A digital speckle pattern interferometer (DSPI) is provided for long-range measurement of displacement of materials within a hazardous environments. A test arm of a portion of coherent beam from a laser is aimed at a selected angle to traverse a distance to a test surface. An input collimator has a lens wide enough to receive a reflected beam from the test surface and is focused at a corresponding distance. The reflected beam is combined with a reference beam split from the coherent radiation onto a camera for measuring displacement of the test surface based on an electronic speckle pattern interferometer (ESPI).

A system and a method for phase extraction of a multi-path interferometer, the method comprising generating a reference signal of a coherence length longer than an arm length difference of the multi-path interferometer; splitting the reference signal into a frequency shifted reference signal and an unshifted reference signal; recombining the frequency shifted reference signal and the unshifted reference signal into a polarization- and frequency-multiplexed reference signal, and feeding the polarization- and frequency-multiplexed reference signal to the multi-path interferometer; detecting frequency shifted and unshifted output signals of the multi-path interferometer; and determining the interferometer phase from the detected signal.

The invention provides a wavelength tracking system comprising a wavelength tracking unit and an interferometer system. The wavelength tracking unit has reflection surfaces at stabile positions providing a first reflection path with a first path length and a second reflection path with a second path length. The first path length is substantially larger than the second path length. The interferometer system comprises: a beam splitter to split a light beam in a first measurement beam and a second measurement beam; at least one optic element to guide the first measurement beam, at least partially, along the first reflection path and the second measurement beam, at least partially, along the second reflection path; a first light sensor arranged at an end of the first reflection path to receive the first measurement beam and to provide a first sensor signal on the basis of the first measurement beam; a second light sensor arranged at an end of the second reflection path to receive the second measurement beam and to provide a second sensor signal on the basis of the second measurement beam; and a processing unit to determine a wavelength or change in wavelength on the basis of the first sensor signal and the second sensor signal.

A system includes a first optical unit that emits light to a measurement target object and receives first interference light incident from the measurement target object, a second optical unit that emits the light to a reference object configured to have a constant optical path length with respect to a temperature fluctuation and receives second interference light incident from the reference object, a spectroscope connected to the first optical unit and the second optical unit and receives the first interference light and the second interference light to be incident, and a control unit connected to the spectroscope, and the control unit calculates a fluctuation rate of a measurement optical path length with respect to a reference optical path length under a predetermined temperature environment on the basis of the optical path length of the reference object calculated on the basis of the second interference light incident on the spectroscope under the predetermined temperature environment, and the reference optical path length of the reference object acquired in advance, and corrects, on the basis of the fluctuation rate, the optical path length of the measurement target object calculated on the basis of the first interference light incident on the spectroscope under the predetermined temperature environment.

Translations of an object in a plurality of different spatial directions are measured using a plurality of interferometers to detect interference with light that has been reflected from a diffusively reflective surface, preferably using diffuse reflection from the same planar surface to measure in each of the different spatial directions. At least the interferometers that measure translation in directions that are not perpendicular to the surface each comprises a single mode fiber and a collimator configured to transmit the outgoing light to the object successively through the single mode fiber and the collimator, and to collect reflection into the single mode fiber with the collimator both along a same beam direction. It has been found that, when reflection of a beam with a beam direction at an oblique angle to a diffusively reflective surface is used, the interference resulting from translation of the object is due substantially only to translation in the beam direction.

There is described a multimode interferometric device and a method for performing multimode interferometry. The device comprises at least one single-mode transmission input connectable to a light source for receiving single-mode light, a multimode output for emitting multimode light and collecting reflected multimode light, at least one photonic lantern operatively connected between the at least one single-mode transmission input and the multimode output and designed for converting the single-mode light into multimode light and converting the reflected multimode light into single-mode light, at least one single-mode reference input for generating at least one interference pattern between the reflected single-mode light and at least one single-mode reference signal, and at least one single-mode output connectable to a photodetector for detecting the at least one interference pattern.

Systems and methods for measuring displacements at the picometer level are provided. A system can include a Michelson interferometer having a fixed arm and a measurement arm. As the length of the measurement arm changes, the output supplied to the interferometer from a variable wavelength light source is changed until the intensity of the resulting inference pattern is maximized. The wavelength of the light at the point the interference pattern is maximized is then measured by mixing light from the light source with the output from a frequency comb generator. The resulting frequency measurement is then converted to a length measurement.

Provided is a system for range detection including at least one beam source arrangement configured to provide illumination of certain coherence length, an optical arrangement, and a detection arrangement including at least one detector unit.

Methods and apparatus are presented for multichannel optical coherence tomography. Light from a wavelength tuneable or steppable optical source is separated into one or more sample beams and one or more reference beams, and the one or more sample beams directed onto a sample to form one or more interaction regions. A plurality of returning probe beams are collected and mixed with the one or more reference beams to form an interference pattern comprising a plurality of interferograms having at least two distinct carrier frequencies. The multichannel optical apparatus can be provided with polarisation discrimination by mixing the returning probe beams with two orthogonally polarised reference beams to form one or more interference patterns each comprising a plurality of interferograms having at least two distinct carrier frequencies. In preferred embodiments each interferogram has a distinct carrier frequency, which may be provided by ensuring that each returning probe beam has a distinct propagation angle with respect to a reference beam. Also presented is a means of generating a plurality of beamlets from a sample beam using a nonreciprocal optical splitter configured to split a beam propagating in a forwards direction into a plurality of beamlets, and to transmit without splitting a beam propagating in the reverse direction.

An apparatus and method for ultrafast real-time optical imaging that can be used for imaging dynamic events such as microfluidics or laser surgery is provided. The apparatus and methods encode spatial information from a sample into a back reflection of a two-dimensional spectral brush that is generated with a two-dimensional disperser and a light source that is mapped in to the time domain with a temporal disperser. The temporal waveform is preferably captured by an optical detector, converted to an electrical signal that is digitized and processed to provide two dimensional and three dimensional images. The produced signals can be optically or electronically amplified. Detection may be improved with correlation matching against a database in the time domain or the spatial domain. Embodiments for endoscopy, microscopy and simultaneous imaging and laser ablation with a single fiber are illustrated.