Multi-wavelength photon density wave (PDW) medical systems, methods, and devices are provided. In one embodiment, a multi-wavelength system may include a sensor, a sensor cable, and a patient monitor. The sensor may have an emitter and a detector configured to pass a multi-wavelength PDW input signal into a patient and receive a resulting multi-wavelength PDW output signal. The sensor cable may couple to the sensor and include two optical cables for transmitting and receiving the multi-wavelength PDW signals. The patient monitor may couple to the sensor cable and generate several single-wavelength PDW input signals by modulating a plurality of light sources. The monitor may include an optical switch configured to time-division multiplex the several single-wavelength PDW wave input signals by selecting one of the single-wavelength PDW signals at one time to produce a multi-wavelength PDW signal which is output from the monitor to the sensor via the sensor cable.