IceCube-Gen2 is under design, including a Phase-1 extension dedicated to the precision study of atmospheric neutrinos and to an improved search for neutrino astrophysical sources. A new level of precision is needed in order to achieve improved performance with respect to IceCube. A complementary calibration system with respect to the one presently installed in IceCube will enable a better understanding of the ice and will therefore significantly reduce systematic effects. We present a novel specialized calibration device named as the Precision Optical Calibration Module (POCAM). The design of the POCAM is based on the principle of an inverted integrating sphere. An appropriately placed matrix of LEDs in combination with a diffusing layer on the inside of the sphere results in a nearly homogeneous light emission. The output of the LEDs is monitored in-situ to high precision by photosensors, ensuring control over the light output. A first complete prototype has been recently developed and deployed within the cubic kilometer scale Gigaton Volume Detector (Baikal-GVD).