The thickness of an at least partially transparent layer is measured using wavelength band limited light, with a coherence length that is less than twice the thickness of the layer. Reflections from layer are fed to a 2-n coupler (n>2) via optical transmission paths of different optical length. The 2-n coupler mix light from the path into n combinations of light from the paths, each combination with a different mutual phase offset between the light from the two paths. This leads to coherent interference between reflections from the front and back of the layer when the difference between the optical lengths of the optical transmission paths compensates for the path between reflection from the front and the back. A processing circuit computes information indicative of a phase difference between the reflections from n intensities of the 2-n coupler. The use of n>2 signals makes it possible to eliminate the influence of reflection amplitude variations on the computed phase difference.

In an in situ interrogation system for multiple wavelength interferometers a fringe spectrum that includes non-quadrature-spaced radiation-intensity samples is analyzed to obtain a high resolution relative phase measurement of the optical path length difference associated with the fringe spectrum. The fringe spectrum can be analyzed to obtain a fringe number and a quadrant as well, which can be combined with the relative phase measurement to obtain a high precision measurement of the absolute optical path length difference. An environmental condition corresponding to the absolute optical path length difference can be measured using the measurement of the absolute optical path length difference including salinity, pressure, density, and refractive index of a medium.

An optical imaging device, including an imaging unit and a measuring device. The imaging unit includes a first optical element group having at least one first optical element, which contributes to the imaging. The measuring device determines an imaging error, which occurs during the imaging, using a capturing signal. The measuring device includes a measurement light source, a second optical element group and a capturing unit. The measurement light source emits at least one measurement light bundle, The second optical element group includes an optical reference element and a second optical element, which guide the measurement light bundle onto the capturing unit, to generate the capturing signal. Each second optical element has a defined spatial relationship with a respective one of the first optical elements, The second optical elements differ from the first optical elements. The measuring device determines the imaging error with the capturing signal.

An interferometric measuring device for measuring a surface or profile of an object includes a beam generating unit operable to generate a measurement beam with a spectral component at a wavelength smaller than 550 nm, a splitter to branch off an object beam and a reference beam from the measurement beam, a measurement probe connected to the beam generating unit and configured to direct the object beam onto the surface and to capture a portion of the object beam reflected from the surface as a signal beam, a signal analyzer connected to a detector unit and operable to derive a distance between the measurement probe and the surface on the basis of signals obtained from first and second detectors operable to detect first and second partial beams from an analysis beam being a recombination of the signal beam and the reference beam.

A method for measuring an item of geometric information of an interface of an optical element including interfaces, with a device configured to direct a measurement beam towards the optical element so as to pass through at least one of the interfaces and be reflected by the interface and generate a reflected beam, to selectively detect an interference signal between the reflected beam and a reference beam, the method including positioning a coherence area at an interface; measuring the interface so as to produce interference signals; and processing the signals including constructing a mathematical interface based on a sub-set of interference signals, determining, based on the mathematical interface and an expected shape of the interface, an item of geometric information of the interface.

An interferometer includes a short-coherence source and an internal path-matching assembly contained within its housing. Because path matching occurs within the housing of the interferometer, it is removed from external environmental factors that affect measurements. Therefore, a single cateye measurement of an exemplary surface can be performed in advance and stored as a calibration for subsequent radius-of-curvature measurements. In one embodiment, a path-matching stage is incorporated into a dynamic interferometer where orthogonally polarized test and reference beams are fed to a dynamic imaging system. In another embodiment, orthogonal linearly polarized test and reference beams are injected into a remote dynamic interferometer by means of one single-mode polarization-maintaining optical fiber.

Apparatus and methods are described for optically analyzing an object having a plurality of layers, without needing to use a reference mirror. An extended broadband light source produces light, and directs the light toward the object, such as to create respective images of the light source on the respective layers of the object. An imaging system gathers light that is reflected from a point of the object into a conjugate point in the detector. The detector determines the thicknesses of the plurality of layers at the point of the object by analyzing, within the gathered light, interference between light reflected from the plurality of layers of the object at the point. Other applications are also described.

A system (10) for measuring a physical characteristic of an object (11) using dual path, two-dimensional Optical Coherence Tomography (OCT) includes an extended broadband light source (13) producing an incident light beam (14) and an interferometer (15) having a beam splitter (16) that splits the incident beam into first and second component (17, 18) beams and directs the second component beam (18) on to a moveable mirror (19) for creating an optical path difference between the first component beam (17) and a reflection (20) of the second component beam. A focusing lens (21) having a focal plane (22) focuses the first component beam and the reflection of the second component beam to form a fringe pattern (23) on the focal plane, and a configurable imaging system (25) images the fringe pattern on to a plane (12) of the object to allow two-dimensional measurement of the object without spatial scanning.

A distance measuring method for measuring surfaces uses a laser source having a frequency that can be modulated to tune a wavelength of a laser beam in a wavelength range. The laser beam is generated with a coherence length to provide a measuring beam and is emitted at the surface, located within a specified distance range, as a measuring beam. The measuring beam is back-scattered by the surface and is received again and used to interferometrically measure the distance from a reference point to the surface. The specified distance range lies at least partly outside of the coherence length. One portion of the laser beam is temporally delayed with respect to another portion, such that the one optical path difference caused by the delay matches the optical path difference that corresponds to a distance in the specified distance range plus or minus the coherence length of the laser.

In an in situ interrogation system for multiple wavelength interferometers a fringe spectrum that includes non-quadrature-spaced radiation-intensity samples is analyzed to obtain a high resolution relative phase measurement of the optical path length difference associated with the fringe spectrum. The fringe spectrum can be analyzed to obtain a fringe number and a quadrant as well, which can be combined with the relative phase measurement to obtain a high precision measurement of the absolute optical path length difference. An environmental condition corresponding to the absolute optical path length difference can be measured using the measurement of the absolute optical path length difference including salinity, pressure, density, and refractive index of a medium.