Abstract: A method and apparatus for detecting spectral properties of a sample are disclosed. Electromagnetic radiation in the Terahertz range emitted from a first laser source is modulated and combined with electromagnetic radiation emitted from a second laser source. The frequency spectrum of the combined signal comprises sidebands which can be tuned to resonate with the frequency spectrum of the sample. Tuning of the sidebands is obtained by tuning the first laser source, the second laser source, or the modulation frequency.

Abstract: An apparatus and method are provided for conducting heterodyne frequency-comb spectroscopy. The apparatus includes a first and second frequency-comb generators for generating corresponding first and second continuous wave laser beams, respectively. The first beam defines a spectrum of light having a plurality of modes spaced by a first frequency. The second beam defines a spectrum of light having a plurality of modes spaced by a second frequency that is greater than the first frequency. The first and second beams are combined and the optical power of the combined beam is monitored with a data acquisition system to record a time trace. The recorded time trace is Fourier transformed such that each of spectrums of the first and second beams will exhibit a low-frequency comb. By superimposing the two combs, a beat frequency in a low-frequency region is assigned to an optical frequency.

Abstract: To provide an optical image measuring apparatus capable of calculating an intensity of a direct current component composed of background light based on a result obtained by detection of interference light and obtaining a signal intensity of the interference light using the calculated intensity. The apparatus includes: an optical interference system to divide a light beam into signal light and reference light, and the signal light propagating through an object to be measured and the reference light are superimposed to produce interference light; beam splitters for dividing it into three interference light beams; shutters to perform sampling; photo detectors for detecting the sampled interference light beams and converting them into electrical signals; and a signal processing portion for calculating the signal intensity of the interference light and the spatial phase distribution thereof based on the electrical signals.

Abstract: This invention relates to a method and apparatus for measuring the phase change of an output optical signal from a device. In one embodiment an input optical signal is split into first and second optical signals, and the first optical signal is passed through the device while applying an external stimulus to the device, to produce an output optical signal having a phase shift. The carrier frequency of the second optical signal is changed, and the output optical signal and the changed second optical signal are then combined. The combined signal is detected in accordance with the external stimulus applied to the device, and the phase change of the output signal of the device is measured as a function of the external stimulus applied to the device.

Abstract: In a method for measuring absorption and reduced scattering coefficients of a multiple scattering medium, a coherent light beam is outputted. The coherent light beam includes linear polarized P and S wave components having mutually orthogonal polarizations and frequencies ?P and ?S, respectively. Then, the coherent light beam is split into a signal beam and a reference beam, which include the P wave and S wave components. The signal beam is subsequently projected into the medium. Optical interference signals of the reference beam and the signal beam penetrating the medium are respectively detected and converted into heterodyne interference electrical signals. Thereafter, the two heterodyne interference electrical signals are compared to obtain amplitude attenuation and phase delay of the signal beam penetrating the medium, from which the absorption and reduced scattering coefficients of the medium at a position where the signal beam penetrated the medium are inferred.

Abstract: A hybrid optical/electronic wavefront sensor includes an electro-acoustical device used to upshift an optical reference signal. An optical test signal and the frequency upshifted optical reference signal are optically heterodyned to create a signal having a frequency equivalent to the beat frequency of the two signals, for example, the RF driving frequency of the Bragg cell. The optically heterodyned signal is then converted by way of a detector to an electronic signal having the same phase as the optical test signal. The output of the detector is a sinusoidal signal having the same phase as the phase of the optical test signal. This signal is filtered by way of an AC filter and mixed with a second clock signal, for example, a clock signal that is offset in frequency from the electro-acoustical drive signal by a frequency, for example, between 100 kHz and 1 MHz. These two signals are mixed by way of a mixer.

