A length of signal guide is connected to a first arm of an interferometer. Respective first phase noise measurements of the phase noise of a combined signal formed by combining respective signals propagated along the first arm and the second arm are determined at a plurality of frequencies while the length of signal guide is connected to the first arm. Based at least in part on the first phase noise measurements, a path length difference between the first and second arms is determined. A length of the first arm or the second arm is adjusted based at least in part on the path length difference.

A semiconductor measurement apparatus may include an illumination unit configured to irradiate light to the sample, an image sensor configured to receive light reflected from the sample and output multiple interference images representing interference patterns of polarization components of light, an optical unit in a path through which the image sensor receives light and including an objective lens above the sample, and a control unit configured to obtain, by processing the multi-interference image, measurement parameters determined from the polarization components at each of a plurality of azimuth angles defined on a plane perpendicular to a path of light incident to the image sensor. The control unit may be configured to determine a selected critical dimension to be measured from a structure in the sample based on measurement parameters. The illumination unit and/or the optical unit may include a polarizer and a compensator having a wave plate.

This disclosure generally relates to an optical coherence tomography (OCT) system. This disclosure particularly relates to an OCT system with a multi-pass dispersion compensation cell incorporated into its reference arm. This disclosure further relates to a hand-held compact OCT system suitable for inspection of an ear of a mammal.

A shape profile measurement device includes a light source configured to generate and emit a light signal, a relay optical system configured to receive the light signal from the light source, perform axial chromatic aberration on the light signal, emit a chromatically dispersed light signal over a plurality of wavelengths to a measurement target, and output a reflected light signal reflected from the measurement target, wherein the chromatically dispersed light signal is focused at different positions along an optical axis of the light signal, a detector configured to detect a wavelength of the reflected light signal, among the plurality of wavelengths, received from the relay optical system; and a processor configured to calculate a shape profile of the measurement target based on a focal position of the wavelength of the reflected light signal.

A high-dispersion retroreflector includes filter glass transparent at least in near infra-red (NIR) wavelengths and configured to cause differential dispersion of incident broadband low-coherent light in the at least NIR wavelengths.

The present invention is the optical fiber sensor, that laser pulses from a laser source are separated into a reference path and a measurement path by the second optical coupler via the first optical coupler, the first FRM is provided at an end of the reference path, the second FRM is provided at an end of the measurement path, and the reference reflected light of the first FRM and the measurement reflected light of the second FRM are interfered at the second optical coupler and are converted into three phases. The first phase pulses are transmitted to the optical synthesis section via the first optical coupler, second phase pulses are transmitted to the optical synthesis section via the first delay section, and third phase pulses are transmitted to the optical synthesis section via the second delay section. The time division pulse train is outputted from the optical synthesis section.