An interferometer has a first input configured to provide a first measurement beam at a first frequency, and a second measurement signal at the first frequency. The interferometer has a second input configured to provide a reference beam at a second frequency that is different than the first frequency; an optical element comprising a first portion comprising a polarization beam splitter; and a diffraction grating disposed over the optical element configured to diffract the first measurement beam and the second measurement beam

A heterodyne optical interferometer incorporates error correction elements to correct a cyclic error that may be present in an interferometric measurement. The cyclic error can be caused by various factors such as an imperfect polarization relationship between two wavelength components, deficiencies in optical propagation paths (such as light leakage), imperfect optical coatings, and/or imperfect components. The cyclic error, which typically manifests itself as erroneous displacement information characterized by a low velocity sinusoidal frequency component, can be reduced or eliminated by using birefringent optical elements and other optical elements to alter certain characteristics of one or both wavelength components and reduce light leakage components in one or more light propagation paths in the heterodyne optical interferometer.

The embodiments herein relate to a method for deriving topography of an object surface. A linearly polarized light wave is directed towards the object surface and a reference surface. Images of reflected linearly polarized light wave for a plurality of wavelengths are obtained. The images are obtained for at least four polarizations for each of the plurality of wavelengths. The reflected linearly polarized light wave is a reflection of the linearly polarized light wave directed towards the object surface and the reference surface. The topography of the object surface based on the obtained images is obtained.

A device for determining a 3D structure of an object having first and second laser emitters which generate laser radiation with first and second different wavelengths, respectively. A first beam splitter splits the laser radiation of each laser emitter into reference and illuminating radiation. The illuminating radiation is adapted to impinge on the object to be measured, be reflected by the object as object radiation, and interfere with the reference radiation to form interference patterns. A detector receives the interference patterns. A selection hologram deflects object radiation which impinges on it within a predefined incidence angle range and passes object radiation which impinges on it outside of the incidence angle range undiffracted. The undiffracted radiation either passes by the determination area of the detector or impinges on the determination area at an angle outside the determination angle range.

A luminous flux including laser light of different wavelengths outgoing from a light source unit is split into two luminous fluxes, the first luminous flux is focused on a sample with an objective lens, and the second luminous flux functions as reference light without radiating it onto the sample. Signal light reflected from the sample and the reference light are multiplexed by a polarized beam splitter and are made to interfere on four photodetectors out of phase in a photodetection unit. A signal processing unit acquires the optical axis distribution of an object in the sample by using the outputs of the plural photodetectors for every input wavelength, acquiring a detection signal and calculating the ratio of intensities of the detection signals at the different input wavelengths for every position in the sample.

A module accommodates multiple superluminescent light emitting diodes, SLEDs, 12r, 12g and 12b. The SLEDs are arranged in an enclosure and output respective light beams to propagate into free space within the enclosure. The individual light beams from the SLED sources are combined into a single beam path within the enclosure using beam combiners 40r-g, 40rg-b. Each beam combiner is realized as a planar optical element, the back side of which is arranged to receive a SLED beam and route it through the optical element to the front side where it is combined with another SLED beam that is incident on and reflected by the front side. The free-space propagating combined beam is output from the module via an optical fiber 42 (or through a window).

An optical distance measurer includes: a beam splitter splitting a laser beam and outputting as measurement light and reference light; a measurement light beam splitter splitting the measurement light and outputting as first measurement light and second measurement light; a reference light beam splitter splitting the reference light and outputting as first reference light and second reference light; a first optical system having a first Rayleigh length, the first optical system emitting the first measurement light to a target object; and a second optical system having a second Rayleigh length different from the first Rayleigh length, the second optical system emitting the second measurement light to the target object; a first receiver receiving the first reference light and first reflection light that is the first measurement light reflected by the target object and outputting a first receiving signal indicating the first reference light and the first reflection light; and a second receiver receiving the second reference light and second reflection light that is the second measurement light reflected by the target object and outputting a second receiving signal indicating the second reference light and the second reflection light.

Systems and methods for dynamic optical interferometer locking using entangled photons are provided. In certain embodiments, a system includes an optical source for generating a pair of photons. Also, the system includes first and second emitter/receivers that emit first and second photons towards first and second remote reflectors and receive reflected first and second photons along first and second optical paths. Additionally, the system includes a mode combiner for combining the reflected first photon and second photon into a first and second output port. Moreover, the system includes a coarse adjuster that performs coarse adjustments and a fine adjuster that performs fine adjustments to the first and second optical paths. Further, the system includes a plurality of photodetectors that detect photons from the first and second output ports. Additionally, the system includes a processor that controls the coarse and fine adjustments based on received signals from the photodetectors.

An ophthalmic apparatus may include: a wavelength sweeping light source; a reference optical system; a calibration optical system; a light receiving element configured to receive calibration interference light which is a combination of calibration light and reference light; and a signal processor configured to sample a calibration interference signal outputted from the light receiving element when it receives the calibration interference light. The signal processor may sample the calibration interference light in at least first and second frequency bands, which are different and used for measuring a specific region of a subject eye. The ophthalmic apparatus calculates a difference between first and second waveforms, the first waveform being a waveform of the calibration interference signal that is sampled in the first frequency band and Fourier transformed, the second waveform being a waveform of the calibration interference signal that is sampled in the second frequency band and Fourier transformed.

A high-resolution phase detection method and system based on a plane grating laser interferometer. The method uses a dual-frequency interferometer to measure the displacement, and the measurement signal processing comprises an integral part and a decimal portion, a phase equation set of a displacement measurement signal is constructed according to a measurement optical path principle of a heterodyne plane grating laser interferometer; a non-linear equation set for which the unknowns are instantaneous phase, interval phase and signal amplitude is established; and the equation sets above are solved by using the least squares method, so as to realize phase discrimination, thereby realizing precise displacement measurement. The method can solve the problems in the traditional time measurement-based phase detection technology, such as low measurement accuracy, and failing to satisfy small measuring range measurement. The measurement method can be applied to systems such as precision manufacturing equipment and lithography machine.