Abstract: A spectrometer (10) for gas analysis is provided, the spectrometer comprising a measurement cell (28) having a gas to be investigated, a light source (12) for the transmission of light (14) into the measurement cell (28) on a light path (16), a filter arrangement (22) having a Fabry-Perot filter (24a-c) in the light path (16), in order to set frequency properties of the light (14) by means of a transmission spectrum of the filter arrangement (22), as well as a detector (36, 38) which measures the absorption of the light (14) by the gas (30) in the measurement cell (28). In this connection the filter arrangement (22) has a plurality of Fabry-Perot filters (24a-c) arranged behind one another in the light path (14) and a control unit (44) for the filter arrangement (22) is provided in order to change the transmission spectrum by setting at least one of the Fabry-Perot filters (24a-c).

Abstract: Disclosed are methods and an assembly for robust one-shot interferometry, in particular for optical coherence tomography according to the spatial domain approach (SD-OCT) and/or according to the light-field approach. In one embodiment, the method and the assembly may be used for measurements on material and living tissue, for distance measurement, for 2D or 3D measurement with a finely structured light source imaged onto the object in a diffraction-limited way, or with spots thereof. The assembly may comprise an interferometer having object and reference arms and a detector for electromagnetic radiation. In other embodiments, during a detection process, a plurality of spatial interferograms may be formed by making an inclined and/or curved reference wavefront interfere with an object wavefront for each measurement point. The resulting spatial interferograms may be detected in a single detector frame and may be further evaluated via a computer program.

Abstract: A method of authenticating a polymer film comprises measuring the thickness of a layer therein by white light interferometry and/or measuring the birefringence of a layer therein. The method, and devices to carry out the method, may be used in security applications, for example to test for counterfeit bank notes.

Abstract: The invention relates to a digital holography method for detecting the vibration amplitude of an object (15) having a vibration frequency ?, comprising: generating object illumination waves (Wt) and reference waves (WLO); acquiring interferograms between the reference wave (WLO) and a signal wave (Ws) by means of a bandwidth ? s detector (19), the reference wave comprising two components ELO1, ELO1 of frequencies ?1, ?2 that are respectively staggered in relation to the laser frequency ?L by a quantity ?1=?1?s and ?2=q?+?2?s, where q is an integer and ?0.5??1, ?2?0.5; and calculating the vibration amplitude of the object from the optical beats spectrum deduced from the complex amplitude of an interferogram.

Abstract: A ring laser gyroscope is provided. The ring laser gyroscope includes an optical ring resonator, an optical source to provide a pump beam at a pump frequency, a beat detector, and an optical clock detector. The pump beam is coupled to the optical ring resonator in the first direction and stimulates a first optical gain curve at a first stokes wave frequency downshifted by a Brillouin stokes frequency from the pump frequency. A first order stimulated Brillouin scattering (SBS) beam propagates in the second direction and a second order SBS beam propagates in the first direction. The beat detector produces an optical beat signal that varies as a function of a frequency difference between the first order SBS beam and the second order SBS beam. The optical clock detector generates a reference frequency signal based on two co-propagating beams.

Abstract: The present invention is directed to the provision of an interferometer and a phase shift amount measuring apparatus that can precisely operate in the EUV region. The interferometer according to the invention comprises an illumination source for generating an illumination beam, an illumination system for projecting the illumination beam emitted from the illumination source onto a sample, and an imaging system for directing the reflected beam by the sample onto a detector. The illumination system includes a first diffraction grating for producing a first and second diffraction beams which respectively illuminate two areas on the sample where are shifted from each other by a given distance, and the imaging system includes a second grating for diffracting the first and second diffraction beams reflected by the sample to produce a third and fourth diffraction beams which are shifted from each other by a given distance.

Abstract: Methods include: directing test light and reference light along different optical paths, where a test object is in a path of the test light; forming an image of the test object on a multi-element detector by directing test light from the test object to the detector; overlapping the reference light with the test light on the detector; detecting an intensity of the overlapped test and reference light with the detector, the intensity being detected at a frame rate; and modulating an optical path difference (OPD) between the test and reference light at the detector while detecting the light intensity. The OPD is modulated at a rate and amplitude sufficient to reduce a contrast of fringes in a spatial interference pattern formed by the light at the detector over a frame of the detector. Accordingly, fringe-free images may be acquired real-time.

