Optical displacement sensor

By configuring the optical path length and grating period to satisfy specific relationships, the optical displacement sensor mitigates light loss, enhancing sensitivity and reducing optical losses, thus improving performance.

JP7840963B2Active Publication Date: 2026-04-06SENSIBEL ACTIESEL SCAB
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Patent Information

Application Number
JP2023535812
Authority / Receiving Office
JP · JP
Patent Type
Patents
Current Assignee / Owner
Priority Date
2020-12-14
Filing Date
2021-12-14
Publication Date
2026-04-06
Estimated Expiration
2041-12-14

AI Technical Summary

Technical Problem

Optical displacement sensors using diffraction gratings suffer from significant light loss due to diffraction, which impairs their performance in terms of sensitivity and signal-to-noise ratio.

Method used

The optical path length between the diffraction grating and reflective surface is configured to satisfy specific relationships with the grating period, such as up to 20% margin of Equation 1 or 3, to ensure that the repeated self-image of the grating coincides with the diffraction grating, allowing more light to be coupled towards the photodetector, thereby reducing optical losses.

Benefits of technology

This configuration enhances the sensitivity of the optical displacement sensor by ensuring that most light is reflected and transmitted back and forth between the diffraction grating and reflective surface, doubling the sensitivity to the movement of the reflecting surface or diffraction grating, and reducing optical losses.

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Abstract

The optical displacement sensor (2) includes a reflecting surface (4) and one or more diffraction gratings (6) that, together with the reflecting surface, each define an interference arrangement. The reflecting surface (4) is movable relative to the diffraction gratings (6), or vice versa. Light from a light source (8) propagates through the interference arrangement and produces an interference pattern at each set of photodetectors (10). Each interference pattern depends on the separation between the reflecting surface (4) and each grating (6). A collimating optical arrangement (14) at least partially collimates the light between the light source (8) and the diffraction grating (6). For the or each interference arrangement, when the reflecting surface (4) or diffraction grating (6) is in a zero-displacement position, the optical path length L of light propagating between the diffraction grating (6) and the reflecting surface (4) satisfies the following relationship to within 20% of j, where n is an integer, and Tz is the Talbot length defined as follows: λ is the wavelength of the light, and p is the grating period of each diffraction grating (6): Alternatively, L is within 20% of p, where m is an odd integer. Additionally or alternatively, the optical displacement sensor (34, 112) may include two or more diffraction gratings (44, 46, 116) and may be configured to provide each separate light beam (62, 64, 132) to each grating (44, 46, 116) using a beam separation arrangement (48, 126) or multiple light source elements.
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