An interferometer for use in remote sensing systems includes a beam splitter that separates an input wave into a reflected wave, which travels along a first optical path within an upper interferometer arm, and a transmitted wave, which travels along a second optical path within a lower interferometer arm. The reflected and transmitted waves are subsequently recombined by the beam splitter for imaging onto a sensor. A highly dispersive element is incorporated into at least one of the pair of interferometer arms. Due to anomalous dispersion, a frequency shift in a wave transmitted through a dispersive element changes the optical path length within its corresponding arm. As a result, the recombined wave produces an interference pattern with a measurable phase change that can be utilized to calculate the original frequency shift in the input wave with great precision and potential sub-Hertz sensitivity.

In order to measure the contrast of interference in an interference-based, closed-loop, phase-modulating optical sensor device, the gain of the feedback loop in a feedback controller is evaluated. This gain is found to be a measure for the contrast. The contrast evaluated in this way can e.g. be used for period-disambiguation when determining the measurand of the sensor device. The sensor device can e.g. be a high-voltage sensor or a current sensor.

Systems, methods and other embodiments associated with spatial-domain Low-coherence Quantitative Phase Microscopy (SL-QPM) are described herein. SL-QPM can detect structural alterations within cell nuclei with nanoscale sensitivity (0.9 nm) (or nuclear nano-morphology) for nano-pathological diagnosis of cancer. SL-QPM uses original, unmodified cytology and histology specimens prepared with standard clinical protocols and stains. SL-QPM can easily integrate in existing clinical pathology laboratories. Results quantified the spatial distribution of optical path length or refractive index in individual nuclei with nanoscale sensitivity, which could be applied to studying nuclear nano-morphology as cancer progresses. The nuclear nano-morphology derived from SL-QPM offers significant diagnostic value in clinical care and subcellular mechanistic insights for basic and translational research. Techniques that provide for depth selective investigation of nuclear and other cellular features are disclosed.

The ROC value of a test surface is measured with a single spectrally-controlled interferometric measurement using a reference source of known ROC. The test surface is placed at the confocal position of the reference surface and the light source is modulated so as to produce localized interference fringes at the location of the test surface. The interference fringes are then processed with conventional interferometric analysis tools to establish the exact position of the test surface in relation to the reference surface, thereby determining the distance between the test surface and the reference surface. The radius of curvature of the test surface is obtained simply by subtracting such distance from the known radius of curvature of the reference surface.

In order to measure the contrast of interference in an interference-based, closed-loop, phase-modulating optical sensor device, the gain of the feedback loop in a feedback controller (12) is evaluated. This gain is found to be a measure for the contrast. The contrast evaluated in this way can e.g. be used for period-disambiguation when determining the measurand of the sensor device. The sensor device can e.g. be a high-voltage sensor or a current sensor.

A laser interferometer includes a light source configured to emit first laser light, an optical modulator including a vibrator and configured to modulate, by the vibrator, the first laser light into second laser light having a different frequency, an optical path switching unit disposed in a first optical path through which the first laser light travels and configured to switch a direction of travel of the first laser light between the first optical path and a second optical path different from the first optical path, a reflector including a light-reflecting surface configured to move along the second optical path and reflect the first laser light traveling through the second optical path, and a photoreceptor configured to receive first interference light of the second laser light and third laser light generated by reflection of the first laser light on an object to be measured, and second interference light of the second laser light and fourth laser light generated by reflection of the first laser light on the light-reflecting surface and output a light-receiving signal.

According to an aspect of the present inventive concept there is provided a system for measuring frequency of a light signal from a chirped laser source, said system comprising: an optical measurement unit configured to receive at least a portion of the light signal, and to output, via an optical hybrid coupler, at least two angle diversity signals based on a difference between a first and second signal formed by splitting the at least portion of the light signal, wherein the second signal is delayed relative to the first signal, and wherein a pair of signals of the at least two angle diversity signals have a fixed phase shift relative to each other; and a control unit configured to: receive the at least two angle diversity signals, generate a complex signal, based on the at least two angle diversity signals, and determine an instantaneous phase of the complex signal for determining an instantaneous frequency of the light signal.