A system for monitoring events using fiber optics has a length of fiber optic cable having a first end, a second end and a detection length disposed between the first end and the second end. An optical signal source introduces an optical signal into the first end of the fiber optic cable. A detector detects a strength of the optical signal at the second end of the fiber optic cable.

Example position detection means and displacement detection devices are described. A relative position detection means optically detects a relative position of displacement of an object to be measured in a measuring direction, including a target mounted on the object to be measured and irradiated with light from a light source; a light receiver for detection of relative position for receiving light by changing polarization state of reflected light at the target with respect to the light; and a relative position information output unit for outputting relative position information based on displacement of the target in the measuring direction based on change of polarization state of the reflected light. The target includes a reflector mounted on the object to be measured and a birefringent member on the reflector and having a thickness changing from a tip to a base end along the measuring direction.

An optical encoder unit includes: a light source having a predetermined light distribution; an optical scale having a polarizer whose polarization direction on a plane is along a predetermined direction, and whose polarization direction is changed according to rotation; and an optical sensor unit including a first photoreceiver, a second photoreceiver, a third photoreceiver, and a fourth photoreceiver for receiving incident light that is light source light from the light source made incident on the respective photoreceivers by passing through or being reflected by the optical scale. An emitting surface of the light source and the optical sensor unit are arranged at positions so as to receive a light intensity that is predetermined times greater or more than that corresponding to dark current of the optical sensor.

The optical fiber sensor device comprises a probe light supply unit, an optical fiber sensor unit, and a polarization state measuring unit. The probe light supply unit generates and outputs a polarization switched light beam by alternately switching a polarized CW light beam in polarization directions orthogonal to each other with elapse of time. The optical fiber sensor unit includes a loop-state optical fiber into which the polarization switched light beam is input and which outputs a light wave reflecting a change of birefringence according to a stress applied from an outside in the polarization switched light beam. The polarization state measuring unit observes polarization states of the respective light waves propagating clockwise and counterclockwise through the optical fiber. The polarization state measuring unit calculates an angular velocity vector .sub.b defined by an equation that specifies a relationship between a temporal change rate ds.sub.out(t)/dt of a Stokes vector s.sub.out(t) giving a polarization state of the light wave from the optical fiber and the Stokes vector s.sub.out(t) for each of the clockwise and counterclockwise light waves. The angular velocity vector .sub.b gives a direction of a rotation center axis and a rotation angular velocity of the Stokes vector s.sub.out(t).

An optical fiber includes multiple optical waveguides configured in the fiber. An interferometric measurement system mitigates or compensates for the errors imposed by differences in a shape sensing optical fiber's response to temperature and strain. A 3-D shape and/or position are calculated from a set of distributed strain measurements acquired for a multi-core optical shape sensing fiber that compensates for these non-linear errors using one or more additional cores in the multicore fiber that react differently to temperature changes than the existing cores.

A polarizing axis detection device includes: an irradiation head 12 that emits sensor light; a stage 11 on which a polarizing plate is mounted and rotated; a light receiving head 13 that receives sensor light through the polarizing plate, and outputs a signal according to the amount of light received; and an arithmetic circuit 15 that detects orientation of a polarizing axis of the polarizing plate based on the output signal, wherein reference data based on an output signal from the light receiving head 13 when a polarizing plate is arranged such that a polarizing axis thereof is directed in a desired direction are stored preliminarily in a storage part, and sensor light is projected to a polarizing plate on the rotating stage, and the arithmetic circuit 15 detects orientation of a polarizing axis of the polarizing plate, based on a signal output from the light receiving part and the reference data.

Disclosed is an optical fiber interferometric system including a light source (1), a fiber optic coil (8), a coil splitter (3), a photodetector (2), and a polarization filtering unit. According to an embodiment, the polarization filtering unit includes a first waveguide polarizer (51), at least one second thin-plate polarizer (52) and an optical waveguide section (12), the at least one second polarizer (52) being disposed in the Rayleigh zone between a first waveguide end (21) of the first polarizer (51) and a second waveguide end (22) of the optical waveguide section (12).

Various embodiments relate to devices for measuring the state of devices and multi-stage rotary encoders as well as to associated sensors. In order to simplify the design of devices which can be read out electronically and multi-turn rotary encoders, according to some embodiments a device having at least one rotatable wheel, at least one light source and at least one polarization sensor is proposed, the wheel being at least partially transparent and polarization-maintaining, parts of the wheel being configured as pole filters, it being possible for light which exits the light source to be polarized by the pole filter and to be received by the polarization sensor.

The invention provides a tilt detecting device, in which a fixed member and a tilting plate are relatively rotatably provided via a pivot member, either one of the fixed member or the tilting plate is integral with the pivot member, comprising a tilt detecting unit provided on either of the fixed member or the tilting plate which relatively rotates with respect to the pivot member, and an angle detection pattern formed on the pivot member, wherein the tilt detecting unit comprises a light source for projecting an illumination light to the pivot member, a photodetection element for receiving the illumination light reflected by the pivot member, an optical system for projecting a pattern image to the photodetection element and an arithmetic unit for detecting a rotation of the pivot member based on a projecting position of the pattern image projected onto the photodetection element when the pivot member rotates.

A measurement scale device includes at least one scale marking, wherein the or each scale marking includes at least one periodic nanostructure that represents scale device information.