Optical systems, devices, and methods are provided for determining various characteristics, such as quantity, movement, distance and speed/velocity of an object relative to the system. The system and method includes an optical transmitter to transmit an output optical signal carrying an electrical reference signal and an optical receiver to receive a reflection of the output optical signal. The receiver includes at least one local oscillator providing local oscillator light at a local oscillator frequency, at least one combiner to combine the reflection of the output optical signal with the local oscillator light into a coupled optical signal. An optical-electrical converter converts the coupled optical signal into a first electrical signal, which is rectified via an envelope detector/rectifier to provide a first rectified electrical signal, which is processed by a signal processor along with the reference signal to calculate various characteristics of an object that reflected the output optical signal, such as the quantity, movement, distance, velocity, etc.