Full-function miniature OEM Modulator Bias Controller (MBC). The Modulator Bias Controller can be used to lock the working point of the modulator at the positive slope quadrature (quad+), negative slope quadrature (quad-), null, or peak points of its characteristic curve. The locking modes and slopes are user selectable. A 1 meter long pigtailed photo-detector with an angled FC/APC connector is included for optical feedback to the bias controller.