Laser diode device including a top electrode with first and second sections

A laser diode device comprising:

• a laminated structure in which a first compound semiconductor layer that has a first conductivity type and is composed of GaN compound semiconductor, a third compound semiconductor layer that has a light emitting region and a saturable absorption region composed of GaN compound semiconductor, and a second compound semiconductor layer that has a second conductivity type different from the first conductivity type and is composed of GaN compound semiconductor are sequentially layered;
• a second electrode formed on the second compound semiconductor layer;
• and
• a first electrode electrically connected to the first compound semiconductor layer,
• wherein the laminated structure has ridge stripe structure,
• the second electrode is separated into a first section to obtain forward bias state by applying a direct current to the first electrode through the light emitting region and a second section to add electric field to the saturable absorption region by an isolation trench, and
• 1.5≦W2/WMIN≦20 is satisfied, where minimum width of the ridge stripe structure is WMIN, and width of the ridge stripe structure of the second section of the second electrode in a first interface between the second section of the second electrode and the isolation trench is W2, and
• wherein the width of the second section of the second electrode is constant in a direction from the first interface between the second section of the second electrode and the isolation trench towards an outer end of the second section opposite to said first interface,
• wherein the width of the first section of the second electrode is constant in a direction from a second interface between the first section of the second electrode and the isolation trench towards an outer end of the first section opposite to said second interface,
• wherein the width of the first section of the second electrode is less than the width of the second section of the second electrode, and
• wherein a width of the isolation trench decreases in a direction from the interface between the second section of the second electrode and the isolation trench to an interface between the first section of the second electrode and the isolation trench.