Abstract: The invention provides an apparatus and method for highly selective and sensitive chemical sensing. Two modes of laser light are transmitted through a waveguide, refracted by a thin film host reagent coating on the waveguide, and analyzed in a phase sensitive detector for changes in effective refractive index. Sensor specificity is based on the particular species selective thin films of host reagents which are attached to the surface of the planar optical waveguide. The thin film of host reagents refracts laser light at different refractive indices according to what species are forming inclusion complexes with the host reagents.

Abstract: An agile optical sensor based on spectrally agile heterodyne optical interferometric confocal microscopy implemented via an ultra-stable in-line acousto-optic tunable filter (AOTF) based interferometer using double anisotropic acousto-optic Bragg diffraction. One embodiment uses a tunable laser as the light source while other embodiments use a broadband source or a fixed wavelength laser as the source. One embodiment uses anisotropic diffractions in an AOTF to generate two near-collinear orthogonal linear polarization and slightly displaced beams that both pass via a test sample to deliver highly sensitive sample birefringence or material optical retardation measurements. A spherical lens is used to form focused spots for high resolution spatial sampling of the test object. The laser and AOTF tuning allows birefringence measurements taken at different wavelengths, one at a time.

Abstract: A system for measuring a displacement along a first axis includes an apparatus movable at least along a second axis perpendicular to the first axis, a measurement mirror mounted to the apparatus at an angle greater than 0° relative to the first axis, and an interferometer with a beam-splitter. The beam-splitter splits an input beam into a measurement beam and a reference beam, directs the measurement beam in at least two passes to the measurement mirror, and combining the measurement beam after said at least two passes and the reference beam into an output beam. At least exterior to the interferometer, the measurement beam travels in paths that are not parallel to the first axis.

Abstract: An apparatus operable to record a spatially low-frequency heterodyne hologram including spatially heterodyne fringes for Fourier analysis includes: a laser; a beamsplitter optically coupled to the laser; an object optically coupled to the beamsplitter; a focusing lens optically coupled to both the beamsplitter and the object; a digital recorder optically coupled to the focusing lens; and a computer that performs a Fourier transform, applies a digital filter, and performs an inverse Fourier transform.

Abstract: An apparatus and a method for generating an optical carrier is disclosed. The apparatus includes: a light source generating a pump light; a SBS generator for stimulated Brillouin scattering the pump light to generate a stokes light from the light source; an attenuator for controlling an amplitude of the pump light from the light source to generate an amplitude controlled pump light; and a detector for heterodyne beating the stokes light and the amplitude controlled pump light to generate an optical carrier.

Abstract: A compact computer-controlled fully-packaged apparatus providing reliable multi-dimensional characterization of spherical objects in a field environment is disclosed. The apparatus has a rugged, free-space, integrated optical system with up to three lasers that generate at a laser-specific wavelength the coherent light with substantially high pointing stability. The apparatus also has a receiver. Each laser generates a pair of beams crossing each other at a predetermined laser specific angle to form a sample volume such that beams from all lasers coincide in the same spot. The receiver has photodetectors to sense the light scattered from a spherical object. Three photodetectors measure a size and one of the three photodetectors measures a first velocity component, a fourth photodetector measures a second velocity component, and a fifth photodetector measures a third velocity component of the spherical object. The velocity components are orthogonal to each other.

Abstract: Systems and methods are described for spatial-heterodyne interferometry for transmission (SHIFT) measurements. A method includes digitally recording a spatially-heterodyned hologram including spatial heterodyne fringes for Fourier analysis using a reference beam, and an object beam that is transmitted through an object that is at least partially translucent; Fourier analyzing the digitally recorded spatially-heterodyned hologram, by shifting an original origin of the digitally recorded spatially-heterodyned hologram to sit on top of a spatial-heterodyne carrier frequency defined by an angle between the reference beam and the object beam, to define an analyzed image; digitally filtering the analyzed image to cut off signals around the original origin to define a result; and performing an inverse Fourier transform on the result.

