Optical path lengths of photon migration in tissue can be determined directly by pulse-time measurement. This makes it possible to quantify tissue hemoglobin concentrations. However, the bulky and expensive solid state/liquid dye laser system is unsuitable for clinical studies. Thus, the design of an efficient phase modulation technology simplifies the methodology and offers continuous reading of tissue photon propagation in tissue. This report describes a 200 MHz time shared Dual Wavelength Phase modulation system, which measures the essential characteristic of light propagation in the body tissues. This system has slow drift over the 7.5 hour period has maximum of 0.04 degree(s)/hr. The noise peak to peak corresponds to 0.9 mm. Noise is maximum when the separation between transmitter and detector is 5 cm in Intralipid solution, with high voltage at 850 v. Applications of the noninvasive devices include measurement of hemoglobin deoxygenation in brain and hemoglobin and myoglobin deoxygenation in human skeletal muscle and animal models. Numerous applications to medical and biological problems now become available.