflection type branching/combining circuits for large-scale integration

The paper describes a 4×4 laser diode optical gate switch made on an InGaAs-GaAs single quantum well GRIN-SCH wafer. The switches were made very compact (only 1.1×1.6 mm) by using Y reflection type optical branching/combining circuit with wide-angle splitting. The light signal launched into an input port is transmitted to an output port through seven gate waveguides and six Y branching circuits. All of the paths between the input and output ports exhibit lossless switching operations when a current of 16 mA (average value) is injected into one gate, The excess loss of the Y branching circuit is estimated to be 0 dB for through coupling and 4 dB for crosscoupling. Good fabrication uniformity of the individual device elements (i.e. the gate waveguide and Y reflection type branching circuit) were confirmed in an area of 10 mm×10 mm, which was one unit of the photolithography process used in the experiments. However, a significant difference in gain characteristics between the input-output paths in the 4×4 switches was observed. The disagreement between the uniformity of the individual elements and the scattering of the path gain characteristics can be explained by the zigzag propagation of the light beam eccentrically launched into the waveguides through the Y reflection type branching circuit