Abstract: A system and a method for remotely sensing global motion of an ensemble of dynamically moving scattering sites. The system comprising a scattering medium under inspection, an optical transceiver and a detector in a double-pass geometry.

Abstract: Systems and methods are described for faster processing of multiple spatially-heterodyned direct to digital holograms.

Abstract: An optical property of a device under test is determined from a detected DUT response signal, or a signal derived therefrom, whereby the DUT response signal represents a signal response of the DUT in response to a composite signal or a signal derived from said composite signal. The composite signal comprises superimposed signals delayed with respect to each other.

Abstract: A method determines power of a modulated signal that is applied to a wavelength meter by summing bin values within a designated bin range of a frequency transformed interferogram representing the modulated signal and provided by the wavelength meter. In a first embodiment of the method, the bin range within which the bin values are summed is designated by mapping a series of signal characteristics indicative of the types of the modulated signals applied to the wavelength meter, to a series of bin spans within the frequency transformed interferograms that represent the modulated signals. The method then enables a selection of a signal characteristic from the series of signal characteristics to identify the modulated signal that is applied to the wavelength meter.

Abstract: A method of making interferometric measurements of an object, the method including: generating an input beam that includes a plurality of component beams, each of which is at a different frequency and all of which are spatially coextensive with each other, some of the components beams having a first polarization and the rest having a second polarization that is orthogonal to the first polarization; deriving a plurality of measurement beams from the plurality of component beams, each of the plurality of measurement beams being at the frequency of the component beam from which it is derived; focusing the plurality of measurement beams onto a selected spot to produce a plurality of return measurement beams; combining each of the return measurement beams of the plurality of return measurement beams with a different corresponding reference beam of a plurality of reference beams to produce a plurality of interference beams; and acquiring a plurality of electrical interference signal values for the selected spot fro

Abstract: An apparatus (1) for analyzing a spectrum of an input signal (x(t)) having at least one line with a center frequency (@s) comprises a mixer (2) for zero-mixing the input signal (x(t)) to produce a base band signal (z(t)) by sweeping a local oscillator frequency (@s) generated by a local oscillator (3) and a resolution filter (4) for filtering the base band signal (z(t)) to produce a filtered base band signal (y(t)). Detector means (7) detects the time of occurrence (ti), the duration (?Ti) and the maximum value (y?i) of several halfwaves of the filtered base band signal (y(t)). Envelope reconstruction means (6) reconstructs the envelope (E(@)) of the spectrum of the input signal (x(t)) by using an estimated amplitude at an estimated center frequency of each line of the input signal (x(t)).

Abstract: The group delay of a DUT is measured by modulating test and reference portions of a local oscillator signal at different frequencies to create modulation sidebands, applying the modulated test portion of the local oscillator signal to the DUT, and then optically mixing the two modulated signals. Optically mixing the two modulated signals translates the optical frequencies down to electrical frequencies. Phase changes that are caused by the DUT are determined by measuring the phase differences between modulation sidebands of the test portion of the local oscillator signal. Frequency translation can be achieved by electrical mixing instead of optical mixing.

Abstract: A phase-diverse coherent optical spectrum analyzer is presented. An optical receiver receives a first input signal and a second input signal, and produces at least a first output signal, a second output signal, and a third output signal based on mixing the first input signal and the second input signal. A processing unit isolates heterodyne components from the first output signal, the second output signal and the third output signal, wherein the heterodyne components comprise a first signal and a second signal that represent the phase-diverse nature of the optical mixing process. Phase diversity of the heterodyning between the first input signal and the second input signal is achieved by the coherent optical spectrum analyzer.

Abstract: The optical sampling system performs by detecting the interference effect which is a linear correlation between the signal lights and the optical pulses, so that both the signal lights and the optical pulses can have relatively low intensities, and the reception sensitivity is high. Also, the pulse width of the optical pulses and the amount of delay given to the optical pulses are the only factors that limit the time resolution, so that it is possible to provide the optical sampling system with excellent time resolution and power consumption properties, and it is possible for the optical sampling system to monitor not only the intensity of the signal lights but also the frequency modulation component as well.

