JPH0663726B2 - Disturbance Rejection Type Heterodyne Interferometry Fiber Optic Sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A conventional optical fiber sensor based on the heterodyne interferometry is
Since the measurement light path and the reference light path are different, they are easily affected by disturbances in the reference light path. With the optical fiber sensor of this patent, it is possible to eliminate the disturbance by forming a differential optical system without using the reference optical path, measuring the phase difference between the two optical paths. A schematic diagram of this device is shown in FIG. In order to explain this principle, the trajectory of the light beam at the tip of the optical fiber is shown in FIG. laser·
Beam is 2 minutes by a beam splitter BS, respectively are incident on the acousto-optic modulation element A ₁ and A _2, emits different f _1, f _2, the beam frequency. The beams of f ₁ and f ₂ enter the optical fibers F ₁ and F ₂ through the lenses l ₁ and l ₂ . The beam of the optical fiber F ₁ passes through the intermediate directional coupler C ₁ , passes through the remaining optical fiber portion, and reaches the optical fiber emission end face. The emitting end face is coated with a dielectric multilayer film rc with a reflectance of 20% to obtain the beat reference light. At the end face, the beam is partially reflected and the optical fiber F ₁
The returning transmitted light at the end face of the optical fiber F ₁ is collimated through the gradient index lens 1 _G after exiting the fiber, and is irradiated onto the measurement object ob. Reflected light is a gradient index lens 1
_The light is incident back to the optical fiber F ₂ through _G. Lesbian l ₂
In the case of the incident light on the optical fiber F ₂ , the same path as that of the optical fiber F ₁ is traced. In the photodetector PM1, the reflected photoelectric vector at the end face rc of the optical fiber F ₁ And the light emitted from the optical fiber F ₂ and reflected by the measuring object ob The beat is observed. Optical fiber F in photodetector PM2
In measurement object ob · out reflected light E ₂ and the optical fiber F ₁ at _second end surfaces rc, reflected light The beat is observed. Phase difference between both beats Φ _{1 −} Φ
_The phase component in the optical fiber that detects ₂ with the phase meter pd is included in both with the same sign, and the displacement vector component Is included with the opposite sign. Therefore, the phase component in the optical fiber is canceled and the displacement vector component is doubled and output from the phase meter. Therefore, the disturbance can be removed and the displacement can be measured with double sensitivity. .

[Brief description of drawings]

FIG. 1 is a schematic diagram of a disturbance elimination type heterodyne interferometry optical fiber sensor. FIG. 2 is a ray tracing diagram for explaining the principle.

Claims (1)

[Claims] 1. The effect of disturbance in a heterodyne interferometry optical fiber sensor is characterized in that the phase in the optical path of the optical fiber is canceled by the differential method by canceling the phase term passing through the same optical fiber core. Interfering device, two different frequency-shifted lasers emitted from two optical fibers.
The output ends of the fibers are arranged in parallel so that the direction of the beam is opposite to the measurement object, and the reflected beams from the measurement object of the beams emitted from the fibers are incident on different fibers. A sensor having a graded-index lens for causing a reference beam and having a vapor-deposited reflective film on the output end face of the fiber having a partial reflectance for splitting into a measurement beam and a reference beam.