Fiber optic interferometer using two wavelengths or variable wavelength

DETAILED DESCRIPTION Accordingly, one object of the present Invention is to provide a novel physical sensor.
Another object is to provide a novel physical sensor utilizing a fiber optic interferometer.
Still another object is to provide a novel physical sensor utilizing a fiber optic interferometer which exhibits high sensitivity while avoiding sensitivity variations due to phase drift.
These and other objects and advantages are provided by a novel physical sensor according to the present Invention which includes a Mach-Zehnder interferometer having an input port, an output port, a sensing light path, and a reference light path.
A transducer is coupled to the sensing path for modulating the phase of light signals passing through the sensing path in response to a physical quantity.
The path lengths of the sensing and reference paths differ by a path length diffference.
The input port is supplied with an input optical signal including a first light component at a first wavelength and a second light component at a second wavelength.
The first and second wavelengths differ by a wavelength difference.
A detector is coupled to receive an output optical signal emanating from the output port for producing an output electrical signal proportional to the intensity of the output optical signal.
The output electrical signal includes a first signal component due to the first light component at the first wavelength and a second signal component due to the second light component at the second wavelength.
The amplitudes of the first and second signal components are related to the physical quantity.
The phases of the first and second signal components differ by an amount proportional to the wavelength difference between the first and second light components of the input optical signal and the path length difference between the sensing and reference paths.
The phase difference may be adjusted such that the sensitivities of the first and second signal components to the physical quantity are never simultaneously at a minimum