Abstract: A frequency-scanning interferometer is modified to include a diffuse reference surface. An illuminating system produces an expanding measuring beam, portions of which reflect from a test object surface and the diffuse reference surface on converging paths to an imaging system. Interference patterns between overlapping images of the object and reference surfaces are generated at a plurality of frequencies for measuring the object surface with respect to the reference surface.

Abstract: Embodiments in accordance with the invention provide an optical spectrum analyzer. The optical spectrum analyzer includes a receiver for receiving an optical local oscillator signal and an unknown optical signal. The receiver outputs three or more phase-diverse heterodyne signals. The phase-diverse heterodyne signals are coupled to a phase quadrature generator. The phase quadrature generator produces a first and second phase quadrature signals that are ninety degrees out of phase with respect to each other. The first and second phase quadrature signals are coupled to a complex signal generator. The complex signal generator produces a complex signal having a positive and negative image. A measurement processing unit determines the phase of the unknown optical signal from the relative difference of the phase of the positive and negative image of the complex signal.

Abstract: The invention is directed to the provision of a device and method for measurement of angle of rotation for measuring in a non-contacting fashion the concentration of an optically active substance such as a sugar, amino acid, vitamin, or the like dissolved in a sample. According to the invention, A coherent beam is split into two beams, one being an object beam and the other being a reference beam, the object beam passed through the sample is converted by a quarter wave plate into mutually perpendicular polarization components having therebetween a phase difference proportional to the angle of rotation produced by the sample, and the angle of rotation produced by the sample is obtained from the phase difference occurring between beat signals produced by causing the object beam with the reference beam.

Abstract: Systems and methods are described for content-based fused off-axis illumination direct-to-digital holography. A method includes calculating an illumination angle with respect to an optical axis defined by a focusing lens as a function of data representing a Fourier analyzed spatially heterodyne hologram; reflecting a reference beam from a reference mirror at a non-normal angle; reflecting an object beam from an object the object beam incident upon the object at the illumination angle; focusing the reference beam and the object beam at a focal plane of a digital recorder to from the content-based off-axis illuminated spatially heterodyne hologram including spatially heterodyne fringes for Fourier analysis; and digitally recording the content based off-axis illuminated spatially heterodyne hologram including spatially heterodyne fringes for Fourier analysis.

Abstract: Time-correlation methods for determining pulse characteristics from a modelocked ultrafast laser include a cross-correlation method and an auto-correlation method. In the cross-correlation method, pulses from the laser and pulses from another modelocked laser are incident on a two-photon detector that responds when the pulses overlap in time. The lasers are synchronized to the same frequency and the phase difference between pulses from the two lasers is varied to vary the temporal pulse overlap while recording the detector response. Pulse characteristics are determined from recorded data representing the detector response as a function of phase difference. In the auto-correlation method, pulses from one laser are divided into two components. One component follows a fixed delay path before being temporally overlapped at the detector with another component that has not been delayed. The temporal overlap is varied by varying the pulse repetition frequency.

Abstract: A CW lightwave modulated by a continuously reiterated binary pseudorandom code sequence is launched into an end of a span of ordinary optical fiber cable. Portions of the launched lightwave back propagate to the launch end from a continuum of locations along the span because of innate fiber properties including Rayleigh scattering. This is picked off the launch end and heterodyned to produce a r.f. beat signal. The r.f. beat signal is processed by a plurality (which can be thousands) of correlator type binary pseudonoise code sequence demodulators respectively operated in different delay time relationships to the timing base of the reiterated modulation sequences. The outputs of the demodulators provide r.f. time-domain reflectometry outputs representative of signals (e.g., acoustic pressure waves) incident to virtual sensors along the fiber at positions corresponding to the various time delay relationships.

