Interferometric determination of distance change with laser diode, high bandwidth detection and fast signal processing

An interferometer for determining a change of distance to an object, the interferometer comprising:

• a laser diode for emission of measurement laser light,
• a reference arm defining a reference optical path length for a reference laser light, wherein the reference laser light is derived from the measurement laser light by use of a beam splitter,
• a measurement arm defining a measurement optical path length for the measurement laser light,
• receiving means for receiving at least a part of the measurement laser light reflected from the object,
• superimposition means for superimposing of the measurement laser light with the reference laser light and thereby providing an interferometric phase,
• a detection unit for continuously detecting the superimposition of the measurement laser light with the reference laser light and providing the interferometric phase and
• a controlling and processing unit at least for determining the change of distance to the object depending on the superimposition,
• wherein the laser diode is configured so that the measurement laser light is emitted with low coherence and broad spectral bandwidth,
• wherein an emitting wavelength of the measurement laser light is fluctuating hop-freely within the spectral bandwidth causing interferometric phase fluctuations,
• wherein the measurement laser light is emitted with a coherence length between one and three meters,
• wherein the controlling and processing unit is adapted for
• execution of a distance measurement functionality on execution of which the determination of the change of distance to the object is performed by continuously detecting the interferometric phase with the detection unit with a first detection rate, the detection rate and a rate for processing of the detected interferometric phase being high enough that the interferometric phase fluctuations are continuously incrementally tracked so that successive interferometric phase states provided by successive detections of the interferometric phase differ by a phase shift of a fraction of π,
• averaging the detected phase fluctuations for a defined averaging time period and deriving an averaged phase, and
• determining the change of distance to the object with a second detection rate in dependency on the averaged phase, the second detection rate being correlated with the averaging time period.

A computer program product with program code being stored on a machine readable, non-transitory medium, the program code being configured to automatically execute and operate the method comprising:

• receiving at least a part of a measurement laser light reflected from an object,
• superimposing the reflected measurement laser light with a reference laser light and thereby providing an interferometric phase and
• determining the change of distance to the object depending on the superimposition, wherein
• the measurement laser light being emitted with low coherence and broad spectral bandwidth, wherein an emitting wavelength of the measurement laser light is fluctuating hop-freely within the spectral bandwidth causing interferometric phase fluctuations, wherein the measurement laser light is emitted with a coherence length between one and three meters,
• continuously detecting the interferometric phase with a first detection rate, the detection rate and a rate for processing of the detected interferometric phase being high enough that the interferometric phase fluctuations are continuously incrementally tracked so that successive interferometric phase states provided by successive detections of the interferometric phase differ by a phase shift of a fraction than π,
• averaging the detected phase fluctuations for a defined averaging time period and deriving an averaged phase, and
• determining the change of distance to the object with a second detection rate in dependency on the averaged phase, the second detection rate being correlated with the averaging time period.