The OPTICAL FREQUENCY DISCRIMINATOR (OFD) system smartly delivers a voltage signal that is proportional to the frequency fluctuations of the input laser beam. This turn-key module is suitable for laser frequency noise characterization and/or for laser frequency stabilization to drastically reduced its optical full width at half maximum linewidth. The OFD features ultralow noise performances being successful in achieving frequency noise level as low as 0.1 Hz2/Hz; and those in a compact and user-friendly package.