Abstract: An optical heterodyne detection system includes a tunable optical pre-selector that is adjusted to track the frequency of a swept local oscillator signal. The tunable optical pre-selector is adjusted in response to a measure of the frequency of the swept local oscillator signal and in response to a measure of a portion of the swept local oscillator signal after the portion of the swept local oscillator signal has optically interacted with the optical pre-selector. In an embodiment, at least some portion of the swept local oscillator signal is modulated before it interacts with the optical pre-selector. In an embodiment, the portion of the swept local oscillator signal that interacts with the pre-selector is detected and used in a feedback control circuit to generate a control signal which causes the error between the center frequency of the pre-selector and the frequency of the swept local oscillator signal to be small.

Abstract: A system for characterizing optical properties of a device under test (DUT) uses an expanded local oscillator signal to perform multiple parallel interferometric measurements. In one system, the expanded local oscillator signal is optically connected to a lens array. The lens array focuses the expanded swept local oscillator signal into multiple beams. The multiple beams are then used in multiple parallel interferometric measurements. The multiple beams may be used as the reference beams or applied to the DUT and used as the test beams depending on the application. The test beams and reference beams are combined to perform the interferometric measurements. In another system, a portion of the expanded local oscillator signal is applied directly to a DUT as the test beam while another portion of the expanded local oscillator signal is used for the reference beam.

Abstract: An optical analyzer and method for measuring optical properties of optical signals utilizes a heterodyne architecture to measure spectral amplitude and phase of a periodically modulated input optical signal, such as an optical signal from a periodically modulated distributed feedback (DFB) laser. The spectral amplitude and phase measurements are derived from a heterodyne signal, which is produced by combining and mixing the input optical signal and a local oscillator (LO) signal. The optical spectrum that is reconstructed from the heterodyne signal includes “inner” spectral peaks that contain phase information of the input optical signal. The inner spectral peaks may be produced by an optical or electrical mixing technique. The spectral phase of the input optical signal is recovered from the inner spectral peaks of the reconstructed optical spectrum.

Abstract: An optical heterodyne detection system includes an attenuator for attenuating an input signal before the input signal is combined with a local oscillator signal. An optimal attenuation level for the input signal, which improves the signal to noise ratio of the heterodyne beat signal, is determined by obtaining a base measurement of an output signal in response to the local oscillator signal and in the absence of the input signal, obtaining sample measurements of the output signal in response to the input signal as a function of different attenuation levels, and determining the optimal attenuation level as a function of the base measurement and the sample measurements. A minimum attenuation level for the input signal, which protects receiver photodetectors from being saturated or damaged, is determined by setting an initial attenuation level and gradually reducing the attenuation level until the voltage limit of the photodetectors is reached.

Abstract: The disclosure relates to optical heterodyne detection cavity ringdown spectroscopy. In one aspect the disclosure relates to an optical system comprising a ringdown cavity cell defining a resonant optical cavity, means for directing coherent light selected from the group consisting of continuous or quasi-continuous light into said optical cavity, means for altering the resonant optical cavity so as to generate a frequency shift of the coherent light in the optical cavity, means for coupling said coherent light into the optical cavity and means for decoupling the frequency shifted coherent light out of said optical cavity, means for optically combining said decoupled frequency shifted coherent light with another portion of coherent light not in optical communication with the optical cavity and means for optical heterodyne detection of the intensity of said combined light. A method for optical detection is also described as well as methods and apparatus for detecting a parameter of a sample.

Abstract: A polarization control system includes a beam source that generates a first beam component containing light with a first polarization and a first frequency and a second beam component containing light with a second polarization and a second frequency. A polarization state modulator adjusts the polarizations of the components for transmission on a single optical fiber. A detector system measures polarizations of the components when output from the optical fiber and determines how to adjust the polarization state modulator in order to give the first and the second components the desired output polarization states. The beam source can be implemented using a Zeeman-split laser, a laser containing a birefringent element, a pair of phase-locked lasers, and/or a variety of configurations of electro-optic or acousto-optic crystals operated to create or enhance the frequency difference between the beam components.