Abstract: Multimode interference can be used to achieve ultra-high resolving powers (e.g., Q>105) with linewidths down to 10 pm at 1500 nm and a broad spectroscopy range (e.g., 400-2400 nm) within a monolithic, millimeter-scale device. For instance, multimode interference (MMI) in a tapered waveguide enables fine resolution and broadband spectroscopy in a compact, monolithic device. The operating range is limited by the transparency of the waveguide material and the sensitivity of the camera; thus, the technique can be easily extended into the ultraviolet and mid- and deep-infrared spectrum. Experiments show that a tapered fiber multimode interference spectrometer can operate across a range from 500 nm to 1600 nm (B=1.0576) without moving parts. The technique is suitable for on-chip tapered multimode waveguides, which could be fabricated in high volume by printing or optical lithography, for applications from biochemical sensing to the life and physical sciences.

Abstract: A detector circuit for a multi-channel interferometer, typically as may be used in an optical coherence tomography device, comprising: a plurality of measurement channels (43) each comprising a measurement detector (31); and a balance channel (44) comprising a balance detector (30), each of the measurement detectors (31) and the balance detector (30) having a light sensitive area and an electrical output configured to output a signal indicative of the intensity of light incident on the light sensitive area, in which each measurement channel (43) is provided with a feedback circuit (40) comprising: a variable gain circuit (35) having an input for the signal from the measurement detector (31) and an output, the variable gain circuit (35) being configured to output at its output the signal received at its input with a variable level of gain; a difference circuit (38) having a first input for the output of the variable gain circuit (35), a second input for the signal from the balance detector (30) and an output,

Abstract: A scanning monochromatic spatial low-coherent interferometer (S-LCI) can be used to simultaneously measure geometric thickness and refractive index. The probe beam of the scanning S-LCI can be an off-axis converging single wavelength laser beam, and the decomposed incident angles of the beam on the sample can be accurately defined in the Fourier domain. The angle dependent phase shift of a plane parallel plate or other sample can be obtained in a single system measurement. From the angle dependent phase shift, the geometric thickness and refractive index of the sample can be simultaneously obtained. Additionally or alternatively, the S-LCI system can interrogate the sample to profile the location and refractive index of one or more layers within the sample using the disclosed techniques.

Abstract: An apparatus, method and computer program for measuring a distance using a self-mixing interference (SMI) unit that generates an SMI signal. The SMI unit comprises a laser emitting a first laser beam directed to an object and wherein the SMI signal depends on an interference of the first laser beam and a second laser beam reflected by the object. A peak width determination unit determines a peak width of the SMI signal, and a distance determination unit determines a distance between the object and the SMI unit depending on the determined peak width of the SMI signal. Since the distance is determined depending on the peak width of the SMI signal, without requiring a laser driving current modulation, advanced electronics for modulating the driving current of the laser are not needed. This reduces the technical efforts needed for determining the distance.

Abstract: A serial weak FBG interrogator is disclosed. The serial weak FBG interrogator may include a CW tunable laser or pulsed laser utilized as a laser source and an EDFA. The serial weak FBG interrogator may also be an interrogation of a single sensor system by utilization of a DFB laser which utilizes a single sensor, which may be an interferometer sensor, an extrinsic Fabry-Perot interferometer or a wavelength-modulated sensor. The serial weak FBG interrogator may also include a computer system or CSPU.

Abstract: A method for optically measuring height profiles of surfaces, in which an image of the height profile is recorded using an optical recording system, is characterized in that the image is a differential interference contrast image and height gradients within the height profile are represented by intensity gradients, which are quantitatively or qualitatively evaluatable. The surfaces can have structures having a defined profile, in which intensity gradients in the differential interference contrast image, which assume, within a specified tolerance and within a specified range, a value which deviates from a predetermined value or assume a selected value from within a specified tolerance and within a specified range, indicate a defect.

