A frequency swept laser source for TEFD-OCT imaging includes an integrated clock subsystem on the optical bench with the laser source. The clock subsystem generates frequency clock signals as the optical signal is tuned over the scan band. Preferably the laser source further includes a cavity extender in its optical cavity between a tunable filter and gain medium to increase an optical distance between the tunable filter and the gain medium in order to control the location of laser intensity pattern noise. The laser also includes a fiber stub that allows for control over the cavity length while also controlling birefringence in the cavity.

Disclosed are several technical approaches of using low coherence interferometry techniques to create an autofocus apparatus for optical microscopy. These approaches allow automatic focusing on thin structures that are positioned closely to reflective surfaces and behind refractive material like a cover slip, and automated adjustment of focus position into the sample region without disturbance from reflection off adjacent surfaces. The measurement offset induced by refraction of material that covers the sample is compensated for. Proposed are techniques of an instrument that allows the automatic interchange of imaging objectives in a low coherence interferometry autofocus system, which is of major interest in combination with TDI (time delay integration) imaging, confocal and two-photon fluorescence microscopy.

An OCT imaging technique capable of suppressing image noise due to reflection on a wall surface of a carrier for carrying an imaging object by a simple configuration is provided. A light regulating member 28 having a transmission pattern where the high transmission parts P1 and the low transmission parts P2 are alternately arranged is placed on a side opposite to the spheroid Sp (imaging object) across the objective lens 27. The transmission pattern is rotationally symmetric with respect to an optical axis AX of the objective lens 27 and a point located at a position point-symmetric with an arbitrary point in the high transmission part with respect to a point where the optical axis of the objective lens intersects with the light regulating surface is included in the low transmission part.

A method for reducing interference from scattered light/reflected light of an interference path by generating carrier through phase. Phase modulation is applied on the terminal of a fiber path, and a target signal is separated from an interference signal by selecting a specific working point, to obtain a purer target signal, thereby lengthening the measurement distance. The signal demodulation manner used in this method is different from the traditional manner of modulation performed by generating a carrier through the phase, and does not need to use the modulation frequency as the reference signal during demodulation, so this manner is easily implemented. The method is applicable to long-distance pipeline monitoring and wide-range fiber perimeter security, and especially to an application environment in which the modulation end is far away from the signal demodulation end. The method can also be applied in an application in which measurement is implemented by modulating an optical transmission phase in a feedback device.

The invention provides a method for calibration of an optical measurement system, which may be a heterodyne interferometer system, wherein a first optical axis and a second optical axis have a different optical path length, the method comprises: .sup.measuring a first measurement value along the first optical axis using a first measurement beam, .sup.measuring a second measurement value along the second optical axis using a second measurement beam, .sup.changing a wavelength of the first measurement beam and the second measurement beam, .sup.measuring a further first measurement value along the first optical axis using the first measurement beam with changed wavelength, measuring a further second measurement value along the second optical axis using the second measurement beam with changed wavelength, .sup.determining a cyclic error of the optical measurement system on the basis of the measured values, and .sup.storing a corrective value based on the cyclic error.

In a method for characterizing the surface shape, the following steps are carried out iteratively: (A) calculating a first figure based on first measurements; (B) subtracting the first figure from first measured values, to determine a first test set-up error; (C) using the first test set-up error for calculating a corrected first figure,; (D) subtracting the corrected first figure from second measured values, to determine a second test set-up error; (E) using the second test set-up error for calculating a corrected second figure; (F) using the corrected second figure for correcting the first test set-up error by subtracting the corrected second figure from the first measured values, to determine a corrected first test set-up error; (G) using the corrected first test set-up error for calculating a first figure corrected once again; and (H) comparing the result with a convergence criterion and optionally repeating steps (A) to (H).

Disclosed is a heterodyne grating interferometry system based on secondary diffraction, including a single-frequency laser, an input optical fiber, an acousto-optic modulator, a reading head, and a measurement grating, an output optical fiber, a photoelectric conversion unit and an electronic signal processing unit, wherein the single-frequency laser emits a single-frequency laser, which enters the acousto-optic modulator through the input optical fiber, and is divided into a reference light and measurement light to be input to the reading head, wherein the reading head and the measurement grating convert the reference light and measurement light into a reference interference optical signal and a measurement interference optical signal and send them to the photoelectric conversion unit through the output optical fiber and wherein the photoelectric conversion unit converts the measurement interference optical signal and the reference interference optical signal into a measurement interference electrical signal and a reference interference electrical signal.

A retroreflecting sensor includes a corner cube retroreflector having three mutually orthogonal reflective surfaces. A sensor element is disposed on at least a portion of one of the reflective surfaces. The sensor element modulates a phase and/or an amplitude of incident light as a function of a measurand so that when illuminated by incident light, a diffraction pattern is reflected to a remote optical imaging device configured to capture and analyze the diffraction pattern to extract measurement data associated with the measurand.