PURPOSE: To enable the fast switching of the optical switch which turns on and off a signal under the control of a carrier injected in an active layer by injecting the carrier with light.
CONSTITUTION: This optical switch has semiconductor laser structure consisting of a semiconductor clad 6 and the active layer 4 and turns on and off signal light under the control of the carrier injected in the active layer 4, and the injection of the carrier is performed with the light. The semiconductor clad 6 and active layer 4 use the light for the carrier injection, so neither the clad 6 nor the active layer 4 needs to be doped. The optical switch is therefore ≤2ps in rising time and falling time and has a response speed of ≥50GHz repetitive frequency. The control signal light and 1.3μm signal light cross each other at right angles, so no influence is exerted upon output light. Further, the control signal is guided as a light signal, so there is no mutual buffering and crosstalk characteristics are improved.