Heterodyne detection

Heterodyne detection is a method of signal processing to detect waves of an unknown frequency by mixing with a reference wave frequency. It is used in the optical system, the image processing, telecommunication and in astronomy to detection and analysis of signals. Wherein radio waves is known as a superheterodyne receiver, wherein light interferometry.

Principle

The reference wave is referred to as a local oscillator. The signal and the local oscillator to be processed through a mixer. The mixture is based on a non-linear product of the input signals, so that at least a part of the output signal is proportional to the square of the input signals.

Be

The electric field of the received signal, and

The local oscillator.

For simplicity, we assume that the output signal of the detector, I, is proportional to the square of the amplitude:

The output signal has high frequency ( and ) and constant components. In the heterodyne detection of the high-frequency components and usually also the constant parts are filtered out. What remains as a mixed product the intermediate sum and difference frequencies. The amplitude of these shares is proportional to the product of the amplitudes of the input signals. With appropriate signal analysis, the phase of the signal can be determined.