Disclosed is an optical sensing device including a source unit providing a beam of light with continuously modulated phase retardation between p- and s-polarization components of the light by employing a LCM; a reference unit receiving a first part of the light to provide a reference signal; a SPR sensing unit receiving a second part of the light to induce a phase retardation change between the p- and s-polarization components due to SPR associated with a sample; a probe unit receiving the light after SPR to provide a probe signal; and a detection unit connected to the reference unit and the probe unit to detect characteristics of the sample by comparing the reference signal with the probe signal. By using active phase modulation technologies and differential phase measurement, it is possible to fulfill chemical and biological detection.