So far, a strong intersubband transition at 1.55-µm wavelength range was very difficult to achieve in GaN/AlN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy (MOVPE) using conventional growth method. This book first provides a general introduction to the physics of intersubband transition in GaN/AlN MQWs and its device applications especially all-optical switches operating at commutation wavelength. Later on, the issues with regard to conventional MOVPE were comprehensively discussed and analyzed. As a solution of these problems, a growth technique called pulse-injection method was employed to achieve intersubband absorption at 1.55-µm wavelength range. The effects of growth parameters on the properties of intersubband transition were investigated and discussed. Various types of AlN-based waveguides, including ridge, high-mesa, and spot-size converter, with GaN/AlN MQWs absorber were designed and fabricated. The saturation of intersubband absorption which determines the functionality of all-optical switch was clearly observed. This book demonstrated the potential of MOVPE-grown GaN/AlN MQWs for intersubband devices operating at communication wavelength.