Abstract: An optical component especially suited for common path heterodyne interferometry comprises a symmetric dual-periscope configuration. Each periscope is substantially identical to the other with regard to certain design aspects. The resulting design is an optical component that is highly stable with variations in temperature and angular deviations.

Abstract: A method of recording a spatially low-frequency heterodyne hologram, including spatially heterodyne fringes for Fourier analysis, includes: splitting a laser beam into a reference beam and an object beam; interacting the object beam with an object; focusing the reference beam and the object beam at a focal plane of a digital recorder to form a spatially low-frequency heterodyne hologram including spatially heterodyne fringes for Fourier analysis; digital recording the spatially low-frequency heterodyne hologram; Fourier transforming axes of the recorded spatially low-frequency heterodyne hologram including spatially heterodyne fringes in Fourier space to sit on top of a heterodyne carrier frequency defined by an angle between the reference beam and the object beam; cutting off signals around an origin; and performing an inverse Fourier transform.

Abstract: Systems and methods are described for spatial-heterodyne interferometry for reflection and transmission (SHIRT) measurements. A method includes digitally recording a first spatially-heterodyned hologram using a first reference beam and a first object beam; digitally recording a second spatially-heterodyned hologram using a second reference beam and a second object beam; Fourier analyzing the digitally recorded first spatially-heterodyned hologram to define a first analyzed image; Fourier analyzing the digitally recorded second spatially-heterodyned hologram to define a second analyzed image; digitally filtering the first analyzed image to define a first result; and digitally filtering the second analyzed image to define a second result; performing a first inverse Fourier transform on the first result, and performing a second inverse Fourier transform on the second result.

Abstract: A system for the in vivo detection of the effects of AD in the interior of an eye. A scanning polarimeter, including a residual retardance canceling system and an improved anterior segment retardance compensator, produces an optical analysis signal representing the birefringence of the retinal nerve fiber layer (RNFL) structures of the eye. The birefringence data is more accurate because of compensation for anterior segment birefringence and residual birefringence of optical components, such as, for example, the beam splitters, lenses, scanners and retarders. An electrical analysis signal representing a large (20 by 40 degrees) retardance map is produced and evaluated by an artificial neural network to produce an analysis classification signal representing the contribution of Alzheimer's disease to the birefringence of the retinal layer corresponding to the relationship of the electrical analysis signal to an analysis signal database.

Abstract: Monitoring an optical signal utilizing optical heterodyne detection involves attenuating an input signal before the input signal is combined with a local oscillator signal. The input signal is attenuated in order improve the signal to noise ratio of the heterodyne signal that is generated when the input signal and the local oscillator signal are combined. The signal to noise ratio of the heterodyne signal improves with attenuation of the input signal, specifically in the case where the intensity noise from the input signal is the dominant noise source, because the heterodyne signal and the intensity noise of the input signal scale differently with attenuation of the input signal.

Abstract: A polarization control system includes a beam source that generates a first beam component containing light with a first polarization and a first frequency and a second beam component containing light with a second polarization and a second frequency. A polarization state modulator adjusts the polarizations of the components for transmission on a single optical fiber. A detector system measures polarizations of the components when output from the optical fiber and determines how to adjust the polarization state modulator in order to give the first and the second components the desired output polarization states. The beam source can be implemented using a Zeeman-split laser, a laser containing a birefringent element, a pair of phase-locked lasers, and/or a variety of configurations of electro-optic or acousto-optic crystals operated to create or enhance the frequency difference between the beam components.

