JPH0345328B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a physical change detection method for optically detecting various physical changes such as ambient temperature, pressure, vibration, electromagnetic field strength, sound waves, and chemical reactions.

Currently, various detectors are used to detect physical changes such as ambient temperature, pressure, vibration, etc. However, since conventional detectors generally use an electrical measurement method, measurement errors are likely to occur due to internal and external noise generated by electromagnetic induction from cables, transformers, etc., and they also use metal. Therefore, it has the drawback of causing adverse effects on non-measuring systems, such as electrical breakdown.

In order to avoid these drawbacks, we developed a Fabry-Perot optical resonator in which a reflective film is applied to both end faces of the optical fiber, taking advantage of the fact that the length of the optical fiber changes due to physical changes such as ambient temperature. It is conceivable to use this method to detect physical changes.

However, when detecting a physical change using this Fabry-Perot optical resonator, although it is possible to detect the change itself, it is not possible to detect its direction.

An object of the present invention is to provide a physical change detection method that can reliably detect physical changes and their directions with high accuracy.

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 systematically shows a physical change detection device 10 used in the method of the present invention, which includes a single or multiple physical change detection device of a predetermined length. Mode optical fiber 12 and reflective films 14 and 1 formed on both end faces thereof
Fabry-Perot optical resonator 1 consisting of
It is equipped with 6. The optical fiber 12 has a core 12a
The optical fiber is composed of a cladding 12b and a coating 12c, but if the propagation mode of this optical fiber is a single mode, the core diameter is extremely small. The reflective films 14, 14' are preferably dielectric multilayer films in which SiO ₂ and TiO ₂ are alternately deposited by vapor deposition or the like.
These reflective films cover the core 12a of the optical fiber 12.
and cladding 12b. The length L of the optical fiber 12 varies from several mm to several mm depending on the object to be measured.
Km, and the reflectance of the reflective films 14 and 14' is
10-100%. When a laser beam enters from one end face of a Fabry-Perot resonator made of such an optical fiber, there is a certain relationship between the radius d of the reflective films 14 and 14', the length L of the optical fiber, and the wavelength λ of the light. If established, resonance will occur.

A laser light source 18 such as a semiconductor laser is provided on one end face of the optical resonator 16.
A laser beam consisting of two frequencies is incident on the optical resonator 16, and an optical-to-electrical conversion means 20 such as an avalanche photodiode is provided on the other end face of the optical resonator 16 to detect the light from the optical resonator 16 and generate an electrical signal. Occur. This electrical signal is detected by electrical detection means 22. This electrical detection means can be, for example, a pulse counter that counts the number of pulses of the electrical signal for reasons to be described later.

Next, describing the operation of the above device, the Fabry-Perot optical resonator 16 is fixed to the radius d of the reflective films 14, 14', the length L of the optical fiber 12, and the wavelength λ of the incident light, as described above. When the relationship holds true, resonance occurs. Therefore, the optical fiber 12
When the length of changes, the resonance goes out, and when the length L at which the above-mentioned constant relationship is established is reached, a resonance state occurs. The length L of the optical fiber 12 changes depending on, for example, the ambient temperature, and therefore, the resonant state and non-resonant state of the optical resonator 16 are repeated in response to changes in the ambient temperature.

FIG. 3 shows the relationship between the time T and the output voltage V of the optical-to-electrical conversion means 20 when a change in ambient temperature and its direction are detected by the method of the present invention using the apparatus shown in FIG. It can be seen that the output voltage V changes in a pulse-like manner as . Therefore, by counting pulses of the output of the optical-to-electrical converting means 20 using the pulse counter, which is the electrical detecting means 22, it is possible to detect changes in the ambient temperature with the passage of time T. Since the waveform consists of a main peak and a sub-peak, the direction of temperature change can be determined from the order in which the main peak and sub-peak appear.
In other words, it is possible to know whether the temperature is rising or falling. In one embodiment of the present invention, on both end faces of a single mode optical fiber with a core of 4 μ, an outer diameter of 125 μ, and a length of 4 cm.
Using a Fabry-Perot optical resonator in which a reflective film is formed by alternately depositing SiO ₂ and TiO ₂ in multiple layers, laser light with a wavelength of around 0.6328 μm from a helium-neon laser is incident on one end face of the optical resonator. Light was applied to the avalanche photodiode from the other end of the optical resonator. At this time, the number of pulses corresponding to the change in ambient temperature was 1 pulse/1 to 2°C.

Note that although the above embodiment deals with detecting temperature, it is also possible to detect pressure, vibration, etc. if the length of the optical resonator changes due to pressure, vibration, distortion such as sound waves, etc. . Furthermore, even if birefringence occurs in the optical fiber due to an electromagnetic field, the output changes, making it possible to measure the electric field strength.Also, damage to the optical fiber coating due to chemical reactions, radiation, mechanical shock, fire, etc. These physical changes can be detected by changing the reflectance of the cladding.
Further, although a single mode optical fiber is used in the above embodiment, a graded index type optical fiber or a multimode optical fiber having a small number of modes may also be used.

Furthermore, spectrum analysis of light can be performed using a similar configuration.

Since the laser light incident on this Fabry-Perot optical resonator consists of two frequencies, it has the practical benefit of being able to reliably detect not only physical changes but also their orientations with high precision. be.

[Brief explanation of drawings]

Fig. 1 is a schematic system diagram of a physical change detection device according to the present invention, Fig. 2 is a cross-sectional view of an optical fiber, and Fig. 3 is a line showing the relationship between time and output voltage as an example of a physical change. It is a diagram. 10... Physical change detection device, 12... Optical fiber, 14, 14'... Reflective film, 16... Fabry-Perot type optical resonator, 18... Laser light source, 20... Optical-electric conversion means, 22... Electricity detection means.

Claims (1)

[Claims] 1. A Fabry-Perot optical resonator in which a reflective film is applied to both end faces of an optical fiber; a laser light source that enters a laser beam into one end face of the optical resonator;
Using optical-to-electrical conversion means that detects laser light from the other end face of the optical resonator and converts it into an electrical signal, and electrical detection means that detects the electrical signal, the laser light consisting of two frequencies is converted to the fabric. Physical change detection characterized by detecting a physical change applied to the optical fiber and its direction from the appearance order of peaks of an electric signal incident on one end face of a Perot type optical resonator and detected by the electric detection means. Method.