Abstract: A spectroscopic sensor 1A comprises an interference filter unit 20A having a cavity layer 21 and first and second mirror layers 22, 23 and a light detection substrate 30 having a light-receiving surface 32a for receiving light transmitted through the interference filter unit 20A. The interference filter unit 20A has a first filter region 24 corresponding to the light-receiving surface 32a and a ring-shaped second filter region 25 surrounding the first filter region 24. The light detection substrate 30 has a plurality of pad units 33a contained in the second filter region 25, while the second filter region 25 is formed with through holes 6 for exposing the pad units 33a to the outside.

Abstract: A photonics integrated system is disclosed, comprising a substrate, an integrated interferometer integrated in the substrate and being configured for receiving radiation from a radiation source, and an integrated spectral filter integrated in the substrate and being configured for receiving radiation from the interferometer. The integrated interferometer has a period and the integrated spectral filter has a bandwidth such that the period of the integrated interferometer is smaller than the bandwidth of the integrated spectral filter. The integrated spectral filter has a periodic transfer characteristic with a period and the system has a bandwidth such that the period of the periodic transfer characteristic of the integrated spectral filter is larger than the bandwidth of the system.

Abstract: Described herein is a hyperspectral imaging system in which a polarizing beam splitter, a Wollaston prism, an optical system, and a plane mirror are arranged on an optical axis of the imaging system. An imaging detector is provided on which radiation is focused by an imaging lens. The Wollaston prism is imaged on itself by the optical system and the plane mirror so that translation of the Wollaston prism in a direction parallel to a virtual split plane of the prism effectively provides an optical path length difference that is the same for all points in the object field.

Abstract: A reference surface is used to develop an empirical plot between a parameter of interest, such as roughness or modulation, and the position of the reference mirror in an interferometer by repeating measurements of the reference surface at different positions of the reference mirror so as to identify the in-focus position of the reference mirror. Serial quality-control measurements of samples of interest are carried out with the reference mirror in such in-focus position until a predetermined quality-control event triggers an automated system re-calibration by re-measuring the reference surface and, if the result does not correspond to the in-focus position of the reference mirror according to the plot, by finding a new in-focus position for the reference mirror using the same plot or, alternatively, a new similarly produced plot. Sample measurements are then resumed with the mirror placed at that new position.

Abstract: An optical device (10) for determining a physical parameter includes: a laser diode (11) for emitting a beam toward a target; an element for detecting (13) an interferometric signal SM(t) which includes the information on the physical parameter to be determined, and which is generated by an interference between the emitted beam and a light beam reflected by the target; element for converting (15) the signal SM(t) obtained by the detection element (13) into a measurement of the physical parameter, the conversion element (15) including: first element (17) for suppressing a continuous component Off(t) of the interferometric signal SM(t); second element (18) for determining interferometric peaks in the interferometric signal SM(t) obtained from the signal obtained at the output of the first element (17). An associated method, particularly suitable for speckle interferometric signals is also described.

Abstract: The invention relates to an integrated optical coupler (1) comprising a substrate (3), at least two planar waveguides (4), which are arranged on or in the substrate (3) and consist of a material having a virtually isotropic refractive index (anisotropy of the refractive index of less than 10?6), and al least three monomode fibers (8, 9, 10) coupled to the planar waveguides (4). One of the monomode fibers (8) is a polarization-maintaining fiber. A fiber optic system according to the invention comprises an integrated optical coupler (1) according to the invention, a light source (21) that is suitable for generating light beams, and a first pigtail fiber (22), which is connected at one end to the light source (21) and at the other end to the polarization-maintaining fiber (8) of the integrated optical coupler (1).

Abstract: A grazing-incidence interferometer includes first and second spaced-apart diffractive optical elements with a generally planar object disposed therebetween. The first diffractive optical element forms sheared first-diffracted-order light beams that reflect from opposite first and second surfaces of the object at grazing-incidence angles, while a zero-diffracted-order light beam goes unreflected. The second diffractive optical element combines the unreflected zero-diffracted-order light beam and the sheared reflected beams to form a collimated, combined beam. A 1× double-telecentric relay system relays the combined beam to a folding optical system that forms first and second interference images on a diffusing screen located at an image plane. Digital images of the first and second interference images are obtained and processed to characterize the thickness variation of the object.