Abstract: In an optical heterodyne surface plasma wave detecting method and apparatus, light that contains correlated P1 and P2 wave components (TM waves) is directed to a total reflective component such that two surface plasma waves are generated at an interface of a metal film and a test object. Light reflected from the total reflective component is detected to obtain an optical heterodyne test signal that is compared with an optical heterodyne reference signal to determine changes in at least one of amplitude and phase of the optical heterodyne signal relative to the optical heterodyne reference signal.

Abstract: A method for optical evaluation of a sample includes scanning a beam of coherent radiation over the sample, whereby the radiation is scattered from the sample, while directing a portion of the scanning beam toward a diffraction grating so that the portion of the beam is scanned over the grating, whereby a frequency-shifted reference beam is diffracted from the grating. The scattered radiation and the frequency-shifted reference beam are combined at a detector to generate an optical heterodyne signal.

Abstract: A wavelength variable light source apparatus includes a light source slot section for generating laser light and a main control section into which the light source slot section is inserted and which is connected to the light source slot section. The main control section optionally varies a wavelength and an output level of the laser light from the light source slot section. An optical connecting mechanism between the light source slot section and the main control section supplies the main control section with a part of laser light from the light source slot section.

Abstract: The present invention relates to an optical sensor of air borne acoustic waves. The sensor comprises means for producing mutually coherent optical sampling and reference beams, which may be combined to form an intermediate frequency carrier, the sampling beam being exposed to the acoustic field, in which acoustic wave induced density variations occur. These density variations produce a variation in the index of refraction and thereupon a phase modulation of the sampling beam. This phase modulation may be recovered by an optical detector and a phase detector as an electrical signal representative of the acoustic signal. The invention has application to security systems.

Abstract: A laser wavelength locking control loop apparatus comprising a wavelength selective device and a photodetector, coupled to a feedback controller circuit. Electromagnetic radiation emitted by the laser device is provided to the wavelength selective device which provides a first output signal at a first wavelength and a second output signal at a second wavelength. The first and second output signals are directed to the photodetector so as to coincide when incident thereupon. A beat signal results from the coincidence of the first and second output signals and this is used to measure wavelength drift.

Abstract: A scatterometer utilizes the dead zone resulting from lockup caused by scatter from a sample located in the optical path of a ring laser at a location where counter-rotating pulses cross. The frequency of one pulse relative to the other is varied across the lockup dead zone.

Abstract: Apparatus and methods of measuring optical waveforms are described. In one aspect, an optical waveform measurement apparatus includes a light wave source, a mixer, a down converter, and a controller. The light wave source is operable to provide an adjustable frequency light wave with a frequency that is adjustable over a target frequency range. The mixer is operable to mix a target modulated optical signal with the adjustable frequency light wave to obtain a mixed signal. The frequency down converter is operable to down convert the mixed signal to obtain a down-converted signal. The controller is operable to extract from the down-converted signal amplitude and phase information relating to the target modulated optical signal and to cause the light wave source to incrementally adjust the frequency of the adjustable frequency light wave over the target frequency range.

Abstract: A device for the inspection of surfaces, notably for the inspection of a surface of a semiconductor (14), which device comprises at least one laser light source (1) and a detector for detecting the light (13) that is reflected from the surface (10) to be inspected; the device also includes at least one mode filter (15; 15.1) for filtering the reflected light.

Abstract: A method and apparatus for monitoring and controlling each of at least one optical signal sources within a WDM system by using beat frequencies derived by combining portions of the optical signals provided by the optical signal sources and a reference optical signal.

Abstract: An interferometer includes a two-frequency laser and a polarizing beam splitter (PBS) that separates a heterodyne beam from the laser into separate beams having different the frequencies and orthogonal polarizations. Optical fibers conduct the separate beams to a beam combiner for interferometer optics. The PBS and/or the beam combiner can use a coating to reflect one linear polarization and transmit an orthogonal linear polarization. To improve extinction ratios in the PBS or the beam combiner, a yaw angle for an input beam is non-zero and corresponds to a peak in the extinction ratio of a reflected beam.